NOlOfl'InSlCl HO! 3'IHOHd 1VOISO'IOOIXOJ.

 

 

 

 

 

 

sfiRVlCE
is“ 3‘0

' Toxicological

Profile . C

i

i

. * DISU LFOTON

US. DEPARTMENT OF HEALTH & HUMAN SERVICES
Public Health Service
Agency for Toxic Substances and Disease Registry

 

 

 

 

i

 

TOXICOLOGICAL PROFILE FOFI
DISULFOTON

Prepared by:

Research Triangle Institute
Under Subcontract N0. 205-93-0606

Prepared for:

US. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Public Health Service
Agency for Toxic Substances and Disease Registry

August 1995

(«'3
3“~ ‘ .

DISULFOTON

DISCLAIMER

The use of company or product name(s) is for identification only and does not imply endorsement by
the Agency for Toxic Substances and Disease Registry.

DISULFOTON iii

UPDATE STATEMENT

Toxicological profiles are revised and republished as necessary, but no less than once every three
years. For information regarding the update status of previously released profiles contact ATSDR at:

Agency for Toxic Substances and Disease Registry fl“, r‘ ‘
Division of Toxicology/Toxicology Information Branch
1600 Clifton Road NE, E-29
Atlanta, Georgia 30333

FOREWORD

This toxicological profile is prepared in accordance with guidelines developed by ATSDR and EPA. The
original guidelines were published in the EederaLRegister on April 17, 1987. Each profile will be revised and
republished as necessary.

The ATSDR toxicological profile succinctly characterizes the toxicologic and adverse health effects
information for the hazardous substance being described. Each profile identifies and reviews the key literature (that
has been peer-reviewed) that describes a hazardous substance's toxicologic properties. Other pertinent literature is
also presented. but described in less detail than the key studies. The profile is not intended to be an exhaustive
document; however, more comprehensive sources of specialty information are referenced.

Each toxicological profile begins with a public health statement, that describes in nontechnical language, a
substance's relevant toxicological properties. Following the public health statement is information concerning levels
of significant human exposure and, where known, significant health effects. The adequacy of information to
determine a substance's health effects is described in a health effects summary. Data needs that are of significance to
protect public health will be identified by ATSDR and EPA. The focus of the profiles is on health and toxicologic
information; therefore, we have included this information in the beginning of the document.

Each profile must include the following:

(A) The examination, summary, and interpretation of available toxicologic information and epidemiologic
evaluations on a hazardous substance in order to ascertain the levels of significant human exposure for the
substance and the associated acute, subacute, and chronic health effects.

(B) A determination of whether adequate information on the health effects of each substance is available or in
the process of development to determine levels of exposure that present a significant risk to human health of
acute, subacute, and chronic health effects.

(C) Where appropriate, identification of toxicologic testing needed to identify the types or levels of exposure
that may present significant risk of adverse health effects in humans.

The principal audiences for the toxicological profiles are health professionals at the federal, state. and local
levels, interested private sector organizations and groups, and members of the public.

The toxicological profiles are developed in response to the Superfund Amendments and Reauthorization Act
(SARA) of 1986 (Public Law 99-499) which amended the Comprehensive Environmental Response, Compensation,
and Liability Act of 1980 (CERCLA or Superfund). This public law directed the Agency for Toxic Substances and
Disease Registry (ATSDR) to prepare toxicological profiles for hazardous substances most commonly found at
facilities on the CERCLA National Priorities List and that pose the most significant potential threat to human health,
as determined by ATSDR and the Environmental Protection Agency (EPA). The availability of the revised priority
list of 275 hazardous substances was announced in the EederaLchister on February 28, 1994 (59 FR 9486). For
prior versions of the list of substances, see EederaLRegister notices dated April 17, 1987 (52 FR 12866); October 20,
1988 (53 FR 41280); October 26, 1989 (54 FR 43619); October 17, 1990 (55 FR 42067); and October 17, 1991 (56
FR 52166); and October 28, 1992 (57 FR 48801).

vi

Foreword

Section 104(i)(3) of CERCLA. as amended. directs the Administrator of ATSDR to prepare a
toxicological profile for each substance on the list.

This profile reflects our assessment of all relevant toxicologic testing and information that has been peer
reviewed. It has been reviewed by scientists from ATSDR. the Centers for Disease Control and Prevention
(CDC), and other federal agencies. It has also been reviewed by a panel of nongovemment peer reviewers and
was made available for public review. Final responsibility for the contents and views expressed in this
toxicological profile resides with ATSDR.

W

David Satcher, M.D.. Ph.D.
Administrator
Agency for Toxic Substances and
Disease Registry

DISULFOTON VII

CONTRIBUTORS

CHEMICAL MANAGERS(S)/AUTHOR(S):

Nickolette Roney
ATSDR, Division of Toxicology, Atlanta, GA

Sharon Wilbur, M.A.
Research Triangle Institute, Research Triangle Park, NC

THE PROFILE HAS UNDERGONE THE FOLLOWING ATSDR INTERNAL REVIEWS:
1. Green Border Review. Green Border review assures consistency with ATSDR policy.

2. Health Effects Review. The Health Effects Review Committee examines the health effects
chapter of each profile for consistency and accuracy in interpreting health effects and
classifying end points.

3. Minimal Risk Level Review. The Minimal Risk Level Workgroup considers issues relevant to
substance—specific minimal risk levels (MRLs), reviews the health effects database of each
profile, and makes recommendations for derivation of MRLs.

4. Quality Assurance Review. The Quality Assurance Branch assures that consistency across
profiles is maintained, identifies any significant problems in format or content, and establishes
that Guidance has been followed.

DISULFOTON ix

PEER REVIEW

A peer review panel was assembled for disulfoton. The panel consisted of the following members:
1; Dr. William Buck, Private Consultant, Consul-Tox, Inc., Tolono, Illinois;

2. Dr. Lucio Costa, Professor and Director, Toxicology Program, School of Public Health and
Community Medicine, Department of Environmental Health, University of Washington,
Seattle, Washington; and

3. Dr. Casey Robinson, Professor of Pharmacodynamics and Toxicology, College of Pharmacy,
Health Science Center, University of Oklahoma, Oklahoma City, Oklahoma.

These experts collectively have knowledge of disulfoton’s physical and chemical properties, toxico-
kinetics, key health end points, mechanisms of action, human and animal exposure, and quantification
of risk to humans. All reviewers were selected in conformity with the conditions for peer review
specified in Section lO4(i)(l3) of the Comprehensive Environmental Response, Compensation, and
Liability Act, as amended.

Scientists from the Agency for Toxic Substances and Disease Registry (ATSDR) have reviewed the
peer reviewers’ comments and determined which comments will be included in the profile. A listing
of the peer reviewers’ comments not incorporated in the profile, with a brief explanation of the
rationale for their exclusion, exists as part of the administrative record for this compound. A list of
databases reviewed and a list of unpublished documents cited are also included in the administrative
record.

The citation of the peer review panel should not be understood to imply its approval of the profile’s
final content. The responsibility for the content of this profile lies with the ATSDR.

DISULFOTON xi

CONTENTS
FOREWORD ............................................................ v
CONTRIBUTORS ......................................................... vii
PEER REVIEW .......................................................... ix
LIST OF FIGURES ....................................................... xv
LIST OF TABLES ....................................................... xvii
1. PUBLIC HEALTH STATEMENT ........................................... 1
1.1 WHAT IS DISULFOTON? ............................................ 1
1.2 WHAT HAPPENS TO DISULFOTON WHEN IT ENTERS THE ENVIRONMENT? . . . 2
1.3 HOW MIGHT I BE EXPOSED TO DISULFOTON? .......................... 2
1.4 HOW CAN DISULFOTON ENTER AND LEAVE MY BODY? .................. 3
1.5 HOW CAN DISULFOTON AFFECT MY HEALTH? ......................... 4
1.6 IS THERE A MEDICAL TEST TO DETERMINE WHETHER I HAVE BEEN

EXPOSED TO DISULFOTON? ......................................... 5

1.7 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT MADE TO
PROTECT HUMAN HEALTH? ........................................ 5
1.8 WHERE CAN I GET MORE INFORMATION? ............................. 6
2. HEALTH EFFECTS ..................................................... 7
2.1 INTRODUCTION .................................................. 7
2.2 DISCUSSION OF HEALTH EFFECTS BY ROUTE OF EXPOSURE .............. 7
2.2.1 Inhalation Exposure ............................................ 9
2.2.1.1 Death ............................................... 9
2.2.1.2 Systemic Effects ........................................ 9
2.2.1.3 Immunological and Lymphoreticular Effects ................... 20
2.2.1.4 Neurological Effects .................................... 20
2.2.1.5 Reproductive Effects .................................... 24
2.2.1.6 Developmental Effects .................................. 24
2.2.1.7 Genotoxic Effects ...................................... 24
2.2.1.8 Cancer ............................................. 24
2.2.2 Oral Exposure ............................................... 25
2.2.2.1 Death .............................................. 25
2.2.2.2 Systemic Effects ....................................... 51
2.2.2.3 Immunological and Lymphoreticular Effects ................... 59
2.2.2.4 Neurological Effects .................................... 59
2.2.2.5 Reproductive Effects .................................... 64
2.2.2.6 Developmental Effects .................................. 65
2.2.2.7 Genotoxic Effects ...................................... 66
2.2.2.8 Cancer ............................................. 67
2.2.3 Dermal Exposure ............................................. 67
2.2.3.1 Death .............................................. 67

2.2.3.2 Systemic Effects ....................................... 68

DISULFOTON xll

3.

4.

2.2.3.3 Immunological and Lymphoreticular Effects ................... 74

2.2.3.4 Neurological Effects .................................... 74

2.2.3.5 Reproductive Effects .................................... . 76

2.2.3.6 Developmental Effects .................................. 76

2.2.3.7 Genotoxic Effects ...................................... 76

2.2.3.8 Cancer ............................................. 76

2.3 TOXICOKINETICS ................................................ 76
2.3.1 Absorption ................................................. 77
2.3.1.1 Inhalation Exposure ...................... ‘ .............. 77

2.3.1.2 Oral Exposure ....................... ' ................. 77

2.3.1.3 Dermal Exposure ...................................... 79

2.3.2 Distribution ................................................. 79
2.3.2.1 Inhalation Exposure .................................... 79

2.3.2.2 Oral Exposure ........................................ 79

2.3.2.3 Dermal Exposure ...................................... 80

2.3.3 Metabolism ................................................. 80
2.3.4 Excretion .................................................. 84
2.3.4.1 Inhalation Exposure .................................... 84

2.3.4.2 Oral Exposure ........................................ 85

2.3.4.3 Dermal Exposure ...................................... 86

2.3.4.4 Other Routes of Exposure ................................ 86

2.3.5 Mechanisms of Action ......................................... 86

2.4 RELEVANCE TO PUBLIC HEALTH ................................... 89
2.5 BIOMARKERS OF EXPOSURE AND EFFECT ............................ 113
2.5.1 Biomarkers Used to Identify or Quantify Exposure to Disulfoton ........... 114
2.5.2 Biomarkers Used to Characterize Effects Caused by Disulfoton ............ 117

2.6 INTERACTIONS WITH OTHER SUBSTANCES ........................... 118
2.7 POPULATIONS THAT ARE UNUSUALLY SUSCEPI‘IBLE ................... 121
2.8 METHODS FOR REDUCING TOXIC EFFECTS ........................... 122
2.8.1 Reducing Peak Absorption Following Exposure ........................ 122
2.8.2 Reducing Body Burden ........................................ 123
2.8.3 Interfering with the Mechanism of Action for Toxic Effects ............... 123

2.9 ADEQUACY OF THE DATABASE .................................... 124
2.9.1 Existing Information on Health Effects of Disulfoton .................... 124
2.9.2 Identification of Data Needs ..................................... 127
2.9.3 Ongoing Studies ............................................. 137
CHEMICAL AND PHYSICAL INFORMATION ................................ 139
3.1 CHEMICAL IDENTITY ............................................. 139
3.2 PHYSICAL AND CHEMICAL PROPERTIES ............................. 139
PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL ....................... 143
4.1 PRODUCTION .............. ‘ ..................................... 143
4.2 IMPORT/EXPORT ................................................. 143
4.3 USE ........................................................... 143

4.4 DISPOSAL ...................................................... 144

DISULFOTON xili

5. POTENTIAL FOR HUMAN EXPOSURE ..................................... 147
5.1 OVERVIEW ..................................................... 147
5.2 RELEASES TO THE ENVIRONMENT .................................. 148

5.2.1 Air ....................................................... 148
5.2.2 Water ..................................................... 150

5.2.3 Soil ...................... ' ................................ 150

5.3 ENVIRONMENTAL FATE ......................... . .................. 150
5.3.1 Transport and Partitioning ....................................... 150

5.3.2 Transformation and Degradation .................................. 154
5.3.2.1 Air ................................................ 154

5.3.2.2 Water .............................................. 154

5.3.2.3 Sediment and Soil ..................................... 155

5.4 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT ............ 157
5.4.1 Air ....................................................... 157
5.4.2 Water ..................................................... 157

5.4.3 Sediment and Soil ............................................ 158
5.4.4 Other Environmental Media ..................................... 158

5.5 GENERAL POPULATION AND OCCUPATIONAL EXPOSURE ............... 160
5.6 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES .................. 161
5.7 ADEQUACY OF THE DATABASE .................................... 162
5.7.1 Identification of Data Needs ..................................... 162
5.7.2 Ongoing Studies ............................................. 165

6. ANALYTICAL METHODS ............................................... 167
6.1 BIOLOGICAL SAMPLES ............................................ 167
6.2 ENVIRONMENTAL SAMPLES ....................................... 169
6.3 ADEQUACY OF THE DATABASE .................................... 173

6.3.1 Identification of Data Needs ..................................... 173
6.3.2 Ongoing Studies ............................................. 174

7. REGULATIONS AND ADVISORIES ....................................... 175

8. REFERENCES ........................................................ 183

9. GLOSSARY ......................................................... 207

APPENDICES
A. USER’S GUIDE .................................................... A-1

B. ACRONYMS, ABBREVIATIONS, AND SYMBOLS .......................... B-l

DISULFOTON

2-1

2-2

2-3

5-1

XV
LIST OF FIGURES
Levels of Significant Exposure to Disulfoton - Inhalation ......................... 16
Levels of Significant Exposure to Disulfoton - Oral ............................. 46
Metabolic Pathways for Disulfoton ........................................ 81
Existing Information on Health Effects of Disulfoton ........................... 125

Frequency of NFL Sites with Disulfoton Contamination ......................... 149

DISULFOTON xvii

2-1

2-3

2-4

3-1

3-2

6-1

6-2

7-1

LIST OF TABLES
Levels of Significant Exposure to Disulfoton - Inhalation ......................... 10
Levels of Significant Exposure to Disulfoton - Oral .............................. 26
Levels of Significant Exposure to Disulfoton - Dermal ............................ 69
Genotoxicity of Disulfoton In Vivo ....................................... 107
Genotoxicity of Disulfoton In Vitro ....................................... 109
Chemical Identity of Disulfoton .......................................... 140
Physical and Chemical Properties of Disulfoton .............................. 141
Analytical Methods for Determining Disulfoton in Biological Samples .............. 168
Analytical Methods for Determining Disulfoton in Environmental Samples ........... 170

Regulations and Guidelines Applicable to Disulfoton ........................... 177

DISULFOTON 1

1. PUBLIC HEALTH STATEMENT

This Statement was prepared to give you information about disulfoton and to emphasize the
human health effects that may result from exposure to it. The Environmental Protection
Agency (EPA) has identified 1,408 hazardous waste sites as the most serious in the nation.
These sites make up the National Priorities List (NFL) and are the sites targeted for long-term
federal clean-up activities. Disulfoton has been found in at least 7 of the sites on the NFL.
However, the number of NFL sites evaluated for disulfoton is not known. As EPA evaluates
more sites, the number of sites at which disulfoton is found may increase. This information
is important because exposure to disulfoton may cause harmful health effects and because

these sites are potential or actual sources of human exposure to disulfoton.

When a substance is released from a large area, such as an industrial plant, or from a
container, such as a drum or bottle, it enters the environment. This release does not always
lead to exposure. You can be exposed to a substance only when you come in contact with it.
You may be exposed by breathing, eating, or drinking substances containing the substance or

by skin contact with it.

If you are exposed to substances such as disulfoton, many factors will determine whether
harmful health effects will occur and what the type and severity of those health effects will
be. These factors include the dose (how much), the duration (how long), the route or
pathway by which you are exposed (breathing, eating, drinking, or skin contact), the other
chemicals to which you are exposed, and your individual characteristics such as age, gender,

nutritional status, family traits, life—style, and state of health.

1.1 WHAT IS DISULFOTON?

Disulfoton is a manufactured substance used as a pesticide to control a variety of harmful
pests that attack many field and vegetable crops. Disulfoton does not occur naturally. The
common trade names for disulfoton are Di-syston, Disystox, Frumin AL, and Solvirex. Pure

disulfoton is a colorless oil with no identifiable odor and taste. The technical product is dark

DISULFOTON 2

1. PUBLIC HEALTH STATEMENT

yellowish, and has an aromatic odor. It does not easily dissolve in water or evaporate to air.
It is most likely to be present in hazardous waste sites with other wastes, either in drums or
mixed with soil. Disulfoton is used to protect small grains, sorghum, corn, and other field
crops; some vegetables, fruit, and nut crops; and ornamental and potted plants against certain
insects. Although it is used primarily in agriculture, small quantities are used on home and
garden plants. Small quantities also are used for other purposes, such as mosquito control in
swamps. The use of disulfoton has decreased in recent years. Chapters 3 and 4 of this

profile provide more information on the physical properties and uses of disulfoton.

1.2 WHAT HAPPENS TO DISULFOTON WHEN IT ENTERS THE ENVIRONMENT?

Disulfoton enters the environment principally when it is applied as a spray or as granules on
field crops, vegetables, potted plants, and home gardens. Disulfoton also can enter the
environment when it accidentally spills or leaks during storage and transport. Disulfoton may
also enter the environment from hazardous waste sites. Environmental contamination by
disulfoton mainly affects soil and water. Natural chemical reactions and bacterial attack
remove disulfoton from soil and water. Such reactions form some by-products that are more
toxic than disulfoton. Fish accumulate disulfoton in their bodies. The levels of disulfoton in
fish can be hundreds of times higher than the level in water. Disulfoton binds moderately
well to soil and typically does not travel deep into soil with rainwater. Disulfoton has been
detected infrequently in groundwater from agricultural soil in California and Virginia. The
estimated amount of time required for the concentration of disulfoton in river water to
decrease to half of its initial level (half-life) is 7 days. The estimated half-life in soil ranges
from 3.5 to 290 days, depending on the nature of the soil and climatic conditions. Chapter 5

provides more information about what happens to disulfoton in the environment.

1.3 HOW MIGHT I BE EXPOSED TO DISULFOTON?

You may be exposed to disulfoton by breathing contaminated air, drinking contaminated
water, and eating contaminated food. Disulfoton is rarely detected in‘ air. In 1980, a low

level of disulfoton was detected in 1 of 123 air samples collected from 10 locations in the

DISULFOTON 3

1. PUBLIC HEALTH STATEMENT

United States. The average concentration at this site was 0.1 nanogram (ng) in 1 cubic meter
of air (1 ng = 1/1,000,000,000th [one billionth] of a gram). Disulfoton has not been detected
in drinking water. Low levels of disulfoton (0.05—l.0 milligram in a kilogram [mg/kg] of
food) (1 mg = 1/ 1,000 [one thousandth] of one gram) are sometimes found in some grains,
fruits, and vegetables treated with this pesticide. Because the levels in food are higher than
levels in air and water, you are more likely to be exposed to disulfoton by eating
contaminated food. The Food and Drug Administration (FDA) estimated that the average
intake of disulfoton in food per day for a 14- to 16-year—old male in the United States from
1986 to 1991 was 0.2 ng/kg (nanograms per kilogram) of body weight. The FDA estimate
for disulfoton intake from foods is 0.07% or less than 1/ 1,000th of the Food and Agriculture
Organization/World Health Organization (FAQ/WHO) acceptable daily intake (ADI) value of
300 ng/kg. The FAO/WHO ADI value is the maximum amount of a chemical which if
ingested over a person’s lifetime appears to be without appreciable health risk. Workers in
industries that manufacture and formulate disulfoton are at a higher risk of exposure.
Workers who spray the pesticide in fields and some farm workers who enter the fields
following spraying also are at a higher risk of exposure than the general population. Among
the general population, people who frequently use the pesticide in their homes and gardens
are potentially at higher risk. People who live near hazardous waste sites that contain
disulfoton also are potentially at a higher risk of exposure. Children playing at or near these
hazardous waste sites may be exposed by touching and eating soil that contains disulfoton.

More information about disulfoton exposure can be found in Chapter 5 of this profile.

1.4 HOW CAN DISULFOTON ENTER AND LEAVE MY BODY?

Disulfoton can easily enter your body when you breathe it in, swallow it, or have skin contact
with it. The amount of disulfoton that enters your body depends on the amount in air, food,
and water, and the length of time you are exposed to it. In an oily mixture, disulfoton may
enter the body through the skin, lungs, or stomach more easily than it would in a water
mixture. After disulfoton enters your body, the blood carries it to your organs and tissues.
Disulfoton generally does not build up in your organs and tissues, but is initially changed to

more harmful substances, which quickly break down to harmless by-products. The harmful

DISULFOTON 4

1. PUBLIC HEALTH STATEMENT

breakdown products inhibit important enzymes (cholinesterases) in the nervous system, and
this action can cause neurological effects. The harmless breakdown products do not have any
known effects on the body. Studies in animals show that disulfoton and/or the breakdown
products completely leave the body through the urine, feces, and exhaled air in about 10 days

or less. More information on how disulfoton moves in the body can be found in Chapter 2.

1.5 HOW CAN DISULFOTON AFFECT MY HEALTH?

In people, disulfoton mainly causes harmful effects to the nervous system. The harmful
breakdown products of disulfoton inhibit cholinesterase activity in the nervous system, which
results in neurological effects. Depending on the amount of disulfoton that enters the body,
neurological effects, such as inhibited cholinesterase activity, narrowing of the pupils,
vomiting, diarrhea, drooling, difficulty in breathing, tremors, convulsions, and even death may
occur. These effects can occur if you breathe in, swallow, or have skin contact with
disulfoton. Exposure to small amounts of disulfoton can sometimes inhibit cholinesterase
activity without causing obvious neurological effects. If you take in disulfoton from food or
water for long periods, you may also become nearsighted. You are less likely to die from
skin contact with disulfoton than from swallowing it, but you may become weak and tired

after skin contact.

Breathing in, swallowing, or having skin contact with high levels of disulfoton can cause
similar neurological effects in animals. The neurological effects of disulfoton are the most
common effects. Animals that swallowed disulfoton for long periods became nearsighted, and
the structures of their eyes were further damaged. Results of animal studies suggest that

female rats and mice are more sensitive to disulfoton than male rats and mice.

We do not know whether disulfoton causes reproductive or birth defects, or cancer in people.
However, some studies suggest that disulfoton may cause reproductive effects in animals.
Some animals that swallowed disulfoton during pregnancy had newborns with underdeveloped
bones, damaged livers and kidneys, and underdeveloped testes. Animals that swallowed

disulfoton for long periods did not develop cancer. Chapter 2 provides more information on

DISULFOTON

1. PUBLIC HEALTH STATEMENT

the harmful effects of disulfoton. Disulfoton has not been classified for carcinogenic effects
by the Department of Health and Human Services (DHHS), the International Agency for
Research on Cancer (IARC), or the EPA.

1.6 IS THERE A MEDICAL TEST TO DETERMINE WHETHER I HAVE BEEN
EXPOSED TO DISULFOTON?

Disulfoton and its breakdown products can be measured in the blood, urine, feces, liver,
kidney, or body fat of exposed people. In cases of occupational or accidental exposure to
disulfoton, the breakdown products are often measured in the urine. The breakdown products
are relatively specific for disulfoton and a few other similar organophosphate pesticides and
can be detected in urine for up to one week after people were last exposed. Because
disulfoton inhibits cholinesterase in blood and in blood cells, inhibition of this enzyme
activity may also suggest exposure to disulfoton. Cholinesterase activity in blood and in
blood cells may remain inhibited for as long as 1—2 weeks after the last exposure. Because
other organophosphate pesticides also inhibit cholinesterase activity in blood and blood cells,
this test is not specific for disulfoton. The measurement of cholinesterase in blood and blood
cells and the amount of disulfoton breakdown products in the urine cannot always predict
how much disulfoton you were exposed to. Your doctor can send samples of your blood or
urine to special laboratories that perform these tests. Chapters 2 and 6 provide more

information about medical tests.

1.7 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT MADE TO
PROTECT HUMAN HEALTH?

The National Institute for Occupational Safety and Health (NIOSH) recommends an exposure

limit of 0.1 mg disulfoton/m3 of air for a 10-hour workday within a 40-hour workweek.

EPA recommends that no more than 10 parts of disulfoton per billion parts (ppb) of water be
present in drinking water that children drink for periods of up to 10 days. Disulfoton in

drinking water should not exceed 3 ppb for children or 9 ppb for adults if they drink the

DISULFOTON 6

1. PUBLIC HEALTH STATEMENT

water for longer periods, and should not exceed 0.3 ppb for adults who will drink the water
during an average lifetime. EPA has designated disulfoton as a hazardous substance, but it
does not intend to cancel or restrict registration of pesticide products containing disulfoton.
Federal regulations limit the amount of disulfoton that factories can release into waste water.

EPA requires industries to report releases or spills of 1 pound or more.

For more information on recommendations by the federal government, please see Chapter 7.

1.8 WHERE CAN I GET MORE INFORMATION?

If you have any more questions or concerns, please contact your community or state health or

environmental quality department or:

Agency for Toxic Substances and Disease Registry
Division of Toxicology

1600 Clifton Road NE, Mailstop E-29

Atlanta, Georgia 30333

(404) 639-6000

This agency can also provide you with information on the location of occupational and
environmental health clinics. These clinics specialize in the recognition, evaluation, and

treatment of illness resulting from exposure to hazardous substances.

DISULFOTON 7

2. HEALTH EFFECTS

2.1 INTRODUCTION

The primary purpose of this chapter is to provide public health officials, physicians, toxicologists, and
other interested individuals and groups with an overall perspective of the toxicology of disulfoton. It
contains descriptions and evaluations of toxicological studies and epidemiological investigations and
provides conclusions, where possible, on the relevance of toxicity and toxicokinetic data to public

health.

A glossary and list of acronyms, abbreviations, and symbols can be found at the end of this profile.

2.2 DISCUSSION OF HEALTH EFFECTS BY ROUTE OF EXPOSURE

To help public health professionals and others address the needs of persons living or working near
hazardous waste sites, the information in this section is organized first by route of
exposure—inhalation, oral, and dermal; and then by health effect—death, systemic, immunological,
neurological, reproductive, developmental, genotoxic, and carcinogenic effects. These data are
discussed in terms of three exposure periods—acute (14 days or less), intermediate (15—364 days), and

chronic (365 days or more).

Levels of significant exposure for each route and duration are presented in tables and illustrated in
figures. The points in the figures showing no-observed—adverse—effect levels (NOAELs) or lowest-
observed-adverse-effect levels (LOAELs) reflect the actual doses (levels of exposure) used in the
studies. LOAELs have been classified into "less serious" or "serious" effects. "Serious" effects are
those that evoke failure in a biological system and can lead to morbidity or mortality (e.g., acute
respiratory distress or death). "Less serious" effects are those that are not expected to cause significant
dysfunction or death, or those whose significance to the organism is not entirely clear. ATSDR
acknowledges that a considerable amount of judgment may be required in establishing whether an end
point should be classified as a NOAEL, "less serious" LOAEL, or "serious" LOAEL, and that in some
cases, there will be insufficient data to decide whether the effect is indicative of significant
dysfunction. However, the Agency has established guidelines and policies that are used to classify

these end points. ATSDR believes that there is sufficient merit in this approach to warrant an attempt

DISULFOTON 8

2. HEALTH EFFECTS

at distinguishing between "less serious" and "serious" effects. The distinction between "less serious"
effects and "serious" effects is considered to be important because it helps the users of the profiles to
identify levels of exposure at which major health effects start to appear. LOAELs or NOAELs should
also help in determining whether or not the effects vary with dose and/or duration, and place into

perspective the possible significance of these effects to human health.

The significance of the exposure levels shown in the Levels of Significant Exposure (LSE) tables and
figures may differ depending on the user’s perspective. Public health officials and others concerned
with appropriate actions to take at hazardous waste sites may want information on levels of exposure
associated with more subtle effects in humans or animals (LOAELs) or exposure levels below which
no adverse effects (NOAELs) have been observed. Estimates of levels posing minimal risk to humans

(Minimal Risk Levels or MRLs) may be of interest to health professionals and citizens alike.

Estimates of exposure levels posing minimal risk to humans (Minimal Risk Levels or MRLs) have
been made for disulfoton. An MRL is defined as an estimate of daily human exposure to a substance
that is likely to be without an appreciable risk of adverse effects (noncarcinogenic) over a specified
duration of exposure. MRLs are derived when reliable and sufficient data exist to identify the target
organ(s) of effect or the most sensitive health effect(s) for a specific duration within a given route of
exposure. MRLs are based on noncancerous health effects only and do not consider carcinogenic
effects. MRLs can be derived for acute, intermediate, and chronic duration exposures for inhalation

and oral routes. Appropriate methodology does not exist to develop MRLs for dermal exposure.

Although methods have been established to derive these levels (Barnes and Dourson 1988; EPA 1990),
uncertainties are associated with these techniques. Furthermore, ATSDR acknowledges additional
uncertainties inherent in the application of the procedures to derive less than lifetime MRLs. As an
example, acute inhalation MRLs may not be protective for health effects that are delayed in
development or are acquired following repeated acute insults, such as hypersensitivity reactions,
asthma, or chronic bronchitis. As these kinds of health effects data become available and methods to

assess levels of significant human exposure improve, these MRLs will be revised.

A User’s Guide has been provided at the end of this profile (see Appendix A). This guide should aid

in the interpretation of the tables and figures for Levels of Significant Exposure and the MRLs.

DlSULFOTON 9

2. HEALTH EFFECTS

2.2.1 Inhalation Exposure
2.2.1.1 Death
No studies were located regarding the lethal effects in humans after inhalation exposure to disulfoton.

In an acute inhalation study, l—hour exposure of male Sprague-Dawley rats to 202.2 mg/m3 disulfoton
resulted in 60% mortality, while no deaths occurred in male rats exposed to $195.1 mg/m3 (Doull
1957). In Holtzman rats, a 1-hour exposure resulted in death of 3 of 6 males at 180.1 mg/m3 and 2 of
6 females at 87.6 mg/m3 (DuBois 1971). No deaths occurred in males at 101.3 mg/m3 or in females
at 75.1 mg/m3. LC50 values reported for Wistar rats were 290 mg/m3 in males and 63 mg/m3 for
females exposed for 1 hour and 60 mg/m3 for males and 15 mg/m3 for females exposed for 4 hours
(Thyssen 1978). When the rats were exposed to disulfoton 4 hours/day for 5 days, a concentration of
9.8 mg/m3 resulted in death of 9 of 10 females within 1—8 days after exposure. N0 males died, and
no deaths occurred in either sex at S 1.8 mg/m3. In a 3—week study, 5 of 10 females exposed
intermittently to 3.7 mg/m3 died after 3—12 exposures, while 3 of 20 females exposed intermittently to
3.1 mg/m3 intermittently died after 8—15 exposures (Thyssen 1980). No deaths occurred in the male
rats in the 3-week study. Based on these data, strain differences in the lethal concentrations of
disulfoton appear to exist in rats, and female rats are definitely more susceptible to the lethality of
disulfoton than male rats. A l-hour exposure of female mice to 53.4 mg/m3 (lowest exposure
concentration) resulted in 10% mortality, and 58.2 mg/m3 resulted in 70% mortality (Doull 1957).
Male mice were not studied; therefore, data are insufficient to make comparisons of the inhalation
lethality of disulfoton between male and female mice, and between rats and mice. The lethality of
disulfoton appears to be related to the cholinergic effects, since such effects as tremors or convulsions
were usually noted in the animals that died (see Section 2.2.1.5). The LC50 values in rats and the
LOAEL values resulting in mortality in rats and mice are recorded in Table 2-1 and plotted in

Figure 2—1.
2.2.1.2 Systemic Effects

No studies were located regarding respiratory, cardiovascular, gastrointestinal, hematological,
musculoskeletal, hepatic, renal, endocrine, dermal, ocular, or body weight effects in humans after

inhalation exposure to disulfoton.

10

DISULFOTON

2. HEALTH EFFECTS

83:83 3:228 6c
- coEnEE 88235.20

 

 

ho chw 52%. ESE u nw 58.3.
$2 :25 2 23:3 .mmmczmamamv .2 m? E F Em m
EofiEcom. 50:892.
60:55.5 6252.3 3238
6:85 523:3: $329
$2 :30 ucm 9.2233 2825 s. fimw .5 -m. «mm a
3030.232
Esau.
€228V
$2 :80 Gen 63: u v.8 E F 83o: 5
EE m A: EOE
:25 m 33.5
82 58:: 623:9 u. 3 {530 5m m
2:. e Ease
2.2 $3.: 6% 0th u. 3 u m Em m
83d u. 3 cause
3.: 882: 88d s. cm E v am v
883 H. mm cause
as. 532:. 83d .2 SN E — a: 9
ass 99 2 39 e2. $3;
{Enema :56 mg n. Sm E F Em N
$.38
.3359
$2 .58 6% <qu 2 «wow E 5.0 am F
5.39
mmamOmxm m._bo<
885.: 5.55 as? sea; 5% >835. is... 2.5..
26.3w 2.2.3 30.. 4552 20:95... 318nm 8
493.. 2:»on . >8.

 

seas-:5 . 53:35 2 Eanoaxm «505.36 .o 230.. .7“ m._m<._.

11

DISULFOTON

2. HEALTH EFFECTS

2... m
{Eu m :3 .28.“:

 

 

89 8.3325 fio .>> 8 x3 m Hm I
2E2n>m
E... w 3 >205
{5% m Eng
82 88...: 6% 8.8 u. tn x.... m .8... 2
£30
wmszn—xm m._.<_nm2mmhz_
EcumEton: 62.83%
50.5%: .co_.m>__mm .953
5.5.5 .mcozgfinz 5.250.
$3 :28 vcm $58.25 .5382... u Tom E _. 3:22 NF
3.3.8:.
Acemmwaou 3.2.8 6.255... 8583::
$9285.05 .0 29¢. 53:8 08.23565
3583:: new £8.85 mSooESE E... .V c823.
£2 :89...» 33.558 8:62.23 m... c. 8.32%.. $8.2. m... n m... u m E. :
53:83 omszofio .oc .
- 8:52... 3823535
.0 2.9m 32%. .Eoo.m n. {m c823.
Rm. 58...... o. 92.3 .mmwccmamam. S. 3 .E v Em or
02.80%: SEWE. GENE. Angus. Sim 3535 A528. 2:2.
26.53 mac—.8 n3.— 4m<oz 20:83... Bin 2
._m<o._ 3.5% - >8.

 

€02.28. 5.5.2.... - 3.8.35 o.u.=monxm.cuo.._=m_m.o 226.. .3 3...:

12

DISULFOTON

2. HEALTH EFFECTS

 

 

Emu 29m;
>32 889.0% «cm: 5 u. hm md :S um
Em 5:50
9:995 .293 9:32
ucm 23.8% 3390:: n. Em m.o 58cm
Em .22“.
mm 0:82..
Em 05me
:55 as 29
c. 80an 83353 9:
c_ 68 9:18.: we... «on:
.mczmesozmma 832$ u. an no 253
Mm 228
RE 0 A: EOE
:55 $5 95 9: com: b02238. 9: 5 {EU m .995
89 :8sz E mac:— uwucofifi “6595 u. Em momcmco bofiEEmzc: m.o fio amwm is m Ex 9
v; :5 um
v; hm.30
3 :50
v; .ooucm
v; Rear.
3 258:
v; .wxmbmsz
v4 ofiEmI
3 0:80
v; 0650
32222 .32 25 o
9: ho coszEng u. v; xiv m in .azumE
32 9.83.6 s 88205 8328: .2: s. 2.0 05$. x; 9 am 9
g: Amp—\WEV AQEEE% Rafi—REV Eflan>m >053§n AC—Ghov 23D:
26:8 32.8 «8.. d3: 228.3. 3.8% 2
.53.. 158.5 .5.

 

AUOSCSCOOV Cozfl—flc—h— - COuOu—SED On EJQOQKW uCflOECO-W *0 20>On— .FnN NJM<P

13

DISULFOTON

2. HEALTH EFFECTS

com: 0:20.300. 05
5 009.050 b20689:

 

 

3 323588 2:. 0 5 >205
009.020 39.9: 0.3% m 525
89 $25 28 £5.00 2 .0823 no 3 x; 0 am 2
RE 0
0.3% m $302003
08— 8.3995 v; :3 nw Em 0F
.0.:0:0..0an>.<_0050.255:—_
n. fin S> um
m fin h0.300
€903 .2060 0200.0.
0:0 05.0000 00000.8: u. fin no.0 .0005
n. fin .mcom
"— fin 0:000:
$259.30.
$0.03: b:&oE>_oa
*0 000E023 00000.05
.00§0o:aE>_ no
0320200 00002003 u fin No.0 2080:
n. fin 0:000
u. fin 2an
:25 b28300. 05
5 009.050 220E593
00320:. 60% .05 90. RE 0 :4. EOE
c. 095. 8 5:90.806 0.3% m 525
82 88:: 05 808.23 n. 0.0 8.0 03m 0.; m a: t
88!... .2020 .20.... A2550 52:0 3.3.! 3.50 2.5..
26.80 32.... 3... ..u<oz >83.% 38% 8
._u<o._ 0589a . 3.

 

escacoov 5:22... - 8.8.35 8 2:896 0:85:20 5 22,3 .3 39:.

14

DISULFOTON

2. HEALTH EFFECTS

Ammflmfioéofi ENE *o
8:525 $8.? .3585

 

 

5.305% 5252.3 9me «ms 2.... m 3 >202...
33205 50632.8 9: 9:3 2:898 .95 xiv m .smic
8m— cgfi .floEm: 283$ Nm 2:: 35 m .2 >926; fio x3 m Em mm
628285.05
£95 ho 8:525
$mwém 63.23565
wgooErcm
*0 coEnEE oxovm-mm 2:. o
.mmflSmmEBco mEmma xiv m :45 .Ecomiv
32 9.88.5 .o 5:525 $33: «A 9.0 x3 9 fix «a
RE m
x26 m 39.5583
82 9.88.6 No x; m Em &
30529502
com: roaming.
on. c_ momcmzo
bofiEEmcE >2
umquEooom mmmcmco
328E mcon 9:08.. 2.5 m A: EOE.
.2995 52% o>=m_o._ xiv m East
82 5996. new 228% 33283 n. fin mod x3 m fix on
8:28.: GEE—5 8,—3.5 Sac: in 55:69.. 325 9:6:
32.8 82.8 83 .532 2285.. 38am 8
d3; 33on . .5.

 

AUgC—«COOV 20:365.: u COaOh—anmn— On eafiaxm «=fl05=m_m *0 20>0n— .FaN MJG<P

15

DISULFOTON

2. HEALTH EFFECTS

$3.me M £5 ”bougamm: u awwm u_m>w_ «omtméflgumémzwmnoéc u ._m<oz ”86.325.30sz n _oxw\om=s_
6.9: u s. u_w>m_ 2825-09guméwzmwnoéwio. n.E<O.. ”=2 aboméozmzcwocoo 85¢. n om0._ x250: u E 2352295: "05on
”.mczmmfiozmmm n 0280 6.992 n n. 08:00qu N bencm ”Ectwu u E60 ”Amimc n v 5.3085680 n 0650 ”£995 >25 u ~>> um

é£=nmtm> :mEsc .2 or van means: 2 mEEEm E02 cozfloafluxm L2 my on 20 582 353.85 cm 3 8056 28 6262588 E2933
:35: m 2 umtm>coo .wsmoaxw EwEE._2:_ .2 3533 cozgcmocoo ”oEBE Yorxm 20 .EE c2292.: cozmsuémfimgmfi cm 9th 2 830
3.539

5:55 .2 or new mamas: 2 2955. E02 cozfloqmim ._2 8 on 8 862 359.88: cm >9 2635 new .cozmzcmocoo E2953 5:52 a 2
332.8 65898 EwEEQE .2 uwumsfim cozmzcmocoo ”mEBE wood 20 SEE _m>w_ gm: .mE_c_E cozflmcg 5:98-238 cm m>tmu 2 now?
.TN 939”. E 9225 2 $889.50 .353: 9......w

 

65585
3.35% 5232.3 SE o A: >202...
83905 .wco_m_=>coo v.25 m .325
82 582% @0822 2825 u. fin 0 Nod {5 m «mm «a
8:28.: AnE‘mEv 8.595 825.5 Eim >333... A525 952.
26:3. 26:8 83 4u<oz 23.5.. 328% 8

 

._m<o.. 35.on . >3.

 

2835.53 5.52:. - 8.2.35 22.58% E8555 3 225.. .3 39:.

16

DISULFOTON

2. HEALTH EFFECTS

 

 

 

 

 

 

 

 

+
_
_
_
_
.—.~ 23» 5 35:0 2 3:88:00 Eon coco 9 :6: 59:5: 0:... "
3.3234302 O n
> 2223 38% 383 m8. 3339 Q _
50:8 :9: .650 " Amiégvmfioum 39:38:93.. . Em . u
98% .2 .26. 32. 3.55.2 _ 8 0.8m S I 882 E _
_
_
>3. _
_
_
0.:
E
Q 5? 5
O O
E a
O O a
a l
ENP .M E. a
O O O I a
O
:
0
09V «‘90
¢
% 9
0/.
Av
32% «E
352‘

scam—ac:— I 53:35 3 953an E3535 uo £90.— . Tn 959".

500.0

"00.0

5.0

F0

or

00—

000 _.
$53.5

17

DISULFOTON

2. HEALTH EFFECTS

 

 

 

 

 

 

 

 

 

 

I 5000.0
>
_
" ._-~ azfl. 5 82cc 2 3:88:00 Eon coco o. :6: .382. 9:.
_ I 2000.0
_
_
_ Am_me_§:m<oz O
_ > 365.5038? ”8:3 82 8396.. Q
n .853 cm... .25 “ Amaécgmsazo 25:85:39 0 am . I _.00.0
_ msmcm.o:o>a;m_._we_c_z _ 88.8 9 I 382 e
_
_
_ >8.
.
_ .
_ .8 .2 .2 .2 20 0
0:.“ O O O O
.8 .9 .9
0 .mm 0 0.9 I rd
0 O
.9 .9 .9 .9 .9
.5 Q .30 O O O
O .9 0.9 .9 .9 .9 .9 .9 .9 .9 .9 .9 .9 I F
0 O O O O O O O O O O O Q
.vm .mm .8 .2 .2 .2 .2 .2 .2 .2 .2 .2 .9 .9
o o o m m e m m m o 0 o o 0
.nm . 2 .9 .9 .9 .9 .9 .9 .9
I I I I I I or
/V ) O O O o» ,v ,~, ,~, 0 o ,0 0
J00 @fg/ {0° 00 ova 00 IVS 00 @04 0V0 «b» 0% 0&9 98 A E 38v
0 O é/ oo .9 Q 0 e v / / 9 0
/ 00.00% 0? ¢ A. 00. / 0/2. 0% be 290 940 «v.
x o o 0/. a 0. do a m. o
«.0 .wyeo/ a) 90+ 90/ 9% 9% @
Au. /9/ / / J
2E2m>w
is. «8.90
0352.52:—

Gwacscoov c2555.. I cou0=3£0 2 Eamonxm =53:ch 20 £05.. . TN 230E

DISULFOTON 18

2. HEALTH EFFECTS

Studies on these end points in animals exposed by inhalation to disulfoton are discussed below. The
highest NOAEL values and all LOAEL values from each reliable study for these end points in animals

in each duration category are recorded in Table 2-1 and plotted in Figure 2-1.

Respiratory Effects. In two separate experiments in which male and female rats were exposed
intermittently for 3 weeks to 0.1, 0.5, or 3.7 mg/m3 in the first experiment, and to 0.02 mg/m3 (males
and females) or 3.1 mg/m3 (females only) in the second experiment, inflammatory changes were found
throughout the respiratory tract at 0.5, 3.1, and 3.7 mg/m3 (Thyssen 1980). These inflammatory
changes were considered to be related to reactive bone marrow changes (see Section 2.2.1.3), which
were minimal in male rats and definite in females in the first experiment. Deaths occurred in the
female rats exposed to 3.1 or 3.7 mg/m3, and mottled, distended, and discolored lungs were found
upon necropsy of the rats that died. Increased incidences of inflammation of the nasal turbinates were
found in male rats, but not female rats, exposed to 1.4 mg/m3 intermittently for 13 weeks (Shiotsuka

1989). These lesions were not found at 0.16 mg/m3.

Cardiovascular Effects. No treatment-related microscopic lesions were found in the hearts of rats
exposed intermittently to 3.7 mg/m3 for 3 weeks (Thyssen 1980) or to 1.4 mg/m3 for 13 weeks
(Shiotsuka 1989).

Gastrointestinal Effects. In the female rats that died during intermittent exposure to 3.7 mg/m3
for 3 weeks, bloated gastrointestinal tracts and ulcer-like foci in the glandular mucosa were found
upon necropsy (Thyssen 1980). Otherwise, no treatment—related histological effects in the
gastrointestinal tract of the surviving females or in males exposed to $3.7 mg/m3 were found.
Likewise, no gastrointestinal tract lesions were found in male or female rats exposed intermittently to

$1.4 mg/m3 for 13 weeks (Shiotsuka 1989).

Hematological Effects. No effects on formed elements of the blood were found upon
hematological examination in rats exposed intermittently to $3.7 mg/m3 for 3 weeks (Thyssen 1980).
However, in a second experiment in which female rats were similarly exposed to 3.1 mg/ma, a
relatively low percentage of lymphocytes and high percentages of polymorphonuclear leukocytes in the
differential leukocyte counts were found. These effects were regarded as a first sign of a response to

the inflammation in the respiratory tract and bone marrow changes observed in these rats (see

DISULFOTON 19

2. HEALTH EFFECTS

Section 2.2.1.3). No hematological effects were observed in rats exposed intermittently to

0.02—O.5 mg/m3 for 3 weeks (Thyssen 1980) or to 1.4 mg/m3 for 13 weeks (Shiotsuka 1989).

Musculoskeletal Effects. No gross or histological lesions were found in bones or skeletal muscle

of rats exposed intermittently to $1.4 mg/m3 for 13 weeks (Shiotsuka 1989).

Hepatic Effects. Clinical chemistry tests and histological examination of livers revealed no hepatic
effects in rats exposed intermittently to $3.7 mg/m3 for 3 weeks (Thyssen 1980) or to $1.4 mg/m3 for
13 weeks (Shiotsuka 1989).

Renal Effects. Clinical chemistry, urinalysis, and histological examination of kidneys revealed no
renal effects in rats exposed intermittently to $3.7 mg/m3 for 3 weeks (Thyssen 1980) or to

$1.4 mg/m3 for 13 weeks (Shiotsuka 1989).

Endocrine Effects. No histological lesions were found in the thyroid or adrenal glands of rats
exposed intermittently to $3.7 mg/m3 for 3 weeks, but females exposed to 3.1 and 3.7 mg/m3 in two
separate experiments had significantly increased absolute and relative adrenal weights (Thyssen 1980).
Since the increase in adrenal weights was consistently observed in both experiments, it was considered
to be related to disulfoton exposure. No histological effects or effects on the weight of the adrenal
gland and no histological effects on the thyroids, parathyroids, pituitary, or pancreas were observed in

rats exposed intermittently to $1.4 mg/m3 for 13 weeks (Shiotsuka 1989).

Dermal Effects. No gross or histological lesions were found in the skin of rats exposed

intermittently to 1.4 mg/m3 for 13 weeks (Shiotsuka 1989).

Ocular Effects. No histological or ophthalmological evidence of ocular effects were found in rats
exposed intermittently to $3.7 mg/m3 for 3 weeks (Thyssen 1980) or to $1.4 mg/m3 for 13 weeks
(Shiotsuka 1989).

Body Weight Effects. Female rats exposed intermittently to 3.7 mg/m3, but not 3.1 mg/m3, for
3 weeks had 12% and 11% lower body weights than controls during weeks 1 and 2, respectively, but
only 5% lower body weight during week 3 (Thyssen 1980). Males similarly exposed to 3.7 mg/m3

had lower body weights than controls, but the difference was never >10%. No effects on body weight

DISULFOTON 20

2. HEALTH EFFECTS

were found in the rats exposed intermittently to 0.5 mg/m3 (Thyssen 1980) or 0.7 mg/m3 (Shiotsuka
1988) for 3 weeks, or 1.4 mg/m3 for 13 weeks (Shiotsuka 1989).

2.2.1.3 Immunological and Lymphoreticular Effects

No studies were located regarding immunological and lymphoreticular effects in humans after

inhalation exposure to disulfoton.

In two separate experiments in which male and female Wistar rats were exposed intermittently for

3 weeks to 0.1, 0.5, or 3.7 mg/m3 in the first experiment, and to 0.02 mg/m3 (males and females) or
3.1 mg/m3 (females only) in the second experiment, inflammatory changes were found throughout the
respiratory tract at 0.5, 3.1, and 3.7 mg/m3 (Thyssen 1980). These inflammatory changes were
considered to be related to reactive bone marrow changes. The reactive bone marrow changes were
not specifically described in the study, but were regarded as minimal in male rats and definite in
female rats in the first experiment. In the second experiment, but not in the first, female rats exposed
to 3.1 mg/m3 had a relatively low percentage of lymphocytes and high percentages of
polymorphonuclear leukocytes in the differential leukocyte counts. These effects were regarded as a
first sign of a response to the inflammation in the respiratory tract and bone marrow changes observed
in these rats. The female rats exposed to 3.1 mg/m3 also had decreased absolute and relative spleen
weight, but histological examination of the spleen and bronchial lymph nodes revealed no treatment-
related effects in males or females exposed to $3.7 mg/m3. In addition, histological examination of
bone marrow, cervical lymph nodes, mesenteric lymph nodes, spleen, and thymus of Fischer 344 rats
exposed intemiittently to $1.4 mg/m3 for 13 weeks revealed no effects (Shiotsuka 1989). The highest
NOAEL values and the LOAEL values for immunological and lymphoreticular effects in rats are

recorded in Table 2-1 and plotted in Figure 2-1.
2.2.1.4 Neurological Effects

Exposure to disulfoton can result in inhibition of cholinesterase activity in blood and at nerve synapses
of muscles, secretory organs, and nervous tissue such as the brain and spinal cord (Murphy 1986).
The accumulation of acetylcholine at these sites (specifically, the nerve synapses and ganglia in these
organs) results in central nervous system, nicotinic, and muscan'nic effects. Clinical signs and

symptoms of neurotoxicity are usually observed in humans and animals that have been acutely

DISULFOTON 21

2. HEALTH EFFECTS

exposed to disulfoton or other organophosphate insecticides. Central nervous system signs and
symptoms include anxiety, restlessness, depression of respiratory and circulatory centers, ataxia,
convulsions, and coma. Nicotinic signs of disulfoton toxicity include muscle weakness, muscle
tremors and fasciculations, and involuntary twitching. Muscle weakness that affects the respiratory
muscles may contribute to dyspnea and cyanosis. Tachycardia may result from stimulation of
sympathetic ganglia in cardiac tissue and may, therefore, mask the bradycardia due to the muscarinic
action on the heart. Nicotinic action at the sympathetic ganglion may also result in pallor, high blood
pressure, and hyperglycemia. Muscarinic signs of disulfoton toxicity include miosis, increased
salivation, sweating, urination and defecation, vomiting and nausea, bronchoconstriction, increased

bronchial secretions, and bradycardia that can progress to heart block.

Inhibition of the two principal human cholinesterases, acetylcholinesterase and pseudocholinesterase,
may not always result in visible neurological effects (Sundlof et a1. 1984). Acetylcholinesterase, also
referred to as true cholinesterase, red blood cell cholinesterase, or erythrocyte cholinesterase is found
in erythrocytes, lymphocytes, and at nerve synapses (Goldfrank et a1. 1990). Inhibition of erythrocyte
or lymphocyte acetylcholinesterase is theoretically a reflection of the degree of synaptic cholinesterase
inhibition in nervous tissue, and therefore a more accurate indicator than pseudocholinesterase activity
of inhibited nervous tissue acetylcholinesterase (Fitzgerald and Costa 1993; Sundlof et a1. 1984).
Pseudocholinesterase (also referred to as cholinesterase, butyrylcholinesterase, serum cholinesterase, or
plasma cholinesterase) is found in the plasma, serum, pancreas, brain, and liver and is an indicator of

exposure to a cholinesterase inhibitor.

Pseudocholinesterase and lymphocyte acetylcholinesterase activities are depressed before erythrocyte
cholinesterase, suggesting that these cholinesterases are more sensitive than acetylcholinesterase
(Fitzgerald and Costa 1993; Iyaniwura 1991; Sundlof et a1. 1984). However, erythrocyte
cholinesterase recovers more slowly (90—120 days) than pseudocholinesterase or lymphocyte
acetylcholinesterase (days to weeks), and is therefore a better indicator after exposure ceases.
Depression in pseudocholinesterase activity only indicates possible exposure to organophosphate(s),
whereas depression in erythrocyte and lymphocyte cholinesterases also indicates a neurological effect,
since they reflect inhibition of brain acetylcholinesterase activity. Recently, it was shown that the
inhibition of lymphocyte acetylcholinesterase activity more closely paralleled the inhibition of brain
acetylcholinesterase than did erythrocyte acetylcholinesterase activity (Fitzgerald and Costa 1993). In

this profile, inhibition in lymphocyte or erythrocyte acetylcholinesterase activity and not

DISULFOTON 22

2. HEALTH EFFECTS

pseudocholinesterase activity is considered as an adverse neurological effect. Based on an evaluation
.by Kaloyanova and E1 Batawi (1991), ATSDR considers a 60% or greater acetylcholinesterase
inhibition as a serious effect and less than 60%, but greater than 20%, acetylcholinesterase inhibition

as a less serious effect.

Nervous system effects may occur in humans after occupational exposure to disulfoton (Wolfe et al.
1978). In this study, mean disulfoton concentrations of 0460—0633 mg/m3 caused a 22.8%
depression in erythrocyte cholinesterase activity in workers at a pesticide-fertilizer mixing operation.
The workers were exposed to disulfoton for 9 weeks, and there were no reports of adverse clinical
signs due to disulfoton exposure. The study was limited in that baseline blood cholinesterase activities
were obtained 2 weeks after the initial exposure and were compared with cholinesterase activities at
9 weeks. Therefore, the actual depression in cholinesterase activity over a 9-week period was
probably >22.8%. In addition, these workers were also derrnally exposed to disulfoton (see

Section 2.2.3.4); therefore, the 22.8% depression in cholinesterase activity was probably due to both
inhalation and dermal exposure. Despite these limitations, the study concluded that because this
depression in cholinesterase activity was only associated with dry mixing operations, the wet mixing

operations are less hazardous to workers.

Neurological effects, such as muscle twitching, ataxia, and increased salivation, urination, defecation,
and lacrimation were observed in male Sprague-Dawley rats exposed to 265.1 mg/m3 and in female
Carworth Farms mice exposed to 253.4 mg/m3 for 1 hour (Doull 1957). Female rats and male mice
were not included in this study. However, the greater susceptibility of female rats to the cholinergic
effects of disulfoton was demonstrated in several experiments in an acute inhalation study using Wistar
rats (Thyssen 1978). In the LC50 determinations in this study, sluggishness, failure to groom, and
typical signs of cholinesterase inhibition (not otherwise described) were observed in male rats exposed
to 2133 mg/m3 and in females exposed to 227 mg/m3 for 1 hour. These signs of toxicity were
observed at lower exposure levels when rats were exposed for 4 hours (in males exposed to

264 mg/m3 and in females exposed to 23.4 mg/m3). These effects were transient, lasting for about
24 hours after exposure. In an experiment designed to examine cholinesterase activity in rats exposed
to 0.5, 1.8, or 9.8 mg/m3 for 4 hours/day for 5 days, erythrocyte cholinesterase activity was depressed
by 30—32% of controls in males exposed to 9.8 mg/m3 and by 17—26% in females at both 1.8 and

9.8 mg/m3. In addition, all rats were reported to display unspecified behavioral disorders at

21.8 mg/m3 and unspecified signs of cholinergic toxicity at 9.8 mg/m3. No inhibition of erythrocyte

DISULFOTON 23

2. HEALTH EFFECTS

cholinesterase activity and no signs of cholinergic toxicity were observed at 0.5 mg/m3. Based on this
NOAEL of 0.5 mg/m3, an acute-duration inhalation MRL of 0.006 mg/m3 was calculated as described
in footnote "b" in Table 2—1. No significant decrease in the activity of brain, serum, or submaxillary
gland cholinesterase was found in female rats exposed to 0.14—0.7 mg/m3 disulfoton for 1 hour/day for
5—10 days (DuBois and Kinoshita 1971). No clinical signs of disulfoton toxicity or other details were

reported.

Signs of cholinergic toxicity and depressions in cholinesterase activities were also observed in rats
exposed to disulfoton for intermediate durations. In Wistar rats exposed intermittently to 0.1, 0.5, or
3.7 mg/m3 for 3 weeks, exposure to 0.1 mg/m3 resulted in brief periods of lethargy after exposure
ended during the last week; exposure to 0.5 mg/m3 resulted in lethargy and failure to groom in males
during the last week and in females during the second and last week; and exposure to 3.7 mg/m3
resulted in muscle tremors, convulsion, increased salivation, and dyspnea in males starting at the end
of the first week and in females during the first week (Thyssen 1980). Erythrocyte cholinesterase
activity was inhibited in males by 24—28% and in females by 27—32% at 3.7 mg/m3. Brain
cholinesterase activity was inhibited in males by 48% at 3.7 mg/m3 and in females by 30% at

0.5 mg/m3 and 58% at 3.7 mg/m3. In a second 3-week experiment to determine a no-effect level for
cholinesterase inhibition in Wistar male and female rats, no clinical signs of neurological effects and
no effects on plasma, erythrocyte, or brain cholinesterase were observed at 0.02 mg/m3 (Thyssen
1980). Female rats exposed to 3.1 mg/m3 had muscle tremors, convulsion, increased salivation, and
dyspnea, confirming the results in the first experiment. Male rats were not exposed to 3.1 mg/m3 in
the second experiment. Based on the NOAEL of 0.02 mg/m3, an intermediate-duration inhalation
MRL of 2x10'4 mg/m3 was calculated as described in footnote "c" in Table 2—1. In Fischer rats
exposed intermittently to 1.4 mg/m3 for 13 weeks, erythrocyte cholinesterase activity was inhibited by
22—28% in males and 26—34% in females, and brain cholinesterase activity was inhibited by 29% in
males and 28% in females (Shiotsuka 1989). Cholinesterase activities were not affected at

$0.16 mg/m3, and no effects on brain weight or histological evidence of lesions in the brain, optic
nerve, sciatic nerve, or spinal cord were found at any exposure level. In a similar study in Fischer 344
rats exposed to lower concentrations for 3 weeks, no significant differences in brain cholinesterase
activities were found at 0.006—0.7 mg/m3 (Shiotsuka 1988). Erythrocyte cholinesterase activity was
statistically consistently decreased at 0.7 mg/m3, but the decreases were never greater than 17% of
control levels. The highest NOAEL values and all reliable LOAEL values for neurological effects in

rats and mice for each duration category are recorded in Table 2-1 and plotted in Figure 2-1.

DISULFOTON 24

2. HEALTH EFFECTS

2.2.1.5 Reproductive Effects

No studies were located regarding reproductive effects in humans after inhalation exposure to

disulfoton.

In rats exposed intermittently to 0.02-3.7 mg/m3 for 3 weeks, measurements of the testes and ovary
weights and histological examination of the testes and ovaries revealed no compound-related effects
(Thyssen 1980). Similarly, no effects on testis or ovary weight and no compound-related histological
lesions in epididymides, prostate, seminal vesicles, testicles, cervix, mammary glands, ovaries, or
uterus were found in rats exposed intermittently to $1.4 mg/m3 for 13 weeks (Shiotsuka 1989).
Reproductive studies in animals given disulfoton by the oral route have demonstrated that disulfoton
produces effects on reproductive parameters (see Section 2.2.2.5); therefore, the above inhalation
concentration levels cannot be considered NOAEL values for reproductive effects because these

inhalation studies did not examine reproductive performance or outcomes.
2.2.1.6 Developmental Effects

No studies were located regarding developmental effects in humans or animals after inhalation

‘ exposure to disulfoton.
2.2.1.7 Genotoxic Effects

No studies were located regarding genotoxic effects in humans or animals after inhalation exposure to

disulfoton.

Genotoxicity studies are discussed in Section 2.4.

2.2.1.8 Cancer

No studies were located regarding cancer in humans after inhalation exposure to disulfoton.

In a 13-week study in rats exposed intermittently to $1.4 mg/m3, the author reported that

comprehensive histological examination of organs and tissues revealed no treatment-related neoplastic

DISULFOTON 25

2. HEALTH EFFECTS

lesions (Shiotsuka 1989). However, chronic-duration inhalation studies, which would be more

appropriate to assess possible carcinogenicity, were not located for disulfoton.

2.2.2 Oral Exposure

2.2.2.1 Death

Only one study was located involving death in humans after ingestion of disulfoton (Hattori et al.
1982). In this case report, a 30-year-old man was found dead after consuming an unknown amount of
disulfoton. He was believed to have been dead for at least 24 hours. Autopsy and histopathological
examination revealed miosis, bubbling saliva from the mouth, pulmonary edema and hemorrhage,
swelling of the glomerulus, and congestion of most organs, which suggested that the man had ingested
an organophosphate. Analysis of urine and blood samples confirmed that disulfoton was the toxicant

responsible for the death.

The dose of disulfoton associated with death following acute oral exposure in animals depends on the
sex, species, and the duration of the exposure. As seen from Table 2—2 and Figure 2-2, female rats
and mice were generally more sensitive than male rats and mice, and rats generally appeared to be
more sensitive than mice, to disulfoton given orally. LD50 values ranged from 1.9 to 3.2 mg/kg in
female rats, 6.2—12.5 mg/kg in male rats (Bombinski and DuBois 1958; Crawford and Anderson 1974;
Gaines 1969; Mihail 1978; Pawar and Fawade 1978), 2.7—8.2 mg/kg in female mice, and

58—193 mg/kg in male mice (Mihail 1978; Pawar and Fawade 1978; Stevens et al. 1972a). In one
LD5O determination in rats, deaths occurred within 6 minutes to 2 days in males and 4 minutes to

3 days in females (Gaines 1969). Oral LD50 values of 10 mg/kg in rats of unspecified sex (Schafer
1972), of 89—108 mg/kg in male guinea pigs (Bombinski and DuBois 1958; Crawford and Anderson
1973), and of 12.7 mg/kg in female guinea pigs (Crawford and Anderson 1973) have also been
reported. A dose of 18 mg/kg was determined to be the minimum dose at which mortality occurred in

wild deer mice of unspecified sex given disulfoton by gavage (Schafer and Bowles 1985).

Deaths occurred on the day of treatment in 4 of 6 female rats at a dose of 2.5 mg/kg and in 1 of
9 female rats at a dose of 1.5 mg/kg, but no deaths occurred in male rats given $5.2 mg/kg (Sheets
1993a). However, in another study using the same strain of rats (Sprague-Dawley), 1 of 5 male rats

died after receiving one dose of 3.5 mg/kg disulfoton, while two more rats died after receiving the

26

2. HEALTH EFFECTS

 

 

63.: mud 69 2:22.
Rel! A839 :3. 88 83: o
Swine
€2.60... 69 $3.39
.82; 36353862: ".3 88 am a
69
2::
3a 96v Ago
52 «3:52 $329
it; :55 99 .23 EN; .2... x.
69 .sz
«8:338 63.: o. 8:0 am o
. 53%...
228%“. 63.: "an 9 53859
EESE 639 23. 88 a: m
63.: "3.. 69 $3.5
£2.93 A899 23 88 am v
8de "Ed 69 €5.29
$2858 639 23 88 am m
#28235 E9 629
ufieoig 6% :9 “SN 88 am N
9238
$2288 83.: "6d 9 .8839
was 223.com 839 2mg 88 am F
525
mmamOnxm w.50<
8:223. 383569 983359 3.2935 .586 3.8: 8.089 .559 .38
26:8 2.2.8 86.. .fi<oz €5.52“. 38% 8
22.23 .5.
._m<o._ 2325

 

DISULFOTON

_050 o COqu—Sflmn 0a 0533mm «CNOECU_W n0 20>OJ N-N NJm<P

27

2. HEALTH EFFECTS

AmoEESozoafio «Emaa
c_ 33.65 .290.

 

 

oEEchono 256 59 Aim:
«8. Iguana .223 c_ 33.83 .206 885 coco «mm C
39:03me
.m_w>o_ 05.223 ucm
o:__mc9um._oc acct: E 69 cam:
83 29535 85205 $9M new MK: n. mad Boocm uoco Km 9
2E8a>m
2.2 8285 83d "EMF csov azv
2322320 250.: Sad ooco 9a :0 m—
ama. 0.8.6 6V 62V
vi 359:3 8mm; 299 3:0 9n :0 3
69
£52 .03 $239
is 2266 60% way .206 u o: 3:22 9
c2233
.22 69 $.39
.13; 8mg: 2a.? 8:0 0302 up
A839:
82 8.26m 30? .0 32:5: Ag 58 2.5
oil-5w 85003:: ca .0 EatoEv 9 8:0 8:22 3
3.235
E: 823“. 83.: "tum Q 538::
9533.1 8mm; 29m 8:0 8:22 o—
ases-c 93%.: 98%.... 983.55 58.3 Assoc 8.08% Egg 2:2.
26:2,... «serum 83 ._m<oz 3532“. 328% m.
I 20:23 . 8.
.— (OJ ihzoonxm

 

DISULFOTON

Augczcoov .20 - 53:35 2 950ng ESE—6W 3 «.054 a." m._m<.r

28

DISULFOTON

2. HEALTH EFFECTS

 

 

.3
>3 3 2980.. 5.;
m >3 8 mcEEmwn Ema .00. .m§>m
82 980 2995 .68 888. Ev: as...
93 2235.“. $8.93 228%ng 5. ca .2. an x; N; am mm
8% >3 3 3989
5.; m 2% a 5%
£995 €03 33902. .00. .m§>m
N8. 380 38.93 252.2% 3: .83.
.23 29.35.“. Sn ESOQEQV S_o.N .>> Um v.3 N; «am vN
$0.83....“
82 Esau. €252.83“. .00. c9305....
new 323“. 2a.. 339.05. 20d 23%... 8:0 «mm mm
.00. $an
3% 25 6.528.
82 .a s 980 59m; 298 3262 $8. sad :5 cm. a o. 3m «N
.00. 9228
Ema Ex— 38%.
«8. ._a s 980 29w; 5 8:88. «one sad <5 8 u o. a... 8
2.35590:
2.9 28.3,. was 5.9.23 .0 m_m>m_ .00. cSmSc
Ea .xmcngm Emacs c. 38.65. mm... 88cm 88 «mm cm
1.53. S. E
as. 2233 85520628 .8. cams).
can EchoEm >555 c. 338.... s.o.m 509...... 8:0 «mm. 3
35.20.6ch
2.8 05.82% .00. .523.
22 Imcfioum >355 c. 336:: s.o.m .085 8:0 “mm. or
855.: 98%.... 33%.... aauaémé 58:5 .88: 058%. .598. 2:9.
32.5w 26:8 83 .932 Econ—.2“. 328% 2
2823 . >8.
.50.. .23on

 

635:3. .80 - coup—=55 8 2:3an ESE—Em S «.05.. a.“ m..m<...

DISULFOTON

2. HEALTH EFFECTS

 

69 A883?
82 83$ 22825.8 2.: 8.2.2.19
can 392“". Ea: 3890:: s. Q— 2531 u m 3522 mm
69 383.2.“
8.9 .nzaa 6253on Ex. 33855
2a mugs“. Ba: 3390:: s. md 25%: u TN 330.2 mm
655 5 Bow 2.989:
:2 9.95 .>xo£mE-m->xofi>;-v .2 mm; 69 .5239
Nepal-$.00»; ho Cozwhoxw UOmmmhoEv n. de u. QN.O hooucm 60:0 «GE Fm
Nm 5:00
9238
69 .3939
~89 985 Nm .3903: coco fix on
69 $.38
89 Aquomam $3850 35 $3889
._d «6 8033 no: 80— Egogv 2 O.N a>> Um D 07—. «ME ON
69
2::
Ema m 6 9:3 REES
52 £995 609 30:32 m .2 g: .3399
.3 a $2.8 e\oow 223553 2 ca :5 E u 8; am an
69:: mcEmEB
89 E92: __m 6 53 2995 E £25.09
23 33:8 68 8032 £6.70: u. o.— u. and as R. u m Em mm
69 coast
o5 .35: A8593 0; u. md $2... 8.8 it mm
8:280: AaaEv gauaev Saubémé £826 650: 0502.9 .5ng 9:6:
32....» 32.8. 33 #302 >885“. 328% 2
I 22.25“. . >8.
4m<0._ 353an

 

 

Agasscoov .20 - :o.o=:n_o 2 953an anficmfi S 205.. a.“ mans.

30

37.5.9 3&on Efln c_

 

88.6% 62.8% 9.6205 A09 35%.
«2.: 380 .8583 .o... .ngs 25 55.;
9a 2.5qu 29368 6 22m 32%: 5a v.2 N; am 8
:2 8285 $9 62V
was 22255 @052: u. md 8:0 .mm 9.
8w8o~mmczoco
58¢ sea 6 852:5
$3 xotoo 359.8 50V 2233
E 90382 25.838 35 .osaanv
89 ._a .m 530 .0 EnEac 08520va EN u or “mm mm
32.56 60:56:03
.:o=m>__mm Steam
mmfldfiosficoimom 69 92260
E 028.6ch Ex F .3859
m «8. .35 980 5 8:88. oboe 2N u 3 am 8
F.
m. 23:8 $.28
U 8% >293: 3923585353 69 63959
a new 880 599 he c0595: #68 EN u or “mm mm
H
z 33:8
ms; 20.384 animaéozoémom 803 69 Ease
Pa 22335 6 52955 $58- Qmfl Sam 8:0 fix mm
232 wEEchoofio 69 53:2
«8. Imcngm Ems 5 88me Sam 85 «mm mm
.8529502
69 25%:
an? .352 395%.: o.m md ammm coco omzos. vm
8:280: fiaubémfiv Sign: 3.2935 .553 A050: 0502..."; €3me 95¢:
25:3. 26:8 83 ._m<oz >82.ch 38am 3
Aug >3..an . >8.
3589a

 

 

DISULFOTON

gonna—83 .80 . :o.o==n_o 2 0.5983 «acorns—mm 3 225.. N.“ m4m<h

31

DISULFOTON

2. HEALTH EFFECTS

33:8
owEQmoéoEEoow Em: go
8:525 $5-2 .2022.

 

 

.mcoumiotms .mmctmfi 69 $an
82 new 5.35.: 96388 g: éamflamv
._a .o ngzom .cosztom. .cozmzfimv Sod v o: Em t.
69
0E: m am
3650: 622838 «5% m .2 $.50
52 new coast: 9.885 g: ézaenwv
.a S agcow .cozmzfim .EEficanxmv SEN u mm; fix me
3:35:33
6:23.383 83.28565 53m
59 Pass. 6255.: mzmmmoxm 83236 new 599 E €25.05
9; agfim 6256 .239: n. o; .o 8:32.: $8-03 n. mad u a fix me
Eozmzfim 69 csmic
29 =23 .3890 mchEZ 283$ u. o; n. md ooco Ex 3.
AmEmu AmEmu A9
5 23:0“ 88285.05 5 33:05 39235.05 2.:
82 £855 95 «£83 £853 98 m To no 69
:85... new 95.. *0 5:525 $8-me n. 0; «Emma go 5:335 05$ m md u. n to u or fix 9
AomEmE
5:285: .amctmE A09 ficgm
82 580 5:sz omegwéoco 25 9%
Ya EEoouE £95 5 338% $3-08 2m x3 N; Em ~¢
8:222... REES gangs: Saubémfiv £29m A052”. 2:00va 3ng 2:3
26.8w 26:3 n8; 4m<02 35:62". 32025 8
! 2038.5 . >8.
._m<3 358.5

 

Aug—5:08 .20 - coup—.35 2 chaoouxm Euoficmm 3 205.. ~.~ m4m<h

32

DISULFOTON

2. HEALTH EFFECTS

 

 

6V
2.:
mg no 6533 55
«8’ .3 s :8» m; u 9 33¢ mm
6V
AmmfioEBm g:
32 new 882 66.58 mTw .5 60V
:85: 9a 25.. .o cozaogmmo 8363 o; no u 2 am an
5:22.035:
6E0
6.8 $.sz
8m— poeox 2m 88 3:22 B
3:02.650:
2252.3 .maEEo 6.9 axis:
£2 :25 2:20 .3523: m_om:EV Qm 0N 8:0 832 cm
33:3
08.285.05.208 Ev AcmEEoIV
E: as am 595 .o 8:325 083 u. owe x; r am 3
95:55.: >002
._o umm: .mEEE. .2089:
6253289 28:3 55;
35.8 38285650
egocEEm E
38.6% $3 .EoEm>oE
>3“. .o 82. REEF. 5E8
.co=mn=moo> 850.6% 69 bamenfiv
«82 986 .225863 28:5 u. who Ed 88 am 8
8:23»: Sfimflsv gang ans—wig scan .98: 058%. 3va 2.5:
32.8 26:8 $3 4932 issue". 328% 2
W34 E323 . >8.
350096

 

$835.58 .20 - 222.35 2 2:3an «anathema 3 £93.. N.~ mqmfi.

DISULFOTON

2. HEALTH EFFECTS

 

 

 

E
63—. 22“; D: U“ Ag Jana—u:
Ea ascemEo 8.0 :5 um as m Em mm
89
Ac=wc2vfioc um >85
22 28.3,. Em 5.228 B 296. 25 3.25
9.6 infinmum Emacs E mwmmtosv Emmod Loo—”Em U mm «mm mm
0.5825
swam
E 8:28
:9 .a s {so :56 RE “.8 x; v 3:22 mm
E A35
9. 8 .28.“:
88. 985 3% «:5 n. 5; u 3 am mm
on: E 852$
.36 883% :tv *0 583 SEN u on fix 3
£25
mmawOmxm m._.<_0m_zmm._.z_
8:280: Sang Eduasv 3:39:95 E$a>m A832“. 05089 3ng Ban:
26:3 26.3w 83 ._m<oz 3:83.". 328nm 2
>8.
l 20:23 .
4m<o._ 350093

 

62.5.53 .80 - 8.2.35 22325 285:? .o 225.. 3 39:

DISULFOTON

2. HEALTH EFFECTS

 

AmmEz @5599,
59 39:: __m E Emu 2995 E ESEBIV
ufifizfiw >uon 3039 $3.05 n. o... u. 8.0 25 um u Nmém Em No
$2 3% 2925 E 8525
.a s 82.8,. >83 883. $8; .2 3 :5 B u 8 am 8
mmd :5 cm
mmd $300
mmd EEO
mmd .60ch
mmd 85¢
93 3.82..
mmd .9383}
mmd ofiEoI
mmd 0:30
$6 2250
E coast
22 ofimugx mmd amom u 8 am on
m:
an”. a
mm“. .o as
.59: van
Avocoa acamEma c2833.,“
actau $32633. 5:25
£0.55 new mmfiEE a 952.95
.2..qu E c. 5% x3 9 HI $.38
82 ?!au: Ego; >39 5 9.320% 65682“. baueawv
93 :85: «or Tm “EM #078 mod no.0 a>> um x3 mp ”Ou— Em mm
8:282... avg... Quuag 333%. Eim A330: 0502.9 3ng Ban:
26:8 26:8 83 .532 >8o=ceu 38am 8

 

4m<04

22.28 . 5.
3.38me

 

Ausczcoo. Eo - 5.2.35 2 2:896 Ecoficma s «.26.. N.“ WEE

DISULFOTON

2. HEALTH EFFECTS

 

E :39
map ._a .0 aozm Ed 9.2. mp 3:02 5
E. .525
«5— 2858. mmd u 8 .mm mm
..a_:o_~o._oan>.Sao_mo3.586.
Ed .2. um
Ed 5.80
Ed 58...".
Ed .33.
Ed 0.5%...
Ed 22.2..
Ed 2.30
Ed 0.9.50
E $.36.
«BF ..a «a .52.". Ed ammm x? 9 3:22 mm
.32.". 8:20
$9 Emu E .5 565.05
.a s 285% 292.. .63 888. «cg H. mm; u. no .2. B u 37:; E. X.
5; .>> um
8.. .280 a.
a... an den .28.“:
282 385 E; .9639: v.3 2 am no
8:28.... gauged gauged 2595.... £816 .33: 8.85 .539 2.5:
«3.8m 26.3w «8.. .932 >235". isoam 8
>8.
- 22.22.. .
.98.. 358.3.

 

 

€35.58 .Eo . 5.2.35 o. 2:896 2.85%....“ .o 0.25.. a.“ 59;

36

2. HEALTH EFFECTS

38.28535

 

 

83.28565 wgooEEm 259ch
*0 coEnEE $00-98 n. 56 *0 coEnEE $NN-VC u. mod
33.285650
33.28565 mgooEEm mgooEEm m: $3 $28.“:
32 8%: .o 8:525 $3-5 2mg .0 8:325 38.9; s. 8.0 28.0 9: 3 am NB
33:8 89285650
$2 :8 822 um. E azv
552; 9a .38 Em :65 .o 8:52;; to 86 x; 2-x am E
AmuEgoEfl
FB— EocsSm $38 2 mama: £99 6 E szv
can {50 5.5395,”. 3390:: ON 9: m fix on
33:8 32m
2% Samoa. mmflmfiwéocorcwom E 3:28
o5 {.20 ESQ *0 coEnEE gummy Emd oE m Em mm
3.58 39235.05 E
82 25; £8on .2 mod a: on :3 $58.“:
28 consents E 5:525 «ogrmmv u. no.0 u mod oE 0 «mm mm
50520502
8:820: figv 93%.»; Saubx‘mEv £083 .830: 05025. 3ng 2:9.
25.8w 26:8 33 456: >835“. 328% 8
I 22.23 . >3.
4m<o._ 3.3on

 

DISULFOTON

$35.53 .20 . 9.22.35 8 Eamonxm =53:ch no «.25.. «.w m._m<h

37

DISULFOTON

2. HEALTH EFFECTS

33.285.05508

 

 

52 is: Susanna 6 8:525 $8 E 223.0;
9a fisfim new 595 3 559:5 «\omt n. and u 3.8 «mm K
952538;
.EzSM $8235.93
59:... 29:2 new 29: *o E 8:33
2.2 .a s 5E 82955 $0 6 Ba «co. E 90 a 3-8 am 9.
AEmEcnflu
9: 5 {ends .comanm 9:
5 3m. S 535 5 «RR
8 33:8 39235.05
*0 5232:. 65.533
3.9 .mmfloamoéocozcm E 8595
.a S comcsom 3 39v. .833 350823 2nd u on Em mm
“39.28565
£8550 25 9:83 n. 85 u. :.o E Essa
«SF 9.8802 _o 5:525 $3.08 .2 3.0 s. no.0 u om fix I
E
am...
a mm". .0
mcan; .28
5:03.85
.5395
.w mEEEEQ
Eozflocmm E x3 9 5E $an
82 555a... 9: .0 88:85 9: 9:26 655.55 $939
new :85: mofiEE on. 2: 5 SEE: n. mod mod is m: “o“. fix an
8:223. 98%.... ganflxbé sunning .536 .23: 228%. A539 2:3
26:8 25:3 28.. 4m<oz €532". 38am 2
- 22.2.5 . 5.
493.. 353.3.

 

Auoaczcoov .80 - couch—ans 8 2:8an Euoficwfi “—o 230.. N-N 39:.

38

DISULFOTON

2. HEALTH EFFECTS

 

6v
2.:
335.3565 ogooEtcm {tum 868$
22 .as 32: 8 8:525 $08 no as m 8o mm
32.8 $9285.05
9:83 new :8 woos 5. mod A“: $319
~an .38 scam v.2 ho coEnEE $5-58 u. Ed u. 3.0 x? 9 330.2 mm
Ezm
c2232 E 3:29
E: ._a .0 £20 E28298 8320:: n. E x3 NT... 3:05. 5
AmEcgoEmz
:9 20535 .258 2 mammz £95 .0 EV Amzv
us .56 z___n$§3 8.398; on: on. N 832 on
eazm
33:8 8:20
$2 39235822308 E 3 585.0;
.3 .c 22.2% 595 3 558:5 {amt n. md u wt. F: E: mm
SEQ
3928565 595
6 822:5 #8 53:8
$8285.05 mgooEEm
,6 8:325 $3-5: 5.0.8.0 .2890
$5.8
$2235.20 £95
6 8:325 $3 .256“
$8235.05 ogooEEm E
“o 8:325 $8-2 .ssm a: E :3. 58%
n82 335 2E: 60.53282 283$ u. find n. r86 x3 or fix 3
gm Agav «mama—.5 augmv—BEV §>w Ace—«OE quoamv Asgmv 0.5m:
328m 26:8 23.. d<oz >88ch 38.5 M.
d3 h”... an 93m. . 8.

 

 

Avoacacoov .20 - :oaozsma 8 953an Euoficwfi “o n_o>o.. N.“ 39:.

39

DISULFOTON

2. HEALTH EFFECTS

 

E
nun. w
an”. s as
-525 new
coaoauoa
5:95
w @55an
A83 «E 5 33:8 x; 9 5E $.38
89 >u3a£ux wmfloamwéoco ESQ ”mcamea .3959
us 82: be 8:325 games 8.0 u mood is 9 No". a: B
inflame—gun
cam—693 wEooon E 3:33
on? .3 .o 5E 2 v0.5 meEE mhv md u mméw Em 8
E
35.3 on". a
3% <0 a 2:3 8% «E s as
33205 .8065 cozflofl .53; new
a. >==n£> .mEsoo cozoauoa
BE. 389.0% 62863 a 295::
cozmuwwm mars... 2925 E a ucszma
a on. EESmE “693.0% x; 9 5—“. 9235
89 >33? 629:2 E a on. Eamon $3995 3:: van 9.58 63953 .8939
new :85: -5.QO .x. 83283 mod .25 am". 389.83 no.0 mood x3 3 ”on. Em ma
02853.52.
892285820
25% ho 8:525
$8-8 ”mmflwamméoco
22 23955 E 8589
.a .0 52%... .6 8:525 $033 86 x; 9. won 3
8:22am snags: gauge. aau‘mémé 5326 E3: 058.5 3.25. 2:9.
26.5w 26:8 28.. . .962 .3532". 328% 2
>
493.. hnmuwwm . 8.

 

 

3035.53 .20 - 5.3.35 2 95396 E50535 we 23...... N-" 39:.

40

DISULFOTON

2. HEALTH EFFECTS

 

 

E in .2an
m8— 86: $585.: 3320:: H. No; x3 873. Em om
5000
mmamOmxm 0.20m20
$95595 an".
E 332 «o amnion?
2.52: $539.23:
2:: .22: 25
Ba 9:65 >823 mac
AmmEEmm;
on". 5 88285.05 E.
232ch 28: E2565
3.8. 3.5 .o 8:325 $91.8 to .98& m a: 8
33:8
$9235.05 522 E 8:33
08— .3 .0 cub... Ema *0 :OEQEE o\o «.mmv md U mméw «mm mm
85%: .53 233$ 33335 22% A28: 8.8%. €39 .52.
30:8 2.2.8 on: .96: 5:8ch 328% 8
I 23950 . >8.
..m<O._ 3.5%

 

33.5.58 .95 - coao=amE 2 c.5396 Euoficma to £96.. a.“ m._m<._.

DISULFOTON

2. HEALTH EFFECTS

 

 

 

 

—.o ~>> um
to 5.80
—.o .Eoo
to .895
ho .22”.
_.o 25%:
fio .9633:
«.0 29:0:
v.0 9.690
to 06.80
$.38
E 33$
at: .36 >98 —.o Q81 :66; Em 5
£8055
8:22.: aflwfié afimflmé gauaémé 2336 A28: usimv 3.26. .59.
25:8 26:8 33 $202 5832". 38am 2
22.8.5 38.
#23 353.5.
$335.53 .20 - 53:35 2 Eamoaxm 235.55 “E 233 N-“ wqmfi.

 

42

DISULFOTON

2. HEALTH EFFECTS

 

 

3% £99; ~62. .2 who .2 Ed
5 338% «om—é: H. No; u Ed :5 am
23° 655 559m: 2 8.0
Acoamutmsowgomc .moEoov mac; ho 5:805me 0:98 u 5.0 ”— mod 5.30
. Eva 2:
*o .62: 63299:an s. mud s. 9.0
$305503 H. me; u. 5.0 .Eoo
H. No;
Sign ozmflocmav Enho s. 3.0 toucm
u. mo; Ecwm
u. «o; 0:32..
E23532. 2 out .2 mud
>326 209:: .320me mmoé u. 5.6 .9303:
H. No; ofiEmI
EomEBmQB m5 8
coszEng 2:930 98 s. mud
53.90%; .mmoonEv H. No; u. Fwd 9:30
M. No; 06.50
395. m5 8
coszEmzs o>=m5aa3m .2 mud E Agazommv
39 096... can waofiEoicflmv H. No; n. 3.0 ammm xzoowéop «mm mm
8:223. 3%.5 9qu $2955. 5226 A23: 058%. Esau. 2.5:
2.23m 2.28m 33 4932 3:83.“. 38% 8
>8.
L 20:83 .
4w<04 Eanoaxm

 

Ava—.5203 .20 - $88.35 2 chanoaxm Eoncmfi *0 203.. N-“ m._m<._.

DISULFOTON

2. HEALTH EFFECTS

 

 

6.
3.8 28:2 2.:
89 95.2 >550 u6:255:38 x25. m 3088
neg £52». .Emumsmzmm .3033 00.0 5.30 S w 000 ma

:0 <5 3
3.0 .0500
3.0 .6005
3.0 ficom
Ed 23%:
3.0 fixwxumaz
3.0 20on
3.0 9:30
3.0 2.9.50

as. E 3088

.a s 5.5.0: 3.0 08m .3 m 000 3

and «>> um
mm.“ .280
and ESQ
mmd .ooucm
mmd .602...
man 35%:
mmd .3933:
and 29:0:
and 2.30
and 2200

E :60.

82 8%: 8.“ Q8”. 2. on 38.2 8
8:23.: Swag 383mg Aiaxbé 28:6 .83: 8.88. .5250 2.6..
«actom 30:5 33 4w<oz in. in 8
.513 g a 5

 

83:280. .20 - 5.2.35 seanaxm 28535 3 «.25.. «.a 3m:

2. HEALTH EFFECTS

caoo case 625.23% 83.285320

ozoc ozao 63.28565 582 .o 8:52.:
ENE .0 5:325 $3 $5 63.235650
63235.20 w$o€£bo ogoecrco
.o 8:525 #35 H. Rd .o 8:325 «$3: m 8.0
Eozfiocwmmu

9.6: 0.30 .omEEmméozo
£95 .0 c2525 o\omm

 

 

 

635505.020 o$ooEtco E :36 8:85
82 8%: .o 8:325 $5-9; 226 286 v.3 839 am 6.
9233
888.3565 u. mod E .oaasawv
mu? ._m 5 >98 595 *0 coEnEEQonméwv 5. mod .2 mod S N-m.F “mm 8—
3050—9502
3: E @938
.a s 5.5.2.. 3.0 S m won 8
E 2.08
89 8%: mmd 2: mm 3:22 mm
$80:
:99: EinficmE 9.: E
23.92;; :8 952$ 5. m3 2 m8
Acozmawu Ev $3 528$
83 8%: 22:2 2295. 28.3 H. 8; u. Ed {5 832 am 8
$.38
A“: .wammamv
map .a 3 >98 to S m-m._ a: 8
._a.:o=20:nE>-Sao_mo_acaEE_
cacao—om 959:3 acuiémé $2935 £21m Rosa: 8.259 3va 95m:
26:8 26:8 an... ._m<oz finance". 3288 2
E823 . >8.
49.5.. 3.53an

 

DISULFOTON

AUGSCSCOOV _N._O u .CO~023w_D Ou QHSMOQXN uflflotmcmm ho m_0>04 N-N MJD<P

45

DISULFOTON

2. HEALTH EFFECTS

5!. 358a n to .Ecumo.c.o..mau u 2.86 69.5% u

8.93» n S 2&2...“ u x Amiga. n x? 50.9.9.0. n amom ._o>c_ 8w:m-om.c>vm-ua>.omno.oc u ..m<OZ .Eofixmtflnomsc. n 3.2332 ”@558 u OE
.29.. n .2 .26. souvoeogéozguoto. n 4.5.. ...... $8 - 88 as... u 80.. $23232. n 2..on 63...? 5...; 69.2% u 9.6. 6.0.52. =0 63.6.. n 60.

a. ”8:883 5:. 9.5 a5 5 ESE .0 Sm ucooow n ma“. €9.9an 3E 9.003 a5 E 9.2:— 3 «On 9.003 n nun.

.8938 .2... 9.8.... 2.. c. 2...... .o .3 .m... u an”. .Saeocoa 3.... .2: 9.. ... 2...... .o .8 9.88 u n E .853... E... .2: 2.. 5 9...... .o .3 .m... u a... .8528 3.... .9: u E
682% .55.... u on. .321... 6.2.... u u. 65.89... n 38cm .35.... u .58 .35. u u .....8mm>o.u.8 u 228 .2338 u 6. .299... .8. u .3 R. 55...... E. u n._ E

.225: o. 29...... ES. 8.5635... .o. 2 J96. a .o 3.. .o. o: 82 .o .88. 2:58.... am 3 32>... 8%

......_.€..a> .85.... .o. o. 9....

$9..ng 99.8 .o .E: .90 8:93.255". a 9.3.. o. um»?

.332?

5:5: .2 or new 9.95: 2 £955 E2. coamfiqabxa .0. o: oo— .o .209 259.8,... cm .3 82>... 30.. $9.3be 99.6 .0 .ES. .90 8.93.2922... cm 03.2. 0. tom?

2 93 9.25.. o. 22...... ES. 8.5.89.5 .o. o: 8. .o .28. 2.5.8.... 5. .3 82>... 36.. 3.33.8... .8... .0 3E... .26.

.555? 59.5.. 5.

xv... .955... .90 8593658 cm 9:2. 0. “.33..
.N-~ 9:9”. :. 3:28 2 3:83:00 .383: 9:...

 

E .3... .28....

 

 

3.3.98... 5. who
82 8.6... 2.96 2.5.... U. 8.. u. E... ...s 873. .am mo.
$283050:
6.
E...
A959 can 029. came .35. m 3.38.
R9 .36 mm: .o .33.... new «.8...ch m6 .> m moo vo—
AQOE :. 39935.05
:5... .o 8:52...
$13 .mm9w.mo:=o..o
«can... .0 8.....2...
.xbném .wm9w.wwc._ozo
2.2 2.695.»... a. 358m.
.3... 5.5.2.. .o 8.5.2... $3-3. id 8... ... m moo 8.
33.8%... {$.13
Ea $2-8 .eowmém
.3 39235.9... 59..
can .mEmm... .o.>oo.£>.m. “.mmd E. $.00.
22 8...... .o 8:33... 2853.3 .22.“ in... o... mm 38.2 No.
88...... .Ewie. as? sigma. 5% .23.. 8.8%. 2.5. 2......
32.8 2.2.8 83 .532 >233... .8.an 3
22.8.5 . >8.
JW<OJ Esq—OE

 

.82....8. .Eo - 56:3... 82.52.... 28553.. 22.3 N.“ 9.9:

46

 

 

 

 

 

 

 

 

 

>
_
_
_
" .~.~ 22¢ 585:0 cumucoaootoogoa :03 2:3: .353;
_
_ 9n. 3530 o
" 3.3234302 O :33. c
_ 335338? 39.8 3o. 8356.. e 8o u
_
_ 528 55.2.0» fifiEEanmao 32.853304 0 88.2 E
" 900:0 5:96. meaEES _ Sodom n: I 5... ._
. Nov.
.90
5v .9. :o
.Nm .5».
O o O .3 a .R O
Q .3 0v 0 ._ 5 EN@ 5w
8 .9. O O O O O
a .Nm O .3 .3 .9 Km EM .8
E Q C . O 0 .MW 6 C .5
H O E 5 .3. .8 to 5m 5 :N an O 3 a
H can on 0...... 080.6 0 E3 59 I O
H O .3 .5 .8 5N and am 0 I t. I I
3 ES .8 .8 .2 E .8 Eva 0M5 :
H cmwm O 0%” O 06 O Q on
. 5— E? I
2 how 'Jhp . Em I
5: 5
I 0
Eur
o ,v 4,. 9 W l ,v o
040 «as as foo A0 009 00,7 @OAI 09 as
/ o o« 9/ oo 9 o x0 04
00 o 0/ W 4 a. 9/. 4/ a?
a o0 lo ,9 o. oo oz
0 x1. 90. 06. a a? ’9
efiv 04 / I 9/
/ 4.,
N 2E2m>m
m
m 323 «E
L 230<
m.
D _w._° l ranch—JED Ow 0h=mOQXW «cagtcgm ho 20>¢J .NIN 0.59"—

Sod

5.0

_..o

or

00 F
ammeBEV

47

DISULFOTON

2. HEALTH EFFECTS

 

 

 

 

 

 

 

 

 

.~.~ 2.3 5335 28:88..8.c.o..582.x2.352ofi
Quasao a J P0006
$353332 0 :38 ..
wagimsofi 82.832 3380.. 6 man u
.858 555%» 335.558.... m3=8.o:m<9 O 88.2 E I: 50.0
98:30:92 8 REES. 804.8 3 I Em .
>8.
I 5.0
.8
O
.8
00 l .
.8 F0
.8
.mw 0.8 .8 .8 .8 .8 .8 .8 .8 .8 .8 .8
$00 00 o 000 00 oo o oo 00 0000 .3 I.
O 0 0E8 E80 E8 .8 E8 E8 0 E8 E8 E8 E8 0
.350 Q .8 .8 C
.8 .8
I or
0
E8
I cow
0 o O 9 .v .~, by ,~, 0 o .v 0 _
o 9 o 9 s o e e s g
40 9% av, 000 80 «a 0% % «a 0,4 ,0. % 333%.
I. /9 a. 0/. A, 0/ /o 4 a!
x0? 0. «o0 0/ 20 $9 oz
0%. s 8.7 omv poo @o 6
«,9 A. «o. A.
2E9m>w
$5. 83:

05.3....2...

€35.33 _m.o I 55:35 2 Eamoaxm E3555 .0 293 .~.~ 0.3m."—

DISULFOTON

2. HEALTH EFFECTS

 

 

 

 

 

 

 

 

finsflhsgsgfiagsfisgg
+ £3.30 a
_ . Eagfingz O 5%... c
“ 3235.28? «3:882 6356.. 6 non u
32...... 98 33.3333 ._ 88: e
" 38855.28» v a O .
_ 3822.26.33.55... 89.83 I a: .
" >8.
_
_
Km .8
o o
e .m. .mo
6 .mn .E
._ .55 .mm .3. .N5
in mm Au 0 O O .55 O O O Q
O D Em C e .8
.mm .mm .30 .Nn O .K
O .E .R 0 .mn
.3 8w . O Q .8
6 O I 0 mm .E .mn O O
.8 .8 e an .E O .8 O
Emm 5%
O 6
.mn .on
Q
E... 5
00 0,0 @A/ 6/
87 J0 J0 00/» 0v
cox 000 0/0 699%
{WU/«v 9% @0/ O/IWOOAV
@/ /.
x a
$5. 33 5

2238.25

508.0

500.0

«8.0

5.0

To

0—.

00 F
Emnbxbé

€352.03 _m.o .. :SozswE 2 9:8qu EmoEcmG *o 293 .N-~ 2:9".

49

DISULFOTON

2. HEALTH EFFECTS

 

 

 

 

 

 

 

 

 

.m-~ 29¢ c_ 8.55 2 3832.8 ER. :08 2 c8: .3E3c 9F
mi 3:50 a Food
AmaEEajmgz 0 Emma ; J
EmEEmvmsmco 82.3 m8. 5:954 6 non u
> AmfiEEmvmfiocw maocOmBZw<04 . 3:02 E
uwocmo cm...“ .550 _
£8:w.o__o>o_xmt_mE_c_2_ omodom n: I fix .
5. I 5.0
39
O 59
0.5— .mm
:9059 .8 .5 O :m :m :m :m :m :m Em :m :m .
82 O O O O O O O O O O 0 ago In *0
Q :9 O O Ozm O O 0 Cam 0 Cam 0 Cam
0 O ummO uva 25 O O 3&0 3m 3m 350 So 3&0 3m 0
50— Km .Nm .Nm .Nm kg
25— Emo—
O O .5 am 0 .8 am am am
. .mm .8 5m .mm .Nm .Nm .8
e a 8m 0 e e
O O O O O e O O I F
59 ENE
. Ema Ema Emm Ema Emm E8 E8 E8 Ema Emm E8 E8
0 O O O O O O O O O O O
& 4/ 2 a o o \v & & ,y a & o I 9
as Os oovfxv/ $0 00 0% 00 09 09 «War 0% we «90 0&9 $9 EmqubEv
00¢ 0va 09 004 44 «9/ a. 000 /é o% 0% 0% 0/0? 4% a? a»,
O 0 J o 0 0. . / A. J
O / 8 O I. 0 «o O )- 0 O
I o 0 / 0 .1 9
$4,. 4. owe/9 «a%%% c
4 A. Ave i.
2E£m>m
E5. 33
2:050

.20 I 58:35 2 Esmoaxm E3535 3 29¢.— .~-~ 959".

DISULFOTON 50

2. HEALTH EFFECTS

same dose for 3 consecutive days (Schwab et a1. 1981). In the same study, 1 of 8 rats died after
receiving either 2.5 or 3.5 mg/kg/day for 6 days. When groups of mice were given 50% of the
derived LDSO (9.6 mg/kg) for 3, 5, and 10 days, mortality was 2 of 8, 2 of 8, and 9 of 20, respectively
(Stevens et al. 1972b). The results suggest that even at half the acute LD50 dose, almost half of the

mice given disulfoton for 10 days died.

In intermediate-duration studies, 1 of 12 female rats given 1.31 mg/kg/day disulfoton in the diet was
found dead on day 48 due to cholinergic effects (tremor, muscle fasciculation) (Sheets 1993b). In
addition, 4 of 71 male rats died when given a diet providing 2.5 mg/kg/day for 30 days (Robinson et
al. 1978), and 5 of 25 female mice died when given a diet providing 26 mg/kg/day disulfoton for

4 weeks (Clark et al. 1971). The reason that mice could tolerate a higher dose in the diet for 4 weeks
compared with single dose LD50 values is probably related to the method of administration (i.e.,

continuous intermittent exposure during feeding versus a single bolus dose by gavage).

In a 2-year dietary study, female rats in the high dose group (1.02 mg/kg/day) had a 40% mortality
rate during the last week of the study compared with 12% in controls (Hayes 1985). While the
mortality rate in the control group was unusually low, the 40% mortality rate in the high dose female
rats was also increased when compared with historical controls, in which the mortality rate ranged
from 18 to 34%. No increase in the mortality rate of male rats was observed. Furthermore, no
increase in the mortality was reported for mice exposed to 2.13 mg/kg/day (males) or 2.53 mg/kg/day
(females) disulfoton in the diet for 23 months (Hayes 1983). These results support the conclusion that
rats are more sensitive than mice and that female rats are more sensitive than male rats to the lethal

effects of disulfoton.

The causes of death in these studies were not specifically mentioned, but disulfoton is a cholinesterase
inhibitor, and animals exposed to disulfoton typically exhibit cholinergic signs of toxicity (see

Section 2.2.2.4).

The LD50 values and the doses associated with death in each species and duration category are

recorded in Table 2-2 and plotted in Figure 2-2.

DISULFOTON 51

2. HEALTH EFFECTS

2.2.2.2 Systemic Effects

Studies regarding the systemic effects that have been observed in humans and animals after oral
exposure to disulfoton are discussed below. The highest NOAEL values and all LOAEL values from
each reliable study for each systemic effect in each species and duration category are recorded in

Table 2-2 and plotted in Figure 2-2.

Respiratory Effects. Intra-alveolar bleeding, edema of the lungs, and blood in the bronchus were
observed at autopsy in a man who had been dead for at least 24 hours after ingesting an unknown
quantity of disulfoton (Hattori et al. 1982). This was the only information found regarding respiratory

effects in humans after oral exposure to disulfoton.

Breathing difficulties were observed in rats given a single gavage dose of 1.0 mg/kg and in mice given
5.0 mg/kg disulfoton (Mihail 1978). Rats given 0.5 mg/kg and mice given 2.5 mg/kg did not display

breathing disorders.

No histopathological lesions were found in the lungs of rats exposed to 0.34 mg/kg/day (males) or
0.55 mg/kg/day (females) (Klotzsche 1972) or mice exposed to 0.63 'mg/kg/day (males) or

0.71 mg/kg/day (females) (Rivett et al. 1972) in the diet for 90 days, or in rats exposed to

$0.21 mg/kg/day (Carpy et al. 1975', Hayes 1985), in mice exposed to 2.13 mg/kg/day (males) or
2.53 mg/kg/day (females) (Hayes 1983), or in dogs exposed to 0.14 mg/kg/day (Hoffman et al. 1975)
in the diet for up to 2 years. In rats exposed to disulfoton in the diet for 2 years, granulomatous and
suppurative inflammation of the lungs was found in the high dose groups (0.75 mg/kg/day in males
and 1.02 mg/kg/day in females) (Hayes 1985). The lung inflammation was considered to be due to
aspiration of the food particles, which in turn may have been associated with the debilitation observed

in the high dose groups.

Cardiovascular Effects. No studies were located regarding cardiovascular effects in humans after

oral exposure to disulfoton.

No histopathological lesions were found in the hearts of rats exposed to $0.55 mg/kg/day (Klotzsche .
1972) or mice exposed to $0.71 mg/kg/day (Rivett et al. 1972) in the diet for 90 days, or in rats
exposed to 0.1 mg/kg/day (Carpy et al. 1975) or $1.02 mg/kg/day (Hayes 1985), in mice exposed to

DISULFOTON 52

2. HEALTH EFFECTS

$2.53 mg/kg/day (Hayes 1983), or in dogs exposed to 0.14 mg/kg/day (Hoffman et al. 1975) in the

diet for up to 2 years.

Gastrointestinal Effects. No studies were located regarding gastrointestinal effects in humans

after oral exposure to disulfoton.

No histopathological lesions were found in the gastrointestinal tracts of rats exposed to 0.34 mg/kg/day
(males) or 0.55 mg/kg/day (females) (Klotzsche 1972) or mice exposed to 0.63 mg/kg/day (males) or
0.71 mg/kg/day (females) (Rivett et al. 1972) in the diet for 90 days, or in rats exposed to

0.1 mg/kg/day (Carpy et al. 1975), in mice exposed to 2.13 mg/kg/day (males) or 2.53 mg/kg/day
(females) (Hayes 1983), or in dogs exposed to 0.14 mg/kg/day (Hoffman et al. 1975) in the diet for up
to 2 years. However, increased incidences of mucosal hyperplasia and chronic inflammation of the
forestomach were observed in female rats given 1.02 mg/kg/day disulfoton in the diet for 2 years
(Hayes 1985). The mucosal hyperplasia was usually diffuse but was sometimes more locally severe
and accompanied by inflammation, fibrosis, and ulceration. The forestomach lesions were not

observed in male rats at £0.75 mg/kg/day or in females at $0.21 mg/kg/day.

Hematological Effects. No studies were located regarding hematological effects in humans after

oral exposure to disulfoton.

Limited information from animal studies suggests that intermediate— or chronic—duration exposure to
disulfoton is not associated with hematological effects. No hematological effects were observed in rats
fed $0.55 mg/kg/day of disulfoton (Klotzsche 1972) or in mice fed $0.71 mg/kg/day (Rivett et al.
1972) for 90 days. In 2-year feeding studies, disulfoton did not cause any hematological effects in rats
(Carpy et al. 1975; Hayes 1985), mice (Hayes 1983), or dogs (Hoffman et al. 1975).

Musculoskeletal Effects. No studies were located regarding musculoskeletal effects in humans

after oral exposure to disulfoton.

Degeneration of ciliary muscle cells was found in the eyes of dogs given disulfoton at doses
20.63 mg/kg/day for 2 years (Ishikawa and Miyata 1980; Suzuki and Ishikawa 1974). The
degenerative changes consisted of the presence of unique membranous structures, displacement of

myofilaments, and lack of clearly defined organelles. The authors suggested that the microsomal

DISULFOTON 53

2. HEALTH EFFECTS

oxidation of disulfoton to an active metabolite that can destroy microsomes may account for the
destructive changes in the ciliary muscle cells (Suzuki and Ishikawa 1974) or that cholinergic
innervation of the iris-sphincter and ciliary muscle by disulfoton resulted in edema of the ciliary
muscles (Ishikawa and Miyata 1980). The degeneration of these cells was believed to be the cause of

myopia (see Ocular Effects below) in these dogs.

Histological examination of the gastrocnemius muscle of rats given a single gavage dose of

55.2 mg/kg (Sheets 1993a) or $1.31 mg/kg/day disulfoton in the diet for 13 weeks (Sheets 1993b)
revealed no treatment-related lesions. No histopathological muscular or skeletal lesions were found in
rats exposed to 0.34 mg/kg/day (males) or 0.55 mg/kg/day (females) (Klotzsche 1972) or mice
exposed to 0.63 mg/kg/day (males) or 0.71 mg/kg/day (females) (Rivett et a1. 1972) in the diet for

90 days, or in rats exposed to $0.21 mg/kg/day (Carpy et a1. 1975; Hayes 1985), in mice exposed to
2.13 mg/kg/day (males) or 2.53 mg/kg/day (females) (Hayes 1983), or in dogs exposed to

0.14 mg/kg/day (Hoffman et a1. 1975) in the diet for up to 2 years. However, reduced skeletal muscle
size and skeletal muscle atrophy were observed in female rats given 1.02 mg/kg/day disulfoton in the
diet for 2 years (Hayes 1985). The skeletal muscle atrophy corresponded to the generalized

debilitation in the high dose females.

Hepatic Effects. No studies were located regarding hepatic effects in humans after oral exposure

to disulfoton.

In animals, the hepatic effects associated with oral exposure to disulfoton included alterations in liver
microsomal enzyme activities, lipid peroxidation, and changes in liver weight. The ability of
disulfoton to affect microsomal enzyme activities appears to depend upon the dose, the duration of
dosing, and the time between dosing and enzyme assays. Microsomal enzyme induction is considered
to be nonadverse unless the induction of enzymes can be linked to more serious liver effects. A single
oral dose (9.6 mg/kg) of disulfoton caused a significant (p<0.05) decrease in in vitro mouse liver
ethylmorphine N—demethylase and reduced nicotinamide adenine dinucleotide phosphate (NADPH)
cytochrome 0 reductase activities, but no significant effect on NADPH oxidase, when assayed 1 hour
after dosing (Stevens et al. 1973). However, a significant increase in liver ethylmorphine
N-demethylase and NADPH oxidase activities, but no significant effect on NADPH cytochrome

c reductase activity or cytochrome P-450 content, was observed in mice given 9.6 mg/kg/day

disulfoton for 3 days and sacrificed 24 hours later for in vitro enzyme assays. When mice were

DISULFOTON 54

2. HEALTH EFFECTS

treated with 8 mg/kg/day for 5 days, the content of cytochrome P—450 was also significantly increased.
Treatment of mice with 9.6 mg/kg/day disulfoton for 3, 5, or 10 days resulted in significant shortening
of the hexobarbital sleeping time, compared with controls, and stimulated the in vitro side chain
oxidation of hexobarbital and the hydroxylation of aniline (Stevens et al. 1972b). Significant increases
in microsomal protein content and delta—aminolevulinic acid synthetase activity, and significant
decreases in ethylmorphine N-demethylase, aminopyrine N-demethylase, and acetanilide hydroxylase
activities were found in the livers from rats given 2 mg/kg or mice given 0.5 or 1.0 mg/kg/day
disulfoton for 1—4 days (Fawade and Pawar 1978, 1980, 1983). Disulfoton also caused an increase in
NADPH-dependent and ascorbate-promoted lipid peroxidation and a decrease in electron transport
elements. The reduction in electron transport elements was thought to be due to loss of integrity of
the membranes and structural alterations in the membrane phospholipids, leading to increased lipid
peroxidation. Disulfoton or its oxygenated metabolite may also have changed the conformation of

heme protein, leading to enhanced lipid peroxidation (Fawade and Pawar 1978).

In intermediate—duration studies, no effects on clinical chemistry indices of liver toxicity and no
histopathological hepatic lesions were found in rats given 0.34 mg/kg/day (males) or 0.55 mg/kg/day
(females) (Klotzsche 1972) or in mice given 0.63 mg/kg/day (males) or 0.71 mg/kg/day (females)
(Rivett et al. 1972) in the diet for 90 days. However, a slight increase in liver weight was observed in

female mice at 0.71 mg/kg/day (Rivett at al. 1972).

Similarly, in chronic feeding studies, no clinical chemistry or histological evidence of liver toxicity
was found in rats (Carpy et al. 1975; Hayes 1985), mice (Hayes 1983), or dogs (Hoffman et al. 1975).
However, trends towards increased liver weights in male rats and decreased liver weights in female
rats fed disulfoton for 1.5—2.0 years were observed (Carpy et al. 1975). The reason for these opposite

trends in male and female rats is not clear.

Renal Effects. The only information found regarding renal effects in humans after oral exposure
to disulfoton was swelling of the glomerulus at autopsy in a man who had been dead for at least

24 hours after ingesting an unknown quantity of disulfoton (Hattori et al. 1982).

Few data were located regarding renal effects in animals after oral exposure to disulfoton, and the
evidence for renal effects due to disulfoton ingestion is inconclusive. Urinalysis and histological

examination revealed no renal effects in rats given $0.55 mg/kg/day disulfoton (Klotzsche 1972) or in

DISULFOTON 55

2. HEALTH EFFECTS

mice given $0.71 mg/kg/day disulfoton (Rivett et a1. 1972) in the diet for 90 days, in rats given

$1.02 mg/kg/day in the diet for 1.5—2 years (Carpy et al. 1975; Hayes 1985), in mice given

$2.53 mg/kg/day in the diet for 23 months (Hayes 1983), or in dogs given 0.14 mg/kg/day in the diet
for 2 years (Hoffman et a1. 1975). Trends towards increased kidney weights in male rats and
decreased kidney weights in female rats fed disulfoton for 1.5—2 years were observed (Carpy et al.
1975). The reason for these opposite trends in male and female rats is not clear. In another study,
absolute and relative kidney weights were significantly increased in females mice fed 2.53 mg/kg/day,
but not in male mice fed 2.13 mg/kg/day, disulfoton for 23 months (Hayes 1983). The increased
kidney weight was thought to be associated with an insignificant increase in the incidence of malignant
lymphoma in the kidney. Since the kidney tumors were not believed to be the result of disulfoton

treatment, the toxicological significance of the increased kidney weight is not clear.

Endocrine Effects. No studies were located regarding endocrine effects in humans after oral

exposure to disulfoton.

Disulfoton exposure altered catecholamine levels in animals, and this hormonal imbalance may be
associated with elevated acetylcholine levels (Brzezinski 1969, 1972, 1973; Brzezinski and Ludwicki
1973; Brzezinski and Rusiecki 1970; Wysocka-Paruszewska 1970, 1971). In these studies, acute
dosing with disulfoton caused increases in urinary and plasma noradrenaline and adrenaline levels,
accompanied by decreases of adrenaline in the adrenal glands, in rats. In addition, the major urinary
metabolite of catecholamine metabolism, 4—hydroxy-3-methoxymandelic acid (HMMA), was recovered
in the urine from rats given acute doses of disulfoton (Wysocka—Paruszewska 1970, 1971). The
maximum level of HMMA in the urine occurred 72 hours after exposure, which coincides with the
time period for maximum urine catecholamine levels. There was a direct relationship between blood
cholinesterase inhibition and catecholamine (adrenaline and noradrenaline) levels in the urine and
blood (Brzezinski and Ludwicki 1973). Maximum inhibition of cholinesterase activity and maximum
plasma catecholamine occurred during the first 1—2 hours after exposure. However, catecholamine
levels returned to normal more rapidly than cholinesterase activity. It was proposed that high levels of
acetylcholine, which are normally associated with cholinesterase activity inhibition, caused a release of

catecholamines from the stores in the adrenals.

Elevated catecholamine concentrations in the urine were also observed in rats dosed with

0.625 mg/kg/day of disulfoton every other day for 76 days (Brzezinski and Rusiecki 1970). Urinary

DISULFOTON 56

2. HEALTH EFFECTS

catecholamine levels plateaued between 16 and 36 days, followed by a gradual decline for the next

40 days. However, these levels were still elevated at day 76.

In 13-week dietary studies, measurement of organ weight and histological examination of adrenals,
pancreas, pituitary, and thyroid revealed no effects in rats at doses $0.55 mg/kg/day (Klotzsche 1972)
or mice at dose $0.1 mg/kg/day (Rivett et a1. 1972)

There was a trend towards increased pituitary weights in male rats and decreased pituitary weights in
female rats-fed disulfoton for 1.5—2.0 years (Carpy et al. 1975). The reason for the opposite trends in
organ weights in males and females and the toxicological significance for these effects is not clear.
Male rats given a high dose (0.75 mg/kg/day) of disulfoton in the diet for 2 years had a significantly
increased incidence of pancreatic atrophy, seen as small focal areas of shrunken acinar cells (Hayes
1985). No histopathological lesion in the pancreas were observed in females at doses

$1.02 mg/kg/day, and no histopathological lesions in the adrenal, pituitary, thyroid, or parathyroid
were found in the male or female rats at any dose. In other chronic dietary studies, no organ weight
changes or histopathological lesions in the adrenals, pancreas, thyroid, parathyroid, or pituitary were
found in mice at doses $2.53 mg/kg/day (Hayes 1983) or dogs at doses $0.14 mg/kg/day (Hoffman et

a1. 1975). The Hoffman study also found no changes or histopathological lesions in parotid in dogs.

Dermal Effects. No studies were located regarding dermal effects in humans after oral exposure to

disulfoton.

In animals, histological examination of skin revealed no lesions in rats exposed to 0.34 mg/kg/day
(males) or 0.55 mg/kg/day (females) (Klotzsche 1972) in the diet for 90 days, or in rats exposed to
0.1 mg/kg/day (Carpy et al. 1975) or in mice exposed to 2.13 mg/kg/day (males) or 2.53 mg/kg/day
(females) (Hayes 1983) in the diet for up to 2 years. However, acanthosis, hyperkeratosis, ulceration
of the skin, exudate formation, and epithelial inclusion cysts were increased in male rats exposed to
0.75 mg/kg/day and female rats exposed to 1.02 mg/kg/day disulfoton in the diet for 2 years (Hayes
1985). No increase in skin lesions was found in the male rats at 0.18 mg/kg/day or in female rats at

0.21 mg/kg/day.

Ocular Effects. The only information regarding ocular effects in humans comes from an

epidemiological study in which a marked increase of myopia in young children was observed

DISULFOTON 57

2. HEALTH EFFECTS

(Ishikawa and Miyata 1980). The increase coincided with an increased use of disulfoton in
combination with other organophosphates to treat food crops. As discussed below, disulfoton caused
myopia in Beagle dogs, providing supportive evidence that disulfoton probably contributed to the

development of myopia in the young children.

Ocular effects such as myopia and astigmatism have been observed in dogs. Myopia and astigmatism
occurred after 12 months in Beagle dogs given 20.63 mg/kg/day disulfoton for 2 years (Ishikawa and
Miyata 1980; Suzuki and Ishikawa 1974). The myopia became progressively worse until cessation of
dosing. As discussed above for musculoskeletal effects, histological examination of the ciliary muscle
cells revealed degenerative changes that were considered to be the cause of the myopia. Cystic
degeneration of the Harderian gland was observed in male rats exposed to 0.75 mg/kg/day and in
female rats exposed to 20.21 mg/kg/day disulfoton in the diet for 2 years (Hayes 1985). In the same
study, the incidence of corneal neovascularization was significantly increased in the high dose rats
(0.75 mg/kg/day in males and 1.02 mg/kg/day in females), while no ocular lesions were found in the
male rats at 0.18 mg/kg/day or in the female rats at 0.06 mg/kg/day. In other studies,
ophthalmological and histological examination of eyes revealed no lesions in rats given a single
gavage dose of 5.2 mg/kg (males) or 1.5 mg/kg (females) (Sheets 1993a); or in rats exposed to

$1.08 mg/kg/day (males) or $1.31 mg/kg/day (females) (Klotzsche 1972', Sheets 1993b) or mice
exposed to 0.63 mg/kg/day (males) or 0.71 mg/kg/day (females) (Rivett et a1. 1972) in the diet for

90 days; or in rats exposed to 0.1 mg/kg/day (Carpy et a1. 1975), in mice exposed to 2.13 mg/kg/day
(males) or 2.53 mg/kg/day (females) (Hayes 1983), or in dogs exposed to 0.14 mg/kg/day (Hoffman et
a1. 1975) in the diet for up to 2 years.

Body Weight Effects. Weight loss or decreased body weight gain is commonly observed in
animals after acute exposure to disulfoton and is one of the typical signs of cholinergic toxicity of
cholinesterase inhibitors (see Section 2.2.1.4). The weight loss or reduced weight gain usually occurs
early in the dosing regimen, but the rate of weight gain recovers with repeated dosing as the animals
become tolerant (Costa et al. 1984, 1986; Fitzgerald and Costa 1992, 1993; Schwab and Murphy 1981;
Schwab et a1. 1981). Many of the acute oral studies conducted in animals showing initial body weight
loss were designed to study the phenomenon and mechanism of tolerance development (see

Section 2.3.5). Rats treated with 2.0 or 2.5 mg/kg/day disulfoton by gavage for 1—10 days initially
exhibited a 20—50% reduction in weight gain (Costa et a1. 1984, 1986; Schwab et a1. 1981, 1983). In

another study, rats exhibited an unspecified, but significant (p<0.01), decrease in body weight gain

DISULFOTON 58

2. HEALTH EFFECTS

within 3 days of a 9-day disulfoton feeding regimen that provided 1 mg/kg/day (Schwab and Murphy
1981). In all of these studies, the effect on weight gain diminished with repeated dosing, suggesting
that the rats became tolerant to disulfoton. In addition, a more severe weight loss (z20%) was
observed in rats given 3.5 mg/kg/day of disulfoton for 3 days than in rats that had previously received
a 2.5 mg/kg/day dose for 6 days and then a 3.5 mg/kg/day dose for an additional 6 days (Schwab et
al. 1981). Although changes in neurological effects are more commonly employed, these studies

suggested that body weight changes can be used to monitor the development of tolerance in rats.

Although the acute studies suggest that with repeated dosing body weight gain recovers after the initial
decrease, the body weight remains lower than the control body weight, as demonstrated in
intermediate-duration studies. Rats given 2.5 mg/kg/day disulfoton for 30 days gained 29% less in
body weight gain than controls (Robinson et al. 1978). In a 62—day feeding study, significantly
(p<0.01) lower body weights were seen in rats within 3 days at 1 mg/kg/day disulfoton (Schwab and
Murphy 1981). Although the rats recovered some of the body weight, the body weights were still
significantly depressed at all weighing times during the 62—day exposure. A 40% decrease in body
weight gain was observed in rats given 1.25 mg/kg/day, but not 0.5 mg/kg/day, disulfoton in the diet
for 141—178 days (Stavinoha et a]. 1969). Weight changes were used as the major criterion for
tolerance development rather than the less objective neurological signs of cholinergic poisoning. The
time for tolerance development increased as the dose of disulfoton increased. In an extensive
reproductive study, body weight gain was marginally depressed by 6—10% in F1 parental females and
9—1 1% in F1 parental males receiving 0.09 mg/kg/day disulfoton in the diet during the premating
period of 13 weeks (Hixson and Hathaway 1986). In other intermediate-duration dietary studies, no
effects on body weight gain were observed in rats given _<.1.3l mg/kg/day (Christenson and Wahle
1993; Klotzsche 1972; Sheets 1993b) or in mice given $0.71 mg/kg/day (Rivett et al. 1972).

In rats given disulfoton in the diet for 2 years, body weight gain was decreased by 11—19% in females
at 1.02 mg/kg/day, but not at 0.2] mg/kg/day, and in males at 0.75 mg/kg/day, but not at

0.18 mg/kg/day (Hayes 1985). In other chronic-duration studies, no effects on body weight were
observed in rats given 0.1 mg/kg/day in the diet (Carpy et al. 1975), in mice given $2.53 mg/kg/day in
the diet (Hayes 1983), or in dogs given 0.14 mg/kg/day in the diet (Hoffman et al. 1975).

DISULFOTON 59

2. HEALTH EFFECTS

2.2.2.3 Immunological and Lymphoretlcular Effects

No studies were located regarding the immunological or lymphoreticular effects in humans after oral

exposure to disulfoton.

In 13-week feeding studies, histological examination of lymph nodes, spleen, and bone marrow of rats
at doses $0.55 mg/kg/day (Klotzsche 1972) and of lymph nodes, spleen, and thymus of mice at

$0.71 mg/kg/day (Rivett et a1. 1972) revealed no treatment—related lesions. In rats given the high
concentration of disulfoton in the diet for 2 years, males (0.75 mg/kg/day) had a significantly
increased incidence of plasma cell hyperplasia in the mandibular lymph nodes, and females

(1.02 mg/kg/day) had a significantly increased incidence of splenic lymphoid follicle depletion (Hayes
1985). The author suggested that plasma cell hyperplasia in the mandibular lymph nodes was
probably a response to upper respiratory tract inflammation, which may have been due to aspiration of
ingested food particles. Histological examination of the mesenteric lymph node or thymus revealed no
treatment-related lesions in either sex at any dose. In other chronic dietary studies, no treatment-
related lesions were found in the lymph nodes, spleen, thymus, or bone marrow of rats at

$0.1 mg/kg/day (Carpy et al. 1975), mice at $2.53 mg/kg/day (Hayes 1983), or dogs at

$0.14 mg/kg/day (Hoffman et a1. 1975).

Down-regulation of cholinergic muscarinic receptors in T-lymphocytes and significantly inhibited
acetylcholinesterase activity in T-lymphocytes were found in rats given 2 mg/kg/day disulfoton by
gavage for 1—2 weeks (Fitzgerald and Costa 1993). The inhibition of T-lymphocyte

acetylcholinesterase activity paralleled that in the brain. The immunological significance of these

neurological effects (see Section 2.2.2.4) is not known.

2.2.2.4 Neurological Effects

Exposure to disulfoton can result in inhibition of acetylcholinesterase activity, with consequent
accumulation of acetylcholine at nerve synapses and ganglia leading to central nervous system,

nicotinic, and muscarinic effects (see Section 2.2.1.4 for more extensive discussion).

In a human case-report study, a 30-year-old man was found dead after consuming an unknown amount

of disulfoton (Hatton' et a1. 1982). Bubbling saliva in the oral cavity and constricted pupils were

DISULFOTON . 60

2. HEALTH EFFECTS

evidence of muscarinic effects. Pulmonary edema and blood in the lungs and bronchus suggested that
death was primarily due to respiratory failure brought on by disulfoton intoxication. Severe signs and
symptoms of disulfoton toxicosis (miosis, salivation, masseteric spasms, and monoplegia) were
observed in a man within 2—3 hours of consuming 3—4 heaping tablespoons of disulfoton (Yashiki et
a1. 1990). The coincidental depression in serum cholinesterase activity and the occurrence of severe
clinical signs suggests that a very severe toxic dose of disulfoton was consumed, and death may have

occurred were it not for the medical treatment.

Disulfoton can interfere with neurotransmitter levels (e.g., acetylcholine, catecholamines) in the brain
of affected animals (Brzezinski 1972; Costa et a1. 1986). A single dose of disulfoton caused a lower
noradrenaline level in the brain of rats compared with the controls, with the greatest decreases (about
0.175 ug/mL and 0.1 ug/mL compared with 0.3 pg/mL in control) at 15 and 120 minutes after dosing
(Brzezinski 1972). Adrenaline levels in the brain, however, showed little difference from control
levels, being slightly increased at 60 minutes and slightly decreased at 120 minutes. The rats exhibited
typical cholinergic signs of disulfoton toxicosis (not otherwise specified). In other acute exposure
studies, brain cholinesterase activity was significantly depressed when rats were given disulfoton for
7—10 days, suggesting elevated brain acetylcholine levels (Costa and Murphy 1983a; Costa et a1. 1986;
Schwab and Murphy 1981; Su et a1. 1971).

Muscle twitching, clonic cramps, and increased salivation were observed in rats given a single gavage
dose of 1.0 mg/kg and in mice given a single oral gavage dose of 5.0 mg/kg (Mihail 1978). Rats
given 0.5 mg/kg and mice given 2.5 mg/kg did not develop these signs. However, in another study,
rats given a single gavage dose of 0.5 mg/kg had tremors (Crawford and Anderson 1974). In an
extensive neurotoxicity screening study, rats were given single gavage doses of disulfoton (0.24, 1.5,
and 5.2 mg/kg in males; 0.24, 0.76, and 1.5 mg/kg for females) (Sheets 1993a). Clinical signs of
cholinergic intoxication consisted of muscle fasciculation, tremors, ataxia, oral stain, urine stain,
diarrhea, or decreased activity in the high dose males (5.2 mg/kg) and high dose females (1.5 mg/kg)
and muscle fasciculation in the mid dose females (0.76 mg/kg). A battery of functional observational
tests revealed effects in both males and female at the mid and high doses. At the mid dose and high
dose, these effects included muscle fasciculation, ataxia, and minimal head or body movement during
open field observation in both sexes and a lower incidence of vocalizations upon removal from the
home cage in females. High dose males also had uncoordinated righting reflex. Results of motor and

locomotor activity tests revealed a 55% and 51% reduced motor activity in high dose males and

DISULFOTON 61

2. HEALTH EFFECTS

females, respectively, and 64% and 62% reduced locomotor activity in high dose males and females,
respectively. Erythrocyte cholinesterase activity was inhibited by 21% in high dose males, 75% in
high dose females, and 53% in mid dose females. No treatment-related effects were observed for
brain weight and extensive histopathological examination of the brain, spinal cord, peripheral nerves

(sciatic, tibial, sural), optic nerves, or gasserian ganglion.

Animals exposed to disulfoton develop typical signs of cholinergic toxicity associated with inhibition
of brain acetylcholinesterase activity after a few oral doses (Costa et a1. 1984; Schwab and Murphy
1981; Schwab et a1. 1981, 1983). However, with subsequent dosing, the severity of the overt
cholinergic effects diminish, while cholinesterase remains inhibited. This phenomenon is known as
tolerance (see Section 2.3.5). Male rats given 2.0 or 2.5 mg/kg/day of disulfoton for 1—14 days
initially exhibited exophthalmia, excessive salivation, urination and defecation, diarrhea. fasciculations.
generalized tremors, flaccidity, and malaise (Costa et a1. 1984; Fitzgerald and Costa 1992, 1993;
Schwab et al. 1981, 1983). Similar effects were observed in female rats after 3 days on a diet that
provided 1 mg/kg/day disulfoton (Schwab and Murphy 1981). A diet that provided 0.38 mg/kg/day
did not cause overt signs of toxicity, but brain acetylcholinesterase was inhibited by 30—35% The
severity of these signs diminished after an unspecified time with repeated dosing. but the signs did not
completely disappear (Costa et a1. 1984; Schwab and Murphy 1981; Schwab et al. 1981. 1983). When
rats were given 3.5 mg/kg/day for 3—4 days, these clinical signs were more severe than those exhibited
by rats pretreated with 2.5 mg/kg/day of disulfoton for 6 days and then given 3.5 mg/kg/day for

6 more days (Schwab et al. 1981). Thus, the rats pretreated with 2.5 mg/kg/day for 6 days became
tolerant to even higher doses of disulfoton. In the same study, heart, ileum, forebrain, and hindbrain
cholinesterase activity was moderately but significantly depressed in rats given seven daily doses of

2 mg/kg/day of disulfoton, followed by four daily doses of 3 mg/kg/day. Furthermore, a 50%
reduction in pancreatic acetylcholinesterase activity was observed in rats given 2 mg/kg/day for

10 days despite the disappearance of clinical cholinergic signs after a few doses (Costa et al. 1984).
This depression in cholinesterase activity suggests that the mechanism associated with disulfoton
toxicity was not impaired, despite the disappearance of overt neurological signs of toxicity following

repeated doses of disulfoton.

Disulfoton caused muscular tremors, unsteadiness, and ataxia in pregnant rabbits after exposure to
1.5—3.0 mg/kg/day on days 6—18 of gestation (Tesh et a1. 1982). Doses of 0.3 or 1.0 mg/kg/day

disulfoton did not affect the pregnant rabbits. In a reproductive study, tremors were observed in high

DISULFOTON 62

2. HEALTH EFFECTS

dose (0.09 mg/kg/day) F0 female rats, but not the mid dose (0.03 mg/kg/day) F0 females, during the
production of the F1 generation (Hixson and Hathaway 1986). Pregnant rats given disulfoton during
gestation had significantly inhibited plasma and erythrocyte cholinesterase activity by 82—90% at

1 mg/kg/day and by 41% at 0.3 mg/kg/day, but not at 0.1 mg/kg/day (Lamb and Hixson 1983). Based
on this NOAEL (0.1 mg/kg/day), an acute oral MRL of 0.001 mg/kg/day was calculated as described

in footnote "b" in Table 2-2.

An intermediate-duration extensive neurotoxicity screening study similar to the acute study described
above was conducted in rats fed disulfoton in the diet that provided doses of 0.063, 0.270, or

1.08 mg/kg/day for males and 0.71, 0.315 or 1.31 mg/kg/day for females (Sheets 1993b). Clinical
signs of cholinergic intoxication consisted of muscle fasciculation, perianal stains, and increased
reactivity in high dose males and females and increased incidence of urine stains in mid and high dose
females. A battery of functional observational tests revealed effects in high dose males and mid and
high dose females. The effects in high dose rats included muscle fasciculations, tremors, increased
defecation, decreased forelimb grip strength, decreased movement, and increased urine stain. Muscle
fasciculations and increased urine stain were also seen in mid dose females. Automated measures of
motor and locomotor activity were reduced on each test occasion (weeks 4, 8, and 13) in the high dose
males and females. Erythrocyte cholinesterase activity was inhibited by 95—100% in high dose rats
and 61—80% in mid dose rats. Brain cholinesterase activity was inhibited by 35% in mid dose males
and 64% in mid dose females and by 75% in high dose males and 87% in high dose females. No
treatment-related effects were observed for brain weight and extensive histopathological examination of

the brain, spinal cord, peripheral nerves (sciatic, tibial, sural), optic nerves, or gasserian ganglion.

In intermediate-duration studies, typical signs of cholinergic poisoning are generally seen only during
the first few days, after which they diminish. However, cholinesterase activity usually remains
inhibited during exposure. Characteristic signs (not otherwise specified) of anticholinesterase
poisoning were observed in rats fed disulfoton for 30 days, and some of the rats recovered (Robinson
et a1. 1978). Brain, stomach, and diaphragm cholinesterase activity were severely depressed. In a
62—day feeding study, rats developed severe cholinergic signs of disulfoton toxicity after 3 days on a
diet providing 1 mg/kg/day disulfoton (Schwab and Murphy 1981). The severity of these signs
decreased but never completely disappeared after 62 days. Brain and diaphragm cholinesterase activity
was depressed at day 6 and remained depressed throughout the study. Sex and strain differences in

rats may influence the ability of disulfoton to inhibit cholinesterase or to elevate acetylcholine levels.

DISULFOTON 63

2. HEALTH EFFECTS

Brain Cholinesterase activity was significantly depressed to about the same extent in Holtzman rats and
Charles River rats fed disulfoton for 141—178 days, but only the Charles River rats had elevated brain
acetylcholine levels (Stavinoha et al. 1969). Cholinesterase activity of erythrocytes and the brain was
inhibited to a greater extent or at lower doses in female rats than in male rats given disulfoton in the
diet for intermediate durations (Christenson and Wahle 1993; Doull and Vaughn 1958; Hayes 1985;
Klotzsche 1972; Ryan et al. 1970). In mice fed diets providing 0.63 mg/kg/day (males) or

0.71 mg/kg/day (females), Cholinesterase was inhibited in all tissues, especially in females, but the
tissues were not specified (Rivett et a1. 1972). In a chronic study in which dogs were given capsules
containing disulfoton for 2 years, erythrocyte Cholinesterase activity was inhibited by 80% after

5 months of exposure to 20.5 mg/kg/day and remained depressed throughout the 2-year duration
(Hikita et a1. 1973). A 22—50% inhibition of erythrocyte Cholinesterase activity and a 33—36%
inhibition of plasma Cholinesterase activity were found in dogs given diets containing disulfoton at a

dose of 0.06 mg/kg/day for 40 weeks (Hoffman et a1. 1975).

Disulfoton has also been studied for behavioral effects. Rats fed 20.5 mg/kg/day disulfoton for

90 days had significantly depressed brain acetylcholinesterase levels (59—74% below control), but the
treated rats had shorter maze running times and made fewer mistakes than the controls (Clark and
Pearson 1973). This unexpected result (improved learning) at reduced brain Cholinesterase levels led
the authors to question the "critical level of 60% reduction" for neurobehavioral effects. In another
behavioral experiment, there was an unexplained increase in exploratory behavior in mice fed
disulfoton for 12 weeks (Clark et al. 1971). Dietary exposure of rats and mice to 2.5 mg/kg/day
disulfoton for 2 months resulted in an increase in the permeability of spinal cord and brain stem
tissues in both species (Clark and Stavinoha 1971). The nature of this change in permeability was not

further investigated.

In a chronic-duration study, a decrease in relative and absolute brain weights was observed in male
rats, but an increase in brain weights was observed in female rats fed disulfoton for 1.5—2.0 years
(Carpy et al. 1975). The reason for and the toxicological significance of these opposite trends in
males and females is not clear. In the same study, plasma, erythrocyte, and brain Cholinesterase
activity was significantly inhibited in both male and female rats. A dose of 0.1 mg/kg/day resulted in
a 21% inhibition of brain Cholinesterase activity in female rats. At 0.05 mg/kg/day, brain
Cholinesterase was inhibited by 11% in male rats. In another chronic dietary study in rats which

provided doses of 0.05, 0.18, and 0.75 mg/kg/day in males and 0.06, 0.21, and 1.02 mg/kg/day in

DISULFOTON 64

2. HEALTH EFFECTS

females, erythrocyte cholinesterase activity was inhibited by 319% and 14-24% in low dose males and
females respectively, 46—67% and 57—77% in mid dose males and females, respectively, and 71—82%
and 75—86% in high dose males and females, respectively (Hayes 1985). Brain cholinesterase activity
was inhibited by 15% and 21% in low dose males and females, respectively; 53% in both mid dose
males and females; and 79% and 82% in high dose males and females, respectively. Relative brain
weight was significantly increased in both high dose males and females. Histological examination
revealed a dose-related increased incidence of optic nerve degeneration that was statistically significant
in mid dose males and mid and high dose females. No treatment-related lesions were found in the
brain, sciatic nerve, or spinal cord. Based on the LOAEL of 0.06 mg/kg/day for erythrocyte and brain
cholinesterase inhibition in female rats, a chronic oral MRL of 6x10'5 mg/kg/day was calculated as
described in footnote "d" in Table 2-2. Significant depression of erythrocyte, plasma, and brain
cholinesterase activity was also found in mice fed disulfoton for 23 months at doses of 2.13 mg/kg/day
(males) and 2.53 mg/kg/day (females) (Hayes 1983). Beagle dogs did not exhibit profound changes in
general appearance or behavior when fed disulfoton (0.03 or 0.14 mg/kg/day) for 2 years (Hoffman et
a1. 1975). However, significant depression of plasma and erythrocyte and brain cholinesterase activity
occurred at 0.14, but not at 0.03 mg/kg/day. No histological lesions were found in the brain. Necrosis
and atrophy of the optic nerve and retina was observed in dogs given disulfoton (0.5—1.5 mg/kg/day)
for 2 years (Uga et al. 1977). The authors regarded the pathological changes in the retina as mild;

however, the nerve fibers in the optic nerve were reduced in number,

The highest NOAEL values and all LOAEL values for neurological effects in all reliable studies in

each species and duration category are recorded in Table 2-2 and plotted in Figure 2-2.
2.2.2.5 Reproductive Effects
No studies were located regarding reproductive effects in humans after oral exposure to disulfoton.

In a dominant lethal test, treatment of male mice with a single oral dose of 5 mg/kg disulfoton had no
effect on male fertility (Herbold 1980). In a three-generation reproductive study, exposure of male and
female rats to disulfoton in the diet at 0.5 mg/kg/day resulted a "slight" reduction of litter sizes in the
third generation (Taylor 1965a). This study was limited by data reporting deficiencies such as lack of
statistical analysis, incomplete necropsy report, and insufficient histopathological data. A more

extensive multigeneration study was conducted in male and female rats exposed to disulfoton in the

DISULFOTON 65

2. HEALTH EFFECTS

diet that provided doses of 0.009, 0.03, and 0.09 mg/kg/day (Hixson and Hathaway 1986). At

0.09 mg/kg/day, decreased reproductive performance occurred, evidenced by a decreased percentage of
females placed for mating and decreased percentage of sperm-positive F0 and F1 parental females. In
addition, decreased maternal weight of F0 and F1 dams during gestation and lactation, decreased litter
counts, viability index, and lactation index, and increased dead births and percentage of dead births
occurred in both generations at 0.09 mg/kg/day. A decrease in F2b litter counts and litter weights
occurred at 0.03 mg/kg/day. Gross and histological examination of the ovary, vagina, uterus, testes,
epididymis, seminal vesicles, and prostate of the F0 and F1 parents revealed no treatment-related
lesions. In an intermediate-duration study, exposure of male and female rats to diets providing

0.5 mg/kg/day disulfoton for 60 days prior to mating and/or during mating resulted in the failure of
two of five females to become pregnant (Ryan et al. 1970). Histological examination of reproductive
organs of males (testes, epididymides, seminal vesicles, prostate glands) and females (ovaries, uteri,
mammary glands) did not reveal any treatment-related lesions in rats fed 0.34 mg/kg/day (males) or
0.55 mg/kg/day (females) (Klotzsche 1972) or in mice fed 0.63 mg/kg/day (males) or 0.7] mg/kg/day
(females) (Rivett et al. 1972) for 90 days, or in rats fed 0.] mg/kg/day (Carpy et al. 1975), in mice fed
2.13 mg/kg/day (males) or 2.53 mg/kg/day (females) (Hayes 1983), or in dogs fed 0.14 mg/kg/day
(Hoffman et al. 1975) for up to 2 years. However, uterine cystic hyperplasia was observed in female
rats given disulfoton in the diet at 1.02 mg/kg/day, but not at 0.21 mg/kg/day, for 2 years (Hayes
1985). Histological examination of the cervix, mammary glands, ovaries, prostate gland, seminal
vesicles, and testes revealed no effects in the rats at any dose level. In the studies that did not assess
reproductive function, the dose levels that were not associated with histopathological lesions in

reproductive organs cannot be considered as NOAEL values.

The reliable NOAEL value for reproductive performance and the LOAEL values for reproductive

effects in each species and duration category are recorded in Table 2-2 and plotted in Figure 2-2.
2.2.2.6 Developmental Effects

No studies were located regarding development effects in humans after oral exposure to disulfoton.
Pregnant rats given disulfoton on days 6—15 of gestation had decreased plasma and erythrocyte

cholinesterase activity at 20.3 mg/kg/day (Lamb and Hixson 1983). Fetotoxic effects included

increased incidences of incomplete ossified parietal bones and stemebrae at 1.0 mg/kg/day, but not at

DISULFOTON 66

2. HEALTH EFFECTS

0.3 mg/kg/day. This was considered as evidence of growth retardation due to maternal toxicity rather
than specific fetotoxic effects. There was no evidence of soft tissue, external, or skeletal
malformations. Pregnant rabbits given high doses of disulfoton (1.5—3.0 mg/kg/day) died or exhibited
cholinergic signs of disulfoton toxicity (Tesh et al. 1982). Generally, there were no adverse effects on
fetal survival, growth, or development. Because of the high mortality of the dams, the initial high
dose (3.0 mg/kg/day) was reduced to 2.0 mg/kg/day and finally to 1.5 mg/kg/day. In animals that
received doses in the range of 1.5—3.0 mg/kg or a combination of doses, no fetotoxic effects were
observed in the offspring. Thus, 1.5 mg/kg/day is considered the NOAEL for developmental effects in
this study. In an intermediate-duration study, exposure of male and female rats to diets providing

0.5 mg/kg/day disulfoton for 60 days prior to mating and/or during mating resulted in a 32.1%
depression in fetal brain cholinesterase activity (Ryan et al. 1970). In a three-generation study in rats,
cloudy swelling and fatty infiltration of the liver, mild nephropathy (females), and juvenile hypoplasia
of the testes were observed in F3b litters (Taylor 1965a). These litters also had significantly depressed
erythrocyte cholinesterase activities. In another multigeneration study in rats, brain cholinesterase
activity was inhibited by 24% and 32% in male and female F 1 a pups, respectively, at 0.03 mg/kg/day
and by 50% and 59% in male and female Fla pups, respectively, at 0.09 mg/kg/day (Hixson and
Hathaway 1986). No inhibition of brain cholinesterase was found in the Fla pups at 0.009 mg/kg/day,
and no grossly observable developmental abnormalities were found in any pups in the F1 or F2
generation. Based on this NOAEL of 0.009 mg/kg/day for brain cholinesterase inhibition in pups, an
intermediate oral MRL of 9x10‘5 mg/kg/day was calculated as described in footnote "c" in Table 2—2.
The highest NOAEL values and all LOAEL values for developmental effects in each reliable study in

each species and duration category are recorded in Table 2-2 and plotted in Figure 2-2.
2.2.2.7 Genotoxic Effects
No studies were located regarding genotoxic effects in humans after oral exposure to disulfoton.

Disulfoton was negative in a dominant lethal test in male mice treated orally with a single dose of

5 mg/kg (Herbold 1980) and in an erythrocyte micronucleus test in mice dosed with 6 or

12 mg/kg/day for 2 days (Herbold 1981). Disulfoton also did not induce micronuclei in erythrocytes
of mice dosed with 2, 4, or 8 mg/kg disulfoton (EPA 1984a; Sandhu et al. 1985), but whether
disulfoton was administered by the oral or intraperitoneal route was not clear. Other genotoxicity

studies are discussed in Section 2.4.

DISULFOTON 67

2. HEALTH EFFECTS

2.2.2.8 Cancer

No studies were located regarding cancer in humans after oral exposure to disulfoton.

No histological evidence of a carcinogenic effect was observed in rats fed $0.1 mg/kg/day disulfoton
for 1.5-2.0 years (Carpy et al. 1975), in rats fed $1.02 mg/kg/day disulfoton for 2 years (Hayes 1985),
or in mice fed $2.53 mg/kg/day disulfoton for 23 months (Hayes 1983). The study by Carpy et a1.
(1975) was limited by insufficient necropsy and histological data and by dosing manipulations. In
addition, there was no evidence of carcinogenicity in Beagle dogs fed disulfoton

(0.02—0.14 mg/kg/day) for 2 years (Hoffman et al. 1975).

2.2.3 Dermal Exposure

2.2.3.1 Death

No studies were located regarding death in humans after dermal exposure to disulfoton.

Dermal LD50 values suggest that, irrespective of strain, female rats are more sensitive than male rats
when disulfoton is administered dermally. The dermal LDS0 for disulfoton was determined to be

15.9 and 3.6 mg/kg in male and female Wistar rats, respectively (Mihail 1978). In Sherman rats, the
dermal LD50 was determined to be 15 and 6 mg/kg in males and females, respectively (Gaines 1969).
In male Sprague-Dawley rats, the dermal LD50 was determined to be 20 mg/kg (DuBois 1957). A
dermal LD50 value of 0.285 mL/kg (187 mg/kg) was reported for rats given a liquid formulation
containing 65.7% disulfoton (Weil et al. 1971). When a granular formulation containing 10%
disulfoton was applied at a dose of 1,280 mg/kg, one of four rats died. The difference in dermal LD50
values is probably related to the different formulations of disulfoton. In a range-finding study, 2 of

2 rabbits died after 1 or 2 applications of 10 mg/kg/day disulfoton was applied to the shorn, unabraded
skin and left for 6 hours (Flucke 1986). None of the rabbits similarly treated with 0.4 or

2.0 mg/kg/day for 5 days died. In a 3-week experiment, similar treatment of rabbits 5 days/week
resulted in death of 5 of 5 females after 1—6 treatments and of 5 of 5 males after 3‘10 treatments with
6.5 mg/kg/day. None of the rabbits treated with $1.6 mg/kg/day for 3 weeks died. The rabbits that
died in these experiments exhibited persistent cholinergic signs of intoxication (muscle spasms,

dyspnea, salivation) before death.

DISULFOTON 68

2. HEALTH EFFECTS

The LD50 values in rats and the LOAEL values for death of rabbits after dermal exposure to

disulfoton are recorded in Table 2-3.

2.2.3.2 Systemic Effects

No studies were located regarding musculoskeletal or ocular effects in humans or animals after dermal
exposure to disulfoton. The highest NOAEL values and all LOAEL values from each reliable study

for systemic end points in animals are recorded in Table 2—3.

Respiratory Effects. No studies were located regarding respiratory effects in humans after dermal

exposure to disulfoton.

In rats exposed to disulfoton applied to clipped dorsal skin at doses of 25—20 mg/kg, breathing
difficulties were noted (Mihail 1978), but it was not clear at which doses this effect was seen. In a
3-week study, in which disulfoton was applied to the shom, unabraded skin of rabbits and left for

6 hours, 5 days/week, necropsy of the rabbits that died within 2 weeks during treatment (100%) with
the high dose of 6.5 mg/kg/day revealed distended, pale, mottled, and fluid—containing lungs (Flucke
1986). The organs and tissues of the high dose rabbits were not examined histologically, but gross
and histological examination of the lungs of rabbits similarly treated with $1.6 mg/kg/day for 3 weeks

revealed no treatment—related lesions.

Cardiovascular Effects. No studies were located regarding cardiovascular effects in humans after

dermal exposure to disulfoton.

Acute dermal exposure to unspecified doses of organophosphorus insecticides, including disulfoton,
was reported to cause protein degeneration and significant circulatory disruptions in heart muscles of
rats, cats, and rabbits (Kundiev and Rappoport 1967). This study is limited by reporting deficiencies
regarding incidences, and by uncertainty about whether the effects were observed in all species and
whether disulfoton was among the insecticides causing these effects. In a 3-week study in which
disulfoton was applied to the shom, unabraded skin of rabbits and left for 6 hours, 5 days/week, gross
and histological examination of the heart revealed no treatment-related lesions at $1.6 mg/kg/day

(Flucke 1986).

69

DISULFOTON

2. HEALTH EFFECTS

at: w 6.53M

 

 

{an m 32H
82 9.8.". 8% o :o: 3 x; m; 58m
$53
2:. o .53
8.: 9.3.“. 8% may or u N; as“:
8de n. on Essa
o5. =2: 8de .2 m9 8% 6m
88: n. ed “5535.
$2 8:30 8de 5. 3 3:0 «am
$58
$3qu
32388 88.; s. cm 88 as
5.3
mmawOAxm m50<

85...... :.%$§ aifié asaié seaming: 8.88. 39m.

26:8 2.28m ”8.. 4932 38262“. 3288

E3 hug.

 

.2Eoo . 53:35 2 2:3an ESE—arm .0 205.. .n.« 39:

70

DISULFOTON

2. HEALTH EFFECTS

 

 

 

AucaBoN
22.3.8 2:. o .3;
89 ESE .3:qu .mEmmqm 2825 m6 u «4 355m.
Amomou
N .o F Sam 3% was 2% 8533
0_mgoc__oco thOGQwCD Uh: 0 302v
82 9.8.“. 8558 £89 may 2 N u m; «Baum
30329502
SE o 6533.
€05 55 {in m :65
82 9.85. 933. c_ 52% 2mg =mEmv Wm x; m; 55mm
.w_:o=o._o:nE>.S8_mo_o::EE_
23% B as:
o. a: 82 £995 6566
98 9.25 82 o: 3 2:5 3 :5 8
m6 E50
3%
.9: 2329 5 22036
85365 new $28 .22
00523.. 53> .985: 2%: Wm .mcmm
6% as 2522 s
.2: 2: 5 62.3 5.3% mm 23%:
6%
«m5 oEEo. 95 E E3: on.
he cozamomammas umvtmEV md 0:30
3% as 95%.. 2.5 o fiaafi
c_ v.95. mcEfiEoo 2:: x25 m 3on
82 $8.“. 62:05 .23 .8253 3 36m x; 3 Easy.
02.296
8:223. Soaking aaubxaé :«Emémé 53:183.“: 228%. 3.39
0:230 25:8 33 4w<oz 30:300..“— 33mm
20.550
3.3%

 

Auoaczcoov .2an . 5.2.35 2 Eamonxm E3555 .0 22.3 .n.~ mans.

71

DISULFOTON

2. HEALTH EFFECTS

Amvxmwz n V? ESSEmQ u 3mm ”_w>m_ «8%-3859823506: u ..m<Oz ”mEE u _2 u_w>m_
fimtw-w9m>um-uoz390-6950. n ._m_<O._ 52 $8 $8 652 u own: 2350; u E :mofiofifiEwc n SmE

62885 n Boucw ”Eaton n

m: ”.mczmQEPfig n 0536 ”wEEE u H.
E8 ”328 u a £92, >08 u :5 am

 

33:8 $9935.05

at; w AucafimN

 

26955 :25 m :on
82 9.8.“. .o 8:525 «Ono- E u. w; to x; m :33.
3032232
w; :5 vm
0.? E50
w; 885
o; i=2...
3 0:32..
o; ofiEmI
m; 0650
BE w AncaaoN
{5% m zozv
82 9.3a m; amwm {5 m :29...
2E3m>m
mmDmOmxm m._.<_oms_mm._.z_
nose—om 33.3.33 ciEmémEv 93333.5 E296 A053. 2:00am. Asng
“ac—how 030—53 OflfiJ Jm<oz \>OCO—Jghl 30—00Qm

 

4m?

20:23
3533m—

 

Auosczcoov .aFcuo - coaozamfi 3 2:3an Enuficma «o «.30.. d-“ m;m<...

DISULFOTON . 72

2. HEALTH EFFECTS

Gastrointestinal Effects. No studies were located regarding gastrointestinal effects in humans

after dermal exposure to disulfoton.

In a 3-week study in which disulfoton was applied to the shom, unabraded skin of rabbits and left for
6 hours, 5 days/week, necropsy of the rabbits that died within 2 weeks during treatment (100%) with
the high dose of 6.5 mg/kg/day revealed marked intussusception of the ileum of one female (Flucke
1986). The gastrointestinal tract of the high dose rabbits or of rabbits similarly treated with

$1.6 mg/kg/day for 3 weeks were not examined histologically.

Hematological Effects. No studies were located regarding hematological effects in humans after
dermal exposure to disulfoton. No hematological effects in rabbits were found at $1.6 mg/kg/day in a
3-week study in which disulfoton was applied to the shom, unabraded skin and left for 6 hours,

5 days/week (Flucke 1986).

Hepatic Effects. No studies were located regarding hepatic effects in humans after dermal

exposure to disulfoton.

Acute dermal exposure to unspecified doses of organophosphorus insecticides, including disulfoton,
was reported to cause protein degeneration and significant circulatory disruptions in the livers of rats,
cats, and rabbits (Kundiev and Rappoport 1967). This study is limited by reporting deficiencies
regarding incidences, and by uncertainties about whether the effects were observed in all species and
whether disulfoton was among the insecticides causing these effects. In a 3-week study in which
disulfoton was applied to the shom, unabraded skin of rabbits and left for 6 hours, 5 days/week, 100%
of the rabbits died within 2 weeks during treatment. Necropsy of the rabbits treated with the high
dose of 6.5 mg/kg/day revealed a lobular pattern in the liver (Flucke 1986). The organs and tissues of
the high dose rabbits were not examined histologically, but clinical chemistry results and gross and
histological examination of the liver of rabbits similarly treated with $1.6 mg/kg/day for 3 weeks
revealed no treatment-related hepatic effects. Slight increases in the absolute and relative liver weights
were found in male rabbits at 1.6 mg/kg/day, but the absence of clinical chemistry and histological

effects indicates that the liver weight change was not toxicologically significant.

Renal Effects. No studies were located regarding renal effects in humans after dermal exposure to

disulfoton.

DISULFOTON 73

2. HEALTH EFFECTS

Acute dermal exposure to unspecified doses of organophosphorus insecticides, including disulfoton,
was reported to cause protein degeneration and significant circulatory disruptions in the kidneys of
rats, cats, and rabbits (Kundiev and Rappoport 1967). This study is limited by reporting deficiencies
regarding incidences, and uncertainties about whether the effects were observed in all species and
whether disulfoton was among the insecticides causing these effects. In a 3—week study in which
disulfoton was applied to the shom, unabraded skin of rabbits and left for 6 hours, 5 days/week, 100%
of the rabbits died within 2 weeks during treatment. Necropsy of the rabbits treated with the high
dose of 6.5 mg/kg/day revealed pale kidneys, with reddened renal pelvis and indistinct structure
(Flucke 1986). The organs and tissues of the high dose rabbits were not examined histologically, but
clinical chemistry and urinalysis results and gross and histological examination of the kidney of rabbits

similarly treated with $1.6 mg/kg/day for 3 weeks revealed no treatment—related renal effects.

Endocrine Effects. No studies were located regarding endocrine effects in humans after dermal

exposure to disulfoton.

In a 3—week study in which disulfoton was applied to the shom, unabraded skin of rabbits and left for
6 hours, 5 days/week, gross and histological examination of the adrenal and thyroid glands revealed no

treatment-related lesions at $1.6 mg/kg/day (Flucke 1986).

Dermal Effects. No studies were located regarding dermal effects in humans after dermal exposure

to disulfoton.

Acute dermal exposure to unspecified doses of organophosphorus insecticides, including disulfoton,
was reported to cause microscopic changes in the blood vessels and fibrous structures in the skin of
rats, cats, and rabbits (Kundiev and Rappoport 1967). Collagen and elastin fibers in the skin and the
blood vessels in the skin appeared to have been affected. These effects were thought to have further
increased the absorption of the insecticides by the skin. This study is limited by reporting deficiencies
regarding incidences, and questions about whether the effects were observed in all species and whether
disulfoton was among the insecticides causing these effects. In a 3-week study in which disulfoton
was applied to the shom, unabraded skin of rabbits and left for 6 hours, 5 days/week, the treated areas
of the skin were observed daily for signs of inflammation (redness and swelling) (Flucke 1986). In
the rabbits that died within 2 weeks during treatment with the high dose of 6.5 mg/kg/day (100%) and

in the rabbits treated with $1.6 mg/kg/day for 3 weeks, no indication of local irritation was found.

DISULFOTON 74

2. HEALTH EFFECTS

The skin of the high dose rabbits was not examined histologically, but histological examination of the

skin of rabbits treated with S 1.6 mg/kg/day for 3 weeks revealed no treatment-related lesions.

Body Weight Effects. No studies were located regarding body weight effects in humans after

dermal exposure to disulfoton.

In a 3-week study in which disulfoton was applied to the shom, unabraded skin of rabbits and left for
6 hours, 5 days/week, little or no feed intake and distinct weight loss occurred up to the time of death
in the rabbits that died within 2 weeks during treatment. Necropsy of the rabbits treated with the high
dose of 6.5 mg/kg/day (100%) (Flucke 1986). No effects on body weight were found in rabbits
similarly treated with $1.6 mg/kg/day for 3 weeks.

2.2.3.3 Immunological and Lymphoreticular Effects

No studies were located regarding immunological and lymphoreticular effects in humans after dermal

exposure to disulfoton.

In a 3-week study in which disulfoton was applied to the shom, unabraded skin of rabbits and left for
6 hours, 5 days/week, 100% of the rabbits died within 2 weeks during treatment. Necropsy of the
rabbits treated with the high dose of 6.5 mg/kg/day revealed small and pale spleens in some cases
(Flucke 1986). The organs and tissues of the high dose rabbits were not examined histologically, but
gross and histological examination of the spleens of rabbits similarly treated with $1.6 mg/kg/day for
3 weeks revealed no treatment—related lesions. The NOAEL value and the LOAEL value for effects

on the spleen in rabbits are recorded in Table 2-3.

2.2.3.4 Neurological Effects

Exposure to disulfoton can result in inhibition of acetylcholinesterase activity, with consequent
accumulation of acetylcholine at nerve synapses and ganglia leading to central nervous system,

nicotinic, and muscarinic effects (see Section 2.2.1.4 for more extensive discussion).

A farmer who had worn disulfoton—contaminated gloves for several days developed signs of disulfoton

toxicity (weakness, fatigue, and cyanosis) and had to be hospitalized (Savage et al. 1971). Because a

DISULFOTON 75

2. HEALTH EFFECTS

considerable amount (not otherwise specified) of disulfoton was detected in the serum and because
blood cholinesterase activity was severely depressed, it can be assumed that the patient had absorbed a
considerable amount of disulfoton through the skin. The patient recovered following treatment for the
toxicosis. Severe neurological signs and symptoms were not reported by workers exposed to
disulfoton during wet or dry mix operations at mean doses of 0013—023 mg/kg/day for 9 weeks at a
pesticide-fertilizer mixing plant (Wolfe et al. 1978). However, erythrocyte cholinesterase activity was
depressed by 22.8% from week 2—9 of the study in workers involved in dry mix operations

(0.23 mg/kg/day). No depression in blood cholinesterase activity was observed in workers involved
with wet mix operations (0.013 mg/kg/day). These workers were also exposed to disulfoton by the
inhalation route (see Section 2.2.1.4). Therefore, the depression in erythrocyte cholinesterase activity
may be due to both absorption of disulfoton through the respiratory tract and through the skin. No
significant reductions in plasma or erythrocyte cholinesterase activities occurred in three employees at
a pesticide formulating plant exposed to disulfoton (unspecified doses) for 25 weeks (Brokopp et al.
1981). Similarly, no reductions in cholinesterase activity were found for eight employees exposed for

shorter periods.

Disulfoton caused muscle twitching and clonic cramps in male and female rats after acute dermal
exposure to doses 2.5—20 mg/kg (Mihail 1978), but it was not clear at which doses these signs were
observed. These neurological effects persisted for an unspecified time after disulfoton was removed
from the skin. Disulfoton also caused depression in skin cholinesterase activity in rats, cats, and
rabbits given acute unspecified dermal doses (Kundiev and Rappoport 1967). This study is limited by
reporting deficiencies regarding incidences and uncertainty about whether the effects were observed in
all species. In a range-finding study, 2 of 2 rabbits died after 1 or 2 applications of 10 mg/kg/day
disulfoton were applied to the shom, unabraded skin and left for 6 hours (Flucke 1986). The rabbits
exhibited cholinergic signs of intoxication (not otherwise specified) before death. None of the rabbits
similarly treated with 0.4 or 2.0 mg/kg/day for 5 days showed cholinergic signs or died. In a 3-week
experiment, similar treatment of rabbits 5 days/week resulted in death of 5 of 5 females after

1-6 treatments and of 5 of 5 males after 3—10 treatments with 6.5 mg/kg/day. Persistent cholinergic
signs (muscle spasm, dyspnea, salivation) were observed in the high dose females after 1 or

2 treatments and in high dose males after 2 treatments. No clinical signs of cholinergic intoxication
were seen in the rabbits treated with 0.4 or 1.6 mg/kg/day, but erythrocyte cholinesterase activity was

inhibited by 21—33% in the female rabbits treated with 1.6 mg/kg/day. The highest NOAEL values

DISULFOTON 76

2. HEALTH EFFECTS

and the LOAEL values for neurological effects in rabbits for the acute and intermediate duration are

recorded in Table 2—3.

2.2.3.5 Reproductive Effects

No studies were located regarding reproductive effects in humans after dermal exposure to disulfoton.
In a 3-week study, in which disulfoton was applied to the shom, unabraded skin of rabbits and left for
6 hours, 5 days/week, gross and histological examination of the testes, epididymides, ovaries, and
uterus revealed no treatment-related lesions at $1.6 mg/kg/day (Flucke 1986). Slight increases in the
absolute and relative testes weights were found in male rabbits at 1.6 mg/kg/day, but the absence of
histological effects indicates that the testes weight change was not toxicologically significant.

Reproductive function was not evaluated.

No studies were located regarding the following effects in humans or animals after dermal exposure to

disulfoton:

2.2.3.6 Developmental Effects

2.2.3.7 Genotoxic Effects

Genotoxicity studies are discussed in Section 2.4.

2.2.3.8 Cancer

2.3 TOXICOKINETICS

The toxicokinetics of disulfoton in humans and animals depends on its physicochemical characteristics
and its metabolism. The lipophilicity of disulfoton indicates that the insecticide should be easily
absorbed by oral, inhalation, and dermal routes. No bioavailability data were located for inhalation
and dermal exposure. However, disulfoton is almost completely absorbed from the gastrointestinal

tract within 2 days after oral exposure. Animal studies suggest that disulfoton is widely distributed

primarily to the liver and in smaller quantities to the kidney, fat, skin, muscle, brain, and other organs.

DISULFOTON 77

2. HEALTH EFFECTS

Disulfoton and/or its metabolites are excreted mainly in the urine of humans and animals, with minor

amounts excreted in the feces and expired air.

Disulfoton causes neurological effects in humans and animals. The mechanism of action on the
nervous system depends on the metabolism of disulfoton to active metabolites. The liver is the major
site of metabolic oxidation of disulfoton to disulfoton sulfoxide, disulfoton sulfone, demeton
S-sulfoxide and demeton S-sulfone, which inhibit acetylcholinesterase in nervous tissue. These four
active metabolites are more potent inhibitors of acetylcholinesterase than disulfoton. Cytochrome
P—450 monooxygenase and flavin adenine dinucleotide monooxygenase are involved in this metabolic
activation. The active metabolites ultimately undergo nonenzymatic and/or enzymatic hydrolysis to

more polar metabolites that are not toxic and are excreted in the urine.

The inhibition of acetylcholinesterase increases the amount of acetylcholine at nerve synapses, which
causes an overstimulation of cholinergic nerves and effector organs. Depending on the dose and its
duration, the resulting cholinergic effects are usually reversible within several days to 2 weeks after
disulfoton exposure has been discontinued. Prolonged exposure to disulfoton results in diminished
cholinergic signs, and affected animals develop tolerance. The down-regulation of cholinergic

receptors due to accumulation of acetylcholine may be associated with disulfoton—induced tolerance.
2.3.1 Absorption
2.3.1.1 Inhalation Exposure

No studies were located regarding absorption in humans or animals after inhalation exposure to

disulfoton.

2.3.1.2 Oral Exposure

Disulfoton and/or its metabolites have been detected in the blood and urine of humans who consumed
unknown amounts of disulfoton solution (Hattori et a]. 1982; Yashiki et a1. 1990). In one case, the
concentration of disulfoton and the sum of its metabolites in the blood were 0.093 nmol/g (25.4 ng/g)
and 4.92 nmol/g, respectively, at =2 hours after ingestion (Yashiki et al. 1990). The 4.92 nmol/g

blood concentration corresponded to 1.35 pg disulfoton/g. Gastrointestinal absorption was not yet

DISULFOTON 78

2. HEALTH EFFECTS

complete, since 3.3 mg of disulfoton were recovered from the stomach contents, which was also
collected at =2 hours after the ingestion. The concentration of metabolites in the urine was not
quantitated. While these data indicate disulfoton is absorbed from the gastrointestinal tract of humans,

the data are not sufficient to estimate the extent or rate of absorption.

Male rats given a single acute dose (1.2 mg/kg) of [HQ-disulfoton eliminated an average of 84.3%,
6.1%, and 9.2% of the dose in the urine, feces, and expired air, respectively, in the 10 days following
exposure (Puhl and Fredrickson 1975). Female rats given 0.2 mg/kg eliminated 78.9%, 7.8%, and
9.2% of the administered radioactivity in the urine, feces, and expired air, respectively, in the same
time period. The data indicate that at least 88-91% of the administered dose was absorbed over the
10-day period. Absorption rates were not determined; however, 50% of the administered dose was
recovered in the urine during the first 4—6 hours after exposure in males and the first 30—32 hours
after exposure in females. Although it was not possible to quantitatively determine the absorption rate
in female rats, the data from the male rats suggest that absorption was almost complete within

12—24 hours of dosing in males. As seen in Section 2.2, female rats are more sensitive to the toxic
effects of disulfoton than male rats; therefore, the females were given a lower dose. Nevertheless, it
took longer for females to excrete 50% of the dose than males. Whether this sex difference is due to

differences in absorption, metabolism, retention, excretion, or a combination of factors is not known.

In another study, rats received [14C]-disu1f0ton at a single oral dose of 0.2 mg/kg or 1.0 mg/kg or
repeated oral doses 0.2 mg/kg/day for 14 days (Lee et a1. 1985). In the rats given a single dose of
0.2 mg/kg, the respective percentages of administered radioactivity 72 hours later in females and males
were: urine, 97.1% and 96.9%; feces, 1.1% and 1.4%; tissues, 0.1% in both sexes; carcass, 0.7% in
both sexes; and cage rinses, 1.0% and 0.9%. In the rats given a single dose of 1.0 mg/kg, the
respective percentages of administered radioactivity for females and males were: urine, 97.5% and
96.9%; feces, 1.7% and 1.9%; tissues, 0.1% and 0%; carcass, 0.5% and 0.4%; and cage rinse, 0.2%
and 0.8%. In the rats given 14 daily doses of 0.2 mg/kg/day, the respective percentages in females
and males were: urine, 97.1% and 98%; feces, 0.5% and 0.7%; tissues, 0.1% and 0.3%; carcass, 0.9%
and 0.5%; and cage rinse, 1.4% and 0.5%. Based on the percentages of administered radioactivity in
the urine, 297% of the administered dose was absorbed from the gastrointestinal tract within 72 hours.
At least 90% of the administered dose was excreted in the urine in the first 24 hours, indicating rapid

absorption. In a preliminary experiment, in which rats were given a single oral dose of 0.2 mg/kg

DISULFOTON 79

2. HEALTH EFFECTS

radioactive disulfoton, urinary excretion was essentially complete within 48 hours, with 61—72%

excreted in urine of females and 31—48% excreted in the urine of males in the first 4 hours.

Gastrointestinal absorption of disulfoton was extensive following oral exposure of rats and guinea pigs,
as evidenced by the small differences in the oral LD50 values versus the intraperitoneal LDSO values
(Bombinski and DuBois 1958). However, the intraperitoneal LD50 values were slightly lower than the

oral LD50 values, suggesting that gastrointestinal absorption is <100%.

2.3.1.3 Dermal Exposure

No studies were located regarding absorption in humans or animals after dermal exposure to
disulfoton. However, data on lethality, other signs of toxicity, and acetylcholinesterase inhibition in
animals after dermal exposure (see Section 2.2.3) suggest that disulfoton can be absorbed from the

skin.

2.3.2 Distribution

2.3.2.1 Inhalation Exposure

No studies were located regarding distribution in humans or animals after inhalation exposure to

disulfoton.

2.3.2.2 Oral Exposure

No studies were located regarding distribution in humans after oral exposure to disulfoton.

Analysis of tissues and blood for radioactivity at various time intervals after rats were dosed with
[14C]—disulfoton (1.2 mg/kg for males, 0.2 mg/kg for females) showed that peak levels occurred

6 hours after dosing (Puhl and Fredrickson 1975). The highest levels were found in the liver (peak
was 3.6 mg/kg for males, 2.3 mg/kg for females). Peak levels in other tissues (kidney, plasma, fat,
whole blood, skin, muscle, and brain in descending order) also generally occurred at 6 hours. At
10 days after dosing, the levels of radioactivity in all tissues decreased; however, low levels were

found in the heart at this sampling time. In Beagle dogs dosed with 0.5—1.5 mg/kg/day disulfoton in

DISULFOTON 80

2. HEALTH EFFECTS

capsules for 2 years, disulfoton was detected in the kidney (0.06 ppm), urine (0.06 ppm), liver
(0.02 ppm), serum (0.04 ppm), brain and spinal cord (0.01—0.02 ppm) (Hikita et al. 1973). Disulfoton
and its metabolites (unidentified) were also detected in small intestine, pancreas, bile, fatty tissue,

thymus, spleen, erythrocytes, extraocular muscle, and muscles of the extremities and torso.
2.3.2.3 Dermal Exposure

No studies were located regarding distribution in humans or animals after dermal exposure to

disulfoton.
2.3.3 Metabolism

Three different pathways are associated with the metabolism of disulfoton: (1) oxidation of the
thioether sulfur to produce sulfoxides and sulfones; (2) oxidation of the thiono sulfur to produce the
oxygen analogs; and (3) hydrolysis of the P-S—C linkage to produce the corresponding
phosphorothionate or phosphate (WHO 1976) (see Figure 2—3). These pathways have been elucidated
from data obtained in humans exposed to disulfoton and from in vivo and in vitro metabolism studies

in rats and mice.

The oxygen analog of disulfoton sulfoxide (demeton S-sulfoxide) and the oxygen analog of disulfoton
sulfone (demeton S-sulfone) were identified in the urine from an 87-year-old man who accidentally
drank an unknown amount of diluted disulfoton (Yashiki et a1. 1990). Disulfoton sulfone and demeton
S-sulfone were the only metabolites of disulfoton detected in the blood of this patient. The authors
did not report whether they detected the products of disulfoton and/or sulfoxide/sulfone hydrolysis,
diethyl phosphate (DEP), diethyl thiophosphate (DETP), and diethyl dithiophosphate (DEDPT) in the
urine. From this case report, there is evidence of oxidation of the thioether and thiono sulfur, which
produces sulfoxides or sulfones and oxygen analogs of disulfoton, respectively. Workers exposed
mainly to disulfoton at a pesticide formulating plant had excreted the metabolites DEP, DETP,
DEDPT, and diethyl phosphorothiolate (DEPTh) in urine after dermal and possibly inhalation exposure
to disulfoton (Brokopp et al. 1981).

Studies in rats and mice indicate that the same pathways operate in humans and rodents. Unidentified

urinary metabolites in mice injected intraperitoneally with 32P—disulfoton were described as hydrolysis

DISULFOTON 81

2. HEALTH EFFECTS

FIGURE 2-3. Metabollc Pathways for Dlsulfoton'

E10 8 s
\" H20 Eto\"
lp—SCHZCHZSCHZCHa ————» P—CH
80 D n BO,
0 t ' I
IS“ 0°" Dlelhylphosphorethionate
[0]
H20
0
805i I
—CH CH CH CH
:Z>P—S 2 2 2 3 H20
Disulfolon sulfoxide
y Y
O O
O
Em. Y
p-s—CHZCH280HZCH3 EO>:I_SCHZCH2 CH20H3
Eto’ Em
D' If t If
oxygen analog sulfoxide '3“ ° on 3" one

(Demelon S-sulfoxide)

V \

aofi Ho2
p— 0H 4—— EOJ>I— SCH2CH2$CH20H3
80/ BO
DielhylphOSphale Oxygen analog sulfone

(Demelon S-sulfone)

' Adapted from WHO 1976

DISULFOTON 82

2. HEALTH EFFECTS

products (March et a1. 1957). The metabolites, disulfoton sulfoxide, disulfoton sulfone, demeton
S-sulfoxide, and demeton S-sulfone were also identified as products of in vitro hepatic disulfoton
metabolism. Disulfoton sulfoxide (11.3%), disulfoton sulfone (2.4%), demeton S-sulfoxide (26.7%),
and demeton S-sulfone (59.6%) were also identified in the livers of rats 30 minutes after
intraperitoneal injection with disulfoton (Bull 1965). Disulfoton sulfone was the only one of these
metabolites not recovered from the liver 120 minutes after exposure. DEP and DETP, formed from
the hydrolysis of disulfoton and/or its oxidation products, were identified as the major urinary
metabolites in rats dosed orally or intraperitoneally in several studies (Bull 1965; Pub] and Fredrickson
1975; Wolfe et a1. 1978). The minor urinary metabolites included disulfoton sulfoxide, demeton
S-sulfoxide, and demeton S-sulfone (Puhl and Fredrickson 1975). Although disulfoton sulfone was not
detected in the urine in this study, it can be assumed that, subsequent to its formation, it was quickly
oxidized to demeton S—sulfone or quickly hydrolyzed to DETP. Furthermore, in another study,
disulfoton sulfone was found in the urine of rats after oral exposure to disulfoton (Lee et a]. 1985).
These findings are consistent with the pathways in Figure 2-3, whereby disulfoton metabolism
proceeds via the sequential oxidation of thioether sulfur and/or oxidative desulfuration followed by
hydrolysis of the ester. The data also suggest that a greater percentage of disulfoton sulfoxide is
oxidized to demeton S-sulfoxide, rather than disulfoton sulfone, to form demeton S-sulfone (Bull
1965). The relative importance of each of the pathways, however, cannot be deduced from relative
percentages of metabolites formed because the final urinary metabolites are common products of
several of the intermediate metabolites (see Figure 2-3). In addition, after a single dose of 0.2 mg/kg
[HQ—disulfoton, disulfoton sulfone, demeton S-sulfone, and demeton S-sulfoxide were found in urine
of males, while only demeton S-sulfone was apparent in the urine of females (Lee et a1. 1985).
However, after dosing with 0.2 mg/kg/day for 14 days, the pattern in males and females was reversed.
This reversed pattern after repeated dosing was more likely due to metabolic rate differences than to a
difference in pathway, since disulfoton sulfone and demeton S-sulfoxide are precursors to the demeton

S-sulfone.

The studies described above support the accepted theory (Eto 1974) that most thioether
organophosphate insecticides, such as disulfoton, first undergo metabolic oxidation to sulfoxides,
sulfones, and their respective oxygen analogs as part of the metabolic activation pathway. These
active metabolites bind to ubiquitous cholinesterase and cause signs of disulfoton toxicity. In the
detoxification pathway, these oxidation products and/or disulfoton subsequently undergo hydrolysis to

more polar metabolites that are eliminated in the urine. Cytochrome P-450 monooxygenase and flavin

DISULFOTON 83

2. HEALTH EFFECTS

adenine dinucleotide (FAD) monooxygenase are thought to be involved in the metabolic activation

pathways.

Generally, organophosphates serve as substrates for the hepatic cytochrome P—450 mixed-function
oxidase (MFO) system. The components of the MFO system include cytochrome P-450, the terminal
oxidase, and NADPH, and NADPH-dependent cytochrome c reductase (Stevens and Green 1974).
Generally, anticholinesterase insecticides such as disulfoton bind to oxidized cytochrome P-450 to
form a disulfotonzcytochrome P-450 complex, which usually produces some form of a Type I spectra
(Stevens et a1. 1973). An electron is then transferred from cytochrome c reductase to cytochrome
P-450 (Gillette et a1. 1972), thereby reducing the disulfoton2cytochrome P—450 complex. Molecular
oxygen then binds to this complex to form a disulfotonzreduced cytochrome P-450:O2 complex (Gigon
et a1. 1969). A second electron from NADPH or reduced nicotinamide adenine dinucleotide (NADH)
then reduces this complex to form an active oxygen intermediate that decomposes with the formation

of the product and oxidized cytochrome P-450 (Hildebrandt and Estabrook 1971).

Flavin monooxygenase specifically oxidizes sulfides to (R)—(+)—sulfoxide enantiomers, while
cytochrome P-450—dependent oxidations yield predominantly sulfoxides in the (S)—(-) configuration
(Light et a1. 1982; Waxman et a1. 1982). Disulfoton has three sulfur atoms that can be oxidized: the
thiophosphoryl or thiono, the thiol, and the thioether. It has been proposed that flavin monooxygenase
cannot catalyze P=S to P=O conversions (Hajjar and Hodgson 1980). The flavin monooxygenase
enzymes metabolize thioether-containing organophosphates to sulfoxides only; that is, there is no
evidence for the formation of any other products such as disulfoton sulfones in the presence of only
FAD monooxygenase (Hajjar and Hodgson 1980). Sequential oxidations by both monooxygenases
(FAD-dependent and cytochrome P-450) may be required to form sulfones (Tynes and Hodgson 1985).
Disulfoton interacted with cytochrome P-450 to markedly inhibit the metabolism of p-nitroanisole and
parathion, both of which have rather high affinities for cytochrome P—450. These findings underscore
the fact that cytochrome P-450 and flavin monooxygenase both have the potential to participate in the

oxidation of the disulfoton.

FAD-dependent monooxygenase, purified from pig liver microsomes oxidized disulfoton (Hajjar and
Hodgson 1982). The product of this reaction was disulfoton sulfoxide. However, disulfoton sulfoxide
was not a substrate for this enzyme, as disulfoton sulfone was not detected. Structure-activity

relationships suggest that substitution by oxygen of either the thiono or thiol sulfur atoms decreases

DISULFOTON 34

2. HEALTH EFFECTS

the activity of FAD-dependent monooxygenase and thus the rate of sulfoxidation. In addition, changes
in the thioether sulfur have a similar effect. Structural changes on the thioether moiety may increase
steric hindrance of the sulfur atom, affect enzyme-substrate binding, and decrease the rate of
sulfoxidation. Thus, disulfoton sulfones were not formed, and further oxidation of the sulfoxides to
sulfones did not involve FAD-dependent monooxygenase, but rather another oxidase or nonenzymatic
reaction. Sulfoxidation was not inhibited by n-octylamine, a known inhibitor of cytochrome P-450-
dependent oxygenation (Hajjar and Hodgson 1982). This finding further suggests that FAD-dependent
monooxygenase may play a greater role than cytochrome P-450 monooxygenase in the oxygenation of
thioether organophosphates. Compared to most other thioether compounds, it was concluded that
disulfoton is among the best known flavin monooxygenase substrates (Poulsen 1981). Compared to
most other organophosphate insecticides (parathion, diazinon, ethion, phorate, azinophosmethyl, methyl
parathion, and ronnel), disulfoton was more rapidly metabolized in the hepatic microsomal oxidative

system involving NADPH from rats, guinea pigs, and monkeys (Rao and McKinley 1969).

The metabolism of disulfoton appears to be similar among similar species. For example, liver
homogenates from rats, guinea pigs, and monkeys were generally more active in metabolizing
disulfoton than liver homogenates from chickens (Rao and McKinley 1969). In addition, pig liver
flavin monooxygenase was more saturable by disulfoton than the mouse liver enzyme (Tynes and
Hodgson 1985). Flavin monooxygenase in pig liver also had a higher affinity (lower Km) than the
mouse enzyme towards disulfoton (Smyser et al. 1985). Rat liver and lung microsomes have lower
flavin monooxygenase activity towards disulfoton than liver or lung microsomes from the mouse or
the rabbit (Tynes and Hodgson 1985). However, flavin monooxygenase activity was greater in rabbit
and mouse lungs than in their respective livers. This disparity between lung and liver tissues was not

observed in rats.

2.3.4 Excretion

2.3.4.1 Inhalation Exposure.

No studies were located regarding the rate or extent of excretion in humans or animals after inhalation

exposure to disulfoton.

DISULFOTON 85

2. HEALTH EFFECTS

2.3.4.2 Oral Exposure

No studies were located regarding the rate or extent of excretion in humans after oral exposure to

disulfoton.

Male rats given a single acute dose (1.2 mg/kg) of [14C]—disulfoton eliminated an average of 84.3%,
6.1%, and 9.2% of the dose in the urine, feces, and expired air, respectively, in the 10 days following
exposure (Puhl and Fredrickson 1975). Female rats given 0.2 mg/kg eliminated 78.9%, 7.8%, and
9.2% of the administered radioactivity in the urine, feces, and expired air, respectively, in the same
time period. Male rats excreted 50% of the administered dose in the urine during the first 4—6 hours
after exposure, while females required 30—32 hours to excrete 50% of the dose in the urine. The
female rats were given a lower dose than the males because female rats are more sensitive than male
rats to the toxic effects of disulfoton (see Section 2.2). Nevertheless, it took longer for females to
excrete 50% of the dose. Whether this sex difference is due to differences in absorption, metabolism,

retention, excretion, or a combination of factors is not known.

In another study, rats received [14C]—disulfoton at a single oral dose of 0.2 mg/kg or 1.0 mg/kg or
repeated oral doses of 0.2 mg/kg/day for 14 days (Lee et al. 1985). In the rats given a single dose of
0.2 mg/kg, the respective percentages of administered radioactivity 72 hours later in females and males
were 97.1% and 96.9% in urine and 1.1% and 1.4% in feces. In the rats given a single dose of

1.0 mg/kg, the respective percentages of administered radioactivity for females and males were 97.5%
and 96.9% post—dosing in urine and 1.7% and 1.9% in feces. In the rats given 14 daily doses of

0.2 mg/kg/day, the respective percentages in females and males were 97.1% and 98% in urine and
0.5% and 0.7% in feces. Thus, the primary route of excretion in all dose groups was via the urine (at
least 97% in each group), and excretion was essentially complete within 72 hours post-dosing, with at
least 90% excreted in the first 24 hours. In a preliminary experiment in which rats were given a
single oral dose of 0.2 mg/kg radioactive disulfoton, urinary excretion was essentially complete within
48 hours, with 61—72% excreted in urine of females and 31—48% excreted in the urine of males in the
first 4 hours. Analysis of expired gases at 24-hour intervals for 144 hours post-dosing in the
preliminary experiment indicated that only 0.5% and 0.2% of the radioactivity in females and males,

respectively, was present in the expired air.

DISULFOTON 86

2. HEALTH EFFECTS

2.3.4.3 Dermal Exposure

No studies were located regarding the rate or extent of excretion in humans or animals after dermal

exposure to disulfoton.

2.3.4.4 Other Routes of Exposure

No studies were located regarding excretion in humans after other routes of exposure to disulfoton.

White rats given a single dose of radiolabeled disulfoton intraperitoneally eliminated the metabolites
phosphoric acid (4.1%), DEP (61.2%), and DETP (24.8%) in urine as a percentage of excretory
metabolites 10—12 hours after exposure (Bull 1965). Approximately 24 and 48 hours after exposure
14.1% and 28.6%, respectively, of the administered dose was excreted in the urine. Excretion rates for
disulfoton and its metabolites were not determined. Mice eliminated 30—60% of the radiolabeled
intraperitoneal dose of disulfoton in the urine and 2—3% in the feces within 96 hours of exposure

(March et al. 1957).

2.3.5 Mechanisms of Action

Disulfoton is readily absorbed from the gastrointestinal tract (Hattori et al. 1982; Lee et al. 1985; Puhl
and Fredrickson 1975; Yashiki et al. 1990). Although information regarding the rate and extent of
absorption of disulfoton after inhalation and dermal exposure was not located, the lipophilic nature of

disulfoton suggests that it is probably absorbed by passive diffusion by these routes as well.

Although there are no known intermediary proteins or other mechanisms associated with distribution
of disulfoton to effector organs or to organs where the compound is likely to be metabolized, binding
studies with other organophosphates suggest that serum albumin may be an important protein involved
with distribution to effector organs (Braeckman et al. 1983). Available data suggest that more
disulfoton is distributed initially to the liver than to any other organ (Puhl and Fredrickson 1975). The
detection of disulfoton metabolites in the liver of rats is consistent with this observation (Bull 1965).
The active metabolites of disulfoton are known to depress the activity of serum, erythrocyte, and brain

cholinesterase (see Section 2.2.2.4).

DISULFOTON 87

2. HEALTH EFFECTS

Metabolism of disulfoton in humans and animals appears to be qualitatively and quantitatively similar
(Brokopp et al. l98l; Bull 1965; Puhl and Fredrickson 1975; Yashiki et al. 1990). The intermediary
products of disulfoton metabolism, rather than disulfoton itself, are responsible for the signs of toxicity
observed in humans and animals exposed to the pesticide. These metabolites (disulfoton sulfoxide,
disulfoton sulfone) and the oxygen analogs (demeton S—sulfoxide and demeton S-sulfone) are oxidation
products of disulfoton and are formed primarily in the liver (Bull 1965; March et al. 1957). In an oral
study in rats, the metabolites, disulfoton sulfoxide, disulfoton sulfone, demeton S—sulfoxide, and
demeton S—sulfone resulted in mortality and signs of toxicity at lower doses than did disulfoton

(Crawford and Anderson 1974).

No information was located regarding the mechanism of excretion of disulfoton and/or its metabolites.
Because disulfoton and its active metabolites are relatively lipophilic, excretion by passive diffusion is

the probable mechanism.

The acute toxic effects of organophosphate insecticides are due primarily to accumulation of
acetylcholine at muscarinic and nicotinic cholinergic receptors (Costa et al. l982b). The accumulation
of this substrate is due to the inhibition of cholinesterase activity by the active metabolites of the
organophosphate (Murphy et al. 1984). In many instances, humans and animals exhibit signs of
toxicity resembling excessive stimulation of cholinergic nerves. Atropine, a cholinergic blocking
agent, has been used to demonstrate that excessive acetylcholine accumulation is related to the
mechanism of toxicity (Bombinski and DuBois 1958). Cholinesterase enzyme kinetics provide further
evidence supporting the proposed mechanism. Studies indicate that the enzyme-acetylcholine complex
and the enzyme—organophosphate complex usually are formed at the same rate (Murphy et al. 1984).
However, the enzyme-acetylcholine complex is hydrolyzed at a much faster rate than the enzyme-
organophosphate complex; the enzyme is therefore regenerated faster in the former case.

Dephosphorylation of the enzyme is a slow reaction, and, therefore rate-limiting.

Signs of disulfoton toxicity, such as muscle tremors, fasciculations, lacrimation, and salivation, in
animals are generally observed after a few daily doses, but begin to diminish in severity as exposure to
disulfoton continues (Bombinski and DuBois 1958). This phenomenon is known as tolerance.
Tolerance appears to be a reproducible phenomenon that does not depend on the organophosphate
insecticide used, the route of administration, or the animal species (Costa et al. 1982b). Several

possible mechanisms have been proposed to explain this phenomenon.

DISULFOTON 88

2. HEALTH EFFECTS

Evidence suggests that tolerance involves the cholinergic system and not the opiate system (Costa and
Murphy 1986). Tolerance to chronic treatment with disulfoton was once thought to be due to
refractoriness of the cholinergic receptor to acetylcholine (Brodeur and DuBois 1964). More recently,
tolerance has been associated more specifically with alterations of cholinergic receptor density, rather
than with changes in binding affinity (Costa et al. 1981, 1982a, 1990; McDonald et al. 1988).
Radiolabeled ligands, such as [3H] quinuclidinyl benzilate ([3H] QNB), which are muscarinic
antagonists that can bind to recognition sites on muscarinic receptors, were used in these studies to
demonstrate that disulfoton caused a reduced number of receptor binding sites in central and peripheral
nerve tissue. However, the binding affinity was not changed in disulfoton-tolerant animals.
Furthermore, the alteration in cholinergic muscarinic receptors was not due to direct binding of
disulfoton and/or its metabolites to the receptor, but due to an adaptive mechanism to overstimulation
by endogenous acetylcholine (Costa et a1. 1981). Disulfoton also caused modulation of M1 and

M2 muscarinic receptor subtypes in the brain of disulfoton—tolerant rats (Fitzgerald and Costa 1992).
However, recovery of M2 muscarinic receptor binding after termination of exposure was slower
compared to the M1 subtype, particularly in the hippocampus. Alteration of muscarinic binding sites
in lymphocytes was also demonstrated (Costa et al. 1990; Fitzgerald and Costa 1993). The rate of
recovery of cholinesterase is much slower than the rate of recovery of [3H] QNB binding in
disulfoton— tolerant animals (Costa et al. 1981). McDonald et al. (1988) hypothesized that the
decrease in muscarinic receptor densities in the hippocampus, cortex, and striatum of the brain was the
reason for memory loss in animals that became tolerant to disulfoton after repeated intraperitoneal
dosing (see Section 2.4). The data from earlier intraperitoneal behavioral studies are not consistent
with this finding (Costa and Murphy 1982). However, these two studies measured different
neurobehavioral end points in different species. In addition, this memory loss has not been reported in
humans. While cholinergic muscarinic signs diminish in severity in disulfoton-tolerant animals,
nicotinic cholinergic signs may persist (McPhillips 1969a). It was proposed that nicotinic receptors
were stable, while muscarinic receptors were labile to acetylcholine accumulation in disulfoton-tolerant
animals (Costa et al. 1982a). However, a decrease in nicotinic acetylcholine receptors in the brain was

subsequently found after repeated administration of disulfoton in rats (Costa and Murphy 1983a).

As supporting evidence for this mechanism (i.e., reduced density of muscarinic receptor binding sites),
subsensitivity to other cholinergic agonists was demonstrated in disulfoton-tolerant animals. The
mechanism for the subsensitivity to cholinergic agonists is probably related to changes in agonist

binding as well as loss of surface receptor labeling by hydrophilic ligands such as

DISULFOTON 89

2. HEALTH EFFECTS

N—methylscopolamine (Costa et al. 1982b; Schwab et al. 1983). Animals made tolerant to disulfoton
were resistant to the lethal or adverse effects of cholinergic agonists, such as carbachol (Brodeur and
DuBois 1964; Costa et al. 1981; Schwab and Murphy 1981) and oxotremorine (Costa et al. 1982b;
McPhillips 1969a), which are not hydrolyzed by acetylcholinesterase. Tissues from animals tolerant to
disulfoton such as the ilea (Foley and McPhillips 1973; McPhillips 1969b; McPhillips and Dar 1967)
and the atria (Perrine and McPhillips 1970; Schwab et al. 1983), were resistant to the effects of
carbachol and/or oxotremorine. Because the uterus and vas deferens have a relatively sparse
parasympathetic innervation compared to the ileum and do not receive a steady flow of impulses via
this system, these tissues were not as subsensitive to carbachol as the ileum (Foley and McPhillips

1973). Thus, acetylcholine accumulation may be a prerequisite for tolerance development.

Other hypotheses have been tested in attempts to explain the mechanism of tolerance. Tolerance may
be associated with interference of acetylcholine synthesis at the presynaptic junction (Costa et al.
1982b). However, no difference in the uptake of choline occurred in the hippocampus from
disulfoton-tolerant mice compared with controls, suggesting that the availability of choline was not
limiting. Noncholinergic mechanisms may also be involved in the development of tolerance. In one
study, the atria from disulfoton-tolerant rats were subsensitive to carbachol and oxotremorine, but there
was no alteration in binding of [3H] QNB when compared with the controls (Schwab et al. 1983).
This finding is inconsistent with the "altered receptor" hypothesis that suggests tolerance is associated
with a decrease in radioligand binding and a concomitant subsensitivity to cholinergic agonists. The
authors proposed that in addition to receptor loss, other mechanisms distal to [3H] QNB binding sites
or removed from the receptor complex may contribute to the subsensitivity of the atria and other

tissues to cholinergic agonist. These and other related mechanisms remain to be studied.
2.4 RELEVANCE TO PUBLIC HEALTH

The lipophilic properties of disulfoton suggest that the compound is likely to be absorbed readily by
the lungs, gastrointestinal tract, and the skin. Toxicokinetic data in humans and animals show that
disulfoton is readily and extensively absorbed by the gastrointestinal tract. Disulfoton and/or its
metabolites are distributed rapidly to tissues such as the liver, kidney, brain, and adipose tissue.
Although the compound is relatively lipophilic, its accumulation in these organs does not appear to be

appreciable. Fifty to ninety percent of the dose administered to rats was eliminated in the urine within

DISULFOTON 90

2. HEALTH EFFECTS

4-32 hours. Disulfoton is rapidly metabolized to its oxygen analogs, which are in turn rapidly

detoxified to water soluble nontoxic metabolites that are eliminated via the urine.

The most significant and sensitive effects resulting from acute, intermediate, or chronic exposure to
disulfoton by the inhalation, oral, or dermal route are neurological. The neurological effects are the
result of inhibition of acetylcholinesterase by active metabolites of disulfoton at nerve synapses;
subsequent accumulation of acetylcholine results in overstimulation of the distal neuron, and more
specifically, in cholinergic effects. Examples of cholinergic effects include salivation, miosis, muscle
tremors, and urinary and fecal incontinence. Convulsions, coma, and death have been associated with
severe disulfoton intoxication. Studies in chickens indicated that disulfoton does not cause delayed
neurotoxicity. Body weight loss is also a common finding in animals and is associated with
cholinesterase inhibition. In addition, disulfoton may alter catecholamine levels in body tissues. The
effects on catecholamine levels appear to be related to the accumulation of acetylcholine. Optic nerve

atrophy and necrosis have also been associated with chronic oral exposure to disulfoton in dogs.

The inhibition of erythrocyte acetylcholinesterase is a very sensitive biomarker of this
acetylcholinesterase inhibition at the nerve synapses, and, therefore, can be regarded as a sensitive
effect as well. Some of these effects have been observed in occupationally exposed individuals and in
a man who accidentally ingested disulfoton. Results from several animal studies support these
findings. The cholinergic effects are usually associated with acute exposure to disulfoton. Prolonged
exposure to disulfoton (5—10 days) generally results in a decrease in the severity of the cholinergic
toxicity, while cholinesterase remains inhibited. This phenomenon, known as tolerance, has been
observed in animals exposed to disulfoton for prolonged periods. A number of studies have

investigated the mechanism of tolerance development.

Hepatic effects have not been observed in humans, but mild hepatic effects were observed in animals
after oral exposure to disulfoton. These hepatic effects include alterations in liver microsomal enzyme
activities and lipid peroxidation. No concurrent histopathological changes in the liver were observed.
Although hepatic effects should be of little concern to exposed humans, caution is advised with
concomitant use of prescription or nonprescription drugs that share a common metabolic pathway with
disulfoton. Results from oral studies suggest that disulfoton may cause myopia in animals and
possibly humans. In one chronic dietary study in rats, effects on eyes (degeneration of the Harderian

gland and corneal neovascularization), lungs (inflammation), stomach (mucosal hyperplasia and

DISULFOTON 91

2. HEALTH EFFECTS

inflammation of the forestomach), skeletal muscle (atrophy due to debilitation), pancreas (atrophy), and
spleen and lymph nodes were seen in some rats, mostly at the highest doses, but the most sensitive
effects were associated with cholinesterase inhibition. Other than the cholinergic effects, none of the
effects were seen in mice or dogs given chronic oral doses, and their relevance to humans are
unknown. Other effects observed in rats exposed to disulfoton by the inhalation route include
inflammation of the nasal turbinates and bone marrow changes, which were related to decreased

lymphocytes and inflammatory changes in the lungs.

No data were located regarding reproductive or developmental effects in humans. However, disulfoton
has caused lower pregnancy rates and reduced litter sizes in animals after oral exposure for
intermediate durations. Fetotoxic effects, such as increased incidences of incomplete ossification of
parietal bones and stemebrae, have been reported in the fetuses of rat dams exposed orally during
gestation. In addition, depression of fetal brain and erythrocyte cholinesterase, fatty infiltration of the
liver, mild nephropathy, and juvenile hypoplasia of the testes occurred in litters of rats exposed orally
in multiple-generation reproductive studies. Although placental transfer of disulfoton and/or its active

metabolites appears to occur, no data were located regarding transfer via the dam’s milk.

Disulfoton has been tested for genotoxicity in a variety of assays with mostly negative results;
however, the few positive results indicate genotoxic potential. Carcinogenicity was not observed in

Beagle dogs, rats, or mice fed disulfoton for 2 years.

Employees at hazardous waste sites, employees at pesticide mixing and formulating plants, and farm
workers are more likely to be exposed to disulfoton than individuals in other occupations. Neurotoxic
effects have been observed in occupationally exposed persons. However, no human data were located
to identify susceptible subpopulations. Animal data suggest that female animals and young animals
are more susceptible to disulfoton toxicosis. Based on the results from animal studies, women and

children could also be more susceptible than men to toxic effects of disulfoton.

DISULFOTON 92

2. HEALTH EFFECTS

Mlnlmal Rlsk Levels for Dlsulfoton

Inhalation MRLs

0 An MRL of 0.006 mg/m3 has been derived for acute-duration inhalation exposure (14 days or

less) to disulfoton.

The MRL is based on a NOAEL of 0.5 mg/m3 for decreased acetylcholinesterase activity in rats
exposed to disulfoton 4 hours/day for 5 days in a study by Thyssen (I978). The NOAEL was adjusted
for intermittent exposure, converted to a human equivalent concentration, and divided by an
uncertainty factor of 30 (3 for extrapolation from animals to humans and 10 for human variability).
Inhibition of erythrocyte cholinesterase activity and unspecified behavioral disorders were observed at
1.8 mg/m3, and unspecified signs of cholinergic toxicity were observed at 9.8 mg/ma. Similar effects
were observed in rats or mice exposed to higher concentrations for shorter durations (Doull 1957;
Thyssen 1978). The NOAEL value of 0.5 mg/m3 is supported by another study, in which no
significant decrease in the activity of brain, serum, or submaxillary gland cholinesterase was found in
rats exposed to 0.14—0.7 mg/m3 for l hour/day for 5—10 days (DuBois and Kinoshita 1971). Mild
depression of erythrocyte cholinesterase activity was reported in workers exposed by the inhalation and

dermal routes (Wolfe et al. 1978).

0 An MRL of 2x104 mg/m3 has been derived for intermediate-duration inhalation exposure
(15—364 days) to disulfoton.

The intermediate MRL is based on a NOAEL of 0.02 mg/m3 for decreased acetylcholinesterase
activity in rats exposed to disulfoton 6 hours/day, 5 days/week for 3 weeks in a study by Thyssen
(1980). The NOAEL was adjusted for intermittent exposure, converted to a human equivalent
concentration, and divided by an uncertainty factor of 30 (3 for extrapolation from animals to humans
and 10 for human variability). In the Thyssen (1980) study, 2 separate 3—week experiments were
conducted. In the first experiment, rats exposed to 0.1, 0.5, or 3.7 mg/m3 showed concentration-
related increased severity of cholinesterase inhibition and cholinergic signs of toxicity, with the lowest
exposure level of 0.1 mg/m3 associated with lethargy during the last week of exposure. At 0.5 mg/m3,
lethargy and failure to groom were observed during the second and third weeks; and at 3.7 mg/m3,

muscle tremors, convulsions, inhibition of brain cholinesterase, and death were observed. Because a

DISULFOTON 93

2. HEALTH EFFECTS

NOAEL could not be established in the first experiment, the second experiment used an exposure level
of 0.02 mg/m3, which resulted in no inhibition of cholinesterase activity or signs of cholinergic
toxicity, and an exposure level of 3.1 mg/m3 to confirm the effects seen at 3.7 mg/m3 in the first
experiment. In a 13-week inhalation study, inhibition of erythrocyte and brain cholinesterase activity
was observed in rats exposed to 1.4 mg/m3, but not 0.16 mg/m", disulfoton 6 hours/day, 5 days/week
(Shiotsuka 1989). Other effects of intermediate-inhalation exposure of rats to disulfoton include
inflammatory changes in the respiratory tract associated with bone marrow changes at 205 mg/m3 and
decreased percentages of lymphocytes with increased polymorphonuclear leukocytes at 3.1 mg/m3,
increased absolute and relative adrenal weight at 3.1 and 3.7 mg/m3 (Thyssen 1980), and increased

incidence of inflammation of the nasal turbinates at 1.4 mg/m3 (Shiotsuka 1989).

An MRL has not been derived for chronic—duration inhalation exposure to disulfoton because no

chronic-duration inhalation studies were located.
Oral MRLs

- An MRL of 0.001 mg/kg/day has been derived for acute—duration oral exposure (14 days or less)

to disulfoton.

The MRL was based on a NOAEL of 0.1 mg/kg/day for decreased cholinesterase activity in rats
treated with disulfoton by gavage on gestation days 6-15 (Lamb and Hixson 1983). Erythrocyte and
plasma cholinesterase activities were significantly inhibited at 0.3 mg/kg/day. Numerous acute oral
studies in rats and mice have found significantly depressed brain or other tissue cholinesterase
activities (Costa and Murphy 1983a; Costa et al. 1984, I986; Schwab and Murphy 1981; Schwab et al.
1981, 1983; Su et al. 1971). Most of these studies used higher doses than those in the Lamb and
Hixson (1983) study. However, a 50% inhibition of brain cholinesterase activity was found in rats
exposed to disulfoton in the diet at 0.26 mg/kg/day for 1 week (Su et al. 1971). which supports the
LOAEL of 0.3 mg/kg/day in the Lamb and Hixson (1983) study. In an extensive acute oral
neurotoxicity study in rats, a NOAEL of 0.24 mg/kg for erythrocyte cholinesterase activity was found
(Sheets 1993a); however this NOAEL value is essentially the same as the LOAIil. values of

0.26 mg/kg/day in the Su et al. (1971) study and 0.3 mg/kg/day in the Lamb and llixson (1983) study.
Other effects of disulfoton in acute oral studies include depression of body weight gain (Schwab and

Murphy 1981; Schwab et a1. 1981, 1083), interference Wllll eatecltolamine levels in body tissues

DISULFOTON 94

2. HEALTH EFFECTS

(Brzezinski 1969; Brzezinski and Ludwicki 1973; Brzezinski and Rusiecki 1970; Wysocka-
Paruszewska 1970, 1971, 1972), and lipid peroxidation in the liver (Fawade and Pawar 1978, 1980,
1983). None of these effects occurred at doses lower than the acute oral NOAEL of 0.1 mg/kg/day for
neurological effects. Furthermore, the NOAEL is an order of magnitude lower than the dose

(1 mg/kg/day) associated with delayed ossification in fetal rats (Lamb and Hixson 1983).

- An MRL of 9x10'5 mg/kg/day has been derived for intermediate-duration oral exposure
(15—364 days) to disulfoton.

The MRL was based on a NOAEL of 0.009 mg/kg/day for decreased brain cholinesterase activity in
Fla pups in a multigeneration feeding study in rats by Hixson and Hathaway (1986). At the LOAEL
of 0.03 mg/kg/day, the brain cholinesterase activity was inhibited 24—32% in the Fla pups and litter
counts and litter weights were decreased in F2b litters. At 0.09 mg/kg/day, effects included tremors in
the F0 females during the production of the F1 generation, decreased reproductive performance,
decreased maternal F0 and F1 weight during gestation and lactation, decreased litter counts and
viability and lactation indices, and increased dead births and percentage dead births. Numerous
interrnediate—duration oral studies in rats, mice, and dogs have found significantly depressed brain or
other tissue cholinesterase activities (Clark and Pearson 1973; Doull and Vaughn 1958; Hayes 1985;
Hoffman et al. 1975; Klotzsche 1972; Rivett et al. 1972; Robinson et al. 1978; Ryan et a1. 1970;
Schwab and Murphy 1981; Sheets 1993b; Stavinoha et al. 1969; Vaughn et a1. 1958). All of these
studies reported cholinesterase inhibition at higher doses than those in the Hixson and Hathaway
(1986) study. In addition, other intermediate-duration oral developmental and reproductive studies in
animals reported depression of brain or erythrocyte cholinesterase activity in the offspring of rats and
reduced litter sizes or failure to produce litters at doses 20.] mg/kg/day (Ryan et al. 1970; Taylor
1965a). In addition, cloudy swelling or fatty livers, mild nephropathy, and juvenile hypoplasia of the

testes occurred in F3 litters (Taylor 1965a).

- An MRL of 6x10'5 mg/kg/day has been derived for chronic-duration oral exposure (2365 days)

to disulfoton.

The MRL is based on a LOAEL of 0.06 mg/kg/day for acetylcholinesterase inhibition in rats exposed
to disulfoton in the diet for 2 years in a study by Hayes (1985) using an uncertainty factor of

1,000 (10 for use of a LOAEL, 10 for extrapolation from animals to human, and 10 for human

DISULFOTON 95

2. HEALTH EFFECTS

variability). The chronic-duration oral studies have found inhibition of brain, erythrocyte, and plasma
cholinesterase in rats given 20.06 mg/kg/day, but not £0.05 mg/kg/day, disulfoton in the diet for
1.5—2 years (Carpy et al. 1975; Hayes 1985) and in mice given 2.13 mg/kg/day (males) and

2.53 mg/kg/day (females), but not $0.5 mg/kg/day, disulfoton for 23 months (Hayes 1983). Dogs
treated with 0.5 mg/kg/day disulfoton in capsules (Uga et al. 1977) and rats given 20.18 mg/kg/day in
the diet (Hayes 1985) for 2 years had optic nerve degeneration. Systemic effects of disulfoton in
chronic oral studies were ocular effects (degeneration of ciliary muscles cells, myopia, and
astigmatism) in dogs at 0.63 mg/kg/day (Ishikawa and Miyata 1980) and cystic degeneration of the
Harderian gland at 0.21 mg/kg/day and corneal neovascularization at 075 mg/kg/day in rats (Hayes
1985). In addition, rats given disulfoton in the diet for 2 years had granulomatous and suppurative
inflammation of the lungs, pancreatic atrophy, dermal lesions, decreased body weight gain, and plasma
cell hyperplasia in the mandibular lymph nodes at 20.75 mg/kg/day, and mucosal hyperplasia and
chronic inflammation of the forestomach and splenic lymphoid follicle depletion at 1.02 mg/kg/day.
In a 2—year feeding study in dogs, erythrocyte and plasma cholinesterase activities were significantly
inhibited at a time—weighted-average dose of 0.14 mg/kg/day, but not at 0.03 mg/kg/day (Hoffman et
al. 1975). Although NOAEL values of 0.03 mg/kg/day in dogs (Hoffman et al. 1975) and of

0.05 mg/kg/day in rats (Carpy et al. 1975; Hayes 1985) were found, the NOAEL values would result
in MRLs higher than the intemiediate—duration oral MRL. Thus, the chronic—duration oral MRL of
6x105 mg/kg/day was based on the LOAEL value of 0.06 mg/kg/day in female rats in the study by
Hayes (1985), using an uncertainty factor of 1,000.

The chronic-duration oral MRL for disulfoton is 6x105 mg/kg/day, and the EPA chronic oral RfD is
4x10‘S mg/kg/day (IRIS 1994). Both of these values are based on the same study (Hayes 1985) and
the identical end point. Even though the MRL and the RfD are essentially the same, they have minor
differences due to the manner in which the exposure doses were calculated. The LOAEL of

0.04 mg/kg/day used by EPA was calculated by multiplying the analytical dietary concentration of
0.8 ppm (nominal concentration of 1 ppm) by the reference rat food consumption factor of 0.05.
However, Hayes (1985) provided an equivalent dose of 0.08 mg/kg/day for the nominal concentration
of 1 ppm, based on actual food consumption and body weight data. The LOAEL of 0.06 mg/kg/day
used in deriving the chronic oral MRL was obtained by multiplying the 0.08 mg/kg/day dose,

corresponding to the nominal concentration of 1 ppm, by the analytical concentration of 0.8 ppm.

DISULFOTON 96

2. HEALTH EFFECTS

Death. No studies were located regarding death in humans after inhalation or dermal exposure to
disulfoton. One case report of human death after acute oral exposure to disulfoton was found (Hattori
et al. 1982). Because an unknown amount was ingested, the lethal dose was not determined. Autopsy
results suggested that death may have been due to asphyxia resulting from respiratory failure.
Pulmonary edema is associated with disulfoton—induced overstimulation of secretory glands and

bronchial secretions in the respiratory tract.

- High mortality was found at 202.2 mg/m3 in male Sprague—Dawley rats (Doull 1957), at 180.1 mg/m3
in male Holtzman rats and 87.6 mg/m3 in female Holtzman rats (DuBois 1971), and at 53.4 mg/m3 in
female mice (Doull 1957) after l-hour exposures; and in female Wistar rats, but not males, at
intermittent exposures 23.1 mg/m3 for 3—15 exposures (Thyssen 1980). LC50 values reported for
Wistar rats were 290 mg/m3 in males and 63 mg/m3 for females exposed for 1 hour, and 60 mg/m3 for
males and 15 mg/m3 for females exposed for 4 hours (Thyssen 1978). Thus, strain-, sex—, and species-
related differences in the inhalation lethality of disulfoton exist. Acute oral LD50 values for rats and
mice also suggest that female rats and mice are more sensitive to disulfoton (1.9—8.2 mg/kg) than male
rats and mice (5.8—19.3 mg/kg) (Bombinski and DuBois 1958; Crawford and Anderson 1974; Gaines
1969; Mihail 1978', Pawar and Fawade 1978; Stevens et al. 1972a) and that rats are generally more
sensitive than mice to disulfoton. However, female guinea pigs appear to be less sensitive than male
guinea pigs (LD50 of 12.7 mg/kg for females and 8.9 mg/kg for males) (Crawford and Anderson 1973).
Acute dermal LD50 studies (Gaines 1969; Mihail 1978), and acute intraperitoneal LD50 studies
(Bombinski and DuBois 1958) also indicate that female rats are more sensitive than male rats and that
young animals are more sensitive than adult animals. The acute dermal LDSO in rats ranges from

3.6 to 187 mg/kg, depending on the formulation (Weil et a]. 1971). Acute dermal exposure resulted in
deaths in rabbits at doses of 65—10 mg/kg/day (Flucke 1986). In most of these studies, the cause of
death was not reported, but may have been due to the cholinergic effects and hypoxia resulting from

bronchoconstriction, excessive respiratory secretions, and erratic, slowed heart rate.

Although the dose levels of disulfoton that would cause death in humans are not known, disulfoton
levels in the workplace, in the ambient environment, in drinking water, or at hazardous waste sites are

probably not high enough to cause death.

DISULFOTON 97

2. HEALTH EFFECTS

Systemic Effects.

Respiratory Effects. Information on respiratory effects due to exposure to disulfoton is very limited.
Exposure to disulfoton causes overstimulation of the muscarinic cholinergic receptors in the respiratory
tract (Murphy 1986). This usually results in excessive bronchial secretions, bronchoconstriction, and
eventually respiratory failure. Pulmonary edema and hemoptysis were recognized as probable causes
of death in a man who ingested an unknown amount of disulfoton (Hattori et al. 1982). Studies
regarding inhalation exposure were concerned primarily with lethality or cholinesterase inhibition.
However, in intermediate-duration inhalation studies in rats, inflammation of the nasal turbinates at

1.4 mg/m3 (Shiotsuka 1989) and inflammatory changes throughout the respiratory tracts, possibly
related to bone marrow changes, at 0.5 mg/m3 (Thyssen 1980) were observed. Breathing difficulties
were observed in rats given a single gavage dose of 1.0 mg/kg, mice given a single gavage dose of
5.0 mg/kg, and rats given single dermal applications of disulfoton (Mihail 1978). In a chronic dietary
study in rats, granulotamous and suppurative inflammation of the lungs occurred at the highest dietary
concentration, but may have been due to aspiration of food particles, since the high dose rats showed
considerable debilitation (Hayes 1885). However, no histopathological lesions were found in the lungs
of rats (Klotzsche 1972) or mice (Rivett et al. 1972) exposed to disulfoton in the diet for intermediate
durations, or in mice (Hayes 1983) or dogs (Hoffman et al. 1975) exposed in the diet for up to

2 years. The likelihood that respiratory effects would occur in humans exposed to disulfoton in the

ambient environment or at hazardous waste sites is negligible.

Cardiovascular Effects. Exposure to disulfoton may cause acetylcholine-mediated overstimulation of
muscarinic receptors in the heart, which can result in bradycardia progressing to fatal heart block
(Murphy 1986). However, no studies were located regarding cardiovascular effects in humans after
inhalation, oral, or dermal exposure to disulfoton. No histopathological lesions were found in the
hearts of rats exposed by the inhalation route for intermediate durations (Shiotsuka 1989; Thyssen
1980), in rats (Klotzsche 1972) or mice (Rivett et al. 1972) exposed in the diet for intermediate
durations, in rats (Carpy et al. 1975; Hayes 1985), mice (Hayes 1983), or dogs (Hoffman et al. 1975)
exposed in the diet for chronic durations, or in rabbits exposed dermally for intermediate duration
(Flucke 1986). However, acute dermal exposure to unspecified doses of organophosphorus
insecticides, including disulfoton, reportedly caused protein degeneration and significant circulatory
disruptions in heart muscles of rats, cats, and rabbits (Kundiev and Rappoport 1967). As discussed in

Section 2.2.3, this study is limited by reporting deficiencies. No changes in blood pressure or heart

DISULFOTON 98

2. HEALTH EFFECTS

rate were found in rats injected intraperitoneally with disulfoton for S30 days (McPhillips and Dar
1967; Perrine and McPhillips 1970). This information is too limited, however, to allow any analysis

of the likelihood of cardiovascular effects occurring in humans exposed to disulfoton in any scenario.

Gastrointestinal Effects. No studies were located regarding gastrointestinal effects in humans after
exposure to disulfoton. Necropsy of rats that died after intermittent inhalation exposure to 3.7 mg/m3
for 3 weeks revealed bloated gastrointestinal tracts and ulcer-like foci in the glandular mucosa of the
forestomach (Thyssen 1980). Mucosal hyperplasia and chronic inflammation of the forestomach was
found in rats given 1.04 mg/kg/day disulfoton in the diet for 2 years (Hayes 1985). However, no
histopathological lesions were found in the gastrointestinal tracts of rats exposed intermittently by
inhalation to 3.1 mg/m3 for 3 weeks (Thyssen 1980) or 1.4 mg/m3 for 13 weeks (Shiotsuka 1989), in
rats exposed to 0.55 mg/kg/day (Klotzsche 1972) or mice exposed to 0.71 mg/kg/day (Rivett et al.
1972) in the diet for 90 days, in rats exposed to $0.75 mg/kg/day (Carpy et al. 1975; Hayes 1985),
mice exposed to 2.53 mg/kg/day (Hayes 1983), or dogs exposed to 0.14 mg/kg/day (Hoffman et al.
1975) in the diet for 2 years, or in rabbits treated dermally with 1.6 mg/kg/day for 3 weeks (Flucke
1986). The likelihood that gastrointestinal effects would occur in humans exposed to disulfoton in the

ambient environment or at hazardous waste sites is negligible.

Hematological Effects. No studies were located regarding hematological effects in humans after
exposure to disulfoton. Rats exposed intermittently for 3 weeks to 3.1 mg/m", but not 3.7 mg/m’, had
decreased percentages of lymphocytes and increased percentages of polymorphonuclear leukocytes,
which represented an early response to the bone marrow changes (see Immunological and
Lymphoreticular Effects below) (Thyssen 1980). No hematological effects were found in rats exposed
by inhalation to lower concentrations for 13 weeks (Shiotsuka 1989); in 90-day dietary studies in rats
(Klotzsche 1972) and mice (Rivett et al. 1972); in the 2-year dietary studies in rats (Carpy et a1. 1975;
Hayes 1985), mice (Hayes (1983), or dogs (Hoffman et al. 1975); or in the 3-week dermal study in
rabbits (Flucke 1986). The results of the animal studies indicate that the potential for hematological

effects is not a concern for humans exposed to disulfoton.

Musculoskeletal Effects. No studies were located regarding musculoskeletal effects in humans after
exposure to disulfoton. Disulfoton injected intraperitoneally in rats for 10 days had no effect on the
contractile mechanism of smooth muscle of the ileum (McPhillips 1969b). No histopathological

muscular or skeletal lesions were found in rats dosed once by gavage with disulfoton (Sheets 1993a),

DISULFOTON 99

2. HEALTH EFFECTS

rats (Klotzsche 1972) or mice (Rivett et a1. 1972) exposed to disulfoton in the diet for 90 days, or in
rats (Carpy et al. 1975), mice (Hayes 1983), or dogs (Hoffman et al. 1975) exposed in the diet for up
to 2 years. However, female rats exposed to the highest dietary concentrations of disulfoton for

2 years had skeletal muscle atrophy, which was probably related to the general debilitation of these
rats (Hayes 1985). Degenerative changes in the ciliary muscle cells of the eye were observed in dogs
exposed orally to disulfoton for 2 years (Ishikawa and Miyata 1980; Suzuki and Ishikawa 1974).
These histopathological changes in the muscle were thought to be associated with myopia, also
observed in the dogs (see Ocular Effects below). Since high incidences of myopia found in children
corresponded with an increased use of disulfoton in combination with other organophosphates to treat
food crops (Ishikawa and Miyata 1980), the possibility that degeneration of ciliary muscle cells occurs

in humans exposed to disulfoton cannot be ruled out.

Hepatic Effects. No studies were located regarding hepatic effects in humans after exposure to
disulfoton. No hepatic effects were found in rats exposed by inhalation (Shiotsuka 1989; Thyssen
1980) or dermally (Flucke 1986) to disulfoton for intermediate durations. However, acute dermal
exposure to unspecified doses of organophosphorus insecticides, including disulfoton, reportedly
caused protein degeneration and significant circulatory disruptions in the liver of rats, cats, and rabbits
(Kundiev and Rappoport 1967). As discussed in Section 2.2.3, this study is limited by reporting
deficiencies. Acute oral exposure of animals to disulfoton has resulted in alterations in hepatic
microsomal enzymes (Fawade and Pawar 1978, 1980, 1983; Stevens et al. 1972b, 1973). Although
inhibition or induction of hepatic microsomal enzymes by disulfoton in the absence of liver pathology
is not an adverse effect, animal studies have demonstrated that disulfoton-pretreated animals are more
susceptible to the toxic effects of several drugs and anesthetics (see Section 2.6). In addition, lipid
peroxidation was also observed in animals after oral exposure to disulfoton (Fawade and Pawar 1978).
Fatty infiltration of the liver was observed in F3" offspring in a three-generation oral study (Taylor
1965a). Although no histopathological changes were observed, increased liver weights were observed
in female mice exposed orally for intermediate durations (Rivett et al. 1972) and in male rats exposed
orally for chronic durations (Carpy et a1. 1975). The increased liver weight may be associated with
liver enzyme induction. However, an unexplained decrease in liver weights was observed in female
rats (Carpy et a1. 1975). Clinical chemistry and histological examination revealed no hepatic effects in
rats (Carpy et al. 1975; Hayes 1985), dogs (Hoffman et a1. 1975), or mice (Hayes 1983) exposed to
disulfoton in the diet for up to 2 years. In an intraperitoneal study, injection of rats, but not mice,

rabbits, or guinea pigs, resulted in a dose-related increase in serum B-glucuronidase activity at

DISULFOTON 100

2. HEALTH EFFECTS

22 mg/kg, but no histopathological lesions in the liver (Kikuchi et al. 1981). In another intraperitoneal
study, injection of rats with 1 mg/kg/day for 10 days resulted in cytoplasmic RNA in much smaller
clumps in the periportal and centrilobular areas of the liver than in control rats (Clark and Stavinoha
1969). The results from these animal studies indicate that hepatic effects in humans exposed to

disulfoton would be mild, if they occurred.

Renal Effects. Glomerular swelling was among the postmortem changes observed in a man who died
after he drank an unknown amount of disulfoton (Hattori et a1. 1982). However, most organs were
congested at autopsy, suggesting that the renal pathology was one of the sequelae of death.
Inconclusive evidence that disulfoton causes renal effects was found in animals. In one study, kidney
weights of male rats increased while kidney weights of female rats decreased during a 2—year feeding
study (Carpy et al. 1975). The toxicological significance of these opposite trends is not clear.
Urinalysis and histological examination of kidneys from animals exposed to disulfoton in the diet for
intermediate (Klotzsche 1972; Rivett et al. 1972) and chronic durations (Carpy et al. 1975; Hayes
1983, 1985; Hoffman et al. 1975), by inhalation for intermediate durations (Shiotsuka 1989; Thyssen
1980), or dermally for intermediate duration (Flucke 1986) revealed no renal effects. However, acute
dermal exposure to unspecified doses of organophosphorus insecticides, including disulfoton,
reportedly caused protein degeneration and significant circulatory disruptions in the kidneys of rats,
cats, and rabbits (Kundiev and Rappoport 1967). As discussed in Section 2.2.3, this study is limited
by reporting deficiencies. These animal studies suggest that the potential for renal effects is not a

concern for humans exposed to disulfoton.

Endocrine Effects. No studies were located regarding endocrine effects in humans after exposure to
disulfoton. No histopathological evidence of lesions in endocrine organs, such as adrenals, thyroids,
pituitary, and pancreas, were found in animals exposed dermally (Flucke 1986) or by inhalation
(Shiotsuka 1989; Thyssen 1980); however, female rats exposed to 3.1 and 3.7 mg/m3 in two separate
intermediate-duration inhalation experiments had significantly increased absolute and relative adrenal
weights (Thyssen 1980). Since the increase in adrenal weights was consistently observed in both
experiments, it was considered to be related to disulfoton exposure. Oral and intraperitoneal exposure
of animals to disulfoton has also resulted in increased urinary or plasma levels of adrenaline or
noradrenaline or their metabolites, accompanied by decreases in adrenaline in the adrenal glands
(Brzezinski 1969, 1972, 1973; Brzezinski and Ludwicki 1973; Brzezinski and Rusiecki 1970;

Wysocka-Paruszewska 1970, 1971), indicating interference with catecholamine levels in body tissues.

DISULFOTON 101

2. HEALTH EFFECTS

These effects may be related to elevated acetylcholine levels, which may cause a release of
catecholamines from the stores in the adrenals. Various scenarios involving human exposure to

disulfoton might result in an increase in the amount of adrenaline released from the adrenals.

Histological examination of endocrine tissues in animals exposed orally to disulfoton for intermediate
(Klotzsche 1972; Rivett et al. 1972) or chronic durations (Carpy et al. 1975; Hayes 1983, 1985;
Hoffman et a1. 1975) has generally shown no treatment-related lesions. However, male rats exposed
chronically to the high dietary concentration had pancreatic atrophy (Hayes 1985). Increased pituitary
weight in male rats and decreased pituitary weight in female rats were reported in another chronic

feeding study (Carpy et al. 1975). The toxicological significance of these findings is unknown.

Dermal Effects. No studies were located regarding dermal effects in humans after exposure to
disulfoton. Dermal lesions consisting of acanthosis, hyperkeratosis, ulceration of the skin, exudate
formation, and epithelial inclusion cysts were found in male and female rats exposed chronically to the
high dietary concentration of disulfoton (Hayes 1985). However, in intermediate-duration studies,
histological examination of skin revealed no lesions in rats exposed by inhalation (Shiotsuka 1989), in
rabbits exposed dermally (Flucke 1986), or in rats (Klotzsche 1972) or mice (Rivett et al. 1972)
exposed in the diet for 90 days. In a chronic-duration study in rats (Carpy et al. 1975), mice (Hayes
1983), or dogs (Hoffman et al. 1975) exposed in the diet for up to 2 years, histological examination of
the skin also revealed no lesions. Acute dermal exposure to unspecified doses of disulfoton appeared
to have caused microscopic changes in the blood vessels and fibrous structures in the skin of rats, cats,
and rabbits (Kundiev and Rappopon 1967). As discussed in Section 2.2.3, this study is limited by
reporting deficiencies. Therefore, exposure to disulfoton in the workplace, in the environment, in

drinking water or food, or at hazardous sites might cause dermal lesions in humans.

Ocular Effects. An epidemiological study suggests that the increased use of disulfoton in combination
with other organophosphates to treat food crops may have increased the incidence of myopia in
children (Ishikawa and Miyata 1980). To determine whether the myopia was associated with
disulfoton exposure specifically, dogs were given disulfoton orally for 2 years. Myopia, astigmatism,
and associated degenerative changes in the ciliary muscle (see Musculoskeletal Effects above) were
observed (Ishikawa and Miyata 1980; Suzuki and Ishikawa 1974). The dog studies support the
evidence for disulfoton-induced myopia in humans. Although other factors may have contributed to

the occurrence of myopia, histopathological changes in the ciliary muscle of the dogs suggest a strong

DlSULFOTON 102

2. HEALTH EFFECTS

cause and effect relationship. Cystic degeneration of the Harderian gland and corneal
neovascularization were observed in rats exposed chronically to disulfoton in the diet (Hayes 1985).
However, in other studies, histological or ophthalmological examination of the eyes revealed no
lesions in rats (Klotzsche 1972) or mice (Rivett et al. 1972) exposed in the diet for 90 days, or in rats
(Carpy et al. 1975), mice (Hayes 1983), or dogs (Hoffman et al. 1975) exposed in the diet for up to
2 years. The rats in the study by Carpy et al. (1975) received lower doses than the rats in the Hayes
(1985) study. The possibility that myopia or other ocular effects may occur in humans exposed to

disulfoton cannot be ruled out.

Body Weight Effects. Weight loss or decreased body weight gain were commonly observed in
animals exposed to disulfoton for acute and intermediate durations (Costa et al. 1984, 1986; Fitzgerald
and Costa 1992, 1993; Robinson et al. 1978; Schwab and Murphy 1981; Schwab et al. 1981, 1983;
Stavinoha et al. 1969; Thyssen 1980). This decrease in weight gain is consistent with disulfoton
neurological toxicosis since cholinergic signs (e.g., nausea, emesis, or diarrhea) will reduce food
ingestion, absorption, and assimilation. Like the other overt signs of disulfoton toxicosis (see
Neurological Effects below), the weight loss is usually transient. In a chronic feeding study, an
11—19% depression of body weight gain occurred in the rats exposed to the high concentration of
disulfoton (Hayes 1985). The decrease in body weight gain was partially due to decreased food
consumption, which was probably related to the general debilitation of the high dose rats.
Intraperitoneal studies also have reported weight loss in animals injected with disulfoton (Costa and
Murphy 1982; Costa et al. 1981; McDonald et al. 1988). Based on the results from animal studies,

weight loss in humans following moderate to severe disulfoton exposure is possible.

Immunological and Lymphoreticular Effects. No studies were located regarding
immunological effects in humans after exposure to disulfoton. However, down-regulation of
cholinergic muscarinic receptors in T-lymphocytes and significantly inhibited acetylcholinesterase
activity in T-lymphocytes were found in rats given 2 mg/kg/day disulfoton orally for 1—2 weeks
(Fitzgerald and Costa 1993). The inhibition of T—lymphocyte acetylcholinesterase activity paralleled
that in the brain. Similar results were found in rats injected intraperitoneally with 2 mg/kg/day
disulfoton for 2 weeks (Costa et al. 1990). The immunological significance of these neurological
effects (see Section 2.2.2.4) is not known. Inflammatory changes throughout the respiratory tract,
associated with bone marrow changes and low percentages of lymphocytes and high percentages of

polymorphonuclear leukocytes in the differential leukocyte counts, were observed in rats exposed to

DISULFOTON 103

2. HEALTH EFFECTS

disulfoton by inhalation for intermediate duration (Thyssen 1980). Female rats exposed by inhalation
to a high concentration in this study also had decreased spleen weights (Thyssen 1980), and rats given
the high concentration of disulfoton in the diet for 2 years had a significantly increased incidence of
plasma cell hyperplasia in the mandibular lymph nodes (males) and a significantly increased incidence
of splenic lymphoid follicle depletion (females) (Hayes 1985). The plasma cell hyperplasia in the
mandibular lymph nodes was probably a response to upper respiratory tract inflammation, which may
have been due to aspiration of ingested food particles. In other inhalation (Shiotsuka 1989), dietary
(Carpy et a1. 1975; Hayes 1983', Hoffman et a1. 1975; Klotzsche 1972; Rivett et a1. 1972), and dermal
(Flucke 1986) studies in animals exposed to disulfoton, histological examination of spleen, thymus,
lymph nodes,'and bone marrow revealed no treatment-related lesions. The relevance of the various

lymphoreticular and possible immunological effects to humans exposed to disulfoton is not clear.

Neurological Effects. The neurological effects of disulfoton depend on its metabolism to active
metabolites which, in turn, inhibit acetylcholinesterase activity at nerve synapses. Inhibition of
acetylcholinesterase activity results in excessive accumulation of acetylcholine which, in turn,
stimulates muscarinic cholinergic receptors located in various organ tissues. The response of these
effector organs to overstimulation is recognized as a neurological effect, and the severity will depend
on such factors as dose, sex, species, and age of the human or animal exposed. Despite mild
depression of erythrocyte cholinesterase activity, neurological effects were not observed in pesticide-
fertilizer mixers after inhalation exposure to 046—0633 mg/m3 disulfoton and dermal exposure to
0.23 mg/kg/day disulfoton (Wolfe et a1. 1978). One case of accidental ingestion of disulfoton resulted
in cholinergic signs including miosis, salivation, masseteric spasms, monoplegia, and depressed serum
cholinesterase activity (Yashiki et a1. 1990). Weakness, fatigue, and cyanosis were observed in a

farmer who, for several days, had worn gloves that were soaked in disulfoton (Savage et a1. 1971).

Neurological effects observed in humans have also been demonstrated in animals after acute and
intermediate oral exposure (Costa et a1. 1984', Crawford and Anderson 1974; Mihail 1978; Schwab and
Murphy 1981; Schwab et a1. 1981, 1983; Sheets 1993a, 1993b), acute and intermediate inhalation
exposure (Doull 1957; Shiotsuka 1989; Thyssen 1978, 1980), and acute dermal exposure (Flucke 1986;
Mihail 1978) to disulfoton. Inhibition of brain acetylcholinesterase and other tissue
acetylcholinesterase activities (Carpy et a1. 1975; Christensen and Wahle 1993; Clark and Pearson
1973; Doull and Vaughn 1958; Flucke 1986; Hayes 1983, 1985; Hikita et al. 1973; Hixson and
Hathaway 1986; Hoffman et a1. 1975; Klotzsche 1972; Robinson et a1. 1970, 1978; Schwab and

DISULFOTON 104

2. HEALTH EFFECTS

Murphy 1981; Schwab et a1. 1981; Sheets 1993a, 1993b; Shiotsuka 1989; Thyssen 1978, 1980) also
have been observed in animals in numerous studies regardless of the route, duration, or animal species.
Female animals appear to be more sensitive than males to the cholinergic effects of disulfoton.
Chronic oral exposure of animals to disulfoton has resulted in necrosis and atrophy of the optic nerve
and retina (Hayes 1983; Uga et al. 1977) and unexplained changes in brain weight (Carpy et a]. 1975).
A 2-month dietary study in rats and mice found that disulfoton exposure increased the permeability of

spinal cord and brain stem tissues (Clark and Stavinoha 1971).

Limited evidence indicates that disulfoton does not cause organophosphate-induced delayed
neurotoxicity in chickens. This syndrome is caused by some phosphate, phosphonate, and
phosphoramidate esters, which are not usually used as insecticides (Ecobichon 1990). Axonal
degeneration followed by myelin degeneration in nerve fibers distal to the nerve cell body are common
histopathological findings in hens with organophosphate-induced delayed neurotoxicity. However, oral
doses of 0, 0.1, 0.6, or 1.5 mg/kg disulfoton for 30 days did not cause demyelination in White
Leghorn hens (Taylor 1965b). Furthermore, White Leghorn hens given two 30 mg/kg oral doses of
disulfoton 21 days apart displayed no signs of delayed neurotoxicity (Hixson 1983). While clinical
signs of cholinergic intoxication (loss of equilibrium, decreased activity, diarrhea, and locomotor
ataxia) were observed on the first treatment day, these signs disappeared within 5 days of treatment.
Histological examination of the sciatic nerve, spinal cord, and brain revealed no treatment-related
lesions. It should be noted that the disulfoton-treated hens in the Hixson (1983) study were also
treated with 0.5 mg/kg atropine intramuscularly 10 minutes prior to disulfoton and with 12.5 mg/kg
pralidoxime chloride (2-PAM) intramuscularly 30 minutes after disulfoton. These antidotes were given
to prevent lethality, but 2-PAM also reverses cholinesterase inhibition, and atropine blocks the
muscarinic and central nervous system toxicity (see Section 2.8.3). Therefore, the administration of
these antidotes may have confounded the conclusion that disulfoton does not cause delayed

neurotoxicity.

Numerous studies indicate that animals develop a tolerance to the cholinergic effects of disulfoton after
a few days of oral exposure (Costa et a1. 1981', Fitzgerald and Costa 1992, 1993; Schwab and Murphy
1981; Schwab et al. 1981, 1983). Animals exposed to disulfoton initially developed cholinergic signs
of toxicity, but with subsequent dosing (5—10 days) these signs almost disappeared, even though
cholinesterase activity remained depressed. Inhibition of brain, erythrocyte, or other tissue

cholinesterase, and typical signs of cholinergic poisoning have also been reported in numerous studies

DISULFOTON 105

2. HEALTH EFFECTS

in which animals received intraperitoneal injections of disulfoton (Bombinski and DuBois 1958;
Brodeur and DuBois 1963, 1964; Costa and Murphy 1982, 1983a, 1986; Costa et al. 1981, 1982a,
1986, 1990; Foley and McPhillips 1973; LeFever and Green 1975; Llorens et al. 1993; McDonald et
al. 1988; McPhillips 1969a; McPhillips and Dar 1967; Perrine and McPhillips 1970; Schwab et al.
1981; Smith et al. 1968; Stavinoha et al. 1969; Westfall et al. 1974).

Animal studies suggest that disulfoton causes neurobehavioral changes; however, most of these
changes do not appear to be adverse. Unexpected faster maze running times and fewer errors were
made by rats fed disulfoton for 90 days, despite a significant depression in brain cholinesterase (Clark
and Pearson 1973). Furthermore, an unexpected increase in exploratory behavior was observed in
mice fed disulfoton (Clark et al. 1971). Disulfoton did not result in impaired memory (assessed by
shock treatment sensitivity and passive avoidance retention) in mice made tolerant by intraperitoneal
injections of disulfoton for 14 days (Costa and Murphy 1982). However, McDonald et al. (1988)
hypothesized that a decrease in muscarinic receptor densities in brain tissues of disulfoton-tolerant rats
was the reason for the observed impairment of spatial memory after intraperitoneal injection with
disulfoton for 14 days. In rats given daily intraperitoneal injections of disulfoton for 30 days, reduced
motor activity occurred at 2.0 mg/kg/day, but tolerance to this effect did not develop (Llorens et al.
1993). Disulfoton had no effect on acquisition or retention of passive avoidance, but impaired
performance in a spatial memory water maze occurred at 2.0 mg/kg/day. This deficit in cognitive

performance occurred at a time when tolerance to overt signs of cholinergic toxicity developed.

Data from the few available case reports and the numerous animal studies strongly suggest that

disulfoton exposure may cause mild to severe neurological effects in humans. Although disulfoton-
associated memory loss has not been reported in humans, there should be concern that occupational
exposure and exposure at hazardous waste sites may interfere with the performance of cognitive and

complex tasks.

Reproductive Effects. No studies were located regarding reproductive effects in humans after
exposure to disulfoton. No effect on male fertility was found in mice treated orally in a dominant
lethal study (Herbold 1980). A 3—generation study demonstrated that a disulfoton diet providing

0.5 mg/kg/day resulted in slightly reduced litter sizes in the third generation of rats (Taylor 1965a). In
a study where males or females were fed disulfoton prior to and/or during mating, the failure of two of

five females to become pregnant indicated that reproductive function in males as well as females may

DISULFOTON 106

2. HEALTH EFFECTS

have been severely affected (Ryan et al. 1970). A more extensive multigeneration feeding study in
rats found decreased reproductive performance, evidenced by a decreased percentage of females placed
for mating and decreased percentage of sperm-positive F0 and F1 parental females, decreased maternal
weight of F0 and F] dams during gestation and lactation, decreased litter counts, decreased viability
and lactation indices, increased dead births and percentage of dead births in both generations, and
decreases in F2b litter counts and litter weights (Hixson and Hathaway 1986). Histological examination
of male and female reproductive organs generally did not reveal any treatment-related lesions in rats
(Carpy et al. 1975; Hayes 1985; Klotzsche 1972; Shiotsuka 1989; Thyssen 1980), mice (Hayes 1983;
Rivett et al. 1972), dogs (Hoffman et al. 1975), or rabbits (Flucke 1986) exposed to disulfoton by any
route. The only exception was uterine cystic hyperplasia in female rats fed the high dietary
concentration of disulfoton for 2 years (Hayes 1985). Reproductive function was not assessed in these
studies. Based on the reproductive studies in animals, the possibility for reproductive effects in

humans exposed to disulfoton cannot be ruled out.

Developmental Effects. No studies were located regarding developmental effects in humans after
exposure to disulfoton. Incomplete ossification of the parietal bones and the stemebrae, but no tissue
malformations were observed in the offspring of rats fed disulfoton during gestation (Lamb and
Hixson 1983). Erythrocyte acetylcholinesterase depression, cloudy swelling and fatty infiltration of the
liver, mild nephropathy, and juvenile hypoplasia of the testes were found in F3b litters in a three-
generation feeding study (Taylor 1965a). Brain cholinesterase depression was also observed in the
fetuses of rat dams fed disulfoton (Ryan et a1. 1970) and in the F,al pups of male and female rats in a
dietary reproduction study (Hixson and Hathaway 1986). Intraperitoneal injection of pregnant mice
with disulfoton on gestation day 11 resulted in 71.4% fetal mortality and decreased litter size (Uzokwu
1974). No malformations were seen. Nevertheless, rabbit fetal survival, growth, and development was
not affected by oral exposure of the dams to disulfoton during gestation (Tesh et al. 1982). Based on
the animal data, the potential for disulfoton to cause fetotoxic and developmental effects in humans

cannot be ruled out.

Genotoxic Effects. No studies were located regarding genotoxicity of disulfoton in humans after
inhalation, oral, or dermal exposure or in animals after inhalation or dermal exposure. The results of
in vivo studies are summarized in Table 2-4. Disulfoton did not induce micronuclei in the erythrocytes
of mice treated orally at 6 or 12 mg/kg/day for 2 days (Herbold 1981) or orally or intraperitoneally at
2, 4, or 8 mg/kg disulfoton (EPA 1984a; Sandhu et al. 1985). Disulfoton was also negative in a

107

DISULFOTON

2. HEALTH EFFECTS

:39 «2230: u

 

owm— 2082...

mer 2096:

Nmmw .mep ._a am 9925
6me ._a .0 Dzucmm ”mwmmr <n_w

Nmmw .wmmw ._m .0 923$
”mmmw ._m 6 :zvcmm ”mpmm— <mm

352 EmEEoo
meooEEm oszoEozoa 26:9:
989 5 6.95928 3 5.83:.

50:58:: B 5:26;.

_m£m_ mammmom. umxc__-xmm

.98 8:02
:83 $302
62.6on 832050

.0: .65 ._o .mmcoanmzcc 8:22

$.mmuocmEE macqomSQ

 

mocmEEm

gamma

ESQ vcw

256% .3: 85on

 

2.: s 5.3.35 .0 E23856 é." WEE.

DISULFOTON 108

2. HEALTH EFFECTS

dominant lethal test in mice given a single oral dose of 5 mg/kg (Herbold 1980). Furthermore,
disulfoton did not induce sex-linked recessive lethal mutations in Drosophila melanogaster (EPA

1981a; Sandhu et al. 1985; Waters et al. 1981, 1982).

Disulfoton has been tested in numerous types of in vitro assays, mainly with negative results (see
Table 2-5). Disulfoton was negative in most assays for reverse mutation in most strains of Salmonella
typhimurium with or without metabolic activation (EPA 1980a; Inukai and Iyatomi 1976; Moriya et al.
1983; Sandhu et al. 1985; Waters et al. 1981, 1982); but positive results were obtained in LT-2 strains
(Hanna and Dyer 1975) and in one assay with strain TA1535 (Moriya et al. 1983; Shirasu et al. 1982,
1984) of S. typhimurium without activation. Results of reverse mutation assays in Escherichia coli
were equivocal; positive results without activation in WP2 strains were reported in one study (Hanna
and Dyer 1975), but negative results in WP2 uvrA with and without activation were found in another
study (EPA 1980a, 1984a; Sandhu et al. 1985; Waters et al. 1981, 1982). Disulfoton was negative in
assays of differential toxicity in S. typhimurium, E. coli, and Bacillus subtilis with or without
activation (EPA 1980a; Herbold 1983; Inukai and Iyatomi 1976; Sandhu et al. 1985; Waters et al.
1981, 1982). Negative results were obtained in assays for reverse mutation, gene conversion, mitotic
crossing over and recombinants, and for primary DNA damage in eukaryotic yeast, Saccharomyces
cerevisiae, with and without activation (Brusick 1981; EPA 1984a; Jagannath 1981; Sandhu et al.
1985; Waters et al. 1981, 1982). However, positive results without activation were obtained in assays
for chiasma frequency (genetic recombinants), mitotic index, chromosomal aberrations, and pollen
fertility in barley (Hordeum vulgaris) (Murty et al. 1983; Panda 1983; Singh et al. 1977). Some
positive and some negative results have been obtained in cultured mammalian cells. Positive or
weakly positive results were obtained for sister chromatid exchanges in Chinese hamster ovary cells
with metabolic activation in two assays (EPA 1984a; Sandhu et al. 1985; Waters et al. 1981, 1982),
but negative results were found in another study (Chen et al. 1981, 1982). Conversely, disulfoton
induced sister chromatid exchanges in Chinese hamster ovary cells without metabolic activation, but
not with metabolic activation, in another study (Putnam 1987). Disulfoton was negative for HGPRT
mutations in Chinese hamster ovary cells with and without activation (Yang 1988). Positive results
without activation were obtained for forward mutations in mouse lymphoma cells, for unscheduled
DNA synthesis in human lung fibroblasts (EPA 1984a; Sandhu et al. 1985; Waters et al. 1981, 1982),
and for growth inhibition and increased protein synthesis in human HeLa cells (Litterst et al. 1969).
However, negative results were found for chromosomal aberrations in human hematopoietic cell lines

(Huang 1973) and for alterations of DNA or RNA synthesis in human HeLa cells (Litterst et al. 1969).

109

2. HEALTH EFFECTS

9.9 .95 van «can:

Nwmw .52 ._m .0 99m; ”mvmm— (am

32 2:29». 95 5.2:

Nwmr .59. ._m 5 92m; ”acmmp .ommw <n_w

£9 .a a 22mm

82 ._m a «€02

vmm— .Nmm— ._m «0 :mflfim ”mmmr ._m E $25.2

5.8 oz

Emu 02

San oz
2% 02
San oz
Emu oz
Emu oz

Emu oz

CozfiuDE 0m5w>01

228. $5.35

5:23.: 3.92”.

CO=N~DE 090>0I

cozmSE 355$

cosmSE $83K

cozmSE $.32“.

2:27. «Es
En «282$.

Poosofiflm
Eusvmwmfiw
Surging .m

00 5F
m9;
5mm 5:

mom Eh
5:5:qu .m

8::
85
895
825
93::
Eurasia .m

8 E»
E=§§§S .m

85
8E5
595

8:9
.22;
Eatzesqa .m

m8 Eh
Eurasia .m

mcfizm NM:

EESEEQE wamcoEEm
umeEmQO 282$.th

mg? .25 was 2ch + 23 oz cozmSE megmm

 

mocQEmm co=m>=om Song; co=m>=om 55> Eon ucw AEmem «mu: 8.00am

 

=38:

 

DISULFOTON

95> E cone—3&0 no >=u_xouocow .m-N m..m<.r

110

DiSULFOTON

2. HEALTH EFFECTS

52 x0535
Nmm— .82 ._m «o 9955

mam. ._m 6 265m 5me «Em
N69. .52. ._m «m 99“;
”mm“: ._m .0 :cucmw
53 Emccmmmw
Name .59 ._m “0 99m;
”mmm— ._m «m :cvcmw ”mvmm— (mm
29 E552 new 53:.
camp <n_m
ommp Sum
89 2005:
mm? .52 ._m «w 92m;

”moor ._m «w :cbcmw ”meme 6%: (mm

mm? .95 new «6ch

Emu oz

Emu oz

Emu 02

Sat 02

Sun 02

cescawficoc 2.23
09.23 <20 meE

maCmEDF—Onvwh
82:6 .o 8:26...

35-95820
0:27: new. 56.0280 950

cozmuaE 0w‘_0>0¢

5:53.: 0292”.

E86. 55.2.5

32x2 32.5550

325 355:5

36:2 3:553

5:92.: 3.92”.

c2232: 8.93.

8 35:28 .m

we 3.6.398 .m

MD 030.398 .m

AD 3.6.323 .m

F rum
an F .0;
8.6328 .m

no
mm‘msfimu 305.5938.“
”5:3...
quwEmQO unabaxam

va. ZR F 0.2
msaaam .m

£52k E
mesa 338m

2339 83
.Eo .m

2336. Es
.3. .m

($3 No.3
.a00 .m

mcfizm Nu:
EataEEQb gocoE‘mm
”wEmEmQO Sergei

 

8:222...

5.2.8 5923

cozméom 53>

 

gamma

.an new

Ema? .mo: 88on

 

€25.83 ES. 5 5.2.35 3 £23.23 .3 39:

111

DISULFOTON

2. HEALTH EFFECTS

Nmmw .52 ._m 5 22m;

mmmr .E .m :zucmm 539 (mm

n09. EmcSm

Near .mev ..m E 9.05; .3.me (mm

Nwmw .mew ._m .0 EEO

mam. ._m .m 2.2mm

82 95>

E... ._m .m 59.6
km. .a .0 35w

mmmw mvcmn.
mmmw mvcmm

8a. ._m .m 25.2

mg? 8.5 tau .3ch

Emu oz

3

San oz

Emu oz

Emu oz

Emu oz

Emu 02

San 02

5:22.: 2958“.

c2558 2an...

mmcmcoxo BEES—.0 .065

09.9.96 2.9.8.5 .666

3553 285050 565

mmcmcoxa EEEEE .066

:2.ng .5“.me

20.5:on .mEomoEoEo
25.5. 8:8

m..co $508 92.8

van 9005 o.co>.5Eo
c. 32.88% .mEomoEoEo
.89.. 2.9.5.

$225880.
2.0ch 5533.. 9:320

cozmuzrc wmhw>0m

5..
A“=8 «60.35:. 830.2

:3. 5..
$.00 «Sofie... 820.2

9.8
>55 53:52 03:20

9.8
ago BEES. 39.20

m; 2.8
ago 5.9.8.. 36:20

m..oo
bm>o 5.95.. 30:20

m..oo
Ego 53:5,. 89.20

”2.8 cm..mEEa§
mucmm $593. .1. >223
mummm 8&9? .1. >23

£53 6599. .I. 3.5m

308
A959? E399... >otmm
.mEmE

3.96 «-5
EataEEQb 33:253.
.95.:on 25>...“on

 

8:92....

8.52.8 59...;

8.52.8 5.;

 

gamma

2.8 new

.Ew.w>w .mo: 3.8mm

 

€35.53 2.: s 5.2.35 .o 2.2.6.83 .3 m._m<..

112

DISULFOTON

2. HEALTH EFFECTS

:39 o>Emoa >283 u TV

£32 o>Ewoa n + 539. 9:30: u I axon "gm—oacoem u (zm ”$9929“ _>mon:ozamoca mcEmamlmcEmeOQE n .EQOI ”Eon o_o_u:cont>xowo n <20

 

mom: ._m 5 «was:
momr ._m am .9.sz
mwmw ..m .0 .9053
mwmw ._m .0 «90::

29 96::

mwmw ._m 5 :zvcmw €ng 43me (mm

mum. .95 new mean:

+

Emu oz
Emu oz
Emu oz
Emu oz

3% 02
Sat 02
Emu 02

San oz

$82.83 £29m
2859?. «ix
£8556 <20
5:52.: £390

mcozmtmnm .mEomoEoEo

£859; <zo 8.8285

5:52.: 029?.

w=mo 32.. caEzr
m=oo 32.. 52:3:
w=oo 33.. 52:3...
m=mo «.3: 5:51

SKI—Ear.
own FI=2nE

VIP FQm
was.

=8 2.2806sz cmEsI

w=mo mm-_>>
$8305: 95. 58::

Exam «-5
8:52:33 £26.53
HmeEmQO ozobmxoi

 

858E”.

cozmzsm 505:5

cozazsm 53>

 

gawwm

.qu ucm

383$ no: 88on

 

€85.83 .5: s 5.2.55 3 £238.85 .3 mam:

DISULFOTON 113

2. HEALTH EFFECTS

While many of the studies on genotoxicity of disulfoton were negative, the positive results indicate a

potential for mutagenic and clastogenic effects in humans exposed to disulfoton.

Cancer. No studies were located regarding cancer in humans after exposure to disulfoton.
Carcinogenic effects were not observed in rats (Carpy et al. 1975; Hayes 1985), mice (Hayes 1983), or
dogs (Hoffman et al. 1975) fed disulfoton for 1.5—2.0 years. There is no reason to believe that

disulfoton is carcinogenic.

2.5 BIOMARKERS OF EXPOSURE AND EFFECT

Biomarkers are broadly defined as indicators signaling events in biologic systems or samples. They
have been classified as markers of exposure, markers of effect, and markers of susceptibility

(NAS/NRC 1989).

A biomarker of exposure is a xenobiotic substance or its metabolite(s), or the product of an interaction
between a xenobiotic agent and some target molecule(s) or cell(s) that is measured within a
compartment of an organism (NAS/NRC 1989). The preferred biomarkers of exposure are generally
the substance itself or substance-specific metabolites in readily obtainable body fluid(s) or excreta.
However, several factors can confound the use and interpretation of biomarkers of exposure. The
body burden of a substance may be the result of exposures from more than one source. The substance
being measured may be a metabolite of another xenobiotic substance (e.g., high urinary levels of
phenol can result from exposure to several different aromatic compounds). Depending on the
properties of the substance (e.g., biologic half-life) and environmental conditions (e.g., duration and
route of exposure), the substance and all of its metabolites may have left the body by the time samples
can be taken. It may be difficult to identify individuals exposed to hazardous substances that are
commonly found in body tissues and fluids (e.g., essential mineral nutrients such as copper, zinc, and
selenium). Biomarkers of exposure to disulfoton are discussed in Section 2.5.1. Biomarkers of effect
are defined as any measurable biochemical, physiologic, or other alteration within an organism that,
depending on magnitude, can be recognized as an established or potential health impairment or disease
(NAS/NRC 1989). This definition encompasses biochemical or cellular signals of tissue dysfunction
(e.g., increased liver enzyme activity or pathologic changes in female genital epithelial cells), as well

as physiologic signs of dysfunction such as increased blood pressure or decreased lung capacity. Note

DISULFOTON 114

2. HEALTH EFFECTS

that these markers are not often substance specific. They also may not be directly adverse, but can
indicate potential health impairment (e.g., DNA adducts). Biomarkers of effects caused by disulfoton

are discussed in Section 2.5.2.

A biomarker of susceptibility is an indicator of an inherent or acquired limitation of an organism’s
ability to respond to the challenge of exposure to a specific xenobiotic substance. It can be an
intrinsic genetic or other characteristic or a preexisting disease that results in an increase in absorbed
dose, a decrease in the biologically effective dose, or a target tissue response. If biomarkers of

susceptibility exist, they are discussed in Section 2.7, Populations That Are Unusually Susceptible.

2.5.1 Biomarkers Used to Identify or Quantify Exposure to Disulfoton

Disulfoton and its metabolites have been measured in various tissues and body fluids (blood, urine,
feces, liver, kidney, and body fat) from humans or animals exposed to disulfoton (Brokopp et al. 1981;
Hattori et a1. 1982; Puhl and Fredrickson 1975; Yashiki et a1. 1990). Because disulfoton is quickly
metabolized, it is rarely detected in the blood or plasma of exposed individuals, but detection of the
insecticide in blood provides conclusive evidence of previous exposure. At ==2—3 hours after a man
accidentally ingested disulfoton, 0.093 nmol/g (4.92 ng/g) of disulfoton and 4.92 nmol/g of total
metabolites were detected in his blood (Yashiki et a1. 1990). In another study, 1.45 nmol/g of
disulfoton was detected in the blood of a man found dead at least 24 hours after he had ingested
disulfoton (Hattori et a]. 1982). In both cases, the original dose was unknown; therefore, a correlation

between disulfoton exposure and blood concentration cannot be made.

The presence of disulfoton and/or its metabolites in the liver appears to be a sensitive indicator of
disulfoton exposure, despite the limited data. Supporting evidence from animal studies indicates that
disulfoton exposure will result in detectable levels in the liver (Bull 1965; Puhl and Fredrickson 1975).

However, monitoring of liver levels would require biopsy, which is not practical.

The presence of disulfoton and/or its metabolites in urine is usually a reliable biomarker of disulfoton
exposure. Specimens of urine collected from 64 locations across the United States, comprising the
sample areas of the Second Health and Nutrition Examination Survey (NHANES 11), reported
detection (detection limit 0.02 ppm) of DEP and DETP at a frequency of 6—7% and DEDPT at a
frequency of <1% of those tested (Murphy et al. 1983). Although no human data were located on the

DISULFOTON 115

2. HEALTH EFFECTS

relationship between the concentration of urinary metabolites and the exposure dose, data from several
animal studies demonstrate that 28.6—98% of the dose was accounted for in the urine 2-10 days
postexposure (Bull 1965; Lee et al. 1985; Puhl and Fredrickson 1975). An unknown amount of
disulfoton sulfoxide and/or demeton S-sulfone was detected in the urine from a person exposed to an
unknown amount of disulfoton (Yashiki et a1. 1990). Results from a human occupational study of
pesticide forrnulators who had worked with disulfoton for 25 weeks showed that the metabolites DEP
(0.01—4.4 ppm), DETP (0.01—1.57), DEDPT (<0.01—0.05 ppm), and DEPTh (<0.01—0.55 ppm) were
detected in the urine (Brokopp et al. 1981). The mean preforrnulation urinary levels were 0.05 ppm
DEP, 0.04 ppm DETP, 0.01 ppm DEDPT, and 0.008 ppm DEPTh. Threshold levels of these
metabolites, defined as two standard deviations above the mean, were 0.13 ppm DEP, 0.12 ppm
DETP, 0.06 ppm DEDPT, and 0.06 ppm DEPTh. Although the excretion of DEP varied considerably
among the individuals, this metabolite was more commonly detected above the threshold level among
these employees. The dialkyl phosphate metabolites are not only very sensitive indicators of
disulfoton exposure, but their presence strongly suggests previous exposure to a diethyl
organophosphate ester. One animal study demonstrated that a greater percentage of the disulfoton
dose was eliminated as DEP (Bull 1965). This provides limited but supporting evidence that DEP is a

more sensitive urinary biomarker than the other metabolites discussed.

A combination of neurological signs is usually a biomarker of organophosphate exposure.
Neurological signs such as pupil miosis, muscular tremors, and increased salivation have been
observed in humans accidentally exposed to disulfoton (Yashiki et al. 1990) and in animals given

disulfoton (Schwab et al. 1981).

Inhibition of erythrocyte acetylcholinesterase activity or serum cholinesterase activity with or without
concomitant neurological signs is usually a good indicator of organophosphate exposure. In addition,
T-lymphocyte acetylcholinesterase activity was found to be rapidly and greatly depressed in rats during
a 14-day daily exposure to disulfoton, but rapidly recovered after exposure (Fitzgerald and Costa
1993). Therefore, T-lymphocyte acetylcholinesterase activity could be used as a biomarker of
exposure to organophosphorus pesticides during exposure, but not once exposure has ceased. The
acetylcholinesterase activity recovered more slowly in erythrocytes than in lymphocytes, indicating the
erythrocyte activity is a better biomarker of exposure once exposure has ceased. However, the severity
of the signs and symptoms and the degree of cholinesterase depression are not always correlated.

Standards for serum cholinesterase activity (175—440 IU) have been established for humans (Yashiki et

DISULFOTON 116

2. HEALTH EFFECTS

a1. 1990), but there is a wide normal range due to the variation in the human population. A man had
depressed blood cholinesterase activity (<10 IU for 5 days and <40 IU for 8 days after exposure) as
well as cholinergic signs of toxicity following accidental ingestion of disulfoton (Yashiki et al. 1990).
As demonstrated in this case, cholinesterase activity can remain depressed for at least a week after
neurological signs have disappeared; therefore, other parameters (e.g., urine metabolites) may help with
the diagnosis. Cholinesterase depression was not observed in 11 employees exposed to disulfoton for
S25 weeks (Brokopp et al. 1981). The presence of urinary metabolites of disulfoton was the only
biomarker of disulfoton exposure. Employees occupationally exposed to disulfoton for 9 weeks had
marked depression of the erythrocyte acetylcholinesterase activity, but no neurological signs (Wolfe et
al. 1978). Urinary metabolites were not reported; therefore, cholinesterase depression was the only
biomarker of exposure. Because organophosphates other than disulfoton and carbamates can depress
cholinesterase activity (Osweiler et al. 1985), cholinesterase activity is not specific for disulfoton
exposure. Furthermore, liver dysfunction, pregnancy, malnutrition, neoplasia, infection, and certain
drugs such as codeine and morphine may lower plasma pseudocholinesterase activity, while
hemoglobinopathies such as sickle cell disease and thalassemia and other anemias may lower

erythrocyte cholinesterase activity (Goldfrank et al. 1990).

Urine catecholamines may also serve as biomarkers of disulfoton exposure. No human data are
available to support this, but limited animal data provide some evidence of this. Disulfoton exposure
caused a 173% and 313% increase in urinary noradrenaline and adrenaline levels in female rats,
respectively, within 72 hours of exposure (Brzezinski 1969). The major metabolite of catecholamine
metabolism, HMMA, was also detected in the urine from rats given acute doses of disulfoton
(Wysocka-Paruszewska 1971). Because organophosphates other than disulfoton can cause an
accumulation of acetylcholine at nerve synapses, these chemical compounds may also cause a release
of catecholamines from the adrenals and the nervous system. In addition, increased blood and urine
catecholamines can be associated with overstimulation of the adrenal medulla and/or the sympathetic
neurons by excitement/stress or sympathomimetic drugs, and other chemical compounds such as
reserpine, carbon tetrachloride, carbon disulfide, DDT, and monoamine oxidase inhibitors (MAO)
inhibitors (Brzezinski 1969). For these reasons, a change in catecholamine levels is not a specific

indicator of disulfoton exposure.

Disulfoton induced the liver MFO system in animals (Stevens et al. 1973). In the same study,

exposure to disulfoton orally for 3 days also increased ethylmorphine N-demethylase and NADPH

DISULFOTON 117

2. HEALTH EFFECTS

oxidase activities, but had no effect on NADPH cytochrome c reductase. Thus, the induction of the
MFO system required repeated dosing with relatively high doses. Furthermore, these changes are not
specific for disulfoton exposure, and these subtle liver effects require invasive techniques in humans to

obtain liver tissue for performance of these enzyme assays.

2.5.2 Biomarkers Used to Characterize Effects Caused by Disulfoton

Disulfoton exposure results in cholinergic signs such as salivation, diarrhea, pupil constriction, muscle
tremors, and weight loss. Ataxia, convulsions, coma, respiratory distress, and death are common signs

associated with a more severe toxicosis. Nervous tissue is evidently the most sensitive target organ.

Because cholinesterase inhibition is a very sensitive biomarker for other chemicals, it is not always
conclusive evidence of disulfoton exposure. However, depression of cholinesterase activity can alert a
physician to the possibility of more serious neurological effects. Erythrocyte acetylcholinesterase
activity more accurately reflects the degree of synaptic cholinesterase inhibition in nervous tissue,
while serum cholinesterase activity may be associated with other sites (Goldfrank et a1. 1990). In
addition, a recent study showed that after rats received oral doses of disulfoton for 14 days,
acetylcholinesterase levels in circulating lymphocytes correlated better with brain acetylcholinesterase
activity than did erythrocyte cell cholinesterase activities during exposure (Fitzgerald and Costa 1993).
However, recovery of the activity in lymphocytes was faster than the recovery of activity in the brain,
which correlated better with the activity in erythrocytes. Animal studies have also demonstrated that
brain acetylcholinesterase depression is a sensitive indicator of neurological effects (Carpy et a1. 1975;
Costa et a1. 1984; Schwab and Murphy 1981; Schwab et al. 1981, 1983); however, the measurement of

brain acetylcholinesterase in humans is too invasive to be practical.

Serum B-glucuronidase activity was increased in a dose-related manner when disulfoton was given
intraperitoneally to rats (Kikuchi et a1. 1981). In the same study, this effect was not observed in mice,
rabbits, or guinea pigs. This enzyme appears to be a useful biomarker of hepatic function in rats

exposed to disulfoton, but may not be a useful biomarker in humans.

Increased levels of urinary catecholamines may also be associated with accumulation of acetylcholine
that resulted from acetylcholinesterase inhibition by disulfoton. No human data were located to

support this, but limited animal data provide some evidence. Disulfoton exposure caused a 173% and

DISULFOTON 118

2. HEALTH EFFECTS

313% increase in urinary noradrenaline and adrenaline levels in rats, respectively, within 72 hours
(Brzezinski 1969). The major metabolite of catecholamine metabolism, HMMA, was also detected in

the urine from rats given acute doses of disulfoton (Wysocka-Paruszewska 1971).

Additional information regarding biomarkers for effects can be found in OTA (1990) and
CDC/ATSDR (1990). A more detailed discussion of the health effects caused by disulfoton can be
found in Section 2.2 of Chapter 2.

2.6 INTERACTIONS WITH OTHER SUBSTANCES

Disulfoton can function as an inhibitor of MFO when given in one or two doses and can potentiate the
toxicity of similarly related compounds. Disulfoton exhibits Type I binding, that is, binding to the
oxidized form of cytochrome P-450, and when given as a single dose, competitively inhibits the
metabolism of other Type I substrates (Stevens et al. 1973). However, it was also reported that
disulfoton was a noncompetitive inhibitor of rat and mouse ethylmorphine N—demethylase (Stevens and
Green 1974; Stevens et al. 1972a). When given as a single dose, disulfoton also appears to inhibit
NADPH cytochrome c reductase (Stevens et al. 1973). Disulfoton was reported to inhibit hexobarbital
metabolism, thereby prolonging hexobarbital sleeping time in mice (Stevens et al. 1972a). This effect
was not due to inhibition of cholinesterase nor was it due to an altered sensitivity of the brain to
barbiturates, but it was associated with inhibition of hepatic MFO metabolism. These investigators
also determined that disulfoton depressed microsomal metabolism of aniline as well as ethylmorphine
in the mouse. A significant decrease in N—demethylase activity of aminopyrine and hydroxylase
activity of acetanilide was observed in animals pretreated orally with disulfoton for 2 successive days,
compared to the control group (Fawade and Pawar 1978). Disulfoton also caused decreased levels of
cytochrome P450 and cytochrome b5 and an increase in NADPH-linked and ascorbate-promoted lipid

peroxidation.

In contrast to the inhibitory effects of acute exposure, repeated dosing with disulfoton induces the
cytochrome P-450 MFO system (Stevens et al. 1973). Disulfoton (V2 LDSO) given orally to mice for

3 days resulted in increased activities of ethylmorphine N-demethylase and NADPH oxidase activities,
but not the activity of NADPH cytochrome c reductase, the rate of reduction of cytochrome P-450, or
the content of cytochrome P-450. The 5-day treatment regimen resulted in increased activities of

ethylmorphine N—demethylase and NADPH oxidase activities, as well as increased cytochrome P-450

DISULFOTON 119

2. HEALTH EFFECTS

content. Apparently, the duration of exposure determines the effect of disulfoton on the various
components of the MFO system. In another study, treatment of mice orally with disulfoton (1/2 LDSO)
for 5 days followed by administration of hexobarbital resulted in an increase in hexobarbital
hydroxylase activity (Stevens et al. 1972b). Therefore, disulfoton-treated mice had shorter
hexobarbital sleeping times. Microsomes from disulfoton—treated mice also had increased activity of
aniline hydroxylase when aniline was added to the incubation mixture. Lower doses of disulfoton for
similar time periods of exposure did not result in significant hepatic enzyme induction. The results
from these studies suggest that depending on the duration of exposure, disulfoton may increase or

decrease the severity of toxicity associated with chemicals that are similarly metabolized.

The toxicity of disulfoton may be altered by pretreatment with inducers or inhibitors of the hepatic
microsomal drug metabolizing system. Phenobarbital causes enzyme repression of flavin-containing
monooxygenase, but it also causes induction of cytochrome P—450 activity (Sipes and Gandolfi 1986).
Therefore, pretreatment with phenobarbital will not result in flavin monooxygenase—mediated activation
of disulfoton to its active metabolite. Cytochrome P-450 can activate disulfoton to its toxic
metabolites as well as detoxify disulfoton by oxidative dearylation and dealkylation to less toxic
metabolites (Ecobichon 1990). However, pretreatment with phenobarbital induced cytochrome P-450
enzymes that functioned more as detoxification enzymes than as activation enzymes (DuBois and
Kinoshita 1968; Pawar and Fawade 1978). Although phenobarbital affects both enzyme systems
differently, the net result is protection from the toxicity of disulfoton. One hundred percent protection
against the toxicity of disulfoton was achieved both in mice and rats pretreated with phenobarbital and
then given disulfoton orally at the LD85 dose level (Pawar and Fawade 1978). Pretreatment with
another enzyme inducer, 3-methylcholanthrene, resulted in only 73% protection against disulfoton
toxicity in both rats and mice. The authors proposed that the different levels of protection were due to
the induction of two different interconvertible forms of cytochrome P-450. Rats pretreated with
phenobarbital were less susceptible to the toxicity of disulfoton (DuBois and Kinoshita 1968). In this
study, the LD50 value for the pretreated group (16.3 mg/kg) was greater than that for the control group
(6.7 mg/kg), suggesting that phenobarbital pretreatment reduced the toxic effects of disulfoton by way
of hepatic microsomal enzyme induction. A 3-day phenobarbital pretreatment also resulted in
increased microsomal protein content and increased aminopyrine N-demethylase activity, but decreased

acetanilide hydroxylase activity, in mice given disulfoton for 3 more days (Fawade and Pawar 1980).

DISULFOTON 120

2. HEALTH EFFECTS

Pretreatment with the Type I substrate, ethylmorphine, resulted in 100% mortality in both rats and
mice, and aminopyrine pretreatment resulted in 100% and 64% mortality in rats and mice,
respectively, exposed to disulfoton (Pawar and Fawade 1978). Nickel chloride, cobalt chloride, or
cycloheximide decreased the levels of cytochrome b5, cytochrome 0 reductase, and total heme in rats
(Fawade and Pawar 1983). These electron transport components were further decreased in rats
pretreated with these inhibitors and given a single dose of disulfoton. Data from this study suggests
an additive effect, since disulfoton also decreases the activities of these components. Evidence of an
additive effect between disulfoton and these metabolic inhibitors was suggested by the decrease in
ethylmorphine N—demethylase and acetanilide hydroxylase activities when rats were given an inhibitor
followed by disulfoton. In another experiment, these inhibitors decreased the activity of

delta-aminolevulinic acid synthetase, but this decrease was reversed when disulfoton was administered.

Although some steroids have been reported to reduce the toxic effects of some insecticides, the steroid
ethylestrenol decreased the rate of recovery of depressed cholinesterase activity in disulfoton-pretreated
rats (Robinson et a1. 1978). The exact mechanism of this interaction was not determined.
Ethylestrenol alone caused a small decrease in cholinesterase activity, and, therefore, resulted in an
additive effect. Rats excreted less adrenaline and more noradrenaline when given simultaneous
treatments of atropine and disulfoton compared with rats given disulfoton alone (Brzezinski 1973).
The mechanism of action of disulfoton on catecholamine levels may depend on acetylcholine
accumulation. In the presence of atropine, the acetylcholine effect on these receptors increases the

ability of atropine to liberate catecholamines.

Cross-tolerance between disulfoton and another organophosphate, chlorpyrifos, was observed in mice
(Costa and Murphy 1983b). Because of this cross-tolerance, a benefit is derived as a result of this
interaction. In the same study, propoxur-tolerant mice were tolerant to disulfoton but not vice versa.
Propoxur (a carbamate) is metabolized by carboxylesterases, and these enzymes are inhibited in
disulfoton-tolerant animals; disulfoton-tolerant animals are more susceptible to propoxur and/or
carbamate insecticides than are nonpretreated animals. In another study, disulfoton-tolerant rats were
tolerant to the cholinergic effects of octamethyl pyrophosphoramide (OMPA) but not parathion
(McPhillips 1969a, 1969b). The authors were unable to explain why the insecticides OMPA and

parathion caused different effects.

DISULFOTON 121

2. HEALTH EFFECTS

2.7 POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE

A susceptible population will exhibit a different or enhanced response to disulfoton than will most
persons exposed to the same level of disulfoton in the environment. Reasons include genetic make-up,
developmental stage, age, health and nutritional status (including dietary habits that may increase
susceptibility, such as inconsistent diets or nutritional deficiencies), and substance exposure history
(including smoking). These parameters result in decreased function of the detoxification and excretory
processes (mainly hepatic, renal, and respiratory) or the pre-existing compromised function of target
organs (including effects or clearance rates and any resulting end product metabolites). For these
reasons we expect the elderly with declining organ function and the youngest of the population with
immature and developing organs will generally be more vulnerable to toxic substances than healthy
adults. Populations who are at greater risk due to their unusually high exposure are discussed in

Section 5.6, Populations With Potentially High Exposure.

No data were located that identify subpopulations of humans more susceptible to the toxic effects of
disulfoton. Animal studies demonstrate that there are sex, age, and liver function differences in the
susceptibility of animals to disulfoton toxicosis. Data from LC50 and LD50 studies suggest that female
rats and mice are more sensitive than male rats and mice to disulfoton after inhalation (Thyssen 1978),
oral (Bombinski and DuBois 1958; Crawford and Anderson 1974; Gaines 1969; Mihail 1978; Pawar
and Fawade 1978), dermal (Gaines 1969; Mihail 1978), or intraperitoneal (Bombinski and DuBois
1958) exposure. Erythrocyte and brain cholinesterase activity was more depressed in female rats than
in male rats (Klotzsche 1972; Ryan et a1. 1970; Thyssen 1980). While absolute and relative brain
weights generally increased in male rats exposed to disulfoton, the trend was reversed in female rats
(Carpy et a1. 1975). In the same study, liver, spleen, kidney, and pituitary weights were increased in
male rats and decreased in female rats. The toxicological significance of these observations is
unknown. Results from toxicokinetic studies showed that male rats eliminated disulfoton faster than
female rats (Lee et a1. 1985; Pub] and Fredrickson 1975). This apparent difference in the toxic
responses of the sexes may have been due to differences in absorption, retention, metabolism, or a

combination of factors.

Animal studies suggest that younger animals are more susceptible to disulfoton toxicosis than older
animals. The intraperitoneal LD50 of disulfoton was lower in weanling rats than in adult rats (Brodeur

and DuBois 1963). These investigators proposed that the relatively slow rate of metabolic

DISU LFOTON 122

2. HEALTH EFFECTS

detoxification and/or incomplete development of detoxification enzymes in weanlings accounted for
the difference in the effects. Calves were more sensitive to disulfoton than yearling cattle, as indicated
by an increase in severe clinical signs and a greater depression of cholinesterase activity in calves

(McCarty et a1. 1969).

Data suggest that animals pretreated with disulfoton or hepatic enzyme inducers were less susceptible
to disulfoton toxicosis than those subpopulations that were not pretreated. Disulfoton-tolerant animal
populations are generally less sensitive to subsequent disulfoton exposure than are nontolerant animals
(Costa et al. 1984; Schwab and Murphy 1981; Schwab et al. 1981, 1983). In addition, animals
pretreated with chemicals that induce MFO (e.g., phenobarbital) were less susceptible to disulfoton

toxicosis (DuBois and Kinoshita 1968; Pawar and Fawade 1978).

2.8 METHODS FOR REDUCING TOXIC EFFECTS

This section will describe clinical practice and experimental research concerning methods for reducing
toxic effects of exposure to disulfoton. However, because some of the treatments discussed may be
experimental and unproven, this section should not be used as a guide for treatment of exposure to
disulfoton. When specific exposures have occurred, poison control centers and medical toxicologists

should be consulted for medical advice.

2.8.1 Reducing Peak Absorption Following Exposure

If disulfoton is inhaled, the victim should be removed to a fresh air environment. Artificial respiration
and the use of oxygen has been recommended (Sittig 1991). Not much can be done to reduce
absorption of disulfoton from the respiratory tract. If disulfoton is ingested, the stomach should be
emptied by inducing emesis or by gastric lavage (Haddad and Winchester 1990). If the patient is
unconscious, means to prevent aspiration are recommended prior to gastric lavage. Because most
organophosphates contain hydrocarbon solvents, which are severe aspiration hazards, the use of
emetics may be contraindicated (Ellenhom and Barceloux 1988). Activated charcoal and a cathartic
should then be given to adsorb any of the remaining disulfoton. Repeated treatment with activated
charcoal may be useful to prevent reabsorption following enterohepatic circulation. In the event of

dermal exposure, contaminated clothing should be removed and the victim should be bathed with soap

DISULFOTON 123

2. HEALTH EFFECTS

and water in an attempt to decontaminate the skin. The eyes should be rinsed with water or

physiological saline if disulfoton entered the eye.

2.8.2 Reducing Body Burden

No information is available regarding methods for specifically reducing the body burden of disulfoton.
Diuresis, dialysis, and hemoperfusion have been used to reduce the body burden of other
organophosphates in humans and animals (Ellenhom and Barceloux 1988). Because disulfoton is
rapidly metabolized to its active metabolites which bind to ubiquitous cholinesterases in nervous tissue,
these methods may not be effective unless started immediately after exposure. However, repeated
administration of activated charcoal/cathartics may prevent possible enterohepatic recirculation of
disulfoton or its metabolites. Administration of oximes, such as 2—PAM, may also increase the
excretion of disulfoton metabolites, since oximes accelerate the hydrolysis of phosphorylated
cholinesterase (Ellenhom and Barceloux 1988; Goldfrank et al. 1990; Haddad and Winchester 1990;
Morgan 1982). However, "aging" of the phosphorylated enzyme may occur after 1—2 days (Ecobichon
1990). Because Z—PAM is unable to reverse cholinesterase inhibition once "aging" has started, 2-PAM
should be administered as soon as possible after exposure or any time following exposure when

clinical signs or symptoms are present.

2.8.3 Interfering with the Mechanism of Action for Toxic Effects

The mechanism of action of disulfoton depends on active metabolites of disulfoton binding to
acetylcholinesterase and causing an accumulation of acetylcholine at the synapse that results in
muscarinic (e.g., salivation) and nicotinic (e.g., muscle tremors) effects. Atropine sulfate has been
used as a therapeutic agent to reduce the severity of disulfoton toxicosis by binding to muscarinic
receptors, thus blocking the muscarinic and central nervous system manifestations (Goldfrank et al.
1990). Atropine also reduces excessive bronchial secretions that can result in bronchopneumonia.

This drug was also used successfully to treat a patient with severe signs of disulfoton toxicosis
(Yashiki et al. 1990). Pretreatment of rats with atropine protected them against an intraperitoneal LD50
dose (Bombinski and DuBois 1958). Oxime derivatives (e.g., 2—PAM), accelerate the hydrolysis of
phosphorylated cholinesterase and hence accelerate regeneration of the active cholinesterase (Ellenhom
and Barceloux 1988; Goldfrank et al. 1990; Haddad and Winchester 1990; Morgan 1982). The oximes

usually reduce both the muscarinic and nicotinic effects of poisoning when administered within

DISULFOTON 124

2. HEALTH EFFECTS

36 hours after organophosphate exposure (Goldfrank et al. 1990; Morgan 1982). However, "aging" of
the phosphorylated enzyme may occur after 1—2 days (Ecobichon 1990). Because 2-PAM is unable to
reverse cholinesterase inhibition once "aging" has started, 2-PAM should be administered as soon as
possible after exposure. Atropine and 2-PAM synergistically alleviate the manifestations of
cholinesterase inhibition when co-administered (Goldfrank et al. 1990). While atropine blocks the
muscarinic effects, 2-PAM regenerates cholinesterase enzymes in sympathetic, parasympathetic, and

central nervous system sites.
2.9 ADEQUACY OF THE DATABASE

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with
the Administrator of EPA and agencies and programs of the Public Health Service) to assess whether
adequate information on the health effects of disulfoton is available. Where adequate information is
not available, ATSDR, in conjunction with the National Toxicology Program (NTP), is required to
assure the initiation of a program of research designed to determine the health effects (and techniques

for developing methods to determine such health effects) of disulfoton.

The following categories of possible data needs have been identified by a joint team of scientists from
ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met would
reduce the uncertainties of human health assessment. This definition should not be interpreted to mean
that all data needs discussed in this section must be filled. In the future, the identified data needs will

be evaluated and prioritized, and a substance-specific research agenda will be proposed.
2.9.1 Existing Information on Health Effects of Disulfoton

The existing data on health effects of inhalation, oral, and dermal exposure of humans and animals to
disulfoton are summarized in Figure 2-4. The purpose of this figure is to illustrate the existing
information concerning the health effects of disulfoton. Each dot in the figure indicates that one or
more studies provide information associated with that particular effect. The dot does not imply
anything about the quality of the study or studies. Gaps in this figure should not be interpreted as
"data needs." A data need, as defined in ATSDR’s Decision Guide for Identifying Substance-Specific
Data Needs Related to Toxicological Profiles (ATSDR 1989), is substance-specific information

necessary to conduct comprehensive public health assessments. Generally, ATSDR defines a data gap

DISULFOTON 125

2. HEALTH EFFECTS

FIGURE 2-4. Existing Information on Health Effects of Disulfoton

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

'\\O
‘9‘
SYSTEMIC «SQ q}
“5‘0 o-\ \0 ($0 690‘ c,
0‘. \ 0 o ~l>
Q, 0 0 0 Q &
‘ka 6‘0 2,60 90‘ 6&0 0“} 0‘0b 4"}0 0&0 0°?“
0° v" \6‘ 6° \6‘ 0° 0° 0° 0° 0’”
Inhalation
Oral 0 0 0
Dermal
Human
6&0
‘0
SYSTEMIC «‘9 \
'3’ '4‘?” 0‘0
{k o 0\09 o$0 6°C? Q 0 450
$0 $5 $0?) ‘os 690 a» 6‘0 90 x0 062}
0° v0 6‘ 0° 00° 0°0° 0° 0°
Inhalation 0 0
Oral oooooooooo
Dermal 0 o o o . 0
Animal

0 Existing Studies

DISULFOTON 126

2. HEALTH EFFECTS

more broadly as any substance-specific information missing from the scientific literature.

As seen from Figure 2-4, data exist regarding neurological effects in humans after inhalation exposure
to disulfoton. The data for neurological effects were derived from medical evaluations of workers at a
pesticide-fertilizer mixing operation. Neurological effects consisted of >22.8% depression in
erythrocyte cholinesterase activity after 9 weeks of exposure to disulfoton. Other severe neurological
effects were not reported. Systemic and neurological effects were observed in humans after accidental
or intentional ingestion of disulfoton. Respiratory and renal effects, more associated with postmortem
changes, were reported in a man who died after ingesting disulfoton. Neurological effects consisted of
miosis, increased salivation, masseteric spasms, and monoplegia. Epidemiological studies suggest that
disulfoton causes myopia in children. Neurological effects were observed in humans after dermal
exposure to disulfoton for acute or intermediate durations. Neurological effects after acute exposure
included weakness, fatigue, and depressed cholinesterase activity. Intermediate dermal exposure

resulted only in erythrocyte cholinesterase depression.

Death and neurological effects were observed in animals after acute— and intermediate-duration
inhalation exposure to disulfoton. Intermediate—duration inhalation studies that investigated systemic
end points, effects in lymphoreticular organs, and effects in reproductive organs were conducted in
rats. Effects consisted of cholinergic signs of disulfoton toxicity, depressed erythrocyte and brain
cholinesterase activity, inflammation in respiratory organs, increased adrenal weight, hematological
effects, and bone marrow changes. Death, systemic effects of acute-, intermediate-, and chronic—
duration exposure, lymphoreticular, neurological, developmental, reproductive, genotoxic, and
carcinogenic effects were investigated in animals after oral exposure to disulfoton. Systemic effects
consisted of respiratory, gastrointestinal, hematological, musculoskeletal, hepatic, renal, endocrine,
dermal, ocular, and body weight effects. Ocular effects consisted of myopia development in dogs and
corneal neovascularization in rats after chronic exposure to disulfoton. Neurological effects consisted
of cholinergic signs of disulfoton toxicity, depressed erythrocyte and brain acetylcholinesterase activity,
and pathology of the optic nerve and retina. Reproductive effects were observed in male and female
rats, and fetotoxicity was reported in several developmental studies. Mostly negative results were
obtained for genotoxicity, and negative results were found in carcinogenicity studies. Death and
cholinergic toxicity were the only reliable effects reported in animal studies regarding acute dermal

exposure to disulfoton. Rabbits that died showed gross effects in the lungs, stomach, liver, kidney,

DISULFOTON 127

2. HEALTH EFFECTS

and spleen upon necropsy. An intermediate-duration dermal study examined all systemic end points,

effects in lymphoreticular and reproductive organs, and neurological effects.

2.9.2 Identification of Data Needs

Acute-Duration Exposure. No studies were located regarding systemic effects in humans after
inhalation or dermal exposure to disulfoton for acute durations. Acute oral ingestion by a man
resulted in death, and respiratory and renal damage were found at autopsy performed at least 24 hours
after death (Hattori et a1. 1982). No studies were located regarding systemic effects in animals after
inhalation exposure for acute durations. Information regarding systemic effects after dermal exposure
is limited to reports of breathing difficulties in rats (Mihail 1978), and degenerative changes in heart,
liver, kidney, and skin of rats, rabbits, and cats (Kundiev and Rappoport 1967). However, these
studies were not very reliable. In addition, gross effects in the lungs, stomach, liver, kidney, and
spleen were observed on necropsy of rabbits that died from cholinergic toxicity after a few dermal
doses in a 3-week study (Flucke 1986). Acute inhalation lethality data are available for rats and mice
(Doull 1957; DuBois 1971; Thyssen 1978, 1980); acute oral LD50 values are available for rats
(Bombinski and DuBois 1958; Crawford and Anderson 1974; Gaines 1969; Mihail 1978; Pawar and
Fawade 1978), mice (Mihail 1978; Pawar and Fawade 1978; Stevens et al. 1972a), and guinea pigs;
(Bombinski and DuBois 1958; Crawford and Anderson 1973); acute dermal lethality data are available
for rabbits (Flucke 1986); and dermal LD50 values are available for rats (DuBois 1957; Gaines 1969;
Mihail 1969). Acute oral studies in animals have identified the liver as a possible target organ,
evidenced by induction or inhibition of liver enzymes (Stevens et al. 1972a, 1972b, 1973) and lipid
peroxidation (Fawade and Pawar 1978). Weight loss in animals also resulted from acute oral exposure
to disulfoton (Costa et a1. 1984, 1986; Schwab and Murphy 1981; Schwab et a1. 1981, 1983). An
acute inhalation MRL of 0.006 mg/m3 was derived based on a NOAEL for acetylcholinesterase
inhibition in rats (Thyssen 1978). An acute oral MRL of 0.001 mg/kg/day was derived from animal
data for acetylcholinesterase inhibition in rat dams exposed during gestation (Lamb and Hixson 1983).
Acute-duration inhalation, oral, and dermal animal studies that perform comprehensive histological
examination and look for other sensitive effects using several exposure concentrations or doses will
provide dose-response data on possible end points other than neurological effects. Attempts to identify
other target organs in animals after acute exposure will increase the weight of evidence that

neurological effects (cholinesterase inhibition) are the most sensitive end points. This information is

DISULFOTON 128

2. HEALTH EFFECTS

important because there are populations surrounding hazardous waste sites that might be exposed to

disulfoton for brief periods of time.

lntermedlate-Duratlon Exposure. No studies were located regarding systemic effects in humans
after inhalation, oral, or dermal exposure to disulfoton for intermediate durations. Intermediate-
duration inhalation studies in rats using several exposure concentrations and that included clinical
chemistry, urinalysis, hematology, and comprehensive gross and histological examinations have been
conducted (Shiotsuka 1989; Thyssen 1980). Inflammation in respiratory tissues, increased adrenal
weight, decreased spleen weight, decreased lymphocytes, body weight gain reductions, bone marrow
changes, and neurological effects were identified. An intermediate-duration inhalation MRL of

2x10“ mg/m3 was derived based on a NOAEL for cholinergic effects and acetylcholinesterase
inhibition in rats (Thyssen 1980). Intermediate-duration oral studies that used several dietary
concentrations and conducted clinical chemistry, urinalysis, hematology, and performed comprehensive
gross and histological examination in rats (Klotzsche 1972) and mice (Rivett et al. 1972) have been
conducted. The liver was identified as a possible target organ, evidenced by a slight increase in liver
weight in female mice (Rivett et al. 1972). Body weight gain reduction, in addition to neurological
effects, also resulted from intermediate oral exposure in animals (Hixson and Hathaway 1986;
Robinson et al. 1978; Schwab and Murphy 1981; Stavinoha et al. 1969). An intermediate-duration
oral MRL of 9x10‘5 mg/kg/day was derived based on a NOAEL for acetylcholinesterase inhibition in
rat pups (Hixson and Hathaway 1986). A 3-week dermal study that used several dose levels and
conducted clinical chemistry, urinalysis, hematology, and performed comprehensive gross and
histological examination has been conducted on rabbits (Flucke 1986). No effects other than
erythrocyte cholinesterase inhibition were found at 1.6 mg/kg/day, but the next higher dose of

6.5 mg/kg/day resulted in 100% deaths. A dermal study that uses doses between these extremes might
provide dose-response information on systemic end points. Additional intermediate-duration animal
studies by the oral and inhalation routes of exposure using doses intermediate between NOAEL values
for effects other than cholinesterase inhibition and doses associated with death and severe neurotoxicity
may be helpful for identifying thresholds for systemic effects. This information is important because
there are populations surrounding hazardous waste sites that might be exposed to disulfoton for

intermediate periods of time.

Chronic-Duration Exposure and Cancer. No studies were located regarding systemic effects in

humans or animals after inhalation or dermal exposure to disulfoton for chronic durations. Results

DISULFOTON 129

2. HEALTH EFFECTS

from an epidemiological study suggest that oral exposure to disulfoton caused myopia in children
(Ishikawa and Miyata 1980). Clinical evidence of myopia in dogs (Ishikawa and Miyata 1980; Suzuki
and Ishikawa 1974) and histopathology of the ciliary muscles in the eyes of dogs (Ishikawa and
Miyata 1980) were observed after chronic oral exposure. Another 2-year oral study was conducted in
dogs, in which clinical chemistry, hematology, and gross and comprehensive histological examinations,
including ophthalmology were performed; no effects for any systemic end points, including ocular,
were found (Hoffman et al. 1975). The doses in this study were about 5 times lower than the doses
that caused myopia and effects in the ciliary muscles. In addition to the 2-year oral studies in dogs,
chronic oral studies have been conducted in rats (Carpy et al. 1975; Hayes 1985) and mice (Hayes
1983). These studies also used several dose levels and conducted clinical chemistry, hematology,
urinalysis and gross and comprehensive histology. No systemic end points were found in the mice.
One study in rats identified the liver and the kidney as possible target organs, suggested by an increase
in liver and kidney weights in male rats (Carpy et al. 1975). The other study in rats found
granulomatous and suppurative inflammation in the lungs, which may have been due to aspiration of
the food particles; mucosal hyperplasia and chronic inflammation of the forestomach, skeletal muscle
atrophy (due to debilitation); pancreatic atrophy; dermal lesions; and decreased body weight gain
(Hayes 1985). In addition, ocular effects consisting of cystic degeneration of the Harderian gland and
corneal neovascularization were observed. The chronic oral dietary studies in rats (Carpy et al. 1975;
Hayes 1985), mice (Hayes 1983), and dogs (Hoffman et al. 1975) established LOAEL and NOAEL
values for acetylcholinesterase inhibition. A chronic inhalation MRL was not derived because no
studies were located. A chronic oral MRL of 6x10'5 mg/kg/day was derived based on a LOAEL for
erythrocyte and brain cholinesterase inhibition in female rats in the study by Hayes (1985). Well-
designed chronic-duration inhalation and dermal studies in rats and mice, in which several dose levels
are used and comprehensive end points are examined, might identify systemic target organs for these
routes and establish dose-response relationships. Although cholinesterase inhibition is the most
sensitive end point, additional chronic dietary studies in mice and dogs could be conducted that use
doses to establish LOAEL and NOAEL values for end points other than cholinesterase inhibition, that
is for systemic target organs. This information is important because there are populations surrounding

hazardous waste sites that might be exposed to disulfoton for long periods of time.

No studies were located regarding cancer in humans after inhalation, oral, or dermal exposure to
disulfoton or in animals after inhalation or dermal exposure. A 13-week inhalation study in rats

reported that comprehensive histological examination of organs and tissues revealed no treatment-

DISULFOTON 130

2. HEALTH EFFECTS

related neoplastic lesions (Shiotsuka 1989); however, a chronic-duration inhalation study would be
more appropriate to assess possible carcinogenicity. Carcinogenicity was not observed in rats (Carpy
et al. 1975; Hayes 1985), mice (Hayes 1983), or dogs (Hoffman et al. 1975) that had been fed a diet
of disulfoton for 1.5—2.0 years. Although there is little reason to suspect that disulfoton is
carcinogenic, chronic inhalation, oral, or dermal studies should include comprehensive histology to

confirm that disulfoton is not carcinogenic.

Genotoxlcity. Disulfoton has been tested in numerous types of assays for genotoxicity. Disulfoton
was positive for unscheduled DNA synthesis in human lung fibroblasts (EPA 1984a; Sandhu et al.
1985) and for growth inhibition in human HeLa cells (Litterst et al. 1969). Disulfoton was negative in
assays for chromosomal aberrations in human hematopoietic cell lines (Huang 1973) and for alterations
in DNA or RNA synthesis in human HeLa cells (Litterst et al. 1969). Disulfoton did not induce
micronuclei in mice exposed orally or intraperitoneally (EPA 1984a; Herbold 1981; Sandhu et al.
1985), dominant lethality in mice exposed orally (Herbold 1980), or sex-linked recessive lethal
mutation in D. melanogaster (EPA 1981a; Waters et al. 1981). Mostly negative results were obtained
in in vitro tests in bacteria and yeast (Brusick 1981; EPA 1980a, 1984a; Herbold 1983; Jagannath
1981; Moriya et al. 1983; Sandhu et al. 1985; Waters et al. 1981, 1982), but a few positive results
were obtained in some strains of S. typhimurium and E. coli (Hanna and Dyer 1975; Moriya et al.
1983; Shirasu et al. 1982, 1984). Disulfoton also produced positive results in several assays in barley
(Murty et al. 1983; Panda 1983; Singh et al. 1977). Some positive and some negative results have
been obtained in cultured mammalian cells. Positive results were found for sister chromatid exchange
in Chinese hamster ovary cells in some studies (EPA 1984a; Putnam 1987; Sandhu et al. 1985; Waters
et al. 1981, 1982), but negative results were obtained in another study (Chen et al. 1981, 1982).
Negative results were also obtained for HGPRT mutations in Chinese hamster ovary cells (Yang
1988). Disulfoton was positive for forward mutation in mouse lymphoma cells (EPA 1984a; Sandhu
et al. 1985; Waters et al. 1981, 1982). Although most assays were negative, the few positive results
suggest a genotoxic potential. However, it is doubtful that additional testing would add meaningful

data.

Reproductive Toxicity. No studies were located regarding reproductive effects in humans after
inhalation, oral, or dermal exposure to disulfoton. Disulfoton did not affect male fertility in mice in an
oral dominant lethal study (Herbold 1980). Slightly reduced litter sizes in third generations were the

findings of a three-generation oral reproductive study in rats (Taylor 1965a). When males and females

DISULFOTON 131

2. HEALTH EFFECTS

were exposed to disulfoton for 60 days prior to and/or during mating, 2 of 5 females failed to become
pregnant (Ryan et al. 1970). Although complete gross anatomical and histopathological examinations
were lacking, the data do suggest that the male and/or female reproductive system may be affected. A
more extensive multigeneration feeding study in rats found decreased reproductive performance of
males and females; decreased maternal weight of F0 and F I dams during gestation and lactation;
decreased litter counts, viability index; and lactation index; increased dead births and percentage of
dead births in both generations; and decreases in sz litter counts and litter weights (Hixson and
Hathaway 1986). However, negative histopathological results were generally obtained from the
examination of male and female reproductive systems in rats exposed by inhalation for 3 or 13 weeks
(Shiotsuka 1989; Thyssen 1980); in rabbits treated dermally for 3 weeks (Flucke 1986); in rats
(Klotzsche 1972) or mice (Rivett et al. 1972) fed disulfoton for 90 days; or in rats (Carpy et al. 1975;
Hayes 1985), mice (Hayes 1983), or dogs (Hoffman et al. 1975) fed disulfoton for =2 years, with the
exception of uterine cystic hyperplasia in female rats fed the high dietary concentration of disulfoton
for 2 years (Hayes 1985). Studies on reproductive function in animals exposed by the inhalation or
dermal routes will help clarify whether disulfoton affects reproduction by these routes as well as the

oral route.

Developmental Toxicity. No studies were located regarding developmental effects in humans
after inhalation, oral, or dermal exposure to disulfoton or in animals after inhalation or dermal
exposure. Developmental effects have been found in animals after acute- and intermediate-duration
oral exposure to disulfoton. Plasma and erythrocyte cholinesterase depression and increased incidences
of incomplete ossified parietal bones and stemebrae were observed in fetuses from rats fed disulfoton
on days 6—15 of gestation (Lamb and Hixson 1983). Bone and soft tissue malformations were not
observed. Effects in fetuses or pups, such as depressed brain cholinesterase activity (Hixson and
Hathaway 1986; Ryan et al. 1970), renal and hepatic pathology, and juvenile hypoplasia of testes
(Taylor 1965a) were also observed in reproductive studies. However, disulfoton did not cause any
fetotoxic effects in the fetuses from pregnant rabbits treated orally with disulfoton during gestation
(Tesh et al. 1982). Additional developmental studies involving inhalation or dermal exposure of

animals to disulfoton might indicate whether fetotoxic effects are route-dependent.

Immunotoxicity and Lymphoreticular Effects. No studies were located regarding
immunological effects in humans after inhalation, oral, or dermal exposure to disulfoton. In two acute

animal studies (Costa et al. 1990; Fitzgerald and Costa 1993), repeated intraperitoneal or oral doses of

DISULFOTON 132

2. HEALTH EFFECTS

disulfoton caused a down-regulation of cholinergic muscarinic receptors in lymphocytes. Although the
effect on lymphocytes is regarded as a neurological effect, secondary effects due to neuroimmuno
interactions are possible and warrant further investigation. After inhalation exposure of rats,
inflammatory changes throughout the respiratory tract (associated with bone marrow changes and low
percentages of lymphocytes and high percentages of polymorphonuclear leukocytes) and decreased
spleen weight were observed (Thyssen 1980). In a chronic dietary study in rats, increased incidence of
plasma cell hyperplasia in the mandibular lymph nodes and a significantly inereased incidence of
splenic lymphoid follicle depletion were observed (Hayes 1985). In other inhalation (Shiotsuka 1989),
dietary (Carpy et a1. 1975; Hayes 1983; Hoffman et a1. 1975; Klotzsche 1972; Rivett et a1. 1972), and
dermal (Flucke 1986) studies in animals exposed to disulfoton, histological examination of
lymphoreticular organs revealed no treatment-related lesions. However, immunological data collected
from animals exposed to disulfoton by all three routes for acute, intermediate, or chronic durations
might indicate whether disulfoton affects the immune system. A battery of immune function tests

would clarify whether disulfoton is an immunotoxicant.

Neurotoxicity. Exposure to disulfoton by the inhalation, oral, or dermal routes has resulted in
neurological effects in humans. Disulfoton can cause erythrocyte cholinesterase depression in humans
after inhalation exposure without other overt neurological effects (Wolfe et al. 1978). The more overt
neurological effects have been observed in humans after oral exposure to disulfoton (Hattori et al.
1982; Yashiki et al. 1990). The clinical signs consisted of muscle tremors and incoordination,
increased salivation, pupil miosis, and even death. Weakness and fatigue (Savage et a1. 1971) and
depressed erythrocyte acetylcholinesterase activity (Wolfe et a1. 1978) were observed in humans after
dermal exposure to disulfoton. No significant depression in brain, serum, or submaxillary gland
cholinesterase activity and no overt signs of neurotoxicity were observed in rats after acute inhalation
(5—10 days) exposure (DuBois and Kinoshita 1971). Inhalation, oral, and dermal exposures of animals
to disulfoton resulted in signs of cholinergic toxicity (Costa et a1. 1984; Doull 1957; Flucke 1986;
Mihail 1978; Schwab and Murphy 1981; Schwab et al. 1981, 1983; Shiotsuka 1989; Thyssen 1980).
These cholinergic signs were similar to those observed in humans and are associated with inhibition of
acetylcholinesterase. Inhibition of brain, erythrocyte, and other tissue acetylcholinesterase activities
(Carpy et a1. 1975; Christenson and Wahle 1993; Clark and Pearson 1973; Doull and Vaughn 1958;
Flucke 1986; Hayes 1983, 1985; Hikita et a1. 1973; Hixson and Hathaway 1986; Hoffman et al. 1975;
Klotzsche 1972; Robinson et al. 1978; Ryan et al. 1970; Schwab and Murphy 1981; Schwab et al.
1981; Sheets 1993a, 1993b; Shiotsuka 1989; Thyssen 1978, 1980) have been observed in animals in

DISULFOTON 133

2. HEALTH EFFECTS

numerous studies regardless of the route, duration, or animal species. The acute and intermediate
inhalation MRLs and the acute, intermediate, and chronic oral MRLs are based on cholinesterase
inhibition. Tolerance was also observed in animals exposed to disulfoton for 25—10 days (Costa et al.
1984; Schwab and Murphy 1981; Schwab et al. 1981, 1983). Neurobehavioral changes were observed
in rats (Clark and Pearson 1973) and mice (Clark et a1. 1971) exposed orally for intermediate
durations. Necrosis and atrophy of the optic nerve and retina in dogs (Uga et al. 1977) were observed
after oral exposure. Based on the results of the human and animal studies, neurological effects (subtle
and/or overt) may occur regardless of the route of exposure. Additional animal studies do not seem to

be warranted at this time.

Epidemiological and Human Dosimetry Studies. Epidemiological studies are limited. A
coincidental increase in the incidence of myopia was observed in young children thought to be orally
exposed to disulfoton (Ishikawa and Miyata 1980). Although there is clinical and histopathological
evidence from animal studies to support the association between myopia and disulfoton exposure, other
neurological effects (i.e., depressed acetylcholinesterase activity) were not reported. Employees
exposed to disulfoton by inhalation and dermal routes (Brokopp et al. 1981; Wolfe et al. 1978) did not
show overt signs of toxicity, but disulfoton exposure was confirmed in part by depressed
cholinesterase activity and/or urinary metabolite identification. These studies are limited because it is
not clear whether inhalation or dermal exposure contributed the most to the observed effects. Future
human epidemiological studies should look for subtle neurological indicators of exposure (i.e.,
erythrocyte or lymphocyte acetyl cholinesterase depression) in addition to the ocular effects already
described. The data would be useful for establishing cause/effect relationships and for future

monitoring of individuals living near hazardous waste sites.
Biomarkers of Exposure and Effect

Exposure. Disulfoton and its metabolites have been detected in the blood and the urine of humans
exposed to disulfoton either accidentally or in the workplace (Brokopp et al. 1981; Hattori et al. 1982;
Wolfe et al. 1978; Yashiki et al. 1990). Whereas, disulfoton and its metabolites were detected in the
blood of humans who ingested unknown quantities of disulfoton (Hattori et al. 1982; Yashiki et al.
1990), urinary metabolites were a better indicator of occupational exposure to the pesticide (Brokopp
et al. 1981; Wolfe et al. 1978). Although no animal studies reported the detection of disulfoton or its

metabolites in blood, data from animal studies demonstrated that urinary metabolites were a reliable

DISULFOTON 134

2. HEALTH EFFECTS

indicator of disulfoton exposure (Bull 1965; Lee et al. 1985; Puhl and Fredrickson 1975). These
animal studies also demonstrated that DEP was a more sensitive urinary biomarker than other
metabolites. DEPs are specific for diethyl organophosphates such as disulfoton. A combination of
neurological signs is usually a biomarker of disulfoton exposure, as demonstrated in humans (Yashiki
et al. 1990) and animals (Schwab et al. 1981). Inhibition of serum cholinesterase and/or erythrocyte
acetylcholinesterase are usually reliable biomarkers of exposure in humans (Wolfe et al. 1978; Yashiki
et al. 1990). Since blood cholinesterase depression was not observed, but urinary metabolites were
detected in exposed employees (Brokopp et al. 1981), urinary metabolites may be a more sensitive
biomarker of disulfoton exposure. Urinary metabolites are generally eliminated within 2 weeks after
the last exposure and are not usually detected beyond this period. However, cholinesterase depression
may be a better biomarker, because the enzyme may remain inhibited for >2 weeks. A recent study
showed that T-lymphocyte acetylcholinesterase activity was rapidly and greatly depressed in rats
during a 14—day exposure to disulfoton, but rapidly recovered after exposure (Fitzgerald and Costa
1993). Therefore, T—lymphocyte acetylcholinesterase levels could be used as a biomarker of exposure
to organophosphorus pesticides during exposure, and could be investigated for use in biomonitoring
worker exposure. Animal studies indicate that nonspecific biomarkers of disulfoton exposure may
include increased urinary levels of catecholamines (Brzezinski 1969) or their metabolite HMMA
(Wysocka—Paruszewska 1971) and increased MFO enzymes (Stevens et al. 1973). No human data
were located to support these findings. Although available biomarkers of exposure for disulfoton are

nonspecific, it is doubtful that further research will identify a more useful and specific biomarker.

Effect. Disulfoton exposure in humans or animals causes characteristic cholinergic effects such as
increased salivatiorr, diarrhea, muscle tremors, and pupillary miosis (Costa et al. 1984; Schwab et al.
1981, 1983; Yashiki et al. 1990). These effects are also associated with exposure to other
organophosphates and are, therefore, not specific to disulfoton. Inhibition of erythrocyte
acetylcholinesterase can alert the physician to the possibility of more serious neurological effects. In
rats, acetylcholinesterase levels in circulating lymphocytes correlated better with brain
acetylcholinesterase activity than did erythrocyte cell cholinesterase activities during exposure, but not
during recovery after exposure (Fitzgerald and Costa 1993). Thus, lymphocyte acetylcholinesterase
activity may be a better biomarker of effect than erythrocyte acetylcholinesterase activity during
exposure, but erythrocyte acetylcholinesterase probably remains the better sentinel for brain
acetylcholinesterase activity after exposure has ceased. However, other organophosphates and also

carbamates can cause this neurological effect. Although animal studies have demonstrated that brain

DISULFOTON 135

2. HEALTH EFFECTS

acetylcholinesterase inhibition is a sensitive indicator of a neurological effect (Carpy et al. 1975), this
measurement is not practical in humans. Increased B—glucuronidase activity (Kikuchi et al. 1981) and
increased urinary catecholamine levels (Brzezinski 1969) observed in animals may be useful
nonspecific biomarkers of effects in humans. There does not appear to be a need for additional

biomarkers of effect.

Absorption, Distribution, Metabolism, and Excretion. No studies were located regarding the
absorption, distribution, metabolism, and excretion of disulfoton by humans or animals after inhalation
or dermal exposure. Limited data exist regarding the absorption, distribution, and excretion after oral
exposure to disulfoton. Data on levels of disulfoton and metabolites excreted in urine and expired air
suggest that some almost complete absorption of an administered dose of disulfoton over 3—10 days
(Lee et a1. 1985; Puhl and Fredrickson 1975). The data are limited regarding the relative rate and
extent of absorption. Animal data suggest that disulfoton and/or its metabolites are rapidly distributed
to the liver, kidney, fat, skin, muscle, and brain, with peak levels occurring within 6 hours (Puhl and
Fredrickson 1975). Elimination of disulfoton and metabolites occurs primarily in the urine, with >90%
excreted in the urine in 3—10 days (Lee et al. 1985; Puhl and Fredrickson 1975). Evidence further
suggests that male rats eliminate disulfoton at a faster rate than females. This difference may be due
to differences in absorption, metabolism, retention, excretion, or a combination of factors. The
metabolic pathways of disulfoton are relatively well understood based on data from animal studies
(Bull 1965; Lee et al. 1985; March et al. 1957; Puhl and Fredrickson 1975). Similar metabolites have
been detected in the urine and tissues from humans exposed to disulfoton (Brokopp et al. 1981;
Yashiki et al. 1990). One study suggests that a greater percentage of disulfoton sulfoxide is oxidized
to demeton S-sulfoxide, rather than disulfoton sulfone to form demeton S-sulfone (Bull 1965).
Additional studies in animals, designed to measure the rate and extent of absorption, distribution, and
excretion of disulfoton after inhalation or dermal exposure would be useful for predicting the

toxicokinetics of disulfoton in humans at an occupational or hazardous waste site.

Comparative Toxicokinetics. The primary target organ for disulfoton in animals and humans is
the nervous system. Other organs, such as the liver, are hardly affected. Since there have been no
toxicokinetic studies in animals or humans exposed by inhalation or dermal routes, it is impossible to
compare animals and humans by these two routes of exposure. Data from occupational studies suggest
that disulfoton was absorbed via inhalation and/or dermal routes of exposure (Brokopp et al. 1981;

Wolfe et a1. 1978); however, the data from these studies on the rate and extent of absorption are

D|SULFOTON 136

2. HEALTH EFFECTS

limited. No animal studies were available for comparison. Although the rate and extent of absorption
was unknown, disulfoton was readily absorbed by two men as demonstrated in two separate studies
(Hattori et al. 1982; Yashiki et al. 1990). In animals, toxicokinetic data are available only in rats
exposed by the oral route (Lee et al. 1985; Puhl and Fredrickson 1975). No studies were located
regarding the distribution of disulfoton following inhalation or dermal exposure in humans or animals.
Although no studies were located regarding the distribution of disulfoton following oral exposure in
humans, data from animal studies were located. Disulfoton and its metabolites were detected in the
liver, kidney, adipose tissue, muscle, skin, and brain (Puhl and Fredrickson 1975). Data from human
(Brokopp et al. 1981; Wolfe et al. 1978; Yashiki et a1. 1990), rat (Bull 1965; Lee et al. 1985; Puhl and
Fredrickson 1975), and mouse (March et al. 1957) studies indicate that similar metabolic pathways
operate in humans and rodents. No studies were located regarding the rate or extent of excretion of
disulfoton in humans or animals after inhalation or dermal exposure. Although no studies were
located regarding the rate or extent of excretion of disulfoton after oral exposure in humans, limited
data for animal studies were located. Data from the only animal study located suggested that most of
the disulfoton was eliminated within 3—10 days of exposure and that male rats eliminated disulfoton at
a faster rate than females (Lee et al. 1985; Puhl and Fredrickson 1975). With intraperitoneal
administration, rats eliminated 28% of the original dose within 48 hours (Bull 1965), and mice
eliminated 30—60% of the original dose within 96 hours (March et al. 1957). There appears to be
insufficient toxicokinetic data to use as a basis for comparison of animals and humans. Additional
studies comparing the rate and extent of absorption, distribution, and elimination in several different

animal species after inhalation, oral, and dermal exposure to disulfoton could be useful.

Methods for Reducing Toxic Effects. No data were located regarding the mechanism of
absorption via the respiratory tract, gastrointestinal tract, or the skin. Besides moving the exposed
individual to a fresh air environment and/or administering oxygen, very little can be done if disulfoton
is inhaled (Sittig 1991). Induction of emesis, gastric lavage, and administration of a saline cathartic
immediately after oral exposure help reduce absorption. Since diuresis, dialysis, and hemoperfusion
have been used to reduce the body burden of other organophosphates (Ellenhom and Barceloux 1988),
it seems reasonable that these methods may also be used to treat disulfoton intoxication. Repeated
administration of activated charcoal and cathartics may prevent possible enterohepatic recirculation of
the parent compound and its metabolites. The treatment protocol also includes interfering with the
known mechanism of action of disulfoton. Atropine is used to block the muscarinic effects of

disulfoton (Goldfrank et al. 1990; Yashiki et al. 1990), and an oxime (e.g., 2-PAM) is given to

DISULFOTON 137

2. HEALTH EFFECTS

accelerate the hydrolysis of phosphorylated cholinesterase, which accelerates regeneration of the active
cholinesterase (Ellenhom and Barceloux 1988; Goldfrank et a1. 1990; Haddad and Winchester 1990;
Morgan 1982). There are numerous treatment protocols that successfully use some or all of the
methods described. Therefore, further studies regarding the reduction of toxic effects for disulfoton

exposure may not be warranted.

2.9.3 Ongoing Studies

A study by SC. Soderholm of the University of Rochester is in progress to relate the deposition
efficiency of volatile aerosols of disulfoton in humans to physical properties of the airborne system,
including exposure concentration, saturation vapor concentration, particle size, and blood/gas partition
coefficient (CRISP Database 1994). Disposition efficiency will be determined from laboratory
experiments and computer modelling. The results of computer models will be compared to measure
disposition efficiencies of disulfoton aerosols in humans. With this information, the inhaled dose in

humans can be estimated.

Studies on particular organophosphates are currently being conducted by EPA to substantiate the
findings that these organophosphates, including disulfoton, are associated with the development of

myopia in humans, as reported in Japanese populations (Dementi 1994).

DISULFOTON 139

3. CHEMICAL AND PHYSICAL INFORMATION

3.1 CHEMICAL IDENTITY

Information regarding the chemical identity of disulfoton is located in Table 3-1.

3.2 PHYSICAL AND CHEMICAL PROPERTIES

Disulfoton is a systemic insecticide/acaricide that belongs to the organophosphate class of pesticides.
Pure disulfoton is a colorless oil with low volatility and water solubility, but is readily soluble in most
organic solvents (Worthing 1987). Information regarding the physical and chemical properties of

disulfoton is located in Table 3-2.

DlSULFOTON 140

3. CHEMICAL AND PHYSICAL INFORMATION

TABLE 3-1. Chemical Identity of Disulfoton

 

 

Characteristic Information Reference

Chemical name 0, O-Diethyl S-[2-(ethylthio)ethyl]- Worthing 1987
phosphorodithioate

Synonym(s) Ethylthiodemeton; M-74; thiodemeton Worthing 1987

Registered trade name(s) Di-Syston; Dithiosystox; Solvirex Worthing 1987
ENT 23347; Frumin AL Merck 1989

Chemical formula CBH1902P83 Worthing 1987

Chemical structure 3 Worthing 1987

CH3CHZSCH20HZSP(OCHZCH3)2

Identification numbers:

CAS Registry 298-04-4 Sittig 1985

NIOSH RTECS TDQ275000 Sittig 1985

EPA hazardous waste PO39 HSDB 1994
OHM/T ADS 7800012 HSDB 1994
DOT/UN/NA/IMCO shipping NA2783/lMO 6.1 HSDB 1994
HSDB 379 HSDB 1994
NCI No data HSDB 1994

 

CAS = Chemical Abstracts Services; DOT/UN/NA/IMCO = Department of Transportation/United Nations/
North America/International Maritime Dangerous Goods Code; EPA = Environmental Protection Agency;
HSDB = Hazardous Substance Data Bank from National Library of Medicine; NCI = National Cancer
Institute; NIOSH = National Institute for Occupational Safety and Health; OHM-TADS = Oil and
Hazardous Materials/Technical Assistance Data System; RTECS = Registry of Toxic Effects of
Chemical Substances

DISULFOTON

3. CHEMICAL AND PHYSICAL INFORMATION

141

TABLE 3-2. Physical and Chemical Properties of Disulfoton

 

 

Property Information Reference
Molecular weight 274.38 HSDB 1994
Color Colorless (pure); yellow Sanborn et al. 1977

Physical state
Melting point
Boiling point

Density:
at 20 °C
at 25 °C
at 30 °C

Odor

Odor threshold:
Water
Air

Solubility:
Water at 20 °C

Organic solvent(s)

Partition coefficients:
Log Kow
Log K0c

Vapor pressure at 20 °C

Henry’s law constant:
at 20 °C
at 30 °C

Autoignition temperature
Flashpoint
Flammability limits

Conversion factors

Explosive limits

(technical)
Oily liquid
No data

113 °C at 0.4 mm Hg;
62 °C at 0.01 mm Hg

1.144 g/cm3
No data
No data

Aromatic (technical product)

No data
No data

25 mg/L; 15.2 mg/L

Readily soluble in most

4.02
3.2; 2.78

1.8x10‘4 mm Hg

2.17x10'6 atm-m3/mol
No data

No data
>180 °F (TOC)
No data

1 mg/m‘3 = 0.089 ppm
(air at 25 °C)

No data

HSDB 1994

Melnikov 1971;
Sanborn et al. 1977

Worthing 1987

HSDB 1994

Sanborn et al. 1977;
Lord and Burt 1964

Sanborn et al. 1977

Bowman and Sans 1983
Flao and Davidson 1982;
Wauchope et al. 1992
Melnikov 1971

Domine et al. 1992

EPA 1984b

EPA 1990b

 

EPA = Environmental Protection Agency; HSDB = Hazardous Substance Data Bank from National
Library of Medicine; TOC = Tag open cup

DISULFOTON 143

4. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL

4.1 PRODUCTION

Disulfoton is produced commercially by a reaction of the sodium salt of 0,0’-diethylhydrogen
phoshorodithioate with 2—chloroethylthioethyl ether (VonRumker et al. 1974). Disulfoton is produced
in the United States by a subsidiary of Bayer AG, Germany. Chemagro of Kansas City, Missouri, a
subsidiary of Bayer AG, produced an estimated 5 million pounds of disulfoton in 1972 (VonRumker et
al. 1974). Disulfoton production has declined in recent years as a result of restricted use due to its
toxicity (EPA 1984b). In 1986, Mobay Corp., Kansas City, Missouri, produced over 2.1 million
pounds of disulfoton in the United States (Goodrich et al. 1991). Since the annual use of disulfoton in
the United States from 1989 to 1991 was 3.06 million pounds (Gianessi and Puffer 1992), the
production volume during this period must have exceeded 3.1 million pounds. In 1994, Miles Inc.,
Agriculture Division, Kansas City, Missouri, a subsidiary of Bayer AG of Germany, produced

disulfoton; however, information on current production volume is not available (SRI 1994).

4.2 IMPORT/EXPORT

In 1972, disulfoton was not imported into the United States, and the exports of disulfoton from the
United States to other countries were negligible (VonRumker et a1. 1974). Import/export data for
disulfoton in recent years were not located; however, since the recent yearly consumption of disulfoton
in the United States is substantially lower than the estimated yearly production capacity of 7 million
pounds at the Kansas City plant (VonRumker et a1. 1974), it is unlikely that disulfoton is being

imported.

4.3 USE

Disulfoton is a systemic organophosphate insecticide/acaricide (i.e., it is absorbed and translocated by
treated plants) effective for controlling a variety of harmful insects that attack many field and
vegetable crops. As emulsifiable concentrates and in granular or pelleted/tableted forms, disulfoton is
used to treat seeds and is applied to soils or plants. Disulfoton is also available in a ready-to—use
liquid formulations (EPA 1984b). Disulfoton is used to protect small grains, sugar cane, sorghum,

com, cotton, cole, root, seed, forage, and other field crops; some vegetable, fruit (strawberry,

DISULFOTON 144

4. PRODUCTION. IMPORT/EXPORT, USE, AND DISPOSAL

pineapple), and nut crops; and forest plantings, ornamental and potted plants (EPA 1984b; VonRumker
et al. 1974). Agricultural uses account for most of its consumption; small quantities are used on home
and garden plants and for other purposes, such as mosquito abatement (VonRumker et al. 1974;
Wamick and Eldredge 1972). Use of disulfoton has declined since the early 1970s. In 1972,

4.9 million pounds of disulfoton were used for agricultural purposes, and only 0.1 million pounds were
used in homes and gardens (VonRumker et al. 1974). Based on state usage data from 33 states for
1982, California use data for 1981, and the EPA Office of Pesticide Programs national survey of
pesticide usage by urban applicators and nurseries, Gianessi (1986) estimated that 2.1 million pounds
of disulfoton were used annually in agriculture during 1981 and 1982. The estimated annual
agricultural use of disulfoton was 2,] million pounds in 1986 (Goodrich et al. 1991) and 3.1 million
pounds in 1989—1991 (Gianessi and Puffer 1992). The use of disulfoton in the production of corn,
wheat, potatoes, and cotton accounted for the largest annual use during 1989—1991 (Gianessi and

Puffer 1992).

4.4 DISPOSAL

The two preferable methods for disposing of wastes containing disulfoton are incineration and alkaline
hydrolysis (HSDB 1994). For disposal of low-viscosity wastes (permitting atomization in the
combustion chamber) containing disulfoton, liquid injection incineration at 650—l,600 °C and a
residence time of 0.1—2 seconds are recommended. For the disposal of viscous and solid wastes,
rotary kiln incineration at 820—l,600 °C and a residence time of seconds to hours, or fluidized bed
incineration at 450—980 °C with a residence time of seconds or longer are recommended. The effluent
gases from the incineration units should pass through scrubbers or other air pollution control devices
(HSDB 1994). Alkaline hydrolysis leads to the complete degradation of disulfoton to non-toxic end
products (alkaline salts of 0,0-dimethylphosphorothioic acid and ethylthioethyl mercaptan). Disulfoton
is resistant to hydrolysis in acid media (Sittig 1980). Acid hydrolysis produces essentially the same
end products; however, the reaction rate is much slower (IRPT C 1985). Fifty percent hydrolysis at
70 °C requires 60 hours at pH 5, but only 7.2 hours at pH 9 (Sittig 1980). In the alkaline hydrolysis
method, the waste should be subjected to hydrolysis with 6% potassium hydroxide in isopropanol
under reflux for 30 minutes (IRPTC 1985) or 5% sodium hydroxide in ethanol for 3 hours (for
2%,10%, and 50% granular formulations) (Dillon 1981). The hydrolyzed product should be adsorbed

on vermiculite, then incinerated or disposed of in a landfill (IRPTC 1985).

DISULFOTON 145

4. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL

The EPA has proposed incineration as the best demonstrated available technology (BDAT) for treating
organophosphorus nonwaste waters (waste containing >1% by weight total suspended solids and >1%
by weight total organic carbon). EPA has demonstrated that rotatory kiln incineration at 1,000 °C was
satisfactory for attaining the proposed treatment standard of a maximum 0.1 mg/kg disulfoton in

treated nonwaste waters (Berlow and Cunningham 1989).

DISULFOTON 147

5. POTENTIAL FOR HUMAN EXPOSURE

5.1 OVERVIEW

Disulfoton enters the environment primarily during its use as an insecticide/acaricide in crops and
vegetables, and in homes and gardens. Other important pathways for disulfoton’s entry into the
environment are the disposal of liquid disulfoton wastes into soil evaporation pits, ditches, ponds
(Winterlin et al. 1989), and hazardous waste sites. Thus, soil is the environmental medium most likely
to be contaminated with disulfoton. The processes that may transport disulfoton from soil to other
environmental media include leaching to groundwater, runoff to surface water, and absorption by
plants (Holden 1986; Mostaghimi et al. 1993; Nash 1974; Plumb 1991; Sanbom et a1. 1977; Spalding
and Snow 1989). Biodegradation, abiotic hydrolysis and, to a lesser extent, sensitized oxidation are
principally responsible for the loss of disulfoton from water (Capel et al. 1988; Mossman et a1. 1988;
Wanner et al. 1989). In a chemical spill in the Rhine River where an initial disulfoton concentration
of 5 u/L was observed, the estimated biodegradation half-life of disulfoton in 10 °C river water was
7—41 days (Wanner et a1. 1989). The measured whole—body bioconcentration factor for disulfoton in
carp was 450, but disulfoton residues disappeared rapidly from the fish when they were placed in
uncontaminated water (Takase and Oyama 1985). Biodegradation and photosensitized oxidation play
major roles in the loss of disulfoton from soil (Gohre and Miller 1986; Wanner et al. 1989; Zepp et a1.
1981). The estimated half-life of disulfoton in soil ranges from 3.5 to 3290 days (Chapman et a1.
1993, 1994a; Garg and Sethi 1980; Greenhalgh 1978', Harris et a1. 1988; Jury et al. 1987a; Menzie
1972).

Disulfoton was detected at a maximum of 4.7 ng/m3 in 1 of 123 ambient air samples from

10 locations in the United States (Carey and Kutz 1985). Disulfoton was qualitatively detected in
groundwater samples from 1 of 479 hazardous waste sites (Plumb 1991) and in runoff water in an
agricultural watershed at concentrations ranging from trace to 0.4 ug/L (Spalding and Snow 1989).
Disulfoton was also detected in groundwater samples from the Nomini Creek Watershed in Virginia at
a mean and maximum concentration of 0.39 ug/L and 2.87 pg/L respectively (Mostaghimi et a1. 1993).
A core soil sample taken from a waste evaporation pit at a depth of 90 cm contained disulfoton at a
concentration of 44 mg/kg (Winterlin et al. 1989). The mean concentration of disulfoton in the bottom

soil of an agricultural tail water pit used to collect irrigation runoff was 13.4 pg/kg.

DISULFOTON 148

5. POTENTIAL FOR HUMAN EXPOSURE

The Food and Drug Administration (FDA) estimated the average dietary intake of disulfoton from
1986—1991 for a 14- to 16-year—old male in the United States at 0.2 ng/kg body weight/day, a quantity
over 1,000 times lower than the Food and Agricultural Organization of the United Nations/World
Health Organization’s (FAQ/WHO) acceptable daily intake (ADI) of 300 ng/kg body weight/day (EPA
1993b; FAQ/WHO 1991; Winter 1992; Yess 1991).

Workers in industries that manufacture and formulate disulfoton, farm workers who enter treated fields
after the insecticide has been applied and, in particular, applicators of the insecticide are at a higher
risk of exposure than the general population. Among the general population, people who use the
insecticide in homes and garden applications are at a higher risk of exposure, as are people who live

near hazardous waste sites containing disulfoton.

Disulfoton has been identified in 7 of the 1,408 hazardous waste sites on the NFL (HazDat 1994).

The frequency of these sites within the United States can be seen in Figure 5-1.

5.2 RELEASES TO THE ENVIRONMENT

5.2.1 Air

Disulfoton may enter the atmosphere during its production and its use as an insecticide/acaricide. Air
emissions from disulfoton production have been reported to be 0.5 kg per 1,000 kg (one metric ton)
(Sittig 1980). Assuming a minimum production volume of 3.1 million pounds (1.4 million kg) per
year, based on Gianessi and Puffer (1992) use estimates for 1989 through 1991, approximately

1,500 pounds (700 kg) are emitted to the atmosphere from production annually. Disulfoton is
primarily released to the atmosphere during application of the granular insecticide by ground broadcast
or aerial application (CPCR 1992). Disulfoton also enters the atmosphere when the emulsifiable
insecticide is sprayed on crops and soil (CPCR 1992), and when the insecticide is aerially applied as a
fog for controlling mosquitos (Racke 1992; Wamick and Eldredge 1972). Although not as significant
a source, unintentional releases of disulfoton into the atmosphere include volatilization of applied

insecticide from soil and plant surfaces, and accidental spills.

149

DISULFOTON

5. POTENTIAL FOR HUMAN EXPOSURE

V00.“ UDDNOI EOL¥ UO>fiL00¥
mwhHm m I thm « ammmm >ozw30mmu

 

* ZOE<ZHE<BZOO 2090,5399 me; mmtm 152 .mo wozmbammm A In mmDUE

DISULFOTON 150

5. POTENTIAL FOR HUMAN EXPOSURE

5.2.2 Water

Other than aerial application over swamps for mosquito abatement, disulfoton is not known to be used
over water. Potential sources of release into surface water include discharge of waste water from
disulfoton manufacturing, formulation, and packaging facilities (HSDB 1994). Leaching and runoff
from treated fields, pesticide disposal pits, or hazardous waste sites may contaminate both groundwater
and surface water with disulfoton. Entry into water can also occur from accidental spills. Small
amounts of volatilized disulfoton may be removed from the atmosphere as a result of wet deposition

and may enter surface water (Racke 1992).
5.2.3 Soil

Disulfoton is released to agricultural, home, and garden soil during direct soil or foliar treatment with
the insecticide and from disposal of disulfoton-containing wastes in hazardous waste sites (HSDB
1994). Much of the foliar-applied disulfoton or its metabolites eventually reach the soil (Racke 1992).
Soil in waste disposal sites may include manufacturing wastes containing disulfoton. A primary
method for disposing of liquid pesticide wastes has been dumping liquid materials into soil
evaporation pits, ditches, and ponds. Topsoil from such discharge areas can be expected to be
contaminated with pesticides, as the soil from one such discharge pit contained disulfoton (Winterlin et
al. 1989). Soil from tail water pits used for collecting irrigation runoff may also be a source of
disulfoton if the soil has been treated with this insecticide (Kadoum and Mock 1978). Small amounts
of disulfoton may enter soil by deposition of aerial disulfoton on land (Racke 1992). Entry may also
occur from spills during storage, transport, or equipment loading and cleaning, although contemporary
management practices significantly reduce the quantities of disulfoton accidentally released during its

use (Racke 1992).

5.3 ENVIRONMENTAL FATE

5.3.1 Transport and Partitioning

There is a paucity of experimental data regarding the transport and partitioning of disulfoton in air.

Given the vapor pressure of 1.8x10'4 mm Hg at 20 °C (Melnikov 1971), disulfoton should exist almost

entirely in the vapor phase in the atmosphere (Eisenreich et a1. 1981). Because of low particle

DISULFOTON 151

5. POTENTIAL FOR HUMAN EXPOSURE

diameter, the removal rate by dry deposition is low for compounds that exist in the vapor phase in the
atmosphere (Schroeder et a1. 1987); therefore, depending on its reactivity characteristics, vapor-phase
disulfoton may travel long distances in the air. The solubility of 25 mg/L (Sanbom et al. 1977)

ensures that at least partial removal of atmospheric disulfoton will occur by wet deposition.

The transport of disulfoton from water to air can occur due to volatilization. Compounds with a
Henry’s law constant (H) of <10‘5 atm—m3/mol volatilize slowly from water (Thomas 1990).
Therefore, disulfoton, with an H value of 2.17x10‘6 atm-m3/mol (Domine et al. 1992), will volatilize
slowly from water. The rate of volatilization increases as the water temperature and ambient air flow
rate increases and decreases as the rate of adsorption on sediment and suspended solids increases
(Dragan and Carpov 1987). The estimated gas-exchange half-life for disulfoton volatilization from the
Rhine River at an average depth of 5 meters at 11 °C was 900 days (Wanner et al. 1989). The
estimated volatilization half-life of an aqueous suspension of microcapsules containing disulfoton at

20 °C with still air was >90 days (Dragan and Carpov 1987).

Adsorption to particulate matter will transport disulfoton from water to suspended solids and sediment
in water. The estimated organic carbon-adjusted soil sorption coefficient (KOC) for disulfoton varies
between 600 and 1,603 (Jury et al. 1987a; Rao and Davidson 1982; Wauchope et al. 1992). This
range of K0C values suggests that disulfoton in water adsorbs moderately to suspended solids and
sediments (Swann et a1. 1983), and this process may transport considerable amounts of disulfoton from

water to particulate matter.

Based on structure activity relationships, certain regression equations have been developed to estimate
disulfoton’s bioconcentration factor (BCF) from its water solubility and Koc values. Based on these
regression equations, the estimated BCF for disulfoton in aquatic organisms is 100—1 10 (Kenaga
1980). A microcosm, simulating paddy fields containing water, sweet potato, tobacco cutworrn
(Spodoptera litura), algae (Spirogyra crassa), red snail (Indoplanorbis exustus), Daphnia, mosquito
larvae (Culex pipiens), and guppies (Labistes reticulatus), was used to assess disulfoton accumulation
in aquatic organisms over a 33-day period (Tomizawa 1980). Whole-body BCF values of 9 and 2,487
were reported for snails and guppies, respectively. The bioconcentration of disulfoton and its
oxidation products (sulfoxide and sulfone) in carp (Cyprinus carpio) was investigated in a continuous-

flow water system for $56 days (Takase and Oyama 1985). The whole-body BCF values in carp were

DISULFOTON 152

5. POTENTIAL FOR HUMAN EXPOSURE

=450 for disulfoton, <1 for the sulfoxide, and <6 for the sulfone. Disulfoton disappeared rapidly from

fish tissues when the fish were transferred to uncontaminated fresh water.

The transport processes that may move disulfoton from soil to other media are volatilization, leaching,
runoff, and absorption by plants. Volatilization of disulfoton from wet soil may be greater than from
relatively dry soil (Gohre and Miller 1986). Like other pesticides, disulfoton in soil partitions between
soil-sorbed and soil-water phases (Racke 1992). This latter phase may be responsible for the
volatilization of disulfoton from soil; however, due to the low Henry’s law constant value, the rate of

disulfoton volatilization from the soil—water phase to the atmosphere would be low.

The reported K0c values of 600—1,603 suggest that the adsorption of disulfoton to soil is moderately
strong and that the rate of leaching may be minor in most soils. Batch-type adsorption tests and soil
column studies showed that the disulfoton adsorption rate in soil increases as the clay content of the
soil increases (King and McCarty 1968; McCarty and King 1966). Disulfoton leaching through Hugo
sandy loam soil was initially rapid, but very little further leaching was observed with an increase in
eluent volume (McCarty and King 1966). For example, 27.5% of disulfoton applied to a 6-inch soil
column eluted with a total of 4 feet of buffered water (pH 7), but only 29% eluted with a total of
110 feet of buffered water. Other investigators concluded from soil column and soil thin-layer
chromatography studies that disulfoton is only very slightly to moderately mobile in soil (Harris 1969;
Helling et al. 1974; Thornton et al. 1976). Mobility may decrease with an increase in soil pH and
organic content (Thornton et al. 1976). The oxidation products of disulfoton (sulfone and sulfoxide)
are less mobile in soils than the parent compound (EPA 1989b). Due to increased polarity, the
mobility of the oxidation products is expected to depend on the soil’s cation exchange properties;
mobility would decrease as the soil’s cation exchange potential increases. Disulfoton has been
detected infrequently and at low concentrations in groundwater from agricultural soil (Holden 1986;
Mostaghimi et al. 1993) and in groundwater from disposal sites (Plumb 1991). These observations

suggest that small amounts of disulfoton can leach through certain soils into groundwater.

Disulfoton is also transported through soils or from soil to surface water (streams or rivers) via runoff.
Pesticides with water solubilities >10 mg/L move mainlyin solution phase in runoff water (Racke
1992). Disulfoton, with a water solubility of 25 mg/L (Sanbom et al. 1977), is expected to be found

mainly in runoff water. In a runoff event from agricultural soil in Nebraska, low levels of disulfoton

DISU LFOTON 153

5. POTENTIAL FOR HUMAN EXPOSURE

were detected both in the dissolved state and in eroding soil particles in the sorbed state (Spalding and

Snow 1989).

Disulfoton is absorbed from soil by the root systems of plants and is translocated to the plant top
(Nash 1974). Plants metabolize disulfoton to its sulfone, sulfoxide, and oxons (Szeto et al. 1983a,
1983b). The concentrations of disulfoton and its metabolites in plant tops depend on the applied
dosage in soil and the type of plants. The level of parent compound and its metabolites reaches a
maximum concentration in plants within days or weeks and then tends to decrease (Nash 1974; Szeto
et al. 1983a, 1983b). When disulfoton was applied to a soil at levels of 0.5 and 4.0 kg active
ingredient per hectare in asparagus field plots, the levels of sulfone, sulfoxide, and oxons in asparagus
ferns increased steadily to maximums of 14 and 6] mg/kg (fresh weight) in 70—85 days and then
declined to 0.4 and 17.1 mg/kg in 147 days; no parent compound was detected at any time after

14 days following application (Szeto et al. 1983a). Similarly, the metabolites of disulfoton were
detected in lettuce grown in a treated field (Szeto et al. 1983b). The residual levels of disulfoton and
its metabolites in vegetables grown on treated soil were highest in carrots, intermediate in Chinese
cabbage, and lowest in turnips (Sanbom et al. 1977). Recently, Chapman et al. (1994b) studied the
effects of multiple soil applications of disulfoton (one treatment each year for 3 years) on enhanced
microbial degradation in soil and subsequent uptake by seed potatoes and foliage. Disulfoton was the
major insecticidal component detected in soil, a minor component of seed potatoes, and was not
detected (<0.02 ppm) in potato foliage during all three treatment years. Disulfoton sulfoxide and

sulfone were the major insecticidal degradation products detected in the seed potatoes and foliage.

In the first year, the maximum concentrations of sulfoxide and sulfone in soil, seed potatoes, and
foliage were approximately 2, 2, and 6 times, respectively, the concentrations of those metabolites
measured in the second and third year treatments. These results demonstrated that enhanced microbial
degradation of relatively minor insecticidal compounds in the soil can significantly affect insecticide
levels in the plant (when these degradation products are the major insecticidal component
accumulated). As the sulfoxide and the sulfone metabolites are the major toxicants in the foliage of
potato plants grown in disulfoton-treated soil, this reduction in toxicant residues over time can be

expected to reduce insecticide efficacy.

DISULFOTON 154

5. POTENTIAL FOR HUMAN EXPOSURE

5.3.2 Transformation and Degradation
5.3.2.1 Air

One of the important reactions for most organic pollutants in the atmosphere is with hydroxyl radicals.
Using an estimation method (Atkinson 1988), the estimated rate constant for the vapor-phase reaction
of disulfoton with hydroxyl radicals is 13.2x10'11 cm3/molecule-sec. Based on this value and
assuming an average atmospheric hydroxyl radical concentration of 5x105 radicals/cm3 (Atkinson
1988), the estimated half-life of disulfoton in the atmosphere due to this reaction is 3 hours.
Therefore, disulfoton is short-lived in the atmosphere. Disulfoton is not susceptible to direct
photolysis in sunlight (Gohre and Miller 1986). As with soil and water (Gohre and Miller 1986; Zepp
et al. 1981), it is possible that disulfoton reacts with singlet oxygen in the atmosphere. The
importance of this reaction for the transformation of disulfoton cannot be assessed because a reaction

rate is unavailable.
5.3.2.2 Water

The three processes responsible for the transformation and degradation of disulfoton in water are
abiotic hydrolysis, photosensitized oxidation, and biodegradation. Disulfoton is most stable towards
hydrolysis in the pH range 1—5 (Muhlmann and Schrader 1957). The experimentally estimated rate
constants for the hydrolysis of disulfoton at 70 °C were 1.16x10'2/hour, 1.56x10'2/hour,
2.50x10'2/hour, 3.22x10'2/hour, and 9.61x10'2/hour at pH of 5, 6, 7, 8, and 9, respectively (Muhlmann
and Schrader 1957). The corresponding estimated half-lives are 60, 44, 27.6, 21.5, and 7.2 hours.
The estimated hydrolysis half-life of disulfoton at 70 °C and pH 6.9 in ethanol—aqueous buffer solution
(20:80) was 32 hours (Ruzicka et al. 1967). Other investigators reported the hydrolysis half-life of
disulfoton under more realistic environmental conditions. For example, estimated hydrolysis half-lives
were 103 days at 25 °C and pH 7 (Ellington et a1. 1988) and 170 days at 11 °C and pH 7.9 (Wanner
et al. 1989). Hydrolysis products of disulfoton are diethylthiophosphoric acid and 2-ethylmercaptothio
ether (Muhlmann and Schrader 1957).

Direct photolysis of disulfoton is negligible, since it does not significantly absorb sunlight (Wanner et
al. 1989). Disulfoton is more likely to react with singlet molecular oxygen (102) produced from the

reaction of certain photochemically excited dissolved organic matters (e.g., humic and fulvic

DISULFOTON 155

5. POTENTIAL FOR HUMAN EXPOSURE

substances) with molecular oxygen in water (Zepp et a1. 1981). The estimated near-surface half-life
for photosensitized oxidation of disulfoton by sunlight available during midwinter in the southern
United States was 3 hours (Zepp and Baughman 1978). Due to light attenuation with increasing water
depth, the half-life of disulfoton due to the oxidation reaction is expected to increase with increasing
water depth. Estimated half-lives due to photosensitized oxidation are 1,000 days at a depth of

5 meters for a winter day and 100 days for a summer day (Wanner et a1. 1989). The products of
photosensitized oxidation are disulfoton sulfone and disulfoton sulfoxide (Mitchell et a1. 1968).
Hydroxyl radicals in natural water also oxidize disulfoton. When a 13 umol solution of disulfoton was
exposed to October sunlight (Davis, California) in the presence of 100 umol hydrogen peroxide, 49%
of the insecticide disappeared in 10.2 days due to reaction with hydroxyl radicals (Draper and Crosby
1984). The rate of this reaction will be slower in natural surface water where the concentration of
available hydroxyl radicals is lower than that available from the photolysis of 100 umol hydrogen
peroxide (levels S30 pmol hydrogen peroxide are generated in eutrophic water) (Draper and Crosby

1984).

Following an accidental discharge of stored chemicals including disulfoton, the estimated
biodegradation half-life of disulfoton in Rhine River water was between 7 and 41 days at 10 °C
(Wanner et al. 1989). Therefore, biodegradation of disulfoton is expected to be important in water,
and the rate will depend on the initial concentration. A theoretical model predicted that over 12 days
biodegradation and photolysis would account for an 80% mass loss of disulfoton in the Rhine River
after an accident spill incident (Mossman et al. 1988); however, the removal of disulfoton by chemical

processes was much slower than by biodegradation (Capel et a1. 1988).

5.3.2.3 Sediment and Soil

Disulfoton in soil and sediment may undergo degradation and transformation by hydrolysis,
photoinduced oxidation, and biotic processes. The hydrolysis of disulfoton may occur in the
soil/sediment—water phase, as opposed to the soil/sediment-sorbed phase. As a result, the rate of
hydrolysis is expected to be comparable to that in water. Based on slow hydrolysis rates observed in
water (see Section 5.3.2.2), hydrolysis of disulfoton in soil is not expected to be significant. A group
of investigators reported the oxidation of disulfoton on soil surfaces by singlet oxygen produced from
sunlight irradiation (Gohre and Miller 1986; Hebert and Miller 1990; Miller et al. 1989). The initial

loss of disulfoton on soil surfaces by photooxidation is quite rapid and slows down as the reaction

DISU LFOTON 156

5. POTENTIAL FOR HUMAN EXPOSURE

proceeds. Thus, attributing the loss to a first-order rate process and assigning a half-life to this process
is misleading (Miller et al. 1989). Although the most rapid oxidation occurred in soil with the lowest
organic carbon, half of the original concentrations of disulfoton in four different soil samples was lost
in =3 days (Gohre and Miller 1986). The rate substantially decreased over the course of irradiation.
The photooxidation of disulfoton occurred appreciably deeper than optical depths (depths for sunlight
penetration in soil) of 0.2—0.3 mm (Hebert and Miller 1990). In aerated and moisture-unsaturated soil,
the photooxidation can proceed up to a soil depth of 2 mm (Hebert and Miller 1990). The primary

photooxidation product was the sulfoxide with trace amounts of the sulfone (Gohre and Miller 1986).

In laboratory tests, several fungi and cultures of actinomycetes isolated from garden soil readily
degraded disulfoton (Bhaskaran et al. 1973). In flooded soil under anaerobic conditions, the reduction
of disulfoton sulfoxide to disulfoton was due to biological conversion (Tomizawa 1975). The
reduction of sulfone to either sulfoxide or sulfide (i.e., disulfoton) was not observed under the same
conditions. Since the bacterial populations in sediments and soils are higher than in typical’surface
waters (Mossman et al. 1988), biodegradation is expected to play a major role in the loss of disulfoton
in soil and sediment, as occurred in the disulfoton spill in the Rhine River (Capel et al. 1988; Wanner

et al. 1989).

Several investigators have reported the rate of overall loss of disulfoton from soil due to all biotic and
abiotic processes. The estimated half-life of disulfoton in soil ranged from 3.5 to 14 days (Chapman
et a1. 1993; Garg and Sethi 1980; Greenhalgh 1978; Harris et al. 1988; Jury et al. 1987a; McCarty and
King 1966; Rao et al. 1985; Shaw 1975), although half-life values of 17 days-and 42 days were
reported for loam and Plainfield sand respectively (Chapman et al. 1994a). A half-life value of

$290 days was also reported for soil (soil type unspecified) (Menzie 1972). The estimated persistence
of disulfoton in soil varied between 28 and >64 days (Belanger and Hamilton 1979; Clapp et al. 1976;
Jury et al. 1987b; Kearney et al. 1969). Soil type and soil temperature influenced the degradation rate
of disulfoton. Disulfoton degraded almost twice as fast over the first 12 weeks post-application in
loam as compared to Plainfield sand; however, the authors believe that lower temperatures may have
contributed to the slower disappearance of disulfoton in the Plainfield sand study (Chapman et al.
1994a). Since the compound degraded faster during winter in Evesboro loamy sand soil than during
summer in Chillum silt loam soil, the authors (Menzer et al. 1970) concluded that soil type was

predominantly responsible, rather than temperature.

DISULFOTON 157

5. POTENTIAL FOR HUMAN EXPOSURE

The presence of light and higher soil pH (pH 8 versus 5) also accelerated degradation of disulfoton in
soil (Shaw 1975). The only metabolites isolated from disulfoton degradation in soil were the sulfoxide
and sulfone (Chapman et al. 1994a, 1994b); only minute amounts of oxons were found (Clapp et a1.
1976; Greenhalgh 1978; Shaw 1975; Szeto et al. 1983a). Diethyl phosphorothioate was identified as
the major metabolite in the aqueous fraction of soil (Shaw 1975). Disulfoton and disulfoton sulfoxide
degraded in $32 days in soil, while disulfoton sulfone persisted for >64 days (Clapp et a1. 1976;
Greenhalgh 1978).

5.4 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT

5.4.1 Air

Disulfoton was detected at maximum and mean concentrations of 4.7 and 0.1 ng/m3 in only 1 of
123 ambient air samples collected from 10 locations in the United States in 1980 (Carey and Kutz

1985; Kutz 1983; Kutz and Carey 1986). No other air monitoring data were located.

5.4.2 Water

Disulfoton was detected in 7 groundwater samples from 28 California counties at a maximum of

6 ug/L from May 1979 to April 1984 (Cohen 1986; Hallberg 1989; Holden 1986). In an earlier
survey of 48 municipal and 6 private groundwater supply systems in California, no disulfoton was
detected at a minimum detection limit of 5 ug/L (Maddy et a1. 1982). Disulfoton was not detected
(detection limit of 1 ug/L) in over 1,508 samples from 358 groundwater wells in Wisconsin during
1980—1984 (Holden 1986; Krill and Sunzogni 1986). As of 1983, disulfoton was not detected
(detection limit not given) in three samples of groundwater from Suffolk County, New York (Holden
1986). Disulfoton was detected in a 1985 survey of groundwater in the Nomini Creek Watershed in
Virginia. The mean and maximum concentrations detected were 0.39 ppb and 2.87 ppb respectively.
The frequency of detection of disulfoton in this watershed was 2.6% (Mostaghimi et a1. 1993).
Disulfoton was qualitatively detected (detection limit of 0.1 pig/L) in three groundwater samples from

1 of 479 hazardous waste disposal sites in the United States (Plumb 1991).

DISU LFOTON 158

5. POTENTIAL FOR HUMAN EXPOSURE

Recently, levels of disulfoton in an agricultural watershed were monitored during a spring runoff event
in Shell Creek, an eastern tributary of the Platte River in Nebraska. The concentrations of disulfoton

in this agricultural watershed ranged from trace to 0.4 ug/L (Spalding and Snow 1989).

During 1981—1985, disulfoton and other pesticides were monitored at three watersheds adjacent to
agricultural production areas: the mouths of the Grand River, the Saugeen River, and the Thames
River, Ontario, Canada (Frank and Logan 1988). At a detection limit of <01 pg/L, no disulfoton was
detected in the river water samples. Disulfoton was also not detected (detection limit of 0.003 pg/L)
in samples of water collected from Lakes Superior and Huron, including Georgian Bay, in 1974

(Glooschenko et al. 1976).
5.4.3 Sediment and Soil

The primary method for the disposal of liquid pesticide wastes in California in the past has involved
soil evaporation pits, ditches, and ponds (Winterlin et al. 1989). A core soil sample taken from one
such pit in northern California contained 44 mg/kg disulfoton at a depth of 90 cm (Winterlin et al.
1989). Disulfoton was detected in six of seven bottom soil samples from tail water pits used to collect
irrigation runoff in Haskell County, Kansas, in 1974. The maximum and mean concentrations of
disulfoton in these samples were 32.7 and 13.42 pg/kg respectively (Kadoum and Mock 1978). At a
detection limit of 0.01 mg/kg, disulfoton was not detected in sediment samples collected from Lakes

Superior and Huron, including Georgian Bay, in 1974 (Glooschenko et al. 1976).
5.4.4 Other Environmental Media

Disulfoton was detected in 1 of 360 food composites collected from different locations in the United
States in fiscal year 1969. The positive sample was a composite of leafy vegetables collected from
Boston, Massachusetts, that contained 2 ug/kg of disulfoton (Comeliussen 1970). From this data, the
estimated daily adult human intake of disulfoton was <1 ug/day in 1969 (Duggan and Comeliussen
1972). During fiscal year 1976, the FDA identified disulfoton in one sample each of cereal
byproducts and leaf and stem vegetables, and in four samples of oilseed byproducts (Duggan et al.
1983). Disulfoton was also detected in one sample of whole grains for animal use and four
miscellaneous animal feed samples (Duggan et al. 1983). The FDA’s monitoring program for

domestic and imported food commodities during fiscal years l978~l982 detected disulfoton in

DISULFOTON 159

5. POTENTIAL FOR HUMAN EXPOSURE

unspecified foods at unspecified concentrations (Yess et a1. 1991). During 1982—1986, the FDA Los
Angeles District Laboratory analyzed 19,851 samples of domestic and imported food and feed
commodities (Luke et a1. 1988). Disulfoton sulfone was detected in 45 samples of 6,391 domestic
agricultural commodities and in 1 sample of 12,044 imported agricultural commodities at
concentrations ranging from 0.05—l.0 mg/kg. In domestic foods, disulfoton sulfone was detected in
broccoli, cabbage, Boston lettuce, butter lettuce, green leaf lettuce, iceberg lettuce, red leaf lettuce,
romaine lettuce, potatoes, and spinach; it was also detected in imported tomatillos (Hundley et a1.
1988). Disulfoton was not detected in 14,492 domestic and imported food samples analyzed as part of
the FDA pesticide monitoring program for 1986—1987 (FDA 1988). Disulfoton was not detected in
various domestic food commodities by state regulatory monitoring activities during fiscal year
1988—1989 (Minyard et al. 1991). In a pesticide residue screening program conducted in 1989—1991
in San Antonio, Texas, on 6,970 produce samples, disulfoton was detected (0.1 ppm detection limit) in
two produce samples (one sample of broccoli and one sample of cabbage) (Schattenburg and Hsu
1992). As part of the FDA’s Pesticide Monitoring Program for domestic and imported foods,
disulfoton residues have been detected in unspecified foods at unspecified concentrations during

1988—1989, 1989-1990, 1990—1991, and 1991—1992 (FDA 1990, 1991, 1992, 1993).

Processing raw food reduced disulfoton levels in some potato products (Kleinschmidt 1971). Total
residues were reduced by 35% with lye peeling. Lye peeling plus the first water blanching reduced
the total disulfoton residue on a dry weight basis by 58, 74 and 61% for french fries, dehydrated

potato cubes and dehydrated mashed potatoes, respectively.

In a study of pesticide residue contamination of processed milk-based and soy-based infant formula,
disulfoton was not detected (detection limit <0.02 pg/g [ppm]) (Gelardi and Mountford 1993). The
EPA Office of Water has recommended that disulfoton residues be monitored by states in their fish
and shellfish contaminant monitoring programs in watersheds where this pesticide is currently used
extensively in agriculture (EPA 1993a). While no fish or shellfish consumption advisories are
currentlyin effect for disulfoton, this contaminant has not been widely monitored in national fish
contaminant monitoring programs (e.g., the EPA National Study of Chemical Residues in Fish or the

US. Fish and Wildlife Service National Contaminant Biomonitoring Program) (EPA 1993a).

DISULFOTON 160

5. POTENTIAL FOR HUMAN EXPOSURE

5.5 GENERAL POPULATION AND OCCUPATIONAL EXPOSURE

The general population is exposed to disulfoton by inhaling air and ingesting drinking water and food
containing disulfoton. Toxicokinetic data show that disulfoton is readily and extensively absorbed by
the gastrointestinal tract (see Section 2.4). The urinary metabolites of disulfoton are DEP, DETP,
DEDPT, and DEPTh (see Section 2.3). Although the occurrence of these phosphate esters in human
urine may not result specifically from exposure to disulfoton, detection of these metabolites in human
urine indicates the possibility of exposure to disulfoton or several other organophosphate insecticides.
Specimens of urine collected at 64 locations across the United States, comprising the sample areas in
NHANES II, reported detection (detection limit 20 ug/L or ppb) of DEP and DETP at a frequency of
6—7% and DEDPT at a frequency of <1% of those tested (Murphy et al. 1983). Other than during
home and garden insecticide application, exposure of the general public to disulfoton from skin contact
with consumer products is not expected. Those among the general population who use the insecticide
for homes and gardens are potentially at higher risk of exposure to disulfoton. It has been estimated
that application to rose plants and other omamentals constitute by far the largest home and garden use

of disulfoton (Whitmore et al. 1992).

Disulfoton has been very infrequently detected in ambient air (0.8% of air samples from 10 cities) and
at very low concentrations (mean of 0.1 ng/m3 in detectable samples) (see Section 5.4.1). Therefore,
the exposure of the general population to disulfoton from inhaling ambient air is probably
insignificant. Disulfoton has never been detected in drinking water (see Section 5.4.2), possibly
because of it occurs at very low concentrations and has only infrequently been detected in groundwater
(Cohen 1986; Hailberg 1989; Holden 1986; Mostaghimi et a]. 1993; Plumb 1991). Therefore, general

population exposure to disulfoton from consumption of drinking water is negligible.

Disulfoton has been detected in some foods (see Section 5.4.4); thus, consumers can be exposed to
disulfoton by ingesting contaminated food. The FDA has estimated daily food intakes of disulfoton
for different age/sex groups in the United States for fiscal years 1982—1984 as follows:

6—11 months = 0.6; 2 years = 1.1; 14-16-year-old females = 0.4; 14—16-year-old males = 0.3;
25—30-year-old females = 0.3; 25—30—year-old males = 0.3; 60—65-year-old females = 0.5; and
60—65-year—old males: 0.6 (ng/kg body weight/day) (Gunderson 1988). The reported corresponding
values for combined disulfoton and its metabolites (e.g., sulfone, sulfoxide, etc.) are 2.2, 4.8, 2.3, 1.8,

2.4, 2.2, 2.9, and 3.0 (ng/kg body weight/day) (Gunderson 1988). The FDA reported the following

DISULFOTON 161

5. POTENTIAL FOR HUMAN EXPOSURE

dietary intakes of disulfoton for different age/sex groups in fiscal year 1990: 6—11 months, <0.1;
l4—l6-year-old males, 0.2; and 60—65-year—old females, 0.3 (ng/kg body weight/day) (FDA 1991,
Winter 1992; Yess 1991). Most recently, the FDA reported the following dietary intakes of disulfoton
(total) for different age/sex groups averaged over 1986—1991: 6—11 months, 0.1; 2 years, 0.3;
l4—16-year—old males, 0.2; 14—16-year—old females, 0.2; 25—30—year—old females, 0.4; 25—30-year-old
males, 0.3; 60—65-year—old females, 0.4; and 60—65-year-old males, 0.3 (ng/kg body weight/day) (FDA
1993). These 1982—1984, 1990, and 1986—1991 intakes estimated from the FDA Total Diet Study
Program show a declining trend in the estimated daily food intakes of disulfoton over the past

10 years. All of the FDA estimated daily food intakes for the various sex and age groups are more
than 1,000 times lower than the FAO/WHO Acceptable Daily Intake (ADI) value of 2,000 ng/kg body
weight/day and an EPA revised reference dose of 40 ng/kg body weight/day ((FAO/WHO 1991; FDA
1991, 1993; Winter 1992; Yess 1991).

Workers involved in the manufacture, formulation, handling, or application of disulfoton, or those
involved in the disposal of disulfoton—contaminated wastes are likely to be exposed to higher
concentrations by dermal contact and inhalation than the general population. When granular disulfoton
was applied at 0.75 active ingredient per acre to a field by air, the estimated inhalation exposure to
disulfoton was 0.02 mg/8-hour day for the pilot and 0.03 mg/8—hour day for the ground staff (Myram
and Forrest 1969). The estimated inhalation exposure to disulfoton for workers using ground machines

was 0.33 mg/8—hour day (Myram and Forrest 1969).

No information was found in the National Occupational Exposure Survey (NOES) conducted by
NIOSH from 1981 to 1983 on the number of workers and the number of facilities where workers
could be potentially exposed to disulfoton in the United States (NOES 1990). NIOSH (1992)
recommends that the exposure level to skin not exceed 0.1 mg/m3 for a 10—hour time weighted average

workday.
5.6 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES

Other than individuals who are occupationally exposed to disulfoton during its production, formulation,
packaging, distribution, use, or disposal, populations exposed to higher than background concentrations
of disulfoton in ambient air include those living near chemical manufacturing or processing sites,

individuals living on farms or in the vicinity of agricultural areas where disulfoton is extensively used,

DISULFOTON 162

5. POTENTIAL FOR HUMAN EXPOSURE

and individuals living near hazardous waste sites. Individuals living near these sites may also be
exposed to potentially higher concentrations of disulfoton or its metabolites in their drinking water if
they obtain tap water from wells near these sources. Children may receive higher disulfoton doses
from dermal exposures if they play on freshly treated soils. In addition, children may receive
potentially higher oral doses from ingestion of disulfoton contaminated soils from their hands while

playing in contaminated areas.
5.7 ADEQUACY OF THE DATABASE

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with
the Administrator of EPA and agencies and programs of the Public Health Service) to assess whether
adequate information on the health effects of disulfoton is available. Where adequate information is
not available, ATSDR, in conjunction with the NTP, is required to assure the initiation of a program
of research designed to determine the health effects (and techniques for developing methods to

determine such health effects) of disulfoton.

The following categories of possible data needs have been identified by a joint team of scientists from
ATSDR, NTP, and EPA. They are defined as substance—specific informational needs that if met would
reduce the uncertainties of human health assessment. This definition should not be interpreted to mean
that all data needs discussed in this section must be filled. In the future, the identified data needs will

be evaluated and prioritized, and a substance-specific research agenda will be proposed.
5.7.1 Identification of Data Needs

Physical and Chemical Properties. As seen in Table 3—2, the relevant physical and chemical
properties of disulfoton are known (Bowman and Sans 1983; Domine et al. 1992; HSDB 1994;
Kenaga and Goring 1980; Melnikov 1971', Merck 1989; Sanbom et al. 1977; Worthing 1987) and
K

predicting the environmental fate and transport of disulfoton based on K and H is possible.

OW’ OC’

Production, Import/Export, Use, Release, and Disposal. Knowledge of production and use
data for a chemical is important in predicting its potential for environmental contamination and human
exposure. Since disulfoton is produced by only one manufacturer (SRI 1994), to maintain

confidentiality, its recent production volume is not known. Similarly, data concerning the import and

DISU LFOTON 163

5. POTENTIAL FOR HUMAN EXPOSURE

export volumes for disulfoton in recent years are not available. Estimates of its yearly use in the
United States are available (Gianessi 1986; Gianessi and Puffer 1992; Goodrich et al.1991;
VonRumker et al. 1974). No information in the available literature was located that indicates
disulfoton’s use in any consumer products other than edible crops and vegetables during and after their
planting (EPA 1984b; VonRumker et al. 1974). Disulfoton enters the environment primarily during its
use as an agricultural insecticide/acaricide on a variety of field and vegetable crops and in its use in
home and garden applications. Disulfoton wastes have been disposed of in soil evaporation pits,
ditches, and ponds (Winterlin et al. 1989) and in hazardous waste sites. Thus, soils are most likely to
be contaminated with this pesticide. Although some information regarding the disposal of wastes
containing disulfoton is available (Berlow and Cunningham 1989; HSDB 1994; IRPTC 1985; Sittig
1980), more detailed information on the method used for the disposal of aqueous wastes would be
helpful. The standards promulgated by the EPA for the disposal of wastes containing disulfoton are

available (Berlow and Cunningham 1989).

According to the Emergency Planning and Community Right-to-Know Act of 1986, 42 U.S.C.
Section 11023, industries are required to submit chemical release and off-site transfer information to
the EPA. The Toxics Release Inventory (TRI), which contains this information for 1988~1992,
became available in May of 1994. This database will be updated yearly and should provide a list of
industrial facilities and emissions. However, no TRI data were located for disulfoton because this

chemical is not required to be reported by chemical producers (EPA 1993b).

Environmental Fate. Information regarding the fate of disulfoton in the air was not located in the
literature. Although the available data indicate that the concentration of disulfoton in air will be low
(Carey and Kutz 1985), more information would help predict the distance of its aerial transport. The
fate of disulfoton in water is better studied (Wanner et al. 1989). Although it has been estimated that
sorption onto particulates and settling into the sediment may not be important for disulfoton in Rhine
River water, more information regarding the relative importance of sorption for disulfoton’s removal
from water to sediment would be helpful (Wanner et al. 1989). There is conflicting evidence in the
literature (Harris 1969; Helling et al. 1974; King and McCarty 1968; McCarty and King 1966)
regarding disulfoton’s mobility in soil. Disulfoton is degraded in soil by hydrolysis, photoinduced
oxidation, and biodegradation (Bhaskaran et al.1973; Capel et al. 1988; Chapman et al. 1993, 1994b;
Gohre and Miller 1986; Hebert and Miller 1990; Miller et al. 1989; Tomizawa 1975; Wanner at al.

DlSU LFOTON 164

5. POTENTIAL FOR HUMAN EXPOSURE

1989). Additional information on degradation of disulfoton in water and air and the fate of the

degradation products in soil would be helpful.

Bloavailability from Environmental Media. Available information regarding the rate of
disulfoton absorption following inhalation, oral, or dermal contact has been discussed in the
Toxicokinetics section (see Section 2.3). Although no data on disulfoton’s bioavailability from
contaminated air are available, the bioavailability from inhalation exposure is expected to be high
because disulfoton is likely to be present in the vapor phase (Eisenreich et al. 1981) and not in the
particulate phase in the adsorbed state. Similarly, no data on the bioavailability of disulfoton from
water and soil or plant material are available; however, disulfoton adsorbs rather strongly to soil
(Harris 1969; Helling et al. 1974; Wauchope et al. 1992). Since the part that remains adsorbed to soil
or sediments may, at most, be partially bioavailable, disulfoton is expected to have reduced
bioavailability from soil and water. Data on the bioavailability of disulfoton from actual

environmental media need further development.

Food Chain Bioaccumulation. Disulfoton bioconcentrates to a moderate extent in fish (Takase
and Oyama 1985; Tomizawa 1980); however, measured bioconcentration factor (BCF) values are not
available for a large number of edible invertebrate and fish species. EPA (1993a) has recently
recommended that states monitor disulfoton in fish and shellfish in watersheds where it is extensively
used, and additional information on disulfoton residues may be available in the future. There is also a
lack of data in the literature regarding the biomagnification potential of disulfoton through aquatic
food chains. Available data on terrestrial food chains indicate that disulfoton is translocated from the
root to aerial parts of the plants, where it is quickly metabolized to sulfone and sulfoxide (Nash 1974;
Szeto et al. 1983a, 1983b). Data regarding the biomagnification potential of disulfoton in terrestrial
and aquatic food chains would be desirable. These data would be helpful in assessing the potential for

human exposure as a result of ingestion of contaminated food.

Exposure Levels in Environmental Media. Although some data on the levels of disulfoton in
ambient air are available (Carey and Kutz 1985), these data are neither current nor general enough to
estimate inhalation exposure to disulfoton for the general population in the United States. No data on
the level of disulfoton in drinking water were located in the literature, although disulfoton has been
detected in groundwater (Cohen 1986; Hallberg 1989; Holden 1986; Mostaghimi et al. 1993). More

recent data regarding the levels of disulfoton in ambient air, in drinking water, and in soil are needed.

DISULFOTON 165

5. POTENTIAL FOR HUMAN EXPOSURE

Data on disulfoton levels in food and recent estimates of human intake of disulfoton from foods are
available (Duggan et a1. 1983; FDA 1990, 1991, 1992, 1993; Gelardi and Mountford 1993; Gunderson
1988; Luke et a1. 1988; Schattenburg and Hsu 1992; Yess 1991).

Reliable monitoring data for the levels of disulfoton in contaminated media at hazardous waste sites
are needed so that the information obtained on levels of disulfoton in the environment can be used in
combination with the known body burden of disulfoton to assess the potential risk of adverse health

effects in populations living in the vicinity of hazardous waste sites.

Exposure Levels in Humans. No data on disulfoton levels in various human tissues and body
fluids of a control population, populations near hazardous waste sites, or occupationally exposed
groups in the United States are available. The levels of disulfoton metabolites (DEP [0.05 ppm],
DETP [0.04 ppm], DEPTh [0.008 ppm], dimethyl phosphate [0.04 ppm], dimethyl thiophosphate
[0.180 ppm], and dimethyl phosphorothiolate [0.004 ppm]) in the urine of disulfoton forrnulators have
been measured (Brokopp et a1. 1981). Data on the levels of disulfoton and its metabolites in body

tissues and fluids are needed to estimate the extent of exposure to disulfoton.

This information is necessary for assessing the need to conduct health studies on these populations.

Exposure Registries. No exposure registries for disulfoton were located. This substance is not
currently one of the compounds for which a subregistry has been established in the National Exposure
Registry. The substance will be considered in the future when chemical selection is made for
subregistries to be established. The information that is amassed in the National Exposure Registry
facilitates the epidemiological research needed to assess adverse health outcomes that may be related

to exposure to this substance.

5.7.2 Ongoing Studies

A search of federal research programs in progress indicates a few projects that would fill some of the
existing data gaps. Drs. Singmaster and Acin-Diaz of the University of Puerto Rico are developing
methods for determining disulfoton residue levels in food commodities and for disulfoton disposal.
Dr. Brady of the University of Georgia is conducting a study to determine disulfoton’s dissipation on

peach fruit, on foliage, in soil, in tank mixes, and in building interiors.

DI SULFOTON 167

6. ANALYTICAL METHODS

The purpose of this chapter is to describe the analytical methods that are available for detecting, and/or
measuring, and/or monitoring disulfoton, its metabolites, and other biomarkers of exposure and effect
to disulfoton. The intent is not to provide an exhaustive list of analytical methods. Rather, the
intention is to identify well-established methods that are used as the standard methods of analysis.
Many of the analytical methods used for environmental samples are the methods approved by federal
agencies and organizations such as EPA and the National Institute for Occupational Safety and Health
(NIOSH). Other methods presented in this chapter are those that are approved by groups such as the
Association of Official Analytical Chemists (AOAC) and the American Public Health Association
(APHA). Additionally, analytical methods are included that modify previously used methods to obtain

lower detection limits, and/or to improve accuracy and precision.

6.1 BIOLOGICAL SAMPLES

Several methods are available for analyzing disulfoton in biological media; some of the commonly
used methods are reported in Table 6-1. A variety of detectors may be used for the gas
chromatographic analysis of disulfoton, but flame photometric detectors are superior because of low
background interference and good reproducibility (Holstege et al. 1991). Mass spectrometric detectors
show high specificity (Kawasaki et a1. 1992) and may also be used to confirm detection by other

methods.

The stability of disulfoton must be considered at all stages of sample storage and analysis.
Organophosphorus insecticides, including disulfoton, react with natural esterases in human tissue and
may reduce the level of free organophosphates (Singh et al. 1986). Besides the esterases,
phosphorylphosphatase in natural tissue hydrolyzes and inactivates organophosphorus compounds
(Singh et a1. 1986). As a result, the amount of organophosphates in blood and excreted in urine will
be considerably less than the amount expected from its concentration at the time of exposure (Hattori

et al. 1982; Singh et al. 1986).

As discussed in Section 2.5.1, the detection of certain thiophosphate esters in human urine may

indicate exposure to disulfoton and/or other organophosphate insecticides. Several methods are

168

9:02:05 :2 858.3 n s=w 5659.8me 39: u ms. E05028 05.2585. 95: u can. ScaSmoEEoEo man u 00

EC: coonoU EEwEEfiEu

DISULFOTON

6. ANALYTICAL METHODS

 

QEEoEom c. :o=:_omm_u

 

Nae ”cozmzcoocoo 6:88; 53> cozomzxm
._m «m roam: canon Emu 02 22.9 mgoo §5E2wom 53> maEmm *0 coszEmmoEoI 9E: van 82m
EaemofiEoEo 5:28 32:39?
>9 cozmcozomt 68:35:th E2398 m: ucm :22.sz
ommw msfiuo 53> cozmgxo $5 imam—hm ScamaofiEoEo EoEoo 5.95%
._m «m IEmm> mo 7:: Emu oz un...._n_\o_® Emaamo .528 >2 5:98:85 6::8 o\o~ 53> .5525 new 6:5 602m
22QO $50 53> cozomzxm
82 88.8 9v 52.9 5263580 .E In 2 Emeuaum ass 3.8 88:33
._m «m cme Amara m7 Emu 02 $5506 >5in ”988m 35¢ 53> cozugxw umEmmE 95: new «.5me
cogzcwocoo Eco
59 93a: SiSmoEEoEo :EBoo >2 nsémflo 88:33; :95:
._m 6 $220: 878 8:3 01500 Em=amo 62.620 wcm_>5mE-_ocm5wE 53> :28me can 52. 9.30m
$3292 .92
Enemofieeco cano >9 a: mm w2__onSwE m
82 393 .53? ”Bow 2389390205 53> coszxo ucm c20=3m§
was 5558 E «9.31 w 09:00 55 cozgcmocoo €585.20 53> cozomzxm 80m. 260
oozeflwm 2989 =E= uo5mE _mo=>_mc< uo5mE 8:96an xEmE macaw
5599... 8:023
waEmw

 

moaeum _8_mo_o_m 5 58:35 mcEEEmo .8 $5522 .8_§_m=< .E m._m<>

DISULFOTON 169

6. ANALYTICAL METHODS

available for the quantitation of organophosphorus metabolites from urine (Bradway et al. 1981;

Daughton et al. 1976; Lores and Bradway 1977; Shafik et al. 1973).

6.2 ENVIRONMENTAL SAMPLES

Analytical methods for determining disulfoton in environmental samples are reported in Table 6-2.
The steps included in the methods are solvent extraction, purification and fractionation, and gas
chromatographic analysis. Other analytical techniques, including capillary gas chromatography with
mass selective detection (Stan 1989), high-perfonnance liquid chromatography with either mass
spectrometric (MS) or MS—MS detection (Betowski and Jones 1988), have been used to determine

disulfoton in environmental samples.

Precautions should be taken to avoid disulfoton loss from stored water, soil, sediment, crop, and
vegetable samples (Belisle and Swineford 1988; Miller et al. 1981; Munch and Frebis 1992; Szeto and
Brown 1982). Disulfoton, disulfoton sulfone, and disulfoton sulfoxide were not recovered from spiked
well water stored 14 days; however, sample extracts were stable for 14 days (84—92% recovery)
(Munch and Frebis 1992). In most environmental samples, disulfoton will be present along with its
environmental transformation products, disulfoton sulfone, disulfoton sulfoxide, disulfoton oxon,
disulfoton oxon sulfone, and disulfoton oxon sulfoxide (Szeto and Brown 1982). Disulfoton and its
oxon are very unstable, and they oxidize rapidly to the corresponding sulfoxides. The sulfoxides are
relatively stable, but they oxidize slowly to their sulfones, which are most stable (Szeto and Brown
1982). Several methods for determining the metabolites of disulfoton in environmental samples are

included in Table 6-2.

Few methods were located for determination of disulfoton in air. Ambient air monitoring data were
reported for samples collected by ethylene glycol impinger samplers with subsequent gas
chromatographic analysis; however, no performance data were reported (Kutz et al. 1976). A method
for determination of organophosphorus pesticides, including disulfoton, in workplace air involves
collection using a combined filter/XAD-2 sorbent sampler and gas chromatography/flame photometric
(FPD) detection (Kennedy et al. 1994). Recovery is very good (>90%) and samples are stable for 30

days when stored cold.

170

DISULFOTON

6. ANALYTICAL METHODS

mwmw
v.2mc_5m new w_m__wm

omamw <mw

mew ._m «m .655—

87mm 93:. tom

Emu 02 <9. mm

E 222322 <9. No

mambo 55:.qu

cE:_oo 00 vcoowm
9.6: cozmctzcoo
.2500 55:58

Dan—“<00

83m 859..

cozmzcwocoo

66:3 5568 96.355
296.5 388... ”$2.25
3255653295 55 cozomzxm

AB? 8522.
25.28 mam 8ch 0&0 mEm:
3-536 8:058 u_m>oEm. 2528

62.25. 9.2559: 5:5 cozogxm

8.55m. = 5535065850
cE:_oo 5n azémflo

62.25. 2255?: 5:5 cozom5xm

8.53. = 5555085020
.528 .3 95:88

.5558

hwwmz wand;

.muflg wad;

 

~82 Em mm £22323 .31 No Em. cacao ”8:25 20559.. 5; 858.5 853285
82.8.33 33% 326.3331 8.0 .26 5:5
82: 8:233 37% 88:8. <9. Qm :8 852: Em. .5. 559.. o. wmcmcoxo .528
Em .82 ._m 6 =mmum 222523 373 5.0.2523 <9. no 9.2.00 22:80 ”8:26 82556:. 5.; 8.895 as; 9.55.0
mam F cozomzxm
mBEEmI ucm 29:58 9 Two <9. oww 9.250 29:30 mam .od 2 In .0 EmEumaEx .055
82 ._m a 289:8 3 <9. to 09.50 9.9.2 5.; 8895-922 .235
5.058me
28655550 cozmzcwocoo
83 9:50 ucm 995N 3 do: wod 5:28 6:0 ”55¢ E8658 5.5 cozomzxm .935
cozmnzog 658m 65:82..
wucaanoo .o 8:62. ”www.m«mmc__o:o-_bmom
mc_c_mEoo-.2_:m €02qu mcEwEom 9.38 83:58.: 55> 8:335
82 9.58 new. 99$ 09% oz .2 5% «5015.0 22.. 2.85.28 .22., 8:85 .o 8:62 .235
5528 5:5 8.3.0me
32 ._m a 585.3. 3-5 55.9. 8.0 8.50 5.2.98 €38 N-o<x..2__. :0 8.52.8 .a 823.25
wocm.w.wm 5.98m. 5.8.9“. 5...: 850E _mo_S_mc< 859.. 85982.". 5.5:. wEEmm

8:092. 2953

 

mmEEum .mucoficogém E c20==m5 mc_:_E._3wo .8 moo—tos— _mu=>_mc< .Né m4m<._.

171

6. ANALYTICAL METHODS

EasmoEEELo
5:28 E 98:85 8.5
95 c2983. Eo=m.Emocoo

u_ocm5mE-::£o._oEo 5:5 $53

mm? ._m a $628 878 93:. 3.0.56 mambo 8358 8.306 28: 889cm. 8038

EQSQOEoEo mason

cE:_oo ucm 52:3 23E. 8% new

.23: >9 91..on 6:865: 5? 5822225

mg? ._m «w _v_o< mnlmm 931 ad 09:00 $368 85258 yo cozowzxw .5355 62m
69wa 6 cozmzcmocoo

60:28 3:25 £208 839%?

5:5 :02th 6.55868 5:5 van

52 ._m 8 8: E 23E mod @266 5:58 22.3 855852 6 c2625 £5: 59".

mumcmmcmctwa E2898 53>
cosmExo flow ococamozaocto

-mucoEo EonEEm «o .5526 302

mm? c2693 3 wEwEaa 8 852985 83805 new

89222 was 55:05 87mm 33E No.0 25656550 5:028 game; 53, cozomzxm 390 maocm>

3:23.

EquQmEoEo c628 B .92 mm

azémflo 6.0m o_oNcwEmaeoEo.E 82.899: m

89 5:5 36:8 2689 8% can c2235

398 9.6 cmEiom om 09.31 F QnEOG ”watoEo 9.25.9: 55> cozombxw x=E 260
Emcmmcmctwa

E2388 >9 3:823 :98
van 258:3 mcEfiEoo c058:

 

AmeonflwE *o cozmgxo ScafimofiEeco 8mm:

98 c20==m6 5:28 >2 9.7.820 msmflwawm

mm? 5505 can 23m .0: or 70mm SEE Ed 09:00 ”2908 35¢ 53> cozogxm. .__o.w
8:232; 2989 Emewm =E= 859: $2592 859: 55932.”. xEmE 2928

c2823 wEEmw

 

DISULFOTON

€352.03 moEEmw .mucoEco.._>:m :_ coup—Ema mEEEouoa .2 moor—no: 30:22.2 .Né m._m<._.

172

DISULFOTON

6. ANALYTICAL METHODS

00300 00:00:08 00050 0:00 u mam ”00200000 030500020
-c0m0Ec u oaz SESQOEoEo 000 02020000 :9: n 00m: 35005908050 00:00E000 _0m n 0&0 320062000030 03 n 00 ”00200000
0E0E0~oca 080: n on“. Soc0m< 02000005 _m~c0Ec0._>cm n <mm 628200 0.3000 cobo0_w u 00w 5200000 00.6502 0E0: __0x_0 n QE<

:8: 00200000 .0E0Eazmso
02800: .6 02:80 “02:2:sz m_ «00F
09953 :0 00 0E30> :00: 000000 53 AmEBE :E: 00200000 00508 £8: 00300000 _0«c0E:.=0:_u

 

 

30052020050
0800 Em 8% Ea 000 E 03.3%
mm? 960.5000 900 02 SEE 5.0 32:08 .030 ”000x0c.\0c9000 £5, cozomzxm 00% :0:
00cmcox0
3000:0005000090 can. 0:0 0.0306 E0200 ”00:0:000000 ”0_E_:8000
50— ._0 «0 =0: :00 0F Twn 33E to 205000 .030 5.3 00:00:06 ”:0=0~_c0moEoI 00:09n_
080.0000”. E0300; E0001 ._E__ uoEmE .00_§_mc< 00508 00:932.". 5308 0.0E0w

5:0900 0_0E0w

 

Auozczcoov 00.083 _0~:0Ecoh_>:m E 5.8.305 mEEEhfloo .8 000505. 30:20.2 .Né m._m<.r

DISULFOTON 173

6. ANALYTICAL METHODS

Overall recoveries are good (>80%) and detection limits are in the low to sub-parts-per-billion (ppb)
range for detennination of disulfoton in water (Borburgh and Hammers 1992; Bourgeois et al. 1993;
EPA 1986a, 1988c). Methods for soil and sediment also provide good recovery (>80%) and detection
limits are in the ppb range (Belisle and Swineford 1988; Szeto and Brown 1982). Methods for
determination of disulfoton in food matrices generally provide acceptable recovery (275%) and

detection limits in ppb range (Hsu et al. 1991; Liao et a1. 1991; Szeto and Brown 1982).

6.3 ADEQUACY OF THE DATABASE

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with
the Administrator of EPA and agencies and programs of the Public Health Service) to assess whether
adequate information on the health effects of disulfoton is available. Where adequate information is
not available, ATSDR, in conjunction with the NTP, is required to assure the initiation of a program
of research designed to determine the health effects (and techniques for developing methods to

determine such health effects) of disulfoton.

The following categories of possible data needs have been identified by a joint team of scientists from
ATSDR, NTP, and EPA. They are defined as substance—specific informational needs that if met would
reduce the uncertainties of human health assessment. This definition should not be interpreted to mean
that all data needs discussed in this section must be filled. In the future, the identified data needs will

be evaluated and prioritized, and a substance-specific research agenda will be proposed.

6.3.1 Identification of Data Needs

Methods for Determining Biomarkers of Exposure and Effect. Analytical methods are
available to determine the concentrations of disulfoton and its metabolites in blood, urine, and other
'body tissue and fluids (Bowman and Beroza 1969; Brokopp et a1. 1981; Hattori et a1. 1982; Holstege
et a1. 1991; Singh et al. 1986', Yashiki 'et a1. 1990). The accuracy of the methods in terms of percent
recovery has been determined. A reasonably low detection limit can be obtained when flame
photometric detection is used to determine disulfoton (Bowman and Beroza 1969; Holstege et a1.
1991). When blood samples were spiked with 0.3 pg/g (ppm) of disulfoton, phosphorodithioate
sulfone, and phosphorothiolate sulfone, and quantitated by gas-chromatography-flame photometric

detection (GC/FPD) method, the recovery of disulfoton and two of its metabolites were in the range of

DISULFOTON 174

6. ANALYTICAL METHODS

101.0—104.6% (Yashiki et al. 1990). In spiked urine samples, the detection limits of four metabolites
of disulfoton (DEP, DETP, DEDPT, and DEPTh) were 0.01 ppm by a GC/FPD method (Brokopp et
al. 1983). Due to the unavailability of data regarding disulfoton concentrations in tissues and body
fluids of the background population, it is not known if the available analytical methods will be
sensitive enough to determine these concentrations. Analytical methods are available for the detection
of 4-hydroxy—3-methoxymandelic (HMMA), the major metabolite of catecholamine metabolism and a
possible biomarker to characterize effects by disulfoton (Wysocka—Paruszewska 1971). It would be
helpful to determine if the available analytical methods can measure disulfoton levels in body tissues
and fluids of the background population. This will permit assessment of the severity of exposure of a

highly exposed population.

Methods for Determining Parent Compounds and Degradation Products in
Environmental Media. Several methods are available for determining disulfoton and its
degradation products in environmental samples such as contaminated water, food, and soil (Edgell et
a1. 1991; EPA 19880; Grant et al. 1969; Ruzicka et a]. 1968; Szeto and Brown 1982; Zweig and
Devine 1969). The specificity and accuracy of the methods are generally well established (see
Table 6-2). In spiked water samples, the mean recoveries of disulfoton, disulfoton sulfone, and
disulfoton sulfoxide were in the range of 86.5—104.0% (Edgell et a]. 1991). The recoveries of
disulfoton and its metabolites in soil and asparagus tissue ranged from 83.5% to 110% (Szeto and
Brown 1982). Consumption of contaminated food is probably the most important route of disulfoton
exposure for the general population. Disulfoton has been found at much lower concentrations than the
ADI value (Winter 1992; Yess 1991). Developing sensitive methods for determining disulfoton in
ambient air and for establishing background levels of disulfoton in environmental samples would be

desirable.
6.3.2 Ongoing Studies

Drs. Singmaster and Acin-Diaz of the University of Puerto Rico are developing methods for
determining disulfoton residue levels in food commodities. No other ongoing studies regarding the
determination of disulfoton and its metabolite and degradation products in biological or environmental

media were found.

DISULFOTON 175

7. REGULATIONS AND ADVISORIES

International, national, and state regulations and guidelines for disulfoton are listed in Table 7-1.

An acute-duration inhalation MRL for disulfoton of 0.006 mg/m3 was derived. The MRL is based on
a NOAEL of 0.5 mg/m3 for lethargy and decreased cholinesterase activity in rats exposed for

4 hours/day, 5 days/week (Thyssen 1978).

An intermediate—duration inhalation MRL for disulfoton of 2x10‘4 mg/m3 was derived. The MRL is
based on a NOAEL of 0.02 mg/m3 for decreased cholinesterase activity in rats exposed for

6 hours/day, 5 days/week for 3 weeks (Thyssen 1980).

An acute-duration oral MRL for disulfoton of 0.001 mg/kg/day was derived. The MRL is based on a
NOAEL value of 0.1 mg/kg/day for decreased cholinesterase activity in rats treated by gavage on
gestation days 6-15 (Lamb and Hixson 1983).

An intermediate-duration oral MRL for disulfoton of 9x10'5 mg/kg/day was derived. The MRL is
based on a NOAEL value of 0.009 mg/kg/day for decreased cholinesterase activity in rat pups in a

multigeneration feeding study in rats (Hixson and Hathaway 1986).

A chronic-duration oral MRL for disulfoton of 6x10‘5 mg/kg/day was derived. The MRL is based on a
LOAEL value of 0.06 mg/kg/day for decreased cholinesterase activity in female rats in a chronic

feeding study (Hayes 1985).

EPA has verified a chronic oral reference dose (RfD) for disulfoton of 4x10‘5 mg/kg/day (IRIS 1994).
The RfD is based on the LOAEL of 0.04 mg/kg/day for cholinesterase inhibition in rats treated with
disulfoton in the diet for 2 years (Hayes 1985).

The chronic-duration oral MRL for disulfoton is 6x10‘5 mg/kg/day, and the EPA chronic oral RfD is
4x105 mg/kg/day (IRIS 1994). Both of these values are based on the same study (Hayes 1985) and
the identical end point. Even though the MRL and the RfD are essentially the same, they have minor
differences due to the manner in which the exposure doses were calculated. The LOAEL of

0.04 mg/kg/day used by EPA was calculated by multiplying the analytical dietary concentration of

DISULFOTON 176

7. REGULATIONS AND ADVISORIES

0.8 ppm (nominal concentration of 1 ppm) by the reference rat food consumption factor of 0.05.
However, Hayes (1985) provided an equivalent dose of 0.08 mg/kg/day for the nominal concentration
of 1 ppm, based on actual food consumption and body weight data. The LOAEL of 0.06 mg/kg/day
used in deriving the chronic oral MRL was obtained by multiplying the 0.08 mg/kg/day dose,

corresponding to the nominal concentration of 1 ppm, by the analytical concentration of 0.8 ppm.

Disulfoton is on the list of chemicals appearing in "The Emergency Planning and Community Right-
to-Know Act of 1986" (EPCRA) (EPA 1988d). Section 313 of Title III of EPCRA requires owners
and operators of certain facilities that manufacture, import, process, or otherwise use the chemicals on

this list to report annually their release of those chemicals to any environmental media.

An Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for
disulfoton does not exist. A US. Court of Appeals decision rescinded the 1989 PELs promulgated by
OSHA (OSHA 1989), which included a PEL for disulfoton. Only PELs in place prior to the 1989 are
now allowed. Disulfoton had no PEL prior to 1989; therefore, it currently has no PEL.

Disulfoton is regulated by the Clean Water Effluent Guidelines as state in Title 40, Sections 400-475,
of the Code of Federal Regulations. The point source category for which disulfoton has a specific

Regulatory Limitation is the organic pesticide chemicals industry (EPA 1978a).

Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), disulfoton is classified for
restrictive use (EPA 1978b).

Under the Resource Conservation and Recovery Act (RCRA), disulfoton is listed as a hazardous waste
when it is a discarded commercial chemical product, off-specification species (e.g., a product that does

not meet purity or property specifications), container residue, and spill residue (EPA 19800).

DISULFOTON

7. REGULATIONS AND ADVISORIES

177

Table 7-1. Regulations and Guidelines Applicable to Disultoton

 

 

Agency Description Information References
INTERNATIONAL
WHO ADI 0.002 mg/kg WHO 1976
Temporary ADI established at 0.001 mg/kg
Guidelines in specific foods:
Alfalfa (hay, clover (hay) 10 mg/kg
Forage crops (green) 5 mg/kg
Vegetables including beans, broccoli, brussel
sprouts. cabbage, cauliflower, celery, lettuce, maize.
potatoes. peanut shells. peas (including pods), rice
(in husk). spinich, sugar beets (roots). tomatoes
Raw grain (except rice and maize) 0.5 mg/kg
Coffee beans, pecans, peanuts (kernels), pineapple, 0.2 mg/kg
soybeans
0.1 mg/kg
NATIONAL
Regulations:
a. Water
EPA OWRS Priority pollutants regulated in pesticide active Yes 40 CFR 455
ingredient manufacturing wastewater EPA 1992a
Priority pollutant effluent limitation for BAT and PSES Yes
Maximum for any 1 day 7.33x10‘3 kg/kkga
Monthly average shall not exceed 3.79x10'3 kg/kkg
Priority pollutant effluent limitation for NSPS and PSNS
Maximum for any 1 day 5.28x10'3 kg/kkg
Monthly average shall not exceed 2.72x10'3 kg/kkg
EPA OW App. D - NPDES Permit Application Testing Yes 40 CFR 122
Requirement. Table V: Toxic and Hazardous EPA 1983
Substances
Form 2D - NPDES Permits Yes 40 CFR 122
EPA 1983
Form 20 - Criteria and Standards for NPDES Yes 40 CFR 125
EPA 1989a
Guidelines for Testing Pollutants Under CWA Yes 40 CFR 136.3
EPA 1973
Substances Prohibited from Underground Injection Yes 40 CFR 148
Control EPA 1989a
Calculating Effluent Limits for Organic Pesticides Yes 40 CFR 455.20
EPA 1978a
Test Methods for Pesticides Yes 40 CFR 455.50
EPA 1992b
b. Other:
EPA OERR Reportable Quantity 1 pound 40 CFR 117.3
EPA 1985
App. 8 - Extremely Hazardous Substance TPQ 500 pounds 40 CFR 855
EPA 1987a
EPA OPP Intent to Cancel or Restrict Registration of Pesticide No
Products Containing Disultoton
EPA OPTS Pesticides Classified for Restrictive Use Yes 40 CFR 152.175

EPA 1978b

DISULFOTON

7. REGULATIONS AND ADVISORIES

178

Table 7-1. Regulations and GuidelinesApplicable to Disulfoton (continued)

 

 

Agency Description Information References
NATIONAL (cont.)
LDR for Newly identified and Listed Hazardous Wastes Yes 58 FR 48092
and Hazardous Soil EPA 1993
EPA OSW Designation of Hazardous Substance Yes 40 CFR 116.4
EPA 1978c
Listing as Hazardous Waste: Discarded commercial Yes 40 CFR 261.33
chemical products oft-specification species, container EPA 1980b
residues. and spill residues thereof
App. Vlll - Listing as Hazardous Waste Constituent Yes 40 CFR 261
EPA 19888
App. II - List of Hazardous and Organic Constituents Yes 40 CFR 258
EPA 1991
Hazardous Wastes from Specific Sources Yes 40 CFR 261.32
EPA 1981c
App. IX - Hazardous Wastes Excluded from Non- 3.34 ppm 40 CFR 261
specific Sources EPA 1984c
App. IX - Groundwater Monitoring List Yes 40 CFR 264
EPA 1987b
LDR - Identification of Waste to be Evaluated by Yes 40 CFR 268.10
August 8. 1988 EPA 1986b
LDR - Treatment Standards Expressed as Waste P039 = 0.017 40 CFR 268.43
Concentrations mg/L (ww) EPA 1988b
P039 = 0.1 mg/kg
(nonww)
K037 = 0.025
m9/1- (WW)
K037 = 0.1 mg/kg
(nonww)
Reportable Quantity 1 lb. 40 CFR 302.4
EPA 1989d
Guidelines:
a. Air
ACGIH TLV TWA 0.1 mg/m3 ACGIH 1994
NIOSH REL TWA 0. 1 mg/m3 (skin) NIOSH 1992
b. Water
EPA ODW One-day health advisory (10 kg child) 0.01 mg/L EPA 1994
10-day health advisory (10 kg child) 0.01 mg/L
Longer-term health advisory (10 kg child) 0.003 mg/L
Longer-term health advisory (adult) 0.009 mg/L
DWEL 0.001 mg/L
Lifetime health advisory (adult) 0.0003 mg/L
c. Other
EPA RtD (oral) 4x10'5 mg/kg/day IRIS 1994

DISULFOTON

179

7. REGULATIONS AND ADVISORIES

Table 7-1. Regulations and Guidelines Applicable to Disulfoton (continued)

 

 

Agency Description Information References
STATE
Regulations and
Guidelines:
a. Air:
Acceptable ambient air concentrations NATlCH 1992
CT 8 hr avg. time 2 pg/m3
FL- Pinella 8 hr avg. time 1 ug/m3
FL—Pinellab 24 hr avg. time 2.:10x10'1 pg/m3
ND 8 hr avg. time 1x10‘3 mg/m3
NV 8 hr avg. time 2x10‘3 mg/m3
TX 30 min avg. time 1 pg/m3
TX Annual avg. time 1x10‘1 pig/m:3
VA 24 hr avg. time 1.7 ug/ma
WA~SWEST 24 hr avg. time 3x10" pg/ma
Air toxics emissions inventory data
MO 1.45 mT/year
(state-wide)
b. Water:
Drinking Water Guidelines FSTRAC 1990
A2 0.3 ug/L
ME 0.3 ug/L
MN 0.3 [lg/L
RI 0.3 ug/L
VT 0.3 pg/L
Water Quality Criteria: Human Health CELDs 1994
NY No detect
Groundwater Quality Standards CELDs 1994
NY No detect
Groundwater Quality Monitoring Parameters CELDs 1994
AL Yes
CO Yes

DISULFOTON 180

7. REGULATIONS AND ADVISORIES

Table 7-1. Regulations and Guidelines Applicable to DIsquoton (continued)

 

Agency Description Information References

 

STATE (Cont)

CA Yes
IL Yes
KY Yes
MN Yes
OH Yes
SC Yes
TN Yes
VA Yes
WV Yes
WI Yes
Hazardous Waste Constituents CELDs 1994
AL Yes
CA Yes
CO Yes
|L Yes
KY Yes
LA Yes
MD Yes
MN Yes
MT Yes
NE Yes
NH Yes
NJ Yes
NY Yes
ND Yes
OH Yes
SC Yes
SD Yes
VA Yes
VT Yes
WI Yes
WV Yes
WY Yes

DISU LFOTON 181

7. REGULATIONS AND ADVISORIES

Table 7-1. Regulations and Guidelines Applicable to Dlsulfoton (continued)

 

Agency Description Information References

 

STATE (Cont)

Maximum Leachable Concentration CELDs 1994
TX 0.1 mg/L

Restricted Pesticides CELDs 1994
AL Yes
CA Yes
FL Yes
ME Yes
MI Yes
on All formulations

>2°/o

WA Yes

 

aEPA limits at facility’s effluent to contain the designated kilograms of the sum of all organic pesticide active ingredients (listed in
40 CFR 455.20(b) which includes disulfoton) per 1000 kg of the sum of all active ingredients manufactured at a facility.

ACGIH = American Conference of Governmental and Industrial Hygienists; ADI = Acceptable Daily Intake; BAT = Available
Technology; CELDs = Computer-aided Environmental Legislative Data System; DWEL = Drinking Water Exposure Level;

EPA = Environmental Protection Agency; FSTRAC = Federal-State Toxicology and Regulatory Alliance Committee; mT = metric
ton; NATICH = National Air Toxics Clearinghouse; NIOSH = National institute of Occupational Safety and Health; NSPS = New
Source Performance Standards; ODW = Office of Drinking Water; OERR = Office of Emergency and Remedial Response;

OPP = Office of Pesticide Programs; OSHA = Occupational Safety and Health Administration; OSW = Office of Solid Waste;
OWRS = Office of Water Regulations and Standards; PEL = Permissible Exposure Limit; PSNS = Pretreatment Standards for
New Sources; REL = Recommended Exposure Level; RfD = Reference Dose; TLV = Threshold Limit Value; TPO = Threshold
Planning Quantity; TWA = Time- Weighted Average; WHO = World Health Organization

DISULFOTON 183

8. REFERENCES

*ACGIH. 1994. 1993-1994 Threshold limit values for chemical substances and physical agents and
biological exposure indices. American Conference of Governmental and Industrial Hygienists.
Cincinnati, OH, 20.

_*Aoki Y, Takeda M, Uchiyama M. 1975. Comparative study of methods for the extraction of eleven
organophosphorus pesticide residues in rice. J Assoc Off Anal Chem 58:1286-1293.

*Atkinson R. 1988. Estimation of gas-phase hydroxyl radical rate constants for organic chemicals.
Environ Toxicol Chem 72435—442.

*ATSDR. 1989. Decision guide for identifying substance-specific data needs related to toxicological
profiles. Agency for Toxic Substances and Disease Registry, Atlanta, GA.

Balcomb R, Stevens R, Bowen C. 1984. Toxicity of 16 granular insecticides to wild-caught
songbirds. Bull Environ Contam Toxicol 33:302-307.

*Barnes DG, Dourson M. 1988. Reference dose (RfD): Description and use in health risk
assessments. Regul Toxicol Pharmacol 8:471-486.

*Belanger A, Hamilton HA. 1979. Determination of disulfoton and permethrin residues in an organic
soil and their translocation into lettuce, onion and carrot. J Environ Sci Health [B] 14:213-226.

*Belisle AA, Swineford DM. 1988. Simple specific analysis of organophosphorus and carbamate
pesticides in sediments using column extraction and gas chromatography. Environ Toxicol Chemistry
72749-752.

*Berlow JR, Cunningham M. 1989. Proposed amendment to final best demonstrated available
technology (BDAT) background document for organophosphorus wastes (K036 nonwastewaters). Vol.
14. NTIS/PB90-166521.

*Betowski LD, Jones TL. 1988. Analysis of organophosphorus pesticide samples by
high—performance liquid chromatography/mass spectrometry and high-performance liquid
chromatography/mass spectrometry/mass spectrometry. Environ Sci Technol 22:1230-1434.

*Bhaskaran R, Kandasawy D, Oblisami G, et a1. 1973. Utilization of disulfoton as carbon and
phosphorus sources by soil microflora. Curr Sci 42:835—836.

*Bombinski, TJ, DuBois KP. 1958. Toxicity and mechanism of action of Di-Syston. Arch Ind
Health 17:192—199.

*Borburgh HJ, Hammers WE. 1992. Extraction of organophosphorous pesticides from water samples
on Bakerbond SPE octadecyl cartridges at the ng/L level. Toxicol Environ Chem 35(1):79-86.

*Cited in text

DlSU LFOTON 184

8. REFERENCES

*Bourgeois D, Gaudet J, Deveau P, et al. 1993. Microextraction of organophosphorous pesticides
from environmental water and analysis by gas chromatography. Bull Environ Contarn Toxicol
50(3):433-440.

*Bowman BT, Sans WW. 1983. Determination of octanol-water partitioning coefficients (Kow) of 61
organophosphorus and carbamate insecticides and their relationship to respective water solubility (S)
values. J Environ Sci Health [B] 13:667-633.

*Bowman MC, Beroza M. 1969. Rapid GLC method for determining residues for fenthion,
disulfoton and phorate in corn, milk, grass and feces. J Assoc Off Anal Chem 52:1231-1239.

*Bowman MC, Beroza M, Gentry CR. 1969. GLC determination of residues of disulfoton,
oxydemetonmethyl, and their metabolites in tobacco plants. J Assoc Off Anal Chem 52:157-162.

*Bradway DE, Moseman R, May R. 1981. Analysis of alkyl phosphates by extractive alkylation.
Bull Environ Contam Toxicol 26:520-523.

*Braekman RA, Audenaert F, Willems JL, et al. 1983. Toxicokinetics of methyl parathion and
parathion in the dog after intravenous and oral administration. Arch Toxicol 54:71—82.

*Brodeur J, DuBois KP. 1963. Comparison of acute toxicity of anticholinesterase insecticides to
weanling and adult male rats. In: Proceedings of the Society for Experimental Biology and Medicine,
Vol. 114. New York, NY: Academic Press, 509-511.

*Brodeur J, DuBois KP. 1964. Studies on the mechanism of acquired tolerance by 0,0—diethyl S—2
(ethylthio) phosphorodithioate (Di-Syston). Arch Int Pharmacodyn Ther 149:560—570.

*Brokopp CD, Wyatt JL, Gabica J. 1981. Dialkyl phosphates in urine samples from pesticide
formulators exposed to disulfoton and phorate. Bull Environ Contam Toxicol 26:524-529.

*Brusick DJ. 1981. Mutagenic evaluation of S76 in the mitotic non-disjunction in Saccharomyces
cerevisiae strain D6. Study No. T3003064. Litton Bionetics Inc., Kensington, MD.

*Brzezinski J. 1969. Catecholamines in urine of rats intoxicated with phosphororganic insecticides.
Dissertationes Pharmaceuticae et Pharmacologicae 21:381-385.

*Brzezinski J. 1972. Effect of poisoning with phosphorus organic insecticides on the catechol amine
levels in rat plasma, brain, and adrenals. Dissertationes Pharmaceuticae et Pharmacologicae
24:217-220.

*Brzezinski J. 1973. The effect of atropine on the levels of adrenaline and noradrenaline changed by
acute poisoning with Di-Syston in rats. Pol J Pharmacol Pharm 25:611-615.

*Brzezinski J, Ludwicki K. 1973. The interrelationship of the changes of acetylcholine esterase and
catecholamines blood and urine levels in rats poisoned with Disyston. Pol J Pharmacol Pharm
25:313-316.

*Brzezinski J, Rusiecki W. 1970. The excretion of catecholamines in rat urine related to Disyston
poisoning. Dissertationes Pharmaceuticae et Pharmacologicae 22:507-511.

DISU LFOTON 185

8. REFERENCES

*Bull DL. 1965. Metabolism of Di-Syston by insects, isolated cotton leaves, and rats. J Econ
Entomol 58:249-254.

*Capel PD, Giger W, Reichert P, et al. 1988. Accidental input of pesticides into Rhine River.
Environ Sci Technol 22:705-717.

*Carey AE, Kutz FW. 1985. Trends in ambient concentrations of agrochemicals in humans and the
environment of the United States. Environmental Monitoring Assessment 52155-163.

*Carpy S, Klotzsch C, Cerioli A. 1975. Disulfoton: 2-Year feeding study in rats. Study no. 47069.
Sandoz Inc., Switzerland.

*CDC/ATSDR. 1990. Biomarkers of organ damage or dysfunction for the renal, hepatobiliary and
immune systems. Atlanta, GA: CDC/ATSDR Subcommittee on Biomarkers of Organ Damage and
Dysfunction, Centers for Disease Control, Agency for Toxic Substances and Disease Registry.
Summary report, August 27, 1990.

*CELDS. 1992. Computer-aided Environmental Legislative Design System. University of Illinois,
Urbana, IL. December 2, 1992.

*CELDs. 1994. Computer-assisted Environmental Legislative Database. University of Illinois,
Urbana, IL. September 17, 1994.

*Cetinkaya M. 1993. Gas chromatographic determination of pesticide residues in hair dyes. Parfuem
Kosmet 74(1):23-25.

*Chapman RA, Harris CR, Tolman JH, et al. 1993. Further comparison of the persistence in clay
loam of single and repeated annual applications of some granular insecticides. J Environ Sci Health
Part B: Pest Food Contamin Agric 28(2):151-170.

*Chapman RA, Harris CR, Tolman JH, et al. 1994b. The persistence of insecticidal chemicals in
soils treated with granular formulations of disulfoton and their uptake by potato plants. J Environ Sci
Health Part B: Pest Food Contamin Agric 29(2):233-245.

*Chapman RA, Tolman JH, Cole C. 1994a. The effect of multiple soil applications of disulfoton on
enhanced microbial degradation in soil and subsequent uptake of insecticidal chemicals by potato
plants. J Environ Sci Health Part B: Pest Food Contamin Agric 29(3):485-506.

*Chen HH, Hsueh JL, Sirianni SR, et al. 1981. Induction of sister-chromatid exchanges and cell
cycle delay in cultured mammalian cells treated with eight organophosphorus pesticides. Mutat Res
88:307-316.

*Chen HH, Sirianni SR, Huang CC. 1982. Sister chromatid exchanges in Chinese hamster cells
treated with seventeen organophosphorus compounds in the presence of a metabolic activation system.
Environ Mutagen 4:621-624.

*Christenson WR, Wahle BS. 1993. Technical grade disulfoton (DI-SYSTON) : a special 6-month
feeding study to determine a cholinesterase no-observed-effect level in the rat. Study No. 91-972—IR,
Report No. 106336. Miles Inc. Agriculture Division, Toxicology, Stilwell, Kansas.

MSULFOTON 186

8 REFERENCES

*Clapp DW, Naylor DV, Lewis GC. 1976. The fate of disulfoton in Portneuf silt loam soil. J
Environ Qual 5:207-10.

*Clark G, Koester AG, Pearson DW. 1971. Exploratory behavior in chronic disulfoton poisoning in
mice. Psychopharmacologia 20: 169-171 .

*Clark G, Pearson DW. 1973. Learning in chronic disulfoton poisoning. J Gen Psychol 89:305-311.

*Clark G, Stavinoha WB. 1969. Alterations in liver RNA induced by atropine and disulfoton.
Toxicol Appl Pharmacol 14:376-379.

*Clark G, Stavinoha WB. 1971. A permeability change in CNS tissue in chronic poisoning with
disulfoton. Life Sci [I] 10:421~423.

*Cohen DB. 1986. Groundwater contamination by toxic substances: A California assessment. ACS
Symposium Series 315. Washington, DC: American Chemical Society, 499-529.

*Comeliussen PE. 1970. Pesticide residues in total diet samples, V. Pestic Monit J 4:89-105.

*Costa LG, Kaylor G, Murphy SD. 1986. Carbachol- and norepinephrine-stimulated phosphoinositide
metabolism in rat brains: Effect of chronic cholinesterase inhibition. J Pharmacol Exp Ther 239:32-37.

*Costa LG, Kaylor G, Murphy SD. 1990. In vitro and in vivo modulation of cholinergic muscarinic
receptors in rat lymphocytes and brain by cholinergic agents. Int J Immunopharmacol 12:67-75.

*Costa LG, Murphy SD. 1982. Passive avoidance retention in mice tolerant to the organophosphorus
insecticide disulfoton. Toxicol Appl Pharmacol 65:451-458.

*Costa LG, Murphy SD. 1983a. [3H]Nicotine binding in rat brain: Alterations after chronic
acetylcholinesterase inhibition. J Pharmacol Exp Ther 226:392-397.

*Costa LG, Murphy SD. 1983b. Unidirectional cross-tolerance between the carbamate insecticide
propoxur and the organophosphate disulfoton in mice. Fundam Appl Toxicol 3:483-486.

*Costa LG, Murphy SD. 1986. Cholinergic and opiate involvement in the antinociceptive effect of
diisopropylfluorophosphate. Pharmacol Biochem Behav 24:733-736.

*Costa LG, Schwab BW, Hand H, et a1. 1981. Reduced [3H]quinuclidinyl benzilate binding to
muscarinic receptors in disulfoton—tolerant mice. Toxicol Appl Pharmacol 60:441-450.

*Costa LG, Schwab BW, Murphy SD. 1982a. Differential alterations of cholinergic muscarinic
receptors during chronic and acute tolerance to organophosphorus insecticides. Biochem Pharmacol
31:3407-3413.

*Costa LG, Schwab BW, Murphy SD. 1982b. Tolerance to anticholinesterase compounds in
mammals. Toxicology 25:79-97.

MSULFOTON 187

8 REFERENCES

*Costa LG, Shao M, Basker K, et al. 1984. Chronic administration of an organophosphorus
insecticide to rats alters cholinergic muscarinic receptors in the pancreas. Chem Biol Interact
48:261-269.

*CPCR. 1992. Crop protection chemicals reference. Di-Syston. 8th ed. New York, NY: Chemical
and Pharmaceutical Press, 1160-1171.

*Crawford LS, Anderson CA. 1973. Acute oral toxicity of Di-Syston technical to guinea pigs Report
no. 39113, Mobay Chemical Corporation, Environmental Health Research Institute, Stilwell, Kansas.

*Crawford LS, Anderson CA. 1974. Acute oral toxicity of several Di-Syston metabolites to female
and male rats. Report no. 39687, Mobay Chemical Corporation, Environmental Health Research
Institute, Stilwell, Kansas.

*CRISP Database. 1994. US Department of Health and Human Services, Public Health Service,
National Institutes of Health, National Institute for Environmental Health Science. August 14, 1994.

*Daughton CG, Crosby DG, Gamas RL, et a1. 1976. Analysis of phosphorus-containing hydrolytic
products of organophosphorus pesticides in water. J Agric Food Chem 24:236-241.

*Dementi B. 1994. Ocular effects of organophosphates: a historical perspective of Saku disease. J
Appl Toxicol 142119-129

*Di Corcia A, Marchetti M. 1992. Method development for monitoring pesticides in environmental
waters: liquid-solid extraction followed by liquid chromatography. Environ Sci Technol 26(1):66-74.

*Dillon AP. 1981. Disposal of selected pesticides. In: Pesticide disposal and detoxification:
processes and techniques. Noyes Data Corporation, Park Ridge, NJ.

*Domine D, Devilliers J, Chastrette M, Karcher W. 1992. Multivariate structure-property
relationships (MSPR) of pesticides. J Pest Sci 35:73-82.

*Doull J. 1957. The acute inhalation toxicity of Di-Syston to rats. Report no. 1802. University of
Chicago, Department of Pharmacology, Chicago, IL.

*Doull J, Vaughn G. 1958. The effects of diets containing Di-Syston. University of Chicago,
Department of Pharmacology, Chicago, IL. (Unpublished study cited in EPA 1987 and WHO 1974).

*Dragan D, Carpov A. 1987. Microencapsulated organophosphorous insecticides. III. Some aspects
on the volatilization of malathion and disulfoton from aqueous suspensions of microcapsules. J
Microencapsul 4:97-105.

*Draper WM, Crosby DG. 1984. Solar photooxidation of pesticides in dilute hydrogen peroxide. J
Agric Food Chem 32:231-237.

*DuBois KP. 1957. The dermal toxicity of Di-Syston to rats. Report no. 2063. University of
Chicago, Toxicity Laboratory, Chicago, IL.

MSULFOTON 188

& REFERENCES

*DuBois KP. 1971. The acute inhalation of DI-SYSTON to rats. Report No. 31029. University of
Chicago, Toxicology Laboratory, Chicago, IL.

*DuBois KP, Kinoshita FK. 1968. Influence of induction of hepatic microsomal enzymes by
phenobarbital on toxicity of organic phosphate insecticides. Proc Soc Exp Biol Med 129:699-702.

*DuBois KP, Kinoshita FK. 1971. Effect of repeated inhalation exposure of female rats to Di-Syston.
University of Chicago, Chicago, IL. Report No. 30571. MRID 87935.

*Duggan RE, Comeliussen PE. 1972. Dietary intake of pesticide chemicals in the United States (III):
June 1968-April 1970. Pestic Monit J 51331-341.

*Duggan RE, Comeliussen PE, Duggan MB, et al. 1983. Pesticide residue levels in foods in the
United States from June 1, 1969 to June 30, 1976. Washington, DC: Food and Drug Administration,
Division of Chemical Technology, 15, 22, 27, 30, 32, 33.

*Ecobichon DJ. 1990. Toxic effects of pesticides. In: Klaasen CD, Amdur MO, Doull J, eds.
Casarett and Doull’s toxicology. 4th ed. New York, NY: Macmillan Publishing Co., 565-622.

*Edgell KW, Jenkins EL, Lopez-Avila V, et a1. 1991. Capillary column gas chromatography with
nitrogen-phosphorus detection for determination of nitrogen- and phosphorus—containing pesticides in

finished drinking waters: Collaborative study. J Assoc Off Anal Chem 74:295-309.

*Eisenreich SJ, Looney BB, Thornton JD. 1981. Airborne organic contaminants in the Great Lakes
ecosystem. Environmental Science and Technology 15:30-38.

*Ellenhom MJ, Barceloux DG. 1988. Medical toxicology. Diagnosis and treatment of human
poisoning. New York, NY: Elsevier, 1075-1076.

*Ellington JJ, Stancil FE, Payne WD, et a1. 1988. Measurement of hydrolysis rate constants for
evaluation of hazardous waste land disposal: Vol. 3. Data on 70 chemicals. Engineering Research
Laboratory, US. Environmental Protection Agency, Athens, GA. EPA/600/S3-88—028. NTIS
PB38-234842/AS.

*EPA. 1973. Environmental Protection Agency. Code of Federal Regulations 40 CFR 136.3.
*EPA. 1978a. Environmental Protection Agency. Code of Federal Regulations 40 CFR 455.20.
*EPA. 1978b. Environmental Protection Agency. Code of Federal Regulations 40 CFR 152.175.
*EPA. 1978c. Environmental Protection Agency. Code of Federal Regulations 40 CFR 116.4.
*EPA. 1980a. Environmental Protection Agency. In vitro microbiological mutagenicity and
unscheduled DNA synthesis studies of eighteen pesticides. Research Triangle Park, NC: Health
Effects Research Laboratory, US. Environmental Protection Agency. EPA-600/1-79-0441.
PB80—133226.

*EPA. 1980b. Environmental Protection Agency. Code of Federal Regulations 40 CFR 261.33.

DISULFOTON 139

8. REFERENCES

*EPA. 1980c. Resource Conservation and Recovery Act (RCRA). US. Environmental Protection
Agency,Washington, DC.

*EPA. 1981a. Environmental Protection Agency. Mutagenesis screening of pesticides: "Drosophila."
Research Triangle Park, NC: Health Effects Research Laboratory, US. Environmental Protection
Agency. EPA-600/1—81-017. PB81-160848.

*EPA. 1981b. Environmental Protection Agency. Code of Federal Regulations 40 CFR 261.32.
*EPA. 1981c. Environmental Protection Agency. Code of Federal Regulations 40 CFR 261.33.
*EPA. 1983. Environmental Protection Agency. Code of Federal Regulations 40 CFR 122.

*EPA. 1984a. In vitro and in vivo mutagenicity studies on environmental chemicals. Research
Triangle Park, NC: Health Effects Research Laboratory, US. Environmental Protection Agency.

EPA—600/ 1 -84-003. PB 84-1 38973.

*EPA. 1984b. Pesticide fact sheet: Disulfoton. Washington, DC: Office of Pesticide and Toxic
Substances, Offices of Pesticide Programs.

*EPA. 1984c. Environmental Protection Agency. Code of Federal Regulations 40 CFR 261.
*EPA. 1985. Environmental Protection Agency. Code of Federal Regulations 40 CFR 117.3.

*EPA. 1986a. Test methods for evaluating solid wastes (SW—846). 3rd ed. Washington, DC: Office
of Solid Waste and Emergency Response, US. Environmental Protection Agency.

*EPA. 1986b. Environmental Protection Agency. Code of Federal Regulations 40 CFR 268.10.
*EPA. 1987a. Environmental Protection Agency. Code of Federal Regulations 40 CFR 355.
*EPA. 1987b. Environmental Protection Agency. Code of Federal Regulations 40 CFR 264.

*EPA. 1987c. Environmental Protection Agency. Hazardous substances; reportable quantity
adjustments; proposed rules. 40 CFR 117 and 302. Federal Register 52:8169.

*EPA. 1988a. Environmental Protection Agency. Code of Federal Regulations 40 CFR 261.
*EPA. 1988b. Environmental Protection Agency. Code of Federal Regulations 40 CFR 268.43.
*EPA. 1988c. Method for the determination of organic compounds in drinking water. Cincinnati,
OH: Environmental Monitoring Systems Laboratory, Office of Research and Development, US.

Environmental Protection Agency. EPA 600/4-88-039.

*EPA. 1988d. The Emergency Planning and Community Right—to-Know Act of 1986 (EPCRA).
Section 313 of Title 111. US. Environmental Protection Agency, Washington, DC.

*EPA. 1989a. Environmental Protection Agency. Code of Federal Regulations 40 CFR 148.

WSULFOTON 190

& REFERENCES

*EPA. l989b. Drinking water health advisory: Pesticides. U.S. Environmental Protection Agency,
Office of Drinking Water Health Advisory. Chelsea, MI: Lewis Publishers, 345-362.

*EPA. 1989c. Interim methods for development of inhalation reference doses. US. Environmental
Protection Agency. EPA/600/8-90/066F.

*EPA. l989d. Environmental Protection Agency. Code of Federal Regulations 40 CFR 302.4.
*EPA. 1989e. Environmental Protection Agency. Code of Federal Regulations 40 CFR 125.

*EPA. 1990. Health and environmental effects document for disulfoton. (Final draft).
Environmental Criteria and Assessment Office, Office of Health and Environmental Assessment, US.
EPA, Cincinnati, OH.

*EPA. 1991. Environmental Protection Agency. Code of Federal Regulations 40 CFR 258.

*EPA. 1992a. Environmental Protection Agency. Pesticide chemicals manufacturing category
effluent limitations guidelines, pretreatment standards, and new source performance standards. 40 CFR
455. Federal Register 57:12560-12601.

*EPA. 1992b. Environmental Protection Agency. Code of Federal Regulations 40 CFR 455.50.

*EPA. 1992c. EPA Method 1657. Methods for the determination of nonconventional pesticides in
municipal and industrial wastewater. US. Environmental Protection Agency.

*EPA. 1993. Environmental Protection Agency. Federal Register 58 FR 48092 .

*EPA. 1994. Drinking water regulations and health advisories. Office of Drinking Water, US.
Environmental Protection Agency, Washington, DC.

*Eto, M. 1974. Organophosphorus pesticides: Organic and biological chemistry. Cleveland, OH:
CRC Press, 123-321.

*FAO/WHO. 1991. Pesticide residues in food-Disulfoton. Report of the Joint Meeting of the FAO
Panel of Experts on Pesticide Residues in Food and the Environment and a WHO Expert Group on
Pesticide Residues. Food and Agriculture Organization of the United Nations and the World Health
Organization, Rome, Italy. Pp. 151-172.

*Farm Chemicals Handbook. 1993. Farm Chemicals Handbook. 1993 ed. Meister Publishing
Company, Willoughby OH.

*Fawade MM, Pawar SS. 1978. Alterations in mixed function oxidase system during thiodemeton
(o-o diethyl S-2(ethylthio) ethyl phosphorothioate) toxicity. Indian J Exp Biol 16:481—484.

*Fawade MM, Pawar SS. 1980. Effect of phenobarbital pretreatment on mixed function oxidase and
lipid peroxidation during thiodemeton toxicity. Indian J Exp Biol 18:645-647.

*Fawade MM, Pawar SS. 1983. Effect of N1Cl2 and cycloheximide on microsomal drug metabolism
and ALA-synthetase during thiodemeton toxicity. Indian J Exp Biol 21:343-346.

DISULFOTON 191

8. REFERENCES

*FDA. 1988. Food and Drug Administration Pesticide Program - Residues in Foods - 1987. J Assoc
Off Anal Chem 71:122A-163A.

*FDA. 1990. Residues in foods, 1989 (3rd annual FDA pesticide residue monitoring program report).
J Assoc Off Anal Chem 73(5):127A-146A.

*FDA. 1991. Residues in foods, 1990 (4th annual FDA pesticide residue monitoring program report).
J Assoc Off Anal Chem 74(5):121A-140A.

*FDA. 1992. Residue monitoring, 1991 (5th annual FDA pesticide residue monitoring program
report). J Assoc Off Anal Chem 75(5):l35A—157A.

*FDA. 1993. FDA monitoring program, 1992 (6th annual FDA pesticide residue monitoring program
report). J Assoc Off Anal Chem 76:127A-148A.

*Fitzgerald BB, Costa LG. 1992. Modulation of M1 and M2 muscarinic receptor subtypes following
repeated organophosphate exposure in rats. Toxicol Appl Pharmacol 117:112—125.

*Fitzgerald BB, Costa LG. 1993. Modulation of muscarinic receptors and acetylcholinesterase
activity in lymphocytes and in brain areas following repeated organophosphate exposure in rats.
Fundam Appl Toxicol 20:210-216.

*Flucke W. 1986. S 276 Technical - Study of subacute dermal toxicity to rabbits. Unpublished
Report 14747 from Bayer AG, Institute of Toxicology, Wuppertal-Elberfeld, Germany.

*Foley DJ, McPhillips JJ. 1973. Response of the rat ileum, uterus and vas deferens to carbachol and
acetylcholine following repeated daily administration of a cholinesterase inhibitor. Br J Pharmacol
48:418-425.

*Foley DJ, Stitzel RE, McPhillips JJ. 1973. The relationship between inhibition of
acetylcholinesterase and sensitivity of the rat ileum to carbachol. Pharmacology 10:298-305.

Frank R, Braun HE, Wilkie I, et al. 1991. A review of insecticide poisonings among domestic
livestock in southern Ontario, Canada, 1982-1989. Can Vet J 32:219—226.

*Frank R, Logan L. 1988. Pesticide and industrial chemical residues at the mouth of the Grand
Saugeen and Thames rivers Ontario Canada 1981—1985. Arch Environ Contam Toxicol 17:741-754.

*FSTRAC. 1990. Summary of state and federal drinking water standards and guidelines.
Washington, DC: Federal—State Toxicology and Regulatory Alliance Committee, Chemical
Communication Subcommittee, February 1990.

*Gaines TB. 1969. Acute toxicity of pesticides. Toxicol Appl Pharmacol 14:515-534.

*Garg AK, Sethi GR. 1980. Persistence of insecticide residues in paddy soil. Ind J Plant Protect
8:157-163.

MSULFOTON 192

8 REFERENCES

*Gelardi RC, Mountford MK. 1993. Infant formulas evidence of the absence of pesticide residues.
Meeting of the American Industrial Health Council on the Domestic Agenda for Risk Assessment,
Washington DC, USA, December 1, 1992. Regul Toxicol Phannacol 17(2 Part 1):l81-192.

*Gianessi LP. 1986. A national pesticide usage data base, summary of report submitted to the office
of standards and regulations, US. EPA under cooperative agreement CR 811858-01-0 by Resources
for the Future, Washington, DC.

*Gianessi LP, Puffer CA. 1992. Insecticide use in US crop production. Resources for the Future,
Washington, DC.

*Gigon PL, Gram TE, Gillette JR. 1969. Studies on the rate of reduction of hepatic microsomal
cytochrome P-450 by reduced nicotinamide adenine dinucleotide phosphate: Effect of drug substrates.
Mol Phannacol 5:109—122.

Gillette JR, Brodie BB, LaDue EN. 1957. The oxidation of drugs by liver microsomes: On the role
of TPHN and oxygen. J Phannacol Exp Ther 119:532-540.

*Gillette JR, Davis DC, Sesame HA. 1972. Cytochrome P—450 and its role in drug metabolism. Ann
Rev Pharrnacol 57-84.

*Glooschenko WA, Sirachan WMJ, Sampson RC]. 1976. Distribution of pesticides and
polychlorinated biphenyls in water, sediments, and seston of the upper Great Lakes-1974. Pestic
Monit J 10:61-67.

*Gohre K, Miller GC. 1986. Photooxidation of thioether pesticides on soil surfaces. J Agric Food
Chem 34:709-713.

*Goldfrank LR, Flomenbaum NE, Lewin NA, et a1. 1990. Goldfrank’s toxicologic emergencies. 4th
ed. Norwalk, CT: Appleton and Lange, 684-692.

*Goodrich JA, Lykins BW Jr, Clark RM. 1991. Drinking water from agriculturally contaminated
groundwater. J Environ Qual 20:707-717.

Gopal PK, Ahuja SP. 1979. Lipid and growth changes in organs of chicks (Gallus domesticus)
during acute and chronic toxicity with disyston and folithion. Indian J Exp Biol 17:1153—1154.

*Grant DL, Sherwood CR, McCully KA. 1969. Gas-liquid and thin-layer chromatography of phorate,
disulfoton and five of their oxidation products. J Chromatogr 44:67-74.

*Greenhalgh R. 1978. Terminal residues of organophosphorus pesticides. Pure Appl Chem
50:513-518.

*Gunderson EL. 1988. FDA total diet study, April 1982-April 1984, dietary intakes of pesticides,
selected elements and other chemicals. J Assoc Off Anal Chem 71:1200-1209.

*Haddad LM, Winchester JF. 1990. Clinical management of poisoning and drug overdose. 2nd ed.
Philadelphia, PA: W.B. Saunders Co., 1079-1081.

mSULFOTON 193

8 REFERENCES

*Hajjar NP, Hodgson E. 1980. Flavin adenine dinucleotide monooxygenase: Its role in the
sulfoxidation of pesticides in mammals. Science 209:1134-1136.

*Hajjar NP, Hodgson E. 1982. Sulfoxidation of thioether—containing pesticides by the flavin-adenine
dinucleotide-dependent monooxygenase of pig liver microsomes. Biochem Pharmacol 31:745-752.

*Hallberg GR. 1989. Pesticide pollution of groundwater in the humid USA. Agric, Ecosys Environ
26:299-368.

*Hanna PJ, Dyer KP. 1975. Mutagenicity of organophosphorus compounds in bacteria and
Drosophila. Mutat Res 28:405-420.

*Harris C1. 1969. Movement of pesticides in soil. J Agric Food Chem 17:88-82.

*Harris CK, Chapman RA, Tolman JH, et a1. 1988. A comparison of the persistence in a clay loam
of single and repeated annual applications of seven granular insecticides used for corn rootworm
control. J Environ Sci Health [B] 23:1-32.

*Hattori H, Suzuki U, Yasuoka T, et a1. 1982. Identification and quantitation of disulfoton in urine
and blood of a cadaver by gas chromatography/mass spectrometry. Nippon Hoigaku Zasshi
36:41 1-413.

*Hayes RH. 1983. Oncogenicity study of disulfoton technical on mice. Study no. 80-271-04.
Mobay Chemical Corporation, Corporate Toxicology Department, Stilwell, Kansas.

*Hayes RH. 1985. Chronic feeding/oncogenicity study of technical disulfoton (Di-Syston) with rats.
Study no. 82-271-01. Mobay Chemical Corporation, Corporate Toxicology Department, Stilwell,
Kansas.

*HazDat. 1994. Agency for Toxic Substances and Disease Registry (ATSDR), Atlanta, GA.
September 8, 1994.

*Hebert VR, Miller GC. 1990. Depth dependence of direct and indirect photolysis on soil surfaces. J
Agric Food Chem 38:913-918.

*Helling CS, Dennison DG, Kaufman DD. 1974. Fungicide movement in soils. Phytopathology
64:1091-1100.

*Herbold B. 1980. Dominant lethal test on male mouse to evaluate 3276 for mutagenic potential.
Report No. 9440. Bayer AG, Institute of Toxicology, Wuppertal-Elberfeld, Germany.

*Herbold B. 1981. Micronucleus test on the mouse to evaluate for mutagenic effect. Report No.
10451. Bayer AG, Institute of Toxicology, Wuppertal-Elberfeld, Germany.

*Herbold B. 1983. POL test on E. coli to evaluate for potential DNA damage. Report No. 12139.
Bayer AG, Institute of Toxicology, Wuppertal-Elberfeld, Germany.

DSULFOTON 194

8 REFERENCES

*Hikita H, Miyata M, Ishikawa S. 1973. [Experimental study of chronic organophosphate (OP)
insecticides in the beagle dogzactivities of cholinesterases and residue of OR] Nichi Gan Kaishi
77:1254—1265. (Japanese) ‘

*Hildebrandt A., Estabrook RW. 1971. Evidence for the participation of cytochrome b5 in hepatic
microsomal mixed—function oxidase reactions. Arch Biochem Biophys 143166-79.

Hill EF, Camardese MD. 1984. Toxicity of anticholinesterase insecticides to birds: Technical grade
versus granular formulations. Ecotoxicol Environ Safety 8:551-563.

Hixson EJ. 1982. Acute oral toxicity of Di-Syston technical in hens. Report no. 341. Mobay
Chemical Corporation, Environmental Health Research Institute, Stilwell, Kansas.

*Hixson EJ. 1983. Acute delayed neurotoxicity study on disulfoton. Toxicology report no. 365
(Study no. 82-418-01). Mobay Chemical Corporation, Environmental Health Research Institute,
Stilwell, Kansas.

*Hixson EJ, Hathaway. 1986. Effect of disulfoton (DI-SYSTON) on reproduction in rats. Study No.
82—671—02. Report No. 90965. Mobay Corporation, Corporate Toxicology Department, Stilwell,
Kansas.

*Hodgson DW, J.F. Thompson, Watts, RR. 1982. Accuracy of pesticide reference standard solutions.
Part 11: Chemical stability under four storage conditions. J Assoc Off Anal Chem 65:94-102.

*Hoffman K, Weischer CH, Luckhaus G, et al. 1975. S 276 (disulfoton) chronic toxicity study on
dogs (two-year feeding experiment). Report nos. 5618 and 45287. AG Bayer, West Germany.

*Holden PW. 1986. Pesticides and groundwater quality. Washington, DC: National Academy Press,
20-21, 44-45, 67, 69.

*Holstege DM, Scharberg DL, Richardson ER, et al. 1991. Multiresidue screen for organophosphorus
insecticides using gel permeation chromatography-silica gel cleanup. J Assoc Off Anal Chem
74:394-399.

Holt TM, Hawkins RK. 1978. Rat hippocampal norepinephrine response to cholinesterase inhibition.
Res Commun Chem Pathol Pharmacol 20:239-251.

*HSDB. 1994. Hazardous Substances Data Bank. National Library of Medicine, National
Toxicology Information Program, Bethesda MD.

*Hsu JP, Schattenberg HJ, Garza MM. 1991. Fast turnaround multiresidue screen for pesticides in
produce. J Assoc Off Anal Chem 74(5):886—892.

*Huang CC. 1973. Effect on growth but not on chromosomes of the mammalian cells after treatment
with three organophosphorus insecticides. Proc Soc Exp Biol Med 142236-40.

*Hundley HK, Cairns T, Luke MA, et a1. 1988. Pesticide residue findings by the Luke method in
domestic and imported foods and animal feeds for fiscal years 1982-1986. J Assoc Off Anal Chem
71(3):875-892.

DISU LFOTON 195

8. REFERENCES

*Inukai H, Iyatomi A. 1976. Disulfoton: mutagenicity test on bacterial systems. Report No. 29.
Nitokuno, Agricultural Chemicals Institute, Laboratory of Toxicology, Japan.

*IRIS. 1994. Integrated Risk Information System. US. Environmental Protection Agency,
Cincinnati, OH. August 1994.

*IRPTC. 1985. IRPTC data profile on: Disulfoton. International Register of Potentially Toxic
Chemicals, United Nations Environment Programme, Geneva, Switzerland.

*Ishikawa S, Miyata M. 1980. Development of myopia following chronic organophosphate pesticide
intoxication: An epidemiological and experimental study. In: Merigan WH, Weiss B, eds.
Neurotoxicity of the visual system. New York, NY: Raven Press, 233-254.

*Iyaniwura IT. 1991. Relative inhibition of rat plasma and erythrocyte cholinesterases by pesticide
combinations. Vet Hum Toxicol 33:166-168.

*Jagannath DR. 1981. Mutagenic evaluation of S276 in the Saccharomyces cerevisiae reverse
mutation induction assay. Study No. T4003065. Litton Bionetics Inc., Kensington, MD.

*Jury WA, Focht DD, Farmer WJ. 1987a. Evaluation of pesticide groundwater pollution potential
from standard indices of soil-chemical adsorption and biodegradation. J Environ Qual 16:422—428.

*Jury WA, Winer AM, Spencer WF, et al. 1987b. Transport and transformation of organic chemicals
in the soil-air-water. Ecosystem 99:119-164.

*Kadoum AM, Mock DE. 1978. Herbicide and insecticide residues in tailwater pits: Water and pit
bottom soil from irrigated corn and sorghum fields. J Agric Food Chem 26(1):45-50.

*Kaloyanova FP, El Batawi MA. 1991. Organophosphorus compounds. In: Human toxicology of
pesticides. Boca Raton, FL: CRC Press, 3-41.

*Kawasaki S, Ueda H, Itoh H, et al. 1992. Screening of organophosphorus pesticides using liquid
chromatography-atmospheric pressure chemical ionization mass spectrometry. J Chromatogr
595:193-202.

*Keamey PC, Woolson EA, Plimmer JR, et al. 1969. Decontamination of pesticides in soil. Residue
Rev 29:137.

*Kenaga EE. 1980. Predicted bioconcentration factors and soil sorption coefficients of pesticides and
other chemicals. Ecotoxicol Environ Safety 4:26-38.

*Kenaga EE, Goring CAI. 1980. Relationship between water solubility, soil-sorbtion, octanol-water
partitioning, and bioconcentration of chemicals in biota. ASTM Special Technical Publication (STP)
707. American Society for the Testing of Materials, Philadelphia, PA.

*Kennedy ER, Abell MT, Reynolds J, et al. 1994. A sampling and analytical method for‘ the
simultaneous detemiination of multiple organophosphorus pesticides in air. ‘Am Ind Hyg Assoc J
55(12):1172—1177.

MSULFOTON 196

& REFERENCES

*Kikuchi H, Suzuki Y, Hashimoto Y. 1981. Increase of Beta-glucuronidase activity in the serum of
rats administered organophosphate and carbamate insecticides. J Toxicol Sci 6:27-35.

*King PH, McCarty PL. 1968. A chromatographic model for predicting pesticide migration in soils.
Soil Science 1062248-261.

*Kleinschmidt MG Jr. 1971. Fate of Di-Syston 0,0-diethyl S-2-(ethylthio) ethyl phosphorodithioate
in potatoes during processing. J Agric Food Chem 19:1196-1197.

*Klotzsche C. 1972. Disulfoton, 90 day feeding study in rats. Sandoz Agroforschung, Switzerland.
Report No. 88585.

*Kordel W, Stutte J, Kotthoff G. 1993. HPLC—screening method for the determination of the
adsorption-coefficient on soil: comparison of different stationary phases. Chemosphere
27(12):2341-2352.

*Krill RM, Sunzogni WC. 1986. Chemical monitoring of Wisconsin’s groundwater. J Am Water
Works Assoc 78:70-75.

*Kundiev YI, Rappoport MB. 1967. [Changes of the skin following application of organophosphorus
insecticides] Vrach Delo 5:106-109. (Russian).

*Kutz FW. 1983. Chemical exposure monitoring. Residue Rev 55:277-292.
*Kutz FW. 1983. Chemical exposure monitoring. Residue Rev 85:277-292.

*Kutz FW, Carey AE. 1986. Pesticides and toxic substances in the environment. J Arboriculture
12:92~95.

*Kutz FW, Yobs AR, Yang HSC. 1976. National pesticide monitoring program. In: R. E. Lee Jr.,
ed. Air Pollution from Pesticides and Agricultural Processes. Cleveland, OH, CRC press. Pp.
95-136.

*Lamb DW, Hixson EJ. 1983. Embryotoxic and teratogenic effects of disulfoton. Study no.
81-611-02. Mobay Chemical Corporation, Kansas City, MO.

*Lee SGK, Hanna LA, Johnston K, et a1. 1985. Excretion and metabolism of Di-Syston in rats.
Unpublished Report MR90946 from Mobay Corporation, USA.

*LeFever GS, Green RD. 1975. The effects of chronic ganglion blockade and chronic cholinesterase
inhibition on the sensitivity of rabbit stomach muscularis to cholinergic and adrenergic agonists. J
Pharmacol Exp Ther 193:739-747.

*Liao W, Joe T, Cusick WG. 1991. Multiresidue screening method for fresh fruits and vegetables
with gas chromatographic/mass spectrometric detection. J Assoc Off Anal Chem 74:554-565.

*Light DR, Waxman DJ, Walsh C. 1982. Studies on the chirality of sulfoxidation catalyzed by
bacterial flavoenzyme cyclohexanone monooxygenase and hog liver flavin adenine dinucleotide
containing monooxygenase. Biochemistry 21:2490-2498.

MSULFOTON 197

a REFERENCES

*Litterst CL, Lichtenstein EP, Kajiwara K. 1969. Effects of insecticides on growth of HeLa cells. J
Agric Food Chem 17:1199-1203.

*Llorens J, Crofton KM, Tilson HA, et a1. 1993. Characterization of disulfoton-induced behavioral
and neurochemical effects following repeated exposure. Fund Appl Toxicol 20:163-169.

*Lord KA, Burt PE. 1964. Effect of temperature on water solubility of phorate and disulfoton.
Chem Ind 1262-1263.

*Lores EM, Bradway DE. 1977. Extraction and recovery of organophosphorus metabolites from
urine using an anion exchange resin. J Agric Food Chem 25:75-79.

*Luke MA, Masumoto HT, Chims T, et a1. 1988. Levels and incidences of pesticide residues in
various foods and animal feeds analyzed by the luke multiresidue methodology for fiscal years
1982-1986. J Assoc Off Anal Chem 71:415—420.

*Maddy KT, Fong HR, Lowe JA, et al. 1982. A study of well water in selected California
communities for residues of 1,3-dichloropropene, chlorallyl alcohol and 49 organophosphate or
chlorinated hydrocarbon pesticides. Bull Environ Contam Toxicol 29:354-359.

*March RB, Fukuto TR, Metcalf RL. 1957. Metabolism of p32-dithio—systox in the white mouse and
American cockroach. University of California, Citrus Experiment Station, Riverside, California.
MRID 83215.

*McCarty PL, King PH. 1966. The movement of pesticides in soils. Purdue University, Engineering
Bulletin Extension Series, 156-171.

*McCarty RT, Haufler M, Osborn MG, et al. 1969. Oral toxicity of four organophosphate
insecticides to farm livestock. Am J Vet Res 1149-1153.

*McDonald Be, Costa LG, Murphy SD. 1988. Spatial memory impairment and central muscarinic
receptor loss following prolonged treatment with organophosphates. Toxicol Lett 40:47-56.

*McPhillips JJ. 1969a. Altered sensitivity to drugs following repeated injections of cholinesterase
inhibitor to rats. Toxicol Appl Pharmacol 14:67-73.

*McPhillips JJ. 1969b. Subsensitivity of the rat ileum to cholinergic drugs. J Pharmacol Exp Ther
166:249-254.

McPhillips JJ, Coon JM. 1966. Adaptation to octamethyl pyrophosphorarnide in rats. Toxicol Appl
Pharmacol 8:66—76.

*McPhillips JJ, Dar MS. 1967. Resistance to the effect of carbachol on the cardiovascular system
and on the isolated ileum of rats after subacute administration of an organophosphorus cholinesterase

inhibition. J Pharmacol Exp Ther 156:507-513.

*Melnikov NN. 1971. Chemistry of pesticides. New York, NY: Springer-Verlag, 368-369.

MSULFOTON 198

& REFERENCES

*Menzer RE, Fontanilla EL, Ditman LP. 1970. Degradation of disulfoton and phorate in soil
influenced by environmental factors and soil type. Bull Environ Contam Toxicol 5:1—5.

*Menzie CM. 1972. Fate of pesticides in the environment. Ann Rev Entomol 17:199-222.

*Merck. 1989. Merck index: an encyclopedia of chemicals, drugs, and biologicals. 11th ed.
Budavari S, ed. Rahway NJ: Merck & Co., Inc.

*Mihail F. 1978. S 276 (Disyston active ingredient) acute toxicity studies. Report no. 7602a. AG
Bayer, Institut fur Toxicologie, West Germany.

*Miller GC, Hebert VR, Miller WW. 1989. Effect of sunlight on organic contaminants at the
atmosphere-soil interface. In: Reactions and movement of organic chemicals in soils. SSSA Special
Publication no. 22, 99-110.

*Miller H, Cramer P, Drinkwine A, et al. 198]. Development of methods for pesticides in
wastewater: Applicability of a general approach. Advances in Identifying and Analyzing Organic
Pollution in Water 1:115-138.

*Minyard JP Jr, Roberts WE. 1991. State findings on pesticide residues in foods:1988 and 1989. J
Assoc Off Anal Chem 74:438-452.

*Mitchell TH, Ruzicka JH, Thomson J, et al. 1968. The chromatographic determination of
organophosphorus pesticides. Part III. The effect of irradiation on the parent compounds. J
Chromatogr 32:17-23.

*Morgan DP. 1982. Recognition and management of pesticide poisonings. 3rd ed. EPA
540/9—80-005. Washington, DC: US. Government Printing Office, 2. '

*Moriya M, Ohta T, Watanabe K, et al. 1983. Further mutagenicity studies on pesticides in bacterial
reversion assay systems. Mutat Res 116:185—216.

*Mossman DJ, Schnoor JL, Stumm W. 1988. Predicting the effects of a pesticide release of the
Rhine River. I Water Pollut Control Fed 60:1806-1812.

*Mostaghimi S, McClellan PW, Cooke RA. 1993. Pesticide contamination of groundwater in
Virginia: BMP impact assessment. Water Sci Technol 28(3):379-387.

Mount ME, Oehme FW. 1981. Brain cholinesterase activity in healthy cattle, swine and sheep and in
cattle and sheep exposed to cholinesterase-inhibiting insecticides. Am J Vet Res 42:1345-1350.

*Muhlmann K, Schrader G. 1957. [Hydrolysis of phosphoric acid ester insecticides]. Z Naturforschg
[B] 12:196-203. (German)

*Munch DJ, Frebis CP. 1992. Analyte stability studies conducted during the national pesticide
survey. Environ Sci Technol 29:921-925.

*Murphy RS, Kutz FW, Strassman SC. 1983. Selected pesticide residues or metabolites in blood and
urine specimens from a general population survey. Environ Health Perspect 48:81-86.

WSULFOTON 199

a REFERENCES

*Murphy SD. 1986. Toxic effects of pesticides. In: Klaasen CD, Amdur MO, Doull J, eds. Casarett
and Doull’s toxicology. 3rd ed. New York, NY: Macmillan Publishing Co., 519-581.

*Murphy SD, Costa LG, Wang C. 1984. Organophosphate insecticide interaction at primary and
secondary receptors. In: Narahashi T, ed. Cellular and molecular neurotoxicology. New York, NY:
Raven Press, 165-176.

*Murty KV, Raju DSS, Sharma CBSR. 1983. Cytogenetic hazards from agricultural chemicals: 7.
Herbicides, fungicides and insecticides screened for effects on chiasmata in Hordeum vulgare.
Biologisches Zentralblatt (Leipzig) 102:571-576.

*Myram C, Forrest JD. 1969. The application of pesticide granules from the air. Chem Ind, 1851.

*NAS/NRC. 1989. Biologic markers in reproductive toxicology. National Academy of
Sciences/National Research Council. Washington, DC: National Academy Press, 15-35.

*Nash RG. 1974. Plant uptake of insecticides, fungicides and fumigants from soils. In: Guenzi WD,
et al. eds. Pesticides in soil and water. Madison, WI: Soil Science of America Inc. Publishers,
257-313.

*NATICH. 1992. National Air Toxics Information Clearinghouse. Research Triangle Park, NC: US.
Environmental Protection Agency, Office of Air Quality Planning and Standards.

*NIOSH. 1992. Recommendations for occupational safety and health compendium of policy
documents and statements. Cincinnati, OH: US. Department of Health and Human Services, Public
Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health.
DHHS (NIOSH) publication no. 92-100.

*NOES. 1990. National occupational exposure survey 1981 - 1983. US. Department of Health and
Human Services, National Institute for Occupational Safety and Health, Cincinnti, OH. July 1, 1990.

*OSHA. 1989. Air contaminants. Final rule. US. Department of Labor. Occupational Safety and
Health Administration. Federal Register 5422936.

*OSHA. 1992. Air contaminants. US. Department of Labor. Occupational Safety and Health
Administration. Federal Register 57:26002.

*Osweiler GD, Carson TL, Buck WB, et a1. 1985. Organophosphorous and carbamate insecticides.
In: Clinical and diagnostic veterinary toxicology. 3rd ed. Dubuque, IA: Kendall/Hunt Publishing Co.,
298-317.

*OTA. 1990. Neurotoxicity: Identifying and controlling poisons of the nervous system. Washington,
DC: Office of Technology Assessment, US Congress. OTA-BA-438. April 1990.

*Panda BB. 1983. Effect of the insecticides, oxydemeton, methyl and thiodemeton, on the mitotic
and meiotic chromosomes of barley (HOrdeum vulgare). Environ Exper Botany 23:293-296.

*Parker CE, Haney CA, Hass JR. 1982. High—performance liquid chromatography-negative chemical
ionization mass spectrometry of organophosphorous pesticides. J Chromatogr 237:233-248.

DISULFOTON 200

8. REFERENCES

*Pawar SS, Fawade MM. 1978. Alterations in the toxicity of thiodemeton due to the pretreatment of
inducers, substrates and inhibitors of mixed function oxidase system. Bull Environ Contam Toxicol
20:805-810.

*Perrine SE, McPhillips JJ. 1970. Specific subsensitivity of the rat atrium to cholinergic drugs. J
Pharmacol Exp Ther 175:496-502.

*Plumb RH Jr. 1991. The occurrence of Appendix IX organic constituents in disposal site ground
water. Ground Water Monit Revue 11:157-164.

*Poulsen LL. 1981. Organic sulfur substrates for the microsomal flavin-containing monooxygenase.
Rev Biochem Toxicol 3:33-49.

*Puhl RJ, Fredrickson DR. 1975. The metabolism and excretion of Di-Syston by rats. Report no.
44261. Mobay Chemical Corporation, Chemagro Agricultural Division, Kansas, MO.

*Putman DL. 1987. Sister chromatid exchange in Chinese hamster ovary (CHO) cells. Study No.
T51596.334. Microbiological Associates Inc., Bethesda, MD.

*Racke KD. 1992. Degradation of organophosphorus insecticides in environmental matrices. In:
Chambers JE, Levi PE, eds. Organophosphates: Chemistry, fate, and effects. San Diego, CA:
Academic Press, 47-78.

*Rao PSC, Davidson JM. 1982. Retention and transformation of selected pesticides and phosphorus
in soil-water systems: A critical review. Engineering Research Laboratory, Office of Research and
Development, Athens, GA. EPA-600/S3-82-060.

*Rao PSC, Homsby AG, Jessup RE. 1985. Indices for ranking the potential for pesticide
contamination of groundwater. Proceedings of the Soil and Crop Science Society of Florida 44:1-8.

*Rao SLN, McKinley WP. 1969. Metabolism of organophosphorus insecticides by liver homogenates
from different species. Can J Biochem 47:1155-1159.

*Rivett KF, Bhatt A, Street AB, et a1. 1972. Thio—demeton/oral toxicity to mice/dietary
administration for three months. Huntington Research Centre, England. Report No. 5505/72/901.

*Robinson CP, Smith PW, Endecott BR. 1978. Depression of cholinesterase activity by ethylestrenol
in organophosphorus-poisoned and normal rats. Toxicol Appl Pharmacol 44:207-211.

*Ruzicka JH, Thompson J, Wheals DD. 1967. The gas chromatographic determination of
organophosphorus pesticides. Part II. A comparative study of hydrolysis rates. J Chromatogr 31:37.

*Ruzicka JH, Thomson J, Wheals BB. 1968. Gas-chromatographic determination of
organophosphorus pesticides. Part V. Studies under field conditions. J Chromatogr 33:430-434.

*Ryan LC, Endecott BR, Hanneman GD, et a1. 1970. Effects of an organophosphorus pesticide on
reproduction in the rat. Department of Transportation, Federal Aviation Administration, Office of
Aviation Medicine, AD 709327.

mSULFOTON 201

8 REFERENCES

*Sanbom J K, Francis BM, Metcalf KL. 1977. The degradation of selected pesticides in soil: A
review of published literature. Cincinnati, OH: US. Environmental Protection Agency. EPA
600/9-77-022.

*Sandhu SS, Waters MD, Simmon VP, et a1. 1985. Evaluation of the genotoxic potential of certain
pesticides used in Pakistan in basic and applied mutagenesis. Basic Life Sci 34:185-219.

*Savage EP, Bagby JR Jr, Mounce L, et a1. 1971. Pesticide poisonings in rural Colorado. Rocky Mt
Med J 68:29-33.

*Schafer EW. 1972. Acute oral toxicity of 369 pesticidal, pharmaceutical, and other chemicals to
wild birds. Toxicol Appl Pharmacol 21:315-330.

*Schafer EW Jr, Bowles WH Jr. 1985. Acute oral toxicity and repellency of 933 chemicals to house
and deer mice. Arch Environ Contam Toxicol 14:111—129.

*Schattenberg HJ 111, Hsu J-P. 1992. Pesticide residue survey of produce from 1989 to 1991. J
Assoc Off Anal Chem Int 75(5):925-933.

*Schroeder WH, Dobson M, Kane DM, et a1. 1987. Toxic trace elements associated with airborne
particulate matter: A review. J Air Pollut Control Assoc 37:1267—1285.

*Schwab BW, Costa LG, Murphy SD. 1983. Muscarinic receptor alterations as a mechanism of
anticholinesterase (EC 3.1.1.7) tolerance. Toxicol Appl Pharmacol 71:14-23.

*Schwab BW, Hand H, Costa LG, et al. 1981. Reduced muscarinic receptor binding in tissues of rats
tolerant to the insecticide disulfoton. Neurotoxicology 22635—647.

*Schwab BW, Murphy SD. 1981. Induction of anticholinesterase tolerance in rats with doses of
disulfoton that produce no cholinergic signs. J Toxicol Environ Health 8:199-204.

*Shafik T, Bradway DE, Enos HF, et a1. 1973. Human exposure to organophosphorus pesticides. A
modified procedure for the gas-liquid chromatographic analysis of alkyl phosphate metabolites in
urine. J Agric Food Chem 21:625-629.

*Shaw HR 11. 1975. The metabolism of DI—SYSTON in soil. Research and Development
Department, Chemagro Division of Baychem Corporation. Report No. 40234.

*Sheets LP. 1993a. An acute oral neurotoxicity screening study with technical grade disulfoton
(DI-SYSTON) in rats. Study No. 92-412—OB, Report No. 103992. Miles Inc. Agriculture Division,
Toxicology, Stilwell, Kansas.

*Sheets LP. 1993b. An Subchronic dietary neurotoxicity screening study with technical grade
disulfoton (DI-SYSTON) in Fischer 344 rats. Study No. 92-472-HS, Report No. 106332. Miles Inc.
Agriculture Division, Toxicology, Stilwell, Kansas.

*Shiotsuka RN. 1988. Pilot assay to assess cholinesterase activity in rats exposed by inhalation to
technical grade disulfoton. Study No. 88-941-AG. Report No. 98358. Mobay Corporation,
Corporate Toxicology Department, Stilwell, Kansas.

MSULFOTON 202

& REFERENCES

*Shiotsuka RN. 1989. Subchronic inhalation toxicity study of technical grade disulfoton
(DI-SYSTON) in rats. Study No. 88—141—UA. Report No. 99648. Mobay Corporation, Corporate
Toxicology Department, Stilwell, Kansas.

*Shirasu Y, Moriya M, Tezuka H, et al. 1982. Mutagenicity screening studies on pesticides. In
Proceedings of the 3rd Environmental Mutagens and Carcinogens International Conference, Sept.
21-27, 1981, Tokyo, 331-335.

*Shirasu Y, Moriya M, Tezuka H, et al. 1984. Mutagenicity of pesticides. Environ Sci Res
31:617-624.

*Singh AK, Hewetson DW, Jordon KC, et al. 1986. Analysis of organophosphorus insecticides in
biological samples by selective ion monitoring gas chromatography-mass spectrometry. J Chromatogr
369:83-96.

*Singh BD, Singh Y, Sarma MDRK, et al. 1977. Cytogenetic aberrations and morphological changes
induced by insecticide treatments of barley seed. Indian J Exp Biol 15:688-691.

*Sipes IG and Gandolfi AJ. 1986. Biotransformation of toxicants. In: Klaasen CD, Andur MO,
Doull J, eds. Casarett and Doull’s toxicology. 3rd ed. New York, NY: Macmillan Publishing Co.,
64-98.

*Sittig M, ed. 1980. Pesticide manufacturing and toxic materials control encyclopedia. Park Ridge,
NJ : Noyes Data Corporation, 366-373.

*Sittig M, ed. 1985. Handbook of toxic and hazardous chemicals and carcinogens, 2nd edition. M.
Sittig, ed. Noyes Publications.

*Sittig M, ed. 1991. Disulfoton. In: Handbook of toxic and hazardous chemicals and carcinogens.
3rd ed. Park Ridge, NJ: Noyes Data Corporation, 695-696.

*Smith PW, Stavinoha WB, Ryan LC. 1968. Cholinesterase inhibition in relation to fitness to fly.
Aerosp Med 39:754-758.

*Smyser BP, Sabourin PJ, Hodgson E. 1985. Oxidation of pesticides by purified microsomal
FAD-containing monooxygenase from mouse and pig liver. Pest Biochem Physiol 24:368-374.

*Spalding RF, Snow DD. 1989. Stream levels of agrichemicals during a spring discharge event.
Chemosphere 19:1129-1 140.

*SRI. 1994. 1994 Directory of chemical producers: United States of America. Menlo Park, CA:
Stanford Research Institute International, 833.

*Stan HJ. 1989. Application of capillary gas chromatography with mass selective detection to
pesticide residue analysis. J Chromatogr 467(1):85-98.

*Stan HJ, Mrowetz D. 1983. Residue analysis of organophosphorus pesticides in food with
2-dimensional gas chromatography using capillary columns and flame photometric detection. J High
Res Chromatogr Chromatogr Commun 6:255-263.

mSULFOTON 203

8 REFERENCES

*Stavinoha WB, Ryan LC, Smith PW. 1969. Biochemical effects of an organophosphorus
cholinesterase inhibitor on the rat brain. Ann N Y Acad Sci 160:378-382.

*Stevens JT, Greene FE. 1974. Alteration of hepatic microsomal metabolism of male mice by certain '
anticholinesterase insecticides. Bull Environ Contam Toxicol 11:538-544.

*Stevens JT, Greene FE, Stitzel RB, et al. 1973. Effects of anticholinesterase insecticides on mouse
and rat liver microsomal mixed function oxidase. In: Deichmann W.B., Ed. Pesticides and the
environment: A continuing controversy. Proceedings of the 8th Inter-American Conference on
Toxicology and Occupational Medicine, University of Miami School of Medicine, 489-501.

*Stevens JT, Stitzel K, McPhillips JJ. 1972a. Effects of anticholinesterase insecticides on hepatic
microsomal metabolism. J Pharmacol Exp Ther 181:576-583.

*Stevens JT, Stitzel R, McPhillips JJ. 1972b. The effects of subacute administration of
anticholinesterase insecticides on hepatic microsomal metabolism. Life Sci (11) 11:423-431.

*Su M, Kinoshita FK, Frawley JP, et al 1971. Comparative inhibition of aliesterases and
cholinesterase in rats fed eighteen organophosphorus insecticides. Toxicol Appl Pharmacol
20:241- 249.

*Sundloff SF, Clemmons RM, Mayer DJ, et al. 1984. Cholinesterase activity in plasma, red blood
cells, muscle, and brain of dogs following repeated exposure to Spotton (Fenthion). Vet Hum Toxicol
26:112—1 17.

*Suzuki H, Ishikawa S. 1974. Ultrastructure of the ciliary muscle treated by organophosphate
pesticide in beagle dogs. Br J Ophthalmol 58:931-940.

*Swann RL, Laskowski DA, McCall P], et al. 1983. A rapid method for the estimation of the
environmental parameters, octanol/water partition coefficient, soil sorption constant, water to air ratio,
and water solubility. Residue Rev 85: 17- 28.

*Szeto SY, Brown MJ. 1982. Gas- -liquid chromatographic methods for detemiination of disulfoton,
phorate, oxydemeton- -methyl and their toxic metabolites in asparagus tissue and soil. J Agric Food
Chem 30: 1082- 1086.

*Szeto SY, Mackenzie JR, Vernon RS, et al. 1983b The degradation of disulfoton in lettuce after
application for control of the lettuce aphid, Nasonovia ribisnigri (Mosley). J Environ Sci Health
B18(6): 725- 731.

*Szeto SY, Vernon RS, Brown MJ. 1983a. Degradation of disulfoton in soil and its translocation into
asparagus. J Agric Food Chem 31:217-220.

Szutowski MM. 1975. Effect of carbon tetrachloride on activation and detoxification of
organophosphorus insecticides in the rat. Toxicol Appl Pharmacol 33:350-355.

*Takase I, Oyama O. 1985. Uptake and bioconcentration of disulfoton and its oxidation compounds
in carp, Cyprinus carpio L. J Pest Sci 10:47-53.

MSULFOTON 204

& REFERENCES

*Taylor RE. 1965a. Di-Syston, three generation rat breeding studies. Harris Laboratories, Inc.
Report No. 17164.

*Taylor RE. 1965b. Report on demyelination studies on hens. Report no. 15107. Harris
Laboratories, Inc.

*Tesh JM, Ross FW, Secher RG, et a1. 1982. S 276: Effects of oral administration upon pregnancy
in the rabbit. Report no. R 2351. Life Science Research, Essex, England.

*Thomas RG. 1990. Volatilization from water. In: Lyman WS, Reehl WF, Rosenblatt DH, eds.
Handbook of chemical property estimation methods. Washington, DC: American Chemical Society,
15-16.

*Thomton JS, Anderson CA. 1968. Determination of residues of Di-Syston and metabolites by
thermionic emission flame gas chromatography. J Agric Food Chem 16:895-898.

*Thomton JS, Hurley JB, Obrist JJ. 1976. Soil thin—layer mobility of twenty-four pesticides
chemicals. Research and Development Department, Chemagro Agricultural Division, Mobay Chemical
Corp. Report No. 51016.

*Thyssen JT. 1978. Acute inhalation toxicity. Report No. 7827. Bayer AG, Institute of Toxicology,
Wuppertal-Elberfeld, Germany.

*Thyssen JT. 1980. Subacute inhalation study on rats. Report No. 9065. Bayer AG, Institute of
Toxicology, Wuppertal-Elberfeld, Germany.

*Tomizawa L. 1975. Degradation of organophosphoms pesticides in soils with special reference to
anaerobic soil conditions. Environ Qual Saf 42117-127.

*Tomizawa L. 1980. Biological accumulation of pesticides in an ecosystem-evaluation of
biodegradability and ecological magnification of rice pesticides by a model ecosystem. Japanese
Agricultural Research Quarterly 14:143-149.

*Tynes RE, Hodgson E. 1985. Magnitude of involvement of the mammalian flavin-containing
monooxygenase in the microsomal oxidation of pesticides. J Agric Food Chem 33:471-479.

*Uga S, Ishikawa S, Mukuno K. 1977. Histopathological study of canine optic nerve retina treated
by organophosphate pesticide. Invest Ophthalmol Vis Sci 16:877~881.

*Uzokwu M. 1974. Comparative fete-toxicity of organophosphate insecticide in mice. Bull Epizoot
Dis Afr 22:161-166.

*Vaughn G, Deiniger E, Doull J. 1958. Determination of a safe dietary level of Di-Syston for dogs.
Department of Pharmacology, University of Chicago, Chicago, IL.

*Vaughn G, Deininger E, Doull J. 1958. Determination of a safe dietary level of Di-Syston for dogs.
University of Chicago, Chicago, IL.

MSULFOTON 205

a REFERENCES

*VonRumker R, Lawless EW, Meiners AF. 1974. Production, distribution, use and environmental
impact potential of selected pesticides. NTIS PB238 795.

*Wanner U, Egli, T., Fleischmann T, et a1. 1989. Behavior of the insecticides disulfoton and
thiometon in the Rhine River.A chemodynamic study. Environmental Science and Technology
23:1232-1242.

*Wamick SL, Eldredge JD. 1972. Human and environmental exposure to pesticides in Utah.
Proceedings of the Utah Academy of Science Arts Letters 49:1972.

*Waters, MD, Nesnow S, Simmon VF, et a1. 1981. Pesticides: Mutagenic and carcinogenic potential.
ACS Symposium Series 160. Washington, DC: American Chemical Society, 89—113.

*Waters MD, Sandhu SS, Simmon VF, et a1. 1982. Study of pesticide genotoxicity. Basic Life Sci
21:275-326.

Watson M Jr, Benson W Jr, Gabica J Jr. 1971. Accidental organophosphate poisoning in cattle,
two case histories. Arch Environ Health 22:582-583.

*Wauchope RD, Buttler TM, Homsby HG, et a1. 1992. The SCS/ARS/CES pesticide properties
database for 'environmental decision-making. Rev Environ Contam Toxicol 12:1-36.

*Waxman DJ, Light DR, Walsh C. 1982. Chiral sulfoxidations catalyzed by rat liver cytochromes
P-450. Biochemistry 21:2499-2507.

*Weil CS, Condra NJ, Carpenter CP. 1971. Correlation of four hour vs. 24 hour contact skin
penetration toxicity in the rat and rabbit and use of the former for prediction of relative hazard of
pesticide formulations. Toxicol Appl Pharmacol 18:734-742.

*Westfall DP, McPhillips JJ, Foley DJ. 1974. Inhibition of cholinesterase activity after
postganglionic denervation of the rat vas deferens: Evidence for prejunctional supersensitivity to
acetylcholine. J Pharmacol Exp Ther 189:493—498.

White DH, Seginak JT. 1990. Brain cholinesterase inhibition in songbirds from pecan groves sprayed
with phosalone and disulfoton. J Wildl Dis 26:103-106.

*Whitmore RW, Kelly JE, Reading PL. 1992. National home and garden pesticide survey. Office of
Pesticides and Toxic Substances, Biological and Economic Analysis Branch, US. Environmental
Protection Agency, Washington, DC. NTIS PB92-174747.

WHO. 1974. 1973 Evaluations of some pesticide residues in food: The monographs. WHO Pesticide
Residue Series no. 3. Geneva, Switzerland: World Health Organization.

*WHO. 1976. 1975 Evaluation of some pesticide residues in food: The monographs. WHO Pesticide
Residue Series no. 5. Geneva, Switzerland: World Health Organization.

*Winter CK. 1992. Dietary pesticide risk assessment. Rev Environ Contam Toxicol 127:23-67.

MSULFOTON 206

& REFERENCES

*Winterlin W, Seiper JM, Craigmill A, et al. 1989. Degradation of pesticide waste taken from a
highly contaminated soil evaporation pit in California USA. Arch Environ Contam Toxicol
18:734-747.

*Wolfe HR, Staiff DC, Armstrong JP, et al. 1978. Exposure of fertilizer mixing plant workers to
disulfoton. Bull Environ Contam Toxicol 20:79-86.

*Worthing CR, ed. 1987. The pesticide manual: A world compendium. 8th ed. Lavenham, Suffolk,
UK: The Lavenham Press, Ltd., 320-321.

*Wysocka-Paruszewska B. 1970. Urine level of 4—hydroxy-3-methoxymandelic acid in urine of rats
poisoned with phosphorus organic insecticides. Dissertationes Pharrnaceuticae et Pharmacologicae
22:485-489.

*Wysocka—Paruszewska B. 1971. Changes in the urine level of 4-hydroxy-3—methoxymandelic acid in
rats related to the degree of intoxication with Di-Syston. Dissertationes Pharrnaceuticae et
Pharrnacologicae 23:271-274.

*Yang LL. 1988. CHO/HGPRT mutation assay. Study No. T5196.332. Microbiological Associates
Inc., Bethesda, MD.

*Yashiki M, Kojima T, Ohtani M, et al. 1990. Determination of disulfoton and its metabolites in the
body fluids of a Di-Syston intoxication case. Forensic Sci Int 48:145-154.

*Yess NJ. 1991. Food and Drug Administration pesticide program residues in food 1990. J Assoc
Off Anal Chem 74:1-20.

*Yess NJ, Houston MG, Gunderson EL. 1991. Food and Drug Administration pesticide residue
monitoring of foods: 1978-1982. J Assoc Off Anal Chem 74:265-272.

*Zepp RG, Baughman GL. 1978. Prediction of photochemical transformation of pollutants in the
aquatic environment. In: Hutzinger U, Van Lilyveld IH, Zoeteman BCJ, eds. Aquatic pollutants.
Oxford: Pergamon Press.

*Zepp RG, Baughman GL, Schlotzhauer PF. 1981. Comparison of photochemical behavior of various
humic substances in water. I. Sunlight induced reactions of aquatic pollutants photosensitized by
human substances. Chemosphere 10:109-117.

*Zweig G, Devine JM. 1969. Determination of organophosphorous pesticides in water. Residue Rev
26:17-36.

DISULFOTON 207

9. GLOSSARY

Acute Exposure — Exposure to a chemical for a duration of 14 days or less, as specified in the
Toxicological Profiles.

Adsorption Coefficient (KM) — The ratio of the amount of a chemical adsorbed per unit weight of
organic carbon in the soil or sediment to the concentration of the chemical in solution at equilibrium.

Adsorption Ratio (Kd) — The amount of a chemical adsorbed by a sediment or soil (i.e., the solid
phase) divided by the amount of chemical in the solution phase, which is in equilibrium with the solid
phase, at a fixed solid/solution ratio. It is generally expressed in micrograms of chemical sorbed per
gram of soil or sediment.

Bioconcentration Factor (BCF) — The quotient of the concentration of a chemical in aquatic
organisms at a specific time or during a discrete time period of exposure divided by the concentration
in the surrounding water at the same time or during the same period.

Cancer Effect Level (CEL) — The lowest dose of chemical in a study, or group of studies, that
produces significant increases in the incidence of cancer (or tumors) between the exposed population
and its appropriate control.

Carcinogen — A chemical capable of inducing cancer.
Ceiling Value — A concentration of a substance that should not be exceeded, even instantaneously.

Chronic Exposure — Exposure to a chemical for 365 days or more, as specified in the Toxicological
Profiles.

Developmental Toxicity — The occurrence of adverse effects on the developing organism that may
result from exposure to a chemical prior to conception (either parent), during prenatal development, or
postnatally to the time of sexual maturation. Adverse developmental effects may be detected at any
point in the life span of the organism.

Embryotoxicity and Fetotoxicity — Any toxic effect on the conceptus as a result of prenatal
exposure to a chemical; the distinguishing feature between the two terms is the stage of development
during which the insult occurred. The terms, as used here, include malformations and variations,
altered growth, and in utero death.

EPA Health Advisory — An estimate of acceptable drinking water levels for a chemical substance
based on health effects information. A health advisory is not a legally enforceable federal standard,
but serves as technical guidance to assist federal, state, and local officials.

Immediately Dangerous to Life or Health (IDLH) — The maximum environmental concentration of
a contaminant from which one could escape within 30 min without any escape-impairing symptoms or
irreversible health effects.

Intermediate Exposure — Exposure to a chemical for a duration of 15-364 days, as specified in the
Toxicological Profiles.

DISULFOTON 208

9. GLOSSARY

Immunologic Toxicity — The occurrence of adverse effects on the immune system that may result
from exposure to environmental agents such as chemicals.

In vitro — Isolated from the living organism and artificially maintained, as in a test tube.
In vivo — Occurring within the living organism.

Lethal Concentrationafl, (LCLO) — The lowest concentration of a chemical in air which has been
reported to have caused death in humans or animals.

Lethal Concentrationm) (LCSO) — A calculated concentration of a chemical in air to which exposure
for a specific length of time is expected to cause death in 50% of a defined experimental animal
population.

Lethal Dose“), (LDLo) — The lowest dose of a chemical introduced by a route other than inhalation
that is expected to have caused death in humans or animals.

Lethal Dosem) (LDSO) — The dose of a chemical which has been calculated to cause death in 50% of
a defined experimental animal population.

Lethal Timem) (LTSO) — A calculated period of time within which a specific concentration of a
chemical is expected to cause death in 50% of a defined experimental animal population.

Lowest-Observed-Adverse-Effect Level (LOAEL) — The lowest dose of chemical in a study, or
group of studies, that produces statistically or biologically significant increases in frequency or severity
of adverse effects between the exposed population and its appropriate control.

Malformations —— Permanent structural changes that may adversely affect survival, development, or
function.

Minimal Risk Level — An estimate of daily human exposure to a dose of a chemical that is likely to
be without an appreciable risk of adverse noncancerous effects over a specified duration of exposure.

Mutagen — A substance that causes mutations. A mutation is a change in the genetic material in a
body cell. Mutations can lead to birth defects, miscarriages, or cancer.

Neurotoxicity — The occurrence of adverse effects on the nervous system following exposure to
chemical.

No-Observed-Adverse-Effect Level (NOAEL) — The dose of chemical at which there were no
statistically or biologically significant increases in frequency or severity of adverse effects seen
between the exposed population and its appropriate control. Effects may be produced at this dose, but
they are not considered to be adverse.

Octanol-Water Partition Coefficient (KW) — The equilibrium ratio of the concentrations of a
chemical in n-octanol and water, in dilute solution.

Permissible Exposure Limit (PEL) — An allowable exposure level in workplace air averaged over
an 8-hour shift.

DISULFOTON 209

9. GLOSSARY

q1* — The upper-bound estimate of the low-dose slope of the dose—response curve as detemrined by
the multistage procedure. The q1* can be used to calculate an estimate of carcinogenic potency, the
incremental excess cancer risk per unit of exposure (usually pg/L for water, mg/kg/day for food, and
ug/m3 for air).

Reference Dose (RfD) — An estimate (with uncertainty spanning perhaps an order of magnitude) of
the daily exposure of the human population to a potential hazard that is likely to be without risk of
deleterious effects during a lifetime. The RfD is operationally derived from the NOAEL (from animal
and human studies) by a consistent application of uncertainty factors that reflect various types of data
used to estimate Rst and an additional modifying factor, which is based on a professional judgment
of the entire database on the chemical. The Rst are not applicable to nonthreshold effects such as
cancer.

Reportable Quantity (RQ) — The quantity of a hazardous substance that is considered reportable
under CERCLA. Reportable quantities are (1) 1 pound or greater or (2) for selected substances, an
amount established by regulation either under CERCLA or under Sect. 311 of the Clean Water Act.
Quantities are measured over a 24-hour period.

Reproductive Toxicity —- The occurrence of adverse effects on the reproductive system that may
result from exposure to a chemical. The toxicity may be directed to the reproductive organs and/or the
related endocrine system. The manifestation of such toxicity may be noted as alterations in sexual
behavior, fertility, pregnancy outcomes, or modifications in other functions that are dependent on the
integrity of this system.

Short-Term Exposure Limit (STEL) — The maximum concentration to which workers can be
exposed for up to 15 min continually. No more than four excursions are allowed per day, and there
must be at least 60 min between exposure periods. The daily TLV—TWA may not be exceeded.

Target Organ Toxicity — This term covers a broad range of adverse effects on target organs or
physiological systems (e.g., renal, cardiovascular) extending from those arising through a single limited
exposure to those assumed over a lifetime of exposure to a chemical.

Teratogen — A chemical that causes structural defects that affect the development of an organism.

Threshold Limit Value (TLV) — A concentration of a substance to which most workers can be
exposed without adverse effect. The TLV may be expressed as a TWA, as a STEL, or as a CL.

Time-Weighted Average (TWA) —— An allowable exposure concentration averaged over a normal 8-
hour workday or 40-hour workweek.

Toxic Dose (TDso) — A calculated dose of a chemical, introduced by a route other than inhalation,
which is expected to cause a specific toxic effect in 50% of a defined experimental animal population.

Uncertainty Factor (UF) — A factor used in operationally deriving the RfD from experimental data.
UFs are intended to account for (1) the variation in sensitivity among the members of the human
population, (2) the uncertainty in extrapolating animal data to the case of human, (3) the uncertainty in
extrapolating from data obtained in a study that is of less than lifetime exposure, and (4) the
uncertainty in using LOAEL data rather than NOAEL data. Usually each of these factors is set equal
to 10.

DISULFOTON 1

APPENDIX A

USER’S GUIDE

Chapter 1
Public Health Statement

This chapter of the profile is a health effects summary written in non-technical language. Its intended
audience is the general public especially people living in the vicinity of a hazardous waste site or
chemical release. If the Public Health Statement were removed from the rest of the document, it
would still communicate to the lay public essential information about the chemical.

The major headings in the Public Health Statement are useful to find specific topics of concern. The
topics are written in a question and answer format. The answer to each question includes a sentence
that will direct the reader to chapters in the profile that will provide more information on the given
topic.

Chapter 2
Tables and Figures for Levels of Significant Exposure (LSE)

Tables (2-1, 2-2, and 2-3) and figures (2—1 and 2-2) are used to summarize health effects and illustrate
graphically levels of exposure associated with those effects. These levels cover health effects observed
at increasing dose concentrations and durations, differences in response by species, minimal risk levels
(MRLs) to humans for noncancer end points, and EPA’s estimated range associated with an
upper-bound individual lifetime cancer risk of 1 in 10,000 to 1 in 10,000,000. Use the LSE tables and
figures for a quick review of the health effects and to locate data for a specific exposure scenario. The
LSE tables and figures should always be used in conjunction with the text. All entries in these tables
and figures represent studies that provide reliable, quantitative estimates of
No-Observed-Adverse-Effect Levels (NOAELs), Lowest-Observed-Adverse-Effect Levels (LOAELs),
or Cancer Effect Levels (CELs). ~

The legends presented below demonstrate the application of these tables and figures. Representative
examples of LSE Table 2-1 and Figure 2-1 are shown. The numbers in the left column of the legends
correspond to the numbers in the example table and figure.

LEGEND
See LSE Table 2-1

(1) Route of Exposure One of the first considerations when reviewing the toxicity of a substance
using these tables and figures should be the relevant and appropriate route of exposure. When
sufficient data exists, three LSE tables and two LSE figures are presented in the document. The
three LSE tables present data on the three principal routes of exposure, i.e., inhalation, oral, and
dermal (LSE Table 2-1, 2-2, and 2-3, respectively). LSE figures are limited to the inhalation
(LSE Figure 2-1) and oral (LSE Figure 2-2) routes. Not all substances will have data on each
route of exposure and will not therefore have all five of the tables and figures.

DISULFOTON 2

APPENDIX A

(2) Exposure Period Three exposure periods - acute (less than 15 days), intermediate (15—364 days),
and chronic (365 days or more) are presented within each relevant route of exposure. In this
example, an inhalation study of intermediate exposure duration is reported. For quick reference
to health effects occurring from a known length of exposure, locate the applicable exposure
period within the LSE table and figure.

(3) Health Effect The major categories of health effects included in LSE tables and figures are
death, systemic, immunological, neurological, developmental, reproductive, and cancer.
NOAELS and LOAELs can be reported in the tables and figures for all effects but cancer.
Systemic effects are further defined in the "System" column of the LSE table (see key number
18).

(4) Key to Figure Each key number in the LSE table links study information to one or more data
points using the same key number in the corresponding LSE figure. In this example, the study
represented by key number 18 has been used to derive a NOAEL and a Less Serious LOAEL
(also see the 2 "l8r" data points in Figure 2—1).

(5) Species The test species, whether animal or human, are identified in this column. Section 2.4,
"Relevance to Public Health," covers the relevance of animal data to human toxicity and Section
2.3, "Toxicokinetics," contains any available information on comparative toxicokinetics.
Although NOAELs and LOAELs are species specific, the levels are extrapolated to equivalent
human doses to derive an MRL.

(6) Exposure Frequency/Duration The duration of the study and the weekly and daily exposure
regimen are provided in this column. This permits comparison of NOAELs and LOAELs from
different studies. In this case (key number 18), rats were exposed to 1,1,2,2-tetrachloroethane
via inhalation for 6 hours per day, 5 days per week, for 3 weeks. For a more complete review
of the dosing regimen refer to the appropriate sections of the text or the original reference paper,
i.e., Nitschke et al. 1981.

(7) System This column further defines the systemic effects. These systems include: respiratory,
cardiovascular, gastrointestinal, hematological, musculoskeletal, hepatic, renal, and dermal/ocular.
"Other" refers to any systemic effect (e.g., a decrease in body weight) not covered in these
systems. In the example of key number 18, 1 systemic effect (respiratory) was investigated.

(8) NOAEL A No-Observed-Adverse-Effect Level (NOAEL) is the highest exposure level at which
no harmful effects were seen in the organ system studied. Key number 18 reports a NOAEL of
3 ppm for the respiratory system which was used to derive an intermediate exposure, inhalation
MRL of 0.005 ppm (see footnote "b").

(9) LOAEL A Lowest—Observed-Adverse-Effect Level (LOAEL) is the lowest dose used in the
study that caused a harmful health effect. LOAELs have been classified into "Less Serious" and
"Serious" effects. These distinctions help readers identify the levels of exposure at which
adverse health effects first appear and the gradation of effects with increasing dose. A brief
description of the specific endpoint used to quantify the adverse effect accompanies the LOAEL.
The respiratory effect reported in key number 18 (hyperplasia) is a Less serious LOAEL of 10
ppm. MRLs are not derived from Serious LOAELs.

(10) Reference The complete reference citation is given in chapter 8 of the profile.

DISULFOTON
APPENDIX A

(11) CEL A Cancer Effect Level (CEL) is the lowest exposure level associated with the onset of
carcinogenesis in experimental or epidemiologic studies. CELs are always considered serious
effects. The LSE tables and figures do not contain NOAELs for cancer, but the text may report
doses not causing measurable cancer increases.

(12) Footnotes Explanations of abbreviations or reference notes for data in the LSE tables are found
in the footnotes. Footnote "b" indicates the NOAEL of 3 ppm in key number 18 was used to
derive an MRL of 0.005 ppm.

LEGEND

See Figure 2-1

LSE figures graphically illustrate the data presented in the corresponding LSE tables. Figures help the
reader quickly compare health effects according to exposure concentrations for particular exposure
periods.

(13)

(14)

(15)

(16)

(17)

(18)

(19)

Exposure Period The same exposure periods appear as in the LSE table. In this example, health
effects observed within the intermediate and chronic exposure periods are illustrated.

Health Effect These are the categories of health effects for which reliable quantitative data

exists. The same health effects appear in the LSE table.

Levels of Exposure concentrations or doses for each health effect in the LSE tables are
graphically displayed in the LSE figures. Exposure concentration or dose is measured on the log

II II

scale y axis. Inhalation exposure is reported in mg/m3 or ppm and oral exposure is reported in
mg/kg/day.

NOAEL In this example, 18r NOAEL is the critical endpoint for which an intermediate
inhalation exposure MRL is based. As you can see from the LSE figure key, the open-circle
symbol indicates to a NOAEL for the test species-rat. The key number 18 corresponds to the
entry in the LSE table. The dashed descending arrow indicates the extrapolation from the
exposure level of 3 ppm (see entry 18 in the Table) to the MRL of 0.005 ppm (see footnote "b"
in the LSE table).

CEL Key number 38r is 1 of 3 studies for which Cancer Effect Levels were derived. The
diamond symbol refers to a Cancer Effect Level for the test species-mouse. The number 38
corresponds to the entry in the LSE table.

Estimated Upper-Bound Human Cancer Risk Levels This is the range associated with the
upper-bound for lifetime cancer risk of 1 in 10,000 to 1 in 10,000,000. These risk levels are
derived from the EPA’s Human Health Assessment Group’s upper-bound estimates of the slope
of the cancer dose response curve at low dose levels (q1*).

Key to LSE Figure The Key explains the abbreviations and symbols used in the figure.

Amvxmmz, n V? 522%9 u ame u_m>m_ Hootmémhgvmfimtwwno
-o: n ._m_<Oz ”GEEOE n oE ”_m>m_ 6293.93-82mwno-~mm>>o_ u Had; xmrso: n E ”39% n U M_m>m_ Homtw 888 u do

 

 

 

 

 

 

 

 

 

 

 

 

 

 

.3E5m:m> cmEzc 52 or .wcmEzs 2 EEEm E0: cozfloambxm L2 o: 09 B 563 bEmtmucs cm >2 822v NF
05m 230qu EmEctsz 5* Emmi—um mmou ”Ema mbr x m 6 3E): _m>mj me REES cozmficE 2m6m§9£ cm @256 2 8w: 9 T
.TN 239“. E mmEcm 2 mucoawmtoo 63:5: 9:. M
£5
AmmEoSmwoacmec {tom
«mm? 3.2 99:2 9:: Jmov 0— x2, morlmn 3:22 o¢
EEO
AQOEB Emma xEvm
«we 32 99:2 95. fig 8 x; 37% am mm
3::
$590 x2<um
mm? ._m 6 9.25 29:2: Jmov om 9: m: 8m mm
a Bocmo
A
m B
m #5838 028:0
W IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
P
A
2.5
$2 v.58
._m 6 928:2 Amaggmgév 9 gm 98¢ {5 9 Em m: T v
a a a a a A, 2522.0, TB
H B I E E _:
mmeOaxm mkiomzmmhz. T N
8:829“. AEQE w:o:ww AEQQV wsocmw 83 Eng 823m c0293 36QO «93m:
#202 30533: 9 >3.
28:3 d<9 9:893
c2555: I _x Eng—:32 B Esmoaxm EmoEcEw ho w_w>w._ .TN m._m<._. T F

 

m._n=>_<m

 

 

DISULFOTON

 

 

 

DISULFOTON

APPENDIX A

 

 

 

 

 

 

 

 

 

 

2

 

 

 

 

 

 

 

I 5000000
.EBQ new 60:8 9: .2 29595 m E mocwfixm w£
>_QE_ 6c ow ucm 3:3me oEmmcoEE w 8886 :2: >35 Ea “57.2 wmou .326. m5 539%: $30 . .
I 50000 0
.222 mEESEooom
w£ :_ 8.55 2 mvcoamwtoo >wxcoE x I FOOOOd
ESQ comm o. :8: .mnEac wzh _m>m._ 62m. 3980 . do . mi 3:50 o
> 8.95:3 d<oz 0 52mm 5 L 500.0
$88 :9: $50 _ EmEEmv myomtm muonmm $2 83954 0 8:22 E
WO—v $023.2 _w>m_ xm: _mEE__>_ _ EmEEmv 38.5 $9me 53w<04 . 0mm _ I FOOd
m_w>w._ wa -0— 3x .
Lwocmo :mEzI m I F0 0
uczom. 5an or >
I uQmEzmm m- _ I *0
_
| v-8 “
_ I _.
$me
fivm ENN me uwr A I O F
5 0 am Gem.“ 0 :m 585 mmm 0;: gm 5 .9
Q .30 Emmum Q Q .00 . O C e EflOVN Q Q . . I 00—.
6 ER 0
o | 89
I 0000*
O ,0 ,N, ,N, ,6 O ,N, [W O
09 as as $9 0&9 es 0% 0&9 as €53 I
o v 9 e x 04 9 x 9/
9 O 0.. l v . I v .
« o o o e o a
* 00 O/ 0/ 0/ 0.1,
44. go o 0,. c I
a at A8
2E9m>m 2E9m>w
$23 $3: $23 v E
833,525 . m~=o<

cosmic... I "X 32—528 2 9.30an EmoEcmfi yo m_m>o._ .TN 2:9". I

 

m¢m2<m

 

 

 

 

mp

 

 

 

S.

 

 

 

m n

 

 

 

 

DISULFOTON 6

APPENDIX A

Chapter 2 (Section 2.4)
Relevance to Public Health

The Relevance to Public Health section provides a health effects summary based on evaluations of
existing toxicologic, epidemiologic, and toxicokinetic information. This summary is designed to
present interpretive, weight-of-evidence discussions for human health end points by addressing the
following questions.

1. What effects are known to occur in humans?
2. What effects observed in animals are likely to be of concern to humans?

3. What exposure conditions are likely to be of concern to humans, especially around hazardous
waste sites?

The section covers end points in the same order they appear within the Discussion of Health Effects
by Route of Exposure section, by route (inhalation, oral, dermal) and within route by effect. Human
data are presented first, then animal data. Both are organized by duration (acute, intermediate,
chronic). In vitro data and data from parenteral routes (intramuscular, intravenous, subcutaneous, etc.)
are also considered in this section. If data are located in the scientific literature, a table of
genotoxicity information is included.

The carcinogenic potential of the profiled substance is qualitatively evaluated, when appropriate, using
existing toxicokinetic, genotoxic, and carcinogenic data. ATSDR does not currently assess cancer
potency or perform cancer risk assessments. Minimal risk levels (MRLs) for noncancer end points (if
derived) and the end points from which they were derived are indicated and discussed.

Limitations to existing scientific literature that prevent a satisfactory evaluation of the relevance to
public health are identified in the Data Needs section.

Interpretation of Minimal Risk Levels

Where sufficient toxicologic information is available, we have derived minimal risk levels (MRLs) for
inhalation and oral routes of entry at each duration of exposure (acute, intermediate, and chronic).
These MRLs are not meant to support regulatory action; but to acquaint health professionals with
exposure levels at which adverse health effects are not expected to occur in humans. They should
help physicians and public health officials determine the safety of a community living near a chemical
emission, given the concentration of a contaminant in air or the estimated daily dose in water. MRLs
are based largely on toxicological studies in animals and on reports of human occupational exposure.

MRL users should be familiar with the toxicologic information on which the number is based.
Chapter 2.4, "Relevance to Public Health," contains basic information known about the substance.
Other sections such as 2.6, "Interactions with Other Substances,” and 2.7, "Populations that are
Unusually Susceptible" provide important supplemental information.

MRL users should also understand the MRL derivation methodology. MRLs are derived using a
modified version of the risk assessment methodology the Environmental Protection Agency (EPA)
provides (Barnes and Dourson 1988) to determine reference doses for lifetime exposure (Rst).

DISULFOTON 7

APPENDIX A

To derive an MRL, ATSDR generally selects the most sensitive endpoint which, in its best judgement,
represents the most sensitive human health effect for a given exposure route and duration. ATSDR
cannot make this judgement or derive an MRL unless information (quantitative or qualitative) is
available for all potential systemic, neurological, and developmental effects. If this information and
reliable quantitative data on the chosen endpoint are available, ATSDR derives an MRL using the
most sensitive species (when information from multiple species is available) with the highest NOAEL
that does not exceed any adverse effect levels. When a NOAEL is not available, a
lowest-observed-adverse-effect level (LOAEL) can be used to derive an MRL, and an uncertainty
factor (UF) of 10 must be employed. Additional uncertainty factors of 10 must be used both for
human variability to protect sensitive subpopulations (people who are most susceptible to the health
effects caused by the substance) and for interspecies variability (extrapolation from animals to
humans). In deriving an MRL, these individual uncertainty factors are multiplied together. The
product is then divided into the inhalation concentration or oral dosage selected from the study,
Uncertainty factors used in developing a substance-specific MRL are provided in the footnotes of the
LSE Tables.

DISULFOTON

ACGIH
ADME
atm
ATSDR
BCF
BSC

C

CDC
CEL
CERCLA
CFR
CLP
cm
CNS

d
DHEW
DHHS
DOL
ECG
EEG
EPA
EKG

F

F1
FAO
FEMA
FIFRA
fpm

ft

FR

g

GC
gen
HPLC
hr
IDLH
IARC
ILO

in

Kd

kg

kkg
KOC

K

0W

APPENDIX B

ACRONYMS, ABBREVIATIONS, AND SYMBOLS

American Conference of Governmental Industrial Hygienists
Absorption, Distribution, Metabolism, and Excretion
atmosphere

Agency for Toxic Substances and Disease Registry
bioconcentration factor

Board of Scientific Counselors

Centigrade

Centers for Disease Control

Cancer Effect Level

Comprehensive Environmental Response, Compensation, and Liability Act
Code of Federal Regulations

Contract Laboratory Program

centimeter

central nervous system

day

Department of Health, Education, and Welfare
Department of Health and Human Services
Department of Labor

electrocardiogram

electroencephalogram

Environmental Protection Agency

see ECG

Fahrenheit

first filial generation

Food and Agricultural Organization of the United Nations
Federal Emergency Management Agency

Federal Insecticide, Fungicide, and Rodenticide Act
feet per minute

foot

Federal Register

gram

gas chromatography

generation

high-performance liquid chromatography

hour

Immediately Dangerous to Life and Health
International Agency for Research on Cancer
International Labor Organization

inch

adsorption ratio

kilogram

metric ton

organic carbon partition coefficient

octanol-water partition coefficient

DISULFOTON

L

LC
LCLO
LCso
LDLo
LDso
LOAEL
LSE

m

mg

min

mL

mm
mm Hg
mmol
mo
mppcf
MRL
MS
NIEHS
N IOSH
NIOSH'IIC
ng

nm
NHANES
nmol
NOAEL
NOES
NOHS
NPL
NRC
NTIS
NTP
OSHA
PEL

Pg

pmol
PHS
PMR

ppb
ppm
ppt
REL
RfD
RTECS
sec
SCE
SIC
SMR

APPENDIX B

liter

liquid chromatography

lethal concentration, low

lethal concentration, 50% kill

lethal dose, low

lethal dose, 50% kill
lowest-observed-adverse-effect level

Levels of Significant Exposure

meter

milligram

minute

milliliter

millimeter

millimeters of mercury

millimole

month

millions of particles per cubic foot

Minimal Risk Level

mass spectrometry

National Institute of Environmental Health Sciences
National Institute for Occupational Safety and Health
NIOSH’s Computerized Information Retrieval System
nanogram

nanometer

National Health and Nutrition Examination Survey
nanomole

no-observed-adverse-effect level

National Occupational Exposure Survey

National Occupational Hazard Survey

National Priorities List

National Research Council

National Technical Information Service

National Toxicology Program

Occupational Safety and Health Administration
permissible exposure limit

picogram

picomole

Public Health Service

proportionate mortality ratio

parts per billion

parts per million

parts per trillion

recommended exposure limit

Reference Dose

Registry of Toxic Effects of Chemical Substances
second

sister chromatid exchange

Standard Industrial Classification

standard mortality ratio

DISULFOTON

STEL
STORET
TLV
TSCA

<mmp§lAA ulvv

mm
Hg

APPENDIX B

short term exposure limit
STORAGE and RETRIEVAL
threshold limit value

Toxic Substances Control Act
Toxics Release Inventory
time-weighted average
United States

uncertainty factor

year

World Health Organization
week

greater than

greater than or equal to
equal to

less than

less than or equal to
percent

alpha

beta

delta

gamma

micron

microgram

'U.S. GOVERNMENT PRINTING OFFICE:1995-639-298

C. BERKELEY LIBRARIES

 

 

lilflllllllllllllimlll

CDBLBGSS‘H

 

H