TOXICOLOGICAL PROFILE FOR

1,1-DICHLOROETHENE

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Agency for Toxic Substances and Disease Registry

May 1994
1,1-DICHLOROETHENE ii

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.
1,1-DICHLOROETHENE III

UPDATE STATEMENT

A Toxicological Profile for 1,1-dichloroethene was released on December 1990. This edition

supersedes any previously released draft or final profile.

Toxicological profiles are revised and republished as necessary, but no less than once every thret:

years. For information regarding the update status of previously released profiles, contact

ATSDR at:

Agency for Toxic Substances and Disease Registry

Division of Toxicology/Toxicology Information Branch

1600 Clifton Road NE, E-29

Atlanta, Georgia 30333



1,1-DICHLOROETHENE vii

CONTRIBUTORS

CHEMICAL MANAGER(S)/AUTHORS(S):

Cassandra Smith-Simon, M.S.

ATSDR, Division of Toxicology, Atlanta, GA

Sanjivani Diwan, Ph.D.

Clement International Corporation, Fairfax, VA

THE PROFILE HAS UNDERGONE THE FOLLOWING ATSDR INTERNAL REVIEWS:

1. Green Border Review. Green Border review assures the 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 endpoints.

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 Reviews. 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 fcllowed.

1,1-DICHLOROETHENE ix

PEER REVIEW

A peer review panel was assembled for 1,1-dichloroethene. The panel consisted of the following

members:

1. Dr. C. Clifford Conaway, Research Scientist, American Health Foundation, Valhalla, New

York

2 . Dr. Arthur Gregory, Private Consultant, Techto Enterprises, Sterling, Virginia

3 . Dr. Nancy Tooney, Associate Professor of Biochemistry, Department of Chemistry,

Polytechnic University, Brooklyn, New York.

These experts collectively have knowledge of 1,1-dichloroethene’s physical and chemical

properties, toxicokinetics, 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 104(i)(13) 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.









1,1-DICHLOROETHENE 1

1. PUBLIC HEALTH STATEMENT

This Statement was prepared to give you information about 1,1-dichloroethene and to

emphasize the human health effects that may result from exposure to it. The

Environmental Protection Agency (EPA) has identified 1,350 hazardous waste sites as the

most serious in the nation. These sites comprise the “National Priorities List” (NPL):

Those sites which are targeted for long-term federal cleanup activities. 1,1-dichloroethene

has been found in at least 492 of the sites on the NPL. However, the number of

NPL sites evaluated for 1,1-dichloroethene is not known. As EPA evaluates more sites,

the number of sites at which 1,1-dichloroethene is found may increase. This information

is important because exposure to 1,1-dichloroethene may cause harmful health effects

and because these sites are potential or actual sources of human exposure to

1,1-dichloroethene.

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 a substance such as 1,1-dichloroethene, 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-DICHLOROETHENE 2

1. PUBLIC HEALTH STATEMENT

1.1 WHAT IS 1,1-DICHLOROETHENE?

1,1-dichloroethene, also known as vinylidene chloride, is a chemical used to make certain

plastics (such as packaging materials, flexible films like SARAN wrap) and flameretardant

coatings for fiber and carpet backing. It is a colorless liquid that evaporates

quickly at room temperature. It has a mild sweet smell and burns quickly.

1,1-dichloroethene is a man-made chemical and is not found naturally in the environment.

Although 1,1-dichloroethene is manufactured in large quantities, most of it is used

to make other substances or products such as polyvinylidene chloride. For information

on the chemical and physical properties and use of 1,1-dichloroethene, see Chapters 3

and 4.

1.2 WHAT HAPPENS TO 1,1-DICHLOROETHENE WHEN IT ENTERS THE

 ENVIRONMENT?

1,1-dichloroethene can enter the environment when it is released to the air during its

production or released to surface water or soil as a result of waste disposal. Most

1,1-dichloroethene evaporates quickly and mainly enters the environment through the air,

although some enters into rivers or lakes. 1,1-dichloroethene can enter soil, water, and

air in large amounts during an accidental spill. 1,1-dichloroethene can also enter the

environment as a breakdown product of other chemicals in the environment.

1,1-dichloroethene behaves differently in air, water, and soil. 1,1-dichloroethene

evaporates to the air very quickly from soil and water. In the air, 1,1-dichloroethene is

broken down by reactive compounds formed by sunlight. 1,1-dichloroethene remains in

the air for about 4 days.

From water, 1,1-dichloroethene evaporates into the air; it breaks down very slowly in

water. We do not know exactly how long 1,1-dichloroethene stays in water. It is not

readily transferred to fish or birds, and only very small amounts enter the food chain.
1,1-DICHLOROETHENE 3

1. PUBLIC HEALTH STATEMENT

In soil, 1,1-dichloroethene either evaporates to the air or percolates down through soil

with rainwater and enters underground water. Small living organisms in soil and

groundwater may transform it into other less harmful substances, although this happens

slowly.

More information on what happens to 1,1-dichloroethene in the environment can be

found in Chapter 5.

1.3 HOW MIGHT I BE EXPOSED TO 1,1-DICHLOROETHENE?

You may be exposed to 1,1-dichloroethene by breathing it when it is in the air or eating

food or water that contains it. You may also be exposed to 1,1-dichloroethene if it

touches your skin. 1,1-dichloroethene is found at very low levels in indoor and outdoor

air (estimated as less than 1 part per trillion parts of air [ppt]). Therefore, the potential

for exposure in the environment is extremely low. The amounts are somewhat higher

near some factories that make or use 1,1-dichloroethene (those that make foodpackaging

films, adhesives, flame-retardant coatings for fiber and carpet backing, piping,

and coating for steel pipes), hazardous waste sites, and areas near accidental spills. The

exact amount of 1,1-dichloroethene in the air near these factories is not known. In air

around waste sites where it has been identified, the amount of 1,1-dichloroethene ranges

from 0.39 to 97 parts 1,1-dichloroethene per billion parts of air (ppb, 1 ppb is 1,000 times

more than 1 ppt). The levels of 1,1-dichloroethene in air around waste sites are usually

much lower than those that have caused health effects in animals. We estimate that

1,1-dichloroethene contaminates the air around 97 chemical factories in the United

States. Factories that make 1,1-dichloroethene are mainly located in Texas and

Louisiana. Measured air levels inside manufacturing plants range from less than 5 to

1900 parts 1,1-dichloroethene per million parts of air (ppm, 1 ppm is 1,000 times more

than 1 ppb).

A small percentage (3%) of the drinking water sources in the United States contain low

amounts of 1,1-dichloroethene (0.2-0.5 ppb with an estimated average of 0.3 ppb). The
1,1-DICHLOROETHENE 4

1. PUBLIC HEALTH STATEMENT

amounts are very low compared with levels that are expected to affect human health.

The concentration of 1,1-dichloroethene in groundwater samples from hazardous waste

sites ranged from 0.001 to 0.09 ppm.

Since 1,1-dichloroethene is used to make some ccmsumer products, exposure might occur

while these products are made or used. For example, the estimated average amount of

1,1-dichloroethene in plastic food-packaging films ranged from <0.02 to 1.26 ppm. The

measured average amount in food wrapped in these films was less than 0.01 ppm. Not

every tested food sample contained 1,1-dichloroethene, so these numbers only reflect the

levels found in food samples tested that did contain 1,1-dichloroethene. The Food and

Drug Administration (FDA) regulates the use of plastic packaging films. The FDA has

determined that the films can contain no more than 10 ppm 1,1-dichloroethene and that

the low levels of 1,1-dichloroethene found in food wrapped in these films present no

health risk to the consumer. Besides environmental exposures, occupational exposure

can occur for workers who are involved in the manufacture and use of 1,1-dichloroethene.

These workers include primarily carpenters, warehouse workers, and machine

operators. More information on human exposure can be found in Chapter 5.

1.4 HOW CAN 1,1-DICHLOROETHENE ENTER AND LEAVE MY BODY?

1,1-dichloroethene can easily enter the body through the lungs as an air pollutant or

through the stomach and intestines if you eat or drink contaminated food or water.

Based on the physical and chemical properties of 1,1-dichloroethene, we think that

1,1-dichloroethene can also enter the body through the human skin. Harmful effects

have occurred in animals after 1,3-dichloroethene was applied to their skin.

Animal studies indicate that following exposure, 1,1-dichloroethene partly leaves the body

through the lungs. The remaining 1,1-dichloroethene breaks down into other substances

that leave the body in the urine within 1-2 days. Some of the breakdown products of

1, 1-dichloroethene such as dithioglycolic acid, are more harmful than 1, 1-dichloroethene.

The way 1,1-dichloroethene and its breakdown products leave the body depends on the
1,1-DICHLOROETHENE 5

1. PUBLIC HEALTH STATEMENT

amount of 1,1-dichloroethene that enters the body. Low or moderate levels breathed in

(25-200 ppm) or taken by mouth (up to 50 milligrams per kilogram of body weight)

leave the body mainly as breakdown products in the urine. As the amount of

1,1-dichloroethene that enters the body increases, more and more 1,1-dichloroethene

leaves the body in the exhaled breath. Whether 1,1-dichloroethene is inhaled or taken by

mouth it leaves the body in about the same way. 1,1-dichloroethene is not stored very

much in the body when low-to-moderate amounts enter the body. More information on

how 1,1-dichloroethene enters and leaves the body is found in Chapter 2.

1.5 HOW CAN 1,1-DICHLOROETHENE AFFECT MY HEALTH?

How a chemical affects your health depends on how much you are exposed to and for

how long. As the level and length of your exposure increase, the effects are likely to

become more severe. Information on the health effects in humans after breathing

1,1-dichloroethene is insufficient. People who breathed high amounts of 1,1-dichloroethene

in a closed space lost their breath and fainted. Some people who breathed

1,1-dichloroethene at work for several years had abnormal liver function. However,

exposure to other chemicals may have also contributed to this effect. Available

information indicates that prolonged inhalation of 1,1-dichloroethene can induce adverse

neurological effects and is possibly associated with liver and kidney damage in humans.

Studies in animals indicate that 1,1-dichloroethene can affect the normal functions of the

liver, kidneys, and lungs. However, the amount of 1,1-dichloroethene in the air to which

the animals were exposed was much higher than the amounts in the air that the general

public usually breathes. Some animals that breathed large amounts of 1,1-dichloroethene

died within a few days. The liver and kidneys of animals were affected after breathing

air that contained 1,1-dichloroethene for days, months, or years. After pregnant rats

breathed 1,1-dichloroethene in air, some of the newborn rats had birth defects.

We have no information on health effects in humans who ate food or drank water that

contained 1,1-dichloroethene. Animals fed food that contained 1,1-dichloroethene or that

had 1,1-dichloroethene placed experimentally in their stomachs developed liver and
1,1-DICHLOROETHENE 6

1. PUBLIC HEALTH STATEMENT

kidney disease, and some even died. These amounts, however, were very much higher

than those which occur in drinking water supplies. Birth defects did not occur in the

newborn of female rats that drank 1,1-dichloroethene.

Spilling 1,1-dichloroethene on your skin or in your eyes can cause irritation. We do not

know what other health effects might occur if 1,1-dichloroethene comes into contact with

your skin for long periods. However, no serious effects or deaths occurred in mice after

small amounts of 1,1-dichloroethene were put on their skin over a period of months. We

do not know whether spilling 1,1-dichloroethene on your skin can cause birth defects or

affect fertility.

We do not know whether coming into contact with 1,1-dichloroethene increases the risk

of cancer in humans. Evidence from epidemiology studies of workers exposed to 1,1-dichloroethene

is inconclusive. Several studies examined the possibility that 1,1-dichloroethene

may increase the risk of cancer in animals. Only one of these studies indicated

that mice breathing 1,1-dichloroethene for 1 year developed kidney cancer, but the

particular type of mouse used may be especially sensitive to 1,1-dichloroethene.

The U.S. Department of Health and Human Services has not classified 1,1-dichloroethene

with respect to carcinogenicity. The International Agency for Research on

Cancer (IARC) has determined that 1,1-dichloroethene is not classifiable as to its

carcinogenicity in humans. The EPA has determined that 1,1-dichloroethene is a possible

human carcinogen. NTP does not include it in its list of substances expected to be

human carcinogens.

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

 EXPOSED TO 1,1-DICHLOROETHENE?

1,1-dichloroethene can be measured in the breath, blood, urine, and body tissues of

individuals who come in contact with the chemical. However, only relatively high levels

of 1,1-dichloroethene in body tissues and fluids can be measured. Because breath
1,1-DICHLOROETHENE 7

1. PUBLIC HEALTH STATEMENT

samples are easily collected, tests of exhaled air are now the most common way to tell

whether a person has been exposed to high levels of 1,1-dichloroethene. One of the

breakdown products of 1,1-dichloroethene, dithioglycolic acid, can also be measured in

urine. None of these tests are regularly available at a doctor’s office because they

require special equipment, but your doctor can tell you where you can get the tests done.

Although these tests can prove that a person has been exposed to 1,1-dichloroethene,

they cannot tell if any health effects will occur. Since most of the 1,1-dichloroethene

leaves the body within a few days, these methods are best for determining whether

exposures have occurred within the last several days. Detection of 1,1-dichloroethene or

its breakdown products in the body may not necessarily mean that exposure to

1,1-dichloroethene alone has occurred. People exposed to 1,1-dichloroethene at

hazardous waste sites were probably also exposed to other organic compounds, that

produce breakdown products similar to those of 1,1-dichloroethene. Other methods for

measuring the effects associated with exposure to 1,1-dichloroethene (such as reduced

enzyme levels) are not specific enough to detect effects caused by exposure to

1,l -dichloroethene alone. More information on the available tests for detecting

1,1-dichloroethene in the body is found in Chapter 6.

1.7 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT MADE TO

 PROTECT HUMAN HEALTH?

The federal government has developed regulatory guidelines and standards to protect

people from the possible health effects of 1,1-dichloroethene. The Occupational Safety

and Health Administration (OSHA) requires workplace exposure limits of 1 ppm or less

for an 9-hour workday to protect workers from noncancer harmful health effects. To

guarantee the maximum protection for human health from the possible cancer effects of

drinking water or eating seafood (fish or shellfish) that contain over a 1,1-dichloroethene

lifetime, the EPA recommends that the level of 1,1-dichloroethene in lakes and streams

should not exceed 0.003 ppm. EPA has determined that drinking water containing

3.5 ppm of 1,1-dichloroethene for adults and 1 ppm for children is not expected to cause

noncancerous harmful health effects. The National Institute for Occupational Safety and
1,1-DICHLOROETHENE 8

1. PUBLIC HEALTH STATEMENT

Health (NIOSH) has recommended that 1,1-dichloroethene is a potential occupational

cancer causing chemical.

The EPA limits the amount of 1,1-dichloroethene permitted in publicly owned waste

water treatment plants. To minimize human exposure to 1,1-dichloroethene, EPA

requires that industry tell the National Response Center when 100 pounds or more of

1,1-dichloroethene have been released in the environment.

For more information on federal and state recommendations, 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, E-29

Atlanta, Georgia 30333

(404) 498-0160

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.
1,1-DICHLOROETHENE 9

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

1,1-dichloroethene. 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 (LSE) 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
1,1-DICHLOROETHENE 10

2. HEALTH EFFECTS

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 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 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 cffccts

(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.

Levels of exposure associated with carcinogenic effects (Cancer Effect Levels, CELs) of

1,l -dichloroethene are indicated in Table 2-1 and Figure 2-1. Because cancer effects could occur

at lower exposure levels, Figures 2-1 and 2-2 also show a range for the upper bound of estimated

excess risks, ranging from a risk of 1 in 10,000 to 1 in 10,000,000 (10-4 to 10-7

), as developed by

EPA.

Estimates of exposure levels posing minimal risk to humans (Minimal Risk Levels or MRLs) have

been made for 1,1-dichloroethene. 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

1990a), uncertainties are associated with these techniques. Furthermore. ATSDR acknowledges
1,1-DICHLOROETHENE 11

2. HEALTH EFFECTS

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.

2.2.1 Inhalation Exposure

2.2.1.1 Death

No studies were located regarding death in humans after inhalation exposure to 1,1-dichloroethene.

However, animal studies indicate that 1,1-dichloroethene is lethal following inhalation

exposure.

The lethality of 1,1-dichloroethene in animals following inhalation exposure varies considerably

and is influenced by such factors as species, strain, sex, and food intake. Differences between

strains could account for the range in reported 4-hour LC 50 values in rats with access to food

(nonfasted rats) (≈6,000-8,000 ppm in males and 10,000 ppm in females) (Siegel et al. 1971;

Zeller et al. 1979a, 1979b). Higher 4-hour LC50 values (10,000-15,000 ppm) have also been

reported for nonfasted rats (sex not specified), but the animals were observed for only 24 hours

(Jaeger et al. 1973c, 1974).

The LC50 values reported for rats that were fasted for 16 hours were generally lower than those

reported for nonfasted rats. For instance, the reported 4-hour LC50 was 415 ppm in fasted male

rats (Zeller et al. 1979b). In fasted female rats, which appear to be more resistant to the

detrimental effects of starvation, the 4-hour LC50 was 6,545 ppm (Zeller et al. 1979b). A study

by Jaeger et al. (1974) compared the effects of food intake on the lethality of male rats exposed

to 1,1-dichloroethene for 24 hours. The results of the study revealed that the LC50 for fasted
1,1-DICHLOROETHENE 12

2. HEALTH EFFECTS

animals was almost 30 times lower than that for nonfasted animals. The proposed mechanism by

which fasting increases the toxicity of 1,1-dichloroethene is discussed in Sections 2.3 and 2.4.

Identical trends are seen in mice and hamsters (i.e., fasted vs. nonfasted and sex influence the

lethality of 1,1-dichloroethene following inhalation exposure). Mice, however, are considerably

more susceptible to the lethal effects of 1,1-dichloroethene than are rats. Reported 4-hour LC50

values in nonfasted mice range from 40 (males) to 200 ppm (females) (Henschler 1979; Oesch et

al. 1983; Short et al. 1977c) and in fasted mice from 40 (males) to 115 ppm (females) (Henschler

1979). Similarly, fasted male Chinese hamsters are more susceptible than fasted females to the

lethal effects of inhaled 1,1-dichloroethene (see Table 2-1) (Henschler 1979; Klimisch and

Freisberg 1979a, 1979b). Death was also reported in two out of three squirrel monkeys exposed

to 25 ppm 1,1-dichloroethene following intermediate exposure (Prendergast et al. 1967).

The LC50 values and all LOAEL values from each reliable study for death in each species and

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

2.2.1.2 Systemic Effects

Limited information is available on the systemic effects of inhaled 1,1-dichloroethene in humans.

This information comes primarily from case reports and/or insufficiently detailed mortality studies

in which the concentration and duration of exposure to 1,1-dichloroethene were not quantified.

Concurrent exposure to other toxic substances cannot be ruled out in most of these cases. Given

these limitations, the information available indicates that inhaled 1,1-dichloroethene can induce

neurotoxicity after acute exposure (EPA 1979b) and that 1,l -dichloroethene is possibly associated

with hepato- and nephrotoxicity after repeated, low-level exposure in humans (EPA 1976).

Considerable information is available on the systemic effects of 1,1-dichloroethene following both

acute, intermediate, and chronic exposure in laboratory animals. The target organs or systems of

1,1-dichloroethene toxicity are reported to be the central nervous system, liver, kidney, and lungs,

with adverse effects occasionally being noted in the heart.











1,1-DICHLOROETHENE 24

2. HEALTH EFFECTS

No studies were located regarding gastrointestinal or musculoskeletal effects in humans or animals

after inhalation exposure to 1,1-dichloroethene.The systemic effects observed following

inhalation exposure are discussed below.

The highest NOAEL values and all LOAEL values from each reliable study for systemic effects in

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

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

inhalation exposure to 1,1 -dichloroethene.

Acute swelling and localized bloody edema and congestion of the lungs are consistently seen at

necropsy in rodents acutely exposed to high levels of 1,1-dichloroethene (≈500-15,000 ppm) via

inhalation (Klimisch and Freisberg 1979a; Zeller et al. 1979a, 1979b); these effects were seen in

hamsters (Klimisch and Freisberg 1979a, 1979b) and along with emphysema in mice (Zeller et al.

1979c) exposed to lower concentrations (150 and 20 ppm, respectively).

Nasal irritation was observed in rats exposed to 200 ppm for 3 weeks (Gage 1970). However, no

histopathological effects attributed to treatment were observed in rats, monkeys, dogs, rabbits, or

guinea pigs exposed to 100 ppm 1,1-dichloroethene intermittently for 6 weeks (Prendergast et al.

1967) or in rats similarly exposed to 75 ppm 1,1-dichloroethene for 18 months (Quast et al. 1986).

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

after inhalation exposure to 1,1-dichloroethene.

Few studies are available that describe adverse cardiovascular effects of 1,1-dichloroethene

following inhalation exposure in laboratory animals. Acute exposure of rats to extremely high

concentrations (25,600 ppm for 10 minutes) produced arrhythmias mediated by the sympathetic

nervous system (Siletchnik and Carlson 1974). These study authors also found that 1,1-dichloroethene

at 25,600 ppm increased the sensitivity of the myocardium to epinephrine, thereby

providing a mechanism for the electrocardiographic changes. These effects are best characterized

as nonspecific neurological effects.
1,1-DICHLOROETHENE 25

2. HEALTH EFFECTS

Cardiac effects such as contraction of the main vessels, and hyperemia were observed following

acute, high-level exposure (≈500-15,000 ppm) to 1,1-dichloroethene (Klimisch and Freisberg

1979a, 1979b; Zeller et al. 1979b). Cardiovascular toxicity was not generally observed after more

prolonged, lower-level exposure and is, therefore, most likely not a concern for prolonged lowlevel

exposure in humans.

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

inhalation exposure to 1,1-dichloroethene.

The available studies did not evaluate the hematological parameters following acute and

intermediate exposure to 1,1-dichloroethene.No hematological alterations were observed in male

rats (Quast et al. 1986) or in mice (Lee et al. 1977) exposed to 75 ppm 1,1-dichloroethene for

18 months or to 55 ppm 1,1-dichloroethene for 12 months, respectively.

Hepatic Effects. Hepatotoxicity has been observed in humans after repeated exposure to

1,1-dichloroethene, presumably by the inhalation route. Preliminary clinical findings of workers

exposed to 1,1-dichloroethene for 6 years or less in a 1,1-dichloroethene polymerization plant

revealed a high incidence of hepatotoxicity. Liver scans and measurements of liver enzymes

revealed 50% or greater loss in liver function in 27 (59%) of the 46 exposed workers (EPA 1976).

These findings must be considered only qualitative in nature since the study provided few details

and no follow-up study has been reported.

In laboratory animals, the liver is a major target organ of 1,1-dichloroethene toxicity following

acute and chronic inhalation exposure. Hepatotoxicity is evident by the appearance of both

biochemical changes (alterations in serum enzyme levels indicative of liver injury and induction of

hepatic enzymes) and marked histological changes (e.g., midzonal and centrilobular swelling of

liver, degeneration, and necrosis of hepatocytes). These effects appear to follow a dose-response

relationship and may also be influenced by duration of exposure. Mice exposed to 50 ppm

1,1-dichloroethene for 6 hours exhibited only slight centrilobular swelling (Reitz et al. 1980;

Watanabe et al. 1980), whereas continuous inhalation exposure of mice to 15 ppm 1,1-dichloroethene

for 23 hours/day for 5 days caused cellular degeneration (Short et al. 1977d). Under the

same exposure regimen for 2 days, hepatic degeneration was seen at 60 ppm (Short et al. 1977d).

Similar results were obtained in four strains of mice that were exposed to 55, 100, or 200 ppm
1,1-DICHLOROETHENE 26

2. HEALTH EFFECTS

1,1-dichloroethene for 6 hours/day, 5 days/week, for 10 days. Hepatotoxic effects characterized by

hepatocellular degeneration and necrosis with centrilobular hepatocellular swelling and

pleomorphism at 100 and 200 ppm were observed in all strains. These effects were more severe

in females (Henck et al. 1979). Severe effects were seen at higher doses in rats for even shorterduration exposures. After inhalation exposure of rats to 200-250 ppm 1,1-dichloroethene for 4

hours the following effects were observed: increased liver weight, increased serum activities of

sorbitol dehydrogenase and ornithine carbamoyl transferase (Jackson and Conolly 1985; Jaeger

1977a, 1977b), and frank hemorrhagic centrilobular necrosis (Reynolds et al. 1980).

The food intake of the organism prior to exposure influences the degree of 1,1-dichloroetheneinduced hepatotoxicity, with more severe effects displayed by animals fasted overnight prior to

exposure. This suggests that a relationship exists between chemical toxicity and depletion of

reduced glutathione (GSH) (Reynolds et al. 1980). For example, results from an acute study in

male rats demonstrated that inhalation exposures to 150 ppm 1,1-dichloroethene for up to

24 hours induced increases in serum enzyme levels indicative of liver dysfunction-alanine aketoglutarate

transaminase (AKT)-in fasted animals to a greater extent compared to nonfasted

animals (Jaeger et al. 1974). A significant increase in the serum enzymes (AKT) was observed in

nonfasted rats exposed to 2,000 ppm or more 1,1-dichloroethene (Jaeger et al. 1974). Gross and

microscopic histopathological and biochemical evidence of hepatotoxicity occurs earlier and is

more extensive in fasted rats following short-term inhalation exposure to 1, 1-dichloroethene.

Exposing fasted rats to 200 ppm 1,1-dichloroethene for 4 hours or less resulted in aberrations in

hepatic GSH levels that preceded and/or accompanied major histological changes (Jaeger et

al. 1975b; McKenna et al. 1978b; Reynolds et al. 1980). As mentioned above, the increased

hepatotoxic effects of 1,1-dichloroethene following inhalation exposure seen in fasted versus

nonfasted animals may be related to depletion of hepatic GSH levels in the fasted animals. GSH

is known to be involved in 1,1-dichloroethene metabolism (see Section 2.3). GSH levels in rats

fed ad libitum exhibited a marked diurnal rhythm; levels were minimal between 7 pm and 1 am

and maximal between 7 am and 1 pm (Jaeger et al. 1973a). This increase was prevented in fasted

rats, with maximal levels reduced by 50%. Furthermore, the I,l-dichloroethene-induced

hepatotoxicity coincided with the reduction in liver GSH levels (Jaeger et al. 1973a). Nonfasted

rats exposed to 1,1-dichloroethene via inhalation during the period of maximal GSH levels

exhibited no signs of hepatotoxicity, but when they were exposed to similar levels of 1, I-dichloro-
1,1- DICHLOROETHENE 27

2. HEALTH EFFECTS

ethene during the diurnal period of minimal GSH levels, 40% died and serum enzyme markers

increased markedly.

The hepatotoxic effects of 1,1-dichloroethene following intermediate or chronic exposure in

animals are similar to those described above for acute exposure (Gage 1970; Lee et al. 1977;

Plummer et al. 1990; Quast et al. 1986). Many of the studies that describe the longer-term effects

of 1,1-dichloroethene in animals are limited in that only a few experimental details were provided

or only one or two doses were studied. These limitations often prevent an adequate assessment

of the quality of the results. Male and female rats exposed for 6 hours/day, 5 days/week, over a

day period, to 125 or 200 ppm 1,1-dichloroethene exhibited liver changes. These changes were

more severe in females and were characterized by a minimal degree of centrilobular fatty

degeneration or hepatocellular necrosis (Quast 1976). Mild dose-related cytoplasmic vacuolation

was observed in male and female rats exposed to 25 or 75 ppm 1, 1-dichloroethene 6 hours/day,

5 days/week, for either 30 or 90 days (Balmer et al. 1976). The study authors considered this

effect reversible. Fatty infiltration of the liver was reported in rats exposed to 25 ppm of

1,1-dichloroethene 6 hours/day, 5 days/week, for 6 months (Quast et al. 1986).

Animals appear to be much less tolerant of continuous exposure (23-24 hours per day) than

intermittent exposure. There was no evidence of toxicity in beagle dogs exposed to 100 ppm of

1,1-dichloroethene for 8 hours/day, 5 days/week, for 42 days, but continuous exposure to 48 ppm

of 1, 1-dichloroethene for 90 days caused marked liver damage (Prendergast et al. 1967). Similarly,

squirrel monkeys continuously exposed to 48 ppm 1, 1-dichloroethene for 90 days exhibited

marked evidence of liver damage (i.e., focal necrosis and hemosiderin deposition). However, no

liver toxicity was apparent following 42 days of intermittent exposure to 100 ppm 1,1-dichloroethene

(Prendergast et al. 1967). It would appear that when animals are exposed to 1,1-dichloroethene

on an intermittent basis, they are better able to compensate for the toxic effects induced

by this chemical. This observation supports the involvement of depletable stores of liver GSH as

a possible mediator of 1,1-dichloroethene-induced hepatotoxicity.

Liver effects in guinea pigs exposed to 5, 15, 25, or 48 ppm of 1,1-dichloroethene for 24 hours per

day for 90 days were mottled livers at 15 ppm, and increased SGPT and AP enzyme levels at 45

ppm (Prendergast et al. 1967). Using a NOAEL of 5 ppm based on liver changes, an
1,1- DICHLOROETHENE 28

2. HEALTH EFFECTS

intermediate inhalation MRL of 0.02 ppm was calculated as described in the footnote in

Table 2-1.

Hepatotoxic effects similar to those discussed above are seen following chronic inhalation

exposure to 1,1-dichloroethene in laboratory animals (Lee et al. 1977; Quast et al. 1986). Female

rats exposed to 1,1-dichloroethene via inhalation at a concentration of 25 ppm for 6 hours/day,

5 days/week, for 18 months, exhibited fatty changes in the liver (Quast et al. 1986). The results of

these studies are only suggestive because of the poor presentation of the data.

Renal Effects. No studies were located regarding renal effects in humans after inhalation

exposure to 1,1-dichloroethene.

Adverse effects have been observed in the kidneys of laboratory animals following acute,

intermediate, and chronic inhalation exposure to 1,1-dichloroethene. These effects are manifested

as enzyme changes (decreases in kidney monooxygenase and epoxide hydrolase levels) (Oesch et

al. 1983), tubular alterations (hemoglobinuria) (McKenna et al. 1978b), gross changes (increase in

organ weight) (Henck et al. 1979; Quast et al. 1986), and histological changes (tubular swelling,

degeneration, and necrosis) (Henck et al. 1979; Jackson and Conolly 1985; Lee et al. 1977;

McKenna et al. 1978b; Prendergast et al. 1967; Reitz et al. 1980; Short et al. 1977d; Watanabe et

al. 1980). Following acute exposure, the range of 1,1-dichloroethene concentrations that

produced the aforementioned effects in rats was 50-300 ppm, with the severity of the kidney

lesions increasing with increasing dose and duration of exposure. Male mice appear to be more

susceptible to the acute nephrotoxic effects of inhaled 1,l-dichloroethene than female mice or

both sexes of rats. Severe histological lesions of the kidney were observed in mice following acute

inhalation exposure to 10-50 ppm of 1,1-dichloroethene (Reitz et al. 1980; Short et al. 1977c;

Watanabe et al. 1980). Similar results were obtained in four strains of mice exposed to 55, 100,

or 200 ppm for 6 hours/day, 5 days/week, for 10 days. Adverse renal effects (characterized by

moderate-to-severe nephrosis) were observed in all strains, with the effects observed

predominantly in the male mice (Henck et al. 1979).

There is evidence that kidney damage in animals after acute inhalation exposure to 1,1-dichloroethene

is reversible, though this may depend on the dose level and duration of exposure. Tubular

regeneration was evident in mice after a single 6-hour exposure to 50 ppm 1,l -dichloroethene
1,1- DICHLOROETHENE 29

2. HEALTH EFFECTS

(Reitz et al. 1980). However, reversibility of kidney damage at higher exposure concentrations

has not been demonstrated.

As was seen with hepatotoxicity, the amount of food intake of the animal appears to be an

important determinant of 1,1-dichloroethene-induced nephrotoxicity. Fasted male rats exposed

once to 200 ppm 1,1-dichloroethene for 6 hours exhibited delayed hemoglobinuria and marked

tubular degeneration, while fed male rats similarly exposed displayed no treatment-related toxic

effects (McKenna et al. 1978b). GSH depletion may play an indirect role in the exacerbation of

1,l -dichloroethene-induced nephrotoxicity in the fasted rat.

The bulk of the information on 1,1-dichloroethene-induced nephrotoxicity in animals comes from

acute experiments, and evidence of nephrotoxicity after intermediate exposure is limited.

Continuous inhalation exposure of rats to 48 ppm 1,1-dichloroethene for 90 days resulted in

nuclear hypertrophy of the renal tubular epithelium (Prendergast et al. 1967). Severe

nephrotoxicity occurred in male mice exposed to 25 ppm 1, 1-dichloroethene 4 hours/day,

4-5 days/week, for 52 weeks (Maltoni et al. 1985). The reversibility of this effect was not

determined. No treatment-related effects were noted in the kidneys of rats chronically exposed to

a concentration of 25 or 75 ppm 1,1-dichloroethene for 6 hours/day, 5 days/week, for 18 months

(Quast et al. 1986). Strain differences may account for the differential susceptibility to

1,l -dichloroethene exposure.

Dermal/Ocular Effects. No studies were located regarding dermal/ocular effects in humans

following inhalation exposure to 1 ,l -dichloroethene.

No eye irritation was observed in rats exposed to an average concentration of 75 ppm 1,1-dichloroethene

for 18 months (Quast et al. 1986).

Other Systemic Effects. No studies were located regarding other systemic effects in humans

after inhalation exposure to 1,1-dichloroethene.

A slight decrease in body weight was reported in rabbits exposed to 25 ppm 1,1-dichloroethene

continuously for 90 days or to 100 ppm 1,1-dichloroethene intermittently for 6 weeks (Prendergast

et al. 1967). Similar results were reported in monkeys exposed to 48 ppm 1,1-dichloroethene
1,1- DICHLOROETHENE 30

2. HEALTH EFFECTS

continuously for 90 days or intermittently to 100 ppm 1,1-dichloroethene for 6 weeks (Prendergast

et al. 1967). Food consumption data were not provided. A decrease in body weight was also

reported in rats exposed to 500 ppm 1,1-dichloroethene intermittently for 3 weeks, but the

magnitude of the effect was not reported (Gage 1970).

2.2.1.3 Immunological Effects

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

exposure to 1,l -dichloroethene.

2.2.1.4 Neurological Effects

Central nervous system depression and symptoms of inebriation, which may progress to

unconsciousness, have been observed in humans after acute exposure to high airborne

concentrations (≈4,000 ppm) of 1,1-dichloroethene (EPA 1979b). Complete recovery generally

occurs if exposure is not prolonged. However, two cases of persistent cranial nerve disorders

were observed following acute inhalation exposure to 1,l -dichloroethene. These cases primarily

involved the trigeminal nerve and, to a lesser extent, the hypoglossal, occipital, auricular, and

cervical cutaneous nerves, as well as the innervation of muscles of mastication and eye muscles.

These two patients were involved in manually cleaning tanks used in the transport of an aqueous

dispersion of 1,1-dichloroethene copolymers. The effects were most likely a result of

dichloroacetylene formation from 1,1-dichloroethene due to heat and the presence of alkali from

the soaps used; chloroacetylenes are highly neurotoxic (Fielder et al. 1985). There is no direct

evidence that 1,1-dichloroethene can produce adverse neurological effects by itself, but it is

possible that similar conditions could occur (i.e., heat and an alkali environment) and cause

neurotoxicity due to chloroacetylenes generated from 1,1-dichloroethene at hazardous waste sites.

Signs of central nervous system toxicity were observed in animals after acute inhalation exposure.

The toxic signs are similar across species and consist primarily of central nervous system

depression, dyspnea, and narcosis, ultimately resulting in death (Klimisch and Freisberg 1979a,

1979b; Zeller et al. 1979a, 1979b). These signs can also be accompanied by lethargy, rough coats,

and a hunched appearance (Zeller et al. 1979b). Acute exposure of rats to extremely high
1,1- DICHLOROETHENE 31

2. HEALTH EFFECTS

concentrations (25,600 ppm for 10 minutes) induced increased sympathetic activity, resulting in

cardiac arrhythmia (Siletchnik and Carlson 1974).

2.2.1.5 Reproductive Effects

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

1,1-dichloroethene.

Premating exposure of male rats to 55 ppm l,1-dichloroethene 6 hours/day, 5 days/week, for

11 weeks did not affect their fertility (Short et al. 1977b); no pre- or post-implantation losses

occurred in untreated pregnant females mated to treated males in a dominant-lethal study.

Similarly, inhalation exposure of male mice to 10 or 30 ppm 1,1-dichloroethene for 6 hours/day

for 5 days appeared to have no adverse effect on fertility (Anderson et al. 1977). Decreased

fertility was observed in rats following inhalation exposure to 50 ppm 1,1-dichloroethene for

5 days. The study authors attributed the decrease to infertility in males that ordinarily might not

have been used but had to be included in the study in order to establish a sufficient group size.

However. this could not be confirmed because of lack of sufficient details.

The highest NOAEL value from a reliable study for reproductive effects in each species and

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

2.2.1.6 Developmental Effects

No studies were located regarding developmental effects in humans following inhalation exposure

to 1,l -dichloroethene.

1,l -Dichloroethene appears to produce both fetotoxic and developmental effects in laboratory

animals (Short et al. 1977a). Prenatal exposure resulted in soft tissue anomalies in rats and

skeletal defects in rats, mice, and rabbits. Maternal toxicity, as evidenced by decreased body

weight and death, was also observed al developmentally toxic doses. Doses of 1,l -dichloroethene

used in these studies ranged from 15 to 449 ppm. Increased mortality was observed in both

pregnant and nonpregnant mice exposed to 144 ppm or more and rats exposed to 57 ppm or

more. Skeletal anomalies in rats and mice and soft tissue anomalies in rats were observed at
1,1- DICHLOROETHENE 32

2. HEALTH EFFECTS

15 ppm. Because of the high incidence of fetal resorptions observed in these initial experiments,

Short et al. (1977a) conducted additional studies in mice. Pregnant animals were exposed via

inhalation to various concentrations of 1,1-dichloroethene ranging from 41 to 112 ppm. The

experiments were performed over different exposure durations that covered various phases of

fetal development. Statistical analysis by two sample rank tests demonstrated that treatmentinduced

increases in resorption frequency were significantly reduced at the shorter exposure

periods, although the treatment-related weight loss was still evident in the dams. The viable pups

demonstrated a variety of soft tissue anomalies, such as hydrocephalus, microphthalmia, cleft

palate, and hydronephrosis. Skeletal anomalies were also observed.

A statistically significant increase in the incidence of skeletal anomalies was observed in the litters

of rats exposed to 80 and 160 ppm 1,1-dichloroethene and in the litters of rabbits exposed to

160 ppm 1,l -dichloroethene (Murray et al. 1979). Developmental effects were evidenced by wavy

ribs and delayed ossification in rat fetuses and skeletal alterations in rabbit fetuses. Fetotoxicity

was indicated by increased resorption. A statistically significant decrease in maternal body weight

gain was also noted at these concentrations. In this study, no statistically significant adverse

effects were noted in rats exposed to 20 ppm or in rabbits exposed to 80 ppm 7 hours daily during

pregnancy. A NOAEL for developmental toxicity following continuous inhalation exposure was

not identified.

The highest NOAEL values and all LOAEL values from each reliable study for developmental

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

2.2.1.7 Genotoxic Effects

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

1,l -dichloroethene.

Dominant lethal gene mutations have not been found to occur after inhalation of 1,1-dichloroethene

vapors in animals (Anderson et al. 1977; Short et al. 1977b). However, 1, 1-dichloroethene

has produced deoxyribonucleic acid (DNA) damage, as indicated by a slight increase in repair

rates in mouse kidney cells in which normal replicative DNA synthesis had been inhibited (Reitz

et al. 1980). Inhalation of 1,1-dichloroethene has been associated with minimal rates of DNA
1,1- DICHLOROETHENE 33

2. HEALTH EFFECTS

alkylation in mouse and rat kidney and liver cells (Reitz et al. 1980). These data suggest that

inhalation exposure of rats to 55 ppm and mice to 10, 30, and 50 ppm of 1,1-dichloroethene for

6 hours/day for 5 days does not lead to significant levels of unrepaired DNA damage in the germ

cells of the testes (as shown by the lack of a dominant lethal effect). However, exposure of mice

and rats to 10 and 50 ppm for 6 hours induces a low incidence of DNA damage in the kidney

cells of mice and minimal alkylation in the liver and the kidney of mice and rats. 1,l -dichloroethene

appears to exert genotoxic effects on somatic cells but not on germ cells.

Other genotoxicity studies are discussed in Section 2.4.

2.2.1.8 Cancer

No relationship between the occurrence of cancer in humans and occupational exposure

(primarily chronic inhalation exposure) to 1,1-dichloroethene has been demonstrated. However,

only two studies were available for analysis. In addition, neither study was large enough to

demonstrate a relationship between cancer and 1,1-dichloroethene unless there was an overt

causality.

Chronic occupational exposure to I,l-dichloroethene was not associated with the occurrence of

angiosarcoma in rubber-plant workers (Waxweiler 1981). Similarly, no association was found

between occupational exposure and cancer mortality in 1,1-dichloroethene production and

polymerization plant workers (Ott et al. 1976). The Ott et al. (1976) study is limited in its

usefulness in assessing the cancer risk to humans exposed to 1,1-dichloroethene. The cohort size

was limited, the observation period was too short, and there was a small number of deaths from

specific causes. No allowance was made for a latency period; thus, potential risk was

underestimated. The Ott et al. (1976) study described liver enzyme changes in two workers and

gave clinical chemistry findings comparing two cohorts. None of the clinical chemistry values were

significantly different between the two cohorts.

The carcinogenicity of 1,1-dichloroethene in laboratory animals following inhalation exposure has

been evaluated in intermediate and chronic studies with rats, mice, and Chinese hamsters (Hong

et al. 1981; Lee et al. 1977, 1978; Maltoni et al. 1982; Quast et al. 1986; Rampy et al. 1977; Viola

and Caputo 1977). Exposure concentrations of 1,1-dichloroethene in these studies ranged from
1,1- DICHLOROETHENE 34

2. HEALTH EFFECTS

10 to 200 ppm. Of the long-term inhalation bioassays conducted in laboratory animals to date,

only the results of a study by Maltoni et al. (1985) in mice have provided some suggestive

evidence of a carcinogenic effect associated with 1,1-dichloroethene exposure.

In a study reported by Maltoni et al. (1985), male and female Swiss mice were exposed by

inhalation to 0, 10, or 25 ppm 1,1-dichloroethene 4 hours/day, 4-5 days/week, for 52 weeks, and

then observed until spontaneous death occurred. Increases in both malignant and nonmalignant

tumors were observed. In female mice of both treatment groups (10 and 25 ppm), increases in

the incidence of carcinomas of the mammary gland occurred; however, no dose-response was

evident. Lung tumors (most of which were benign pulmonary adenomas) increased in males at

10 ppm and in males and females at 25 ppm. Although the study authors stated that these

increases were statistically significant, no statistical analyses were presented. The study authors

concluded that no dose-response relationship could be established for either increased tumor

incidence. Of the 150 high-dose males in the 25-ppm group examined, 28 had renal

adenocarcinomas, but no such tumors were found in either the 30 males in the low-dose (10 ppm)

group or the 186 control males. Renal adenocarcinomas are rare tumors in the Swiss mouse.

The kidney tumors were accompanied by severe nephrotoxic effects including nephrosis.

Moreover, an increased incidence of renal tumors in the male mice was only observed at doses

that induced toxicity and which approximated the acutely lethal concentration. Only one female

developed kidney tumorsj but there appeared to be no difference between the sexes with regard

to the incidence of regressive changes in the kidney. Thus, it does not appear that the occurrence

of nephrosis necessarily predisposes the animal to the development of kidney tumors.

An increased incidence of malignant mammary tumors and leukemia was reported in rats exposed

to 100 ppm 1,1-dichloroethene 4-7 hours/day, 5 days/week, for 104 weeks (Cotti et al. 1988;

Maltoni et al. 1985). Pregnant female rats were exposed on gestation day 12; the exposures

continued in dams and ≈50% of the offspring (in 12-day and older embryos via transplacental

exposure, followed by inhalation exposure for all progeny from this group) for 104 weeks. The

remaining ≈50% were exposed for 15 weeks only. The highest tumorigenic response was seen in

offspring treated for 104 weeks. The study authors concluded that under these exposure

conditions (high doses during and after embryonal development), 1,1-dichloroethene is

carcinogenic in rats. However. the results of this study are not definitive since the, study authors
1,1- DICHLOROETHENE 35

2. HEALTH EFFECTS

did not present statistical analyses and used ambiguous terminology (i.e., “total malignant tumors”)

to present the results.

Results of other inhalation studies with laboratory animals were negative regarding carcinogenicity

(Hong et al. 1981; Lee et al. 1977, 1978; Maltoni et al. 1982; Quast et al. 1986; Rampy et

al. 1977; Viola and Caputo 1977). In studies by Lee et al. (1977, 1978), CD-l mice and CD rats

were exposed to 0 or 55 ppm 1,1-dichloroethene for 1 year. Few hepatic hemangiosarcomas,

hepatomas, bronchioalveolar adenomas, and skin keratoacanthomas were observed in

experimentally treated mice; however, some of the rats exposed to 55 ppm 1,1-dichloroethene

developed hemangiosarcomas of the mesenteric lymph nodes and the subcutaneous tissue. The

incidence of these lesions, however, was not statistically significant. In a follow-up study,

curcinogenicity was examined in rats and mice during a 12-month period (Hong et al. 1981).

Except for mammary tumors in female mice, no significant increase in cumulative tumor incidence

was observed in either species at 55 ppm 1,1-dichloroethene. The increased tumor incidences

observed in the studies by Lee et al. (1977, 1978) and Hong et al. (1981) were not statistically

significant.

Male and female Sprague-Dawley rats were exposed to 0, 25, or 75 ppm 1,1-dichloroethene via

inhalation for 18 months (Quast et al. 1986). A statistically significant increase (p<0.05) in

adenocarcinomas of the mammary gland was noted in the low-dose females (25 ppm). The study

authors did not consider this increase related to 1,1-dichloroethene exposure because the

incidence of mammary gland adenocarcinomas in the treatment groups was within the range of

historical control data and was not dose related.

Both female and male rats were exposed to 0, 10, 25, 50, 100, or 150 ppm 1,l-dichloroethene for

52 weeks (Maltoni et al. 1985). The incidence of total mammary tumors (fibroadenomas,

carcinomas, sarcomas, carcinosarcomas) increased in females in the 10- and l00-ppm exposure

groups. However, evidence for a carcinogenic effect from inhalation exposure to 1,1-dichloroethene

in this study was inconclusive because there was no clear dose-related increase in total r

mammary tumor incidence, the latency time for mammary tumor incidence was similar in all

treated and control groups, the incidence (62%) of spontaneous mammary tumors in controls was

high, and the incidence of mammary gland carcinomas in treated groups was lower than that of

controls.
1,1- DICHLOROETHENE 36

2. HEALTH EFFECTS

The effects of chronic inhalation exposure of CD-1 mice and CD rats to 55 ppm 1,1-dichloroethene

for 12 months was studied by Lee et al. (1978, 1979). There was no statistically significant

increase in tumors at any of the sites examined compared to the respective control animals.

However, 2 of 35 treated male rats and 3 of 35 treated mice exhibited hemangiosarcomas, an

uncommon tumor type, while ncme were found in the controls. The study authors claimed that

rats were more resistant than mice to the carcinogenic effects of 1,1-dichloroethene, but the data

do not support this since there was no significant increase in the incidence of tumors in either

species and the incidence of hemangiosarcomas was practically the same for the two species. The

short duration of this study may have precluded observing tumors that have a longer latency

period.

In a follow-up study, CD-1 mice and CD rats were exposed to 55 ppm 1,1-dichloroethene by

inhalation for 1, 3, or 6 months (mice) or 1, 3, 6, or 10 months (rats) followed by a 12-month

observation period (Hong et al. 1981). There was no statistically significant increase in the

incidence of tumors in any of the treated animals compared to untreated animals. However, the

study was limited by the following factors: high mortality occurred; a small number of animals

(three to seven per sex per group) was used which decreased the ability of the study to detect a

tumorigenic response; and the exposure durations were considerably less than the expected

lifetime of the mice.

The negative findings of various inhalation studies may be partially explained by inadequate test

conditions. Chronic-duration animal studies at or near the maximum tolerated dose are necessary

to ensure an adequate power for the detection of carcinogenic activity (EPA 1986e). Study

limitations for many of these investigations included less than lifetime exposure, use of

concentrations well below or above the maximum tolerated dose, small numbers of animals, and/or

limited gross or microscopic examinations (Hong et al. 1981; Lee et al. 1977, 1978; Maltoni et

al. 1982, 1985; Quast et al. 1986; Rampy et al. 1977; Viola and Caputo 1977). These limitations

impair the sensitivity of a test to detect a carcinogenic response.

EPA has derived an inhalation unit risk of 5x10-5 μg /m3

 for cancer risk associated with inhalation

exposure to 1,1-dichloroethene based on the study by Maltoni et al. (1985) in mice (IRIS 1992).

EPA indicates, however, that it may not be appropriate to use this inhalation unit risk if the air

concentration exceeds 0.05 ppm. The air concentrations associated with the upper bound for an
1,1- DICHLOROETHENE 37

2. HEALTH EFFECTS

individual lifetime cancer risk of 10-4 to 10-7 are 5x10-4 to 5x10-7 ppm. This range is plotted in

Figure 2-1. The exposure concentration associated with an increased incidence of kidney

adenocarcinoma (25 ppm) in male mice is presented in Table 2-1 and plotted in Figure 2-1.

2.2.2 Oral Exposure

2.2.2.1 Death

No studies were located regarding death in humans after oral exposure to 1,1-dichloroethene.

Death has been observed in laboratory animals following oral exposure to 1,1-dichloroethene.

The database on the lethality of ingested 1,1-dichloroethene in animals consists primarily of

gavage studies in fasted rats. However, there were a few studies located regarding death in mic,

or other species.

Reported oral LD50 values in rats are ≈1,500 mg/kg (Jenkins et al. 1972; Jones and Hathway

1978a). The threshold for mortality in male rats is 50 mg 1,1-dichloroethene/kg in corn oil

(Andersen and Jenkins 1977). The limited data available for mice indicate that this species is

considerably more sensitive than rats to the lethal effects of ingested 1,1-dichloroethene.

Reported LD50 values in mice are ≈200 mg/kg (Jones and Hathway 1978a).

Since all available data are from fasted animals, it is not possible to determine whether the

amount of food intake of the animal influenced the lethality of ingested 1,1-dichloroethene, as it

does during inhalation exposure. It has been demonstrated by Jenkins et al. (1972) that

adrenalectomy in rats exacerbates the lethal effects of ingested 1,1-dichloroethene. These

investigators reported an oral LD50 of 81 mg/kg for 1,1-dichloroethene in adrenalectomized rats.

The mechanism and significance of this effect are unclear but probably involves a compromise in

the animal’s response to stress.

Oral administration of a single dose of 1,1-dichloroethene to fasted rats revealed that young male

rats (100-200 g) appeared to be more susceptible than older rats to its lethal effects (Andersen

and Jenkins 1977). This age-dependent difference in toxicity was not seen in females. Male mice
1,1- DICHLOROETHENE 38

2. HEALTH EFFECTS

fasted before inhalation exposure showed signs of enhanced 1,1-dichloroethene toxicity compared

to nonfasted rats.

In summary, ingested 1,1-dichloroethene is very toxic in at least two species of laboratory animals.

Young animals and those with compromised stress responses appear to be most susceptible to

these effects (Gosselin et al. 1984).

All LD50 values and LOAEL values from each reliable study for death in each species and

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

2.2.2.2 Systemic Effects

No studies were located regarding systemic effects in humans following oral exposure.

1,1-dichloroethene has been shown to adversely affect several organ systems in laboratory

animals. The major target organs of 1,1-dichloroethene toxicity in animals are the liver and

kidney. In addition, some studies suggest that 1,1-dichloroethene may induce adverse effects on

the respiratory and gastrointestinal systems following oral exposure.

No studies were located regarding cardiovascular, musculoskeletal, or dermal/ocular effects in

animals following oral exposure to 1,l -dichloroethene. The systemic effects observed after oral

exposure are discussed below.

The highest NOAEL values and all LOAEL values from each reliable study for systemic effects in

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

Respiratory Effects. No histopathological changes were observed in the lungs of nonfasted or

fasted rats administered a single gavage dose of 200 mg/kg 1,1-dichloroethene in either corn oil,

mineral oil, or an aqueous solvent (Chieco et al. 1981).

Pulmonary injury was observed in mice exposed to a single oral dose of 200 mg/kg (Forkert et

al. 1985). Histopathological changes were observed in Clara cells within 24 hours, and these were

accompanied by pulmonary edema, and hemorrhage. This damage appeared to be reversible;






1,1- DICHLOROETHENE 45

2. HEALTH EFFECTS

cellular regeneration was evident within 5 days of treatment. The relevance of these findings to

human exposure is questionable.

Gastrointestinal Effects. Edema of the forestomach was observed in fasted and nonfasted rats

after a single gavage dose of 200 mg/kg (Chieco et al. (1981). However, this alteration was not

associated with any discernible degenerative changes, and its relevance to human exposure is

unknown. No acute-duration studies of 1,1-dichloroethene administered in food were located.

Hematological Effects. A significant increase (p<0.001) in plasma free hemoglobin was

observed in fasted rats administered a single dose of 200 mg/kg 1,1-dichloroethene in mineral oil

or in corn oil (Chieco et al. 1981). The effect was not as marked, although still significant

(p<0.05), when 1,1-dichloroethene was given to nonfasted rats in either vehicle. According to the

investigators, the effect does not represent a true hematological effect but is due to hemolysis of

red cells trapped in the congested sinusoids of the injured liver.

No significant changes in hematological or clinical chemistry parameters were observed in dogs

exposed to 25 mg/kg/day 1,1-dichloroethene in drinking water for 97 days (Quast et al. 1983).

Similar results were observed in rats exposed to <30 mg/kg/day in drinking water for 2 years

(Quast et al. 1983; Rampy et al. 1977).

Hepatic Effects. 1,1-dichloroethene is hepatotoxic in laboratory animals, particularly after

ingestion of an acute dose. A complete spectrum of effects indicative of liver toxicity has been

observed in animals following acute oral administration of 1,1-dichloroethene, and their incidence

and severity tend to be dose related. Significant increases in serum enzyme markers of liver

damage or dysfunction (aspartate transaminase, ALT and alanine transaminase, AST) have been

noted in fasted rats after the ingestion of a single dose of 50 mg/kg or more (Andersen and

Jenkins 1977; Jenkins and Andersen 1978; Moslen et al. 1989b). Acute exposure to 25 mg/kg or

more induced bile canalicular injury in fasted rats (Kanz and Reynolds 1986; Moslen et al. 1989a).

Histological evidence of liver damage as seen by the presence of pyknotic cells was noted

following oral administration of 100 mg/kg to rats (Kanz et al. 1991). Ultrastructural changes in

hepatocellular organelles such as morphological changes in bile canaliculi and plasma membranes

have also been noted in fasted rats after a single dose of 25 mg/kg (Kanz and Reynolds 1986).
1,1- DICHLOROETHENE 46

2. HEALTH EFFECTS

The food intake of animals and the dosing vehicle influence the hepatotoxicity of orally

administered 1,l -dichloroethene in animals. Fasting exacerbates 1,l -dichloroethene-induced

hepatotoxicity; nonfasted animals exhibit only mild effects at comparable doses (i.e., increases in

organ weight) (Andersen and Jenkins 1977; Andersen et al. 1980; Chieco et al. 1981; Jenkins and

Andersen 1978). The hepatotoxic effects of 1,1-dichloroethene in rats tend to be more severe

when administered in mineral or corn oil than in 0.5% aqueous Tween 80 (Chieco et al. 1981).

Study authors have suggested that an aqueous solution of Tween 80 facilitates the clearance of

1,l -dichloroethene from the body.

One study was located regarding hepatic effects in animals after intermediate exposure to

1,1-dichloroethene. No exposure-related gross or histopathological changes were observed in the

livers of beagle dogs given 25 mg/kg/day in drinking water for 97 days (Quast et al. 1983).

Chronic studies have been performed in rats ingesting low levels (9-20 mg/kg/day) of 1,l-dichloroethene for 2 years. The results indicated few treatment-related changes. After 1 year of

treatment, only a minimal increase in cytoplasmic vacuolation of hepatocytes was noted (Rampy et

al. 1977). After 2 years, a minimal amount of hepatocellular swelling with midzonal fatty change

was reported (Quast et al. 1983). Slight hepatocellular changes were observed in rats exposed to

1,1-dichloroethene in the drinking water at levels of 9 mg/kg/day in utero, during lactation, and

through weaning into adulthood (Nitschke et al. 1983). A chronic oral MRL of 0.009 mg/kg

(Quast et al. 1983) was calculated for 1,1-dichloroethene, as described in the footnote in

Table 2-2.

Renal Effects. Evidence for 1,1-dichloroethene-induced kidney dysfunction has been observed in

laboratory animals following acute oral exposure. Fasted rats given single gavage doses of

200 mg/kg or more in corn oil exhibited increased plasma urea and creatinine levels (at

400 mg/kg) ( Jenkins and Andersen 1978). Histopathological changes (vacuolizalion, pigmentation,

tubular dilation, and necrosis) were observed at 400 mg/kg. These changes were more severe in

females, though some recovery was evident in females 96 hours after exposure. Histological

changes such as granular heme casts in Henle’s loop were observed in the kidneys of nonfasted

and fasted rats administered single doses of 200 mg/kg by gavage in either corn oil, mineral oil, or

an aqueous solvent (Chieco et al. 1981). As noted for hepatic effects, fasting exacerbates
1,1- DICHLOROETHENE 47

2. HEALTH EFFECTS

1,l -dichloroethene-induced nephrotoxicity in animals; no renal effects were observed in nonfasted

animals administered single doses of 400 mg/kg (Jenkins and Andersen 1978).

No renal effects were noted in animals following intermediate (Quast et al. 1983) or chronic

(Rampy et al. 1977) oral exposure to 1,1-dichloroethene at doses of 30 mg/kg/day or less.

Other Systemic Effects. No studies were located regarding other systemic effects in humans

after oral exposure to 1,1-dichloroethene.

No effect on body weight was reported in rats following acute oral exposure to 200 mg/kg/day

(Chieco et al. 1981).

2.2.2.3 Immunological Effects

No studies were located regarding immunological effects in humans or animals after oral exposure

to 1,1-dichloroethene.

2.2.2.4 Neurological Effects

No studies were located regarding neurological effects in humans after oral exposure to

1,l -dichloroethene.

No adverse neurological effects on were identified after oral administration of 1,1-dichloroethene

for any exposure duration in animals. The appearance and demeanor of the test animals were not

affected in either an intermediate feeding study in dogs (25 mg/kg/day for 97 days) or a chronic

study in rats (30 mg/kg/day or less for 2 years) (Quast et al. 1983). However, these results are

only suggestive because no sensitive neurological tests were performed.

2.2.2.5 Reproductive Effects

Only one human study was located regarding neural tube defects in newborns after transplacental

exposure to 1,l-dichloroethene via contaminated water (NJDH 1992a, 1992b). However, these

data provide only suggestive evidence and therefore, should be interpreted with caution.
1,1- DICHLOROETHENE 48

2. HEALTH EFFECTS

1,1-dichloroethene (99.5% purity) was administered in the drinking water of rats at dosages of

30 mg/kg/day or less for three generations. No dose-related changes were seen in reproduction or

neonatal development (Nitschke et al. 1983). The study employed sufficient number of animals

and used three dose levels. The NOAEL value for reproductive effects is listed in Table 2-2 and

plotted in Figure 2-2.

2.2.2.6 Developmental Effects

Only one human study was located regarding neural tube defects in newborns after transplacental

exposure to 1,1-dichloroethene via contaminated water (NJDH 1992a, 1992b). However, these

data provide only suggestive evidence and, therefore, should be interpreted with caution.

No effect on the number of implantations, live fetuses, or resorptions, sex ratio, or fetal weight

were observed among the offspring of rats administered 40 mg/kg/day in the drinking water on

gestation days 6 through 15 (Murray et al. 1979). The incidence of malformations, considered

individually or collectively, among the rats given 1,1-dichloroethene was not significantly different

from that of controls. There was, however, a marginal increase in crown-rump length in treated

rats; the significance of this effect is unclear.

The highest NOAEL values for developmental effects in rats after acute exposure are listed 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 or animals after oral exposure to

1,l -dichloroethene.

Genotoxicity studies are discussed in Section 2.4.

2.2.2.8 Cancer

No studies were located regarding cancer in humans after oral exposure to 1,1-dichloroethene.
1,1- DICHLOROETHENE 49

2. HEALTH EFFECTS

A number of chronic studies in rats and mice have evaluated the carcinogenicity of 1,1-dichloroethene

by oral exposure (Maltoni et al. 1982, 1985; NTP 1982; Ponomarkov and Tomatis 1980;

Quast et al. 1983; Rampy et al. 1977). Dosages of 1,1-dichloroethene in these studies ranged

from 0.5 to 150 mg/kg/day. Administration was by gavage with the exception of two studies in

which 1,1-dichloroethene was administered daily in the drinking water (Quast et al. 19%; Rampy

et al. 1977). Major organs and tissues of treated and control animals in these investigations were

subjected to both gross and microscopic examination.

A trend toward increased incidence of malignant and nonmalignant tumors in 1,1-dichloroethenetreated animals has been reported (NTP 1982; Ponomarkov and Tomatis 1980; and Quast et al.

1983). For example, rats exposed in utero to a single dose of 150 mg/kg I,l-dichloroethene and

given weekly gavage doses of 50 mg/kg 1,1-dichloroethene from weanilg until 120 weeks of age

had increased incidences of meningiomas and liver cell adenomas and {arcinomas compared to

controls, but the difference was not statistically significant (Ponomarkob and Tomatis 1980).

However, hyperplastic nodules of the liver in these animals were significantly increased (p=0.04).

No significant increase in tumor incidence was seen in dams receiving a single oral dose of

150 mg/kg 1,1-dichloroethene (Ponomarkov and Tomatis 1980). Another study showed that male

rats treated by gavage with 5 mg/kg 1,1-dichloroethene for 2 years had an increased incidence of

pheochromocytomas, but when compared with control animals, the difference was not statistically

significant (NTP 1982).

Statistically significant increases in certain types of tumors and cancers have been reported in

bioassays in which rats and beagles were orally exposed to 1,1-dichloroethene (Quast et al. 1983);

however, investigators discounted these results for various reasons. In a 2-year study by Quast et

al. (1983), doses of 7, 10, and 20 mg/kg/day and 9, 14, and 30 mg/kg/day were administered in the

drinking water of male and female rats, respectively. A statistically significant increase (p<0.05)

in the incidence of combined mammary gland fibroadenomas and adenofibromas was noted in

low-dose females. Because the incidence of these types of tumors was within the normal range of

historical control data and because these tumors were not observed in higher-dose females or in

treated males, the study authors did not consider these increases to be related to 1,1-dichloroethene

ingestion. Thus, the results of the study are of questionable biological significance.
1,1- DICHLOROETHENE 50

2. HEALTH EFFECTS

Clinical signs of toxicity were not generally observed in the various oral carcinogenicity studies on

1,1-dichloroethene; consequently, maximum tolerated doses may not have been achieved (NTP

1982; Ponomarkov and Tomatis 1980; Quast et al. 1983; Rampy et al. 1977). Chronic-duration

animal studies at or near the maximum tolerated dose are necessary to ensure an adequate power

for the detection of carcinogenic activity (EPA 1986e). Two of the oral carcinogenicity studies

also used exposure periods that were less than lifetime (52-59 weeks); however, the animals were

observed for 136 or 147 weeks allowing an adequate latency period for the development of lateappearing

tumors (Maltoni et al. 1982, 1985).

EPA has derived an oral cancer slope factor (q1*) of 0.6 (mg/kg/day)-1 for cancer risk associated

with oral exposure to l,l-dichloroethene based on the study by NTP (1982) in rats (IRIS 1992).

The doses associated with the upper bound for individual lifetime cancer risk of 10-4 to 10-7 are

1.7x10-4 to 1.7x10-7 mg/kg/day. This range is plotted in Figure 2-2. At the highest dose level

tested, 5 mg/kg/day, the incidence of pheochromocytomas increased in male rats, but the increase

was not statistically significant.

2.2.3 Dermal Exposure

2.2.3.1 Death

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

1,l -dichloroethene.

2.2.3.2 Systemic Effects

No studies were located regarding respiratory, cardiovascular, gastrointestinal, hematological,

musculoskeletal, hepatic, or renal effects in humans or animals after dermal exposure to

1,l -dichloroethene. The dermal/ocular effects observed after dermal expostire are discussed below.

Dermal/Ocular Effects. Liquid 1,1-dichloroethene is irritating when applied to the skin of

humans (EPA 1979b) and animals (Torkelson and Rowe 1981) after exposures lasting only a few

minutes. Details concerning these studies are lacking, but it has been suggested that these irritant

effects may be due to the inhibitor,p-hydroxyanisole (monomethyl ether of hydroquinone,
1,1- DICHLOROETHENE 51

2. HEALTH EFFECTS

MEHQ), present in these formulations. MEHQ is an antioxidant which on contact results in skin

depigmentation at concentrations of 0.25% or more (Busch 1985). Similarly, 1,1-dichloroethene is

an ocular irritant in humans (EPA 1979b); this effect has also been ascribed to MEHQ.

2.2.3.3 Immunological Effects

No studies were located regarding immunological effects in humans or animals after dermal

exposure to 1,1-dichloroethene.

2.2.3.4 Neurological Effects

Two cases of persistent nerve disorders were reported in subjects involved in manually cleaning

tanks used to transport 1,1-dichloroethene copolymers (Fielder et al. 1985). The study is limited

by a small sample size, lack of details regarding concentration, and a possible exposure via

inhalation route.

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

exposure to 1,l-dichloroethene:

2.2.3.5 Reproductive Effects

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

No studies were located regarding cancer in humans after dermal exposure to 1,1-dichloroethene.

The carcinogenicity of 1,1-dichloroethene following dermal exposure has been evaluated by Van

Duuren et al. (1979). In this study, 1,1-dichloroethene doses of 40 or 121 mg (1,333 or

4,033 mg/kg, respectively) in acetone were applied three times weekly for 588 days or less to the

skin of Swiss mice. No skin tumors were noted in treated animals. Increased incidences of
1,1- DICHLOROETHENE 52

2. HEALTH EFFECTS

pulmonary papillomas and squamous-cell carcinomas of the forestomach were observed in treated

mice; the incidences of these tumors, however, were not statistically different from controls. The

results suggest 1,1-dichloroethene is inactive as a complete carcinogen (an agent that, if applied in

sufficient concentrations, can induce tumors by itself) when applied repeatedly to the mouse skin.

The ability of 1,1-dichloroethene to act as a tumor initiator in the skin of Swiss mice was

evaluated by Van Duuren et al. (1979). In two-stage tumorigenesis, a subthreshold dose of a

tumor initiator is applied. An initiator does not generally produce tumors at this dose but causes

“dormant” cell changes so that later repeated applications of a promoter (an agent that by itself

will not produce tumors) will induce benign and malignant tumors at the site of application.

1,1-dichloroethene (121 mg or 4,033 mg/kg) in acetone was applied to the skin once, followed

2 weeks later by dermal application of the tumor promotor, phorbol myristate acetate (TPA),

three times a week for 576 days or less. Untreated, vehicle-treated, and TPA-only-treated animals

served as negative controls. A statistically significant (p<0.005) increase in the incidence of skin

papillomas was recorded in treated mice compared to controls. These results indicate that

1,1-dichloroethene is a tumor-initiating agent in the Swiss mouse skin test.

2.3 TOXICOKINETICS

Data regarding toxicokinetics of 1,1-dichloroethene in humans are not available. Studies in

animals indicate that 1,1-dichloroethene is readily absorbed and rapidly distributed in the body

following inhalation and oral exposure. The oral absorption rate greatly depends on the type of

vehicle used. Oily vehicles facilitate uptake. Uptake of 1,1-dichloroethene vapors is duration and

dose dependent. However, the percentage of 1,1-dichloroethene uptake decreases as the

exposure concentration increases, until an equilibrium is reached. 1,1-dichloroethene distributes

mainly to the liver and kidney and does not appear to be stored or accumulated in the tissues. It

is metabolized by the hepatic microsomal cytochrome P-450 system. This process gives rise to

several possible reactive intermediates thought to be responsible for 1,1-dichloroethene toxicity.

The major detoxification route for these intermediates are hydroxylation and conjugation with

GSH. Therefore, metabolic interventions that deplete GSH (treatment with drugs, fasting, etc.)

tend to increase 1,1-dichloroethene toxicity. Excretion of metabolites occurs primarily via the

urine and exhaled air. Unmetabolized parent compound may also be eliminated via exhaled air.

After high-level exposures, greater percentages of the dose are exhaled as unchanged 1,1-dichloro-
1,1- DICHLOROETHENE 53

2. HEALTH EFFECTS

ethene. The physical/chemical properties of 1,1-dichloroethene indicate that absorption of

1,l -dichloroethene via dermal exposure is possible in humans. Information on the disposition and

metabolism of 1,1-dichloroethene following chronic-duration exposures was not available.

2.3.1 Absorption

2.3.1.1 Inhalation Exposure

No studies were located regarding the absorption of 1,1-dichloroethene in humans following

inhalation exposure.

Studies in laboratory animals have demonstrated that 1,1-dichloroethene was rapidly absorbed

following inhalation exposure (Dallas et al. 1983; McKenna et al. 1978b). No studies were

located that described transport mechanisms for 1,1-dichloroethene absorption. Since 1,1-dichloroethene

is a small organic molecule with chemical and physical properties similar to lipid soluble

anesthetics, it is expected to penetrate pulmonary membranes easily and to enter the blood stream

rapidly. Substantial levels of the parent compound were found in the venous blood of rats within

2 minutes after inhalation exposure (Dallas et al. 1983). Absorption of 1,l-dichloroethene was duration

and dose-dependent, as shown in Figure 2-3. The percentage of systemic uptake decreased with

time from the onset of exposure until an equilibrium was reached within 1 hour. Once

equilibrium was reached, percentage uptake varied inversely with dose. The cumulative uptake of

1,1-dichloroethene following inhalation exposure was linear for levels of 150 ppm or less.

However, at 300 ppm a steady state was never achieved. This finding indicates that 1,1-dichloroethene

absorption following inhalation exposure was saturable at high levels, and the kinetics at

these levels are best described by a cubic curve (Dallas et al. 1983).

2.3.1.2 Oral Exposure

No studies were located regarding absorption in humans after oral exposure to 1,1-dichloroethene.

Studies in animals clearly indicated that doses of 1,1-dichloroethene ranging from 10 to 100 mg/kg

were rapidly and almost completely absorbed from the gastrointestinal tract of rats and mice

following oral administration in corn oil (Jones and Hathway 1978a; Putcha et al. 1986). Rapid

1,1- DICHLOROETHENE 55

2. HEALTH EFFECTS

absorption occurred following oral administration of 200 mg/kg in an aqueous emulsion, as

evidenced by the observation that the largest percentage of the dose was exhaled during the initial

15-minute period (Chieco et al, 1981). Peak blood levels were achieved in rats within

2-8 minutes after oral administration (Putcha et al. 1986). When 0.5-50 mg/kg of radiolabeled

1,1-dichloroethene was given to female rats, ≈10% of the parent compound was recovered in the

expired air by 1 hour after exposure, indicating that oral absorption was rapid (Reichert et

al. 1979). After oral administration to rats of 1,1-dichloroethene labeled with radioactive carbon

(

14C), 81-99.8% of the administered radioactivity was recovered within 72 hours (Reichert et al.

1979). Studies have shown that 9-21% was recovered in the expired air, 53.9% in urine, 14.5%

in feces, 2.8% in the carcass, and 7.5% in the cage rinse following oral administration of 1 or

5 mg 14C-1,1-dichloroethene/kg (McKenna et al. 1978a; Reichert et al. 1979). After a dose of

50 mg 14C-1,1-dichloroethene/kg, 19% and 29% of the parent compound was excreted via lungs in

nonfasted and fasted rats, respectively (McKenna et al. 1978a). These results suggest that

1,1 -dichloroethene may be rapidly and completely absorbed in humans following oral exposure

(e.g., via ingestion of contaminated groundwater).

2.3.1.3 Dermal Exposure

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

1,l -dichloroethene. Nonetheless, the physical/chemical properties of 1,l -dichloroethene indicate

that dermal absorption of 1,1-dichloroethene is probable. 1,1-dichloroethene is a small organic

molecule with properties similar to the lipid-soluble anesthetics. Thus, liquid 1,1-dichloroethene is

expected to readily penetrate the skin, which is a lipid-rich tissue. However, with a vapor

pressure of greater than 500 torr at room temperature, the rate of evaporation would be rapid

leaving only a short time for skin penetration.

2.3.2 Distribution

2.3.2.1 Inhalation Exposure

No studies were located regarding distribution in humans after inhalation exposure to 1,l-dichloroethene.
1,1- DICHLOROETHENE 56

2. HEALTH EFFECTS

Following inhalation exposure of rats to 10 or 200 ppm of 14C-labeled 1,1-dichloroethene, the

highest level of radioactivity was found in the liver and kidneys after 72 hours, with only very

small amounts present in other tissues (McKenna et al. 1978b). These authors found that the

tissue burden/g of tissue (mg equivalents of 14C-1,1-dichloroethene/g of tissue/total mg equivalents

recovered per rat) in the liver, kidneys, and lungs of fasted rats were significantly greater than in

nonfasted rats at both exposure levels, even though the total accumulation of 14C in fasted rats

was less than in nonfasted rats. The results of this study suggest that in fasted rats the 14C is

retained in specific target tissues and not distributed randomly in all tissues.

Preferential accumulation of radioactivity was reported in the kidney and liver of rats exposed to

2,000 ppm radiolabeled 1,1-dichloroethene for 2 hours (Jaeger 1977a). Fasted rats had higher

levels of label than nonfasted rats in these tissues. Examination of l4C activity at the subcellular

level in these two tissues revealed that significantly more water-soluble 14C activity was present in

the cytosolic fractions of fasted rats. This observation suggests that distribution pathways for

metabolism differ according to the amount of food ingested by the animals.

2.3.2.2 Oral Exposure

No studies were located regarding distribution in humans after oral exposure to 1,1-dichloroethene.

1,1-dichloroethene was rapidly distributed to all tissues examined following a single oral dose of

the 14C-labeled compound to rats (Jones and Hathway 1978b). The highest amount of

radioactivity was found in the liver and kidneys within 30 minutes of administration. More

general redistribution throughout the soft tissues of the body followed.

2.3.2.3 Dermal Exposure

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

1.1-dichloroethene.
1,1- DICHLOROETHENE 57

2. HEALTH EFFECTS

2.3.2.4 Other Routes of Exposure

In a study by Okine et al. (1985) in which mice were administered a single intraperitoneal

injection of 125 mg/kg of 14C-l ,l -dichloroethene, radioactivity was distributed to some extent to

all examined tissues with peak levels seen 6 hours after administration. The highest levels of

radioactivity were found in the kidney, liver, and lung with lesser amounts in the skeletal muscle,

heart, spleen, and gut.

2.3.3 Metabolism

No studies were located regarding metabolism in humans following inhalation, oral, or dermal

exposure to 1,1-dichloroethene.

Some evidence from animal studies suggests that at least the initial metabolic transformations in

humans may be similar to those described in animals. Liver cells from a human subject together

with Arochlor- pretreated S-9-activated 1,1-dichloroethene induced unspecified mutagenic

metabolites in Salrnonella typhimutium assay (Jones and Hathway 1978c). This suggests that

reactive metabolites may also be produced in humans.

The metabolism of 1,1-dichloroethene following oral administration in rats has been extensively

studied (Jones and Hathway 1978a, 1978b; McKenna et al. 1978a; Reichert et al. 1979). These

studies demonstrate that 1,l-dichloroethene undergoes biotransformation, and several metabolites

have been identified. An overall summary of the metabolic pathway of 1,1-dichloroethene in

animals is presented in Figure 2-4.

A physiologically based pharmacokinetic model for 1,1-dichloroethene based on its oxidative

metabolism by the P-450 cytochrome system and subsequent conjugation with GSH, a principal

pathway, was developed by D’Souza and Anderson (1988) (see Figure 2-5). Their model

demonstrates that because 1,l-dichloroethene has a low blood-to-air partition coefficient and

saturable metabolism, the metabolism of 1,1-dichloroethene is sensitive to the rate of absorption.

Furthermore, 1,1-dichloroethene’s metabolic pathway (i.e., the percentage of l,l-dichloroethenc

exhaled, metabolized, and conjugated with GSH) is different for different routes of exposure and


1,1- DICHLOROETHENE 60

2. HEALTH EFFECTS

dose levels. This model, which the study authors verified experimentally, is useful in predicting

the kinetics and potential toxicity of 1,1-dichloroethene under various exposure conditions.

The hepatic cytochrome P-450 isozyme, P-450 2E1, is believed to play a role in the metabolic

toxification of DCE in the liver (Kainz et al. 1993). An initial step in the metabolism of

1,1-dichloroethene may be the formation of the epoxide (oxirane) intermediate,

1,1-dichloroethylene oxide; however, this reactive compound has never been isolated after

1,1-dichloroethene administration in laboratory animals (Jones and Hathway 1978b; McKenna et

al. 1977; Reichert et al. 1979).

An alternate metabolic scheme that does not go through the epoxide intermediate was proposed

based on studies in isolated hepatocytes by Liebler et al. (1985, 1988) and is presented in

Figure 2-6.

The main biotransformation pathways for 1,1-dichloroethene in the rat may involve conjugation

with GSH, either with the epoxide or following rearrangement of the epoxide to

chloroacetylchloride, with subsequent hydrolysis to monochloroacetic acid. This is consistent with

the observation that exposure to 1,1-dichloroethene depletes GSH levels in the liver (Jaeger et

al. 1974; Reichert et al. 1978; Reynolds et al. 1980). For example, Reynolds et al. (1980)

reported a linear relationship in rats between intraperitoneally administered 1,1-dichloroethene

and GSH depletion over the range of 20-100 mg/kg; above this level GSH depletion reached a

plateau. The maximum reduction seen (70%) occurred 4 hours after treatment, with a

subsequent gradual recovery to normal levels within 24 hours. These findings have led several

investigators to suggest that 1,1-dichloroethene-induced hepatotoxicity is related to the depletion

of hepatic GSH levels, thereby permitting the reactive intermediate to bind to and alkylate

hepatic macromolecules instead of being detoxified, ultimately leading to cell death (Jaeger et

al. 1974; McKenna et al. 1977, 1978a; Reynolds et al. 1980).

Conjugation of monochloroacetic acid with GSH followed by β-thionase activity appeared to be

the major metabolic route on a quantitative basis in rats since thiodiglycollic acid was the

predominant urinary metabolite (Jones and Hathway 1978a), this metabolite, however, only

comprised 25% of l4C urinary activity in another study (McKenna et al. 1978c). Forty-five

percent of the activity was contributed by S-(2-hydroethyl)-N-acetylcysteine. Other metabolites

1,1- DICHLOROETHENE 62

2. HEALTH EFFECTS

identified in this pathway include monochloroacetic acid itself, thioglycolic acid, and dithioglycollic

acid. However, direct GSH detoxication of the epoxide also apparently occurred to a significant

degree, as demonstrated by the formation of glutathionyl acetyl chloride with subsequent

breakdown to an N-acetyl cysteine derivative.

Evidence suggests that enzymatic hydration of the epoxide by epoxide hydrolase is a minor

pathway in the metabolism of 1,1-dichloroethene in rats. Exacerbation of 1,1-dichloroetheneinduced

toxicity in rats by diethyl maleate and various epoxide inhibitors following inhalation

exposure was directly related to their ability to decrease GSH levels, rather than their ability to

competitively inhibit epoxide hydrolase (Andersen et al. 1980).

An alternative metabolic pathway (i.e., one not involving GSH conjugation) to account for the

presence of the metabolite methylthioacetylaminoethanol was proposed by Reichert et al. (1979).

They suggested that chloroacetylchloride, instead of being hydrolyzed to monochloroacetic acid,

reacts with membrane phosphatidyl ethanolamine, which is enzymatically cleaved to yield the

ethanolamine derivative of chloroacetic acid. The thiomethyl group is then probably transferred

from methionine to the metabolite as a result of direct nucleophilic attack.

The pathways of 1,1-dichloroethene metabolism in the mouse were similar to those seen in the rat

except that the rate of metabolism was greater in the mouse (i.e., a greater proportion of

administered 1,1-dichloroethene was metabolized per given dose level by the mouse than the rat)

(Jones and Hathway 1978a). A predominant urinary metabolite of 1,1-dichloroethene found in

mice was the N-acetylcysteine derivative produced by GSH conjugation to detoxify the epoxide

intermediate. In mice there were quantitatively greater amounts of water-soluble urinary

metabolites present in the urine (and consequently less parent compound in the expired air)

attesting to a greater metabolic capacity. Furthermore, β-thionase activity was more pronounced

since more dithioglycollic acid was found than thiodiglycollic acid (Jones and Hathway 1978a). In

addition, Oesch et al. (1983) pointed out that 1,1-dichloroethene may have different effects on

cytosolic GSH transferase activity and that this difference may have contributed to the species

differences observed.

14C- 1,1-DICHLOROETHENE covalently binds preferentially to liver and kidney tissues following

administration, which may provide a basis f& the toxic effects seen in these organs (Jaeger et al.
1,1- DICHLOROETHENE 63

2. HEALTH EFFECTS

1977a; McKenna et al. 1977, 1978a). A linear increase in the amount of covalently nound

radioactivity in the liver of rats exposed to 10-200 ppm 14C- 1,l -dichloroethene by inhalation for

6 hours was reported by McKenna et al. (1977). However, GSH depletion plateaued at about

200 ppm. Therefore, the actual amount of reactive metabolite formed and available for binding

was probably determined by a combination of both activation and detoxication pathways.

The increased severity of hepatotoxic and nephrotoxic effects induced by 1,1-dichloroethene in

the mouse, compared to the rat, may be partially explained by the observation that greater

amounts of covalently bound reactive material were found in these two tissues in the mouse than

in the rat following exposure to the same dose of 1,1-dichloroethene (McKenna et al. 1977).

Levels of covalently bound material were six times higher in the mouse kidney than in the rat

kidney (McKenna et al. 1977). Similar results were reported by Short et al. (1977d) when a single

dose of 14C-1,1-dichloroethene was injected intraperitoneally into mice. The highest level of

covalently bound radioactivity was seen in the mouse kidney. The study authors found that

pretreatment with disulfiram also reduced the amount of covalent binding. The study authors

speculated that disulfiram may reduce the activation of 1,1-dichloroethene and increase the extent

of its detoxification. Thus conjugation of reactive intermediates of l,l-dichloroethetle with GSH

is a major detoxification mechanism in laboratory animals because it reduces the amount of

reactive material available to covalently bind to cellular macromolecules.

1,1-dichloroethene can also potentially form adducts with hemoglobin, as has been observed with

ethylene oxide (Tornyvist et al. 1986). Electrophilic intermediates, such as the epoxide formed in

1,1-dichloroethene metabolism, may bind to proteins in hemoglobin, similar to reactions

demonstrated for liver and kidney (McKenna et al. 1977).

2.3.4 Excretion

2.3.4.1 Inhalation Exposure

No studies were located regarding excretion in humans following inhalation exposure to

1,l -dichloroethene.
1,1- DICHLOROETHENE 64

2. HEALTH EFFECTS

Elimination of 1,1-dichloroethene by rats following inhalation exposure to low levels is rapid, with

the majority of the compound eliminated as metabolites in the urine, and very little (1% of the

administered dose) eliminated as the unchanged parent compound in the expired air (McKenna et

al. 1973). After exposure to low levels (25-150 ppm) of 1,1-dichloroethene, steady-state levels

of 1,1-dichloroethene in the expired air are achieved within 30-45 minutes, indicating that

elimination is first-order at low levels of exposure (Dallas et al. 1983). Steady-state levels of

1,1-dichloroethene in expired air are never reached when exposure levels approach 200-300 ppm

because metabolic processes are saturated. When metabolic processes become saturated,

increased amounts of 1,1-dichloroethene can easily be eliminated unchanged via the lung, since

1,1-dichloroethene is volatile (VP=500 torr at 20°C) and relatively insoluble in blood. Following

cessation of exposure, concentrations of 1,1-dichloroethene in both blood and breath were

observed to fall rapidly (Dallas et al. 1983). Similar results were reported by McKenna et

al. (1978b).

1, 1-dichloroethene exhibited a biphasic elimination profile following inhalation exposure in rats

(McKenna et al. 1978b). The first phase had a half-life of about 20 minutes for the elimination

of unchanged 1,1-dichloroethene in breath and 3 hours for the elimination of water-soluble

metabolites in urine. The second phase had a half-life of about 4 hours in breath and 20 hours in

urine. The bulk of the material was eliminated in both the breath and the urine during the rapid

phase. Fasting did not appear to affect the elimination kinetics of 1,1-dichloroethene following

inhalation exposure in rats (McKenna et al. 1978b).

Information is limited on elimination in mice following inhalation exposure to 1,1-dichloroethene.

However, McKenna et al. (1977) reported that at low levels of exposure (10 ppm for 6 hours),

somewhat smaller amounts of unchanged 1,1-dichloroethene were eliminated in the expired air of

mice and larger amounts of water-soluble metabolites were found in the urine of mice compared

to levels observed in rats. This indicates that mice metabolize 1,1-dichloroethene at a greater rate

than rats.

2.3.4.2 Oral Exposure

No studies were located regarding excretion in humans following oral exposure to 1,1-dichloroethene.
1,1- DICHLOROETHENE 65

2. HEALTH EFFECTS

Elimination of 1,1-dichloroethene and its metabolites following oral administration in rats is very

similar to that seen following inhalation exposure. Following oral administration of 1 mg/kg

14C-1,1-dichloroethene in corn oil, less than 1% of the administered dose was excreted unchanged

in the expired air, with 8-14% of the administered dose recovered as 14C-carbon dioxide. The

bulk of the administered 14C-1,1-dichloroethene (44-W% of the administered dose) was

eliminated in the urine within 3 days, most within the first 24 hours. Smaller amounts of water-soluble

metabolites (8-16% of the administered dose) were found in the feces (Jones and

Hathway 1978b; McKenna et al. 1978a; Reichert et al. 1979). Following the oral administration

of higher doses to rats (50 mg/kg 14C-1,1-dichloroethene), a higher proportion of unchanged

parent compound (16-30% of the administered dose) was excreted in the breath with a

concomitant reduction in the amount of expired carbon dioxide (3-6% of the administered dose)

and urine metabolites (35-42% of the administered dose) (Jones and Hathway 1978b; McKenna

et al. 1978a; Reichert et al. 1979). Similar but more marked trends were observed at even higher

doses (Chieco et al. 1981; Jones and Hathway 1978b). Thus, metabolic processes become

saturated at rather low dose levels.

The elimination of orally administered 1,1-dichloroethene is triphasic according to Putcha et

al. (1986); however, McKenna et al. (1978b) and Reichert et al. (1979) reported that elimination

is biphasic. The first phase identified by Putcha et al. (1986) occurred almost immediately, within

the first few minutes after exposure, and the second two phases corresponded to those observed

by the other investigators. Half-lives for the two phases of elimination after inhalation exposure

were 20 minutes and 1 hour in the breath and 6 hours and 17 hours in the urine.

The amount of food ingested in the previous 24 hours slightly modifies the elimination of

1,1-dichloroethene by rats after oral administration. It was found that 19% of a 50-mg/kg dose

was excreted unchanged via the lungs of nonfasted rats, whereas 29% was excreted by fasted rats

(McKenna et al. 1978b). This finding provides evidence that fasted rats eliminate unchanged

1,1-dichloroethene to a greater extent than nonfasted rats. However, elimination of nonvolatile

metabolites was slightly greater in nonfasted animals than in fasted animals, indicating a reduced

capacity for metabolism in fasted rats.
1,1- DICHLOROETHENE 66

2. HEALTH EFFECTS

Mice eliminate more 1,1-dichloroethene as water-soluble metabolites in the urine than do rats at

comparable doses (Jones and Hathway 1978a). These results suggest that mice also metabolize

orally administered 1,1-dichloroethene to a greater extent than rats.

2.3.4.3 Dermal Exposure

No studies were located regarding the excretion of 1,1-dichloroethene in humans or animals

following dermal exposure to 1,1-dichloroethene.

2.3.4.4 Other Routes of Exposure

Using the physiologically based pharmacokinetic model developed for 1,l -dichloroethene discussed

in Section 2.33, D’Souza and Anderson (1988) demonstrated that the half-life of 1,1-dichloroethene

in blood is not representative of metabolism rates, but rather more closely corresponds to

reeyuilibration of 1,1-dichloroethene from fat. Consequently, rats with a greater amount of fat

deposits had longer 1,1-dichloroethene blood half-lives following intravenous administration. This

finding could have important implications for obese individuals exposed to high levels of

1,1-dichloroethene.

2.3.5 Mechanisms of Action

The specific mechanism by which 1,1-dichloroethene is transported across the gastrointestinal wall

or across the pulmonary epithelium is not known. However, because of its high lipid solubility, it

is expected that 1,1-dichloroethene will easily penetrate biological membranes following a

concentration gradient. Similarly, no information was found regarding the mechanism by which

1,1-dichloroethene is transported in the blood; however, it is reasonable to assume that

I,1 dichloroethene will dissolve in the lipid fraction of the blood.

It is well known that the toxicity of 1, 1-dichloroethene is due to biotransformed 1,1-dichloroethene

and not to the parent compound (Andersen et al. 1978, 1980; Jaeger et al. 1977a; Jones

and Hathway 1978c). 1,1-dichloroethene is initially oxidized by the hepatic cytochrome P-450

system with the formation of reactive and electrophilic products such as epoxides, acyl chlorides,

and halogenated aldehydes, which are responsible for the liver toxicity via alkylation of
1,1- DICHLOROETHENE 67

2. HEALTH EFFECTS

macromolecules (Forkert et al 1986). These reactive intermediates form GSH S-conjugates by

the action of glutathione S-transferases located in the hepatic cytosol and microsomes. GSH

S-conjugates that are primarily secreted from the hepatocytes into plasma and S-conjugates

entering the circulation after reabsorption from the small intestine are ultimately delivered to the

kidney where they undergo glomerular filtration (Dekant et al. 1989). In the kidney, GSH Sconjugates

may be metabolized to the corresponding cysteine S-conjugate, which may be

acetylated to form the corresponding mercapturic acid and excreted in the urine (Vamvakas and

Anders 1990). However, cysteine S-conjugates may also be metabolized by β-lyase, an enzyme

located in the renal proximal tubule cells; the resulting unstable thiols in turn yield electrophilic

products whose interactions with macromolecules are associated with nephrotoxicity. In summary,

GSH S-conjugate formation of nephrotoxic haloalkenes competes with hepatic cytochrome P-450

for substrates. The relative extent of these reactions in vivo appears to be decisive for the

initiation of adverse effects either in the liver (via oxidation products generated by P-450 system)

or in the kidney (via formation and renal processing of S-conjugates).

2.4 RELEVANCE TO PUBLIC HEALTH

Exposure to 1,l -dichloroethene in an occupational setting is most likely to occur via a

combination of the inhalation and dermal routes. The general population is most likely to be

exposed to 1,1-dichloroethene by inhalation of contamination and oral consumption of

contaminated food or water. Limited information is available on the human health effects

following exposure to 1,1-dichloroethene. This information comes primarily from case reports

and/or insufficiently detailed mortality studies wherein the concentration and duration of exposure

to 1,1-dichloroethene were not quantified. Concurrent exposure to other toxic substances cannot

be ruled out in most of these cases. Nevertheless, the information available indicates that

relatively high concentrations of inhaled 1,1-dichloroethene can induce adverse neurological

effects after acute-duration exposure, and that 1,1-dichloroethene is associated with liver and

kidney toxicity in humans after repeated, low-level exposure. Considerable information exists

regarding the effects of 1,1-dichloroethene in animals after inhalation and oral exposure. The

liver and kidney, and possibly the lungs, can be considered target organs for 1,1-dichloroethene by

both routes of exposure. In addition, cardiovascular, neurological, developmental, and genotoxic

effects were reported after inhalation of 1,1-dichloroethene, and gastrointestinal effects occurred

after oral exposure. The evidence for 1,1-dichloroethene carcinogenicity is inadequate in humans
1,1- DICHLOROETHENE 68

2. HEALTH EFFECTS

and is limited in animals. Information regarding toxicokinetics in animals suggests that

1,1-dichloroethene does not tend to accumulate in the body. Background levels found in air and

drinking water supplies (see Section 5.4) are not likely to cause adverse health effects in humans.

For populations living near waste sites and/or facilities that manufacture or store 1,1-dichloroethene,

the most likely routes of exposure are inhalation and oral (through contaminated water).

There is convincing evidence from animal studies to indicate that 1,1-dichloroethene toxicity is

mediated by metabolism to reactive intermediates that act at the cellular level to ultimately

compromise the viability of the target tissues. While the metabolic pathways for 1,l -dichloroethene

are similar in the rat and mouse, the rate of metabolism is greater in the mouse, resulting

in greater concentrations of toxic metabolites. Thus, the severity of 1,1-dichloroethene-induced

toxicity in humans probably depends on the extent to which 1,1-dichloroethene is metabolized and

which intermediates are formed.

Groups of people who should be specifically cautioned against exposure to 1,1-dichloroethene

include the very young; the elderly; pregnant women; those who ingest alcohol; people using

phenobarbital (or possibly other hepatic enzyme-inducing drugs); people who, for whatever

reason, are fasting; and those with cardiac, hepatic, renal, and certain central nervous system

dysfunctions.

Minimal Risk Levels for 1,1-Dichloroethene

Inhalation MRLs

• An MRL of 0.02 ppm has been derived for intermediate-duration inhalation exposure

(15-364 days) to 1,1-dichloroethene. This MRL is based on a NOAEL of 5 ppm for hepatic

effects in guinea pigs continuously exposed to 1,1-dichloroethene (Prendergast et al. 1967).

Increased SGPT and alkaline phosphatase activity and decreased lipid content were

observed at 48 ppm.

An MRL has not been derived for acute inhalation exposure (14 days or less) to 1,1-dichloroethene.

A study by Reitz et al (1980) reported adverse kidney effects in mice exposed to 10 ppm

for 6 hours. This appears to be the most sensitive end point identified; however, study limitations,
1,1- DICHLOROETHENE 69

2. HEALTH EFFECTS

such as the small number of animals used (three to six males) and the ambiguous description of

the incidence of the lesions (0-20% of the animals), precluded derivation of an acute-duration

inhalation MRL. In addition, an acute-duration MRL could not have been derived since the

renal effects occurred at a lower concentration than did effects following intermediate-duration

exposure to 1,l -dichloroethene.

An MRL has not been derived for chronic inhalation exposure (365 days or more) to 1,1-dichloroethene. Adverse hepatic effects were observed in rats exposed to a concentration of 25 ppm

1,1-dichloroethene 6 hours/day, 5 days/week, for 18 months (Quast et al. 1986). Few chronic

inhalation studies were identified, and the one conducted by Quast et al. (1986) provided the

most complete information and identified the most sensitive end point. However, a serious

LOAEL of 15 ppm for developmental effects in rats and mice following acute exposure to

1,1-dichloroethene was reported by Short et al. (1977a) which precluded derivation of a chronicduration inhalation MRL.

Oral MRLs

• An MRL of 0.009 mg/kg/day has been derived for chronic-duration oral exposure (365 days

or more) to 1,1-dichloroethene. This MRL is based on the development of hepatocellular

changes observed in rats exposed to 50 ppm 1,1-dichloroethene (converted by the

investigators to a dose of 9 mg/kg/day based on body weight and water consumption data) in

utero, during lactation, and through weaning into adulthood (Quast et al. 1983). These

results are supported by several other chronic-duration studies that fc>und similar hepatic

effects in rats at comparable doses of 1,1-dichloroethene.

An MRL has not been derived for acute oral exposure (14 days or less) to 1,1-dichloroethene.

With the exception of a developmental study in rats (Murray et al. 1979), all the acute-duration

studies administered a single dose of 1,1-dichloroethene, and although Murray et al. (1979)

defined a NOAEL of 40 mg/kg/day, this NOAEL is too close to the 50-mg/kg dose that caused

death in fasted rats (Andersen and Jenkins 1977).
1,1- DICHLOROETHENE 70

2. HEALTH EFFECTS

An MRL has not been derived for intermediate oral exposure (15-364 days) to 1,1-dichloroethene.

Only one study reported data after intermediate-duration exposure to 1,1-dichloroethene

(Quast et al. 1983). This study could not define a dose-response relationship for any examined

end point and reported a NOAEL of 25 mg/kg/day.

Death. No deaths have been reported in humans following 1,1-dichloroethene exposure.

1,1-dichloroethene was lethal to animals following acute exposures to high levels via the

inhalation or oral routes. 1,1-dichloroethene-induced lethality appeared to be influenced by the

fasting of the animal regardless of exposure route, with LD50 values for fasted animals generally

significantly lower than those reported for nonfasted animals (e.g., Chieco et al. 1981; Jaeger et

al. 1973c; Jenkins and Andersen 1978; Siegel et al. 1971). Young males appeared to be affected

to a greater extent by fasting than females. Experimental evidence suggests that this enhanced

toxicity in fasted animals resulted from increased levels of reactive intermediates of 1,1-dichloroethene

available for binding to macromolecules in target tissues after fasting (McKenna et

al. 1978b). Nonfasted rats that were exposed to 20,000 or 32,000 ppm of 1,1-dichloroethene by

inhalation for 1 hour survived for at least 24 hours (Carlson and Fuller 1972). However, when

comparable animals were pretreated with the microsomal enzyme inducers phenobarbital or

methylcholanthrene, these exposure levels were lethal to nearly all of the animals within 2 hours,

suggesting that lethality was due to increased formation of toxic metabolites. However, Carlson

and Fuller (1972) found that pretreating rats with two different inhibitors of microsomal

metabolism, which presumably would reduce the formation of reactive intermediates (SKF 525A

and Lilly 18947), prior to inhalation exposure to 1,1-dichloroethene also reduced the survival time.

Other inhibitors of microsomal metabolism (carbon disulfide and diethyldithiocarbamate) were

found to protect mice against all 1,1-dichloroethene-induced toxic effects at low doses following

intraperitoneal injection (Masuda and Nakayama 1983). These results indicate that

biotransformation plays an important role in the expression of 1,1-dichloroethene-induced effects.

Increased susceptibility of fasted animals to the lethal effects of 1,1-dichloroethene may occur

because fasting depleted GSH in the target tissues and less GSH was available to bind to the

active intermediate (Jaeger et al. 1973a).

Mice are more sensitive than rats to the lethal effects of inhaled 1,1-dichloroethene (see

Figure 2-1) (Jaeger et al. 1974). This differential sensitivity also has been observed by the oral
1,1- DICHLOROETHENE 71

2. HEALTH EFFECTS

exposure route (Jenkins et al. 1972; Jones and Hathway 1978a). Pharmacokinetic studies suggest

that, relative to rats, the rate of metabolism is higher in mice, resulting in a greater degree of

damage from the increased levels of electrophilic species capable of reacting with intracellular

macromolecules (McKenna et al. 1977; Reitz et al. 1980).

Although animal studies indicate that amount of food ingested affects 1,1-dichloroethene-induced

lethality, how the amount of food ingested prior to exposure affects the susceptibility of humans

to the toxic effects of 1,1-dichloroethene is not known. Human subpopulations probably exist

with differing biochemical capacities for 1,1-dichloroethene metabolism and thereby are more or

less able to form reactive intermediates. It is not known whether these differing biochemical

capacities would affect an individual’s susceptibility to 1,1-dichloroethene-induced lethality. Orally

ingested 1,l-dichloroethene at sufficiently high doses is likely to cause death in humans, and

younger members (particularly males) of the population at hazardous waste sites may be at higher

risk.

Systemic Effects

Respiratory Effects. No information regarding respiratory effects in humans was located.

Irritation of the mucous membranes of the upper respiratory tract and pulmonary congestion,

hyperemia, and morphological changes were seen at necropsy in rats and mice acutely exposed to

high levels of 1,1-dichloroethene via inhalation (Henschler 1979; Klimisch and Freisberg 1979a;

Zeller et al. 1979b). Chronic inhalation exposure to 1,1-dichloroethene was associated with

similar adverse respiratory effects (Gage 1970; Prendergast et al. 1967; Quast et al. 1986). These

effects appeared to be rather nonspecific and probably resulted from 1,1-dichloroethene’s

irritating properties. Therefore, these data suggest that any possible nongenotoxic respiratory

effects associated with inhalation exposure to 1,1-dichloroethene (particularly acute exposure) in

humans may be a consequence of local nonspecific irritation.

However, a local nonspecific irritant effect cannot explain the pulmonary injury observed in mice

following the oral administration of a single-dose of 1,1-dichloroethene. The effects seen included

histopathological changes in Clara cells. These effects were considered reversible since cellular

regeneration was evident within 3 days of treatment (Forkert et al. 1985). Clara cell


1,1- DICHLOROETHENE 74

2. HEALTH EFFECTS

culminate in cell death (Luthra et al. 1984). Results of in vitro studies in liver perfusates have

suggested that 1,1-dichloroethene metabolism reduces the viability of liver cells (Reichert et al.

1978). This was demonstrated by Kainz et al. (1993) who determined that mouse hepatocytes

incubated with 1,1-dichloroethene experienced a concentration-dependent leakage of lactate

dehydrogenase (LDH) into the cellular medium. Histochemical and biochemical evidence support

the concept that plasma membranes and mitochondrial membranes may be the primary foci of

acute hepatocellular injury in fasted rats (Jaeger 1977; Reynolds et al. 1980). Phospholipase A2

activation may also be part of the sequence of events (Glende and Recknagel 1992).

In conclusion, 1,1-dichloroethene induces hepatotoxicity in humans. This is supported by evidence

in animals following both inhalation and acute and repeated oral exposures. However, humans,

particularly those exposed by inhalation to high levels of 1,1-dichloroethene in occupational

settings or in areas surrounding hazardous waste sites and those with compromised hepatic

function, may be at risk for 1,1-dichloroethene-induced liver toxicity.

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

1,1-dichloroethene.

Renal toxicity (e.g., enzyme changes, hemoglobinuria, increases in organ weight, and tubular

swelling, degeneration, and necrosis) has been observed following both inhalation and oral

exposure to 1,1-dichloroethene in animals (Jackson and Conolly 1985; Lee et al. 1977; McKenna

et al. 1978a; Oesch et al. 1983; Short et al. 1977d). Fasted animals (particularly males) were again

more susceptible to these effects than nonfasted animals (Chieco et al. 1981; McKenna et

al. 1978b), and mice were more susceptible than rats, as was seen for 1,1-dichloroethene-induced

hepatotoxicity (Reitz et al. 1980; Short et al. 1977c; Watanabe et al. 1980). There is some

evidence that the kidney damage induced by acutely inhaled or ingested 1,1-dichloroethene may

be reversible (Jenkins and Andersen 1978; Reitz et al. 1980), and the amount of reversibility is

concentration and duration dependent. As indicated in Section 23.5, kidney toxicity has been

attributed to the formation of cysteine S-conjugates that may be metabolized by β-lyase, located in

the proximal tubule cells, to unstable thiols that yield electrophilic products that interact with

macromolecules.
1,1- DICHLOROETHENE 75

2. HEALTH EFFECTS

Though data on kidney toxicity in humans following exposure to 1,1-dichloroethene do not

currently exist, evidence from animal studies in two species suggest that nephrotoxicity may also

occur in humans, particularly following acute exposure to 1,1-dichloroethene. The fact that

adverse renal effects were rarely seen following more prolonged exposure to 1,l-dichloroethene

(except in male mice), coupled with the observation that the acute nephrotoxic effects at lower

doses were reversible, suggest that up to a point the damaged cells can be replaced. The renal

effects of chronic-duration exposure to 1,1-dichloroethene in humans are not known but are

probably minimal at concentrations generally experienced.

Immunological Effects. No studies were located regarding immunological effects in humans and

animals after 1,1-dichloroethene exposure by any route. Therefore, the potential for 1,1-dichloroethene

to cause immunological effects in humans exposed in the environment or at hazardous

waste sites cannot be assessed.

Neurological Effects. Central nervous system toxicity has been observed in humans acutely

exposed to high concentrations (≈4,000 ppm) of inhaled 1,1-dichloroethene (EPA 1979b).

Complete recovery occurred if exposure was not prolonged.

In addition, signs of central nervous system toxicity were the predominant effects observed in

animals after acute inhalation exposure to high concentrations of 1,1-dichloroethene. These signs

and symptoms observed in humans and in animals are consistent with a narcotic effect of

1,1-dichloroethene, which is observed with many other organic solvents. Effects on the nervous

system were not observed following lower oral dose or repeated inhalation exposures to

1,1-dichloroethene in animals. However, these studies did not utilize comprehensive neurological

testing that may have detected subtle neurological effects. The available information is

insufficient to predict whether or not exposure to low levels of 1,1-dichloroethene by the

inhalation, oral, or dermal routes of exposure represent a neurological hazard for humans.

Reproductive Effects. The only study reported in humans regarding reproductive effects of

1,1-dichloroethene provides only suggestive evidence of neural tube defects in newborns (NJDH

1992a, 1992b). Therefore, these data should be interpreted with caution.
1,1- DICHLOROETHENE 76

2. HEALTH EFFECTS

Premating exposure of male rats to 1,1-dichloroethene by the inhalation route had no effect on

reproductive end points (Anderson et al. 1977; Short et al. 1977b). Similarly, no reproductive

effects were reported in a three-generation drinking water study with 1,1-dichloroethene in rats

(Nitschke et al. 1983). The biological significance of these findings in animals with regard to

potential reproductive effects of 1,1-dichloroethene in humans is not known.

Developmental Effects. The only study reported in humans regarding reproductive effects of

1,1-dichloroethene provides very weak suggestive evidence of neural tube defects in newborns

(NJDH 1992a, 1992b). Therefore, these data should be interpreted with caution. An increased

incidence of congenital cardiac malformations was observed in infants born to mothers who had

consumed water contaminated mainly with trichloroethylene and to a lesser extent with

1,1 dichloroethene and chromium during the first trimester of pregnancy (Goldberg et al. 1990).

Although exposure to other chemicals was simultaneous, this finding may be relevant since

1,1-dichloroethene induced a dose-related increase in various congenital cardiac defects in rat

fetuses after intrauterine administration of 1,1-dichloroethene to the dams (Dawson et al. 1990).

Since 1,1-dichloroethene was not supplied by a natural route of exposure, the results of this study

should be interpreted with caution (Dawson et al. 1990). Based on studies by Short et

al. (1977a), 1,1-dichloroethene has weak teratogenic effects in laboratory animals (rats and mice).

Developmental toxicity was enhanced following inhalation exposure to 1,1-dichloroethene,

compared to oral exposure. Developmental toxicity was often observed at doses of 1,1-dichloroethene

that also induce maternal toxicity in animals. Studies by Murray et al. (1979)

demonstrated that the sensitivity of pregnant rats to 1,1-dichloroethene was greater by inhalation

than by ingestion. After inhalation exposure at 80 and 160 ppm for 7 hours/day on gestation

days 6-18, 1,1-dichloroethene produced maternal toxicity, increased resorption and skeletal

alterations. Except for a marginal increase in mean fetal crown-rump length in the offspring, no

adverse effects were noted in rats receiving 40 mg/kg/day in drinking water. The author

hypothesized a possible mechanism to explain the route-dependent differences in 1,1-dichloroetheneinduced toxicity was as follows: since detoxication of 1,1-dichloroethene occurred via

conjugation of its active metabolites with GSH (McKenna et al. 1977) and GSH levels undergo

diurnal variations (Jaeger et al. 1973a), was speculated that sufficient GSH levels were available

to detoxify 40 mg/kg administered in drinking water over a 24-hour period, but not when the

animals were exposed via inhalation between 8:30 am and 3:30 pm (Murray et al. 1979). When
1,1- DICHLOROETHENE 77

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1,l -dichloroethene doses are converted into equivalent units, animals exposed by inhalation

received ≈76.6 and 153 mg/kg/day (assuming all 1,1-dichloroethene was absorbed by the lungs)

compared to 40 mg/kg/day in drinking water. Thus, a difference in total dose may also explain the

greater toxicity seen following inhalation exposure.

Based on studies in laboratory animals, it is prudent to consider that potential adverse maternal

and developmental effects could occur in humans exposed to 1,1-dichloroethene.

Genotoxic Effects. The available data suggest that 1,1-dichloroethene produces genotoxic

effects in a number of test systems. The results of in vitro and in vivo studies indicate that

1,1 -dichloroethene exhibited mutagenic properties upon metabolic activation (i.e., the presence of

an exogenous mammalian metabolic system was required) in bacteria and yeast and that it induced

gene conversion in yeast. It was also widely mutagenic in plant cells without activation by

mammalian metabolic systems. 1,1-dichloroethene induced chromosome aberrations and sister

chromatid exchanges in cultured mammalian cells in vitro and DNA damage in mice in vivo.

1,1-dichloroethene was genotoxic in several in vitro test systems. A metabolic activation system is

usually required for activity. Results of in vitro genotoxicity studies are shown in Table 2-3. Gene

mutations were observed in bacteria, yeast, and plant cells (Bartsch et al. 1975, 1979; Bronzetti et

al. 1981; Greim et al. 1975; Jones and Hathway 1978c; Oesch et al. 1983; Van’t Hof and Schairer

1982) and it induced gene conversion in yeast (Bronzetti et al. 1981; Koch et al. 1988). Dosedependent increases in the frequency of euploid whole chromosome segregants were noted in

Aspergillus nidulans (Crebelli et al. 1992). Both base-pair substitution and frameshift mutations

were reported in Salmonella typhimurium after continuous exposure to 1,1-dichloroethene vapors

(Bartsch et al. 1975, 1979; Jones and Hathway 1978c; Oesch et al. 1983). Another study reported

negative results from tests in Salmonella (Mortelmans et al. 1986). However, the Mortelmans et

al. (1986) study incorporated single doses of 1,1-dichloroethene into warmed incubation medium

instead of exposing the bacteria continuously to vapor. Given that l,l-dichloroelhene is very

volatile and would be expected to escape from the culture, continuous exposure to vapor is

considered a mere reliable method. 1,1-dichloroethene was mutagenic in Salmonella after

metabolic activation with an exogenous activation system derived from human liver cells (Jones

and Hathway 1978c), thus supporting the ccmcept that the human liver is capable of activating

1,1-dichloroethene into mutagenic metabolites.

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In cultured mammalian cells, 1,1-dichloroethene was negative in a point mutation assay in

8-azaguanine and ouabain-resistant V79 Chinese hamster lung cells (Drevon and Kuroki 1979),

but it produced chromosomal aberrations and sister chromatid exchanges in a Chinese hamster

lung fibroblast cell line (Sawada et al. 1987) and in mouse lymphoma cells (McGregor et al. 1991)

in the presence of a metabolic activation system.

1,1-dichloroethene has also been tested in several in vivo studies in animals. Results of in vivo

genotoxicity studies are shown in Table 2-4. Negative results were reported in assays for

dominant lethal mutations in mice (Anderson et al. 1977) and rats (Short et al. 1977b) and in a

micronucleus test in mice using both the bone marrow assay system following gavage

administration and the transplacental assay system following intraperitoneal administration to

pregnant mothers (Sawada et al. 1987). 1,1-dichloroethene inhalation was associated with low

rates of DNA alkylation in the livers and kidneys of mice and rats, compared to

dimethylnitrosamine-treated controls. Furthermore, DNA repair mechanisms were induced in the

kidneys of mice in cells in which normal replicative DNA synthesis had been inhibited. A

significant increase in DNA repair rates was not observed in 1,1-dichloroethene treated mouse

liver nor in the kidneys or liver of rats (Reitz et al. 1980). In a mouse host-mediated assay

system, 1,1-dichloroethene was mutagenic and induced gene conversion in yeast (Bronzetti et al.

1981).

In vitro and in vivo studies indicate that 1,1-dichloroethene exhibits some mutagenic properties

upon metabolic activation. But there is no direct evidence that exposure to 1,1-dichloroethene

causes genotoxic effects in humans. However, the evidence that a metabolizing enzyme system

derived from human liver could activate 1,1-dichloroethene into mutagenic metabolites (Jones and

Hathway 1978c) suggests that 1,1-dichloroethene may be considered a potential genotoxic threat

to humans. It must be mentioned, however, that human liver cells overlaid with mammalian tissue

post-mitochondrial SC) (prepared from Aroclor 1254-induced rats) were activated, and human

tissue not overlaid with S9 did not activate 1,1-dichloroethene into mutagenic metabolites (Jones

and Hathaway 1978c).

Cancer. Data regarding carcinogenic effects of 1,1-dichloroethene in humans were limited to

results from an occupational exposure study (Ott et al. 1976). The assumption is made that

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exposure occurred mainly via inhalation, although dermal contact cannot be ruled out.

Limitations in these studies, such as small cohort size and short observation periods greatly

diminished their usefulness for assessing the carcinogenic potential of 1,1-dichloroethene in

humans.

The carcinogenicity of 1,1-dichloroethene following inhalation, oral, dermal, and subcutaneous

exposure has been evaluated in mice (Hong et al. 1981; Lee et al. 1978; Maltoni et al. 1985; Van

Duuren et al. 1979) rats (Hong et al. 1981; Maltoni et al. 1982, 1985; NTP 1982; Ponomarkov

and Tomatis 1980; Quast et al. 1983, 1986; Rampy et al. 1977; Viola and Caputo 1977) and

Chinese hamsters (Maltoni et al. 1985). Of the carcinogenicity bioassays conducted to date, only

the results of a single inhalation study in mice by Maltoni et al. (1985) provide evidence of a

positive carcinogenic effect from 1,1-dichloroethene exposure. In this study, increases in renal

adenocarcinomas were noted in male Swiss mice exposed to 25 ppm 1,1-dichloroethene via

inhalation. Mammary gland carcinomas and lung tumors, most of which were benign pulmonary

adenomas, were also observed in this study. Results of all other carcinogenicity studies with

laboratory animals have been negative. Increases in a variety of malignant and nonmalignant

tumors were reported in studies involving inhalation and oral exposure; however, these increases

either were not statistically significant or were not considered by the respective authors to be

exposure related (Lee et al. 1977, 1978; Maltoni et al. 1985; NTP 1982; Ponomarkov and Tomatis

1980; Quast et al. 1983, 1986). Study limitations for several of the investigations included less

than lifetime exposure, use of doses below the maximum tolerated dose, small numbers of animals,

and limited gross and microscopic examinations. Such limitations reduce the sensitivity of a

bioassay system to detect a carcinogenic response.

The carcinogenicity of 1,1-dichloruethene in mice treated by dermal application and by

subcutaneous injection was evaluated by (Van Duuren et al. 1979). 1,1-dichloroethene was

inactive as a complete carcinogen when applied repeatedly for a lifetime to the skin of mice and

did not induce local malignancies when administered chronically to mice by subcutaneous

injection. However, a dermal initiation-promotion study with Swiss mice has shown that

1,1-dichloroethene was active as a tumor-initiating agent. A statistically significant increase in the

incidence of skin papillomas was noted in Swiss mice treated dermally initially with 1,1-dichloroethene

and subsequently with the tumor-promoting agent phorbol myristate acetate (Van Duuren

et al. 1979).
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On the basis of the suggestive inhalation study by Maltoni et al. (1985), 1,1-dichloroethene should

be regarded as a possible animal carcinogen and, therefore, as a possible human carcinogen.

Results of studies with laboratory animals indicating nonsignificant or non-dose-related increases

in various malignant and nonmalignant tumors following oral or inhalation exposure provide

limited but suggestive support that 1,1-dichloroethene may be a weak carcinogen (Lee et al. 1978,

1977; Maltoni et al. 1985; Ponomarkov and Tomatis 1980; Quast et al. 1986, 1983). The positive

initiation-promotion study by Van Duuren et al. (1979) also suggests that 1,1-dichloroethene in

concert with tumor-promoting agents can induce cancer, but a relationship between this test and

human cancer has not been demonstrated.

In experimental studies with mice, it has been observed that doses of 1,1-dichloroethene that

induce renal tumors also induce renal tissue damage (degeneration and necrosis) (Maltoni et

al. 1985; Reitz et al. 1980; Watanabe et al. 1980). These tumorigenic doses, however, are

associated in mice with only minimal DNA alkylation and DNA repair (Reitz et al. 1980). These

findings suggest that kidney toxicity may play a contributing role in the induction of renal tumors

(Watanabe et al. 1980), and that tumors observed in mice exposed to 1,1-dichloroethene may be

the result of the chemical’s toxic effect upon nongenetic carcinogenic mechanisms (Reitz et

al. 1980). However, 1,1-dichloroethene is mutagenic in lower organisms and the same nephroses

present in males was present in females but no tumors developed.

It has been suggested that the toxic and carcinogenic effects of 1,1-dichloroethene may depend on

species, strain, and sex of the tested animals (Maltoni et al. 1985). Results of studies suggest that

male Swiss mice are more susceptible to the toxic effects of 1,1-dichloroethene than female Swiss

mice, rats, or hamsters (Maltoni et al. 1985; Oesch et al. 1983). Pharmacokinetic studies also

suggest that compared to rats, mice have a greater rate of 1,1-dichloroethene activation to

electrophilic species capable of reacting with intracellular macromolecules (McKenna et al. 1977;

Reitz et al. 1980).

NTP originally described the carcinogenic effects of oral administration of 1,1-dichloroethene in

both sexes of Fischer-344 rats and B6C3F1 mice as negative. This term has subsequently been

changed to no evidence. EPA (IRIS 1992) has classified 1,1-dichloroethene as a Group C agent

(possible human carcinogen). This category applies to chemicals for which there is limited

evidence of carcinogenicity in animals and inadequate evidence in humans. IARC (1987) has
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2. HEALTH EFFECTS

classified 1,1-dichloroethene as a Group 3 chemical (not classifiable as to human carcinogenicity).

1,1-Dichloroethene is not included in the Sixth Annual Report on Carcinogens, which is a list of

compounds that may reasonably be anticipated to be carcinogens published by the U.S. Public

Health Service (NTP 1991).

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 1,l -dichloroethene 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 that these markers are not

often substance specific. They also may not be directly adverse, but can indicate potential health
1,1- DICHLOROETHENE 84

2. HEALTH EFFECTS

impairment (e.g., DNA adducts). Biomarkers of effects caused by 1,1-dichloroethene 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 1,1-dichloroethene

Exposure to 1,1-dichloroethene can be determined by the appearance of 1,1-dichloroethene in

exhaled air and/or the appearance of metabolites such as dithioglycollic acid in urine (see

Section 6.1). However, because 1,1-dichloroethene is rapidly eliminated from the body, such

determinations can prove useful only for detecting recent exposure (within days). Furthermore,

because other structurally similar compounds such as vinyl chloride can give rise to the same

metabolic products as 1, 1-dichloroethene, formation of adducts with hemoglobin and detection of

urinary metabolites cannot be considered as specific biomarkers of exposure to 1,l-dichloroethene.

Data from available studies have been insufficient to correlate levels of 1,1-dichloroethene in the

environment with levels in breath. In an investigation of trace organic compounds in human

breath, a 60-minute: sampling period yielded 13.0 μg of 1,1-dichloroethene in the breath (volume

unspecified) of one individual (Conkle et al. 1975). This value was corrected for the amount of

1,l-dichloroethene in the air supplied to the individual during the sampling period. The study

authors attributed the amount of 1,1-dichloroethene in the individuals’s breath to previous

exposure; however, no levels of previous exposure to 1,1-dichloroethene were reported for the

test subject. The breath of 1 out of 12 subjects tested by Wallace et al. (1984) contained

1,1-dichloroethene; however, the levels were not specified. No environmental levels of

1,l-dichloroethene were reported for this study. Twelve percent of breath samples from

50 residents of New Jersey contained measurable amounts of 1,1-dichloroethene, ranging from

0.2 to 2 μg/m3

 of expired air (Wallace et al. 1986). Increased liver enzyme (AST, ALT)
1,1- DICHLOROETHENE 85

2. HEALTH EFFECTS

activities were reported in two workers exposed to 1,1-dichloroethene (Ott et al. 1976). However,

these enzyme markers are not specific to 1,1-dichloroethene induced liver toxicity because they

can be indicative of the detoxification process.

2.5.2 Biomarkers Used to Characterize Effects Caused by 1 ,I -Dichloroethene

As indicated in Sections 2.2 and 2.3, the liver and kidney are primary target organs for

1,l -dichloroethene exposure. Exposure to 1,1-dichloroethene (depending on dose and duration of

exposure) increases serum levels of certain liver enzymes such as SGOT (AST), SGPT (ALT),

and others, which is taken as an indication of liver injury. However, this effect is caused by other

halogenated alkenes as well such as vinyl chloride, and cannot be considered as a specific

indicator of 1,l -dichloroethene effects.

Occupational exposure studies have investigated health effects associated with exposure to

1,1-dichloroethene. Because of the small cohort size and concurrent exposure to other

compounds, the information from these studies is not sufficient to correlate levels of 1,1-dichloroethene

in the environment with health effects. A study of 138 workers exposed to 1,1-dichloroethene

(time-weighted-average concentrations ranging from <5 to 70 ppm) and copolymers other

than 1,l -dichloroethene reported no statistically-related changes attributable to 1,l -dichloroethene

in long-term mortality or health-inventory findings (Ott et al. 1976). No association between

occupational exposure to 1,1-dichloroethene (with concurrent exposure to other chemicals) and

incidence of angiosarcomas of the liver in workers was found by Waxweiler (1981).

Inhalation exposure to 50 ppm 1,1-dichloroethene was associated with minimal rates of DNA

alkylation in liver and kidney cells of experimental rats and mice (Reitz et al. 1980).

Additional details regarding biomarkers of effects for 1,1-dichloroethene may be found in the

CDC/ATSDR Subcommittee Report on Biological Indicators of Organ Damage (CDC/ATSDR

1990) or in the Office of Technology Assessment report on neurotoxicity (OTA 1990). A more

detailed discussion of health effects attributed to exposure to 1,1-dichloroethene can be found in

Section 2.2 of Chapter 2 in this document.
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2. HEALTH EFFECTS

2.6 INTERACTIONS WITH OTHER CHEMICALS

As discussed in previous sections, it is apparent that the toxicity of 1,1-dichloroethene is largely

due to the formation of toxic intermediates during metabolism in vivo. The production and

biotransformation of toxic metabolic intermediates of 1,1-dichloroethene can be greatly influenced

by various metabolic inhibitors and inducers, and by the availability of precursors of compounds

involved in detoxication, such as GSH.

Microsomal mixed-function oxidases (MFOs) are a group of enzymes involved in the

biotransformation and detoxication of xenobiotics such as 1,1-dichloroethene. Inhibitors of some

microsomal MFOs include the compound SKF-525-A, disulfiram, and other dithiocarbamates, such

as thiram and diethyldithiocarbamate. These compounds reduce the toxic effects of 1,1-dichlorethene

in the liver, probably by inhibiting the enzymes responsible for the formation of reactive

toxic intermediates (Masuda and Nakayama 1983; Short et al. 1977c). Pretreatment with

intracellular cysteine precursor, L-2-oxothiazolidine-4-carboxylate is also used to protect against

1,1-dichloroethene toxicity in this way (Moslen et al. 1989b). Inhibitors of metabolic enzymes

responsible for the breakdown of these reactive intermediates may also enhance the toxicity of

1,1-dichloroethene. For example, 1,1,1-trichloropropane and other inhibitors of epoxide hydrolase

can potentiate the toxicity of 1,1-dichloroethene (Jaeger 1977). Other chemicals that reduce the

activity of metabolic enzymes and show some protective effects against the toxicity of 1,1-dichloroethene

include pyrazole, 3-aminotriazol (Andersen et al. 1978).

Pretreatment of rats with acetaminophen greatly increased lethality and the hepatotoxic effects of

1,1-dichloroethene (Wright and Moore 1991). Although the depletion of glutathione was not

discussed, the study authors concluded that acetaminophen produces alterations that make

hepatocytes more susceptible to 1,l-dichloroethene injury.

Enzyme inducers (enhancers) may either protect against or exacerbate the toxicity of 1,1-dichloroethene.

Induction of enzymes involved in the formation of toxic intermediates potentiates

1,l -dichloroethene-induced toxicity following 1,1-dichloroethene exposure; conversely, induction of

enzymes responsible for the biodegradation of the toxic intermediate(s) decreases toxicity.

Examples of compounds that induce MFOs and increase toxic effects upon exposure to

1,1-dichloroethene include ethanol and acetone (Charbonneau et al. 1991; Hewitt and Plaa 1983;
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2. HEALTH EFFECTS

Kainz et al. 1993; Sato et al. 1983). In acetone-pretreated rats, mixtures containing chloroform or

carbon tetrachloride plus 1,1-dichloroethene increased hepatotoxic responses additively

(Charbonneau et al. 1991).

Many inducers of MFO enzymes (e.g. P-450) do not increase the hepatotoxicity of l,l-dichlorocthene,

perhaps because they stimulate enzyme systems not involved in the metabolism of

1,1-dichloroethene. An example of a P-450 inducer is phenobarbital (Carlson and Fuller 1972).

Jenkins et al. (1971) found that pretreatment of rats with phenobarbital followed by oral

administration with 1,1-dichloroethene had a protective effect against liver damage, while Carlson

and Fuller (1972) found that pretreatment of rats with phenobarbital followed by inhalation

exposure to 1,1-dichloroethene increased mortality but had no effect on hepatotoxicity. This

discrepancy may be due to differences in routes of administration and indicators of toxicity

examined.

Thyroidectomy protected rats from the hepatotoxic effects of 1,1-dichloroethene, probably by

increasing the amount of hepatic GSH (Szabo et al. 1977). Thyroxine replacement in

thyroidectomized rats exacerbated the liver damage seen upon subsequent exposure to

1,1-dichloroethene (Szabo et al. 1977).

Pretreatment of animals with compounds that deplete GSH levels (such as buthionine

sulfoximine) increases the amount of liver damage caused by 1,1-dichloroethene exposure

(Reichert et al. 1978). Conversely, pretreatment of animals with supplements containing high

concentrations of the amino acids cysteine and/or methionine, both of which are metabolic

contributors of the sulfhydryl group required for GSH biosynthesis, has had a protective effect

against the toxicity of 1,1-dichloroethene (Short et al. 1977d).

2.7 POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE

A susceptible population will exhibit a different or enhanced response to 1,1-dichloroethene than

will most persons exposed to the same level of 1,1-dichloroethene 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
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the detoxification and excretory processes (mainly hepatic, renal, and respiratory) or the preexisting

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.

Specific information regarding human subpopulations that are unusually susceptible to the toxic

effects of 1,1-dichloroethene were not located. However, animal studies have suggested that

there are factors that may predispose some groups of the population to an increased risk for the

toxic effects of 1,1-dichloroethene. These factors are discussed below.

The influence that dietary intake can have upon the metabolism and detoxification of xenobiotics

has been well documented. Fasting is known to modify the metabolism and toxicity of a variety of

halogenated alkenes (Andersen et al. 1978; Nakajima et al. 1982). As discussed in previous

sections, the liver MFO activity in fasted animals or animals kept on a low carbohydrate diet was

enhanced when exposed to 1,1-dichloroethene, compared to that in similarly exposed control

(carbohydrate-fed) animals (McKenna et al. 1978a; Nakajima et al. 1982). Fasting prior to

1,1-dichloroethene exposure resulted in an earlier appearance of hepatic lesions, a more extensive

distribution of lesions and a reduced ability to metabolize high doses of 1,1-dichloroethene when

compared to control (nonfasted) rats (Jaeger et al. 1974; McKenna et al. 1978a; Reynolds and

Moslen 1977).

Sex differences in the toxic response to 1,1-dichloroethene have been observed in animals. For

example, in a chronic inhalation exposure study in rats, hepatotoxic effects occurred at lower

1,1-dichloroethene concentrations in female rats than in male rats (25 and 75 ppm, respectively)

(Quast et al. 1986). Fasted male animals, particularly young males, appear to be more susceptible

to the toxic effects of 1,1-dichloroethene than fasted females, as evidenced by their enhanced

responses at lower doses of 1,1-dichloroethene.

Individuals taking certain drugs or who have pre-existing liver, kidney, thyroid, or cardiac disease

may be at greater risk for 1,1-dichloroethene-induced toxicity. Acetaminophen is prescribed to
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some rheumatic patients at doses up to 4 grams per day (Insel 1990). Such individuals may be

highly susceptible to the effects of 1,l-dichloroethene (Wright and Moore 1991). Phenobarbital,

even though somewhat protective against 1,1-dichloroethene-generated liver damage (Carlson and

Fuller 1972), has sensitized the heart to 1,l -dichloroethene-induced arrhythmias (Siletchnik and

Carlson 1974). Since phenobarbital is sometimes used as a soporific, and by those with various

forms of epilepsy or seizure disorders, people who are taking this medication or those with

pre-existing arrhythmic heart conditions should not be exposed to high levels of 1,l-dichloroethene.

Ethanol increases the amount of 1,1-dichloroethene-induced hepatotoxicity observed in

rats, which suggests that alcohol ingestion could exacerbate 1,1-dichloroethene-induced toxicity in

exposed individuals. Therefore, individuals taking medicine that contains alcohol or individuals

drinking alcoholic beverages may be more susceptible to the toxic effects of 1,1-dichloroethene.

Thyroidectomy, either chemical or surgical, can protect against the hepatotoxicity associated with

inhalation of 1,1-dichloroethene. Conversely, thyroxine treatment to replace or supplement

normal thyroid function increases the amount of liver damage upon subsequent exposure to

1,1-dichloroethene in animals (Szabo et al. 1977). Individuals with liver or kidney disease or those

with an acute hypersensitivity to 1,1-dichloroethene should avoid exposure to 1,1-dichloroethene.

Specific data concerning teratogenicity in humans exposed to 1,l-dichloroethene were not found

in the literature. 1,1-dichloroethene has been described as a possible teratogen responsible for

soft-tissue anomalies in rats and skeletal defects in mice, rats, and rabbits, often at levels that

produced clear evidence of toxicity in the dam. It would be prudent for pregnant women to avoid

exposure to 1,1-dichloroethene.

To conclude, groups of people who should be specifically cautioned against exposure to

1,1-dichloroethene include the very young; the elderly; the pregnant; those ingesting large

amounts of acetaminophen as medication; those that ingest large amounts of alcohol; people

using phenobarbital (or possibly other hepatic enzyme-inducing drugs); those receiving thyroid

replacement therapy or those who are hyperthyroid; people who, for whatever reason, are fasting;

and those with cardiac, hepatic, renal, and certain central nervous system dysfunctions.
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2.8 METHODS FOR REDUCING TOXIC EFFECTS

This section will describe clinical practice and research concerning methods for reducing toxic

effects of exposure to 1,l -dichloroethene. However, because some of the treatments discussed

may be experimental and unproven, this section should not be used as a guide for treatment of

exposures to 1,1-dichloroethene. 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

Treatment for exposure to 1,1-dichloroethene is essentially supportive after the individual is

removed from the contaminated environment (Haddad and Winchester 1990). The following

steps have been suggested in an acute exposure situation to reduce the possibility of 1,1-dichloroethene

absorption. If 1,1-dichloroethene is swallowed and the victim is conscious, water or milk

can be administered to minimize mucosal irritation (Anonymous 1991). Activated charcoal can be

administered to inhibit absorption in the intestine. Following dermal contact, the affected areas

are flushed with water. No specific information was located regarding reducing peak absorption

of 1,l -dichloroethene following inhalation exposure.

2.8.2 Reducing Body Burden

No information was located regarding retention of 1,1-dichloroethene or its metabolites in humans

exposed to 1,1-dichloroethene. However, if the toxicokinetic mechanisms described in animals are

suggestive for humans, the metabolites are eliminated mainly in the urine. Therefore, increasing

diuresis may be a way of reducing the body burden of 1,1-dichloroethene metabolites.

2.8.3 Interfering with the Mechanism of Action for Toxic Effects

No information was located in the available literature regarding clinical or experimental methods

that can block the mechanism of toxic action of 1,1-dichloroethene in humans.

Although the exact mechanism of action of 1,1-dichloroethene in humans is not known both

humans and animal studies have identified the liver as the target organ for 1,1-dichloroethene. In
1,1- DICHLOROETHENE 91

2. HEALTH EFFECTS

experimental animals, 1,1-dichloroethene-induced hepatotoxicity is primarily due to reactive

metabolic products that arise from biotransformation reactions initiated by the cytochrome P-450

enzymatic system. It is, therefore, not unreasonable to assume that 1,1-dichloroethene-induced

liver toxicity in humans is also caused by 1,1-dichloroethene metabolites. If this premise is

accepted, then two general types of biochemical manipulations could be envisioned to reduce

1,1-dichloroethene-induced toxicity. The first one would be to prevent biotransformation into

reactive intermediates. This could be done by inhibiting enzymes responsible for these processes.

The second alternative would be to ensure that adequate amounts of GSH are available (for

example by administering precursors of GSH) in the liver in order to form S-conjugates with

metabolic intermediates that can be eliminated in the urine. In fact, such interventions have been

shown to protect against 1,1-dichloroethene-induced liver damage in rats (Moslen et al. 1989c).

Based on the fact that I,l-dichloroethene does not appear to accumulate in tissues, these

experimental procedures are likely to be more useful shortly after exposure to 1,1-dichloroethene

rather than after prolonged exposure to low levels of 1,1-dichloroethene, which may occur to

populations near waste 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 1,1-dichloroethene 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 1,1-dichloroethene.

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.
1,1- DICHLOROETHENE 92

2. HEALTH EFFECTS

2.9.1 Existing Information on Health Effects of 1,1-Dichloroethene

The existing data on health effects of inhalation, oral, and dermal exposure of humans and

animals to 1,1-dichloroethene are summarized in Figure 2-7. The purpose of this figure is to

illustrate the existing information concerning the health effects of 1,1-dichloroethene. 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 more broadly as any substance-specific

information missing from the scientific literature.

Figure 2-7 depicts the existing health effects information on 1,1-dichloroethene for a specific

route and duration of exposure. There is little information available concerning the long-term

health effects of 1,1-dichloroethene in humans following inhalation exposure. Most of the

information concerning health effects in humans is reported in occupational studies that are

difficult to interpret because of limitations in study design (e.g., exposure levels and duration

cannot be quantified and concurrent exposure to other toxic substances cannot be ruled out). No

information concerning oral or dermal exposure to 1,1-dichloroethene in humans was found in the

reviewed literature.

The systemic effects of 1,1-dichloroethene in animals following inhalation and oral exposure have

been studied in a variety of species following acute, intermediate, and chronic exposure durations.

No studies were located regarding immunological effects in humans or animals following

inhalation or oral exposure. One oral exposure study reported observations of the “appearance”

and “demeanor” of test animals, but this was not considered a good analysis of possible

neurological or behavioral effects. Genetic effect end points were examined following inhalation

exposure only. Carcinogenicity studies in animals following exposure by the oral, inhalation, and

dermal routes are available.

1,1- DICHLOROETHENE 94

2. HEALTH EFFECTS

2.9.2 Identification of Data Needs

Acute-Duration Exposure. No data were located indicating specific organs or systems as targets

for 1,l -dichloroethene in humans by any route of exposure. The data in experimental animals

such as rats and mice suggest that the liver and kidneys are the primary targets for acute-duration

exposure to 1,1-dichloroethene by inhalation and oral routes of exposure (Anderson et al. 1980;

Chieco et al. 1982; Henck et al. 1979; Jenkins and Anderson 1978; McKenna et al. 1975; Moslen

et al. 1989b; Reynolds et al. 1980). Data regarding the dermal route of exposure were not

located. Although the kidney was. identified as the most sensitive organ in acute inhalation

studies (Henck et al. 1979; McKenna et al. 1978b; Reitz et al. 1980), these studies were

considered inadequate for derivation of an acute inhalation MRL, largely because of the small

numbers of animals used and lack of clarity in the presentation of the results. The data in

experimental animals were insufficient to derive an acute oral MRL mainly because the lowest

dose associated with systemic effects (Moslen et al. 1989a) was also found to cause lethality in

fasted rats (Anderson and Jenkins 1977). Information regarding the cause of death in the acuteduration

studies would be useful. Acute-duration studies by the dermal route using

14C-1,l -dichloroethene would provide useful information regarding absorption, distribution and

kinetics of excretion. Results of these studies coupled with available knowledge on the toxicity

and toxicokinetics should suffice. This information may be relevant for populations surrounding

hazardous waste sites that might be exposed to 1,1-dichloroethene for brief periods. Acute

industrial exposure is, however, more likely. Pharmacokinetic data do not suggest route-specific

target organs. Since 1,1-dichloroethene is rapidly excreted, it is not expected to accumulate in

tissues.

Intermediate-Duration Exposure. No data were located that identified target organs in humans

following intermediate exposure to 1,1-dichloroethene by any route of exposure. Information is

available on the systemic toxicity of 1,1-dichloroethene following inhalation and oral exposure in

rats, guinea pigs, dogs, and monkeys. These data indicate that the liver and kidneys are target

organs for intermediate exposure to 1,1-dichloroethene (Prendergast et al. 1967). An MRL was

derived for inhalation exposure based on hepatic effects in guinea pigs (Prendergast et al. 1967).

Only one study was identified that described the effects of 1,1-dichloroethene in animals (dogs)

after oral intermediate exposure (Quast et al. 1983). The lack of supporting data precluded

derivation of an oral MRL. Additional studies conducted in rats via oral route for intermediate
1,1- DICHLOROETHENE 95

2. HEALTH EFFECTS

exposure would be useful for setting the maximum tolerated dose for oral chronic studies. Data

on dermal exposure in animals are not needed. This information may be relevant for populations

surrounding hazardous waste sites that might be exposed to 1,1-dichloroethene for brief periods.

There are no pharmacokinetic data that would suggest route-specific target organs.

Chronic-Duration Exposure and Cancer. No data were located that identified target organs in

humans following chronic exposure to 1,1-dichloroethene by the oral and dermal routes. Hepatic

effects described in occupationally exposed humans (EPA 1976) are supported by data in animals

(Quast et al. 1983, 1986) but data from animal studies are sparse. An MRL was derived for oral

exposure based on hepatic effects in rats (Quast et al. 1983). There are no pharmacokinetic data

that would suggest route-specific target organs. Dermal exposure data are lacking. Studies with

well-designed experiments and complete dose and time protocols, and measuring all sensitive

toxicological end points, would provide valuable information on the health effects associated with

long-term exposure to 1,l-dichloroethene. These chronic studies could provide information on

subtle toxicological changes in organs associated with prolonged exposure to low levels of

1,l-dichloroethene. This information may be relevant for populations surrounding hazardous

waste sites that might be exposed to 1,1-dichloroethene for long periods.

Available data are insufficient to permit an evaluation of the carcinogenic risk of 1,1-dichloroethene

in humans. The data from animal studies are limited in their usefulness because of flaws

in the experimental design (e.g., doses that are too low) (Maltoni et al. 1985; NTP 1982;

Ponomarkov and Tomatis 1980; Quast et al. 1983; Rampy et al. 1977). An inhalation study in

mice described a positive carcinogenic response in the kidney (Maltoni et al. 1985). This study,

however, has been regarded as inconclusive since it appears that tumors were not observed in the

absence of nephrotoxicity. Swiss mice, in fact, are much more susceptible to the nephrotoxic

effects of 1,1-dichloroethene than other species, or even other strains of mice. Additional

information of the carcinogenicity of 1,1-dichloroethene from well conducted animal bioassays and

epidemiological studies using various routes of exposure would be useful in predicting the

likelihood that such a response occurs in humans.

Genotoxicity. No studies were identified that evaluated genotoxic effects of 1,1-dichloroethene

in humans following any route of exposure, or in animals following oral or dermal exposure.

Studies by the oral and dermal routes could help develop dose-response relationships for these
1,1- DICHLOROETHENE 96

2. HEALTH EFFECTS

routes. Several in vitro studies (Table 2-3 in Section 2.3.1.1) suggest that 1,1-dichloroethene, only

in the presence of activating systems, is mutagenic in both prokarydc and eukatydc organisms.

These results are consistent with the idea that a reactive metabolic intermediate(s), and not the

parent compound, is (are) responsible for the genotoxic properties of 1,1-dichloroethene. With

the exception of a weakly positive response in mouse kidney cells (Reitz et al. 1981), 1,1-dichloroethene

tested negative in in vivo rodent assays following acute and intermediate inhalation or

acute oral exposure to 1,1-dichloroethene (Anderson et al. 1977; Sawada et al. 1987; Short et al.

1977b). Cytogenetic analysis of human populations exposed to 1,1-dichloroethene in occupational

settings would provide an opportunity to assess the genotoxic potential of this chemical in

humans.

Reproductive Toxicity. The only study reported in humans regarding reproductive effects

following oral exposure to 1,1-dichloroethene provides evidence of neural tube defects in children

(NJDH 1992a, 1992b). However, these data are only suggestive and therefore, should be

interpreted with caution. No information is available regarding reproductive effects of

I,l-dichloroethene in humans following inhalation or dermal routes of exposure or in animals

following dermal exposure. Only one multigeneration study was identified in rats (Nitschke et al.

1993). This study was conducted by the oral route, and the results were negative. Studies were

identified that examined the reproductive effects of 1,1-dichloroethene after acute inhalation

exposure in rats (Short et al. 1977b) and mice (Anderson et al. 1977). No adverse reproductive

effects were observed in either one of these studies. Available pharmacokinetic data do not

suggest route-specific target organs. Multigeneration studies by the inhalation and dermal routes

would add information that could be relevant to humans.

Developmental Toxicity. The only study available in humans following oral exposure to

1,1-dichloroethene provides evidence of neural tube defects in children (NJDH 1992a, 1992b).

However, these data are only suggestive and therefore, should be interpreted with caution. No

relevant information is available indicating that 1,1-dichloroethene affects development in humans

by any route of exposure or in animals following dermal exposure. Numerous studies have been

conducted in rats by the inhalation route (Murray et al. 1979; Short et al. 1977a, 1977b). Based

on the results of these studies no-observed-effect level could not be identified because the study

authors did not use concentrations below those that produced adverse effects. Therefore, studies

using lower exposure concentrations of 1,1-dichloroethene would provide useful information.
1,1- DICHLOROETHENE 97

2. HEALTH EFFECTS

Only one oral exposure study in rats was located (Murray et al. 1979), and this study used only

one exposure level. No pharmacokinetic data are available that would indicate the transplacental

transfer of 1, l-dichloroethane. However, the available developmental toxicity studies suggest that

l,l-dichloroethane can be potentially toxic to the developing fetus. Therefore, additional oral

studies using a range of doses would provide useful information.

Immunotoxicity. No information is available indicating that the immune system is a target f&

1,1-dichloroethene in humans or animals. Batteries of immune function tests have not been

performed in the available acute-, intermediate-, and chronic-duration studies. Studies conducti

tests for immunocompetence and histopathological observations of organs and tissues involved il

immunological response would provide valuable information. Dermal sensitization studies in

animals might provide information on whether 1,1-dichloroethene is likely to cause an allergic

response. Available toxicokinetic data do not suggest route-specific target organs.

Neurotoxicity. Neurobehavioral toxicity studies of acute inhalation exposures to 1,1-dichloroethene

in both humans (EPA 1979b) and animals (Henschler 1979; Klimisch and Freisberg 1979a,

1979b; Zeller et al. 1979a, 1979b) are inadequate. This limited information suggests that the

nervous system can be affected by exposure to rather high concentrations of 1,1-dichloroethene.

Information by other routes of exposure is lacking. Available toxicokinetics data do not suggest

route-specific target organs. Studies by the inhalation, oral, and dermal routes, as well as tests for

neurological impairment in animals, might provide information that could be relevant to humans.

Epidemiological and Human Dosimetry Studies. Most of the available information on the

adverse effects of 1,1-dichloroethene in humans comes from cases of acute poisoning occurring

primarily in the workplace. Limitations inherent in these studies include unquantified exposures,

concentrations and durations, as well as concomitant exposure to other toxic substances. The few

available industrial surveys and epidemiological studies are limited in their usefulness because of

small sample size, short follow-up periods, and/or brief exposure periods. Despite their

inadequacies, studies in humans indicate that 1,1-dichloroethene can cause central nervous system

toxicity and irritation of the mucous membranes (EPA 1979b; Quast et al. 1986). There is also

some evidence to suggest that repeated exposure to 1,1-dichloroethene is associated with liver

damage in humans (EPA 1976). Well-controlled epidemiological studies of people living near

areas where 1,1-dichloroethene has been detected in surface water and groundwater, in the
1,1- DICHLOROETHENE 98

2. HEALTH EFFECTS

vicinity of industries releasing 1,1-dichloroethene, near hazardous waste sites, and of people

occupationally exposed could add to and clarify the existing database on 1,l-dichloroetheneinduced human health effects. However, such studies would probably be very difficult to conduct

since the majority of exposed workers are carpenters, warehousemen, and machine operators for

whom exposure information and health follow-up is difficult to obtain, and the exposed

population is either decreasing or difficult to define. Furthermore, a study of human populations

residing near hazardous waste sites or production sites would also be difficult to conduct because

of the difficulty in obtaining meaningful historical estimates of exposure, historical medical data,

and comprehensive follow-ups.

Biomarkers of Exposure and Effect

Exposure. Information regarding populations exposed specifically to 1,1-dichloroethene is not

available; therefore, no known biomarker of exposure to 1,1-dichloroethene has been identified in

humans. However, if 1,1-dichloroethene is metabolically disposed of by humans in a way similar

to that observed in animals, 1,1-dichloroethene in expired air could be a biomarker of recent

exposure to relatively high concentrations of 1,1-dichloroethene.Similarly, urinary excretion of

metabolites such as thioglycollic acid could also be considered a biomarker of recent exposure. It

must be mentioned, however, that the urinary metabolites would not be specific biomarkers for

1,1-dichloroethene exposure since other chemicals have similar urinary metabolites. Hence, the

development of methods to detect alternative biomarkers, specific to 1,l -dichloroethene exposure

would be useful.

Effect. Information regarding populations exposed specifically to 1,1-dichloroethene is not

available. Limited information indicate that serum levels of certain enzymes indicative of liver

damage may be elevated in humans exposed to 1,1-dichloroethene (EPA 1976). However, the

elevation of liver enzymes is triggered by exposure to many other chemicals; hence, elevation of

these enzymes cannot be considered a specific biomarker for 1,1-dichloroethene. Research

leading to the identification of specific DNA adducts formed after 1,1-dichloroethene exposure

would be valuable. This would facilitate medical surveillance leading to early detection of

potentially adverse health effects and possible treatment.
1,1- DICHLOROETHENE 99

2. HEALTH EFFECTS

Absorption, Distribution, Metabolism, and Excretion. There are no quantitative data

regarding absorption in humans by the inhalation, oral, or dermal route. The animal data indicate

that 1,1-dichloroethene is efficiently absorbed by the inhalation (Dallas et al. 1983; McKenna et

al. 1978b) and oral routes (Jones and Hathway 1978a; McKenna et al. 1978a; Putcha et al. 1986).

These studies have been conducted mostly in rats and mice. Dermal absorption data are lacking,

but absorption by this route should be suspected based on the physical and chemical properties of

1,1-dichloroethene and the fact that the fact that the Sencor mouse test was positive for initiation

of papillomas.

No data were located regarding distribution of 1,1-dichloroethene or its metabolites in humans.

Animal data regarding inhalation exposure (Jaeger et al. 1977a) and oral exposure (Jones and

Hathway 1978b) to 1,1-dichloroethene indicate that 1,1-dichloroethene (or metabolites) distributes

preferentially to the liver, kidney, and lung and that in general 1,1-dichloroethene does not

accumulate in tissues. Additional data on the distribution of 1,1-dichloroethene following dermal

exposure would be useful since humans can be exposed via this route as well. Studies regarding

distribution through the placenta were not available.

Data regarding biotransformation of 1,1-dichloroethene in humans are not available. The use of

human cell systems in culture might be considered a useful alternative to studying the metabolic

fate of 1,l dichloroethene in individuals. The metabolism of 1,l -dichloroethene has been

extensively studied in rats and mice following inhalation and oral exposure (Jones and Hathway

1978a, 1978b; McKenna et al. 1977, 1978a; Reichert et al. 1979). Experimental evidence indicates

that the metabolism of 1,1-dichloroethene is a saturable process. Although information regarding

metabolism following dermal exposure is lacking, there is no reason to believe that other pathways

would operate after exposure by this route.

Data regarding excretion of 1,1-dichloroethene in humans are not available. Urinary excretion of

metabolites is the main route of elimination of 1,1-dichloroethene metabolites in animals after

inhalation (McKenna et al. 1978b) and oral exposure (McKenna et al. 1978a; Reichert et al.

1979). After exposure to high concentrations of 1,l -dichloroethene, however, elimination of

unchanged 1, 1-dichloroethene in expired air was observed (Jones and Hathway 1978b; McKenna

et al. 1978a, 1978b; Reichert et al. 1979). No studies were located regarding excretion following

dermal exposure to 1,l -dichloroethene.
1,1- DICHLOROETHENE 100

2. HEALTH EFFECTS

Comparative Toxicokinetics. No direct information exists to assess whether humans handle

1,1-dichloroethene in a way similar to that observed in animals. Toxicokinetics studies have been

performed mainly in rats and mice, and the results suggest that no qualitative differences exist

between these two species, although mice seem to metabolize 1,1-dichloroethene to a greater

extent than rats (Jones and Hathway 1978a, 1978b; McKenna et al. 1977, 1978a; Reichert et al.

1979). Experiments in animals (mostly rats and mice) indicate that the liver, kidney, and lungs are

common target organs across species. Data from occupationally exposed humans suggest that the

liver is a target organ in humans (EPA 1976). Once reliable end points are determined in species

other than rats and mice, it would be important to verify that primates are affected in a similar

manner, in order to ensure that no unforeseen health effects might occur in humans.

Methods for Reducing Toxic Effects. There are no specific established methods or treatment

for reducing absorption of 1,l -dichloroethene. Studies aimed at elucidating this mechanism would

provide useful information. No information is available regarding the mechanism by which

1,1-dichloroethene distributes to tissues in the body. There are no well-established methods or

treatment for reducing the body burden of 1,1-dichloroethene or metabolites or for prevention of

toxicity following long-term exposure. The mechanism of toxicity of 1,1-dichloroethene in humans

is not known, but there is evidence that 1,1-dichloroethene toxicity in animals is due to a reactive

intermediate and not the parent compound (Dekant et al. 1989; Vamvakas and Anders 1990).

Experimental methods exist that can prevent the toxic action of 1,1-dichloroethene in animals

(i.e., administration of precursors of GHS) (Moslen et al. 1989b), but it is not known whether

these methods are relevant to humans. Studies in primates could provide information regarding

the mechanism of action of 1,1-dichloroethene that may be more relevant to humans than data

obtained in rats and mice. Methods for mitigation of the adverse health effects induced by

1,1-dichloroethene in animals have involved administering the substance prior to exposure

(Anderson et al. 1978).

2.9.3 On-going Studies

Studies being conducted by C.H. Tamburro and coworkers at the University of Louisville School

of Medicine will continue medical surveillance of chemical industry workers exposed to vinylidene

chloride with regard to gastrointestinal, pulmonary, brain, and hematopoietic cancers (IARC

lW2).
1,1- DICHLOROETHENE 101

2. HEALTH EFFECTS

Studies by Mary T. Moslen and coworkers at the University of Texas Medical Branch at

Galveston are using 1,1-dichloroethene to selectively damage bile canaliculi to study liver function

(Moslen 1993).

1,1- DICHLOROETHENE 103

3. CHEMICAL AND PHYSICAL INFORMATION

3.1 CHEMICAL IDENTITY

The chemical formula, structure, synonyms, and identification numbers for 1,1-dichloroethene are

listed in Table 3-1.

3.2 PHYSICAL AND CHEMICAL PROPERTIES

Important physical and chemical properties of 1,1-dichloroethene are listed in Table 3-2.



1,1- DICHLOROETHENE 107

4. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL

4.1 PRODUCTION

1,1-dichloroethene does not occur naturally (EPA 1985a), but it is found as the result of the

breakdown of polyvinylidene chloride products in landfills. It is produced commercially by the

dehydrochlorination of 1,1,2-trichloroethane with excess lime or caustic. As an inhibitor of the

polymerization reaction, 200 ppm γ-hydroxyanisole is added, then later removed by distillation or

washing (Grayson 1985). Typically, a commercial grade contains 99.8% 1,1-dichloroethene (EPA

1985a).

1,1-dichloroethene polymerizes after the addition of an initiator by either an ionic or a free radial

reaction. 1,1-dichloroethene can polymerize spontaneously at room temperature following

addition of peroxides (Grayson 1985).

1,1-dichloroethene is manufactured in chemical plants located in Texas and Louisiana. Currently,

there are two major producers, Dow Chemical and Pittsburgh Paint and Glass (PPG) Industries

(Burke 1987; EPA 1977; SRI 1991). Production capacity in 1985 was 178 million pounds/year

(EPA 1985a). This has decreased from 1977, when production capacity was estimated at

270 million pounds (EPA 1977). In 1988, plant capacity at PPG Industries was estimated at

64 million pounds/year (PPG Industries 1988). Estimated 1989 production is 230 million pounds

(CMA 1989).

According to the 1991 Toxic Chemical Release Inventory (TRI), 23 facilities manufactured or

processed 1,1-dichloroethene in 1991 (TRI91 1993). All 23 of these facilities reported the

maximum amount of 1,1-dichloroethene that they would have on site. These data are listed in

Table 4-l. The TRI data should be used with caution since only certain types of facilities are

required to report.. This is not an exhaustive list.

1,1- DICHLOROETHENE 109

4. PRODUCTION, IMPORT, USE, AND DISPOSAL

4.2 IMPORT/EXPORT

In 1986, 217,000,000 pounds of 1,1-dichloroethene were imported into the United States (SRI

1987). No data are available on the export levels.

4.3 USE

Monomeric 1,1-dichloroethene is used as an intermediate for captive organic chemical synthesis

and in the production of polyvinylidene chloride copolymers. These polymers, which have been

commercially important since their introduction in the early 1940s are used extensively in many

types of flexible packing materials (including barrier, multilayer, and monolayer), as flame

retardant coatings for fiber and carpet backing, and in piping, coating for steel pipes, and adhesive

applications (EPA 1977). The major application of polyvinylidene chloride copolymers is the

production of flexible films for food packaging (SARAN and VELON wraps). 1,1-dichloroethene

is found in many food and other packaging materials. At one time, SARAN wrap was

found to contain up to 30 ppm 1,1-dichloroethene (Birkel et al. 1977). The plastic packaging

films can contain no more than 10 ppm 1,1-dichloroethene (FDA 1988). The coating applicable

to fresh citrus fruit (minimum amount required for intended use) is <25% aqueous solution (FDA

1982). Because of the instability of the polymer, 1,1-dichloroethene is usually used as a

copolymer with acrylonitrile, vinyl chloride, methacrylonitrile, and methacrylate (Grayson 1985;

Rossberg et al. 1986).

4.4 DISPOSAL

1,1-dichloroethene is classified as a llammable liquid (Weiss 1986). As such, the EPA (1987a)

requires compliance with the regulations of the Resource Conservation and Recovery Act

(RCRA) when producing, treating, transporting, storing, or disposing of this substance. Current

disposal regulations of 1,1-dichloroethene require dissolving it in combustible solvents and scatter

spraying the solvent into a furnace with an afterburner and alkaline scrubber. However, the

criteria for land treatment and burial is undergoing significant revision (HSDB 1992). The waste

mother liquor probably contains higher concentrations (>200 ppm) of the inhibitor, MEHQ.

1,1- DICHLOROETHENE 111

5. POTENTIAL FOR HUMAN EXPOSURE

5.1 OVERVIEW

The primary sources of 1,1-dichloroethene in the environment are related to the synthesis,

fabrication, and transport of 1,1-dichloroethene and the fabrication of its polymer products.

Because of the volatile nature of the chemical, releases to the atmosphere are the greatest source

of ambient 1,1-dichloroethene. Smaller amounts of the chemical are released to surface water

and soil, primarily as a result of waste disposal. 1,1-dichloroethene in waste water should

partition to the atmosphere as a result of volatilization during treatment processes. Most of the

1,1-dichloroethene released to the environment partitions to air or water, including groundwater

(Table 5-l).

1,1-dichloroethene has been identified in at least 492 of the 1,350 hazardous waste sites on the

EPA National Priorities List (NPL) (HAZDAT 1992). However, the number of sites evaluated

for 1,1-dichloroethene is not known. The frequency of these sites can be seen in Figure 5-l. Of

these sites, 1 is located in the Commonwealth of Puerto Rico (not shown).

1,1-Dichloroethene is rapidly transformed in the troposphere, where oxidation by hydroxyl radicals

is the dominant transformation process. Biotransformation is believed to be the dominant

transformation process for 1,1-dichloroethene in groundwater, although this process is probably

not important in aerobic surface waters. Biotransformation in soil has not been studied

extensively, but it has been shown to occur by methanogenic organisms. Biotransformation will be

more important in subsurface soils, because 1,1-dichloroethene in surface soils will volatilize to

the atmosphere. 1,1-dichloroethene has been detected in air, surface water, groundwater, and

soil, with the frequency of detection and the concentrations greatest near source areas (e.g.,

industrial areas, landfills, hazardous wastes sites).

The potential for human exposure to 1,1-dichloroethene is greatest for those at its point of

production, formulation, or transport. Occupational exposure to 1,l -dichloroethene may occur by

inhalation or dermal contact. Members of the general public may be exposed by inhalation or by

ingesting contaminated drinking water. Those who live near hazardous waste sites contaminated


1,1- DICHLOROETHENE 114

5. POTENTIAL FOR HUMAN EXPOSURE

with 1,1-dichloroethene, especially those who receive their drinking water from underground

sources, may potentially be exposed to 1,1-dichloroethene, the levels of which cannot be

established at present. Quantitative data that address levels of human exposure to 1,1-dichloroethene

are limited.

5.2 RELEASES TO THE ENVIRONMENT

5.2.1 Air

Air releases are the largest source of 1,1-dichloroethene releases to the environment, and

emissions from polymer synthesis and fabrication industries contribute most to overall atmospheric

loading. Singh et al. (1981) have estimated that air emissions of 1,1-dichloroethene from polymer

synthesis in the United States range between 2% and 5% of the annual production. EPA (1985a)

estimated total annual air emissions of 1,1-dichloroethene of ≈650 tons/year, which was 0.8% of

the production volume for that year. Over one-half of that total (355 tons) was from the polymer

production/fabrication industries. The remaining emissions were from monomer synthesis

(223 tons/year; 34%) and monomer storage, handling, and transportation (73 tons/year; 11%).

Small amounts of 1,1-dichloroethene (not quantified) were estimated to be released during the

incineration (disposal) of polymer products containing the 1,1-dichloroethene monomer,

1,1,1-trichloroethane, and other chlorinated solvents (Oki et al. 1990; Yasuhaka and Morita 1988).

Crume (1991) reported that 1,1-dichloroethene can be released to the atmosphere by air

stripping contaminated groundwater. This process transfers groundwater contaminants into the

gaseous phase and subsequently releases them into the atmosphere with no further treatment (the

releases were not quantified). However, more recent data indicate that both the number of

emission point sources and the total amount of 1,1-dichloroethene released to the atmosphere are

much less than EPA’s earlier estimates. This decrease is the result of shifts away from the use of

the compound by processors and improvements in control technology. For example, survey data

submitted by the Chemical Manufacturers Association to EPA indicate that ≈103.4 tons of

1,1-dichloroethene per year are released from manufacturing and processing facilities (CMA

1989).

According to the TRI91 (1993), an estimated total of 285,190 pounds (129.3 metric tons) of

1,1-dichloroethene, amounting to 99.7% of the total environmental release, was discharged to the
1,1- DICHLOROETHENE 115

5. POTENTIAL FOR HUMAN EXPOSURE

air from manufacturing and processing facilities in the United States in 1991. The data listed in

TRI should be used with caution since only certain types of facilities are required to report. This

is not an exhaustive list.

Hazardous waste sites and landfills where 1,1-dichloroethene have been improperly disposed of

are additional potential sources of release of the chemical to the atmosphere because of

volatilization (see Section 5.4.1).

5.2.2 Water

Industrial releases of 1,1-dichloroethene to surface water contribute to the overall environmental

loading of the chemical but to a much lesser extent than atmospheric emissions. Liquid effluents

produced during polymerization operations are estimated to contribute ≈2 tons of waste

1,1-dichloroethene each year (Neufeld et al. 1977). Other potential industrial sources of waste

1, 1-dichloroethene in surface water are metal finishing and nonferrous metals manufacturing

industries, soap and detergent manufacturers, electric coil coating and battery manufacturers, coal

mines, laundries, and industries involving paint and ink formulation. 1,1-dichloroethene has been

measured in raw waste water from these industries at mean concentrations of 3-760 μg /L (EPA

1981).

According to TRI91 (1993), an estimated total of 832 pounds (0.4 metric tons) of 1,1-dichloroethene,

amounting to 0.29% of the total environmental release, was discharged to water from

manufacturing and processing facilities in the United States in 1991 (TRI91 1993). An estimated

total of 94 pounds (0.043 metric tons), amounting to 0.03% of the total environmental release,

was discharged to publicly owned treatment works. The TRI data should be used with caution

since only certain types of facilities are required to report.

Hazardous waste sites where 1,1-dichloroethene has been improperly disposed are additional

potential sources of the chemical, although there are no quantitative data available to address

how much 1,1-dichloroethene enters the environment from this source. In addition, surface water

or groundwater contaminated with l,l,l-trichloroethane, tetrachloroethylene, 1,1,2-trichloroethylene,

and 1,2-dichloroethane can be an additional source of 1,1-dichloroethene through

biotic or abiotic elimination or dehydrochlorination transformations (Baek et al. 1990; Cline and
1,1- DICHLOROETHENE 116

5. POTENTIAL FOR HUMAN EXPOSURE

Viste 1985; Lesage et al. 1990; McCarty et al. 1986). Hydrolysis of 1,1,1-trichloroethane in water

or water/sediment systems will result in the formation of 1,1-dichloroethene by elimination,

although it is a very slow process, with a half-life of -1 year (Haag and Mill 1988). Total releases

of 1,1-dichloroethene from these sources have not been quantified or estimated.

5.2.3 Soil

Limited information is available on the releases of 1,1-dichloroethene to soil. An estimated total

of 180 pounds/year of 1,1-dichloroethene are disposed of in municipal landfills as residual

monomer in some consumer products on a national basis (Neufeld et al. 1977).

According to TRI91 (1993), an estimated total of 15 pounds (0.007 metric tons) of 1,1-dichloroethene,

amounting to 0.005% of the total environmental release, was discharged to soil from

manufacturing and processing facilities in the United States in 1991 (TRW1 1993). The TRI data

should be used with caution since only certain types of facilities are required to report.

5.3 ENVIRONMENTAL FATE

5.3.1 Transport and Partitioning

The tendency of a chemical to partition between soil, water, sediment, air, and biota can be

inferred from its physical/chemical properties. Based on a vapor pressure of 592 mmHg

(Verschueren 1983), most of the 1,1-dichloroethene released into the environment will ultimately

partition into the atmospheric compartment as shown by the vapor partitioning model of Mackay

and Paterson (1981) although other factors such as water solubility may affect the rate at which

the partitioning will occur. In localized situations, intervening processes such as

biotransformation, may alter this outcome.

As the magnitude of the Henry’s law constant for 1,1-dichloroethene, 0.19 atmospheres m3

/mole

(Pankow and Rosen 1988), indicates, 1,1-dichloroethene is likely to partition readily into the

atmosphere from water. Because of this, 1,1-dichloroethene is generally not found in surface

water in high concentrations. Studies on atmospheric removal processes indicate that once in the
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5. POTENTIAL FOR HUMAN EXPOSURE

atmosphere, 1,1-dichloroethene is unlikely to be removed by physical processes such as wet

deposition (e.g., rain) or by adsorption to atmospheric particulates (EPA 1980d).

1, 1-Dichloroethene spilled onto surface soil will also tend to partition to the atmosphere, while

some of the chemical may percolate into the subsurface soil. Once in the subsurface soil,

1,1-Dichloroethene will partition between soil and water. 1,1-dichloroethene has high water

solubility and a small log soil organic carbon sorption coefficient (Koc) value of 1.81 (EPA 1982)

indicating that 1, 1-dichloroethene will migrate through soil without significant retardation by

adsorption to organic carbon. Similarly, 1,1-dichloroethene will migrate relatively freely within

groundwater.

1,1- Dichloroethene in surface water is unlikely to partition significantly into aquatic organisms.

Although measured bioconcentration factors were not located in the available literature,

partitioning of 1,1-dichloroethene from water into aquatic organisms can be predicted in part by

the magnitude of the octanol/water partition coefficient (Kow) value. The chemicals with a log

Kow of <4.0 are unlikely to bioaccumulate to hazardous levels in human food chains (Veith et al.

1985). The log Kow is 2.13 (Veith et al. 1985) and based upon this calculation, bioaccumulation

in the human food chain is not expected to be significant for this compound.

5.3.2 Transformation and Degradation

Transformations of 1,1-dichloroethene can occur from the reaction with radical species in the

atmosphere and from biodegradation under anaerobic conditions in soil or water.

5.3.2.1 Air

Atmospheric degradation of 1,1-dichloroethene is expected to be dominated by gas-phase

oxidation with photochemically produced hydroxyl radicals. An experimental rate constant for this

process of 8.11x10-12 cm3

/molecule-second at 25°C has been determined (Tuazon et al. 1988) and

has been recommended as the best value in an extensive review of the reaction of hydroxyl

radicals with organic compounds (Atkinson 1989). Using an average atmospheric hydroxyl radical

concentration of 5x105

 molecule/cm3, a half-life of 2-3 days can be calculated for this process

(EPA 1980d; Tuazon et al. 1988). A higher atmospheric concentration of hydroxyl radicals
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5. POTENTIAL FOR HUMAN EXPOSURE

(106

 molecules/cm3) will reduce the half-life of 1,1-dichloroethene to 4-20 hours (Grosjean 1990).

The products from this reaction are phosgene, formaldehyde, and chloroacetyl chloride (Tuazon

et al. 1988).

Atmospheric degradation of 1,1-dichloroethene may also occur by a gas-phase reaction with other

atmospheric oxidants, namely ozone and nitrate radicals, although these processes are too slow to

successfully compete with the reaction of 1,1-dichloroethene with hydroxyl radicals (Grosjean

1990). An experimental rate constant for the gas-phase reaction of ozone with 1,1-dichloroethene

of 3.7x1011 cm3

/molecule-second at 25°C (Atkinson and Carter 1984) translates to an

atmospheric half-life of more than 10 years for this process using an average atmospheric ozone

concentration of 7x1011 molecule/cm3

. Nitrate radicals are destroyed by sunlight, and the

oxidation of organic compounds by this oxidant is only important at night. The rate constant for

the oxidation of 1,1-dichloroethene by nitrate radicals, 1.78x10-15 cm3

/molecule-second at 25°C

(Sabljic and Gusten 1990), translates to a half-life of 19 days in a moderately polluted atmosphere,

although at nitrate concentrations of 50 ppt the half-life may be reduced to 6 days (Grosjean

1990). Reaction products of 1,1-dichloroethene with hydroxyl radicals and nitrates in air include

chloroacetyl chloride, phosgene, formaldehyde, carbon monoxide, and nitric acid (EPA 1983a).

Another process for release of organic compounds in the atmosphere is by direct photolytic

degradation; however, because chloroethenes do not adsorb radiation at wavelengths <300 nm to

any significant extent (EPA 1980d; Tuazon et al. 1988), this process is not an important

degradation pathway for 1,1-dichloroethene.

5.3.2.2 Water

Biotransformation under anaerobic conditions is believed to be the dominant transformation

process for 1,1-dichloroethene in groundwater. However, Ensign et al. 1992 observed that

1,1-dichloroethene was not degraded efficiently by propylene-grown Xanthobacter- cells (strain

Py2) under anaerobic conditions. The environmental media was not reported. The importance of

this process under aerobic conditions, such as those normally found in ambient surface water, has

not been determined. Conflicting results have been obtained for the aerobic degradation of

1,1-dichloroethene. Several investigations (Bouwer et al. 1981; McCarty et al. 1986; Pearson and

McConnel 1975) have uncovered no evidence for biotransformation of chlorinated ethenes such
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5. POTENTIAL FOR HUMAN EXPOSURE

as 1,1-dichloroethene under aerobic conditions. In contrast, Tabak et al. (1981) reported

transformation of 54% of 5 mg/L and 30% of 10 mg/L test concentrations of 1,1-dichloroethene

under aerobic conditions within 1 week after incubation with a domestic waste water seed; these

removal figures were adjusted to account for volatilization losses from control flasks of 24% for

the 5 mg/L and 15% for the 10 mg/L test concentrations.

Under anaerobic conditions (such as those that occur in groundwater), the importance of

biotransformation is more clearly defined. McCarty et al. (1986) found that 1,1-dichloroethene

was nearly quantitatively reduced to vinyl chloride under methanogenic conditions after 108 days.

In another study, vinyl chloride was produced from the reductive dechlorination of 1,1-dichloroethene

by microorganisms in anoxic microcosms after l-2 weeks of incubation (Barrio-Lage et al.

1986). Wilson et al. (1986) studied the behavior of 1,1-dichloroethene in authentic aquifer

material known to support methanogenesis. The disappearance of this compound was observed

with an initial long lag time, and vinyl chloride, a daughter product of degradation, was found in

trace amounts. Baek et al. (1990) also observed the formation of vinyl chloride under anaerobic

conditions when 1,1-dichloroethene was incubated with digested sludge under both fermentive am

methanogenic conditions. Vinyl chloride has been classified as a possible human carcinogen by

EPA (EPA 1985a); ATSDR has produced a toxicological profile on this compound (ATSDR

1990).

Photolysis and hydrolysis of 1,1-dichloroethene in natural aquatic media are not significant

processes (EPA 1982). The estimated half-life for hydrolysis of 1,1-dichloroethene at 25°C under

neutral (or slightly basic) conditions is 1.2x108

 years (Jeffers et al. 1989). Similarly, oxidation is

not a significant transformation mechanism for 1,1-dichloroethene in aqueous environments.

Degradation rates due to reactions with singlet oxygen and the peroxy radical are not estimated to

be environmentally significant in aquatic systems (EPA 1980e).

5.3.2.3 Sediment and Soil

A methane-utilizing culture isolated from lake sediment was able to degrade 600 ng/mL

1,l-dichloroethene to 200 ng/mL under aerobic conditions within 2 days. The end products were

nonvolatile and did not include vinyl chloride which is known to be formed under anaerobic

conditions (Fogel et al. 1986).
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5. POTENTIAL FOR HUMAN EXPOSURE

5.4 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT

5.4.1 Air

The National Ambient Volatile Organic Compound Database, updated in 1988 to include ambient

and indoor volatile organic compounds (VOCs) concentrations in urban, rural, remote, source-dominated

and indoor environments, reports an ambient daily average concentration for

1,1-dichloroethene of 4.6 ppb (Shah and Heyerdahl 1988). The ambient average concentration

represents contributions from rural, suburban, urban, and source-dominated sites. In a survey of

the indoor air of 26 homes and apartments near Research Triangle Park, North Carolina,

1,1-dichloroethene was found in 4 of 15 summer samples at a mean concentration of 47.3 ppb and

4 of 16 winter samples at a mean concentration of 7.1 ppb (EPA 1985). The EPA TEAM (Total

Exposure Assessment Measurement) studies measured 1,1-dichloroethene concentrations in

1,085 personal air samples collected from 350 New Jersey residents (discrepancy in the actual

number of residents sampled) over three seasons. Only 77 (7%) of the samples had measurable

concentrations of 1,1-dichloroethene, and 107 (10%) of the samples had trace levels. The

detection limit ranged from 3 to 14 μg /m3

 (Wallace 1991).

The results of an on-site field data collection program based on short-term studies conducted in

seven U.S. cities indicated that 1,1-dichloroethene was present in air at an average concentration

range of 0.005-0.03 ppb in various cities (Singh et al. 1981, 1982). 1,l -Dichloroethene was

detected in 24 of 79 ambient air samples (collected from 1986 to 1987 in the Kanawha Valley,

West Virginia; Los Angeles, California; and Houston, Texas) at a mean concentration of 0.84 ppb

(Pleil et al. 1988). It was also found in 33 of 35 ambient air samples (collected in Newark, New

Jersey, July-August 1981) at a geometric mean concentration of 0.38 ppb (Harkov et al. 1987).

Corresponding values for Elizabeth and Camden, New Jersey, were 33 of 34 samples at a mean

concentration of 0.35 ppb and 28 of 30 samples with a mean concentration of 0.36 ppb,

respectively (Harkov et al. 1987).

1,1-Dichloroethene has been measured in air in the vicinity of five of six hazardous waste sites as

well as a sanitary landfill in New Jersey (1983-1984), with arithmetic mean concentrations ranging

from 0.39 to 38.9 ppb measured at waste sites, and an arithmetic mean concentration of 2.6 ppb

measured at the sanitary landfill. The highest concentration measured at these six sites was
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5. POTENTIAL FOR HUMAN EXPOSURE

97 ppb (Harkov et al. 1985; LaRegina et al. 1986). Although quantitative information on the air

concentrations of 1,1-dichloroethene at hazardous waste sites on the NPL is not available,

1,1-dichloroethene is probably present in air at those NPL sites where it has been measured in

either the soil, surface water, or groundwater.

5.4.2 Water

1,1-dichloroethene concentrations >5 mg/L have been measured in raw waste water from the

metal finishing and nonferrous metals manufacturing industries (EPA 1981). Lower

concentrations (<l mg/L) have been measured in raw waste water from industries involving paint

and ink formulation, soap and detergent manufacturing, coil coating, battery manufacturing, coal

mining and laundries (EPA 1981). Treated waste waters from all these industries ranged from < 1

to 4 mg/L (EPA 1981). According to the STORET database maintained by the EPA, 1,1-dichloroethene

has been detected in 3.3% of 1,350 effluent samples monitored nationwide (Staples et al.

1985).

1,1-dichloroethene has been detected in surface waters sampled near industrial sites at

concentrations ranging from less than 1 to 550 μg/L (Going and Spigarelli 1977). According to

the STORET database maintained by the EPA, 1,1-dichloroethene has been detected in 6% of

8,714 surface water samples monitored nationwide (Staples et al. 1985). However, no 1,1-dichloroethene

was detected in raw surface water during a 105-city survey of U.S. cities (Coniglio and

Miller 1980). 1,1-dichloroethene has been detected infrequently at low concentrations in urban

runoff that will contribute to surface water concentrations. The Nationwide Urban Runoff

Program (NURP), initiated to evaluate the significance of priority pollutants in urban storm water

runoff, report a detection frequency of only 3%, with a concentration range of 1.5-4 μg/L (Cole

et al. 1984).

About 3% of the drinking water supplies in the United States have been found to contain

1,1-dichloroethene at 0.2-0.5 μg/L (estimated mean 0.3 μg /L) concentration in an EPA survey

(EPA 1985a). 1,1-dichloroethene was also detected (quantification limit of 0.2 ppb) in 2.3% of

the 945 samples of finished drinking water taken from community-based groundwater sources in a

nationwide survey (Rajagopal and Li 1991, Westrick et al. 1984). The maximum concentration of

1, 1-dichloroethene detected in the positive samples was 6.3 μg/L (subset median values were
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5. POTENTIAL FOR HUMAN EXPOSURE

0.28-1.2 μg/L). 1,1-dichloroethene was detected in 9 of 466 U.S. drinking water wells sampled in

the 1982 Ground Water Supply Survey at a median concentration of 0.3 μg/L (Cotruvo 1985).

1,1-dichloroethene has been detected in 25.2% of 178 contaminated sites monitored under the

Comprehensive Emergency Response, Compensation, and Liability Act (CERCLA) making it the

fifth most frequently detected organic contaminant at these sites (Plumb 1987). Contamination of

groundwater at an industrial site in Waite Park, MN, resulting from the mishandling of waste

product, paint, and solvent led to a maximum 1,1-dichloroethene concentration of 88 μg/L in deep

monitoring wells and 22 μg/L in shallow wells (ATSDR 1990). This aquifer contamination led to

a maximum 1,1-dichloroethene concentration of 94 μg/L in Waite Park municipal wells resulting

in this city’s water supply being listed as an NPL site. The disposal of organic chemicals in

trenches at a waste disposal site near Ottawa, Canada, resulted in 1,1-dichloroethene

groundwater concentrations ranging from 0.9 to 60 μg/L in 43% of samples taken from a 37-well

monitoring network in 1988 (Lesage et al. 1990). Leachate originating from the Orange County

and Alachua Municipal Landfills in north central Florida resulted in groundwater contamination

near the landfills. The average concentration of 1,1-dichloroethene in wells sampled near the

Orange County Landfill and the Alachua Municipal Landfill was 0.12 and < 1.0 μg/L, respectivel

(Hallbourg et al. 1992). 1,1-dichloroethene has also been detected in groundwater sampling

surveys conducted in New Jersey (Cain et al. 1989; Fusillo et al. 1985).

The concentration of 1,l -dichloroethene in leachate from the Moyer Landfill in Collegeville,

Pennsylvania, classified as an NPL site by the EPA in 1982, ranged from 1 to 2 ppb (Varma

1985). In a 1987-1988 survey of groundwater contamination at 19 municipal and 6 industrial

landfills in Wisconsin, 1,l-dichloroethene was detected at 1 site at an average concentration of

3.4 μg/L (Battista and Connelly 1988).

5.4.3 Sediment and Soil

No information is available on ambient concentrations of 1,1-dichloroethene in soil, although this

chemical is often found at hazardous waste sites. Because of the tendency of 1,1-dichloroethene

to partition into the atmosphere, with remaining material having the potential to percolate into

groundwater, ambient concentrations in surface soil are expected to be low. No information is

available on the concentration of l-l-dichloroethene in sediment.
1,1- DICHLOROETHENE 123

5. POTENTIAL FOR HUMAN EXPOSURE

5.4.4 Other Environmental Media

1,1-dichloroethene copolymers are used in the manufacture of films used in food packaging.

Residual 1,1-dichloroethene monomer has been detected at concentrations of <0.02-1.26 ppm in

retail food packaging films containing polyvinylidene chloride; residues in a variety of foodstuffs

wrapped with the films were in the range of ≤0.005-0.01 ppm (Gilbert et al. 1980).

Concentrations of residual 1,1-dichloroethene in household films used to package food were

reported by Birkel et al. (1977) to be 6.5-10.4 ppm (average 8.8 ppm). At one time, some films

contained as much as 30 ppm 1,1-dichloroethene (Birkel et al. 1977). No information on the

levels of 1,1-dichloroethene in humans was located.

1,1-dichloroethene was detected in a composite sample of Rigolets clams obtained from Lake

Pontchartrain, Louisiana, in 1980 at a concentration of 4.4 ppb wet weight (Ferrario et al. 1985).

5.5 GENERAL POPULATION AND OCCUPATIONAL EXPOSURE

Information on exposure of the general population to 1,1-dichloroethene is limited. An EPA

TEAM study conducted from 1980 to 1987, reported that the average exposure of the general

population to 1,1-dichloroethene is 6.5 μg / m3

 based on personal air samples from 350 homes in

New Jersey (Wallace 1991).

The National Occupational Hazard Survey (NOHS), conducted by the National Institute for

Occupational Safety and Health (NIOSH), estimated that 56,857 workers in 3,853 plants were

potentially exposed to 1,1-dichloroethene in the workplace in 1970 (NIOSH 1976). These

estimates were derived from observation of the actual use of 1,1-dichloroethene (1%), the use of

trade-name products known to contain 1,1-dichloroethene (19%), and the use of generic products

suspected of containing the compound (80%). The largest numbers of exposed workers were

special trade contractors or in the fabricated metal products industry or wholesale trade industry.

The occupational groups of exposed workers consisted of carpenters, warehousemen (not

otherwise classified), and miscellaneous machine operators.

Data from a second workplace survey, the National Occupational Exposure Survey (NOES),

conducted by NIOSH from 1980 to 1983, indicated that 2,679 workers, including 291 women, in
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5. POTENTIAL FOR HUMAN EXPOSURE

97 plants were potentially exposed to 1,1-dichloroethene in the workplace in 1980 (NIOSH 1984).

The greatest number of exposed workers were chemical technicians. All estimates were derived

from observations of the actual use of the compound.

Neither the NOHS nor the NOES databases contain information on the frequency, concentration,

or duration of exposure of workers to any of the chemicals listed therein. Rather, they only

provide estimates of workers potentially exposed to the chemicals.

Varying occupational exposure levels can be found in the literature. Reported ranges of

concentrations associated with the monomer and polymer plants are ≈23-25 ppb and 6-12 ppb,

respectively (Walling 1984). Exposure concentrations ≤1,900 ppm have been reported in a

copolymer monofilament fiber production plant (Ott et al. 1976). However, in polymer

manufacturing plants, worker exposure has been reported as <5 ppm (Jaeger 1975). Wallace

(1991) reported an exposure concentration of 120 ppm for a cabinet maker; however, the

concentration decreased to 14 ppm when measured during a different season (the seasons were

not reported).

1,1-dichloroethene was produced in significant amounts that under certain conditions may

approach 100%, from the thermal degradation of methyl chloroform (Glisson et al. 1986). This

implies that inadvertent exposure to 1,1-dichloroethene may occur in many industrial situations

when methyl chloroform is used in the vicinity of operations involving heat, such as welding or

soldering and metal cleaning. 1,1-dichloroethene has also been detected as a pyrolysis product of

the pesticide endosulfan in tobacco smoke (Chopra et al. 1978).

The Occupational Safety and Health Administration (OSHA) recently reduced the 8-hour timeweightedaverage (TWA) permissible exposure level (PEL) to 1 ppm (OSHA 1989), which should

limit future workplace exposures to low levels of this compound.

5.6 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES

Human exposure to 1,1-dichloroethene is potentially highest in workplace settings and among

populations residing in the vicinity of hazardous waste sites where the compound may contaminate

environmental media.
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5. POTENTIAL FOR HUMAN EXPOSURE

The presence of residual monomeric 1,1-dichloroethene in polymeric food wraps and other

consumer products is another potential source of human exposure. Exposure from these sources

is difficult to estimate. However, there is no evidence in the literature to implicate consumer

products as major sources of 1,1-dichloroethene exposure (EPA 1985a).

In addition to releases from hazardous waste sites, ambient air and water may be contaminated

with 1,l -dichloroethene by releases from industrial production and polymerization processes (EPA

1977, 1985a; Wang et al. 1985a, 1985b). Levels are significantly higher in areas surrounding

production sites (EPA 1977, 1985a).

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 1,1-dichloroethene 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 1,1-dichloroethene.

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. Available data adequately characterize the physical and

chemical properties of 1,1-dichloroethene (HSDB 1992; Merck 1983) (see Chapter 3).

Production, Import/Export, Use, and Disposal. 1,1-dichloroethene is produced commercially.

The estimated production of the compound in 1989 totalled 230 million pounds, up from an
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5. POTENTIAL FOR HUMAN EXPOSURE

estimated production capacity of 178 million pounds/year in 1985. 1,1-dichloroethene is used as

an intermediate in the synthesis of other organic chemicals and polymers, including flexible films

for food packaging. Monomeric 1,1-dichloroethene has been detected in many food packaging

materials and foodstuffs. 1,1-dichloroethene is released mainly to the atmosphere. EPA requires

compliance with RCRA regulations when producing, treating, storing, or disposing of 1,1-dichloroethene.

Current disposal regulations require dissolving the compound in combustible solvents and

scatter spraying the solvent into a furnace with an afterburner and alkaline scrubber. Additional

information on the current criteria for land treatment and burial and on the amounts of

1,1-dichloroethene disposed of by incineration versus landfilling would be helpful.

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 1990,

became available in May of 1992. This database will be updated yearly and should provide a list

of industrial production facilities and emissions.

Environmental Fate. The available data suggest that 1,1-dichloroethene can undergo

transformation due to the reaction with radical species in the atmosphere and biodegradation

under anaerobic conditions in water and under aerobic conditions in soil (Ensign et al. 1992;

Foget et al. 1986; Grosjean 1990; Tabak et al. 1981; Tuazon et al. 1988). The atmospheric halflife

of 1,1-dichloroethene in air following hydroxyl radical reaction is estimated to be 4-20 hours,

and the products of this reaction are phosgene, formaldehyde, and chloroacetyl chloride (Tuazon

et al. 1988). The estimated half-life for hydrolysis of 1,1-dichloroethene at 25°C under neutral

conditions is 1.2x108

 years (Jeffers et al. 1989). 1,1-dichloroethene is reduced to vinyl chloride

under methanogenic conditions (McCarty et al. 1986). In a methane-utilizing culture from lake

sediment, 1,1-dichloroethene was degraded under aerobic conditions within 2 days; the end

products, although unspecified, did not include vinyl chloride. More information is needed to

define these processes and to quantify degradation rates. Such information would be helpful in

understanding the fate of nonvolatilized 1,1-dichloroethene in these media.

Bioavailability from Environmental Media. The monitoring data available indicate that

1,1-dichloroethene is present in some samples of air, water, soil, and foodstuffs (EPA 1981, lW5a;

Gilbert et al. 1980; Shah and Heyerdahl 1988; Singh et al. 1981; Verma 1985). Animal studies
1,1- DICHLOROETHENE 127

5. POTENTIAL FOR HUMAN EXPOSURE

indicate that 1,l -dichloroethene is absorbed following inhalation and oral exposure. 1,l -dichloroethene

and its metabolites can be measured in the breath, blood, urine, and adipose tissue of

humans. Thus, it can be concluded that 1,1-dichloroethene is bioavailable from the environment.

Good quantitative data that correlate varying levels in the environment with levels in the body

and health effects and data on the extent to which 1,1-dichloroethene can be absorbed from

various media (i.e., soil) are lacking. This information may be difficult to obtain since

environmental levels can fluctuate widely and exposure may be sporadic.

Food Chain Bioaccumulation. No information was found regarding the bioconcentration of

1,1-dichloroethene in plants, aquatic organisms, or animals. On the basis of the log octanol/water

partition coefficient value of 2.13 (EPA 1982), bioconcentration of the compound to significant

levels by terrestrial or aquatic organisms is not expected. No data were located regarding the

biomagnification of 1,1-dichloroethene in terrestrial or aquatic food chains. Given the expected

limited bioconcentration (Barrio-Lage et al. 1986; Wilson et al. 1986) of the compound in the

tissues of terrestrial and aquatic organisms, and the extent to which 1,1-dichloroethene undergoes

biotransformation, biomagnification in terrestrial and aquatic food chains is not expected.

Additional experimental data to confirm this predicted limited food chain bioaccumulation of

1,1-dichloroethene would be helpful in evaluating the relative significance of this route of

exposure.

Exposure Levels in Environmental Media. Data on the concentrations of 1,1-dichloroethene

in surface water, soil, and food, are limited (EPA 1981, 1985a; Gilbert et al. 1980; Shah and

Heyerdahl 1988; Singh et al. 1981; Verma 1985). More data are needed to provide a more

complete characterization of human exposure. The concentration of 1,1-dichloroethene in the air

above hazardous waste sites and in groundwater near them is not well documented. The available

data indicate that human exposure may occur because of 1,1-dichloroethene’s presence in these

environmental media. Additional monitoring data will better address the degree to which it

occurs.

Reliable monitoring data for the levels of 1,1-dichloroethene in contaminated media at hazardous

waste sites are needed so that the information obtained on levels of 1,1-dichloroethene in the

environment can be used in combination with the known body burden of 1,1-dichloroethene to
1,1- DICHLOROETHENE 128

5. POTENTIAL FOR HUMAN EXPOSURE

assess the potential risk of adverse health effects in populations living in the vicinity of hazardous

waste sites.

Exposure Levels in Humans. Although an analytical method is available to detect 1,1-dichloroethene

in human tissue, no studies were found that measured its levels in human tissues. Most of

the data on exposure levels of 1,1-dichloroethene are based on occupational studies conducted

under controlled environmental conditions (Walling 1984), and these data are not current. More

current information on the potential exposure resulting from residence in the vicinity of

hazardous waste sites would provide a more accurate characterization of human exposure in the

United States.

This information is useful for assessing the need to conduct health studies on these populations.

Exposure Registries. No exposure registries for 1,l -dichloroethene 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 On-going Studies

One on-going study on the environmental fate, including the accumulation and biodegradation of

1,1-dichloroethene was located. The study is being conducted by the EPA, and further details are

not available (EXICHEM 1993). Remedial investigations and feasibility studies at NPL sites

known to have 1,1-dichloroethene contamination (NPLTD 1988) should be completed in the near

future and may add to the current knowledge regarding the transport and degradation of

1,l -dichloroethene in the environment.

Environmental monitoring conducted in conjunction with remedial investigation/feasibility studies

at hazardous waste sites on the NPL should add to the current database on environmental levels

of 1,1-dichloroethene.
1,1- DICHLOROETHENE 129

5. POTENTIAL FOR HUMAN EXPOSURE

As part of the Third National Health and Nutrition Evaluation Survey (NHANES III), the

Environmental Health Laboratory Sciences Division of the National Center for Environmental

Health and Injury Control, Centers for Disease Control, will be analyzing human blood samples

for 1,1-dichloroethene and other volatile organic compounds.

Studies being conducted at the University of California, Riverside, will use cis- and trans-1,2-

dichloroethene as surface probes to evaluate interactive mechanisms with individual soil

constituents (CRIS USDA 1993). These data will give an indication of the frequency of

occurrence and background levels of these compounds in the general population.

1,1- DICHLOROETHENE 131

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 1,1-dichloroethene, its metabolites, and other biomarkers of

exposure and effect to 1,1-dichloroethene. 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 MATERIALS

The analytical methods used to quantify 1,1-dichloroethene in biological samples are summarized

below. Table 61 lists the applicable analytical methods for determining 1,1-dichloroethene in

biological specimens.

1,1-Dichloroethene exposure can be monitored by measuring the levels in blood, expired air and

urine (Ashley et al. 1992; McKenna et al. 1978a; Pellizari et al. 1985; Raymer et al. 1990, 1991;

Wallace et al. 1984). 1,1-dichloroethene also distributes preferentially to liver, kidney, and to a

lesser extent, adipose tissue. Methods are available to measure 1,1-dichloroethene and/or its

metabolites in these tissues as well (Lin et al. 1982). Purge-and-trap gas chromatography/mass

spectrometry (GC/MS) is the most commonly used method to detect 1,1-dichloroethene in

biological samples. The purge-and-trap technique involves bubbling an inert gas through the

sample to purge the volatile compounds out of solution. The compounds are then trapped in a

cold trap (cry&rapping) or adsorbed on a suitable adsorbent such as Tenax. The next step is

thermal desorption of the trapped solutes and their subsequent transfer to an analytical column.

GC/MS allows the detection of compound at the ppb level. Capillary GC affords the highest

resolution of complex mixtures, even when other volatile organic compounds are present that
1,1- DICHLOROETHENE 132

6. ANALYTICAL METHODS

could conceivably mask or interfere with the detection of 1,1-dichloroethene. Furthermore,

specific GC-detectors, as well as mass selective detectors, enable the quantitation of 1,1-dichloroethene

even when it is not fully separated from other compounds. It is difficult to accurately

measure biological concentrations of 1,1-dichloroethene and correlate these measurements to

actual exposure concentrations because of the chemical’s short half-life and conversion into

metabolites. The concentration of 1,1-dichloroethene in biological media is continually changing

by virtue of its rapid release into the air or biotransformation into other compounds. More

information on methods for the analysis of 1,1-dichloroethene in biological materials, including

sample preparation techniques, can be found in the references cited in Table 6-1.

Environmental exposure to 1,1-dichloroethene at hazardous waste sites may often include

exposure to other chlorinated hydrocarbons. 1,1-dichloroethene exposure can be monitored by

direct measurement of the parent compound or its metabolites. It is difficult to distinguish

metabolites of 1,1-dichloroethene in the body because some of the same metabolites may be

formed as a result of exposure to other chlorinated hydrocarbons.

Determination of 1,1-dichloroethene in breath samples by GC/MS is the most commonly used

method of monitoring exposure to 1,1-dichloroethene (Pellizzari et al. 1985; Raymer et al. 1990,

1991). Sensitivity is in the low ppb range. Recovery is adequate. Various other techniques are

being studied and developed to monitor 1,1-dichloroethene in expired air using reversible

adsorption (Contant et al. 1984) and impregnated tape methods for continuous monitoring

(Denenberg and Miller 1974). Recently, a portable device for measuring 1,1-dichloroethene in

alveolar breath was described (Raymer et al. 1990).

1,1-dichloroethene has been measured in whole blood samples using purge-and-trap GC/MS

(Ashley et al. 1992). This method shows excellent sensitivity (low ppt levels) and good precision

(<20% coefficient of variation). Recoveries were high (> 100%). The reason for the high

recoveries was not clear but was suggested to be due to the inability to accurately assess the levels

of the volatile compounds in the unspiked blood which served as a baseline for recovery

calculation. The measurement of 1,1-dichloroethene adducts with DNA in lymphocytes or

hemoglobin may also be useful in monitoring exposure to 1,1-dichloroethene. Such a method has

been established in hemoglobin for another volatile organic compound, ethylene oxide (Tornqvist

et al. 1986). Because human hemoglobin has a half-life of ≈60 days (although half-lives of

1,1- DICHLOROETHENE 134

6. ANALYTICAL METHODS

hemoglobin adducts are somewhat reduced), monitoring of 1,1-dichloroethene adducts with

hemoglobin can be a valuable tool for estimating exposure over longer periods.

1,1-dichloroethene has been detected in urine using GC/MS; however, low recoveries were

obtained (McKenna et al. 1978a). Sensitivity and precision data were not reported.

6.2 ENVIRONMENTAL SAMPLES

The analytical methods used to quantify 1,1-dichloroethene in environmental samples are listed in

Table 6-2. The analytical methods required by EPA (1984a, 1984b, 1984c) for the analysis of

1,1-dichloroethene in water and waste water are described in procedures 601 (GC/ECD), 624

(GC/MS), and 1624 (GC/MS). The sensitivity for these methods is in the ppb range. These are

testing procedures required under the Clean Water Act for sites discharging municipal and

industrial waste water. The method required by the EPA Contract Laboratory Program (CLP)

for analysis of 1,1-dichloroethene and other volatile organic compounds is hexadecane extraction,

fc>llowed by determination of approximate concentration using GC and flame ionization detection

(FID), and final quantitative analysis using GC/MS (EPA 1986a, 1986b).

GC/FID is used to detect 1,1-dichloroethene in air samples (Foerst 1979; NIOSH 1984; Taylor

1978). The sensitivity of this procedure is in the low ppm range. Recovery is good. GC/MS is

used to determine 1,1-dichloroethene in water, waste water discharges, and soil samples with

sensitivities in the ppb-range. DeLeon et al. (1980) measured levels of 1, 1-dichloroethene in soil

and chemical waste; this method had a limit of detection of 10 ppm. In addition, GC/MS is used

to determine levels of 1,1-dichloroethene in fish tissue (Easley et al. 1981 and Hiatt 1983).

GC/ion trap detection (ITD) is used for drinking water. Sensitivity is in the ppb range and

recovery is good. Purge-and-trap GC/MS is used for measuring volatile chlorinated hydrocarbons

in ground water (Barber et al. 1992). The detection limit for this method is 0.2 μg /L. At

concentrations 1, 1-dichloroethene ranging from 0.2 to 100 μg /L, recoveries were good, ranging

from 85% to 142%. The high recoveries (>100% ) o were the result of using a calibration curve

that spanned more than three orders of magnitude. Precision was excellent (33% RSD).

Purgeable organic chloride (POCl) analysis can be used as a complimentary method for use with

GC/MS. Purge-and-trap CC/MS and POCl analysis gave data of similar accuracy and precision at

spiked concentrations of >l μg /L. Lower recoveries and poor precision were obtained at a


1,1- DICHLOROETHENE 137

6. ANALYTICAL METHODS

spiked concentration <1 μg /L. Detection limits using POCL analysis were 0.2 μg /L as well.

POCI analysis is useful for screening samples for volatile chlorinated hydrocarbons; however, it is

not suitable as an independent method of analysis. Purge-and-trap GC/flame ionization detector

(ECD) has also been used to measure 1,1-dichloroethene in tap water (Driss and Bouguerra

1991). Recovery (76.6%) and precision (1.6% RSD) for this method were good. The detection

limit was not reported. Gilbert et al. (1980) detected 1,1-dichloroethene in food at levels <5 ppm

using headspace GC/ECD. These food products were packaged in polyvinylchloride films. Birkel

et al. (1977), using GSC/MS, detected levels of between 6.5 and 10.4 ppm of 1,1-dichloroethene

in Saran food packaging films. Complete descriptions of these techniques can be found in the

references cited in Table 6-2.

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 1,1-dichloroethene 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 1,1-dichloroethene.

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. Except for the measurement

of 1,l-dichloroethene in breath within a short period after exposure, there are no other

biomarkers of exposure or effect unique to 1,1-dichloroethene. Analytical methods exist for

determining 1,1-dichloroethene in breath (Contant et al. 1984; Denenberg and Miller 1974;
1,1- DICHLOROETHENE 138

6. ANALYTICAL METHODS

Pellizzari et al. 1985; Raymer et al. 1990; Wallace et al. 1984), blood (Ashley et al. 1992), and

urine (McKenna et al. 1978a). These methods have acceptable quantification limits and are

capable of determining exposure.

There are few analytical methods used to determine 1,1-dichloroethene in biological samples.

The current emphasis is on (a) measuring the compound of interest at the ppb level accurately

and consistently, (b) refining sample preparation techniques, and (c) modifying the analytical

procedure to obtain better resolution with higher sensitivity. Analytical methodology to

distinguish exposure to 1,1-dichloroethene from compounds with similar metabolic profiles is not

available. Accuracy, precision, and recovery data are also lacking since the available information

concentrates on the extension of detection limits of 1,1-dichloroethene rather than meeting

quality control objectives necessary for analytical method standardization.

Methods for Determining Parent Compounds and Degradation Products in Environmental

Media. There are media-specific standardized methods available for detecting 1,1-dichloroethene

in environmental samples. Accuracy data and sample detection limit data are available for the

EPA-approved methods; however, this information is incomplete for other analytical methods.

This may be because of the lack of adequate data to determine method accuracy, precision, or

recovery values. A better resolution and sensitivity are achievable with the application of the

proper GC capillary column and selection of the correct detector or detector combination

(Kirshen 1984).

Methods are available to detect 1,1-dichloroethene in air, water, sediment, soil, sludge, liquid

waste, food, and fish (Barber et al. 1992; Coutant 1984; DeLeon et al. 1980; Driss and Bouguerra

1991; Easley et al. 1981; Eichelberger et al. 1990; EPA 1984a, 1984c, 1986a, 1986b; Foerst 1979;

Gilbert et al. 1980; Hiatt 1983; NIOSH 1984; Taylor 1978). The standardized methods can

detect 1,l-dichloroethene at ppt levels in air and mg/L levels in water. In addition, numerous

techniques for the analysis of 1,1-dichloroethene are reported in the open literature (Constant et

al. 1984; EPA 1986a, 1986b; Gilbert et al. 1980; Pellizzari et al. 1985; Tornqvist et al. 1986).

The known degradation products of 1,1-dichloroethene containing chlorine are volatile organic

compounds and are often detected and quantified along with 1,1-dichloroethene in monitoring

experiments (although they likely arose from anthropogenic sources). Thus, experimental
1,1- DICHLOROETHENE 139

6. ANALYTICAL METHODS

methods used to detect 1,1-dichloroethene are sufficient to quantify its chlorinated degradation

products.

6.3.2 On-going Studies

No on-going studies concerning techniques for measuring and determining 1,1-dichloroethene in

environmental samples were identified.

One on-going study on the development of analytical methods for human monitoring exposure to

1,1-dichloroethene was located (EXICHEM 1993). The study is being conducted by the EPA.

Further details are not available .

The Environmental Health Laboratory Sciences Division of the National Center for

Environmental Health and Injury Control, Centers for Disease Control, is developing methods for

the analysis of 1,1-dichloroethene and other volatile organic compounds in blood. These methods

use purge and trap methodology, high resolution gas chromatography, and magnetic sector mass

spectrometry which gives detection limits in the low parts per trillion (ppt) range.

1,1- DICHLOROETHENE 141

7. REGULATIONS AND ADVISORIES

Table 7-1 summarizes international, national, and state regulations and guidelines on human

exposure to 1,l dichloroethene.

ATSDR has derived an MRL of 0.02 ppm for intermediate-duration inhalation exposure based on

a NOAEL of 5 ppm for liver effects in guinea pigs (Prendergast et al. 1967).

ATSDR has derived an MRL of 0.009 mg/kg/day for chronic-duration oral exposure based on a

LOAEL of 9 mg/kg/day for liver effects in rats (Quast et al. 1983).

A oral reference dose (RfD) of 0.009 mg/kg/day has been verified by EPA for 1,1-dichloroethene

(IRIS 1992). The RfD is based on a LOAEL of 50 ppm of 1,1-dichloroethene in the drinking

water for liver effects in rats (Quast et al. 1983). EPA has given 1,1-dichloroethene a Group C

weight-of-evidence carcinogenicity classification (probable human carcinogen) (IRIS 1992).

The Clean Water Effluent Guidelines regulate 1,1-dichloroethene for the following industrial

point sources: electroplating, organic chemicals production, rubber manufacturing, asbestos

product manufacturing, timber products processing, metal finishing, paving and roofing, paint

formulating, ink formulating, gum and wood chemicals manufacturing, carbon black

manufacturing, coil coating, and electrical and electronic components manufacturing (EPA 1986).

The FDA has limited the amount of 1,1-dichloroethene that can be present in foodwrap to

10 ppm (FDA 1988).



1,1- DICHLOROETHENE 145

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1,1- DICHLOROETHENE 171

9. GLOSSARY

Acute Exposure - Exposure to a chemical for a duration of 14 days or less, as specified in the

Toxicological Profiles.

Adsorption Coefficient (Koc) - 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.

Rioconcentration 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.
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9. GLOSSARY

Intermediate Exposure - Exposure to a chemical for a duration of 15-364 days, as specified in the

Toxicological Profiles.

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 Concentration(LO) (LCLO) - The lowest concentration of a chemical in air which has been

reported to have caused death in humans or animals.

Lethal Concentration (50) (LC50) - 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(LO) (LDLO) - The lowest dose of a chemical introduced by a route other than

inhalation that 1s expected to have caused death in humans or animals.

Lethal Dose (50) (LD50) - The dose of a chemical which has been calculated to cause death in

50% of a defined experimental animal population.

Lethal Time(50) (LT50) - 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.
1,1- DICHLOROETHENE 173

9. GLOSSARY

Octanol-Water Partition Coefficient (Kow) - 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 s-hour shift.

q1* - The upper-bound estimate of the low-dose slope of the dose-response curve as determined

by the multistage procedure. The ql* can be used to calculate an estimate of carcinogenic

potency, the incremental excess cancer risk per unit of exposure (usually μg /L for water,

mg/kg/day for food, and μg /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 RfDs and an additional modifying factor, which is based on

a professional judgment of the entire database on the chemical. The RfDs 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.
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9. GLOSSARY

Toxic Dose (TD50) - 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 RtD 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.
1,1- DICHLOROETHENE A-1

APPENDIX A

USER’S GUIDE

Chapter 1

Public Health Statement

This chapter of the profile is a health effects summary written in nontechnical language. Its intended

audience is the general public especially people living in the vicinity of a hazardous waste site or

substance 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 substance.

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 by duration

of exposure and end point and to illustrate graphically levels of exposure associated with those effects.

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)

for Less Serious and Serious health effects, or Cancer Effect Levels (CELs). In addition, these tables

and figures illustrate 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 1O,OOO,OOO. The LSE tables and figures can be used 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 witb the text.

The legends presented below demonstrate the application of these tables and figures. A representative

example 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

sufftcient data exist, 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 @SE Figure 2-2) routes.

(2). Exposure Duration Three exposure periods: acute (14 days or less); intermediate (15 to

364 days); and chronic (365 days or more) are presented within each route of exposure. In this

example, an inhalation study of intermediate duration exposure is reported.
1,1- DICHLOROETHENE A-2

APPENDIX A

(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.

(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 define a NOAEL and a Less Serious LOAEL

(also see the two “18r” data points in Figure 2-1).

(5). Species The test species, whether animal or human, are identified in this column.

(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 lS), rats were exposed to [substance x] via

inhalation for 13 weeks, 5 days per week, for 6 hours per day.

(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, one systemic effect (respiratory)

was investigated in this study.

(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”).

(10). LOAEL A Lowest-Observed-Adverse-Effect Level (LOAEL) is the lowest exposure level 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 end point used to quantify the adverse effect accompanies the

LOAEL. The “Less Serious” respiratory effect reported in key number 18 (hyperplasia)

occurred at a LOAEL of 10 ppm.

(11). Reference The complete reference citation is given in Chapter 8 of the profile.

(12). CEL A Cancer Effect Level (CEL) is the lowest exposure level associated with the onset of

carcinogenesis in experimental or epidemiological studies. CELs are always considered serious

effects. The LSE tables and figures do not contain NOAELs for cancer, but the text may report

doses which did not cause a measurable increase in cancer.

(13). 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 LSE 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 levels for particular exposure duration.


1,1- DICHLOROETHENE A-5

APPENDIX A

(13). Exposure Duration 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.

(14). Health Effect These are the categories of health effects for which reliable quantitative data

exist. The same health effects appear in the LSE table.

(15). Levels of Exposure Exposure levels for each health effect in the LSE tables are graphically

displayed in the LSE figures. Exposure levels are reported on the log scale “y” axis.

Inhalation exposure is reported in mg/m3 or ppm and oral exposure is reported in mg/kg/day.

(16). NOAEL In this example, 18r NOAEL is the critical end point for which an intermediate

inhalation exposure MRL is based. As you can see from the LSE figure key, the

open-circle symbol indicates 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).

(17). CEL Key number 38r is one of three studies for which Cancer Effect Levels (CELs) were

derived. The diamond symbol refers to a CEL for the test species (rat). The number 38

corresponds to the entry in the LSE table.

(18). 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 EPA’s Human Health Assessment Group’s upper-bound estimates of the slope

of the cancer dose response curve at low dose levels (ql’).

(19). Key to LSE Figure The Key explains the abbreviations and symbols used in the figure.

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 toxicological, epidemiological, 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 discusses health effects by end point. Human data are presented first, then animal data.

Both are organized by route of exposure (inhalation, oral, and dermal) and by duration (acute,

intermediate, and 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.
1,1- DICHLOROETHENE A-6

APPENDIX A

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. MRLs for noncancer end points if derived, and the end

points from which they were derived are indicated and discussed in the appropriate section(s).

Limitations to existing scientific literature that prevent a satisfactory evaluation of the relevance to

public health are identified in the Identification of Data Needs section.

Interpretation of Minimal Risk Levels

Where sufficient toxicologic information was available, MRLs were derived. MRLs are specific for

route (inhalation or oral) and duration (acute, intermediate, or chronic) of exposure. Ideally, MRLs can

be derived from all six exposure scenarios (e.g., Inhalation - acute, -intermediate, -chronic; Oral -

acute, -intermediate, - 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 substance emission, given the concentration of a contaminant in air or the

estimated daily dose received via food or water. MRLs are based largely on toxicological studies in

animals and on reports of human occupational exposure.

MRL users should be familiar with the toxicological information on which the number is based.

Section 2.4, “Relevance to Public Health,” contains basic information known about the substance.

Other sections such as 2.6, “Interactions with Other Chemicals” 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 used by the Environmental Protection Agency

(EPA) (Barnes and Dourson 1988; EPA 1989a) to derive reference doses (RfDs) for lifetime exposure.

To derive an MRL, ATSDR generally selects the end point 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

effects (e.g., systemic, neurological, and developmental). In order to compare NOAELs and

LOAELs for specific end points, all inhalation exposure levels are adjusted for 24hr exposures and all

intermittent exposures for inhalation and oral routes of intermediate and chronic duration are adjusted

for continuous exposure (i.e., 7 days/week). If the information and reliable quantitative data on the

chosen end point 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. The NOAEL is the most suitable end point for deriving an MRL. When a NOAEL is

not available, a Less Serious LOABL can be used to derive an MRL, and an uncertainty factor of (1,

3, or 10) is employed. MRLs are not derived from Serious LOAELs. Additional uncertainty factors

of (1, 3, or 10 ) are used for human variability to protect sensitive subpopulations (people who are

most susceptible to the health effects caused by the substance) and (1, 3, or 10) are used for interspecies

variability (extrapolation from animals to humans). In deriving an MRL, these individual

uncertainty factors are multiplied together. Generally an uncertainty factor of 10 is used; however, the

MRL Workgroup reserves the right to use uncertainty factors of (1, 3, or 10) based on scientific

judgement. The product is then divided into the adjusted 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.