TOXICOLOGICAL PROFILE FOR

HEXACHLOROBUTADIENE

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Agency for Toxic Substances and Disease Registry

May 1994
HEXACHLOROBUTADIENE 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.
HEXACHLOROBUTADIENE iii

UPDATE STATEMENT

Toxicological profiles are revised and republished as necessary, but no less than once every three years. For

information regarding the update status of previously released profiles, contact ATSDR at:

Agency for Toxic Substances and Disease Registry

Division of Toxicology/Toxicology Information Branch

1600 Clifton Road NE, E-29

Atlanta, GA 30333















HEXACHLOROBUTADIENE 1

1. PUBLIC HEALTH STATEMENT

This Statement was prepared to give you information about hexachlorobutadiene 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. Hexachlorobutadiene has been found in at

least 45 of the sites on the NPL. However, the number of NPL sites evaluated for

hexachlorobutadiene is not known. As EPA evaluates more sites, the number of sites at

which hexachlorobutadiene is found may increase. This information is important because

exposure to hexachlorobutadiene may cause harmful health effects and because these sites are

potential or actual sources of human exposure to hexachlorobutadiene.

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 hexachlorobutadiene, 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.
HEXACHLOROBUTADIENE 2

1. PUBLIC HEALTH STATEMENT

1.1 WHAT IS HEXACHLOROBUTADIENE?

Hexachlorobutadiene, also known as HCBD, perchlorobutadiene, or Dolen-Pur-, is a colorless

liquid. It does not evaporate or burn easily. Hexachlorobutadiene has a turpentine-like odor.

Most people will begin to smell a mild to pungent odor if the compound is present in air at

1 part hexachlorobutadiene per million parts of air (ppm). It is not known how it tastes or at

what level people can taste it.

Hexachlorobutadiene does not occur naturally in the environment. It is formed during the

processing of other chemicals such as tetrachloroethylene, trichloroethylene, and carbon

tetrachloride. Hexachlorobutadiene is an intermediate in the manufacture of rubber

compounds and lubricants. It is used as a fluid for gyroscopes, a heat transfer liquid, or a

hydraulic fluid. Outside of the United States it is used to kill soil pests.

More information on the properties and uses of hexachlorobutadiene is found in Chapters 3

and 4.

1.2 WHAT HAPPENS TO HEXACHLOROBUTADIENE WHEN IT ENTERS THE

 ENVIRONMENT?

Hexachlorobutadiene is released to the environment in air, water, and soil, mainly as a result

of its disposal following industrial use. Most of the hexachlorobutadiene wastes are

destroyed by burning; some are released to the air in this process. It is not known what

happens to hexachlorobutadiene after it enters the air. Based on the information we have on

similar compounds, it may be broken down by sunlight and react with gases in the

atmosphere. It is not known what chemicals are formed by these reactions or if the

compounds formed are harmful. Based on the properties of similar compounds, one-half of

the hexachlorobutadiene in the air is expected to be broken down to other chemicals within

60 days.
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1. PUBLIC HEALTH STATEMENT

Hexachlorobutadiene may be released to water during disposal of factory waste. It is not

known what happens to it in water or how long it remains there. Hexachlorobutadiene that is

present in water may pass into the air or soil in small amounts. Small amounts of

hexachlorobutadiene may be released to soil as a result of disposal of industrial wastes

containing it. It is not known what happens to hexachlorobutadiene after it contacts soil.

Because hexachlorobutadiene binds to most soils, it is expected to remain there for some

time. The hexachlorobutadiene present in sandy soils may move through the soil to

underground water, However, no information was found on how much reaches the

underground water or how long it stays in the water. Hexachlorobutadiene can build up in

fish and shellfish, where waters are contaminated. It is not known if hexachlorobutadiene

builds up in plants.

More information on what happens to hexachlorobutadiene in the environment may be found

in Chapters 4 and 5.

1.3 HOW MIGHT I BE EXPOSED TO HEXACHLOROBUTADIENE?

You may be exposed to hexachlorobutadiene by breathing contaminated air, eating

contaminated food, drinking contaminated water, or by direct skin contact with this chemical.

People working in the industrial facilities where hexachlorobutadiene is formed or used may

be exposed. Concentrations found in outside air were 2-3 parts hexachlorobutadiene per

trillion parts of air (ppt). Levels were much higher in or near industrial facilities where

hexachlorobutadiene is formed or used. One survey detected air concentrations ranging from

22 to 43,000 ppt in a production facility. No information is available on how many workers

are potentially exposed to hexachlorobutadiene.

Although hexachlorobutadiene is not very soluble in water, small amounts may be found in

some public drinking water (less than 1 part hexachlorobutadiene per billion parts water

[ppb]). It may also be found in underground water near hazardous waste sites.

Hexachlorobutadiene has no agricultural or food chemical uses in the United States.
HEXACHLOROBUTADIENE 4

1. PUBLIC HEALTH STATEMENT

Levels ranging from 0.1 to 4.7 milligrams per kilogram have been found in fish and shellfish

because the compound is present in some surface water.

Exposure at waste sites is most likely to occur from the landfill disposal of waste by-products

originating from chlorinated hydrocarbon manufacture.

More information on how you may be exposed to hexachlorobutadiene is found in Chapter 5.

1.4 HOW CAN HEXACHLOROBUTADIENE ENTER AND LEAVE MY BODY?

Hexachlorobutadiene may enter your body through the lungs when you breathe air

contaminated with it. It also may enter your body if you drink water or eat food

contaminated with hexachlorobutadiene. With the exception of fish and shellfish, however,

hexachlorobutadiene has not been found in food. The amount of hexachlorobutadiene that

enters your body by these routes depends on how much of the chemical you eat or drink.

What happens to hexachlorobutadiene when you breathe vapors of the compound is not

known, but it most likely moves across your lungs into your bloodstream. In animal studies,

most of the hexachlorobutadiene is changed by the body into more toxic compounds. It is

not known how rapidly hexachlorobutadiene and its breakdown products are removed from

your body through your urine and feces. Some is expected to remain in your body fat for

long periods.

More information on how hexachlorobutadiene enters and leaves the body is given in

Chapter 2.

1.5 HOW CAN HEXACHLOROBUTADIENE AFFECT MY HEALTH?

In one study of workers at a solvent production plant who breathed hexachlorobutadiene for

long periods, the compound was shown to affect the function of the liver. Because the

workers were also exposed to other solvents (carbon tetrachloride and perchloroethylene), it
HEXACHLOROBUTADIENE 5

1. PUBLIC HEALTH STATEMENT

is not certain if this effect was caused by hexachlorobutadiene alone. Studies in mice showed

that brief exposure to high concentrations of hexachlorobutadiene irritate the nose. The

effects of breathing low levels of hexachlorobutadiene are not known.

Ingestion of hexachlorobutadiene damaged the kidneys of rats and mice and, to a lesser

extent, the liver of rats. These effects occurred after both short- and long-term exposures at

very low dose levels. Young rats were affected more than adult rats. The kidneys of female

rats appeared to be affected more than those of males. On the other hand, the liver of male

rats was affected, but the liver of female rats was not. It is not clear if the differences

between the sexes might be seen in humans. Kidney, brain, and liver damage were also seen

in rabbits after contact of their skin with the compound for a short period.

Hexachlorobutadiene decreased fetal body weight in rats, but did not affect fetal development

or impair their ability to produce offspring. The lungs, heart, brain, blood, muscles, and

skeleton in rats or mice were not damaged after short- or long-term exposure.

Studies in rats indicate that hexachlorobutadiene may increase the risk of kidney cancer if

exposures occur for long periods. The International Agency for Research on Cancer (IARC)

has determined that hexachlorobutadiene is not classifiable as to its carcinogenicity in

humans, but indicated that there was limited evidence that hexachlorobutadiene was

carcinogenic in rats. EPA has determined that hexachlorobutadiene is a possible human

carcinogen.

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

 EXPOSED TO HEXACHLOROBUTADIENE?

Exposure to hexachlorobutadiene can be determined by measuring the chemical or its

breakdown products in blood, urine, or fat. These tests are not usually performed in most

doctors’ offices because special equipment is needed. Samples can be collected and sent to

special laboratories to determine if you were exposed to hexachlorobutadiene. These tests
HEXACHLOROBUTADIENE 6

1. PUBLIC HEALTH STATEMENT

cannot determine how much of the chemical you were exposed to or if adverse health effects

will occur as a result of the exposure.

More information on how hexachlorobutadiene can be detected in your body is found in

Chapters 2 and 6.

1.7 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT MADE TO

 PROTECT HUMAN HEALTH?

The federal government has develped guidelines and standards to protect the public from

excess exposure to hexachlorobutadiene. EPA has recommended guidelines on how much

hexachlorobutadiene can be present in drinking water for specific periods of time without

causing adverse health effects in humans. EPA recommends that exposures in children

should not exceed 0.3 milligrams per liter of water (mg/L) for 10-day periods, or 0.1 mg/L

for more than 7 years. If adults are exposed for long periods (more than 7 years), EPA

recommends that exposure levels should not exceed 0.4 mg/L.

Hexachlorobutadiene has been named a hazardous substance by EPA. If quantities equal to

or greater than 1 pound are released to the environment, the National Response Center of the

federal government must be notified immediately.

The Occupational Safety and Health Administration (OSHA) recommends that exposure to

hexachlorobutadiene not exceed 0.02 ppm for an 8-hour workday over a 40-hour workweek.

This limit is not enforced by the federal government, but it is the law in at least 25 states.

The National Institute for Occupational Safety and Health (NIOSH) classifies

hexachlorobutadiene as a potential occupational carcinogen. Because there is potential for

effects following contact of the chemical with the skin, measures should be taken to minimize

skin exposure.
HEXACHLOROBUTADIENE 7

1. PUBLIC HEALTH STATEMENT

More information on federal government guidelines and standards on hexachlorobutadiene is

found in 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) 639-6000

This agency can also provide you with information on the location of occupational and

environmental health clinics. These clinics specialize in the recognition, evaluation, and

treatment of illness resulting from exposure to hazardous substances.

HEXACHLOROBUTADIENE 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

hexachlorobutadiene. It contains descriptions and evaluations of toxicological studies and

epidemiological investigations and provides conclusions, where possible, on the relevance of toxicity

and toxicokinetic data to public health.

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

2.2 DISCUSSION OF HEALTH EFFECTS BY ROUTE OF EXPOSURE

To help public health professionals and others address the needs of persons living or working near

hazardous waste sites, the information in this section is organized first by route of exposure -

inhalation, oral, and dermal; and then by health effect - death, systemic, immunological,

neurological, reproductive, developmental, genotoxic, and carcinogenic effects. These data are

discussed in terms of three exposure periods - acute (14 days or less), intermediate (15 - 364 days),

and chronic (365 days or more).

Levels of significant exposure for each route and duration are presented in tables and illustrated in

figures. The points in the figures showing no-observed-adverse-effect levels (NOAELs) or lowest-observedadverse-effect levels (LOAELs) reflect the actual doses (levels of exposure) used in the

studies. LOAELs have been classified into “less serious” or “serious” effects. “Serious” effects are

those that evoke failure in a biological system and can lead to morbidity or mortality (e.g., acute

respiratory distress or death). “Less serious” effects are those that are not expected to cause

significant dysfunction or death, or those whose significance to the organism is not entirely clear.

ATSDR acknowledges that a considerable amount of judgment may be required in establishing

whether an end point should be classified as a NOAEL, “less serious” LOAEL, or “serious” LOAEL,

and that in some cases, there will be insufficient data to decide whether the effect is indicative of

significant dysfunction. However, the Agency has established guidelines and policies that are used to

classify these end points. ATSDR believes that there is sufficient merit in this approach to warrant an
HEXACHLOROBUTADIENE 10

2. HEALTH EFFECTS

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 Levels of Significant Exposure (LSE) tables and

figures may differ depending on the user’s perspective. Public health officials and others concerned

with appropriate actions to take at hazardous waste sites may want information on levels of exposure

associated with more subtle effects in humans or animals (LOAEL) or exposure levels below which

no adverse effects (NOAELs) have been observed. Estimates of levels posing minimal risk to humans

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

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

hexachlorobutadiene are indicated in Table 2-2. Because cancer effects could occur at lower exposure

levels, Figures 2-l and 2-2 also show ranges 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 hexachlorobutadiene. 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

1990h), uncertainties are associated with these techniques. Furthermore, ATSDR acknowledges

additional uncertainties inherent in the application of the procedures to derive less than lifetime

MRLs. As an example, acute inhalation MRLs may not be protective for health effects that are

delayed in development or are acquired following repeated acute insults, such as hypersensitivity
HEXACHLOROBUTADIENE 11

2. HEALTH EFFECTS

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 hexachlorobutadiene.

In animals, all mice that were exposed to vapors of 50 ppm hexachlorobutadiene for 5 days died, but

no deaths occurred at 10 ppm (NIOSH 1981).

2.2.1.2 Systemic Effects

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

effects in humans or animals after inhalation exposure to hexachlorobutadiene. Limited data are

available on hepatic effects in humans and on the respiratory and renal effects of hexachlorobutadiene

in animals. These effects are discussed below. The highest NOAEL value and all LOAEL values

from each reliable study for systemic effects in each species and duration category are recorded in

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

Respiratory Effects. Respiratory rates were decreased in mice exposed to vapors of

hexachlorobutadiene at concentrations of 155 ppm or greater for 15 minutes. The authors

characterized the responses as a reaction to nasal irritation (de Ceaurriz et al. 1988). Nasal irritation

and respiratory difficulty was also reported in rats exposed to vapors at a concentration of 250 ppm

for 2 days (4 hours/day) or 100 ppm for 12 days (6 hours/day) (Gage 1970). Breathing difficulty

occurred even with exposure to 25 ppm for 15 days (6 hours/day).


HEXACHLOROBUTADIENE 14

2. HEALTH EFFECTS

Hepatic Effects. Although the liver is not a major target of hexachlorobutadiene toxicity, there is

some indication that it may be adversely affected following exposure in humans. Serum bile acids

(deoxycholic acid, glycinedeoxycholic acid, taurine-chenodeoxycholic acid, and total deoxycholate)

increased following chronic exposure in workers to estimated exposure levels of 0.005-0.02 ppm

(Driscoll et al. 1992). It should be noted that the workers were also potentially exposed to other

solvents (carbon tetrachloride and perchloroethylene). For this reason, and the fact that data are

absent on morphological changes as well as other effects on liver function, the practical importance of

this finding is reduced.

Renal Effects. Mice that were exposed to vapors of hexachlorobutadiene (2.75-25 ppm) for 4 hours

showed an increase (4-91%) in the number of damaged cortical renal tubules (de Ceaurriz et al.

1988). Degeneration of the tubule midsection resulted from exposures to 250 ppm

hexachlorobutadiene for 4 hours on each of 2 consecutive days (Gage 1970). Damage (not specified)

to renal proximal tubules was also reported in rats exposed to vapors at a concentration of 25 ppm for

15 days (6 hours/day); the kidneys were pale and enlarged. At a higher concentration (100 ppm),

degeneration of renal cortical tubules with epithelial regeneration occurred after 12 days of exposure

(Gage 1970). Quantitative data on renal effects were limited.

2.2.1.3 Immunological Effects

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

exposure to hexachlorobutadiene.

2.2.1.4 Neurological Effects

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

to hexachlorobutadiene.

2.2.1.5 Reproductive Effects

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

hexachlorobutadiene.
HEXACHLOROBUTADIENE 15

2. HEALTH EFFECTS

In animals, the frequency of abnormal sperm morphology did not increase significantly over controls

in mice exposed to concentrations of 10 ppm hexachlorobutadiene (NIOSH 1981). When mice were

exposed to 50 ppm (the only other concentration tested), all animals died during the 5 week posttreatment

period. Thus, a reliable NOAEL value for reproductive effects cannot be identified for this

study. When rat dams were exposed to vapors of hexachlorobutadiene (up to 15 ppm) during

gestation (gestation days 6-20), the mean number of implantation sites, total fetal loss, resorptions

and number of live fetuses were comparable to unexposed controls (Saillenfait et al. 1989).

Studies evaluating the genotoxic potential of hexachlorobutadiene indicate that hexachlorobutadiene

does not affect fertility in male rats. In dominant lethal tests in rats, fertility indices, number of

corpora lutea or implantations, or the frequency of early death did not differ between animals that

inhaled vapors of hexachlorobutadiene at concentrations up to 50 ppm and their unexposed controls

(NIOSH 1981).

2.2.1.6 Developmental Effects

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

hexachlorobutadiene .

In animals, data are limited to one intermediate-duration study in which rats were exposed to vapors

of hexachlorobutadiene at concentrations up to 15 ppm during gestation days 6-20 (Saillenfait et al.

1989). The only effect observed was a reduction (p < 0.01) in fetal body weights at concentrations of

15 ppm (highest dose tested). No fetotoxic effects were observed at concentrations of 10 ppm or less.

Embryotoxicity was not observed at any dose tested and there were no exposure-related external,

visceral, or skeletal anomalies. It should be noted that reduced maternal body weight gain was

observed at the 15 ppm vapor concentration.

The highest NOAEL value and a LOAEL value for developmental toxicity in rats are recorded in

Table 2-l and plotted in Figure 2-l.
HEXACHLOROBUTADIENE 16

2. HEALTH EFFECTS

2.2.1.7 Genotoxic Effects

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

hexachlorobutadiene.

Hexachlorobutadiene did not cause dominant lethal mutations in rats after inhalation of vapors at

concentrations of 10 or 50 ppm for up to 5 days (NIOSH 1981). Similarly, there were no increases

in the frequency of chromosomal aberrations in bone marrow cells of rats exposed to 10 ppm for up

to 5 days (NIOSH 1981).

Other genotoxicity studies are discussed in Section 2.4.

2.2.1.8 Cancer

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

hexachlorobutadiene. However, EPA has derived an inhalation unit risk of 0.022 (mg/m3

)

-1 (IRIS

1993), based on oral exposure data (see Section 2.2.2.8). Exposure levels corresponding to excess

cancer risks of 10-4 to 10-7 are shown in Figure 2-l.

2.2.2 Oral Exposure

2.2.2.1 Death

No studies were located regarding death in humans after oral exposure to hexachlorobutadiene.

Acute oral exposures to hexachlorobutadiene were lethal in rats. Young rats were more sensitive to

compound exposure than adult rats. LD50 values for adult rats were 580 mg/kg (males) and

200-400 mg/kg (females). The LD50 values for weanling male and female rats were 65 and

46 mg/kg, respectively (Kociba et al. 1977a). Important experimental details of this study were not

available for review.

Mice exposed to 1,000 and 3,000 ppm hexachlorobutadiene in their diet (19-36 mg/kg/day) died after

3-5 days (NTP 1991; Yang et al. 1989). Animals exposed to 30-300 ppm (3-49 mg/kg/day)
HEXACHLOROBUTADIENE 17

2. HEALTH EFFECTS

survived the 15 day exposure period. Survival was not reduced in rats exposed to 100 mg/kg/day

hexachlorobutadiene for 30 days or at dose levels of 15.6 mg/kg/day for 13 weeks (Harleman and

Seinen 1979) and 100 mg/kg/day (Kociba et al. 1971). Mice survived dose levels of up to

19.2 mg/kg/day for 13 weeks (NTP 1991). In lifetime studies, survival was reduced significantly in

male rats exposed to hexachlorobutadiene at a dose level of 20 mg/kg/day (Kociba et al. 1977a).

Although the cause of death was not reported, renal damage, a major effect manifested by this

compound, may have been a contributing factor.

A LOAEL value for lethality in rats after chronic exposure is recorded in Table 2-2 and plotted in

Figure 2-2.

2.2.2.2. Systemic Effects

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

musculoskeletal, hepatic, renal, or dermal/ocular effects in humans after oral exposure to

hexachlorobutadiene for any duration category.

Studies have been conducted in animals to evaluate the respiratory, cardiovascular, gastrointestinal,

hematological, musculoskeletal, hepatic, and renal effects. These effects are discussed below. No

studies were located on dermal/ocular effects. 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. Intermediate-duration (30-148 days) exposure to 20 mg/kg/day (Schwetz et al.

1977) or 100 mg/kg/day (Kociba et al. 1971) and lifetime exposures to 20 mg/kg/day (Kociba et al.

1977a) did not cause treatment-related lesions of the lungs or changes in lung weight in rats exposed

to hexachlorobutadiene at dose levels of 20 mg/kg/day.

Cardiovascular Effects. Hexachlorobutadiene did not alter heart weights or cause treatment-related

lesions of the heart in rats or mice exposed for intermediate durations (90-148 days) at dose levels of

19.2-20 mg/kg/day (NTP 1991; Schwetz et al. 1977; Yang et al. 1989) and 100 mg/kg/day (Kociba

et al. 1971) or after lifetime exposure at dose levels of 20 mg/kg/day (Kociba et al. 1977a).









HEXACHLOROBUTADIENE 27

2. HEALTH EFFECTS

Gastrointestinal Effects. Intermediate-duration (30-148 days) exposure did not cause treatment-related

histopathological lesions in the esophagus, stomach, small intestines, or large intestines in rats

exposed to hexachlorobutadiene at dose levels up to 20 mg/kg/day (Schwetz et al. 1977) or levels up

to 100 mg/kg/day (Kociba et al. 1971). Lifetime exposure at dose levels of 20 mg/kg/day (Kociba

et al. 1977a) did not result in any effect on this system.

Hematological Effects. Evaluations of hematological parameters in rats revealed no treatment-related

alterations in packed cell volume, red blood cell count, hemoglobin concentration, total white

blood cell count, or differential white blood cell count in animals exposed to a dose level of 15.6 or

20 mg/kg/day after intermediate duration exposure (90-148 days) (Harleman and Seinen 1979;

Schwetz et al. 1977). Similarly, one lifetime oral exposure (20 mg/kg/day) also did not cause

hematological effects (Kociba et al. 1977a). However, in another study, hemoglobin concentration

increased in rats at dose levels from 10-100 mg/kg/day, but not at 3 mg/kg/day. Other hematologic

parameters, as mentioned above, were within normal values (Kociba et al. 1971).

Musculoskeletal Effects. No treatment-related lesions of the musculoskeletal system were observed

in rats exposed to dose levels of 20 mg/kg/day hexachlorobutadiene for up to 148 days (Harleman and

Seinen 1979; Schwetz et al. 1977) or 2 years (Kociba et al. 1977a).

Hepatic Effects. An animal study revealed that hexachlorobutadiene can affect the liver. However,

the effects were less serious compared to effects in the kidney at the same dose. Liver weights were

decreased in female rats fed 5 mg/kg/day or greater hexachlorobutadiene for 4 weeks (Jonker et al.

1993b). Histological examinations were not performed. However, evaluation of serum biochemical

parameters in males revealed increased enzyme activity (aspartate aminotransferase, p < 0.02) and

total bilirubin levels (p < 0.02) at doses of 20 mg/kg/day (highest dose tested). Cytoplasmic

basophilia and liver weights were increased in male rats exposed to hexachlorobutadiene by gavage at

dose levels of 6.3 mg/kg/day or greater for 13 weeks; treatment-related lesions were not observed in

females (Harleman and Seinen 1979). In another study, hepatocellular swelling occurred at a dose

level of 30 mg/kg/day and liver weights decreased at dose levels of 30-100 mg/kg/day or greater in

female rats that were fed diets containing hexachlorobutadiene for 30 days (Kociba et al. 1971).

Males were not evaluated concurrently. Although histological lesions were not observed in lifetime

studies, urinary excretion of coproporphyrin increased at dose levels of 20 mg/kg/day, suggesting

alterations in heme synthesis in the liver (Kociba et al. 1977a).
HEXACHLOROBUTADIENE 28

2. HEALTH EFFECTS

Renal Effects. The kidney appears to be the primary target organ following oral exposure to

hexachlorobutadiene. Focal necrosis and increased urinary parameters (lactate dehydrogenase,

N-acetyl-β-glucosaminidase) were reported in rats administered hexachlorobutadiene (100 mg/kg) for

24 hours (Jonker et al. 1993a). These effects were not seen at 10 mg/kg. In acute studies in which

rats were fed hexachlorobutadiene (4.6 mg/kg/day) in the diet for 14 days, there was degeneration of

tubular epithelial cells mainly confined to the straight limbs of the proximal tubules located in the

outer zone of the medulla (Harleman and Seinen 1979). Similar effects were seen following

intermediate-duration exposure in other species. Cell necrosis and regeneration were found as well as

tubular epithelial cell degeneration in rats exposed to dose levels of 30-100 mg/kg/day for 30 days

(Kociba et al. 1971). Diffuse tubular cytomegaly was observed in the cortex of the kidneys at dose

levels of 5 mg/kg/day or greater in rats following oral exposure to hexachlorobutadiene for 4 weeks

(Jonker et al. 1993b). Tubular degeneration also occurred in mice at dose levels from

0.2-19.2 mg/kg/day in females exposed to hexachlorobutadiene for 13 weeks (NTP 1991; Yang et al.

1989). Based on a value of 0.2 mg/kg/day, an intermediate oral MRL was calculated as described in

the footnote in Table 2-2.

Kidneys were roughened and had a mottled cortex in males exposed to dose levels of 2 and

20 mg/kg/day for 148 days (Schwetz et al. 1977). Alterations in the kidney were also observed

following longer exposures. For the most part, these effects were manifested as renal tubular

hyperplasia which occurred at dose levels of 2 and 20 mg/kg/day, but not at a dose level of

0.2 mg/kg/day (Kociba et al. 1977a). Kidney weights were also affected. Intermediate- and chronicduration oral exposures caused increased relative kidney weights or kidney/body weight ratios at dose

levels from 2-20 mg/kg/day (Jonker et al. 1993b; Kociba et al. 1977a; NTP 1991; Schwetz et al.

1977; Yang et al. 1989).

Impaired kidney function accompanied morphological evidence of kidney damage. The ability to

concentrate urine was significantly reduced in female rats at dose levels from 2.5-15.6 mg/kg/day for

13 weeks. The same effect was observed in males at 15 mg/kg/day (Harleman and Seinen 1979). On

the other hand, alterations in various clinical chemistry indices (e.g., blood urea nitrogen, creatinine,

y-glutarnyl transpeptidase, and alanine aminotransferase) were comparable to untreated controls in rats

exposed to hexachlorobutadiene at dose levels up to 20 mg/kg/day up to 148 days (Harleman and

Seinen 1979; Schwetz et al. 1977). Plasma urea levels decreased (p < 0.05) in female rats at dose
HEXACHLOROBUTADIENE 29

2. HEALTH EFFECTS

levels of 1.25 mg/kg/day or greater and in males at 20 mg/kg/day, while creatinine levels decreased

(p < 0.05) in females at dose levels of 5 mg/kg/day or greater for 4 weeks (Jonker et al. 1993b).

2.2.2.3 Immunological Effects

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

hexachlorobutadiene.

In animals, histological examination of lymphoid organs including the thymus and spleen did not

reveal treatment-related lesions at dose levels up to 100 mg/kg/day rats (Harleman and Seinen 1979;

Kociba et al. 1971, 1977a). Depletion and necrosis of lymphoid tissue in the lymph nodes, spleen,

and thymus were noted in mice exposed to lethal doses of hexachlorobutadiene in the 2-week

component of the NTP (1991) study. However no abnormalities in these tissues were seen after 13-

week exposures to doses of up to 19.2 mg/kg/day (NTP 1991; Yang et al. 1989). Tests on effects of

immune function have not been evaluated.

2.2.2.4 Neurological Effects

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

hexachlorobutadiene.

In animals, ataxia, and demyelination and degeneration of femoral nerve fibers were observed in rat

dams exposed to dose levels of 150 mg/kg/day for up to 10 weeks (Harleman and Seinen 1979);

however, no treatment-related brain lesions were seen following exposure to hexachlorobutadiene

(Harleman and Seinen 1979; Kociba et al. 1971; NTP 1991; Schwetz et al. 1977; Yang et al. 1989).

On the other hand, the mean brain/body weight ratio increased at dose levels of 10-100 mg/kg/day,

but histopathological lesions were not seen at dose levels of 100 mg/kg/day or less (Kociba et al.

1971). Exposure to hexachlorobutadiene did not alter brain weights and there were no treatment-related

histopathological lesions of the brain, spinal cord, and sciatic nerve in rats exposed to

hexachlorobutadiene (20 mg/kg/day) for 2 years (Kociba et al. 1977a). Neurochemical and

neurophysiological parameters have not been monitored.
HEXACHLOROBUTADIENE 30

2. HEALTH EFFECTS

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

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

2.2.2.5 Reproductive Effects

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

hexachlorobutadiene.

In animals, fertility was reduced 100% in Wistar-derived rat dams administered 150 mg/kg/day

hexachlorobutadiene during a 10-week study. The mean litter size and the resorption rate did not

differ significantly from controls in dams fed 15 mg/kg/day during an 18-week study (Harleman and

Seinen 1979). The actual total exposure time for this study is not clear; the rats were exposed for at

least 10 weeks at the high dose and 12 weeks (of an 18-week study) at the low dose. No

determination of a reliable LOAEL or NOAEL value was possible for this study. In another study,

fertility, gestation, viability, and lactation indices were comparable in treated and control groups of

Sprague-Dawley rats at dose levels of 20 mg/kg/day for 148 days (Schwetz et al. 1977). No

significant changes were seen in sperm count or incidence of abnormal sperm in mice exposed to

hexachlorobutadiene (19 mg/kg/day) for 13 weeks (NTP 1991; Yang et al. 1989). Lifetime exposures

up to 20 mg/kg/day did not reveal treatment-related lesions in the reproductive organs (Kociba et al.

1977a).

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

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

2.2.2.6 Developmental Effects

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

hexachlorobutadiene.

In animal studies, rat dams were fed hexachlorobutadiene at dose levels of 15 mg/kg/day during

gestation (as part of an 18-week study). Rat pup weights were reduced at birth and weaning.

However, embryotoxicity and teratogenicity were not observed at this dose (Harleman and Seinen

1979). In another study, body weight was decreased (p < 0.05) on day 21 of lactation in rat pups
HEXACHLOROBUTADIENE 31

2. HEALTH EFFECTS

from dams exposed to hexachlorobutadiene at dose levels of 20 mg/kg/day throughout gestation and

lactation; body weights were not reduced in pups from dams exposed to 2 mg/kg/day. No other signs

of fetotoxicity were evident at doses up to 20 mg/kg/day. Teratogenic effects were not observed nor

was hexachlorobutadiene embryotoxic at the doses tested (Schwetz et al. 1977).

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 2-2 and plotted in Figure 2-2.

2.2.2.7 Genotoxic Effects

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

hexachlorobutadiene.

In animals, there is some evidence that hexachlorobutadiene interacts with genetic material. Male rats

administered a single gavage dose of hexachlorobutadiene (20 mg/kg/day) showed a 40% increase in

renal deoxyribonucleic acid (DNA) repair and 0.78 alkylations per million nucleotides (Stott et al.

1981). On the other hand, when hexachlorobutadiene was administered in the diet, it did not cause

chromosomal aberrations in rat bone marrow cells (Schwetz et al. 1977).

Other genotoxicity studies are discussed in Section 2.4.

2.2.2.8 Cancer

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

hexachlorobutadiene.

Studies in rats reported renal tubular adenomas and adenocarcinomas in male and female animals at

doses of 20 mg/kg/day (Kociba et al. 1977a). Metastasis to the lungs was observed. Combined

incidences of renal tubular neoplasms in males (9/39, 23 %) and in females (6/40, 15 %) increased

(p < 0.05) over controls (males-l/90, females-0/90, 0%). The tumor incidence was not increased in

the 0.2 and 2 mg/kg/day dose groups but there were some indications of hyperplasia in animals

exposed to 2 mg/kg/day. The EPA (1990f) evaluated these data and calculated a human potency

factor of 7.8x10-2 (mg/kg/day)-1 (q1*), representing a 95% upper confidence limit of extra lifetime
HEXACHLOROBUTADIENE 32

2. HEALTH EFFECTS

human risk. Based on this value, cancer risk levels of 10-4, 10-5, and 10-6 correspond to exposures of

0.001, 0.0001, 0.00001 mg/kg/day.

2.2.3 Dermal Exposure

2.2.3.1 Death

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

During the 14 day observation period some rabbits (2-8) died after 8-hour exposure to doses of

775-1,550 mg/kg applied directly to shaved skin (3.2 cm2

), but no deaths occurred in the 388 mg/kg

dose group. The author calculated an LD50 of 1,116 mg/kg from these data (Duprat and Gradiski

1978). Central nervous system depression was evident, as manifested by stupor. Some animals were

weak and anorexic, while others showed signs of dyspnea and cyanosis. The lungs, liver, and

kidneys were congested in animals that died. Death was reportedly due to respiratory or cardiac

failure.

A LOAEL value for lethality in rabbits after acute-duration exposure is recorded in Table 2-3.

2.2.3.2 Systemic Effects

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

musculoskeletal, hepatic, renal, dermal/ocular, or other effects in humans after dermal exposure to

hexachlorobutadiene. Liver, kidney, and dermal/ocular effects were reported in animals. These

effects are discussed below. All LOAEL values for systemic effects in rabbits after acute-duration

exposure are recorded in Table 2-3.

Hepatic Effects. Hydropic changes, fatty degeneration, and glycogen reduction were observed in

rabbits after exposure of the skin to 388 mg/kg or greater hexachlorobutadiene for 8 hours (Duprat

and Gradiski 1978). These effects were reversible within 3 weeks.

HEXACHLOROBUTADIENE 34

2. HEALTH EFFECTS

Renal Effects. Acute-duration dermal exposure in rabbits caused tubular necrosis 24 hours after

exposure at dose levels 388 mg/kg or greater (Duprat and Gradiski 1978). The effects were partly

reversible, as evident by epithelial regeneration 2 and 5 weeks after exposure.

Dermal/Ocular Effects. Skin necrosis was evident at the site of application in rabbits after exposure

of the skin to dose levels of 388 mg/kg hexachlorobutadiene for 8 hours (Duprat and Gradiski 1978).

However, most skin lesions had healed within 2 weeks.

2.2.3.3 lmmunological Effects

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

to hexachlorobutadiene.

2.2.3.4 Neurological Effects

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

hexachlorobutadiene.

Rabbits exposed to doses of 388-1550 mg/kg applied to shaved skin exhibited evidence of aneral

nervous system depression (stupor) during exposure and in the l-2 hour period after exposure

(Duprat and Gradiski 1978).

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

exposure:

2.2.3.5 Developmental Effects

2.2.3.6 Reproductive Effects

2.2.3.7 Genotoxic Effects

Genotoxicity studies are discussed in Section 2.4.
HEXACHLOROBUTADIENE 35

2. HEALTH EFFECTS

2.2.3.8 Cancer

No studies were located regarding carcinogenic effects in humans after dermal exposure to

hexachlorobutadiene.

Hexachlorobutadiene did not produce skin papillomas, carcinomas, or tumors at distant sites in mice

after application of dose levels of 2-6 mg/mouse for 440-594 days (Van Duuren et al. 1979). Data

from this exploratory study are not sufficient to rule out carcinogenic effects via dermal exposure.

2 . 3 TOXICOKINETICS

In analogy with other unsaturated chlorinated compounds, hexachlorobutadiene absorption presumably

occurs across the lipid portion of the intestinal matrix rather than by active or protein-facilitated

transport. After absorption, most of the hexachlorobutadiene is carried to the liver where it is

conjugated with glutathione and excreted in the bile. Mono- and bis-substituted glutathione conjugates

are formed. The bile also contains the cysteinyl/glycinyl and cysteinyl derivatives of the glutathione

conjugate. Biliary metabolites are resorbed from the intestines and undergo enterohepatic

recirculation.

Hexachlorobutadiene and its metabolites preferentially distribute to the kidney, liver, adipose deposits,

and possibly the brain. Some hexachlorobutadiene metabolites inhibit mitochondrial metabolism and

react with DNA, resulting in cell death or tumorigenesis. Hexachlorobutadiene metabolites are

excreted in the urine and feces. There is limited degradation to carbon dioxide which is exhaled from

the lungs.

2.3.1 Absorption

2.3.1.1 Inhalation Exposure

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

hexachlorobutadiene. The occurrence of effects after exposure (de Ceaurriz et al. 1988; Gage 1970)

indicate that absorption does occur.
HEXACHLOROBUTADIENE 36

2. HEALTH EFFECTS

2.3.1.2 Oral Exposure

No studies were located regarding absorption in humans after oral exposure to hexachlorobutadiene.

There have also been no direct studies of absorption in animals although data on excretion and

distribution provide information which suggests that absorption does occur from the gastrointestinal

tract (Reichert et al. 1985). In animals, absorption is rapid and virtually complete at low doses of

hexachlorobutadiene (1 mg/kg). At a higher dose (50 mg/kg), unmetabolized hexachlorobutadiene is

found in the fecal matter (Reichert et al. 1985).

When Alderley Park rats were given a single dose of 200 mg/kg of radiolabeled hexachlorobutadiene

and sacrificed at 2, 4, 8, and 16 hours, an autoradiogram of longitudinal sections of whole animals

sacrificed 4 hours after dosing demonstrated that the label was concentrated in the intestines. The

intestinal label was determined to be 85% unmodified, unabsorbed hexachlorobutadiene. At 8 hours,

the intestinal concentration of the label was no longer apparent as hexachlorobutadiene was absorbed

and distributed to the tissues (Nash et al. 1984).

Most of the data pertaining to oral administration of hexachlorobutadiene utilized triglycerides (corn

oil or tricaprylin) as a gavage dosing medium. Because of its high lipophilicity and low water

solubility, it is likely that the absorption of hexachlorobutadiene from an aqueous solution would

differ from that from a triglyceride media. When 1 mg/kg hexachlorobutadiene in tricaprylin was

administered to female Wistar rats 30.61% was excreted in the urine over 72 hours (Reichert et al.

1985), while when the same dose in aqueous polyethylene glycol solution was given to male Sprague

Dawley rats, only 18% was in the urine (Payan et al. 1991). These data suggest that absorption from

the lipid solvent was greater than that with the aqueous solvent.

2.3.1.3 Dermal Exposure

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

hexachlorobutadiene. In animals, pure hexachlorobutadiene (388-1,550 mg/kg) applied to the skin of

rabbits was completely absorbed in 8 hours (Duprat and Gradiski 1978).
HEXACHLOROBUTADIENE 37

2. HEALTH EFFECTS

2.3.2 Distribution

Hexachlorobutadiene has been identified in samples of human adipose tissue (Mes et al. 1985). The

tissue samples were obtained from cadavers and, thus, no data were available pertaining to the route

of exposure.

2.3.2.1 Inhalation Exposure

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

hexachlorobutadiene.

2.3.2.2 Oral Exposure

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

In animals, 5-14 % of (14C) radiolabeled hexachlorobutadiene was retained in the tissues and carcass

72 hours after compound administration (Dekant et al. 1988a; Reichert et al. 1985). The kidney

(outer medulla), liver, and adipose tissue appeared to concentrate hexachlorobutadiene label when

single doses of up to 200 mg/kg (14C) hexachlorobutadiene in corn oil were administered by gavage

(Dekant et al. 1988a; Nash et al. 1984; Reichert et al. 1985). In one report, the brain was also

determined to contain a relatively high concentration of label 72 hours after exposure (Reichert et al.

1985). Label in the kidney 72 hours after exposure was more extensively covalently bound to

proteins than that in the liver (Reichert et al. 1985).

Levels of label in the liver, kidney, and plasma were determined for the donor and recipient rats

when secretions from bile duct cannulated donor rats, given a dose of 100 mg/kg hexachlorobutadiene

were infused directly into the bile duct of nonexposed recipient rats, and thereby into their intestines

(Payan et al. 1991). In the donor rats, after 30 hours, the kidney contained 0.26% of the dose, the

liver 0.11%, and the plasma 0.013% from the intestinally absorbed material. In the recipient rats,

the kidney contained 0.15% of the dose, the liver 0.97%, and the plasma 0.009% from the resorbed

biliary metabolites. For each tissue the level of label from resorbed metabolites was about two-thirds

of that from the original dose. The kidneys contained more of the label than the liver in both

instances, clearly identifying the kidneys as a target organ.
HEXACHLOROBUTADIENE 38

2. HEALTH EFFECTS

2.3.2.3 Dermal Exposure

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

hexachlorobutadiene.

2.3.2.4 Other Exposure Routes

In a study using doses of 0.1 and 300 mg/kg intraperitoneally-administered hexachlorobutadiene, the

label was found in the liver, kidney, and adipose tissue. Very little of the label was found in the

brain, lung, heart, and muscle tissue at 48 hours after dosing (Davis et al. 1980). The reported levels

in the brain in this study differ from those reported at 72 hours following oral administration

(Reichert et al. 1985). This may indicate that there is a gradual deposition of labeled

hexachlorobutadiene and/or its metabolites in the brain lipids over time.

2.3.3 Metabolism

2.3.3.1 Inhalation Exposure

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

hexachlorobutadiene.

2.3.3.2 Oral Exposure

No studies were located regarding metabolism in humans after oral exposure to hexachlorobutadiene.

There is a considerable amount of information available concerning the metabolism of

hexachlorobutadiene in animals. Figure 2-3 presents a proposed metabolic pathway for

hexachlorobutadiene. This pathway is based on the metabolites identified in urine and bile using

chromatographic techniques.

Most of the absorbed hexachlorobutadiene is transported via the portal circulation to the liver where it

is conjugated with glutathione (Garle and Fry 1989). In rat livers both mono- and di-substituted

conjugates have been identified (Jones et al. 1985), whereas mice appear to produce only the

HEXACHLOROBUTADIENE 40

2. HEALTH EFFECTS

monosubstituted conjugate (Dekant et al. 1988a). There was a dose-related decrease in hepatic levels

of glutathione following exposure to hexachlorobutadiene, and pretreatment of experimental animals

with agents that interfere with glutathione synthesis or conjugation reactions decreased the amount of

glutathione conjugate that can be synthesized (Gietl and Anders 1991). There appears to be no

oxidation of the hexachlorobutadiene by the mixed function oxidase system enzymes prior to

conjugation (Garle and Fry 1989).

Glutathione conjugate is excreted with the bile into the intestinal tract. A portion of the material is

hydrolyzed with the removal of glutamate or glutamate and glycine from the glutathione tripeptide to

form the cysteine derivative or the cysteineiglycine derivative (Gietl et al. 1991; Gietl and Anders

1991; Nash et al. 1984). In one study, the glutathione conjugate accounted for 40 % of the label in

the bile and the cysteine derivative for 15% of the label. Another 45% of the label was present as

unidentified compounds (Nash et al. 1984).

The conversion of the glutathione conjugate to its cysteinyl derivative is mediated, at least in part, by

enzymes in the intestinal epithelial cells. S-(Pentachlorobutadienyl)glutathione and

S-(pentachlorobutadienyl)-L-cysteine are partially reabsorbed from the intestines and transported to the

liver and subsequently to the body tissues (Gietl et al. 1991). Only a portion of the reabsorbed

material is taken up by the liver for additional metabolism. When liver uptake of the glutathione

conjugate was measured using perfused rat livers, the maximum uptake observed was 39% (Koob and

Dekant 1992). A portion of this material was re-excreted in bile without any metabolic modification.

The cysteine conjugate, acetylated cysteine conjugate, and six bis-substituted metabolites were

synthesized from the glutathione conjugate and excreted in bile. Two of the bis-substituted

metabolites were identified as the bis-1,4-glutathione conjugate and the bis-1,4-cysteine conjugate.

The cysteine conjugate was taken up by the liver to a greater extent than the glutathione conjugate

(Koob and Dekant 1992). Up to 79% of the cysteine conjugate was absorbed, but this metabolite

appeared to be toxic to the liver and caused decreased bile flow within 20 minutes. There were only

small portions of the cysteine derivative and acetylated cysteine derivative in the bile. Bis-substituted

derivatives, including the 1-cysteinyl-4-glutathionyl tetrachlorobutadiene, bis-1,4-cysteinyl

tetrachlorobutadiene, and 1-cysteinyl-4-cysteinyl glycine tetrachlorobutadiene, were formed.
HEXACHLOROBUTADIENE 41

2. HEALTH EFFECTS

Additional processing of the hexachlorobutadiene metabolites produces the compounds identified in

the urine (1,1,2,3-tetrachlorobutenoic acid, 1,1,2,3,4-pentachloro-1:3-butadienyl sulfenic acid,

N-acetyl-S-l, 1,2,3,4-pentachlorobutadienyl-L-cysteine, S-l, 1,2,3,4-pentachlorobutadienylmercaptoacetic

acid, 1,1,2,3,4-pentachlorobutadiene methylthioether, and 1,1,2,3,4-pentachlorobutadiene carboxymethylthioether)

(Dekant et al. 1988b; Nash et al. 1984; Reichert and Schutz 1986; Reichert et al. 1985).

A very small portion of the absorbed hexachlorobutadiene is oxidized to carbon dioxide. This

pathway can be saturated since an increase in the hexachlorobutadiene dose does not cause a

corresponding increase in excretion of labeled carbon dioxide (Dekant et al. 1988b; Payan et al.

1991; Reichert et al. 1985).

2.3.3.3 Dermal Exposure

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

hexachlorobutadiene.

2.3.4 Excretion

2.3.4.1 Inhalation Exposure

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

hexachlorobutadiene.

2.3.4.2 Oral Exposure

No studies were located regarding excretion in humans after oral exposure to hexachlorobutadiene.

In animals, hexachlorobutadiene and its metabolites are excreted in exhaled air, urine, and feces. In

studies where radiolabeled (14C) hexachlorobutadiene was administered at doses of 1, 30, 50, or

100 mg/kg, 4-8% of the dose was removed from the body in the exhaled air as unmetabolized

hexachlorobutadiene and carbon dioxide within the 72 hours after compound administration (Dekant

et al. 1988b; Payan et al. 1991; Reichert et al. 1985).
HEXACHLOROBUTADIENE 42

2. HEALTH EFFECTS

With single doses ranging from 1 to 200 mg/kg 14C hexachlorobutadiene, the percent of the label in

the urine ranged from 4.5 to 30.6% with the highest percentage associated with the lowest dose

(Dekant et al. 1988b; Nash et al. 1984; Reichert and Schutz 1986; Reichert et al. 1985). At the

higher doses urinary excretion values of 5 to 10% were common (Nash et al. 1984; Reichert and

Schutz 1986). Some of the hexachlorobutadiene label excreted in the urine originates from the biliary

metabolites reabsorbed from the intestinal tract and processed by the kidneys for excretion.

The contribution of reabsorbed biliary metabolites to urinary excretion is reflected in the differences

in urinary excretion of label from bile duct cannulated rats and noncannulated rats. When a dose of

1 mg/kg hexachlorobutadiene in polyethylene glycol solution was given to bile duct cannulated male

rats, the urine contained 11% of the label after 72 hours; in noncannulated rats given the same dose it

contained 18 % of the label (Payan et al. 1991). When a dose of 100 mg/kg was given, the urine of

the cannulated rats contained 7 % of the label and the urine of the noncannulated rats contained 9 %

after 72 hours.

Metabolites identified in the urine include: S-( 1,1,2,3,4-pentachlorobutadienyl)glutathione; S-

(1,1,2,3,4-pentachlorobutadienyl) cysteine; 1,1,2,3 ,-tetrachlorobutenoic acid; 1,1,2,3,4-pentachloro1: 3-butadienyl sulfenic acid; N-acetyl-S- 1,1,2,3,4-pentachlorobutadienyl)-L-cysteine; S-pentachlorobutadienylmercaptoacetic acid; 1,1,2,3,4-pentachlorobutadiene methylthioether and 1,1,2,3,4-pentachlorobutadiene

carboxymethylthioether (Dekant et al. 1988b; Nash et al. 1984; Reichert and Schutz 1986; Reichert et al. 1985).

Fecal excretions contained unmetabolized, unabsorbed hexachlorobutadiene plus a portion of the

hepatic metabolites excreted with the bile. At the lower doses almost all of the label in the feces

originated with the biliary metabolites, whereas at the higher doses there was also some unabsorbed

hexachlorobutadiene in the fecal matter (Dekant et al. 1988b). In rats given 200 mg/kg, feces

collected during the 5-day period contained a total of 39 % of the dose. Only 5 % was excreted in the

first 2 days after dosing. In another study, the feces and contents of the gastrointestinal tract

contained 62 % of a 1 mg/kg dose and 72 % of a 100 mg/kg dose (Payan et al. 1991). The only

metabolite that had been identified in the feces is S-( 1,1,2,3,4-pentachlorobutadienyl) glutathione

(Dekant et al. 1988b), although unidentified metabolites were also present and most likely included

the cysteine derivatives.
HEXACHLOROBUTADIENE 43

2. HEALTH EFFECTS

In one study where a single 200 mg/kg dose was given to rats by gavage, 35% of the label was found

in the bile in the first 2 days after dosing. The biliary label was equally distributed over the 2 days of

collection. In a different study, 66% of a 1 mg/kg dose was excreted in the bile of bile duct

cannulated rats in 72 hours and 58 % of a 100 mg/kg dose (Payan et al. 1991).

Secretions from bile duct cannrulated rats given a dose of 100 mg/kg hexachlorobutadiene were

infused directly into the bile duct of nonexposed rats (Payan et al. 1991). The levels of label in the

urine, bile, and feces of both the donor and recipient rats were measured 30 hours after dosing. The

label in the urine and bile of the recipient rats represented label that was reabsorbed from the

gastrointestinal tract. It was determined that 80% of the biliary metabolites were reabsorbed and only

20% remained in the feces and gastrointestinal tract.

2.3.4.3 Dermal Exposure

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

hexachlorobutadiene.

2.3.4.4 Other Exposure Routes

The distribution of radiolabel in excreta was measured in male rats for the 72 hour period after

intravenous administration of doses of 1 or 100 mg/kg (Payan et al. 1991). At both doses about 8%

of the radiolabel was exhaled. The amount of label in the urine was 21% of the low dose and 9% of

the high dose; the amount in the feces was 59% of the low dose and 72% of the high dose. In a

parallel study, the fecal, urinary, and biliary excretions were measured for rats with cannulated bile

ducts. The urine contained 6-7 % of the dose and the feces less than 0.5 % for both doses. The bile

contained 89% of the 1 mg/kg dose and 72% of the 100 mg/kg dose.

2.3.5 Mechanism of Toxicity

Much of the data related to the mechanism of hexachlorobutadiene toxicity indicate that the

intermediates produced by modification of the S- 1,1,2,3,4-pentachlorodienyl cysteine derivative are

responsible for the observed effects on the proximal tubules of the nephrons. The cysteine derivative

is formed from the hexachlorobutadiene conjugate in the liver, intestines, and/or kidney through the
HEXACHLOROBUTADIENE 44

2. HEALTH EFFECTS

action of γ glutamyl transferase which removes the glutamate from the glutathione tripeptide followed

by the action of a peptidase that removes the glycine from the carboxy terminus.

The cysteine derivative is further metabolized to simpler sulphur derivatives through the action of βlyase. β-Lyase is present in the rodent liver, intestines, and kidneys (MacFarlane et al. 1989; Jones

et al. 1988). In the kidney, the highest concentration of β-lyase is located in the pars recta of the

proximal tubule, the same area that is damaged by hexachlorobutadiene. It should be noted that

β-lyase has been detected in the entire proximal segment (Jones et al. 1988). It is present in both the

cytosol and mitochondria and is pyridoxal phosphate dependent (MacFarlane et al. 1989). It degrades

the cysteine conjugate to pyruvate, ammonia, and one or more reactive thiols (Dekant et al. 1990b;

Schnellmann et al. 1987). A highly reactive thioketene (Figure 2-3) may form as an intermediate and

cause local tissue damage (Dekant et al. 1991; Koob and Dekant 1992).

The effects of the cysteine conjugate on the activity of the cells of the proximal tubules was evaluated

in cells from New Zealand white rabbits (Schnellmann et al. 1987). These studies indicate that the

metabolites of the cysteine conjugate alter the action of the mitochondria in a two phase process. The

first phase apparently causes an uncoupling of oxidative phosphorylation thereby preventing the

generation of ATP. The deficiency of ATP in turn limits ATP dependent active transport in the

tubules, inhibiting reabsorption processes. In the second phase, inhibition of cytochrome c-cytochrome

oxidase activity and electron transport occur (Schnellmann et al. 1987). These changes

result in cell damage as reflected in a decrease in the cellular retention of lactate dehydrogenase

approximately 1 hour after exposure.

The carcinogenic properties of hexachlorobutadiene are proposed to result from binding of the

sulfenic acid degradation product or a thioketene intermediate to cellular DNA (Dekant et al. 1990b;

Henschler and Dekant 1990). Cell necrosis is thought to stimulate replication of cells with altered

DNA, enhancing tumorigenesis.

2.4 RELEVANCE TO PUBLIC HEALTH

Data regarding the effects of exposure to hexachlorobutadiene on humans are sparse. Serum bile

acids were increased in workers exposed to vapor concentrations of 0.005-0.02 ppm. These effects

could not be attributed to hexachlorobutadiene alone because the workers were also potentially
HEXACHLOROBUTADIENE 45

2. HEALTH EFFECTS

exposed to other chemicals (carbon tetrachloride and perchloroethylene) and there were no

background data on employee health, smoking habits, alcohol consumption, or other confounding

variables. Animals have been studied more extensively. Although there are studies available on the

systemic (respiratory) effects following inhalation, data are not sufficient to identify a reliable

NOAEL value by this route. Much of the available data involve oral exposures in rats. The primary

health effect associated with intermediate-duration and chronic-duration oral exposures to

hexachlorobutadiene is kidney damage, which occurred in this organ at doses of 0.2 to 20 mg/kg/day.

The liver was affected to a lesser extent and effects occurred at doses of 6.3 or 15.6 mg/kg/day.

Acute dermal studies, although limited, confirm the toxic effects of hexachlorobutadiene on these

organs.

Hexachlorobutadiene did not adversely affect reproduction in animals except at high doses

(150 mg/kg/day for 10 weeks). Although there was some evidence of fetotoxicity in animals after

inhalation (10 ppm) or oral (15 mg/kg/day) exposure, embryolethality and teratogenicity were not

detected. Oral studies in animals indicate that hexachlorobutadiene may increase the risk of renal

cancer at dose levels of 20 mg/kg/day. The effects of hexachlorobutadiene are most pronounced after

repeated chronic exposure to low doses, suggesting that effects are cumulative. For this reason, there

is greater concern for populations living near hazardous waste sites, where exposure to low levels

may occur for long periods of time, than for acute exposure scenarios.

Minimal Risk Levels for Hexachlorobutadiene

Inhalation MRLs

Inhalation MRLs have not been derived for any duration category due to the lack of sufficient data to

identify a target organ and reliable NOAEL values.

Oral MRLs

• An MRL of 0.0002 mg/kg/day has been derived for intermediate-duration oral exposure

to hexachlorobutadiene.
HEXACHLOROBUTADIENE 46

2. HEALTH EFFECTS

This MRL was derived using a LOAEL value of 0.2 mg/kg/day, based on the presence of

kidney damage in female mice (NTP 1991). Tubular cell degeneration and regeneration in

the renal cortex were found in treated animals.

Other intermediate-duration oral studies confirm that the kidney is the primary target organ

following oral exposure to hexachlorobutadiene. Renal damage, characterized as tubular

hyperplasia, tubular epithelial degeneration, and tubular regeneration, was seen at dose

levels of 2 mg/kg/day or greater (Harleman and Seinen 1979; Schwetz et al. 1977). A

chronic study in rats reported renal tubular hyperplasia at dose levels of 2 mg/kg/day or

greater (Kociba et al. 1977a).

No data were located on the effects of acute-duration oral exposure in humans. Two studies are

available on the acute oral toxicity in animals. A LOAEL value of 4 mg/kg/day (based on kidney

effects) was reported in one study in rats exposed to hexachlorobutadiene for 14 days (Harleman and

Seinen 1979). On the other hand, a NOAEL value of 10 mg/kg was reported for kidney effects in a

24-hour rat study (Jonker et al. 1993a). Neither of these studies was considered suitable for the MRL

determination because of the small numbers of animals evaluated.

No data were located on the effects of chronic-duration exposure in humans. A chronic-duration

study in animals revealed tubular hyperplasia in rats at dose levels of 2 mg/kg/day or greater (Kociba

et al. 1977a), but not at 0.2 mg/kg/day, the LOAEL for kidney effects from the intermediate-duration

study in mice. Because the intermediate-duration MRL protects against chronic exposures, a chronic

MRL has not been proposed.

Death. No studies were located regarding lethality in humans. Hexachlorobutadiene reduced

survival in rats following acute- and chronic-duration exposures. Young rats may be more sensitive

than adult rats. Acute oral doses of 580 mg/kg (male) and 200-400 mg/kg (female) were lethal to

50% of adult rats. Death occurred at lower dose levels in weanling females (46 mg/kg) and males

(65 mg/kg) (Kociba et al. 1977a). However, in a rat reproduction study in which dams received

intermediate-duration oral exposures to hexachlorobutadiene at doses of 20 mg/kg/day during

gestation (days 1 to 22) and lactation (days l-21), pup survival was not affected even at doses that

were maternally toxic (Schwetz et al. 1977). Acute-duration dermal exposures (775 mg/kg) can also

reduce survival (50%) in animals (Duprat and Gradiski 1978). Based on these considerations,
HEXACHLOROBUTADIENE 47

2. HEALTH EFFECTS

lethality may be of concern in humans following exposure to hexachlorobutadiene. The basis for

differential susceptibility between adult and young rats may be due to metabolic differences or

differences in disposition of hexachlorobutadiene. As discussed in Section 2.3.2, hexachlorobutadiene

distributes to body fat. The smaller fraction of fat in the newborn reduces the amount of sequestered

hexachlorobutadiene; therefore, more of the compound may reach target organs (Hook et al. 1983).

Systemic Effects

Respiratory Effects. No studies were located regarding respiratory effects in humans. The only data

available indicating respiratory effects were reports of irritation of the nasal cavity in mice after acute

(15 minutes) inhalation of vapors of hexachlorobutadiene at concentrations of 155 ppm or greater (de

Ceaurriz et al. 1988). The importance of this finding to human health is uncertain.

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

animals, intermediate-duration or chronic-duration oral exposure to hexachlorobutadiene at dose levels

up to 100 mg/kg/day did not cause treatment-related lesions of the heart in rats or mice (Kociba et al.

1971, 1977a; NTP 1991; Schwetz et al. 1977; Yang et al. 1989). On the other hand, heart weights

decreased significantly in mice at doses of 16.8 mg/kg/day (NTP 1991; Yang et al. 1989) or

65 mg/kg/day or greater in rats (Kociba et al. 1971). There were no histopathological lesions.

Because treatment-related lesions were not observed even at doses higher than those causing other

organ toxicity, cardiovascular toxicity may not be an area of concern in humans following exposure to

hexachlorobutadiene.

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

Intermediate-duration (up to 100 mg/kg/day) or chronic-duration oral (20 mg/kg/day) exposure to

hexachlorobutadiene did not cause treatment-related lesions of the gastrointestinal tract in rats (Kociba

et al. 1971, 1977a; Schwetz et al. 1977). Because histological lesions were not observed even at

doses higher than those causing other organ toxicity, gastrointestinal toxicity may not be an area of

concern in humans following exposure to hexachlorobutadiene.

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

studies evaluating the hematological effects of hexachlorobutadiene involved mainly intermediate-duration

and chronic-duration oral exposures up to 20 mg/kg/day in rats (Harleman and Seinen 1979;
HEXACHLOROBUTADIENE 48

2. HEALTH EFFECTS

Kociba et al. 1977a; Schwetz et al. 1977). There was increased hemoglobin concentration in rats

after intermediate-duration oral exposure (10 mg/kg/day or greater) (Kociba et al. 1971). However,

hematocrit, red blood cell, and differential leucocyte counts were comparable to untreated controls.

For this reason, hematological effects may not be an area of major concern in humans following

exposure to hexachlorobutadiene.

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

Intermediate-duration or chronic-duration oral exposure to hexachlorobutadiene at dose levels up to

20 mg/kg/day did not cause treatment-related lesions of the musculoskeletal system in rats (Harleman

and Seinen 1979; Kociba et al. 1977a; Schwetz et al. 1977). Because histological lesions were not

observed even at doses higher than those causing other organ toxicity, musculoskeletal effects may not

be an area of concern in humans following exposure to hexachlorobutadiene.

Hepatic Effects. Data in humans are limited to one study which reported significant dose-related

increases in the concentration of serum bile acids in workers after inhalation exposure to

hexachlorobutadiene (0.005-0.02 ppm) (Driscoll et al. 1992). The practical importance of this

finding is reduced because workers were also potentially exposed to other solvents (carbon

tetrachloride and perchloroethylene) and background information on other confounding variables was

minimal. No studies were located regarding other hepatic effects in humans.

In animals, liver damage may occur after oral exposure to hexachlorobutadiene; however, the effects

are less severe than those associated with renal damage. Intermediate-duration oral exposures caused

liver damage in male rats at dose levels of 6.3 mg/kg/day or greater (Harleman and Seinen 1979;

Kociba et al. 1971). Histological lesions were not found in female rats. Relative liver weights were

increased in female rats, but occurred at higher dose levels (15 mg/kg/day) than in male rats

(6.3 mg/kg/day). In another study, liver weights were decreased in female rats at dose levels of

5 mg/kg/day or greater following exposure to hexachlorobutadiene for 4 weeks (Jonker et al. 1993b).

In the same study, serum biochemical parameters (aspartate aminotransferase activity and total

bilirubin) were increased at doses of 20 mg/kg/day. Urinary excretion of coproporphyrin increased at

dose levels of 20 mglkglday in lifetime studies; however, histopathological lesions were not found

(Kociba et al. 1977a).
HEXACHLOROBUTADIENE 49

2. HEALTH EFFECTS

Dermal studies in which rabbits received applications of hexachlorobutadiene (775 mg/kg or greater)

directly to the skin identified hepatocyte damage and fatty degeneration of the centrilobular area as

effects of exposure. Effects were reversible within 3 weeks (Duprat and Gradiski 1978). Studies

using intraperitoneal injection support findings of morphological alterations in the liver. A single

intraperitoneal dose of hexachlorobutadiene (100 mg/kg or greater) caused disruption of mitochondria

in periportal hepatocytes which resulted in an influx of water and ions into the cell without effects on

the sodium pump (Lock et al. 1982, 1985). Alterations in serum biochemical parameters have been

reported following intraperitoneal injection. Alkaline phosphatase activity increased (p < 0.05) at

doses of 52 mg/kg/day or greater (Bai et al. 1992). Aspartate aminotransferase activity and total

bilirubin levels decreased (p < 0.05) at a dose of 104 mg/kg/day (highest dose tested).

Renal Effects. No studies were located regarding renal effects in humans. Acute-, intermediate- and

chronic-duration oral studies in rats and mice revealed that the kidney is the primary target organ for

hexachlorobutadiene toxicity. Acute exposure (24 hours) to hexachlorobutadiene (100 mg/kg or

greater) caused focal necrosis and an increase in plasma creatinine levels (Jonker et al. 1993a). When

rats were exposed to hexachlorobutadiene (5 mg/kg/day) for 4 weeks, tubular cytomegaly was

reported (Jonker et al. 1993b). Tubular cell degeneration and regeneration in the renal cortex

occurred in female mice at dose levels of 0.2 mg/kg/day for 13 weeks (NTP 1991; Yang et al. 1989).

Tubular degeneration and cell necrosis occurred in rats after short duration exposures (30-148 days)

at dose levels of 20 or 30 mg/kg/day (Harleman and Seinen 1979; Kociba et al. 1971; Schwetz et al.

1977).

Lifetime exposures at dose levels from 2.5 mg/kg/day revealed renal hyperplasia in rats (Kociba et al.

1977a). For the most part, kidney lesions were more pronounced in females and occurred at lower

dose levels. Morphological changes were found in female rats in the 2.5 mg/kg/day dose groups,

whereas comparable alterations were first seen in male rats at dose levels of 6.3 mg/kg/day. Kidney

weights or kidney/body weight ratios were increased at dose levels causing morphological damage

(Harleman and Seinen 1979; Kociba et al. 1977a; NTP 1991; Schwetz et al. 1977; Yang et al. 1989).

Results of evaluations of impairment in kidney functions were consistent with morphological

alterations. The capacity to concentrate urine was reduced in female rats at dose levels of

2.5 mg/kg/day and in males at 15 mg/kg/day (Harleman and Seinen 1979). Although histological

lesions were not evident at the low dose in this study, kidney damage has been reported at comparable

dose levels following chronic oral exposures (Kociba et al. 1977a).
HEXACHLOROBUTADIENE 50

2. HEALTH EFFECTS

Biochemical indices (blood urea nitrogen, creatinine) were comparable to controls at dose levels up to

20 mg/kg/day in some studies (Harleman and Seinen 1979; Kociba et al. 1977a; Schwetz et al. 1977).

However, blood urea levels increased significantly at dose levels of 200 mg/kg (highest dose tested)

and creatinine levels increased at 100 mg/kg in an acute study (24 hours) (Jonker et al. 1993a).

Similarly, urinary lactate dehydrogenase and N-acetyl-β−glucosaminidase increased significantly in the

24 hours after exposure to a single dose of 100 mg/kg or greater. In a different study, blood

creatinine levels decreased in females at dose levels of 5 mg/kg/day or greater, while blood urea

levels decreased at doses of 1.25 mg/kg/day or greater hexachlorobutadiene for 4 weeks (Jonker et al.

1993b). Although statistically significant differences in biochemical parameters were found, the

importance of these effects is reduced because the effects were not completely dose-related.

Accordingly, these parameters may not be reliable indicators of renal damage following

hexachlorobutadiene exposure.

Kidney damage was also seen following an 8 hour dermal exposure in rabbits that received

applications of hexachlorobutadiene (775 mg/kg or greater). The effects were reversible within

3-5 weeks (Duprat and Gradiski 1978). Intraperitoneal studies revealed patterns of damage similar

to those for other routes and duration categories. Species differences were reported. Renal tubular

necrosis was evident in rats and was confined mainly to the straight limb of the proximal tubules

involving the medulla. Effects were evident within 24 hours at dose levels of 100 mg/kg (Lock and

Ishmael 1979). At higher (200 mg/kg) doses, necrosis was evident by 8 hours (Ishmael et al. 1982).

Studies in mice also revealed that hexachlorobutadiene causes damage to the proximal tubules of the

kidney; effects were observed at lower dose levels (50 mg/kg) than in rats and were observed in both

the cortex and the medulla (Ishmael et al. 1984). It was also noted that active regeneration of the

tubular epithelium was evident by 5 days after treatment, and by 14 days, tubular morphology had

returned to normal (Ishmael et al. 1984).

Metabolites of hexachlorobutadiene (glutathione conjugate, cysteine conjugate, and its N-acetyl

cysteine conjugate) produced effects at lower doses than the parent compound after intraperitoneal

injection and there was differential susceptibility between sexes (Ishmael and Lock 1986). A single

intraperitoneal dose of 25 mg/kg of the conjugates caused minimal to moderate necrosis in males and

severe necrosis in females. On the other hand, a comparable dose caused no effect in males and

females after exposure to the parent compound (Ishmael and Lock 1986).
HEXACHLOROBUTADIENE 51

2. HEALTH EFFECTS

One or two hexachlorobutadiene metabolites appear to cause some of the compound-induced renal

damage (see Section 2.3.5) and are more toxic than the parent compound, causing comparable lesions

in the kidneys at lower doses. These active thioacylating metabolites are capable of modifying DNA,

as indicated by the isolation of sulfur-containing nucleides from hydrolyzed DNA from renal cells

exposed to the hexachlorobutadiene cysteine derivative (Vamvakas et al. 1988b).

Overall, the kidney is highly susceptible to the toxicity of hexachlorobutadiene, in contrast to other

organs, due to the activity of β-lyase and other mercapturic acid processing enzymes (Vamvakas et al.

1988b). The greater sensitivity of females may be due to differences in renal enzymes responsible for

the tissue levels of the active metabolites (Hook et al. 1983). Based on data in animals, renal toxicity

is a major concern in humans who may be chronically exposed to this material from hazardous waste

sites or other sources.

Dermal/Ocular Effects. No studies were located regarding dermal/ocular effects in humans. Acuteduration dermal exposure caused skin necrosis in rabbits; however, effects were reversible within

2 weeks (Duprat and Gradiski 1978). Nasal irritation resulted from 15 minute exposure to vapor

concentrations of 155 ppm (de Ceaurriz et al. 1988). No dermal/ocular effects were seen following

intermediate- or chronic-duration dermal exposure in rabbits. Based on acute effects in rabbits,

hexachlorobutadiene may pose some risk to humans following skin contact with the chemical depending

on the area exposed. Inhalation of vapors may cause irritation of the nasal mucosa.

Immunological Effects. No studies were located regarding immunological effects in humans. Oral

intermediate or chronic exposures to hexachlorobutadiene did not produce treatment-related

histopathological lesions in lymphoid tissue (spleen or thymus) in mice (NTP 1991; Yang et al. 1989)

or rats (Harleman and Seinen 1979; Kociba et al. 1971, 1977a) after 13 weeks of exposure. Necrosis

of lymphoid tissue did occur in the spleen, lymphoids, and thymus of mice exposed to lethal doses

(NTP 1991; Yang et al. 1989). No data are available on immunological effects following acute-duration

oral exposure. In the absence of tests that evaluate impairment of immune functions, firm

conclusions cannot be made about the potential for hexachlorobutadiene to affect immune processes in

humans.

Neurological Effects. No studies were located regarding neurological effects in humans.

Intermediate oral exposure to hexachlorobutadiene caused damage to the nervous system in rats.
HEXACHLOROBUTADIENE 52

2. HEALTH EFFECTS

Ataxia associated with demyelination and fragmentation of femoral nerve fibers was reported in adult

female rats that received 150 mg/kg hexachlorobutadiene. Effects were not seen at lower dose levels

(15 mg/kg/day) (Harleman and Seinen 1979). No neurological effects were reported following

chronic oral exposures (Kociba et al. 1977a). Dermal application of 388-1550 mg/kg induced stupor

in rabbits during the 8-hour exposure period and for the 2-hour period immediately after exposure

(Duprat and Gradiski 1978). Although neurological symptoms were not present in all studies, these

data, and the fact that hexachlorobutadiene has been found in brain tissue, suggest neurological effects

may occur in humans following hexachlorobutadiene exposure.

Reproductive Effects. No studies were located regarding reproductive effects in humans. Acute-duration

inhalation exposure to hexachlorobutadiene (10 ppm) did not adversely affect sperm

morphology in mice (NIOSH 1981). In a developmental toxicity study, the mean number of

implantation sites, total fetal loss, and live fetuses per litter in rat dams exposed to 15 ppm

hexachlorobutadiene during gestation were comparable to unexposed controls (Saillenfait et al. 1989).

No data were found on intermediate- or chronic-duration inhalation exposure in mice. Intermediate-duration

oral exposure did not adversely affect fertility, gestation, viability, and lactation indices in

rats at dose levels of 20 mg/kg/day (Schwetz et al. 1977). Similarly, hexachlorobutadiene did not

adversely affect mean litter size and resorption rate in rats fed 15 mg/kg/day hexachlorobutadiene

(Harleman and Seinen 1979). There were no histological lesions in the gonads or accessory sex

organs after intermediate- or chronic-duration exposures (Kociba et al. 1977a; Schwetz et al. 1977).

Based on these data and the fact that the compound has not been detected in reproductive tissue,

hexachlorobutadiene does not appear to pose a significant risk to human reproduction.

Developmental Effects. No studies were located regarding developmental effects in humans. In

intermediate-duration inhalation animal studies, fetal body weight was reduced in rat pups following

exposure of dams to hexachlorobutadiene vapors at concentrations of 15 ppm for 15 days (Saillenfait

et al. 1989). After intermediate oral exposure in rat dams administered hexachlorobutadiene (during

gestation and lactation) at dose levels of 20 mg/kg/day, body weights decreased on lactation day 21

(Schwetz et al. 1977) and pup weights were reduced at dose levels of 15 mg/kg/day for 6 weeks

(during gestation and lactation) during an 18 week study (Harleman and Seinen 1979). In both cases,

no other fetotoxic effects were reported. Similar results were found in rat pups of dams administered

a single dose of hexachlorobutadiene by intraperitoneal injection at dose levels of 10 mg/kg (Hardin

et al. 1981). Because the fetotoxic effects occurred at concentrations that were also maternally toxic
HEXACHLOROBUTADIENE 53

2. HEALTH EFFECTS

and the fact that embryolethality and major malformations were not observed, it is not likely that low

levels of hexachlorobutadiene will pose any significant risk to renal development and function in

humans.

Genotoxic Effects. No studies were located regarding genotoxic effects in humans. For the most

part, acute inhalation studies evaluating chromosomal damage in rats and gene mutation in Drosophila

revealed that hexachlorobutadiene is not mutagenic (NIOSH 1981). On the other hand, results of oral

studies in rats do not agree suggesting differences in activation and detoxification.

Hexachlorobutadiene can affect genetic material as evident by the induction of DNA repair and

alkylation (Stott et al. 1981) (Table 2-4). The compound did not cause chromosomal aberrations in

rat bone marrow cells (Schwetz et al. 1977).

Several in vitro assays have been evaluated; however, results were mixed, suggesting differences in

activation and detoxification mechanisms (Table 2-5). In bacterial assay systems employing

Salmonella typhimurium, hexachlorobutadiene was not mutagenic either in the presence or absence of

metabolic activation (DeMeester et al. 1980; Haworth et al. 1983; Reichert et al. 1983; Stott et al.

1981; Vamvakas et al. 1988a) or in the presence of activation (Roldan-Arjona et al. 1991). On the

other hand, results were positive in other bacterial assays employing S. typhimurium (Reichert et al.

1984; Roldan-Arjona et al. 1991; Vamvakas et al. 1988a). Certain metabolites of

hexachlorobutadiene have also been evaluated. Monooxidation products of hexachlorobutadiene were

mutagenic in Salmonella with and without metabolic activation (Reichert et al. 1984). Similarly,

monooxidation products induced unscheduled DNA synthesis as well as morphological transformations

in cultured Syrian hamster embryo fibroblasts (Schiffmann et al. 1984). However, results did not

agree for hexachlorobutadiene in an in vitro unscheduled DNA synthesis assay employing rat

hepatocytes (Stott et al. 1981). Studies of cysteine conjugates of hexachlorobutadiene reported that

N-acetyl-S-pentachlorobutadienyl-L-cysteine (mercapturic acid) and D,L-homocysteinate derivatives

were mutagenic in S. typhimurium, while mercaptoacetic acid and methylthioether derivatives were

inactive (Wild et al. 1986). In other tests employing S. typhimurium, one cysteine conjugate was

mutagenic both with and without activation (Dekant et al. 1986). Overall, results suggest that

genotoxicity may not be a major factor in the toxicity of hexachlorobutadiene in humans. On the

other hand, some influence of genetic mechanisms cannot be ruled out since there was limited

evidence of renal DNA repair and alkylation (Stott et al. 1981).



HEXACHLOROBUTADIENE 57

2. HEALTH EFFECTS

Cancer. No studies were located regarding the carcinogenic potential of hexachlorobutadiene in

humans. It is carcinogenic in rats after lifetime oral exposures. The incidence of adenomas and

adenocarcinomas in the kidney increased over control levels at doses of 20 mg/kg/day. Two

neoplasms metastasized to the lungs (Kociba et al. 1977a). The IARC (1979) evaluated the

carcinogenic potential of hexachlorobutadiene and concluded there was limited evidence that

hexachlorobutadiene is carcinogenic in rats. EPA considers hexachlorobutadiene to be a possible

human carcinogen (Group C) (IRIS 1993).

Several studies have assessed the mechanism of hexachlorobutadiene-induced renal tumorigenesis (see

Section 2.3.5). The carcinogenic properties of hexachlorobutadiene may result from binding of

intermediary metabolites to cellular DNA (Dekant et al. 1990b; Henschler and Dekant 1990). In

addition, the occurrence of renal tubular regeneration suggests that cell repair processes which induce

the replication of cells with altered DNA may be a factor in the tumorigenesis process. Based on

carcinogenic effects in rats, exposure to hexachlorobutadiene may pose some risk for development of

kidney tumors in humans.

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
HEXACHLOROBUTADIENE 58

2. HEALTH EFFECTS

are commonly found in body tissues and fluids (e.g., essential mineral nutrients such as copper, zinc,

and selenium). Biomarkers of exposure to hexachlorobutadiene 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 impairment (e.g., DNA adducts).

Biomarkers of effects caused by hexachlorobutadiene 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 Hexachlorobutadiene

Human exposure to hexachlorobutadiene can be determined by measuring the parent compound in

blood and adipose tissue (Bristol et al. 1982; Mes et al. 1985). Data in animals are limited, but do

suggest that hexachlorobutadiene can be detected in urine and exhaled air. Approximately 4-31% of

the administered radioactivity was detected in the urine of mice or rats within 72 hours following the

administration of single oral doses of 14C-hexachlorobutadiene (l-200 mg/kg) (Dekant et al. 1988b;

Nash et al. 1984; Reichert and Schutz 1986; Reichert et al. 1985). No information was located on

how long before it can no longer be detected. Unmetabolized hexachlorobutadiene was detected in

exhaled air after animals were given doses of l-100 mg/kg (Dekant et al. 1988b; Payan et al. 1991;

Reichert et al. 1985).

Cysteine conjugates of hexachlorobutadiene are converted to thio derivatives (e.g., 1,1,2,3,4-

Pentachlorobutadiene methylthioether and 1,1,2,3,4-pentachlorobutadiene carboxy methylthioether) which

have been detected in urine (Reichert et al. 1985). Accordingly, tests to determine concentrations of
HEXACHLOROBUTADIENE 59

2. HEALTH EFFECTS

these sulfur derivatives in urine may be useful in determining if exposure to hexachlorobutadiene has

occurred.

2.5.2 Biomarkers Used to Characterize Effects Caused by Hexachlorobutadiene

Data are sparse regarding biomarkers of the effects of hexachlorobutadiene in humans. Workers

chronically exposed to the compound (along with carbon tetrachloride and perchloroethylene) had

increased serum bile acids (Driscoll et al. 1992). Because the workers were also exposed to other

chemicals, effects reported cannot be attributed to hexachlorobutadiene alone.

As discussed in Section 2.2, renal damage is the primary toxic effect associated with exposure to

hexachlorobutadiene in animals (Harleman and Seinen 1979; Kociba et al. 1971, 1977a; NTP 1991;

Schwetz et al. 1977). Because hexachlorobutadiene-induced renal damage is mostly to the proximal

convoluted tubules, tests to determine increases in urine glucose creatinine and alkaline phosphatase

activity, as well as molecular weight pattern of proteins excreted in the urine, may be useful

indicators of kidney damage. Urine volume and specific gravity may be evaluated as part of the

overall assessment of kidney damage after exposure to hexachlorobutadiene. Excretion of urinary

coproporphyrin was increased in animals at dose levels that did not induce renal tumors. This

parameter may be useful in the overall assessment of potential exposure to hexachlorobutadiene. The

characteristics renal damage associated with hexachlorobutadiene exposure may also occur with other

compounds (e.g., S-C 1,2-dichlorovinyl cysteine and mercuric chloride). Therefore, these parameters

are not specific for hexachlorobutadiene exposure. Additional information concerning biomarkers for

effects on the immune, renal, and hepatic systems can be found in the CDC/ATSDR Subcommittee

Report on Biological Indicators of Organ Damage (CDC/ATSDR 1990), and on the neurological

system in the Office of Technology Assessment Report on Identifying and Controlling Poisons of the

Nervous System (OTA 1990).

2.6 INTERACTIONS WITH OTHER CHEMICALS

Several studies have been conducted to assess factors which influence the toxicity of

hexachlorobutadiene. Most of these studies have involved effects of mixed function oxidase activity

(MFO) on renal toxicity. The administration of MFO inhibitors including SKF-525A (Lock and

Ishmael 1981) and piperonyl butoxide (Davis 1984; Hook et al. 1982) did not alter
HEXACHLOROBUTADIENE 60

2. HEALTH EFFECTS

hexachlorobutadiene-induced renal damage. Similar results were reported in tests evaluating MFO

inducers such as phenobarbital (Lock and Ishmael 1981), β-naphthoflavone, isosafrole, and Aroclor

1254 (Hook et al. 1982). Renal toxicity was not exacerbated by prior exposure to ketonic solvents

(Hewitt and Brown 1984).

There are reports of interactions of hexachlorobutadiene with other chemicals. Combined

administration of minimally toxic doses of hexachlorobutadiene with mercuric chloride and potassium

dichromate for 24 hours caused synergistic effects as evident by marked increases in urinary

(6-24 hour) alkaline phosphatase, lactate dehydrogenase and N-acetyl-β-glucosaminidase activities, as

well as more severe tubular necrosis than caused by treatment with hexachlorobutadiene alone (Jonker

et al. 1993a). Antagonistic effects were evident as characterized by smaller increases in urinary γ-glutamyl

transferase activity compared to treatment with hexachlorobutadiene alone. Combined

administration of the same chemicals did not cause additive interactions regarding biochemical

parameters or histopathological changes in the kidney (Jonker et al. 1993a). An additional study

revealed that when animals are treated for 4 weeks with minimally toxic doses of hexachlorobutadiene

in combination with other chemicals (mercuric chloride, δ-limonene, and lysinoalanine), there is an

increase in growth retardation and renal toxicity (renal weight, urine concentrating ability, and renal

structure) in male rats but not in females (Jonker et al. 1993b).

2.7 POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE

A susceptible population will exhibit a different or enhanced response to hexachlorobutadiene than

will most persons exposed to the same level of hexachlorobutadiene in the environment. Reasons

include genetic make-up, developmental stage, age, health and nutritional status (including dietary

habits that may increase susceptibility, such as inconsistent diets or nutritional deficiencies), and

substance exposure history (including smoking). These parameters result in decreased function of the

detoxification and excretory processes (mainly hepatic, renal, and respiratory) or the pre-existing

compromised function of target organs (including effects or clearance rates and any resulting endproduct

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.
HEXACHLOROBUTADIENE 61

2. HEALTH EFFECTS

Studies in animals revealed that hexachlorobutadiene causes damage to the proximal tubules of the

kidney and, to a lesser extent, to the liver. Accordingly, people with preexisting kidney and liver

damage may have compromised organ functions and are expected to be more vulnerable to chemical

insult than people with normal kidney and liver functions. Infants are more likely to be affected

following exposure to hexachlorobutadiene than adults. Studies in animals showed that young rats

were more sensitive to the acute lethal effects of hexachlorobutadiene than adults. This greater

susceptibility in newborns can be attributed to immature organ systems.

2.8 METHODS FOR REDUCING TOXIC EFFECTS

This section will describe clinical practice and research concerning methods for reducing toxic effects

of exposure to hexachlorobutadiene. 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

hexachlorobutadiene. 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

Exposure to hexachlorobutadiene can occur by inhalation of vapors, ingestion, and dermal contact.

The compound can cause kidney damage and, to a lesser extent, liver damage after ingestion or if it

comes in contact with skin.

Information regarding methods for reducing absorption following exposure to hexachlorobutadiene

was obtained primarily from the HSDB. No other sources were available. If inhalation of

hexachlorobutadiene has occurred, movement of the patient to fresh air is recommended. No specific

treatment is available; however, patients are usually monitored for respiratory distress, respiratory

tract irritation, bronchitis and pneumonia. If there has been substantial ingestion of the compound,

syrup of ipecac is administered within 30 minutes of ingestion to induce vomiting. Syrup of ipecac is

usually not given in cases of severe central nervous system depression or coma because there is risk

of pulmonary aspiration. The absorption of hexachlorobutadiene may be reduced following oral

exposure by binding the compound in the gastrointestinal tract. Activated charcoal in the form of

aqueous suspension or sorbitol slurry may be administered for this purpose. However, if syrup of

ipecac is given within 1 hour of ingestion of activated charcoal, it is not effective. Another suggested
HEXACHLOROBUTADIENE 62

2. HEALTH EFFECTS

treatment following oral ingestion of hexachlorobutadiene may be a cathartic, such as magnesium or

sodium sulfate to speed fecal excretion. Lipids are not usually given by mouth because this may

increase absorption. In cases where hexachlorobutadiene has been splashed into the eyes, irrigation

with copious amounts of water for 15 minutes has been recommended. In order to minimize

absorption through the skin, areas of skin that have come in contact with the compound should be

washed with soap and water.

2.8.2 Reducing Body Burden

No information was located on the retention of hexachlorobutadiene or its metabolites in humans. In

animals, the compound and its metabolites were detected in urine and areas extent in breath within

3 days after exposure. Adverse effects were seen within 24 hours, suggesting that the compound and

its metabolites are toxic while retained in the body.

There are no specific treatments for reducing the body burden following absorption of

hexachlorobutadiene. As discussed in Section 2.3, there is extensive reabsorption and enterohepatic

recirculation of biliary metabolites, which are thought to play a major role in the nephrotoxicity of the

compound. One approach to reducing body burden may involve the administration of compounds that

would decrease reabsorption of biliary metabolites. Activated charcoal may be used for this purpose.

2.8.3 Interfering with the Mechanism of Action for Toxic Effects

No information is available on treatment methods that employ substances that interfere with the

mechanism of toxicity of hexachlorobutadiene. Studies in animals indicate that hexachlorobutadiene

exerts its effects on the proximal tubules of the kidney. The major portion of the toxicity of

hexachlorobutadiene results from initial formation of glutathione conjugates of the compound and the

subsequent uptake of the glutathione-derived conjugates by renal tissues through an organic transport

mechanism. Thus, prevention of transport of conjugate anions may reduce the toxicity associated

with exposure to hexachlorobutadiene. Use of a uricosuric agent such as probenecid may be an

effective treatment. In animals, probenecid blocked the accumulation of a mercapturic acid derivative

of hexachlorobutadiene, in renal tissue, the extent of covalent binding of radioactivity to renal protein,

and the nephrotoxicity (Lock and Ishmael 1985).
HEXACHLOROBUTADIENE 63

2. HEALTH EFFECTS

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 hexachlorobutadiene 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 hexachlorobutadiene.

The following categories of possible data needs have been identified by a joint team of scientists from

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met

would reduce the uncertainties of human health assessment. This definition should not be interpreted

to mean that all data needs discussed in this section must be filled. In the future, the identified data

needs will be evaluated and prioritized, and a substance-specific research agenda will be proposed.

2.9.1 Existing Information on Health Effects of Hexachlorobutadiene

The existing data on health effects of inhalation, oral, and dermal exposure of humans and animals to

hexachlorobutadiene are summarized in Figure 2-4. The purpose of this figure is to illustrate the

existing information concerning the health effects of hexachlorobutadiene. 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.

As shown in Figure 2-4, information was located regarding health effects of hexachlorobutadiene in

humans after inhalation exposure but not after oral or dermal exposure.

HEXACHLOROBUTADIENE 65

2. HEALTH EFFECTS

In animals, information exists on lethality, acute systemic effects (respiratory), reproductive and

developmental effects, and cancer following inhalation exposure, but none was found on other

systemic effects after acute, intermediate, or chronic exposure. Much of the information in animals

focused on oral exposure. Lethality, systemic effects after acute, intermediate and chronic exposures,

immunotoxicity, developmental effects, reproductive effects, genotoxicity, and cancer have been

evaluated. Reports on dermal exposure after direct application to the skin involved lethality, acute

systemic effects (kidney, liver, dermal/ocular), and cancer.

2.9.2 Identification of Data Needs

Acute-Duration Exposure. No data are available on the effects of hexachlorobutadiene in humans

after acute exposure by inhalation, oral, and dermal routes. Hexachlorobutadiene (50 ppm) was lethal

in mice after acute (5 days) inhalation exposure and caused irritation of the nasal cavities following

15 minute exposures to concentrations of 15 ppm or greater (de Ceaurriz et al. 1988; NIOSH 1981).

Because sufficient data are not available to determine target organs or determine critical effect levels,

an acute inhalation MRL cannot be determined.

In one acute-duration (24-hour) oral study in rats, hexachlorobutadiene caused focal necrosis of the

kidneys and increased urinary biochemical parameters at doses of 100 mg/kg (Jonker et al. 1993a).

Another acute-duration (14 days) oral exposure study revealed that hexachlorobutadiene caused renal

tubular epithelial degeneration in rats at dose levels of 4.6 mg/kg/day or greater but no effects were

seen in the liver up to doses of 35 mg/kg/day (Harleman and Seinen 1979). The number of animals

in both of these studies were small and, thus, the data were not suitable for derivation of an MRL.

Acute-duration dermal exposure to hexachlorobutadiene (388 mg/kg) caused liver and kidney damage

in rabbits. For the most part, these effects were reversible within 2-5 weeks (Duprat and Gradiski

1978). In the same dermal study, some rabbits died within 24 hours after exposure to 775 mg/kg

hexachlorobutadiene applied directly to the skin for 8 hours, but no deaths occurred at dose levels of

388 mL/kg (Duprat and Gradiski 1978). However, due to the lack of an appropriate methodology for

the development of dermal MRLs, no dermal MRLs were derived. Although the vapor pressure of

hexachlorobutadiene limits vapor concentration in the air, short-term inhalation exposures are possible

and worthy of investigation. There is potential for oral exposures in populations living near
HEXACHLOROBUTADIENE 66

2. HEALTH EFFECTS

hazardous waste sites; therefore, additional short-term animal studies by oral routes may be useful to

more thoroughly assess the potential human health risk.

Intermediate-Duration Exposure. No data are available on the effects of hexachlorobutadiene in

humans after intermediate-duration inhalation, oral, or dermal exposures. In animals, data on

inhalation exposure are limited to one developmental toxicity study in rats in which maternal body

weights were reduced at a concentration (15 ppm) that was also fetotoxic (Saillenfait et al. 1989).

Oral studies revealed kidney damage in female mice at dose levels of 0.2 mg/kg/day (NTP 1991;

Yang et al. 1989). This LOAEL was used to derive an intermediate-duration oral MRL of

0.0002 mg/kg/day .

Liver damage was evident in male rats at dose levels of 6.3 mg/kg/day but not at dose levels of

2.5 mg/kg/day for 13 weeks (Harleman and Seinen 1979). Treatment-related histopathological

hepatic lesions were not seen in females. Some serum biochemical parameters (aspartate

aminotransferase and total bilirubin), were increased at doses of 20 mg/kg/day for 4 weeks (Jonker

et al. 1993b). No data are available on the effects of hexachlorobutadiene in animals after

intermediate-duration dermal exposure. Inhalation exposure to vaporous hexachlorobutadiene can

occur when this material is exposed to the environment. Studies of toxicity from material absorbed

through the lungs are justified.

Chronic-Duration Exposure and Cancer. Data in humans are limited to one study that reported

increases in serum bile acids in workers chronically exposed to vapors of hexachlorobutadiene

(0.005-0.02 ppm). Because workers were also potentially exposed to other chemicals (carbon

tetrachloride and perchloroethylene), these effects cannot be attributed to hexachlorobutadiene

exposure alone. No studies are available on the effects of hexachlorobutadiene in humans after oral

or dermal exposure.

In animals, a chronic-duration oral rat study showed that the kidney was the target organ following

chronic exposure to hexachlorobutadiene. Kidney damage as well as evidence of impaired kidney

function were evident in female rats at dose levels of 2 mg/kg/day, but not at 0.2 mg/kg/day (Kociba

et al. 1977a). Since the intermediate-duration oral MRL is protective against affects on the kidney

following lifetime exposure, a chronic MRL was not derived. Data are not available to derive a
HEXACHLOROBUTADIENE 67

2. HEALTH EFFECTS

chronic inhalation MRL. This data need can be evaluated after the results of the suggested acute- and

intermediate-duration research becomes available.

No epidemiological studies of hexachlorobutadiene are available. The occurrence of renal tumors

after chronic oral exposure in rats suggests carcinogenicity may be an area of concern following

occupational exposure to hexachlorobutadiene and long-term exposures from waste sites.

Genotoxicity. No information is available on the genotoxic effects of hexachlorobutadiene in

humans. Following exposure to hexachlorobutadiene, results were negative in in vivo rat and

Drosophila tests that evaluated gene mutation and chromosomal damage (NIOSH 1981). The results

were negative in in vitro tests evaluating gene mutation (De Meester et al. 1980; Haworth et al. 1983;

Reichert et al. 1983; Vamvakas et al. 1988a) and DNA repair in Salmonella tests (with and without

metabolic activation), and positive in mammalian assay systems using Syrian hamster cells

(Schiffmann et al. 1984); the overall results were not consistent. Studies of hexachlorobutadiene

metabolites have indicated that some of the cysteine derived metabolites are mutagenic while others

are not (Wild et al. 1986). Additional studies of the genotoxicity of intermediary metabolites are

needed.

Reproductive Toxicity. No data are available on the reproductive toxicity of hexachlorobutadiene

in humans. Hexachlorobutadiene did not cause adverse reproductive effects in mice or rats after

inhalation or oral exposures, even at dose levels causing kidney and liver damage (Harleman and

Seinen 1979; Kociba et al. 1977a; NIOSH 1981; NTP 1991; Saillenfait et al. 1989; Schwetz et al.

1977). No data are available on the reproductive toxicity of hexachlorobutadiene after dermal

exposure. Based on existing data in animals, it does not appear that exposure to the compound would

pose any significant risk to human reproduction.

Developmental Toxicity. No studies were located regarding developmental effects in humans.

Inhalation and oral studies in rat pups revealed that hexachlorobutadiene is fetotoxic, but not

embryotoxic or teratogenic, at dose levels that are also maternally toxic (Harleman and Seinen 1979;

Saillenfait et al. 1989; Schwetz et al. 1977). Additional oral studies in another species would be

useful in clarifying the apparent lack of significant effects of hexachlorobutadiene on development.

Systemic toxicity studies in rabbits suggest there is potential for dermal absorption to
HEXACHLOROBUTADIENE 68

2. HEALTH EFFECTS

hexachlorobutadiene (Duprat and Gradiski 1978). However, the toxicokinetics of this compound by

this route has not been evaluated.

Immunotoxicity. No data are available on the immunotoxicity of hexachlorobutadiene in humans

following inhalation, oral, or dermal exposure. Data in animals are limited to intermediate and

chronic oral studies which examined histological lesions of lymphoid tissue (spleen or thymus) in

mice and rats. These studies did not reveal treatment-related lesions except at lethal doses (Harleman

and Seinen 1979; Kociba et al. 1971, 1977a; NTP 1991; Schwetz et al. 1977; Yang et al. 1989).

Additional studies to evaluate immune function via the oral route would be useful to determine

whether this system is susceptible to hexachlorobutadiene toxicity.

Neurotoxicity. No data are available on the neurotoxicity of hexachlorobutadiene in humans after

inhalation, oral, or dermal exposure. Histological lesions were not found in the brain in rats

(Harleman and Seinen 1979; Kociba et al. 1971; Schwetz et al. 1977) or mice (NTP 1991; Yang

et al. 1989). Brain weights were increased after intermediate-duration oral exposure (Kociba et al.

1971). However, such increases were attributed to decreases in body weight gain. Neurological

effects were not seen after chronic-duration oral exposure in rats (Kociba et al. 1977a). A

comprehensive battery of neurophysiological and neurochemical tests has not been performed and is

needed to provide a more thorough assessment of the potential for hexachlorobutadiene to affect the

nervous system in humans.

Epidemiological and Human Dosimetry Studies. Information is not available on the adverse

health effects of hexachlorobutadiene in humans. Data on rats and mice identified the kidney as the

target organ following oral exposure (Harleman and Seinen 1979; Kociba et al. 1971, 1977a; NTP

1991; Yang et al. 1989). Other studies involving inhalation or dermal exposures confirm this finding

(de Ceaurriz et al. 1988; Duprat and Gradiski 1978). Well-conducted epidemiological studies are

needed to determine if similar patterns of damage occur in humans. More importantly, evidence of

cancer in animals is sufficient to cause concern for populations which may be exposed to low levels of

hexachlorobutadiene for long periods of time.

Biomarkers of Exposure and Effect. There is no single biological indicator of exposure to

hexachlorobutadiene. Various tests of renal function and biochemical changes associated with renal

damage may be measured to detect effects resulting from short-term, intermediate, and long-term
HEXACHLOROBUTADIENE 69

2. HEALTH EFFECTS

exposure. Because similar effects can also occur following exposure to other substances, these tests

are not specific for hexachlorobutadiene exposure. Although hexachlorobutadiene and its metabolites

are excreted in urine, the metabolism of the compound has not been characterized in humans.

Additional tests addressing the dose-response relationship between hexachlorobutadiene excretion in

breath and the excretion of sulfur-containing metabolites in urine would prove valuable.

Absorption, Distribution, Metabolism, and Excretion. Data are available on the

pharmacokinetics of hexachlorobutadiene in animals by the oral route, but not in humans. There are

no data in humans or animals on exposures to hexachlorobutadiene by the inhalation or dermal routes.

Because of the key role of the liver in producing the metabolites which are responsible for the

nephrotoxicity of this compound, knowledge of the pharmacokinetics of inhalation and dermal

exposures would be valuable. Oral studies reported the presence of the enzymes responsible for the

glutathione conjugation reaction and the subsequent formation of derivatives in the liver, intestines,

and kidney. It is not known at this time how hexachlorobutadiene is distributed and metabolized by

inhalation and dermal routes. It is postulated that distribution and metabolism by these routes would

be similar to that for the oral route.

Comparative Toxicokinetics. There are no data on metabolism of hexachlorobutadiene in humans.

On the other hand, toxic metabolites and proposed mechanism of renal toxicity have been evaluated in

animals employing both in vivo and in vitro test systems (Dekant et al. 1990b; Schneumann et al.

1987). It is not known if similar metabolic pathways and metabolites occur in humans.

Methods for Reducing Toxic Effects. Sufficient methods and treatments are available for

reducing peak absorption of hexachlorobutadiene following oral exposure and for limiting the

concentrations in the body tissues if absorption has occurred (HSDB 1993). However, antidotal

methods have not been established that would be effective in treating overdoses of

hexachlorobutadiene, based on interference with the mechanism of action of the compound. A key

factor in the overall toxicity of hexachlorobutadiene is the accumulation of glutathione derived

conjugates in renal tissue due to hexachlorobutadiene-induced impairment of organic ion transport and

secretion. Further studies to identify ways to prevent or reduce accumulation in the target tissue are

warranted.
HEXACHLOROBUTADIENE 70

2. HEALTH EFFECTS

2.9.3 On-going Studies

A study is being conducted by R.G. Schnellmann (University of Georgia) for the National Institute of

Environmental Health Sciences to evaluate the mechanism of nephrotoxicity of halocarbons, including

hexachlorobutadiene. The mechanism of how metabolites alter proximal tubular cellular physiology

to produce toxicity is being investigated, with particular emphasis on the effects of metabolites on

mitochondria (CRISP 1993).
HEXACHLOROBUTADIENE 71

3. CHEMICAL AND PHYSICAL INFORMATION

3.1 CHEMICAL IDENTITY

Information regarding the chemical identity of hexachlorobutadiene is located in Table 3-l.

3.2 PHYSICAL AND CHEMICAL PROPERTIES

Information regarding the physical and chemical properties of hexachlorobutadiene is located in

Table 3-2.



HEXACHLOROBUTADIENE 75

4. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL

4.1 PRODUCTION

Hexachlorobutadiene was first prepared in 1877 by the chlorination of hexyl oxide (IARC 1979).

Commercial quantities of hexachlorobutadiene have never been produced in the United States. The

primary source of hexachlorobutadiene found in the United States is inadvertent production as a waste

by-product of the manufacture of certain chlorinated hydrocarbons, such as tetrachloroethylene,

trichloroethylene, and carbon tetrachloride (EPA 1980; Yang 1988). In 1982, EPA reported an

annual volume of about 28 million pounds of hexachlorobutadiene inadvertently produced as a waste

by-product from this source (EPA 1982b; HSDB 1993). Table 4-l summarizes information on U.S.

companies that reported the production, import, or use of hexachlorobutadiene in 1990 based on the

Toxics Release Inventory TRI90 (1992). The TRI data should be used with caution since only certain

types of facilities are required to report. This is not an exhaustive List.

4.2 IMPORT/EXPORT

Since 1974, most hexachlorobutadiene used commercially in the United States has been imported from

Germany. Imported quantities remained fairly constant in the late 1970s, averaging about

500,000 pounds annually, but dropped to 145,000 pounds in 1981 (EPA 1980; 1982d). More recent

information on the volume of imported hexachlorobutadiene is not available (NTP 1991).

4.3 USE

Hexachlorobutadiene is used as a chemical intermediate in the manufacture of rubber compounds

(EPA 1982d). Lesser quantities of hexachlorobutadiene are used as a solvent, a fluid for gyroscopes,

a heat transfer liquid, hydraulic fluid, and as a chemical intermediate in the production of

chlorofluorocarbons and lubricants (EPA 1980; IARC 1979; Verschueren 1983). Small quantities are

also used as a laboratory reagent (EPA 1982d). In the international market, Russia is reported to be

one of the major users of hexachlorobutadiene, where it is used as a fumigant on grape crops.

HEXACHLOROBUTADIENE 77

4. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL

Hexachlorobutadiene is also used as a fumigant in France, Italy, Greece, Spain and Argentina (IARC

1979; NTP 1991). Prior to 1975, the largest domestic use of hexachlorobutadiene was for the

recovery of “snift” (chlorine-containing) gas in chlorine plants (HSDB 1993). More recent

information from U.S. chlorine producers indicates that hexachlorobutadiene is no longer used for this

process (EPA 1982d; IARC 1979).

4.4 DISPOSAL

Waste streams resulting from the inadvertent production of hexachlorobutadiene as a byproduct of

certain chlorinated hydrocarbons typically contain 33-80% hexachlorobutadiene. These wastes are

disposed of by various methods. Over the last decade, disposal practices have shifted from landfilling

to incineration. Incineration, which is considered the preferred method of disposal, reportedly

achieves greater than 99.9% destruction efficiency (EPA 1982d). In 1982, approximately 68% of an

estimated 27 million pounds of hexachlorobutadiene wastes were disposed of by incineration, 32% by

deep well injection, and less than 0.2% by hazardous waste landfill operations (EPA 1982d).

The generation, treatment, storage and disposal of hexachlorobutadiene-containing wastes are subject

to regulation under RCRA (see Chapter 7). Underground injection of hexachlorobutadiene is subject

to permits issued under an Underground Injection Control program promulgated under the Safe

Drinking Water Act (EPA 1982d).

According to TRI90 (1992), 84,345 pounds of hexachlorobutadiene were transferred to landfills

and/or other treatment/disposal facilities and 958 pounds were sent to publicly-owned treatment works

in 1990.

HEXACHLOROBUTADIENE 79

5. POTENTIAL FOR HUMAN EXPOSURE

5.1 OVERVIEW

There are no known natural sources of hexachlorobutadiene which contribute to environmental levels.

The main source of hexachlorobutadiene in the United States is its production as a by-product of

chlorinated hydrocarbon synthesis. An estimated 100,000 pounds of this by-product are released to

the environment each year. The majority of hexachlorobutadiene-containing waste is disposed of by

incineration, with lesser amounts disposed by deep well injection and landfill.

Literature data regarding the fate and transport of hexachlorobutadiene are limited. Much of the

available information consists of modeling based on the physical and chemical properties of

hexachlorobutadiene, and the monitoring data. These data indicate that hexachlorobutadiene will bind

to soil particles and sediments, and is found in air and water bound to particulates. Some

volatilization of hexachlorobutadiene from surface waters and soils may also occur. The

bioconcentration of hexachlorobutadiene has been reported in fish and shellfish with considerable

variability between species (EPA 1976; Oliver and Niimi 1983; Pearson and McConnell 1975).

Data regarding the transformation and degradation of hexachlorobutadiene are limited. Much of the

available information consists of modeling based on the monitoring data and by analogy to structurally

similar compounds. Hexachlorobutadiene may react with reactive oxygen species in air for which the

half-life has been estimated to range from months to years. Under aerobic conditions, but not

anaerobic conditions, hexachlorobutadiene undergoes complete biodegradation in water. The

observations in water are believed to hold true for soils as well.

Low levels of hexachlorobutadiene can be detected in air, water, and sediment. Atmospheric levels

of hexachlorobutadiene in rural and urban air samples typically range from 2 to 11 ppt, with a mean

value of 2-3 ppt. Higher levels can be detected at areas near industrial and chemical waste disposal

sites and production sites. Hexachlorobutadiene is infrequently detected in ambient waters, but has

been detected in drinking water at levels of 2-3 ppt. Sediments contain higher levels of

hexachlorobutadiene than the waters from which they were obtained. Foodstuffs generally do not
HEXACHLOROBUTADIENE 80

5. POTENTIAL FOR HUMAN EXPOSURE

contain detectable levels of hexachlorobutadiene, with the exception of fish, in which concentrations

of 0.1-4.7 mg/kg have been reported.

Hexachlorobutadiene has been detected in human adipose tissue and blood samples. These data

indicate that exposure to hexachlorobutadiene does occur in humans, however route-specific estimates

of hexachlorobutadiene exposure were not located. Based on monitoring data, individuals who work

in hexachlorobutadiene-producing facilities, live at or near hazardous waste facilities, or consume

large amounts of hexachlorobutadiene-contaminated fish may have above-average exposures to

hexachlorobutadiene.

Hexachlorobutadiene has been identified in at least 45 of the 1,350 hazardous waste sites that have

been proposed for inclusion on the EPA National Priorities List (NPL) (HazDat 1993). However, the

number of sites evaluated for hexachlorobutadiene is not known. The frequency of these sites within

the United States can be seen in Figure 5-l.

5.2 RELEASES TO THE ENVIRONMENT

5.2.1 Air

There are no known natural sources of hexachlorobutadiene which contribute to environmental levels.

The predominant source of hexachlorobutadiene is inadvertent production from the synthesis of

certain chlorinated hydrocarbons (EPA 1982b). In 1975, the production of hexachlorobutadiene in

the United States was estimated to be 8 million pounds, with 0.1 million pounds released to the

environment (NSF 1975). Sixty-eight percent of the 27 million pounds of hexachlorobutadiene waste

generated in the United States in 1982 was disposed of by incineration. This process typically obtains

a 99.99% destruction efficiency, indicating that approximately 1,900 pounds were released to the

atmosphere. According to TRI90 (1992), an estimated total of 4,906 pounds (2.2 metric tons) of

hexachlorobutadiene, amounting to 82% of the total environmental release, was discharged to the air

from manufacturing and processing facilities in the United States in 1990 (see Table 5-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.


HEXACHLOROBUTADIENE 83

5. POTENTIAL FOR HUMAN EXPOSURE

5.2.2 Water

Hexachlorobutadiene may be released to underground and surface waters through discharge from

industrial facilities, by leaching from industrial discharges, by leaching from landfills or soils, or by

urban runoff. Hexachlorobutadiene was detectable in 1.6% of 1,190 industrial effluent samples

reported in the EPA Storage and Retrieval (STORET) database (Staples et al. 1985). The median

concentration for all samples, including nondetects was < 6 ppb. This chemical was also detected in

leachate from an industrial landfill at a concentration of 0.109 ppm (Brown and Donnelly 1988) and

from a hazardous waste site (Hauser and Bromberg 1982). In 1982, of the 27 million pounds of

hexachlorobutadiene waste produced in the United States as a by-product of chlorinated hydrocarbon

production, 9 million pounds was disposed of by deep well injection (EPA 1982b). According to

TR190 (1992), an estimated total of 715 pounds (0.3 metric tons) of hexachlorobutadiene, amounting

to 12% of the total environmental release, was discharged to the water from manufacturing and

processing facilities in the United States in 1990 and 330 pounds (about 6%) was disposed of by

underground injection (see Table 5-l).

5.2.3 Soil

Hexachlorobutadiene may be released to soil by disposal of wastes in landfill operations. In 1982,

only 0.2% of the 27 million pounds of hexachlorobutadiene waste produced as a by-product of

chlorinated hydrocarbon-synthesis was disposed of in landfill operations (EPA 1982b). These data

indicate that the release to soil was approximately 54,000 pounds. According to TR190 (1992), no

hexachlorobutadiene was discharged to the soil from manufacturing and processing facilities in the

United States in 1990 (see Table 5-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.

5.3 ENVIRONMENTAL FATE

5.3.1 Transport and Partitioning

Hexachlorobutadiene can exist in the atmosphere as a vapor or adsorbed to airborne particulate

matter. The atmospheric burden of hexachlorobutadiene has been estimated to be 3.2 and 1.3 million

kg/year for the northern and southern hemispheres, respectively (Class and Ballschmiter 1987).
HEXACHLOROBUTADIENE 84

5. POTENTIAL FOR HUMAN EXPOSURE

Significant dispersion of hexachlorobutadiene has been confirmed by the detection of

hexachlorobutadiene at areas which are far removed from release sources (Class and Ballschmiter

1987). A high partition coefficient (log Koc) value of 3.67 (Montgomery and Welkom 1990) for

hexachlorobutadiene indicates that adsorption to soils with high organic carbon content can occur.

Wind erosion of contaminated surface soils can then lead to airborne hexachlorobutadiene-containing

particulate matter. Levels of hexachlorobutadiene have been detected in fly ash from the incineration

of hexachlorobutadiene-containing hazardous waste (Junk and Ford 1980). The transport of

particulate matter is a function of particle size and wind speed, however no data were located

regarding the transport of hexachlorobutadiene-containing particles in air.

Transport and partitioning of hexachlorobutadiene in water involves volatilization to the atmosphere

and sorption to soil and sediments particulates. The high partition coefficient (log Kow) of 4.78

(Montgomery and Welkom 1990) for hexachlorobutadiene leads to preferential partitioning to

sediments and biota over water. Environmental surveys generally report higher levels of

hexachlorobutadiene in sediments than in the waters that contain them (Elder et al. 1981; EPA 1976;

Oliver and Charlton 1984). Hexachlorobutadiene has a vapor pressure of 0.15 mmHg (25°C)

(Montgomery and Welkom 1990), indicating that volatilization from water occurs. Volatilization is

reduced by adsorption to organic material in the water.

The transport and partitioning of hexachlorobutadiene in soils involve volatilization and adsorption.

An estimated high partition coefficient (log Koc) of 3.67 (Montgomery and Welkom 1990) for

hexachlorobutadiene in soil indicates that soil adsorption can occur, particularly in soils with a high

organic carbon content. Sorption was the predominant fate process for hexachlorobutadiene during

anaerobic digestion of sludges (Govind et al. 1991). Data indicate that hexachlorobutadiene is mobile

in sandy soils which have relatively low organic-carbon contents (Piet and Zoeteman 1980).

Volatilization from surface soils is relatively low; binding to the organic carbon content of the soil

further reduces hexachlorobutadiene release.

In rainbow trout the bioconcentration factor (BCF) was dependent on water concentration (Oliver and

Niimi 1983). At low concentrations of 0.10 ng/L a BCF of 5,800 was obtained, compared to a value

of 17,000 obtained with higher water concentrations of 3.4 ng/L. Hexachlorobutadiene preferentially

accumulates in the liver of fish (Pearson and McConnell 1975). In mussels, the BCF was determined

to be between 900 and 2,000 (Pearson and McConnell 1975). However, lower values were obtained
HEXACHLOROBUTADIENE 85

5. POTENTIAL FOR HUMAN EXPOSURE

for algae, crayfish, and bass (160, 60, and 29, respectively) (EPA 1976). The EPA is reviewing new

BCF data and has recommended a value of 392 (EPA 1989a).

5.3.2 Transformation and Degradation

5.3.2.1 Air

No data were located regarding the transformation and degradation of hexachlorobutadiene in air.

Based on the monitoring data, the tropospheric half-life of hexachlorobutadiene was estimated by one

author to be 1.6 years in the northern hemisphere (Class and Ballschmiter 1987). However, analogy

to structurally similar compounds such as tetrachloroethylene indicates that the half-life of

hexachlorobutadiene may be as short as 60 days, predominantly due to reactions with photochemically

produced hydroxyl radicals and ozone (Atkinson 1987; Atkinson and Carter 1984). Oxidation

constants of < 103

 and 6(m • hr)-1 were estimated for reactions with singlet oxygen and peroxy

radicals, respectively (Mabey et al. 1982).

5.3.2.2 Water

Data concerning the transformation and degradation of hexachlorobutadiene in waters are limited.

Under aerobic conditions, hexachlorobutadiene underwent complete biodegradation after 7 days in

water inoculated with domestic sewage (Tabak et al. 1981). Biodegradation of hexachlorobutadiene

also occurred during anaerobic digestion of wastewater sludges, although sorption was the

predominant fate process (Govind et al. 1991). However, biodegradation did not occur in anaerobic

waters (Johnson and Young 1983). Based on monitoring data, the half-life of hexachlorobutadiene in

rivers and lakes was estimated to be 3-30 days and 30-300 days, respectively (Zoeteman et at. 1980).

Data regarding the hydrolysis or photolysis of hexachlorobutadiene in water were not located.

5.3.2.3 Sediment and Soil

Data regarding the transformation and degradation of hexachlorobutadiene in soil were not located.

However, based on the observation that hexachlorobutadiene was completely biodegraded in water

under aerobic conditions (Tabak et al. 1981), biodegradation probably occurs in nonarid soils as well.
HEXACHLOROBUTADIENE 86

5. POTENTIAL FOR HUMAN EXPOSURE

5.4 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT

5.4.1 Air

In the United States, the reported average concentration of hexachlorobutadiene, based on 72 samples

from urban and source dominated areas, was 36 ppt (0.38 μg/m3

) (Shah and Heyerdahl 1988; Shah

and Singh 1988). Hexachlorobutadiene levels ranging from 2 to 11 ppt were reported in a number of

cities (Pellizzari 1978; Singh et al. 1980; Singh et al. 1982). Higher levels of hexachlorobutadiene

were reported in Niagara Falls, with concentrations of up to 37 ppt detected in ambient air levels and

up to 38 ppt detected in the basement air of homes near industrial and chemical waste disposal sites

(Pellizzari 1982).

Occupational exposures can be significantly higher for individuals who work at plants that produce

chlorinated hydrocarbons. Maximum air levels off plant property, at a plant boundary, and within a

plant were reported to be 22 ppt, 938 ppt, and 43,000 ppt, respectively (Li et al. 1976).

5.4.2 Water

Hexachlorobutadiene has been detected in some surface waters but the incidence of detection is low.

It was detected in 0.2% of 593 ambient water samples in the STORET database with a median level

for all samples of less than 10 ppb (Staples et al. 1985). Hexachlorobutadiene was detected in 1 of

204 surface water sites sampled across the United States with a concentration of 22 ppb (Ewing et al.

1977). Low levels of hexachlorobutadiene were detected in the Niagara River at 0.82 ppt (Oliver and

Charlton 1984). Hexachlorobutadiene was not detected in rainwater (Pankow et al. 1984) or urban

storm water runoff (Cole et al. 1984) in a number of U.S. cities. It has not been detected in open

ocean waters; however, the coastal waters of the Gulf of Mexico were reported to contain 3-15 ppt

(Sauer 1981).

Low levels of hexachlorobutadiene (less than 1 ppb) may be found in drinking water (EPA 1989a).

Finished drinking water samples from two U.S. cities were found to contain 1.6 ppt and 2.7 ppt,

respectively (Lucas 1984). Hexachlorobutadiene was also detected in groundwater at 6 of 479 waste

disposal sites in the United States (Plumb 1991).
HEXACHLOROBUTADIENE 87

5. POTENTIAL FOR HUMAN EXPOSURE

5.4.3 Sediment and Soil

Hexachlorobutadiene adsorbs to sediments in contaminated water. Sediments from the Niagara River

were found to contain 2.9-l 1 μg/kg (Oliver and Charlton 1984). Sediments from the Great Lakes

were reported to contains levels of hexachlorobutadiene typically ranging from 0.08 to 120 μg/kg

(Fox et al. 1983; Oliver and Bourbonniere 1985; Oliver and Charlton 1984). Data regarding the

levels of hexachlorobutadiene in soils were not located. Hexachlorobutadiene was not detectable in

any of 196 sediment samples reported on the STORET database (Staples et al. 1985). The median

detection limit was < 500 ppb.

5.4.4 Other Environmental Media

Hexachlorobutadiene was detected in several foodstuffs in the United Kingdom (McConnell et al.

1975) and Germany (Kotzias et al. 1975), but it was not detected in the United States in milk, eggs,

or vegetables even when the samples were obtained from within a 25-mile radius of facilities

producing chlorinated hydrocarbons (Yip 1976; Yurawecz et al. 1976). Fish samples from the

Mississippi River were found to contain hexachlorobutadiene levels ranging from 0.1 to 4.7 mg/kg

(Laska et al. 1976; Yip 1976; Yurawecz et al. 1976). Fish from the Great Lakes generally did not

contain detectable levels of hexachlorobutadiene (Camanzo et al. 1987; DeVault 1985) with the

exception of trouts from Lake Ontario, which were reported to contain 0.06-0.3 mg/kg (Oliver and

Niimi 1983). Hexachlorobutadiene was not detectable in any of 51 biota samples reported on the

STORET database (Staples et al. 1985).

Hexachlorobutadiene was not detected in sewage influents (Levins et al. 1979) or in sewage samples

(EPA 1990g).

5.5 GENERAL POPULATION AND OCCUPATIONAL EXPOSURE

The general population can be exposed to low levels of hexachlorobutadiene in air, food, and water.

Estimates of source or route-specific exposures to humans were not located. Hexachlorobutadiene has

been detected in human adipose tissue with a concentration ranging from 0.8 to 8 μg/kg wet weight

(McConnell et al. 1975; Mes et al. 1982). Higher concentrations were reported in human liver

samples with values ranging from 5.7 to 13.7 μg/kg wet weight (McConnell et al. 1975). These data
HEXACHLOROBUTADIENE 88

5. POTENTIAL FOR HUMAN EXPOSURE

indicate that exposure to hexachlorobutadiene occurs in humans, but do not identify sources or routes

of exposure. Although exposure from foods is probably a minor route of exposure, people who

consume large amounts of fish obtained from contaminated waters may be exposed to significant

quantities of hexachlorobutadiene. Similarly, persons who live in source-dominated areas or work in

plants that produce chlorinated hydrocarbons may be exposed to significant levels of

hexachlorobutadiene in the air. No information was found on the number of workers potentially

exposed to hexachlorobutadiene.

5.6 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES

People who live in source-dominated areas (at or near hazardous waste sites or chlorinated

hydrocarbon production plants) and workers in these areas are potentially exposed to high levels of

hexachlorobutadiene. Individuals who consume large amounts of fish from contaminated waters may

also be exposed to above-average levels of hexachlorobutadiene.

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 hexachlorobutadiene 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 hexachlorobutadiene.

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.
HEXACHLOROBUTADIENE 89

5. POTENTIAL FOR HUMAN EXPOSURE

5.7.1 Identification of Data Needs

Physical and Chemical Properties. The physical and chemical properties of hexachlorobutadiene

are sufficient to make estimations on its fate in the environment. No data regarding the odor

threshold of hexachlorobutadiene in water were located.

Production, Import/Export, Use, Release, and Disposal. Hexachlorobutadiene is not produced

for commercial purposes in the United States, however small amounts are imported from Germany.

Hexachlorobutadiene is mainly produced as a by-product of chlorinated hydrocarbon synthesis and is

a primary component of “hex-wastes” (EPA 1982b). Its uses as a pesticide and fumigant have been

discontinued. Hexachlorobutadiene is disposed chiefly by incineration, and to a lesser extent by deep

well injection and landfill operations (EPA 1982b). More recent production and release data would

be helpful in estimating human exposure to hexachlorobutadiene.

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. Much of the environmental fate information on hexachlorobutadiene consists

of modeling based on its physical and chemical properties and its similarity to related compounds.

Further studies which determine the extent to which hexachlorobutadiene volatilizes from surface

waters and soils, and the effects of organic-carbon content on this process would be helpful. Studies

which experimentally determine the specific reactions and rates which drive the degradation of

hexachlorobutadiene in air, water, and soil would be valuable. Data are lacking on

hexachlorobutadiene adsorption to soil or its biodegradation in this medium. More information on the

fate of the compound in soil would be useful since this medium may be a pathway of exposure for

populations living near emission sources.

Bioavailability from Environmental Media. Toxicity studies in animals indicate that absorption of

hexachlorobutadiene through the gastrointestinal tract, respiratory tract, and skin can occur. Studies
HEXACHLOROBUTADIENE 90

5. POTENTIAL FOR HUMAN EXPOSURE

which identify the relationship between absorption and the matrix of soils, sediments, and foods

would be useful in establishing whether or not absorption is significantly affected by such factors.

Food Chain Bioaccumulation. Bioconcentration factors have been determined for algae, shellfish,

and fish and exhibit a wide range (29-17,000) (EPA 1976; Oliver and Niimi 1983; Pearson and

McConnell 1975). This wide range may be explained in part by species differences in metabolism or

differences in concentrations tested. Studies also indicate that hexachlorobutadiene preferentially

accumulates in the livers of fish. Further studies which might explain the wide range of BCF values

would be helpful. No information was located regarding the bioaccumulation of hexachlorobutadiene

in plants or aquatic organisms. More information is needed to determine the importance of

terrestrial/aquatic food chain bioaccumulation as a potential human exposure pathway.

Exposure Levels in Environmental Media. Data are available on the occurrence of

hexachlorobutadiene in air, water, and foodstuff. The majority of the monitoring data on

hexachlorobutadiene are outdated and therefore more recent information on the levels typically found

in the environment would allow for more accurate estimation of human exposures, and could also

serve to indicate time-dependent trends when compared with older data. No data were located

regarding the occurrence of hexachlorobutadiene in groundwater or soil.

Reliable monitoring data for the levels of hexachlorobutadiene in contaminated media at hazardous

waste sites are needed so that the information obtained on levels of hexachlorobutadiene in the

environment can be used in combination with the known body burden of hexachlorobutadiene to

assess the potential risk of adverse health effects in populations living in the vicinity of hazardous

waste sites.

Exposure Levels in Humans. Hexachlorobutadiene has been detected in human adipose tissues and

blood (Bristol et al. 1982; Mes et al. 1985). Studies which establish a correlation between exposure

levels in environmental media and the resulting levels in human tissues and excreta would be valuable

in predicting exposures and corresponding health risks in humans who live at or near hazardous waste

sites and who are likely to be exposed to hexachlorobutadiene.

This information is necessary for assessing the need to conduct health studies on these populations.
HEXACHLOROBUTADIENE 91

5. POTENTIAL FOR HUMAN EXPOSURE

Exposure Registries. No exposure registries for hexachlorobutadiene 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

No on-going studies were located regarding the environmental fate or potential for human exposure to

hexachlorobutadiene.

HEXACHLOROBUTADIENE 93

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 hexachlorobutadiene, its metabolites, and other biomarkers of

exposure and effect to hexachlorobutadiene. 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

Gas chromatography (GC) with an electron-capture detector (ECD) and/or GC with detection by mass

spectrometry (MS) have been used to measure hexachlorobutadiene concentrations in human blood

and adipose tissue (Bristol et al. 1982; LeBel and Williams 1986; Mes et al. 1985) and in rat liver

tissue (Wang et al. 1991). In gas chromatography, samples dissolved in a volatile solvent are injected

into a heated column with a stationary phase consisting of silica coated with a liquid phase. An inert

gas carries the sample through the column, and the partitioning of hexachlorobutadiene between the

mobile and stationary phases gives it a characteristic retention time which is used to identify it.

Electron-capture detectors use a radioactive source such as 63Ni to generate electrons that are captured

by the chlorine atoms in hexachlorobutadiene. Reduction in electron flow by this capture produces a

characteristic signal for hexachlorobutadiene. Identity of hexachlorobutadiene is confirmed by

detection by mass spectroscopy, which provides specific identification by a characteristic ion

fragmentation pattern.

Biological samples are prepared for analysis by extraction with organic solvents. This extract from

blood may be used directly (Bristol et al. 1982; Kastl and Hermann 1983), but extracts from adipose

or liver tissue are cleaned up by gel permeation chromatography (GPC), which separates
HEXACHLOROBUTADIENE 94

6. ANALYTICAL METHODS

hexachlorobutadiene from higher molecular weight lipids, and/or by passage through a Florisil

column which retains lipids and other contaminants (LeBel and Williams 1986; Mes et al. 1985).

These methods provide 42- 122 % recovery and can detect < 1 μg/L hexachlorobutadiene in blood and

1 μg/kg hexachlorobutadiene in fat (Bristol et al. 1982; LeBel and Williams 1986; Mes et al. 1985;

Wang et al. 1991). No information was located on methods for detection of hexachlorobutadiene

metabolites or other biomarkers of hexachlorobutadiene exposure or effect.

Table 6-l summarizes the methods used for sample preparation and analysis of hexachlorobutadiene in

biological samples.

6.2 ENVIRONMENTAL SAMPLES

Hexachlorobutadiene in environmental samples is also measured using GC coupled with ECD, MS, a

halogen electrolytic conductivity detector (HECD), or a photoionization detector (PID) (APHA 1992a,

1992b; EPA 1982a, 1982c, 1986, 1989c, 1989d, 1990b, 1990d, 1990e). Several methods have been

used for extraction of hexachlorobutadiene from environmental samples. Standard methods for

analysis of air involve pumping the air through a material that will adsorb hexachlorobutadiene or

through a cold trap to condense the hexachlorobutadiene (EPA 1990b; NIOSH 1990). Purge-and-trap

methods are used to extract hexachlorobutadiene from water, soil, or solid waste (APHA 1992b; EPA

1989c, 1989d, 1989e, 1990e). Purge-and-trap methods involve bubbling an inert gas through the

sample, trapping the hexachlorobutadiene in a tube containing a sorbent material, and then heating the

sorbent tube and flushing the hexachlorobutadiene into a GC. Soil, sediment, and waste samples are

mixed with water prior to purging (EPA 1990e). An alternative way to prepare water, soil, or solid

waste samples for GC analysis is to extract with methylene chloride or some other organic solvent;

for waste water, soil, and solid waste samples, the organic extracts are cleaned up by gel permeation

chromatography (GPC) or Florisil adsorption chromatography (FAC) (APHA 1992a; EPA 1982a,

1982c, 1986). Purge-and-trap methods generally provide > 90% recovery, while organic extraction

may have lower and more variable recovery rates (APHA 1992a, 1992b; EPA 1982a, 1982c, 1989c,

1990e).

Gas chromatographic methods with ECD and other detectors have a detection limit for

hexachlorobutadiene of 0.02-0.05 μg/L in water (EPA 1982a, 1989c, 1989d, 1989e). Detection

limits for soil and solid waste are usually higher, depending on matrix interferences, extraction, and

HEXACHLOROBUTADIENE 96

6. ANALYTICAL METHODS

clean up procedures (EPA 1986, 1990e). Detection by MS is most specific because identification is

based on the characteristic mass ion as well as the retention time. Newer MS methods can achieve

detection limits of 0.04-0.11 μg/L in water, comparable to ECD (EPA 1982a, 1989e).

Table 6-2 summarizes some of the methods used for sample preparation and analysis of

hexachlorobutadiene in environmental samples.

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 hexachlorobutadiene 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 hexachlorobutadiene.

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. Hexachlorobutadiene can be

measured in human blood and adipose tissue, with detection limits < 1 μg/L in blood and 1 μg/kg wet

weight of adipose tissue (Bristol et al. 1982; LeBel and Williams 1986; Mes et al. 1985). No

hexachlorobutadiene was detected in blood from controls or residents near a hazardous waste site

(Bristol et al. 1982), indicating that the method was not sensitive enough to measure background

levels of hexachlorobutadiene in the general population. It is likely that this method would be

sensitive enough to measure levels at which biological effects occur. Hexachlorobutadiene was

detected in adipose tissue of victims of accidental and nonaccidental deaths, with about twice as much


HEXACHLOROBUTADIENE 99

6. ANALYTICAL METHODS

in accident than nonaccident victims (Mes et al. 1985). This indicates that the GC/ECD and GC/MS

method is sensitive enough to measure background levels of hexachlorobutadiene in the general

population as well as levels at which biological effects occur. No data were located concerning

methods to measure hexachlorobutadiene metabolites in biological samples; such methods would be

useful if it were established that hexachlorobutadiene metabolite levels were reliable markers of

exposure to hexachlorobutadiene.

No data were located concerning methods to measure biological markers of hexachlorobutadiene

effects. Research into biomarkers of effect would be most useful if performed in conjunction with

development of sensitive, specific, and reliable methods for measuring the biomarker(s) of effect.

Methods for Determining Parent Compounds and Degradation Products in Environmental

Media. Methods for detection of hexachlorobutadiene in air, water, soil, solid waste, and food are

all based on gas chromatography (APHA 1992a, 1992b; EPA 1982a, 1982c, 1986, 1989c, 1989d,

1989e, 1990b, 1990e). Existing methods for analysis of air and water appear to be sufficiently

sensitive, specific, and reliable to measure background levels in the environment. Matrix interference

and contamination by co-eluting chemicals may limit the sensitivity and specificity of methods for

analysis of hexachlorobutadiene in soil and solid waste (EPA 1986, 1990e). Supercritical fluid

extraction, which uses carbon dioxide liquified above 31°C at high pressure, might provide efficient

extraction of hexachlorobutadiene from large samples (Walters 1990). Supercritical fluid

chromatography may provide an alternate approach to GC for analysis of hexachlorobutadiene and

other compounds from complex environmental samples (Pospisil et al. 1991). An immunoassay for

heptachlor has been developed which shows 1.6 % cross-reactivity with hexachlorobutadiene (Stanker

et al. 1990). Development of an immunoassay specific for hexachlorobutadiene could provide a

rapid, inexpensive, and sensitive method for detecting hexachlorobutadiene in environmental samples.

No data were located concerning methods to measure hexachlorobutadiene degradation products in the

environment. Degradation products are likely to be compounds that could be separated either by GC

or by high performance liquid chromatography (HPLC) (for oxidized, polar degradation products).

Mass spectrometry would be likely to be the most specific method to identify such products.

Development of methods to measure hexachlorobutadiene degradation products would be useful for

assessing the fate of hexachlorobutadiene in the environment.
HEXACHLOROBUTADIENE 100

6. ANALYTICAL METHODS

6.3.2 On-going Studies

No information was located concerning on-going studies for improving methods of analysis of

hexachlorobutadiene, its metabolites, or other biomarkers of exposure and effect to

hexachlorobutadiene in biological materials or environmental samples.
HEXACHLOROBUTADIENE 101

7. REGULATIONS AND ADVISORIES

Because of its potential to cause adverse health effects in exposed people, a number of regulations and

guidelines have been established for hexachlorobutadiene by various international, federal, and state

agencies. These values are summarized in Table 7-l.

The ATSDR has calculated an intermediate-duration exposure oral MRL of 0.0002 mg/kg/day, based

on a LOAEL of 0.2 mg/kg/day for the presence of kidney damage in female mice (NTP 1991).

The EPA has derived a chronic oral RfD of 2x10-4 mg/kg/day for hexachlorobutadiene (EPA 1993).

This RfD is based on a LOAEL of 0.5 mg/kg/day for renal effects in mice exposed via the diet for

13 weeks (Yang et al. 1989). Since this RfD is currently under review by EPA and has been

withdrawn from EPA’s Integrated’Risk Information System (IRIS 1993), it is subject to change.



HEXACHLOROBUTADIENE 105

8. REFERENCES

ACGIH. 1986. Documentation of the Threshold Limit Values and Biological Exposure Indices. 5th

ed. American Conference of Governmental Industrial Hygienists, Cincinnati, OH.

*ACGIH. 1991. Threshold limit values for chemical substances and physical agents and biological

exposure indices for 1991 to 1992. American Conference of Governmental Industrial Hygienists,

Cincinnati, OH.

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HEXACHLOROBUTADIENE 121

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HEXACHLOROBUTADIENE 122

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HEXACHLOROBUTADIENE 129

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.

Bioconcentration Factor (BCF) - The quotient of the concentration of a chemical in aquatic

organisms at a specific time or during a discrete time period of exposure divided by the concentration

in the surrounding water at the same time or during the same period.

Cancer Effect Level (CEL) - The lowest dose of chemical in a study, or group of studies, that

produces significant increases in the incidence of cancer (or tumors) between the exposed population

and its appropriate control.

Carcinogen - A chemical capable of inducing cancer.

Ceiling Value - A concentration of a substance that should not be exceeded, even instantaneously.

Chronic Exposure - Exposure to a chemical for 365 days or more, as specified in the Toxicological

Profiles.

Developmental Toxicity - The occurrence of adverse effects on the developing organism that may

result from exposure to a chemical prior to conception (either parent), during prenatal development,

or postnatally to the time of sexual maturation, Adverse developmental effects may be detected at any

point in the life span of the organism.
HEXACHLOROBUTADIENE 130

9. GLOSSARY

Embryotoxicity and Fetotoxicity - Any toxic effect on the conceptus as a result of prenatal

exposure to a chemical; the distinguishing feature between the two terms is the stage of development

during which the insult occurred. The terms, as used here, include malformations and variations,

altered growth, and in utero death.

EPA Health Advisory - An estimate of acceptable drinking water levels for a chemical substance

based on health effects information. A health advisory is not a legally enforceable federal standard,

but serves as technical guidance to assist federal, state, and local officials.

Immediately Dangerous to Life or Health (IDLH) - The maximum environmental concentration of

a contaminant from which one could escape within 30 min without any escape-impairing symptoms or

irreversible health effects.

Intermediate Exposure - Exposure to a chemical for a duration of 15-364 days, as specified in the

Toxicological Profiles.

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 is expected to have caused death in humans or animals.
HEXACHLOROBUTADIENE 131

9. GLOSSARY

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.

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 8-hour shift.
HEXACHLOROBUTADIENE 132

9. GLOSSARY

q1* - The upper-bound estimate of the low-dose slope of the dose-response curve as determined by

the multistage procedure. The q1* can be used to calculate an estimate of carcinogenic potency, the

incremental excess cancer risk per unit of exposure (usually 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.
HEXACHLOROBUTADIENE 133

9. GLOSSARY

Threshold Limit Value (TLV) - A concentration of a substance to which most workers can be

exposed without adverse effect. The TLV may be expressed as a TWA, as a STEL, or as a CL.

Time-Weighted Average (TWA) - An allowable exposure concentration averaged over a normal 8-

hour workday or 40-hour workweek.

Toxic Dose (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 RfD from experimental data.

UFs are intended to account for (1) the variation in sensitivity among the members of the human

population, (2) the uncertainty in extrapolating animal data to the case of human, (3) the uncertainty

in extrapolating from data obtained in a study that is of less than lifetime exposure, and (4) the

uncertainty in using LOAEL data rather than NOAEL data. Usually each of these factors is set equal

to 10.
HEXACHLOROBUTADIENE A-l

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-l 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, Minima1 Risk Levels (MRLs) to humans for

noncancer end points, and EPA’s estimated range associated with an upper-bound individual lifetime

cancer risk of 1 in 10,000 to 1 in 10,000,000. 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 with the text.

The legends presented below demonstrate the application of these tables and figures. A representative

example of LSE Table 2-l and Figure 2-l are shown. The numbers in the left column of the legends

correspond to the numbers in the example table and figure.

LEGEND

See LSE Table 2-1

(1). Route of Exposure One of the first considerations when reviewing the toxicity of a substance

using these tables and figures should be the relevant and appropriate route of exposure. When

sufficient data 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 (LSE 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.
HEXACHLOROBUTADIENE 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-l).

(5) Species The test species, whether animal or human, are identified in this column. Species

(6) Exposure Frequency/Duration The duration of the study and the weekly and daily exposure

regimen are provided in this column. This permits comparison of NOAELs and LOAELs from

different studies. In this case (key number 18), rats were exposed to [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”).

(9) LOAEL A Lowest-Observed-Adverse-Effect Level (LOAEL) is the lowest exposure level used

in the study that caused a hannful 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.

(10) Reference The complete reference citation is given in Chapter 8 of the profile.

(11) 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.

(12) Footnotes Explanations of abbreviations or reference notes for data in the LSE tables are found

in the footnotes. Footnote “b” indicates the NOAEL of 3 ppm in key number 18 was used to

derive an MRL of 0.005 ppm.

LEGEND

See 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.


HEXACHLOROBUTADIENE 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 (q1*).

(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.
HEXACHLOROBUTADIENE 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 LOAEL 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.