Hazard Summary
Hexachlorobenzene is formed as a byproduct during the manufacture of other chemicals. It was widely
used as a pesticide until 1 965. Chronic (long-term) oral exposure to hexachlorobenzene in humans results
in a liver disease with associated skin lesions. Epidemiologic studies of persons orally exposed to
hexachlorobenzene have not shown an increased cancer incidence. However, based on animal studies that
have reported cancer of the liver, thyroid, and kidney from oral exposure to hexachlorobenzene, EPA has
classified hexachlorobenzene as a probable human carcinogen (Croup B2). Very little inhalation data are
Please Note: The main sources of information for this fact sheet are EPA's Integrated Risk Information System (IRIS) (5),
which contains information on oral chronic toxicity and the Reference Dose (RfD), and the carcinogenic effects of
hexachlorobenzene including the unit cancer risk for inhalation exposure, and the Agency for Toxic Substances and
Disease Registry's (ATSDR's) Toxicological Profile for Hexachlorobenzene. (1)
•	There are currently no commercial uses of hexachlorobenzene in the United States. (1)
•	Hexachlorobenzene was used as a pesticide until 1 965 and was also used in the production of rubber,
aluminum, and dyes and in wood preservation. (1)
•	Hexachlorobenzene is currently formed as a byproduct during the manufacture of other chemicals (mainly
solvents) and pesticides. (1)
Sources and Potenti al Exposure
•	Inhalation exposure to hexachlorobenzene may occur through proximity to industrial sites where it is
formed as a byproduct or to waste facilities where it is disposed. (1)
•	Occupational exposure, via inhalation and dermally, can occur at industries where hexachlorobenzene is
produced as a byproduct. (1)
•	Exposure to hexachlorobenzene can also occur through consuming foods tainted with hexachlorobenzene.
•	Hexachlorobenzene has been listed as a pollutant of concern to EPA's Great Waters Program due to its
persistence in the environment, potential to bioaccumulate, and toxicity to humans and the environment
Assessing Personal Exposure
•	Medical tests can measure levels of hexachlorobenzene in the fat or blood. (1)
Health Hazard Information
Acute Effects:
•	No information is available on the acute (short-term) effects of hexachlorobenzene in humans. (1,3)

•	Acute animal tests in rats and mice have shown hexachlorobenzene to have low-to-moderate acute toxicity
from oral exposure. (4)
Chronic Effects (Noncancer):
•	Humans who ingested hexachlorobenzene in heavily contaminated bread during a 4-year poisoning
incident were sickened with a liver disease with associated skin lesions (porphyria cutanea tarda). (1)
•	Very little data are available on the health effects of hexachlorobenzene in humans or animals following
inhalation exposure.
•	Animal studies have reported effects on the liver, skin, immune system, kidneys, and blood from chronic
oral exposure to hexachlorobenzene. (1,3)
•	EPA has determined that there are inadequate data to establish a Reference Concentration (RfC) for
¦	The California Environmental Protection Agency (CalEPA) has established a chronic inhalation reference
exposure level of 0.003 milligrams per cubic meter (mg/m ) for hexachlorobenzene. The CalEPA reference
exposure level is a concentration at or below which adverse health effects are not likely to occur. It is not a
direct estimator of risk but rather a reference point to gauge the potential effects. At lifetime exposures
increasingly greater than the reference exposure level, the potential for adverse health effects increases. (6)
•	The Reference Dose (RfD) for hexachlorobenzene is 0.0008 milligrams per kilogram body weight per day
(mg/kg/d) based on liver effects in rats. The RfD is an estimate (with uncertainty spanning perhaps an order
of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is
likely to be without appreciable risk of deleterious noncancer effects during a lifetime. (5)
¦	EPA has medium confidence in the study used as the basis for the RfD because it had an unusual dosing
scheme making it difficult to determine the true doses received by each experimental group; high
confidence in the database due to the extensive number of quality research studies available; and
consequently medium confidence in the RfD. (5)
Reproductive/Developmental Effects:
•	One human study reported abnormal physical development in young children who ingested contaminated
bread during a 4-year poisoning incident. (1)
•	Hexachlorobenzene has been found to decrease the survival rates of newborn animals and to cross the
placenta and accumulate in fetal tissue in several animal species. (3)
•	Neurological, teratogenic, liver, and immune system effects have been reported in the offspring of animals
orally exposed to hexachlorobenzene while they were pregnant. (1)
Cancer Risk:
•	Human data regarding the carcinogenic effects of hexachlorobenzene are inadequate. (5)
•	Hexachlorobenzene, when administered orally, has been shown to induce tumors of the liver, thyroid, and
kidney in several animal species. (1,3,5)
•	EPA has classified hexachlorobenzene as a Group B2, probable human carcinogen. (5)
•	EPA uses mathematical models, based on animal studies to estimate the probability of a person developing
cancer from breathing air containing a^specified concentration of a chemical. EPA calculated an inhalation
unit risk estimate of 4.6 x 1 0 (|jg/m ) . EPA estimates that, if an individual were to continuously breathe
3	-6	3
air containing hexachlorobenzene at an average of 0.002 |jg/m (2.0 x 1 0 mg/m ) over his or her entire
lifetime, that person would theoretically have no more than a one-in-a-million increased chance of
developing cancer as a direct result^of breathing air containing this chemical. Similarly, EPA estimates that
breathing air containing 0.02 |jg/m (2.0 x 1 0 mg/m ) would result in not greater than a one-in-a-
hundred thousand increased chance of developing cancer, and air containing 0.2 |jg/m (2.0 x 1 0
4	3
mg/m ) would result in not greater than a one-in-ten thousand increased chance of developing cancer.
For a detailed discussion of confidence in the potency estimates^ please see IRIS. (5)
•	EPA has calculated an oral cancer slope factor of 1.6 (mg/kg/d) . (5)

Physical Properties
¦ Hexachlorobenzene is a white crystalline solid which is not very soluble in water. (1)
•	The odor threshold for hexachlorobenzene is not available.
•	The chemical formula for hexachlorobenzene is C CI , and the molecular weight is 284.8 g/mol. (1)
6 6 -5
•	The vapor pressure for hexachlorobenzene is 1.09 x 1 0 mm Hg at 20 °C, and it has a log octanol/water
partition coefficient (log K ) of 6.1 8. (1)
Conversion Factors:
3	3
To convert concentrations in air (at 2 5°C) from ppm to mg/m : mg/^m = (ppm) x (molecular weight of the
compound)/(24.45). For hexachlorobenzene: 1 ppm = 11.6 mg/m .
Health Data from Inhalation Exposure
Regulatory, advisory
Health numbers'
LC50 (rats) (3,600 rng/nrf)
CalEPA reference exposure
level (0.003 rng/nrf)
AC Gl H T LV (0 j00 2 nng/nfl
	Cancer Risk Level
1 in a million risk
— Ref.
ACGIH TLV—American Conference of Governmental and Industrial Hygienists' threshold limit value expressed as a
time-weighted average; the concentration of a substance to which most workers can be exposed without adverse
LC50 (Lethal Concentration 50)—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.
The health and regulatory values cited in this factsheet were obtained in December 1999.
Health numbers are toxicological numbers from animal testing or risk assessment values developed by EPA.

Regulatory numbers are values that have been incorporated in Government regulations, while advisory numbers
are nonregulatory values provided by the Government or other groups as advice. ACGIH numbers are advisory.
These cancer risk estimates were derived from oral data and converted to provide the estimated inhalation risk.
Summary created in April 1 992, updated January 2000
1.	Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for
Hexachlorobenzene(Update). Public Health Service, U.S. Department of Health and Human Services, Atlanta,
GA. 1996.
2.	U.S. Environmental Protection Agency. Deposition of Air Pollutants to the Great Waters. First Report to
Congress. EPA-453/R-93-055. Office of Air Quality Planning and Standards, Research Triangle Park, NC.
3.	U.S. Department of Health and Human Services. Hazardous Substances Data Bank (HSDB, online database).
National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1 993.
4.	U.S. Department of Health and Human Services. Registry of Toxic Effects of Chemical Substances (RTECS,
online database). National Toxicology Information Program, National Library of Medicine, Bethesda, MD.
5.	U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on Hexachlorobenzene.
National Center for Environmental Assessment, Office of Research and Development, Washington, DC.
6.	California Environmental Protection Agency (CalEPA). Technical Support Document for the Determination of
Noncancer Chronic Reference Exposure Levels. Draft for Public Comment. Office of Environmental Health
Hazard Assessment, Berkeley, CA. 1997.
7.	American Conference of Governmental Industrial Hygienists (ACGIH). 1 999 TLVs and BEIs. Threshold Limit
Values for Chemical Substances and Physical Agents, Biological Exposure Indices. Cincinnati, OH. 1 999.