E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Publication Date: 9/93
TRADE OR OTHER NAMES
Trade names for this product include HCB, Anticarie, Ceku C.B., and
No Bunt. This compound should not be confused with benzene hexachloride
(hexachlorocyclohexane, HCH), also known as lindane. This compound also
has non-pesticidal industrial uses.
Hexachlorobenzene is a chlorinated hydrocarbon fungicide used as a
seed treatment, especially on wheat. Hexachlorobenzene controls bunt.
It may be used with or without other seed treatments.
Hexachlorobenzene has been banned from use in the United States.
Hexachlorobenzene is considered non-toxic for acute exposure and
thus there is no signal word required on the label. Single doses of HCB
are relatively non-toxic though repeated doses, even at small amounts
are toxic (14, 10).
Unlike humans, rodents exhibit neurological symptoms including
tremors, paralysis, muscle incoordination, weakness and convulsions at
high single doses (3). The LD50 for rats is 10,000 mg/kg and guinea
pigs can tolerate a dose greater than 3,000 mg/kg. The oral cat and rat
LD50 are 1,700 and 4,000 mg/kg, respectively (12). Inhalation LC50
values of hexachlorobenzene for the cat, rat and mouse are 1600, 3,600,
and 4,000 mg/m3, respectively (12). These values indicate that a
substantial concentration of the pesticide needs to be present for acute
effects to be seen. The pesticide does not carry a signal word on the
label because the acute LD50 for the product is so high.
Despite its low acute toxicity, hexachlorobenzene is toxic to
humans and animals when long-term exposure occurs. The product has been
banned for most food crop uses throughout the world due to its chronic
In Turkey, many people eating HCB contaminated flour developed a
skin ailment, porphyria cutanea tarda. The ailment is characterized by
blistering of the skin. The skin was sensitive to light and was easily
infected. Recovery usually followed termination of exposure (3,10)
although many people were seriously disfigured and at least 10% of those
people affected died. Twenty years after the incident, some individuals
were still suffering from the effects of hexachlorobenzene exposure (3).
Estimates of the daily intake of the compound in the contaminated wheat
range from 50 to 200 mg/day over "relatively long periods" (3).
Rats fed up to small amounts continuously in their diet were
observed through two successive litters. Death of most of the newborn
rats was observed at the highest dose and was related to both the
maternal dose and cumulative exposure through milk. The dams suffered
lung damage (3).
Several studies with rats and mice have shown birth defects due to
HCB (10). At doses well below the LC50, changes occurred in rib
development and cleft palate formation in rats. Kidney malformations
and decreased body weight were also noted. It is possible that the
compound could cause birth defects in human populations chronically
HCB was shown to be non-mutagenic in several tests with bacteria
and was mutagenic with yeast cells. No generalizations to humans may be
drawn based on this limited information (4).
Hexachlorobenzene is an animal carcinogen and is considered to be a
probable human carcinogen. Six-week-old hamsters given relatively high
doses (up to 200 mg/kg) in their diet for a lifespan developed liver and
thyroid tumors. Mice fed for two years had liver cell tumors the low
doses (12-24 mg/kg/day).
Rats fed diets containing up to 32 mg/kg/day HCB in corn oil showed
tissue changes which were confined to the liver and the spleen.
Studies on adult female beagles fed HCB for 21 days showed that a
minimally toxic dose was 50 mg/kg/day. Changes in the liver and the
central nervous system were judged to be hexachlorobenzene induced (3).
Fate in Humans and Animals
Nursing monkeys given moderate amounts of hexachlorobenzene for
sixty days by tube feeding generally remained healthy, but some infant
mortality occurred. Similar effects have occurred in heavily exposed
humans (1). Rats excrete intact hexachlorobenzene in bile and also
slowly break it down to form pentachlorophenol and other compounds that
are excreted in the urine (6). Applicators with up to 310 ppb in their
blood showed no physical or biochemical effects. In rats, half of a
single dose of the product is lost within 3-4 months but in monkeys it
takes 2.5 to 3 years (3).
Japanese quail tolerated diets containing 200 ppm, but had an LC50
of 568 ppm with the onset of signs at 3 days. This indicates that the
compound is moderately toxic to the organism. In pullets, more than
half of the residue was excreted in egg yolks within a months time.
Hexachlorobenzene is slightly toxic to fish. The 96-hour LD50 for
channel catfish is 11-16 mg/l and for coho salmon it is greater than 50
mg/l. Rainbow trout have been shown to accumulate residues of 3,800 to
8,900 times the exposure level of 0.1 to 2.0 ppb within 28 days.
Likewise, Daphnia accumulated residues nearly 900 times exposure levels
of 0.05 to 0.15 micrograms/l within 48 hours. The half-life for loss
from Daphnia was 44 hours. Neither trout nor Daphnia significantly
degraded hexachlorobenzene (8).
The compound is non-toxic to bees.
HCB completely degraded to pentchlorophenol in hydrosoil samples.
Evaporation is rapid while it is on soil surfaces, but less so when it
is mixed into the soil (3). Soil, aerially sprayed, had about one half
of the initial applied amount after 14 days, one quarter of the amount
after three months and only 3.4% after a year and a half. Water, which
began with 6.5 ppb HCB, was found to contain 3 ppb parent, 0.34 ppb
pentachlorophenol and a few other materials. Hexachlorobenzene has been
found in well water in several States at low concentrations ranging from
1 ppb to 5.6 ppb and only in a very small percentage of all of the wells
Residues in grass were only at 1% of the initial amount after 15
days, and 0.01% after 19 months. The bioaccumulation ratio in algae is
570, with most of the dose as parent compound, indicating little
degradation (8) in these organisms.
|NOEL (rat): ||0 0.08 mg/kg/day
|DWEL: ||0.03 mg/l
|RfD: ||0.0008 mg/kg/day (EPA)
|LEL: ||0.29 mg/kg/day (rat)
|CAS #: ||118-74-1
|Chemical name: ||hexachlorobenzene
|Chemical class/use: ||chloro-aromatic herbicide
|Solubility in water: ||0.005 ppm at 25 degrees C
|Solubility in other solvents: ||pratically insoluble in ethanol; soluble in hot benzene, chloroform and ether
|Melting Point: ||231 degrees C (pure); 220 degrees C (technical)
|Vapor Pressure: ||1.089 x 10 to the minus 5 power mm Hg at 20 degrees C
|Henry's Law Constant: ||0.12 atm m3/mol
1041 Beunos Aires,
Argentina, South America
Review by Basic Manufacturer:
Comments solicited: October, 1992
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