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Hexachlorobenzene

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.

INTRODUCTION

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.

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

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.

CHRONIC TOXICITY

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 toxicity.

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).

Reproductive Effects

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).

Teratogenic Effects

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 exposed.

Mutagenic Effects

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).

Carcinogenic Effects

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).

Organ Toxicity

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).

ECOLOGICAL EFFECTS

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.

ENVIRONMENTAL FATE

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 tested (13).

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.

Exposure Guidelines:

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)

Physical Properties:

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

BASIC MANUFACTURER

Atanor S.A.
Sarmiento 329
1041 Beunos Aires,
Argentina, South America
Telephone 311-5394
Telex 23428

Review by Basic Manufacturer:

Comments solicited: October, 1992
Comments received:

REFERENCES

  1. Gosselin, R.E., R.P. Smith, H.C. Hodge (1984). Clinical Toxicology of Commercial Products, Williams and Wilkins, Baltimore, MD.
  2. Johnson, W.W. and M.T. Finley (1980). Handbook of Acute Toxicity of Chemicals to Fish and Aquatic Invertebrates. U. S. Dept of the Interior, Fish and Wildlife Service, Resource Publication 137.
  3. National Library of Medicine (1992). Hazardous Substances Databank. TOXNET, Medlars Management Section, Bethesda, MD.
  4. U.S. Environmental Protection Agency (1987). Health Advisory, Office of Drinking Water.
  5. Hill, E.F. and M.B. Camardese (1986). Lethal Dietary Toxicities of Environmental Contaminants and Pesticides to Coturnix. U.S. Dept of the Interior, Fish and Wildlife Service, Technical Report 2.
  6. Menzie, Calvin M. (1980). Metabolism of Pesticides, Update III. U. S. Dept of the Interior, Fish and Wildlife Service, Special Scientific Report, Wildlife No. 232.
  7. Beall, M.L., Jr. (1976). Persistence of Aerially Applied Hexachlorobenzene on Grass and Soil. J. Environ. Qual. 5:4:367-369.
  8. Metcalf, R.L., I.P. Kapoor, Po-Yung Lu, C.K. Schuth, and P. Sherman (1973). Model Ecosystem Studies of Environmental Fate of Six Organochlorine Pesticides, Environmental Health Perspectives, Experimental Issue 4:35-44.
  9. Worthing, Charles R., Editor (1983). The Pesticide Manual, A World Compendium. The British Crop Protection Council, The Ravenham Press Limited, Ravenham, Suffolk, England.
  10. Edwards, I. Ralph, Donald G. Ferry, and Wayne A. Temple.
  11. Fungicides and Related Compounds. in Handbook of Pesticide Toxicology, Volume 3 Classes of Pesticides. Wayland J. Hayes and Edward R. Laws Editors. Academic Press, Inc. NY.
  12. National Institute for Occupational Safety and Health (1983 Supplement) Registry of Toxic Effects of Chemical Substances, U.S. Dept of Health and Human Services,Public Health Service, Centers for Disease Control, Cincinnati, OH.
  13. Occupational Health Services, (1988). Hazardline, New York, NY.
  14. Williams, W. Martin, Patrick W. Holden, Douglas W. Parsons, and Matthew N. Lorber. Pesticides in Ground Water Data Base 1988 Interim Report. 1988. E.S. EPA, Office of Pesticide Programs, Environmental Fate and Effects Division.
  15. Ecobichon, Donald J. (1991). Toxic Effects of Pesticides in Casarett and Doull's Toxicology: The Basic Science of Poisons, Fourth Edition. Mayo O.Amdur, John Doull, and Curtis D. Klaassen editors. Pergamon Press, NY.