Atmosphere

Air toxics and indoor air quality in Australia

State of knowledge report
Environment Australia, 2001
ISBN 0 6425 4739 4

Part C: Factsheets (continued)

Hexachlorobenzene (HCB)

Substance name: Hexachlorobenzene
CASR number: 118-74-1
Molecular formula: C6Cl6
Synonyms: Perchlorobenzene; benzene hexachloro; HCB; bunt-cure; pentachlorophenyl chloride; and Julian's carbon chloride

Physical and chemical properties

HCB occurs as white needles, very slightly soluble in water. It is slightly soluble in cold alcohol, soluble in benzene, chloroform, ether, carbon disulfide, and boiling alcohol.

Melting point (pure): 230°C
Boiling point (pure): 332°C
Specific gravity: 2.044
Vapour density: 9.83

Hexachlorobenzene has a very low chemical and biochemical reactivity. This is reflected in its long persistence in the environment. HCB is combustible and decomposes to produce toxic fumes at high temperatures. It reacts violently with dimethyl formamide above 65°C.

Common uses

There are currently no commercial uses of HCB in Australia. HCB has been widely used as a pesticide to protect the seeds of onions and sorghum, wheat, and other grains against fungus, but is no longer registered for this use in Australia. It was also used in the production of fireworks, ammunition, rubber, aluminium and dyes, and in wood preservation.

Sources of emissions

Point sources

Sources include the aerospace industry, sanitary services, agricultural chemicals manufacturers; industries involved in the manufacture of solvents, other chlorine-containing compounds and pesticides; wood-preserving plants; and municipal waste incinerators.

Diffuse sources

Diffuse sources include small incinerators and agricultural run-off, especially from grain applications (HCB may be present for years after its use was banned because this substance is persistent in the environment).

Natural sources

None known.

Mobile sources

None known.

Consumer products that may contain HCB

HCB has been banned from use as a pesticide in Australia. No consumer products should intentionally contain it. However, it is a global pollutant and may be found as a contaminant in a variety of foods.

Health effects

How might I be exposed to HCB?

People may be exposed to HCB if they live near an industrial site where it is used or produced as a byproduct, or a waste dump where it has been discarded. At these sites HCB may be carried in the air on dust particles. If you work in an industry that produces the chemical unintentionally as a byproduct or uses HCB, you may also be exposed to HCB particles or dust particles that carry HCB.

Exposure to HCB can occur through eating and drinking contaminated foods and liquids, such as milk, other dairy products, meat, and poultry. When HCB is eaten in combination with fat or oil, the body takes up more of it than when it is consumed in drinking water. HCB is usually not present in drinking water, due to its low water solubility.

By what pathways might HCB enter my body?

HCB can enter the body when someone ingests HCB-contaminated food, breathes HCB particles in the air, and/or through skin contact with HCB. Following intake, HCB rapidly spreads to many tissues in the body, especially to fat. HCB will remain in your body, especially in fat, for years. A large portion of HCB in fat can be transferred in human milk.

Health guidelines

There are no national guidelines.

What effect might HCB have on my health?

The heath effects caused by breathing HCB-contaminated particles or by getting HCB on your skin are not known. Porphyria-induced skin disorders have been reported in humans following the ingestion of bread prepared from grain containing HCB. There is evidence that HCB is toxic to young children; offspring nursing from HCB exposed mothers are exposed through the milk. HCB has been found to decrease the survival rates of young children. Therefore, nursing infants may be particularly susceptible due to the transfer of HCB through maternal milk. This has been confirmed by experiments on animals. Other animal studies show that ingestion of HCB on a long-term basis can harm the liver, immune system, kidneys and blood and can produce eruptions and pigmentations of the skin. Studies in animals also suggest that ingestion of enough HCB on a long-term basis can lead to cancer of the liver and thyroid. HCB is classified by the National Occupational Health and Safety Commission (NOHSC) as a category 2 carcinogen (substance which should be regarded as if it is carcinogenic to humans).

Environmental effects

Environmental fate and transport

HCB has been detected in environmental samples from around the world, and is recognised as a global pollutant.

HCB is a highly persistent compound, with a reported field half-life in soil of up to 7.5 years. It is moderately to strongly bound by most soils. Data from testing on hydro-soils indicate that it may be degraded both aerobically and anaerobically. It has low water solubility and thus is likely to show low mobility in the soil environment. However, its lengthy persistence means that even low mobility may result in appreciable travel; therefore, HCB may pose some risk of groundwater contamination. HCB has been found in well water at low concentrations of up to 5.6 ppb and only in a very small percentage of all the wells tested.

HCB has low water solubility, so it would probably reach surface waters via surface run-off by attachment to soil particles. Once in the aquatic environment, it is likely to be short-lived, as it is known to undergo rapid degradation in inoculated hydro-soil samples under both aerobic and anaerobic conditions.

High levels can build up in fish, marine mammals, birds, lichens, and animals that eat lichens or fish. Levels can also build up in wheat, grasses, some vegetables, and other plants.

Environmental guidelines

Australian Water Quality Guidelines for Fresh and Marine Waters (ANZECC 1992):

What effect might HCB have on the environment?

Acute toxic effects may include the death of animals, birds, or fish, and death or low growth rate in plants. Acute effects are seen two to four days after animals or plants come in contact with a toxic chemical substance. Chronic toxic effects may include shortened lifespan, reproductive problems, lower fertility, and changes in appearance or behaviour.

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