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Environmental impact

Hexachlorobenzene is among the most persistent environmental pollutants because of its chemical stability and resistance to degradation. If released to the atmosphere, hexachlorobenzene exists primarily in the vapor phase and degradation is extremely slow.
Past disposal methods for industrial wastes containing hexachlorobenzene included incineration, disposal in landfills, discharge to municipal sewage treatment plants, and emission to the atmosphere. Landfill disposal of hexachlorobenzene can lead to migration of the compound via water and sublimation of the compound into the air.
Halflife estimations for hexachlorobenzene in the atmosphere are highly variable and depend on region of occurrence. Longrange global transport is possible from the tropic/temperate to the polar regions. Physical removal of hexachlorobenzene from the air may occur via washout by rainfall or snowfall, or via dry deposition. If it is released to the soil, it adsorbs strongly to the soil particles. HBC halflife existence in soil depends on temperature and moisture of surrounding environment. In tropics evaporation is faster and microorganisms degree it faster. If released to water, volatilization from the water column will be moderately rapid and taking into consideration that HCB does not dissolve in water very well and the high organic carbon partition coefficient (KOC), most of it will remain in particles on the bottom of lakes, rivers, or streams.

Half-life of hexachlorobenzene in the environment
Environmental mediumHalf life [years]

Atmosphere

0.63 – 6,28       

     Tropical/subtropical regions0,63
     Temperate/boreal regions1,94
     Polar region6,28
Soil3 – 6
Surface waters2.7 – 5.7
Ground waters5.3 – 11.4

The most possible way of being exposed to hexachlorobenzene is by eating and/or drinking contaminated foods and liquids, such as milk, other dairy products, meat, and poultry, if the animals from which these products are obtained have been exposed to HCB contamination. Additionally, fat and oil in food may increase the amount of hexachlorobenzene that enters the body from food. An estimated average yearly uptake of 1 microgram per kilogram (μg/kg) of body weight has been calculated for exposure to contaminated food.
Exposure by breathing contaminated air is estimated to be 0.01 μg/kg/year. This is 100 times less than the exposure from eating contaminated foods. Exposure to hexachlorobenzene may occur near an industrial site where it is produced as an unintentional byproduct or as a minor part of another chemical product or near a hazardous waste site where hexachlorobenzene has been discarded. At these sites, HCB may be carried in the air on dust particles but exposure may also occur through contact with contaminated soil.
Because HCB does not dissolve easily in water, it is usually not present in high concentrations in drinking water; therefore exposure to this substance through drinking water is limited. Drinking contaminated water is estimated to contribute only very small amounts (0.00085 μg/kg/year).
Low levels of hexachlorobenzene have been found in the fatty tissues of almost all people tested. These amounts are most likely the result of low levels in food.

 


Structure formula of HCB


3D structure of HCB