beta-Hexachlorocyclohexane

CAS RN:319-85-7

Exposure Summary

beta-Hexachlorocyclohexane's foreign production in the insecticide BHC (technical HCH, containing roughly 60-70% alpha-, 10-15% gamma-, 5-12% beta-, and 6-10% delta and 3-4% epsilon-hexachlorocyclohexane), may result in beta-hexachlorocyclohexane's release to the environment through various waste streams. Non-US use of BHC insecticide will result in beta-hexachlorocyclohexane's direct release to the environment. BHC was banned in the US in 1976 and in Canada in 1971; however, it may still be used in some countries. If released to air, a vapor pressure of 3.6X10-7 mm Hg at 20 deg C indicates beta-hexachlorocyclohexane will exist in both the vapor and particulate phases in the atmosphere. Vapor-phase beta-hexachlorocyclohexane will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 28 days. Particulate-phase beta-hexachlorocyclohexane will be removed from the atmosphere by wet and dry deposition. beta-Hexachlorocyclohexane does not contain chromophores that absorb at wavelengths >290 nm and, therefore, is not expected to be susceptible to direct photolysis by sunlight. If released to soil, beta-hexachlorocyclohexane is expected to have low to slight mobility based upon log Koc values of 3.25-3.50. Volatilization from moist soil surfaces is not expected based upon a Henry's Law constant of 4.4X10-7 atm-cu m/mole. beta-Hexachlorocyclohexane is not expected to volatilize from dry soil surfaces based upon its vapor pressure. Studies in soil indicate that beta-hexachlorocyclohexane undergoes little to no biodegradation aerobically with slightly more degradation under anaerobic conditions. If released into water, beta-hexachlorocyclohexane is expected to adsorb to suspended solids and sediment based upon the Koc values. beta-Hexachlorocyclohexane was completely biodegraded in 20 days under methanogenic conditions in a percolation column experiment using acclimated sediment. Volatilization from water surfaces is not expected based upon this compound's Henry's Law constant. Reported BCFs of 273-1485 in a variety of fish species suggest bioconcentration in aquatic organisms is high to very high. Hydrolysis is likely to occur slowly based on hydrolysis half-lives of 1.2 and 0.8 years at pH values of 7 and 8, respectively, for the alpha isomer. Occupational exposure to beta-hexachlorocyclohexane should be very low or non existent. Monitoring data indicate that the general population may be exposed to beta-hexachlorocyclohexane mainly through ingestion of imported food, lesser exposure may occur from ingestion of drinking water and inhalation of air. (SRC)
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