Alpha- and beta- hexachlorocyclohexanes / published under the joint sponsorship of the United Nations Environment Programme, the International Labour Organisation, and the World Health Organization

ABSTRACT

Evaluates the risks to human health and the environment posed by exposure to alpha- and beta-hexachlorocyclohexanes (HCH). These two isomers are by-products in the manufacturing of lindane, and may be present in this pesticide as impurities. Alpha- and beta-HCH are also present in technical-grade HCH, which is used in agriculture and wood protection. Most environmental releases are linked to the use of technical-grade HCH and to the inappropriate disposal of residues produced when lindane is purified. Alpha- and beta-HCH are evaluated in separate monographs, which cover sources of human and environmental exposure, levels detected in different environmental media, behaviour in the environment, metabolic fate in different organisms, and toxic effects on experimental animals, humans, and plant and animal species. Both isomers are noted to be universal environmental contaminants, with concentrations detected in samples of air, rain water, fresh water, sea water, soil, sediment, and numerous plant and animal species, as well as in several important food items. A review of studies on environmental behaviour and metabolic fate concludes that alpha- and beta-HCH, when compared with lindane, are characterized by a higher bioconcentration in the environment, a slower rate of biodegradation by ultraviolet light, and a slower rate of elimination from organisms. Concerning sources of human exposure, studies show that, in industrialized countries, more than 90% of human intake occurs through the consumption of contaminated food, with the highest concentrations found in fat-containing food items. Current exposures via food are judged to be low and gradually decreasing, supporting the conclusion that these isomers pose no serious health threat to the general public. A review of findings from toxicity studies in laboratory animals identifies growth retardation and effects on the liver and kidney as the major consequences of acute exposure. Although a neoplastic response was observed in some studies, the report concludes that this response is most likely due to a non-genotoxic mechanism. In its concluding section, the report expresses serious concern over the widespread pollution of the environment with these isomers. As neither has any insecticidal action, the report concludes that use of technical-grade HCH products containing high concentrations of alpha- and beta-HCH is never justified