Technical hexachlorocyclohexane (HCH) is a mixture of various HCH isomers; alpha (alpha), beta (beta), delta (delta) and gamma (gamma) (also known as lindane). Both technical HCH and gamma-HCH have been globally used as insecticides, and gamma-HCH also for medical treatment in humans and animals. The insecticidal activity can be almost exclusively attributed to the gamma-isomer. In some areas in the world these compounds are still in use. Because of the lipophilic properties and persistence in the environment, beta-HCH followed by alpha-HCH and to a less extent gamma-HCH may give rise to bioaccumulation and biomagnification through the food chain. HCHs are rapidly absorbed from the gastrointestinal tract, pass the placenta and are transferred into milk. The toxicity of the isomers varies, gamma-HCH being the most acutely neurotoxic followed by alpha-HCH beta-HCH penetrates less readily into the central nervous system, is more persistent and tends to accumulate in the body over time. All isomers cause liver hyperplasia and/or liver tumours. Except for experimental animals there are relatively few data on toxicity in other animal species. Neurotoxicity and liver effects have been reported in fish and ruminants. There is a lack of data on dose-effect relationship, particularly for fish and ruminants beta-HCH has weak estrogenic activity. alpha- and beta-HCH are tumour promoters in rat liver. HCHs were classified by IARC in group 2B (possibly carcinogenic) on the basis of inadequate evidence for carcinogenicity to humans, sufficient (for technical grade and the alpha-isomer) and limited evidence for carcinogenicity to animals (for beta- and gamma-HCHs). Data on occurrence in various feed categories including fish feed indicate levels in the mu g/kg range of alpha-, beta- and gamma-HCH. Accumulation data in fish exposed through feed is lacking. The contamination route of HCHs into feed is not clear. However, the global trade of feedingstuffs and feed ingredients from regions with ongoing or recent use of HCHs may be a major source. A European reporting system, allowing for exposure assessment of undesirable substances in feed is missing. Recent assessments of human dietary exposure to HCHs in Europe are scarce. Considering the available intake data from Czech Republic, Canada and USA and taking into account the decreasing concentration of HCHs in breast milk (about 80 % since the eighties in Germany), current exposure through food is likely to be very low. beta-HCH is usually still present but aand gamma-HCH are only occasionally found in human milk samples from European Countries, which banned the production and use of technical HCH in the late 1970s. Some East European and developing countries with a longer use of technical HCH show higher contamination levels in breast milk.
