2. Relevance to Public Health 2.1 Background and Environmental Exposures to Hexachlorocyclo- Hexane in the United States

Hexachlorocyclohexane (HCH) is a synthetic chemical consisting of eight isomers. Only four of these isomers—α-HCH, β-HCH, γ-HCH, and δ-HCH—are of commercial significance. γ-HCH, commonly referred to as lindane, is used as seed treatment for barley, corn, oats, rye, sorghum, and wheat. It is also used in very small quantities as a prescription medication for the treatment of scabies and head lice in humans. The FDA does not recommend the use of γ-HCH in infants or in children or adults weighing less than 50 kg. In the past, γ-HCH was used in veterinary products to control mites, lice, and other pests, but recent data suggest that no products are currently registered in the United States for this use. Other HCH isomers, as well as technical-grade HCH, are used either as fungicides or in the synthesis of other chemicals. Technical-grade HCH is comprised of 60–70% α-HCH, 5–12% β-HCH, 10–15% γ-HCH, 6– 10% δ-HCH, and 3–4% ε-HCH. Technical-grade HCH was banned for production and use in the United States in 1976, but still may be used in other countries in small quantities.