Gamma-HCH Lindane

Meera P, Rao PR, Shanker R, Tripathi O (1992) Immunomodulating effects of gamma-HCH (lindane) in mice. Immunopharmacol Immunotoxicol, 14 261-282. 

The first commercially available HCH insecticide sometimes misleadingly called benzene hexachloride (BHC) was a mixture of isomers, principally alpha HCH (65-70%), beta HCH (7-10%), and gamma HCH (14-15%). Most of the insecticidal activity was due to the gamma isomer (Figure 5.1), a purified preparation of which (>99% pure) was marketed as lindane. In Western countries, technical HCH was quickly replaced by lindane, but in some other countries (e.g., China) the technical product, which is cheaper and easier to produce, has continued to be used. HCH has been used as a seed dressing, a crop spray, and a dip to control ectoparasites of farm animals. It has also been used to treat timber against wood-boring insects. 

Technology isoproturon, simazine, aldrin (HHDN), terbuthylazine, lindane (gamma-HCH), chlortoluron, atrazine, desethyl-atrazine (GC-FID and HPLC-UV) 10 pi (HPLC-UV)... 

HCH, sometimes misleadingly termed benzene hexachloride (BHC), exists in a number of different isomeric forms of which the gamma isomer has valuable insecticidal properties. These were discovered during the 1940s, and HCH came to be widely used as an insecticide to control crop pests and certain ectoparasites of farm animals after the Second World War. Crude technical BHC, a mixture of isomers, was the first form of HCH to be marketed. In time, it was largely replaced by a refined product called lindane, containing 99% or more of the insecticidal gamma isomer. 

Chlorination of benzene gives an addition product that is a mixture of stereoisomers known collectively as hexachlorocyclohexane (HCH). At one time, this was incorrectly termed benzene hexachloride. The mixtnre has insecticidal activity, though activity was found to reside in only one isomer, the so-called gamma isomer, y-HCH. y-HCH, sometimes under its generic name lindane, has been a mainstay insecticide for many years, and is about the only example of the chlorinated hydrocarbons that has not been banned and is still available for general use. Although chlorinated hydrocarbons have proved very effective insecticides, they are not readily degraded in the environment, they accumulate and persist in animal tissues, and have proved toxic to many bird and animal species. 

These are usually abbreviated as HCHs for obvious reasons. The most well known of these compounds is lindane, which is also known as the gamma isomer of HCH or y-HCH. Its structure is given below. 

Lindane is absorbed from the gastrointestinal tract, the respiratory tract, and skin. The metabolism of lindane is complex and involves a number of pathways depending on which isomer of hexachlorocyclohexane (HCH) is involved (lindane is the gamma (y) isomer). It is nonetheless rapid. Lindane is metabolized in the liver by microsomal enzymes. The main pathways include stepwise elimination of chlorines to form tri- and tetrachloro-phenols and conjugation with sulfates or glucuron-ides and subsequent elimination. Other metabolic pathways involve the production of mercaptura-tes. These water-soluble products are eliminated in the urine. Lindane is bound by serum proteins in the blood. Storage is in adipose tissue and other... 

Metabolic patterns of lindane presented by many working groups differ more or less from each other. With regard to the investigation of microbial metabolism this is based obviously on the fact that anaerobic and aerobic metabolisms of HCH are not always comparable. Under anaerobic conditions fast dehydrogenation takes place yielding gamma-... 

The discussion on the importance of the lindane metabolite gamma-PCCH in warm-blooded organisms continues. All published schemes of lindane metabolism, however, include gamma-PCCH even if authors have not been able to identify this metabolite (see in Engst et al. 1977 b. Figs. 2 and 5). Gamma-PCCH formation by microbes and in plants is a frequently confirmed fact. The importance of PCCH as a key metabolite of HCH was supported by considerations of Tanaka et al. (1977), Figure 5 and 6. 

---