Microbial degradation of gamma-hexachlorocyclohexane (lindane)

Abstract

Organochloride compounds are known to be highly toxic and persistent, causing serious water and soil pollution. Hexachlorocyclohexane (HCH) is the term which collectively identifies the eight isomers of the hexachlorocyclohexane and they are denoted by the greek letters α, β, γ, δ, etc. Among the eight isomers, gamma-hexachlorocyclohexane (γ-HCH or lindane), is the only one with insecticidal properties. γ-HCH has been mainly used in agriculture and vector control programmes. HCH isomers are recognized for their toxicity, persistence in the environment and potential carcinogenic effects. Lindane is a neurotoxin that interferes with GABA neurotransmittor function. In humans, lindane affects the nervous system, liver and kidneys, and may be a carcinogen. Because of this, lindane, a cheap and effective insecticide, is banned in many other countries, while still being used or have been banned only recently in India. Their extensive use has resulted in a widespread occurrence of residues in the environment and in food products. Residues of γ-HCH have been reported from different soil and water systems in India. Efforts have been made for the remediation of soils and groundwater contaminated with the toxic and persistent HCH isomers through biodegradation processes. Microorganisms capable of degrading HCH isomers have received considerable attention as they provide the possibility to be utilized for in situ detoxification. γ-HCH degrading microorganisms, many bacteria and a few fungi, have been isolated and employed for bioremediation of lindane contaminated soil and water systems. The genes and enzymes involved in the γ-HCH degradation pathway have been investigated.