Description:
During the production of the pesticide Lindane (gamma-hexachlorocyclohexane (HCH)), about 85% of the product consisted of isomers such as alpha-, beta- and delta-HCH. They were discarded into the environment, causing serious soil pollution. Aerobic biodegradation mineralizes alpha-, gamma-, and delta-HCH, whereas beta-HCH persists. Therefore, the degradation of beta-HCH and the other isomers was studied under anaerobic conditions by Peter Middeldorp (Environmental Science and Technology (1996) 30(7):2345-2349), in order to develop an anaerobic soil treatment process. beta-HCH was found to anaerobically biodegrade to benzene and chlorobenzene, both of which can undergo further degradation aerobically. The pathway from beta-HCH to benzene and chlorobenzene is the first anaerobic pathway in the EAWAG-BBD. This pathway can be carried out by a Dehalobacter sp. in coculture with a Sedimentibacter sp. ([http://www.ncbi.nlm.nih.gov/pubmed/16329975|van Doesburg et al., 2005]). A second, aerobic, beta-HCH metabolic pathway is mediated by haloalkane dehalogenase LinB in Sphingomonas paucimobilis UT26. The stereochemistry of the 2,3,4,5,6-pentachlorocyclohexanol has not been determined; the stereoisomer shown is based on beta-HCH. The pentachlorocyclohexane is not further metabolized ([http://www.ncbi.nlm.nih.gov/pubmed/15812056|Nagata et al., 2004]). The biodegradation pathway for gamma-hexachlorocyclohexane is found elsewhere.