Degradation and Metabolization of Lindane and Other Hexachloro- cyclohexane Isomers by Anaerobic and Aerobic Soil Microorganisms

Microbial Metabolization of Hexachlorocyclohexane, Anaerobic and Aerobic Microorganisms, Dechlorination of Hexachlorocyclohexane Microbial degradation of lindane or other hexachlorocyclohexane isomers has been observed to occur more rapidly in flooded than in upland soils. Experiments with a mixed bacterial flora enrich­ ed anaerobically from soils showed a rapid dechlorination and degradation of lindane. Screening studies with pure bacteria indicated that Clostridium spp. and several representatives of Bacillus spp. and Enterobacteriaceac effectively degraded lindane, while representatives of Lactobacillaceae and Propionibacterium were inactive. During degradation organic bound chlorine was released as chloride and nearly chlorine-free, partly volatile metabolites were formed. The chloride formation was promoted by the addition of glucose, pyruvate or formate. Lindane was the most easily degraded isomer, while α-and especially β-and δ-hexachlorocyclo-hexane was also, but more slowly, dechlorinated. These isomers are relatively frequently observed as environmental contaminants, their occurrence might be caused by their greater persistence or / and by an isomerization of the γ-into α-and other isomers during microbial incubation as it was discussed by several authors. Experiments, however, whether or not this isomerization can be carried out by microbes, were negative or showed that it only can occur to a very minor extent. Aerobic degradation of lindane proceeded only slowly and chiefly by formation of chlorinated aromatic compounds. One of the main intermediate metabolites seemed to be γ-pentachlorocyclo-hexene which was further transformed by the release of HCl or hydrogen and by addition of water. During anaerobic incubation, γ-tetrachlorocyclohexene intermediately occurred which was further dechlorinated to nearly chlorine-free compounds.