Degradation of soil-applied isomers of hexachlorocyclohexane by a Pseudomonas SP

Abstract

A Pseudomonas sp., that readily degraded α-,β- and γ-isomers of hexachlorocyclohexane (HCH) in a mineral salts medium under aerobic conditions, was tested for its ability to degrade these isomers after their application to two soils under flooded or nonflooded conditions. Interestingly, the concentration of soil-applied α- and γ-HCH decreased from the original concentration of 5 μg g^-1 soil to undetectable amounts within 10-20 days in soils inoculated with Pseudomonas sp., and the loss of both isomers was more pronounced under nonflooded conditions than under flooded conditions. During the corresponding period, there was no appreciable loss of either isomer from uninoculated soils. The degradation of β-HCH was not accelerated by bacterial inoculation of the soils under either water regime despite the ability of the bacterium to degrade this isomer when added to the mineral salts medium. The rapid degradation of α- and γ-HCH, and not β-HCH, in inoculated soils is attributed to the ability of the bacterium to utilize α- and γ-HCH, and not β-HCH, for growth. Addition of sodium acetate to the mineral salts medium enhanced the bacterial degradation of β-HCH implicating cometabolism and retarded the degradation of γ-HCH.