ACCELERATED AEROBIC DEGRADATION OF GAMMA-HEXACHLOROCYCLOHEXANE IN SUSPENSIONS OF FLOODED AND NON-FLOODED SOILS PRETREATED WITH HEXACHLOROCYCLOHEXANE

A commercial wettable-powder formulation (50% a.i.) of hexachlorocyclohexane (HCH) was applied to unplanted and planted (to rice) soils under flooded and non-flooded conditions at 1 kg a.i. ha-1 at 15-day intervals. A mineral salts medium supplemented with gamma-HCH as a sole source of C was inoculated with suspensions from HCH-treated and untreated soils (unplanted or planted to rice) and incubated under aerobic conditions. Gamma-HCH disappeared completely within 10 days from the aerobically incubated medium inoculated with the suspension from the treated soil compared to less than 30% loss from the uninoculated medium or from the medium inoculated with the suspension from the untreated soil, during the corresponding period. Soil samples from HCH-treated flooded pots lost their capacity for accelerated degradation of gamma-HCH after autoclaving. The addition of HCH clearly stimulated aerobic degradation of gamma-HCH, even in predominantly anaerobic flooded soil. The factor responsible for the accelerated degradation of gamma-HCH in pretreated soil was not detected in the deeper layers (> 10 cm) of flooded soil and in fields that had dried following the rice harvest.