Enhanced biodegradation of γ‐hexachlorocyclohexane (γ‐HCH) in HCH (commercial) acclimatized flooded soil: Factors affecting its development and persistence

Moist surface soil samples from a flooded soil, pretreated twice with a commercial formulation of an isomeric mixture of hexachlorocyclohexane (commercial HCH) to induce accelerated aerobic biodegradation of γ‐HCH, were incubated at 20, 25 and 35°C with and without replenishment of water lost by evaporation. Soil samples, kept continuously moist, retained the capacity for accelerated aerobic biodegradation of added γ‐HCH even after 40 days incubation at all three temperatures, but the enhancement factor (causing accelerated degradation of γ‐HCH) was inactivated at 25 and 35°C, and not at 20°C, within 20 days when commercial HCH‐acclimatized soil samples were subjected to moisture stress. Evidence suggested that temperature‐induced moisture stress caused the inactivation of the enhancement factor, especially at 35°C. The enhancement factor developed almost with equal ease in both rice‐straw‐amended and unamended soil irrespective of water regime (flooded or non‐flooded) after multiple applications of a commercial formulation of HCH. The population of γ‐HCH‐degrading aerobic, but not anaerobic, micro‐organisms increased distinctly after each successive application of commercial HCH, interestingly at identical rates in both flooded and non‐flooded soils.Sphingomonas paucimobilis isolatedfrom flooded soil degraded α‐,β‐,δ‐ and γ‐isomers of HCH under aerobic conditions.