ENHANCED BIODEGRADATION OF GAMMA-HEXACHLOROCYCLOHEXANE (GAMMA-HCH) INHCH (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 hexachlorocyclohexa ne (commercial HCH) to induce accelerated aerobic biodegradation of ga mma-HCH, were incubated at 20, 25 and 35-degrees-C with and without re plenishment of water lost by evaporation. Soil samples, kept continuou sly moist, retained the capacity for accelerated aerobic biodegradatio n of added gamma-HCH even after 40 days incubation at all three temper atures, but the enhancement factor (causing accelerated degradation of gamma-HCH) was inactivated at 25 and 35-degrees-C, and not at 20-degr ees-C, within 20 days when commercial HCH-acclimatized soil samples we re subjected to moisture stress. Evidence suggested that temperature-i nduced moisture stress caused the inactivation of the enhancement fact or, especially at 35-degrees-C. The enhancement factor developed almos t with equal ease in both rice-straw-amended and unamended soil irresp ective of water regime (flooded or non-flooded) after multiple applica tions of a commercial formulation of HCH. The population of gamma-HCH- degrading aerobic, but not anaerobic, micro-organisms increased distin ctly after each successive application of commercial HCH, interestingl y at identical rates in both flooded and non-flooded soils. Sphingomon as paucimobilis isolated from flooded soil degraded alpha-, beta-, del ta- and gamma-isomers of HCH under aerobic conditions.