Persistence of gamma-BHC and beta-BHC in Indian rice soils under flooded conditions

The relative persistence of [¹⁴C]-gamma-BHC and [¹⁴C]-beta-BHC in Indian rice soils under flooded conditions was studied. In alluvial, laterite and pokkali (acid sulphate, saline) soils, rapid degradation of both isomers occurred; in sandy and kari (acid sulphate, saline) soils, both isomers persisted even after 41 days of flooding. The rapid degradation of BHC isomers in the former three soils was related to highly negative redox potentials within 20 days of flooding in contrast to oxidised conditions in sandy and kari soils even after 41 days. During the degradation in the soils, beta-BHC showed longer lag than gamma-BHC. Results suggest that the degradation of beta-BHC commences at a potential lower than that required for gamma-BHC degradation. Greater decomposition of gamma-BHC occurred in rice straw-amended soils than in unamended soils when the insecticide was incorporated to the soils in an aqueous solution. Addition of BHC isomers to the soils in ethanol resulted in comparable rates of rapid decomposition in both rice straw-amended and unamended soils, since ethanol was as effective as rice straw in lowering the redox potentials of the soils favouring BHC decomposition in unamended soil as well.