LEACHING OF HEXACHLOROCYCLOHEXANE ISOMERS IN A FLOODED FIELD UNPLANTED OR PLANTED TO RICE

Leaching of alpha-, beta-, gamma- and delta-isomers of hexachlorocyclohexane (HCH) in a commercial formulation, sprayed to a flooded field (unplanted or planted to rice) at 1.0 kg a.i. ha(-1) on gamma-isomer basis, was studied with the help of field-installed porous moisture extraction cups. Residues of HCH-isomers in the surface field water and leachates (at 15, 30 and 60 cm) were higher in planted field than in unplanted field, probably due to less volatilization of HCH-isomers under the crop cover. HCH-isomers, with the exception of beta-isomer, migrated to 30 cm depth; beta-isomer did not move beyond 15 cm depth possibly due to lower amount of this isomer available for leaching while alpha-HCH was detected even at 60 cm depth. gamma-Tetrachlorocyclohexene, a predicted metabolite of gamma-HCH in anaerobic environments, was detected in the the leachate even at 60 cm depth.