Fate of endosulfan in cotton soil under sub-tropical conditions of northern India

Terrestrial field studies were conducted with endosulfan during the 1989-90 Kharif season in bare cotton soil, to investigate the fate of endosulfan and its downward movement under sub-tropical conditions of northern India. Field experiments consisted of spray application of endosulfan at 875 g ha(-1) 42 and 63 days after the assumed date of sowing in two separate treatments. Soil samples drawn periodically from different depths were analysed by GC-ECD (Ni-63) for endosulfan and its breakdown products. Dissipation of the total endosulfan residues occurred to an extent of 92-97% in the first four-week period and by about 99% in 238 days in two distinct phases in first-order kinetics. Residue half life (T-1/2) varied from 39 to 42 days. The parent compound metabolized to endosulfan-diol and endosulfan sulfate. Endosulfan-diol remained confined in the upper 5-cm layer and dissipated completely in 28 days whereas endosulfan sulfate was first detectable seven days after treatment and persisted until the end of the experiment, remaining confined in the upper 0-10 cm soil layer. The beta-isomer also did not leach down beyond 10 cm depth.