Behaviour of Fipronil in Paddy Field Ecosystem

Abstract

Under normal environmental conditions, fipronil insecticide degrades into a number of metabolites like fipronil sulfone, sulfide, desulfinyl, etc. They can persist in environment for longer duration and can have adverse effect on soil, water bodies along-with persistence of residuals in edibles and other plant by-products like straw. In order to evaluate the impact of using fipronil in paddy field ecosystem and to provide basic information for its degradation behavior, a field experiment was done by applying the insecticide @ 56 and 112 g a.i./ha following standard agronomic conditions. Soil and water samples were collected periodically. Paddy grain, husk and straw samples were collected at harvest. Fipronil residues were analyzed by GC-MS tandem mass spectrometry. In soil, more than 48 % residues degraded in 7 days and reached below detectable limit after 49 days with half-life period of 9.29 and 10.13 days at two doses showing degradation rate to be biphasic with first order kinetics. In field water, residues reached below detectable limit on 49th day at single dose with half-life period of 14.71 days where as at double dose application, 91.52 % fipronil was found dissipated on 49th day after application with half-life period of 14.31 days. In rice grains, husk and straw, fipronil residues were found below MRL at single dose.