Persistence of fipronil and its metabolites in sandy loam and clay loam soils under laboratory conditions

Samples of sandy loam and clay loam soils were collected from different geographical locations of Punjab. These soils were autoclaved at 120 °C at 15 psi for 15 min to destroy the microbes responsible for the degradation of pesticides before initiating the experiment. Each soil was fortified at three levels of fipronil i.e. 100, 200 and 400 mg kg−1. The whole experiment was conducted at 25 ± 2 °C under laboratory conditions. The residues of fipronil and its metabolites were quantified by Gas Liquid Chromatograph (GLC) and confirmed by Gas Liquid Chromatograph–Mass Spectrometry (GC–MS). The limit of quantification of fipronil and its metabolites was worked out to be 0.001 mg kg−1. The residues of total fipronil in sandy loam and clay loam after 7 d of its application @ 100 mg kg−1 were found to be 74.30 and 82.50 mg kg−1, respectively. Fipronil residues were degraded to amide, sulfone and sulfide in both soils. Desulfinyl metabolite was not found in any of the sample. The persistence of fipronil was found to be more in clay loam soil than sandy loam soil. Total fipronil residues were not found to follow the first order kinetics. Half-life (T1/2) of total fipronil was observed to be 30.10, 33.44 and 33.44 d following application of fipronil @ 100, 200 and 400 mg kg−1, respectively in sandy loam soil. In clay loam soil, half-life values were observed to be 37.63 d following application of fipronil at all three treatments.

► Fipronil residues were degraded to amide, sulfone and sulfide.
► Desulfinyl metabolite was not found in any of the sample.
► Persistence of fipronil was found to be more in clay loam soil than sandy loam soil.
► Total fipronil residues were not found to follow the first order kinetics.