Fate of a phenylpyrazole in vegetation and soil under tropical field conditions

The fate of fipronil, a phenylpyrazole insecticide, and its metabolites und er tropical conditions was studied in soil and in vegetation after treatmen t for locust control. Two different plots were treated with a formulation o f fipronil at doses of 5 and 10 g of active ingredient ha(-1), respectively . Vegetation and soil at depths of 0-5 and 5-20 cm were sampled for up to 2 months after treatment. After extraction and purification on fipronil immu noaffinity cartridges, residues were analyzed by gas chromatography using e lectron capture and mass detectors. In soil, a rapid initial decrease of fi pronil was observed with a rapid formation of the sulfone and the photodegr adate; the amide and the sulfide were not detected. In vegetation, a rapid initial decrease of fipronil was also observed with a rapid formation of mo stly the sulfone; the photodegradate and the sulfide were also detected but at much lower concentrations. The metabolites resulting from the degradati on of fipronil were similar in both soil and vegetation, but their relative concentrations were lifferent.