Degradation Of Fipronil Research Articles

The fate of fipronil in modular estuarine mesocosms.

The degradation and corresponding product manifold for the pesticide fipronil was determined in three replicate estuarine mesocosms. Aqueous fipronil concentrations rapidly decreased over the 672 h timescale of the experiment (95% removal). Loss was apparently first-order in fipronil, although there appeared to be a change in the removal mechanism after 96 h that corresponded to a dramatic slowdown in its disappearance. The reduction product of fipronil, fipronil sulfide, was not detected in the water column; however, it formed rapidly in sediments and was identified as the major product of fipronil degradation in the system (20% yield at 672 h, with respect to initial fipronil concentration). Fipronil sulfone is thought to form primarily via biological oxidation; and, although it was generated rapidly in the water column (10% yield), only trace amounts were detected in the sediment (1% yield). The direct photolysis product of fipronil, fipronil desulfinyl, was present in all samples; it formed rapidly in the water column (4% yield) and partitioned into the sediment phase (7% yield) over the course of the experiment. The mass balance on fipronil and associated products was 42% at 672 h.

Laboratory and field studies on the degradation of fipronil in a soil

Degradation of a new insecticide/termiticide, fipronil, in a soil was studied in the laboratory and field. Three metabolites of fipronil (desulfinyl, sulfide, and sulfone derivatives) were identified from soils after treatment. Laboratory studies showed that soil moisture content had a great effect on the degradation rate of fipronil and products formed. High soil moisture contents (>50%) favored the formation of a sulfide derivative of fipronil by reduction, whereas low soil moisture (<50%) and well-aerated conditions favored the formation of fipronil sulfone by oxidation. Microorganisms in soil accelerated the degradation of fipronil to sulfide and sulfone derivatives. The third transformation product, a desulfinyl derivative, was formed by photodecomposition of fipronil in water and on the soil surface under sunlight. The desulfinyl derivative degraded rapidly in field soils with a half-life of 41–55 days compared with an average half-life of 132 days for fipronil. The half-life of the 'total toxic component' (fipronil and its metabolites) in field soil was 188 days on average.

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

The fate of fipronil, a phenylpyrazole insecticide, and its metabolites under tropical conditions was studied in soil and in vegetation after treatment for locust control. Two different plots were treated with a formulation of 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 immunoaffinity cartridges, residues were analyzed by gas chromatography using electron capture and mass detectors. In soil, a rapid initial decrease of fipronil was observed with a rapid formation of the sulfone and the photodegradate; the amide and the sulfide were not detected. In vegetation, a rapid initial decrease of fipronil was also observed with a rapid formation of mostly the sulfone; the photodegradate and the sulfide were also detected but at much lower concentrations. The metabolites resulting from the degradation of fipronil were similar in both soil and vegetation, but their relative concentrations were different.

Kinetics and Mechanisms of Abiotic Degradation of Fipronil (Hydrolysis and Photolysis)

The abiotic degradation of fipronil (compound I), a phenylpyrazole insecticide, was studied in aqueous solution and on the surface of two soils from Niger (Saguia and Banizoumbou) and one Mediterranean soil (Montpellier). The rate of hydrolysis of fipronil in solution was measured at different values of pH and temperature. The pH was an influencing factor: hydrolysis kinetics were pseudo-first-order, the half-life being 770 h at pH 9.0, 114 h at pH 10.0, 11 h at pH 11.0, and 2.4 h at pH 12.0. Fipronil was stable under acid (pH 5.5) and neutral conditions. The Arrhenius relation was verified over the temperature range 22−45 °C: the activation energy was 62 kJ mol-1 and the calculated entropy change −32 J mol-1. Compound II [5-amino-3-carbamoyl-1-(2,6-dichloro-4-(trifluoromethyl)phenyl)-4-[(trifluoromethyl)sulfinyl]pyrazole] was the only hydrolysis product detected. The hydrolysis reaction mechanism involves nucleophilic addition of OH- to the polar nitrile bond, producing a hydroxyimine which then underg...