Persistence of spiromesifen in soil: influence of moisture, light, pH and organic amendment

Abstract

Persistence of spiromesifen in soil as affected by varying moisture, light, compost amendment, soil sterilization and pH in aqueous medium were studied. Degradation of spiromesifen in soil followed the first-order reaction kinetics. Effect of different moisture regimes indicated that spiromesifen dissipated faster in submerged soil (t _1/2 14.3–16.7 days) followed by field capacity (t _1/2 18.7–20.0 days), and dry soil (t _1/2 21.9–22.9 days). Dissipation was faster in sterilized submerged (t _1/2 17.7 days) than in sterilized dry (t _1/2 35.8 days). Photo spiromesifen metabolite was not detected under different moisture regimes. After 30 days, enol spiromesifen metabolite was detected under submerged condition and was below detectable limit (<0.001 μg g⁻¹) after 90 days. Soil amendment compost (2.5 %) at field capacity enhanced dissipation of the insecticide, and half-life value was 14.3 against 22.4 days without compost amendment. Under different pH condition, residues persisted in water with half-life values 5.7 to 12.5 days. Dissipation in water was faster at pH 9.0 (t _1/2 5.7 days), followed by pH 4.0 (t _1/2 9.7 days) and pH 7.2 (t _1/2 12.5 days). Exposure of spiromesifen to different light conditions indicated that it was more prone to degradation under UV light (t _1/2 3–4 days) than sunlight exposure (t _1/2 5.2–8.1 days). Under sunlight exposure, photo spiromesifen metabolite was detected after 10 and 15 days as compared to 3 and 5 days under UV light exposure.