Degradation of Mepronil (Basitac®) in Soils under Submerged Conditions in the Laboratory

Abstract

The degradation of [aniline-U-14C]mepronil in a volcanic ash soil (Aso) and an alluvial soil (Kikugawa) was studied under submerged conditions in the laboratory. After incubation of the soil containing 14C-mepronil at 1.6 ppm in a biometric flask in the dark at 29°C for 80 days, the soil was sequentially extracted with methanol/water (2/1) and acetonitrile (extractable) and the residue (bound) was extracted with dichloromethane after treatment with 12 n-NaOH/methanol (1/3) at 70°C for 2 hr. Mepronil was the major constituent in both extracts. Its half-life was 46 and 50.5 days in Aso and Kikugawa soils, respectively, but counting mepronil bound in soils, the half-life extended to 117 and 120 days, respectively. The degradation products were tightly bound on soil particles and the extractable amounts were small. Four of the 7 products were identified as 1-hydroxy-3-oxo-2-(3′-isopropoxy-phenyl)isoindoline, 3′-isopropoxy-2-hydroxymethylbenzanilide, 3′-hydroxy-2-methylbenz-anilide and 3′-(1-hydroxymethylethoxy)-2-methylbenzanilide, indicating that hydroxylation occurs on the three positions of the mepronil molecule. © 1980, Pesticide Science Society of Japan. All rights reserved.