Degradation of Fenpyroximate in Upland Soils under Laboratory Conditions

IZAWA Yoshio, HIRANO Atsuko, FUNAYAMA Shunji, UCHIDA Matazaemon

doi:10.1584/jpestics.18.67

Degradation of [pyrazole-3-¹⁴C]-or [benzyl ring-14C(U)]fenpyroximate (tert-butyl (E)-α-[1, 3-dimethyl-5-phenoxypyrazol-4-ylmethyleneamino-oxy]-p-toluate) was studied in Ehime (diluvial) and Kanagawa (volcanic ash) soils under upland laboratory conditions. Soils (25g) fortified with ¹⁴C-fenpyroximate (1.30-2.12ppm) were incubated at 25°C for 112 days in the dark. The compound degraded with half-lives of 34.3-49.7 days in the Ehime soil and of 26.3-35.6 days in the Kanagawa soil. In the soil extracts, twelve degradation products were identified by TLC-co-chromatography, with authentic compounds. Major degradation products were (E)-4-[(1, 3-dimethyl-5-phenoxypyrazol-4-yl)-methyleneaminooxymethyl]benzoic acid (5), 1, 3-dimethyl-5-phenoxypyrazole-4-carboxylic acid (12) and 1, 3-dimethyl-5-phenoxypyrazole-4-carbonitrile (9). In both soils, ¹⁴C-carbon dioxide liberated from [pyrazole-¹⁴C]fenpyroximate during the 112 days accounted for 16.9-17.1% of the applied radioactivity, and that from [benzyl-¹⁴C]fenpyroximate for 51.2-64.6%. Fenpyroximate degradation and CO₂ evolution were negligible in sterilized soils during the incubation. It was assumed that fenpyroximate degraded through hydrolysis of tert-butyl ester, isomerization or cleavage of the oxime ether structure, N-demethylation, oxidation of the methyl group at the 3-position on the pyrazole ring and hydroxylation of the phenoxy ring, and that it finally mineralized to CO₂ and/or bound to soil organic matter.

Degradation of Fenpyroximate in Upland Soils under Laboratory Conditions

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