Degradation and metabolism of Oxamyl and phenamiphos in soils

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Abstract
Degradation and metabolism of the nonvolatile nematicides‐insecticides [14C]oxamyl and [14C]phenamiphos (P) were investigated using three Southeastern U.S. soils (Arredondo sand, Cecil sandy loam and Grenada silt loam). Oxamyl in moist soils (10 and 33 kPa) was rapidly mineralized to CO2, with N,N‐dimethyl‐2‐(methylthio)acetamide oxime (DMAO) being the major intermediate metabolite. Half‐lives (t½) for extractable 14C in [14C]oxamyl treated soils ranged from 8 to 50 d. Although the principal 14C component in organic solvent extracts was oxamyl, 4 to 27% of applied 14C in the extracts were found to be associated with metabolites. Consequently, t½ values for oxamyl would be smaller than t½ values for extractable 14C. Oxidation of ? to phenamiphos sulfoxide (PSO) in Arredondo soil was rapid. PSO was then slowly degraded to phenamiphos sulfone (PSO2), and at the same time PSO was also hydrolyzed to PSO phenol. Total toxic residue (TTR = ? + PSO + PSO2) in moist soil (10 and 33 kPa) disapppeared more rapidly than in dry soil (100 and 1500 kPa). t½ values for TTR in Arredondo soil held at various soil‐water tensions ranged from 38 to 67 d.

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