31P-NMR evaluation of organophosphorus pesticides degradation through metal ion promoted hydrolysis

The degradation of some organophosphorus pesticides (OPPs) in the presence of metal ions was studied by ³¹P-NMR spectroscopy. Both ³¹P-NMR and gas chromatography/mass spectroscopy results were used in order to determine the nature of metabolites formed after degradation. The degraded organophosphorus pesticide were investigated for chlorpyrifos and phoxim in the presence of several metal ions including Hg²⁺, Cu²⁺, Cd²⁺, Ni²⁺, Pb²⁺, and Ag⁺. ³¹P-NMR results indicated Ag⁺ and Hg²⁺ ion promoted degradation of OPPs and other metal ions formed complex with OPPs and cannot degrade OPPs. We found that the degradation of chlorpyrifos and phoxim with Ag⁺ or Hg²⁺ led to the formation of O,O-diethyl-O-methyl phosphorothionate, (C₂H₅O)₂(CH₃O)PS, at metal ion/pesticide mole ratios ≤1.0 and completely decomposed at a higher mole ratio of 10. Finally, the method was successfully applied to the degradation study of a number of technical and formulated pesticides in the presence of Ag⁺ ion at a metal ion/pesticide mole ratio of 10.