Photodegradation chemistry of the insecticide phosmet in lipid models and in the presence of wool wax, employing a 15N-labeled compound

The organophosphorus insecticide phosmet is commonly used for plant protection as well as against pests on animals. Phosmet features numerous degradation pathways induced by UV irradiation. In this study, we focused on the reaction possibilities of phosmet in the presence of lipophilic substances with olefinic structure elements, as they are frequently found in animal fur lipids, especially in wool wax. In the first step, simple models were employed to characterize the structural types of formed photoaddition products. On irradiation in the presence of cyclohexene, three photoaddition products were identified, a (4pi + 2pi) cycloaddition product of phosmet and cyclohexene and two diastereoisomer carbinols. Likewise, in more sophisticated models employing fatty acid methyl esters for irradiation experiments, phosmet was readily photodegraded. In the presence of methyl oleate, also 1:1 photoaddition products could easily be identified by means of liquid chromatography-mass spectrometry, using a stable isotope-labeled phosmet (15N-phosmet, 50 at. %) for the photolysis experiments. To converge from models to the more complex natural environment of animal skin lipids, irradiation experiments of phosmet in the presence of wool wax were performed. After 24 h of irradiation, only a remnant of 1.4% of the initial phosmet was detectable. Phosmet-oxon was detected in concentrations up to 27.3 mol %.