Photodegradation of fenitrothion and parathion in tomato epicuticular waxes

Photodegradation of C-14-labeled fenitrothion ([O,O-dimethyl O-(3-methyl-4-nitrophenyl) phosphorothioate]) and parathion ([O,O-diethyl O-(4-nitrophenyl) phosphorothioate]) was conducted on a series of solid surfaces including isolated tomato fruit and leaf cuticle waxes. The wax-coated glass plate gave the comparative degradation of fenitrothion observed for the intact plant but both surfaces of octaclecyl-capped silica gel and poly(tetrafluoroethylene) enhanced its volatilization. Photoinduced desulfuration and ester cleavage were common to both pesticides in waxes, but formation of the azo derivative was found to be a major degradation pathway characteristic of parathion. The modified electronic states of the nitro group by introduction of m-methyl group accounted for this different photoreactivity based on molecular orbital calculations.