SOLAR PHOTOOXIDATION OF PESTICIDES IN DILUTE HYDROGEN-PEROXIDE

Dilute H2O2 (5-100 .mu.M) initiated photooxidation of thiolcarbamate, chlorophenoxy acid, organophosphorus, N-methylcarbamate, cyclodiene and other classes of commercial pesticides in sunlight and near-UV light. Levels of photodecomposition in 100 .mu.M H2O2 were increased by factors of 1.5 to > 25 with the greatest rate enhancements for compounds with low direct photolysis rates (and weak absorption at 290 nm). Hydroxyl free radicals (HO.cntdot.) were major reactants in the system as demonstrated by isomer distributions for the hydroxylation of nitrobenzne and by the quenching of nitrobenzene oxidation with added methanol. HO.cntdot. mechanisms were proposed to account for the photoinduced epoxidation and rearrangement of aldrin to dieldrin and photoaldrin, respectively. H2O2 also initiated photochemical S oxidation, aromatic ring hydroxylation, N-dealkylation and oxidations at saturated carbons of the herbicides molinate and thiobencarb. H2O2 promoted photooxidation reactions at concentrations that occurred naturally in agricultural irrigation water and other surface waters.