Pesticide Reactivity toward Hydroxyl and Its Relationship to Field Persistence

To estimate the reactivity of organic pesticides toward hydroxyl, a standard competitor, p -nitroso- N, N -dimethylaniline (PNDA), competes with a particular compound for the radicals produced by the photolysis of hydrogen peroxide. The rate at which the pesticide competes with PNDA for hydroxyl determines its reactivity. Of 10 pesticides tested, carbaryl was the most reactive, carbofuran and MCPA were of intermediate reactivity, and hexazinone was one of the least reactive. Experiments in irradiated field water, both in the laboratory and in sunlit rice paddies, showed that pesticide dissipation rates followed the order of reactivity with hydroxyl radical.