PESTICIDE REACTIVITY TOWARD HYDROXYL AND ITS RELATIONSHIP TO FIELD PERSISTENCE

To estimate the reactivity of organic pesticides toward hydroxyl, a st andard 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, carba ryl was the most reactive, carbofuran and MCPA wee of intermediate rea ctivity, and hexazinone was one of the least reactive. Experiments in irradiated field water, both in the laboratory and in sunlit rice padd ies, showed that pesticide dissipation rates followed the order of rea ctivity with hydroxyl radical.