Pesticide photoproducts: generation and significance

As with the parent pesticide, the significance of a pesticide photoproduct depends on its concentration in a given environmental compartment, its toxicity, and exposure of the organism or ecosystem of interest. This requires an understanding of the production and environmental chemistry of each photoproduct as well as its toxicity. While these data are generally available for the parent pesticide, they are rarely determined in detail for the photoproducts. Although the environmental photochemistry of each pesticide is different, some generalizations can be made. Photochemical oxidations, reductions, hydrolytic reactions, and isomerizations often generate products identical to those of metabolic and nonbiological transformations. The chemistry and environmental stability of each individual photoproduct can be substantially different from those of the original pesticide and other products. With several notable exceptions, however, photoproducts are generally less stable to environmental forces and less toxic than the parent pesticide, at least to the target organism. A most significant exception is the P = S to P = O conversion in the organophosphorus insecticides. This sunlight promoted reaction is important in treated fields and has been implicated as a cause of injury to farmworkers.