Pesticides and other trace micropollutants released to the aquatic environment are subject to hydrolysis, oxidation-reduction, and photodecomposition. Kinetic treatments of hydrolysis and direct photolysis processes have been successful in allowing accurate extrapolation of laboratory studies to field conditions. The most recent hydrolysis models account for not only specific acid-base catalysis, but also the impact of suspended sediments. Nonbiological oxidations and reductions, although demonstrated in numerous recent studies, are not well enough understood at this time to be described by mathematical models based on chemical kinetics. Indirect photolysis processes involve a variety of excited state and/or reactive chemical species. Recent research in this area has been directed at measurement or estimation of steady-state reactant concentrations in natural waters. Further basic research into aquatic chemistry and photochemistry will provide the basis for accurate modeling of other abiotic pesticide degradation processes.