In the environment, hydrolysis reactions can be mediated biologically or occur via abiotic processes. For biotic hydrolysis reactions, the rate of hydrolysis often is proportional to bacterial biomass and/or specific enzyme concentrations (activities) in the medium. In abiotic hydrolysis reactions, the hydrolysis rates can be a function of chemical parameters such as H ion activity (pH), dissolved organic matter, and dissolved metal ions. For many compounds, both abiotic and biotic processes contribute to the disappearance of pollutants in the environment. The focus of the paper is on the factors that influence the rate of abiotic hydrolysis reactions in soils and sediments. (Copyright (c) 1989 Soil Science Society of America and American Society of Agronomy.)