International Union of Pure and Applied Chemistry Chemistry and the Environment Division Commission on Water and Soil Chemistry* Modeling Lifetime and Degradability of Organic Compounds in Air, Soil, and Water Systems

Degradability of organic compounds in air, soil, and water is the most important factor for evaluating their environment fate as well as possible adverse effects to humans and the environment. The primary degradation process in the troposphere is the reaction with the hydroxyl radical. For water and soil compartments, the primary degradation process is biodegradation. The objectives of this report are: (i) to review published models and their evaluation studies, (ii) to perform an in-house evaluation of general models for estimating tropospheric degradation and biodegradation of organic compounds, and (iii) to recommend reliable procedures for estimating degradability of organic compounds in the environment. The extensive evaluation procedure has shown that the most accurate method for estimating tropospheric degradation is Atkinson’s group contribution method. Although this method has some limitations, it seems to be a method of choice. A viable alternative to Atkinson’s method is a direct calculation, performed today almost routinely, of the reaction rate constants with hydroxyl radicals. Recently, a methodology based on reliable semiempirical potential energy surfaces was developed that enables the calculation of reaction rate constants within a factor of 2 of their measured values. A partial least squares (PLS) model and a set of seven biodegradation rules have been found to be the most reliable in estimating complete biodegradation of organic compounds. However, it is recommended to use all four evaluated methods to estimate biodegradation in the environment. If their results agree, such estimates are very reliable.