Factors Controlling the Biodegradation of Chemicals in Soils

The natural biodegradation of chemicals in the environment is controlled by both the compounds’ characteristics (e.g., hydrophobicity), the environment’s characteristics (e.g., soil organic matter content) and the activity of the microbial population. Simplified biodegradability tests under laboratory conditions and in the absence of soil often show higher rates (given that sufficient and appropriate microorganisms are present). This could be explained by differences in compound bioavailability. Thus, standardized laboratory tests are not by themselves good predictors of environmental half-lives. In order to rapidly construct an environmental database, over 800 scientific articles were examined providing a subset of 75 publications with 26 different soils and 55 different compounds (given a total of 150 data). Sensitivity studies based on derived correlations show that not all environmental characteristics are relevant to predicting environmental half-lives. In addition, most chemicals studied are reputed to be difficult to degrade, which lessens the influence of environmental characteristics relative to molecular ones. In general, however, derived correlations show that under optimum or near optimum environmental conditions, biodegradation rates are controlled by molecular characteristics whereas under more extreme conditions biodegradation rates are controlled by environmental conditions.