Prediction of Biodegradablity from Chemical Structure

Biodegradation is an important process in the environmental fate of substances. Therefore, biodegradation is considered for several legislative purposes, such as Priority Setting, Risk Assessment and Classification and Labelling of substances within the European Union. For these purposes, it is important whether a substance is readily or not-readily biodegradable according to EU and OECD test guidelines. For many existing substances, the experimental biodegradation data have been derived under non-standard test conditions which complicates the interpretation of test results. Furthermore, results from different studies may not be consistent. (Quantitative) Structure Activity Relationships ((Q)SARs) may assist in the evaluation of experimental data. Therefore, a model has been developed that predicts whether a substance is readily biodegradable or not-readily biodegradable under MITII test conditions. The model is based on a set of 600 substances, all having MITI I test results and 111 predefined structural fragments. The model is generated by Partial Least Squares (PLS) discriminant analysis. The model is both internally cross validated and externally validated with 198 substances that were not used in the model development. Both readily and not-readily biodegradable substances were predicted correctly for >86 % of the substances in the external validation set. The model has been developed in line with the principles on Use of QSARs laid down in the EU Technical Guidance Documents on Risk Assessment.