STRUCTURAL REQUIREMENTS FOR ANAEROBIC BIODEGRADATION OF ORGANIC-CHEMICALS - A FRAGMENT MODEL ANALYSIS

A computer-automated structure evaluation program (MCASE) has been use d to analyze rates of aquatic anaerobic biodegradation of a set of div erse organic compounds, and a predictive model for this endpoint has b een developed. The model was evaluated in terms of possible anaerobic metabolic steps. The most important fragments linked to biodegradabili ty (biophores) were aromatic and aliphatic thiol, methoxy, and alcohol groups and the carboxylic ester group. Fragments that can possibly in hibit anaerobic biodegradation were also identified but were not signi ficant. A metabolic transformation step is proposed for all identified fragments. Our results are therefore such that the most likely transf ormation under anaerobic conditions is anticipated when biophores are present in the molecule, while nonbiodegradability is assumed when non e of these fragments are present. The number of correct classification s by the model is over 93%. When predictions for all compounds were ge nerated using cross-validation of the model, 84% of the overall predic tions were correct. However, when only the predictions of possible bio degradability under anaerobic conditions are considered, the number of correct predictions is over 89%, whereas the percentage of correct pr edictions for nonbiodegradability is only 64%. It is therefore conclud ed that the analysis given in this contribution yields a model that ca n predict anaerobic biodegradability, but the assumption that the abse nce of a biophore leads to nonbiodegradability is not valid. Predictio ns of nonbiodegradability of compounds are therefore unreliable, proba bly due to the limited amount of data on anaerobic biodegradation avai lable for use in this study.