Estimation of compartmental half-lives of organic compounds -: Structural similarity versus EPI-Suite

A k Nearest Neighbors (KNN) approach is developed to extrapolate from existing serniquantitative compartmental half-lives of organic compounds to respective data for untested substances. It is based on the evaluation of structural similarity through atom-centered fragments (ACFs). For the model development and leave-one-out cross-validation, a set of 293 compounds with reference half-lives for the four compartments air, water, soil, and sediment was taken from literature. Comparative analysis of the model performance with results based on EPI-Suite predictions of degradation rates due to indirect photolysis, biodegradation, and hydrolysis demonstrates the superiority of the new approach to predict compartmental half-lives. The latter are needed as input information for modeling the multimedia fate and life-time of organic compounds. The discussion includes an analysis of the problems associated with converting process-specific loss rates into compartmental half-lives.