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 semiquantitative 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.