Predicting Partition Coefficients of Short-Chain Chlorinated Paraffin Congeners by Combining COSMO-RS and Fragment Contribution Model Approaches

Chlorinated paraffins (CPs) are highly complex mixtures of polychlorinated n-alkanes with differing chain lengths and chlorination patterns. Knowledge on physicochemical properties of individual congeners is limited but needed to understand their environmental fate and potential risks. This work combines a sophisticated but time-demanding quantum chemically based method COSMO-RS and a fast-running fragment contribution approach to establish models to predict partition coefficients of a large number of short-chain chlorinated paraffin (SCCP) congeners. Molecular fragments of a length of up to C₄ in CP molecules were counted and used as explanatory variables to develop linear regression models for predicting COSMO-RS-calculated values. The resulting models can quickly provide COSMO-RS predictions for octanol–water (K_ow), air–water (K_aw), and octanol–air (K_oa) partition coefficients of SCCP congeners with an accuracy of 0.1–0.3 log units root mean squared errors (RMSE). The model predictions for K_ow agree with experimental values for individual constitutional isomers within 1 log unit. The ranges of partition coefficients for each SCCP congener group were computed, which successfully reproduced experimental log K_ow ranges of industrial CP mixtures. As an application of the developed approach, the predicted K_aw and K_oa were plotted to evaluate the bioaccumulation potential of each SCCP congener group.