Two-Phase System Model to Assess Hydrophobic Organic Compound Sorption to Dissolved Organic Matter

The equilibrium partition of organic compounds to dissolved organic matter (DOM) is an essential process that affects their environmental risks. Traditional models cannot accurately assess this process as the variability of DOM is not properly accounted for. The two-phase system (TPS) model was developed with the consideration of the variability that stems from both organic compounds and DOM. In this study, we examined the applicability of the TPS model for the prediction of the organic carbon-water partition coefficient (K_OC) of hydrophobic organic compound (HOC) sorption to aquatic and sediment DOM using a diverse set of 17 organic compounds and 53 DOM samples. The TPS model showed good predictive power (RMSE < 0.20) without calibration, outperforming currently used linear free energy relationship models (RMSE > 0.28). The significance of DOM properties in the sorption behavior was quantitatively analyzed based on the TPS model. The spatial pattern of K_OC for HOC sorption to aquatic DOM in Lake Taihu, the third largest freshwater lake in China, was assessed using the TPS model. Our results suggest that the TPS model has great potential to facilitate the routine assessment of the partition behavior of HOCs in aquatic systems for environmental risk assessment.