Predicting dissolved organic carbon partition and distribution coefficients of neutral and ionizable organic chemicals

Estimating KDOC (dissolved organic carbon/water partition coefficient) and DDOC (dissolved organic carbon/water distribution coefficient) of neutral and ionizable organic chemicals is a crucial task for assessing mobility, modelling transport, environmental fate of a variety of chemicals and for evaluating their bioavailability in terrestrial and aquatic environments. A critical literature search of reliability-selected KDOC and DDOC values was performed to setup novel predictive relationships for KDOC and DDOC of neutral and ionizable organic chemicals. This goal was pursued by using: 1) LSER (linear solvation energy relationship) models to predict KDOC for neutral chemicals using Abraham solute parameters calculated for different DOC sources (all DOC sources together, soil porewater, surface water, wastewater and Aldrich humic acid (HA)); 2) linear regressions for predicting DDOC of organic acids from the octanol/water partition coefficient (Log KOW or Log P) and the dissociation constant (pKa), accounting separately for the contribution of the neutral and ionic fraction. The proposed models predicted Log KDOC and DDOC values within a root mean square deviation (RMSD) generally smaller than 0.3 log units.