Distribution of PAHs and PCBs to dissolved organic matter: High distribution coefficients with consequences for environmental fate modeling

Dissolved organic carbon/water distribution coefficients (KDOC) were measured for a selection of PCBs with octanol/water partition coefficients (KOW) ranging from 105.6 to 107.5. A solid phase dosing and sampling technique was applied to determine KDOC to Aldrich humic acid. This technique is in particular suitable for determining the distribution of very hydrophobic chemicals to complex matrices like humic acids. The KDOC values were calculated from the experimental data using a linear model. Determined KDOC’s were evaluated in relation to octanol/water partition coefficients of the test compounds, and compared to literature data. Measured KDOC values were somewhat higher than literature data, which can probably be attributed to the overestimation of freely dissolved aqueous concentration as a result of incomplete phase separation in other studies, and to the unique character of Aldrich humic acid as a “sorbent” or co-solute or to the fact that Aldrich humic acid is not a typical DOC, and other (adsorption) processes can occur. This study reports DOC distribution coefficients that belong to the highest ones ever measured. In addition, the DOC distribution was discussed in relation to current risk assessment modeling.