Evaluation of the partitioning of hydrophobic pollutants between aquatic and solid phases in natural systems

Sorption partition coefficients are commonly used to quantify the distribution of organic pollutants between the aqueous and particulate phase of natural aqueous systems. Lotse et al. [6] found a significant increase in partitioning as the solid concentration decreases. Pollutants with larger partition coefficients have a more pronounced effect on the observed partitioning with changes in solid concentration. In the present study, partition coefficients for sediment-water systems were determined using Second Songhua River sediment. The effect of added DOC (using 12.5 ppm fulvic acid) and centrifuge speed on the partitioning of pollutants were studied. Dissolved organic carbon (DOC), nonsettling micro-particles (NSPs) and light absorption were also analyzed. From the results, the solids effect can be attributed to a transfer of solute-binding material from the solid phase to the liquid phase during the course of the partitioning procedure. This material, whether DOC or NSPs in nature, was not removed from the liquid phase during the separation procedure and possessed a higher capacity for the solute than the water itself. It increases the amount of solute in the liquid phase and makes the observed partition coefficients decrease. The true partition coefficients (Koct) of 11 constituents have been calculated from the observed partition coefficients at different solid concentrations. The values of Koct approach a constant and cannot be affected by the solid concentration. It supports the explanation describing the effect of solids.