Estimating the bioavailable aqueous concentration of organic micropollutants with an equilibrium solid phase extraction

Many organic micropollutants show a reduced bioavailability in the presence of dissolved organic matter, which is explained by reduction of the freely dissolved aqueous concentration. In the present study, this reduction was measured, using equilibrium partitioning of micropollutants between water and a hydrophobic solid phase (C-18 Empore disk). The solid phase was exposed in prepared aqueous solutions which contained several micropollutants and Aldrich humic acid at different concentrations. The initial uptake rate of the micropollutants on the solid phase was measured and shown to be linear related to the freely dissolved concentration in the solution. Partitioning coefficients of tetra and hexachlorobenzene, pentachloroaniline, iodofenphos and DDT towards Aldrich humic acid were calculated. The relation between uptake rate and freely dissolved concentration was shown to be almost constant for all five pollutants, despite their difference in hydrophobicity and molecular weight.