Estimating impact of humic acid on bioavailability and bioaccumulation of hydrophobic chemicals in guppies using kinetic 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. The partition coefficient between organic matter and the aqueous phase, K(DOC), is used to describe the distribution of neutral hydrophobic micropollutants. In the present study, the freely dissolved concentration was measured using partitioning of micropollutants between water and a hydrophobic solid-phase filter disk (C-18 Empore disk). Slivers of the disk were exposed in aqueous solutions that contained several micropollutants and Aldrich humic acid at different concentrations. Initial uptake rates of the micropollutants from water to disk (k1) were measured to estimate the freely dissolved concentration in the solution. Partition coefficients, K(DOC), of tetra- and hexachlorobenzene, pentachloroaniline, iodofenphos, and p,p' DDT were calculated. These values were comparable to earlier, published K(DOC)s toward Aldrich humic acid. In a validation experiment, the uptake rates of three chlorobenzenes in guppy (Poecilia reticulata) were measured in the absence and presence of humic acids. The lowering of the uptake rates in guppy was correctly predicted with the K(DOC) values from the Empore disk experiment. These findings suggest that the proposed method to measure the freely dissolved concentration is a valid tool to predict the bioavailability of hydrophobic compounds in the aqueous environment