SORPTION OF BENZO[A]PYRENE AND PHENANTHRENE ON SUSPENDED HARBOR SEDIMENT AS A FUNCTION OF SUSPENDED SEDIMENT CONCENTRATION AND SALINITY - A LABORATORY STUDY USING THE COSOLVENT PARTITION-COEFFICIENT

The sorption of benzo[a]pyrene (BaP) and phenanthrene (PHE) on sediment collected in the harbor of Rotterdam was studied in batch experiments using C-14-labeled compounds. In order to simulate various estuarine conditions, we investigated the effects of various sediment concentrations and salinities on sorption of these compounds. We determined the apparent partitioning as well as the cosolvent partitioning between the liquid and solid phases. The apparent partition coefficient (K-p(App)) is influenced by the presence of colloids and dissolved organic matter. The influence of these components is minimized by the use of the cosolvent method in which the partition coefficient (K-p*) is determined by extrapolation of the partition coefficients obtained in a variety of solutions with water and methanol. The effect of sediment concentration on sorption was investigated at five different sediment concentrations ranging from 0.064 to 10.8 g/L. In contrast to K-p*, K-p(App) was found to be sensitive to the sediment concentration. Log K-p* (with K-p* in L/kg), determined for different sediment concentrations, was 5.2-6.3 for BaP and 2.8-3.6 for PHE, whereas log K-p(App) was 4.1-5.6 for BaP and 2.9-4.0 for PHE. The salt concentration was varied with dilutions of Milli-Q water and seawater; the salinity ranged from 0 to 35. The influence of salinity on K-p* was small; the increase in log K-p* from freshwater to seawater is approximately 0.2 for BaP and 0.1 for PHE.