Sorption of phthalate esters and PCBs in a marine ecosystem

Dialkyl phthalate esters (DPEs) are widely used industrial chemicals with octanol-seawater partition coefficients ranging between 10(1.80) for dimethyl phthalate to 10(10.0) for diiso-decyl phthalate, indicating a propensity to sorb strongly to particulate matter in aquatic environments. Sorption plays a key role in controlling the long-term fate of DPEs in aquatic systems and exposure to organisms in aquatic food-webs. However, field observations of the sorption of many commercial DPEs do not exist. To characterize the sorptive nature of DPEs in a real-world aquatic ecosystem, we measured concentrations of DPEs congeners, commercial DPE mixtures, and 10 polychlorinated biphenyls (PCBs) in water, suspended sediments, and bottom sediments of a marine inlet. Sorption coefficients of spiked and native DPEs and PCBs between suspended sediments and water indicate that the apparent sorptive nature of DPEs and PCBs is substantially greater than expected from K(ow)-based sorption models. Particulate and dissolved organic matter showed similar (i.e., not statistically different) sorption affinities for native analytes. The apparent fraction of the total aqueous concentration of DPEs that is freely dissolved and absorbable via the respiratory tract of aquatic organisms varied from virtually 100% for DMP to 0.0003% for C10. The observed decline in concentration of most DPEs between suspended and bottom sediments, compared to an increase in the concentration of high Kow PCBs, suggests that the rate of desorption and degradation of DPEs exceeds that of organic carbon mineralization and contributes to the previously observed lack of biomagnification of DPEs in the aquatic food-web of this system.