Enrichment of marine sediment colloids with polychlorinated biphenyls: Trends resulting from PCB solubility and chlorination

Colloids have been shown to significantly affect the bioavailability and transport of anthropogenic contaminants in the environment. In this study, the three phase distributions (i.e., dissolved, colloidal, and particulate) of approximately 75 PCB congeners were measured in a marine sediment core from New Bedford Harbor, MA. These distributions are the first report of colloid-PCB interactions in an environmentally contaminated sediment. Colloids <1.2 mu m in size were isolated from interstitial waters using reverse-phase chromatography with size-selected C-18 Regardless of solubility or chlorination, the majority of PCBs were associated with the particulate phase. PCBs were distributed in filtered interstitial waters between colloidal and dissolved phases as a function of solubility and degree of chlorination. Interstitial dissolved PCB concentrations generally agreed with literature-reported solubilities. The magnitude of colloid-PCB interactions increased with decreasing PCB solubility and increasing PCB chlorination. Di- and trichlorinated PCBs were approximately 40% and 65% colloidally bound, respectively, while tetra-, penta-, hexa-, hepta-, and octachlorinated PCBs were about 80% colloidally bound. As core depth increased,the magnitude of PCB-colloid interactions also increased. The relationships of organic carbon-normalized colloidal partitioning coefficient (K-coc) to K-ow for several PCB congeners were not linear and suggest that interstitial waters were not equilibrated. Possible explanations for disequilibria include slow colloid-PCB sorption kinetics, steric hindrance, and decreased colloid stability. These data support model laboratory studies that found that most nonpolar high molecular weight organic contaminants present in sediment interstitial waters are colloidally bound and not truly dissolved.