ENRICHMENT OF MARINE SEDIMENT COLLOIDS WITH POLYCHLORINATED-BIPHENYLS- TRENDS RESULTING FROM PCB SOLUBILITY AND CHLORINATION

Colloids have been shown to significantly affect the bioavailability a nd 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 mar ine sediment core from New Bedford Harbor, MA. These distributions are the first report of colloid-PCB interactions in an environmentally co ntaminated sediment. Colloids <1.2 mu m in size were isolated from int erstitial waters using reverse-phase chromatography with size-selected C-18 Regardless of solubility or chlorination, the majority of PCBs w ere associated with the particulate phase. PCBs were distributed in fi ltered interstitial waters between colloidal and dissolved phases as a function of solubility and degree of chlorination. Interstitial disso lved PCB concentrations generally agreed with literature-reported solu bilities. The magnitude of colloid-PCB interactions increased with dec reasing PCB solubility and increasing PCB chlorination. Di- and trichl orinated PCBs were approximately 40% and 65% colloidally bound, respec tively, while tetra-, penta-, hexa-, hepta-, and octachlorinated PCBs were about 80% colloidally bound. As core depth increased,the magnitud e of PCB-colloid interactions also increased. The relationships of org anic carbon-normalized colloidal partitioning coefficient (K-coc) to K -ow for several PCB congeners were not linear and suggest that interst itial waters were not equilibrated. Possible explanations for disequil ibria include slow colloid-PCB sorption kinetics, steric hindrance, an d decreased colloid stability. These data support model laboratory stu dies that found that most nonpolar high molecular weight organic conta minants present in sediment interstitial waters are colloidally bound and not truly dissolved.