The chemical, physical and biological fate of polychlorinated biphenyls in the tidal Christina Basin

The Christina Basin is a tributary of the Delaware Estuary in the Mid-Atlantic region of the eastern USA. Surface water, sediment, and biota samples were collected concurrently from three contrasting, historically industrialized sites in the tidal waters of the Christina Basin in the fall of 2007 in order to characterize the processes responsible for polychlorinated biphenyl (PCB) contamination of the aquatic food web. Three aspects of PCB fate were investigated: (1) partitioning of PCBs in the water column; (2) exchange of PCBs between the water column and bottom sediments; and (3) bioaccumulation of PCBs into and through the food web.;PCB partitioning in the water column was well described by a 3-phase equilibrium model including freely dissolved chemical, DOC-bound chemical and POC-bound chemical. The data support the parsimonious result that K oc = Kow. Partitioning between truly dissolved PCB and DOC-bound PCB was found to follow the relationship KDOC = 0.049Kow when all congeners are considered and KDOC = 0.016Kow when non-ortho and mono-ortho chlorine substituted congeners are excluded. Enhanced sorption was observed for non-ortho and mono-ortho chlorine substituted PCB congeners with log Kow < 6. The enhanced sorption is attributed to black carbon which preferentially sorbs these congeners.;Exchange of PCB between the water column and bed sediments was evaluated using a steady-state mass balance modeling framework. The model was used to deduce that exchange at one site is controlled by strong particle mixing and by pore water diffusion at the other two sites. These classifications are consistent with the physical attributes of the sites. Enhanced sorption was also observed in the sediments and black carbon is thought to be responsible. The enhancement in the sediments involved both planar and nonplanar congeners, a finding attributed to a higher ratio of black carbon to natural organic carbon in the sediments compared to the water column.;Bioaccumulation of PCB in the food web was observed at all trophic levels. Accumulation was found to depend on exposures from the water and sediment as well as on the lipid content of the organisms. Bioaccumulation factors (BAFs) based on lipid normalized biota concentrations and freely dissolved chemical were shown to depend strongly on the hydrophobicity of the individual congeners and the degree of ortho chlorine substitution. Ortho chlorine substitution appeared to influence both bioavailability and metabolism. The site with the greatest proportion of sand-sized particles and lowest TOC had the highest lipid normalized PCB concentration in the top predator fish even though the site did not have the highest freely dissolved PCB concentration in the water column. PCB and stable isotope data revealed some biomagnification as a result of trophic transfer, but this increase was fairly small. Observed log BAFs were compared to log BAFs predicted using the AQUAWEB bioaccumulation model.