Interactions of polychlorinated biphenyls with the air, water, and sediments of the Delaware River Estuary

The cycling of polychlorinated biphenyls (PCBs) within the rural/urban/industrial Delaware River watershed was examined to establish mass loading rates for management purposes and to assess historic trends in PCB inputs and mobilization. Simultaneous measurements of PCBs in the air and water over the Delaware River Estuary were taken in support of the Total Maximum Daily Load (TMDL) process conducted by the Delaware River Basin Commission (DRBC). Gas-phase concentrations of SigmaPCBs ranged from 110-1350 ng m-3, while dissolved water concentrations were between 420 and 1650 ng L-1. Air-water gas exchange fluxes of SigmaPCBs showed net volatilization for all samples, with values ranging from 360-3000 ng m-2 d-1. There is a high degree of uncertainty associated with these flux estimates, but the direction of PCB movement (net volatilization from the water to the air) can be stated with 95% confidence for all but 16 congeners.; Sediment concentrations of PCBs were measured in the Estuary in order to understand PCB behavior over time from the sediment history, as well as to examine present-day PCB trends in surficial sediments. Peak SigmaPCB concentrations ranged between 250 and 2410 ng/g dry wt. and concentrations generally declined with proximity to the surface. The SigmaPCB concentrations found in the sediments of the Delaware are comparable in magnitude to those seen in Chesapeake Bay and showed declining trends similar to those found in the Great Lakes.; Indirect atmospheric deposition parameters for PCBs were calculated for watersheds in the Delaware River Estuary. Tributary PCB loads and atmospheric PCB concentrations were used to understand the pass-through efficiencies for nine rivers/creeks that appeared to be atmospherically driven. Pass-through efficiencies were ≤ 5% for PCB homologues 3-6, but ranged from 3-18% for homologue group 7 and 2-17% for homologue group 8. Thus, pass-through efficiencies increased with increasing chlorination, with a dropoff at the octachlorinated homologue. This trend suggests that transfer of PCBs from the atmosphere to the River via the watershed is more efficient for high molecular weight PCBs than for low molecular weight PCBs. These selected watersheds, therefore, may be at or close to equilibrium with respect to gaseous exchange of PCBs.