Figure 27.5. Net air-water exchange fluxes (ngm-2 d-1) ofPCB homologs measured in Raritan Bay during 1999-2001 (black bars) and wet plus dry atmospheric deposition fluxes measured at Jersey City during 1998-2001. The total interaction of the estuary with the atmosphere, encompassing gas exchange, dry and wet deposition, results in a net loss oflowMWPCBs (congeners containing 3-4 chlorines) from the water column, but a net input of PCBs containing 6-9 chlorines.
total atmospheric fluxes increase by five to ten times. These fluxes are lower than the PCB accumulation rates in wetland sediments at the lower end of Long Island Sound, which may represent an atmospheric input signal (personal communication; B. Brownawell, State University ofNew York at Stony Brook).
The absorptive input of gaseous PCBs dominates the atmospheric deposition signal. However the high concentrations of PCBs in the water column of the estuary coming from upstream flow in the Hudson River, other tributary inputs, and discharges from the approximately twenty wastewater treatment facilities contribute toalarge volatilization flux (for example, see Totten et al., 2001, and Yan, 2003). Totten et al. (2001) and Yan (2003) report the absorptive, volatilization, and net fluxes of PCBs from the estuary for July 1998 through April 2001 based on simultaneously measured air and water concentrations of PCBs in Raritan Bay and New York Bay and estimated air-water fluxes based on fugacity gradients and mass transfer driven by wind-induced turbulence. Not surprisingly, volatilization greatly exceeds absorption, even though absorption dominates total atmospheric deposition.
Figure 27.5 demonstrates that air-water exchange (the balance between gas absorption and volatilization) is dominated by low molecular weight PCBs (those with three or four chlorines). For these congeners, the dry and wet deposition fluxes are comparatively small, and the overall interaction of the estuary with the atmosphere results in a net loss of these congeners. In contrast, for the high molecular weight PCBs (those having six or more chlorines), air-water exchange is near equilibrium, such that wet and dry deposition result in a net loading of PCBs from the atmosphere to the estuary. Thus the total interaction of the estuary with the atmosphere, encompassing gas exchange, dry and wet deposition, probably results in a net loss of low MW PCBs (congeners containing 3-4 chlorines) from the water column, but a net input of PCBs containing 6-9 chlorines.
Compared with other inputs of PCBs to the New York/New Jersey Harbor Estuary, atmospheric de-positionis small. DurellandLizotte (1998) estimate that the twenty-six water pollution control plants on the estuary discharge about 88 kg of PCBs per year into the estuary. In addition, Farley et al. (1999) estimate that the annual input of PCBs from the upper Hudson River at the Federal Dam in Troy,
NewYorkis about 250 kg (1997 numbers). Assuming that the plume of atmospheric contamination extends throughout the New York/New Jersey Harbor Estuary (surface area ~ 811 km2 from Klinkhammer and Bender, 1981), the current estimates of atmospheric deposition result in about 13-41 kg yr-1 of EPCBs being deposited into the estuary.
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