HA1 Contaminated Harbour and River Sediment
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() PCB desorption from Hudson River sediments during realistic bottom shear and water column turbulence.
Schneider, A.1, Porter, E.1, Baker, J.1, 1 University of Maryland Chesapeake Biological Laboratory, Solomons, Maryland, USA
ABSTRACT- From the late 1940's until 1977 two General Electric plants discharged between 200,000 and 1.3 million pounds of PCBs into the upper Hudson River. The river's sediments are the largest reservoir of PCBs, especially in the Thompson Island Pool (TIP) downstream from the plants. Mass balance calculations based on concentration of PCBs in water flowing into and out of the TIP suggest 150 kg PCB/year are released from sediment into the water column. Field studies and detailed modeling efforts indicate that PCB release from sediments under realistic mixing conditions is the key geochemical process controlling both 'natural recovery' and the efficacy of proposed dredging operations. In this study, the desorption rates of individual PCB congeners from Hudson River sediment were measured by resuspending field-collected sediments into clean water in large mesocosms and measuring the resulting dissolved phase PCB concentrations by solid-phase microextraction. During each resuspension event, the total suspended solids concentration in the tanks rose rapidly and reached a steady state concentration around 80 mg/L in approximately four hours. The resuspended particles were enriched in total PCBs and organic carbon relative to the bulk sediment. At steady state, the median particle diameter, as measured by laser light scattering, was 180 
m, and 60% of the particles were in the medium size fraction (63-<250 
m), 30% in the coarse fraction (250-500 m), and 10% in the fine fraction (2.5-<63 m). Preliminary results indicate PCB congeners rapidly desorbed from resuspended particles and reached steady state in approximately four hours; much faster than predicted by kinetic desorption models. The release of PCBs from the resuspended particles appeared to reach steady state on time scales similar to floc formation. Two to 22% of the PCB mass on the resuspended particles desorbed into the dissolved phase during resuspension.
Key words: Hudson River, PCBs, desorption