Defining the sources of airborne polychlorinated biphenyls: evidence for the influence of microbially dechlorinated congeners from river sediment?

Sampling on Akwesasne Mohawk Nation lands during 1993 yielded elevated poly chlorinated biphenyl (PCB) concentrations comparable with those of other ar eas impacted by the discharge of PCBs. The summer air PCB congener-specific pattern in proximity to three Superfund sites along the St. Lawrence River suggests that the volatilization of Aroclor 1248, used extensively at all three downwind sites, is the dominant source. A dechlorinated source, presu mably From river sediment and waters, is a minor contributor (similar to 12 %) to the pattern. These two sources can account for similar to 80% of the observed pattern. At a small cove adjacent to an industrial landfill, summe r concentrations exceeded those measured in the winter by a factor of 27. A t all sample sites during the summer months (June-August), concentrations a nd chlorine to biphenyl ratios increased, and similar congener-specific PCB patterns were observed. During the colder months, PCB concentrations at al l sites decreased bur: were elevated with respect to those measured elsewhe re in the Great Lakes region during the same time period.