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Sampling on Akwesasne Mohawk Nation lands during 1993 yielded elevated polychlorinated biphenyl (PCB) concentrations comparable with those of other areas 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, presumably from river sediment and waters, is a minor contributor (~12%) to the pattern. These two sources can account for ~80% of the observed pattern. At a small cove adjacent to an industrial landfill, summer concentrations exceeded those measured in the winter by a factor of 27. At all sample sites during the summer months (June-August), concentrations and chlorine to biphenyl ratios increased, and similar congener-specific PCB patterns were observed. During the colder months, PCB concentrations at all sites decreased but were elevated with respect to those measured elsewhere in the Great Lakes region during the same time period.