Composition of PCBs and PAHs in the Montreal Urban Community Wastewater and in the Surface Water of the St. Lawrence River (Canada)

Samples of treated wastewater drawn from the effluent of the Montreal Urban Community (MUC), Canada, and surface water samples from the St. Lawrence River were collected in 1993 and 1994 and analysed for PCBs and PAHs. The average concentrations of Σ13 PCBs and Σ14 PAHs in the effluent were 1.34 ± 0.71 ng L-1 and 326 ± 229 ng L-1, respectively. PCB concentrations in the effluent did not show any clear seasonal pattern in the effluent but PAH concentrations increased during the winter period. In the effluent plume, both PCB and PAH concentrations increased significantly between the upstream control site and the effluent outfall, and subsequently decreased. The profiles of PCB congeners were similar within the effluent plume and also among water masses of the St. Lawrence River. PAH profiles were also similar within the effluent plume, but were different across the two water masses of the St. Lawrence River. Based on the composition of PCB congeners, atmospheric inputs appear to represent the major source of PCBs in the St. Lawrence River. The sources of PAHs in the MUC effluent and in the St. Lawrence River water would appear to be, respectively, petroleum products and combustion-derived products.