PCBs and PAHs in the Montreal Urban Community (Quebec, Canada) wastewater treatment plant and in the effluent plume in the St Lawrence River

Samples of raw and treated wastewater were collected at the Montreal Urban Community (Canada) sewage treatment plant between July and October 1993 and analysed for PCBs and PAHs. Water samples were also collected in the effluent plume in the St Lawrence River during the same period. The average concentrations of Σ13 PCBs in raw wastewater and treated wastewater were 4.3 and 1.4 ng/l. respectively. For PAHs, average concentrations in raw wastewater and treated wastewater were 1.5 and 0.4 μg/l, respectively. The removal rates for PCB congeners and individual PAHs ranged from 33 to 100%. Approximately 1 kg of PCBs and 0.26 tonnes of PAHs were discharged annually by the MUC wastewater treatment plant to the St Lawrence River. Levels of PCBs and PAHs increased significantly at the effluent outfall in the river compared to those measured at the upstream site. In the effluent plume, concentrations of PCBs and PAHs reached background levels at approximately 13 and 6 km downstream from the effluent outfall, respectively.