Urban stormwater contamination by polychlorinated biphenyls (PCBs) and its importance for urban water systems in Switzerland.

Like other persistent organic pollutants (POPs), polychlorinated biphenyls (PCBs) are still present in the environment despite their almost worldwide prohibition. A study was conducted over 1 year in Switzerland to analyze the source and load of PCBs in urban stormwater and their importance in urban water systems. The mean PCB concentrations of 89 rain events were determined in five different strictly separate drainage systems (three in Lausanne and two in Geneva). The mean concentrations of PCBs in stormwater ranged from values below the detection limit (0.11-0.24 ng/l) to 403 ng/l. A model for the wet and dry deposition of PCBs based on these results estimates that their concentration in rainwater has remained practically constant (35 ng/l) over a period of 12 years. A mass balance of Swiss levels estimates a total input load of PCBs in the urban water systems at 110-125 kg/year. The contribution of stormwater is 75-94 kg/year in combined sewer systems and 23-34 kg in separate sewer systems. This mass balance illustrates that a major part of the PCB load in the environment or in WWTP sludges originates from urban stormwater. This result was confirmed by a fingerprint of PCB congeners in stormwater, which showed a pattern identical to that found in sewage sludge in combined sewer systems.