Science of the Total Environment 322 (2004) 179–189 0048-9697/04/$ - see front matter  2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0048-9697(03)00361-9 Urban stormwater contamination by polychlorinated biphenyls (PCBs) and its importance for urban water systems in Switzerland Luca Rossi *, Luiz de Alencastro , Thomas Kupper , Joseph Tarradellas a, b b b Swiss Federal Institute for Environmental Science and Technology (EAWAG), Uberlandstrasse 133, Dubendorf 8600, Switzerland a ¨ ¨ Swiss Federal Institute of Technology, Laboratory of Environmental Chemistry and Ecotoxicology (CECOTOX), Lausanne, b Switzerland Received 4 July 2002; accepted 20 December 2002 Abstract 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 ngyl) to 403 ngyl. 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 ngyl) 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 kgyyear. The contribution of stormwater is 75–94 kgyyear 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.  2003 Elsevier Science B.V. All rights reserved. Keywords: Polychlorinated biphenyls; Urban stormwater; Fingerprint; Mass balance; Wastewater treatment plant sludge 1. Introduction Polychlorinated biphenyls (PCBs) are toxic pol- lutants characterized by persistence in the atmos- phere and an ability to be transported over long distances and to accumulate in food chains (Chev- reuil et al., 1998; Chiu et al., 2000). PCBs are ubiquitous in the environment and can be detected *Corresponding author. Tel.: q41-1-823-53-78; fax: q41- 1-823-53-89. E-mail address: luca.rossi@eawag.ch (L. Rossi). in many components of the biosphere. Estimates of their toxic potential and possible oestrogenic effects require a good knowledge of the relevant sources of contamination. Despite their prohibition in Switzerland, recent PCB analyses in fish and WWTP (wastewater treatment plant) sludges showed no significant changes in comparison with previous studies. Moreover, with the exception of point sources—such as old electrical manufactur- ing or contaminated sites—the main diffuse PCB sources entering the aquatic environment in urban