Polychlorinated biphenyls in stormwater runoff entering the tidal Anacostia River, Washington, DC, through small urban catchments and combined sewer outfalls.

To investigate the loadings, solid-water partitioning, transport dynamics, and sources of polychlorinated biphenyls (PCBs) in urban stormwater runoff entering into the lower tidal Anacostia River, which flows south of Washington, DC, USA, storm and base flow samples were collected in six branches. Stormwater runoff contained elevated levels of PCBs (9.82 to 211 ng/L) higher than base flow by up to 80-fold. The present study suggests that input of PCBs from Lower Beaverdam Creek is likely to be greater than those from the two major branches (Northeast and Northwest Branches) that were believed as primary source areas. PCBs in storm flow were significantly enriched in the particle phase, which accounted for more than 90% of the total PCBs. Particles were the primary vector transporting PCBs into the Anacostia River, suggesting that removal of particles in stormwater runoff using best management practices (BMPs) such as post treatment system likely decrease PCBs significantly. PCB congener patterns found in stormwater samples clearly explain stormwater runoff is a major transport pathway adding substantial amount of PCBs to the tidal Anacostia River.