Surface waters are highly manipulated in many cities in Europe, and the flow is largely impacted by discharges of stormwater and combined sewer overflow. Toxicity tests shown adverse effects in some of these recipients due to the presence of xenobiotic organic carbons (XOCs). Harrestrup Å, situated in the City of Copenhagen, is one of these recipients, where biotest using algae showed measurable toxicity in eight samples taken in 2003. Twenty-five different XOCs were quantified in the same samples. The present study aimed at identifying the most relevant XOCs out of these 25 to be selected for further analysis with respect to potential source control options.

Fourteen XOCs (56%) were identified to constitute a potential hazard based on the RICH evaluation (Ranking and Identification of Chemical Hazards), while 9 XOCs (36%) were found to constitute a hazard towards the aquatic ecosystem based on an environmental-concentration/predicted-no-effect-concentration-quotient. The quantified levels did, however, fulfil the Danish and European surface water quality criteria (QC) and environmental quality standards (ESQ). Thus, although the QC and ESQ are met there is an actual risk due to stormwater-related pollutants. This clearly illustrates that there is a need for monitoring the stormwater quality in order to protect the ecosystems. It also shows that actions are needed to implement source control options and emission barriers.

Twelve XOCs were selected for further evaluation of possible source control option to be implemented in order to improve the water quality. These are five pesticides (diuron, glyphosate, isoproturon, MCPA, terbutylazine), 4 PAHs (acenaphthene, fluoranthene, fluorene, pyrene), 3 others (LAS, nonylphenol and dinitro-o-cresol).