Accumulation pattern and possible adverse effects of organic pollutants in sediments downstream of combined sewer overflows

The present study was conducted to investigate sediment accumulation patterns of PAHs, PCBs, flame retardants and pesticides along 100 m transects downstream from three different combined sewer overflows (CSOs). Additionally, the concentrations of PAHs and PCBs were quantified to allow a characterization of the sediment quality. The suspect screening revealed that usually more substances, especially pesticides and flame retardants, were detected in sediments located in the vicinity of CSOs. Except for PAHs at Location 1 and 3, all substances followed the same accumulation pattern, showing higher contaminations in sediments sampled downstream from the CSOs compared to an upstream located reference site. With increasing distance to the respective input, sediment concentrations decreased. Different accumulation patterns of PAHs at Locations 1 and 3 were related to high background concentrations of the receiving creek. Although the general contamination patterns were similar, the level of contamination was different at each location. PAH concentrations are indicative for the occurrence of sediment toxicity at Location 3. However, higher background concentrations in the receiving creek compared to concentrations present in the retention zone indicate a higher probability for sediment toxicity due to inherited waste or contamination from upper reaches. PCBs introduced by the sewer outfall at Location 1 significantly increased the toxic potential of sediments located in the vicinity of the CSO. The retention zones at Locations 2 and 3 appeared to be a good measure to trap particles and their associated pollutants before they accumulate in the creek sediments where they became potentially harmful for the aquatic biota. Based on this study recommendations for sampling strategies were concluded to harmonize sampling designs in studies analyzing the impact of point sources on the sediment quality and to minimize misinterpretation of results. [Display omitted] •Combined sewer overflows (CSOs) as a pollution source for organic trace pollutants•Accumulation patterns of organic pollutants in sediments downstream from CSOs•Higher occurrence of pesticides and flame retardants downstream from CSOs•Elevated PCB background and CSOs clearly increased the toxic potential of sediments.•Recommendations for sampling strategies to analyze the impact of CSOs on sediments