Concerns about environmental contamination by organic micropollutants (OMPs) are increasing, due to their potential bioaccumulative and toxic properties. This study evaluated the risk posed by OMPs to aquatic ecosystems in Swedish freshwaters. The assessment was based on measured environmental concentrations (MEC) of OMPs in surface waters upstream and downstream of Swedish wastewater treatment plants (WWTPs). A novel optimised risk quotient (RQf) was used to identify potential high-risk

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... ces in the aquatic environment. A secondary objective was to assess the impact of WWTP effluent on aquatic ecosystems using a novel impact factor (I) based on the risk quotient (RQ). Among the 126 substances investigated, four compounds (metformin, N,N-dimethyltetradecylamine, oxazepam, and venlafaxine) were identified as likely to pose a risk to aquatic ecosystems in Swedish surface waters (RQf>1), and five compounds (clindamycin, gemfibrozil, sertraline, o-desmethylvenlafaxine, and diclofenac) were identified as posing a moderate risk to aquatic ecosystems ( 0.1 <RQf<1). WWTP effluent appeared to pose an environmental risk for all recipient sites, but the impact of calculated RQ was site-specific. These results can be used by authorities to prioritise OMPs and contaminated hotspots, in order to decrease negative impacts on aquatic ecosystems. SYNOPSIS: A novel optimised risk assessment approach for identification of high-concern organic micropollutants in aquatic environments.