Effect-based nationwide surface water quality assessment to identify ecotoxicological risks.

A large portion of the toxic effects observed in surface waters cannot be attributed to compounds regularly measured by water authorities. Hence, there is an urgent need for an effect-based monitoring strategy that employs bioassays to identify environmental risks. The aim of the present study was to perform an effect-based nationwide water quality assessment to identify ecotoxicological risks in a wide variety of surface waters. At 45 locations silicone rubbers and polar organic chemical integrative samplers were exposed to surface water for 6 weeks. Alongside the passive samplers an in-situ daphnid test was performed. Subsequent to field exposure, accumulated compounds were extracted from the passive samplers after which a battery of in vivo and in vitro bioassays was exposed to the extracts. The bioassay battery was selected such that it could identify the risks posed by a wide range of chemical pollutants and their transformation products, while simultaneously allowing for targeted identification of groups of compounds that cause specific effects. Bioassay responses were compared to effect-based trigger values to identify potential ecotoxicological risks at the investigated locations. Responses were observed in all bioassays, and trigger values were exceeded in 9 out of the 21 applied assays, allowing for ranking of the investigated locations based on ecotoxicological risks. No relationship between land use and the identification of ecotoxicological risks was observed. Based on the results, considerations regarding future improvements of effect-based monitoring are given. It is concluded that effect-based water quality assessment allowed prioritization of sites based on ecotoxicological risks, identified the presence of hazardous compounds regardless of being listed as priority substances, and meanwhile could prevent costly chemical analysis at sites with low ecotoxicological risks.