Suchergebnisse

The environmental risk assessment (ERA) focusses on individual chemicals, while non-target organisms in the environment are exposed simultaneously to a multitude of substances from various sources. In the aquatic environment, effluents of wastewater treatment plants (WWTPs) represent a key source for co-incidental mixtures of chemicals from various uses. The aim of the present project was to explore the consideration of mixtures of chemicals released via WWTPs in an ERA. Based on a literature survey and own data on human pharmaceuticals and other substances typically present in the effluents of WWTPs, 20 substances were selected. In total, 33 single-substance and 24 mixtures were assessed in chronic toxicity tests with cyanobacteria, green algae, the water plant Lemna minor and the freshwater crustacean Daphnia magna. The results from the mixture tests provided consistent evidence that the aquatic toxicity of mixtures with regard to chronic endpoints can be predicted by the concept of concentration addition (CA) with less than 3-fold deviation. Evidence for synergistic interaction with respect to CA of the two antibiotics sulfamethoxazole and trimethoprim in primary producers was detected, which calls for further investigations. Furthermore, mixture tests demonstrated that the presence of 50% (v:v) WWTP effluent in the test medium did not impact the predictability of mixture toxicity. With regard to mixture concentrations changing during the exposure time, as it is typical for WWTP effluents, the average mixture concentrations appeared to underestimate chronic mixture effects on reproduction of D. magna, while the peak concentrations provided a better estimate. Single-substance risk assessments were compared to risk assessments for selected mixture scenarios based on different approaches. A mixture assessment factor applied in the ERA of single substances and its appropriate size is discussed in view of a prospective consideration of environmental mixtures of unknown composition in the single-substance ERA.