Open Access

The European Community has set a milestone in the European water policy in 2000: all water directives and policies were united into one comprehensive document – the European Water Framework Directive (EU WFD). The EU WFD requires the monitoring of 45 priority substances, primarily in the water phase, which is not related to a substantial amount of chemicals available on the market worldwide (about 50,000). About 60% of these are human and environmentally toxic. Hence, the currently monitored 45 priority substances are not even close to being sufficient to provide a comprehensive picture of the actual chemical pollution in the aquatic environment. Furthermore, the EU WFD in its original shape paid less attention to sediments as an important source and sink for chemical contamination. Under stable hydrological conditions, polluted old sediments are covered by less polluted younger sediments preventing erosion of deeper sediment layers and, therefore, the release of particle-bound contaminants. However, urbanization, deforestation, flooding, dredging, riverbed renaturation, and stormwater overflow basin releases can lead to an unpredictable release of particle-bound pollutants. Therefore, in 2008, sediments were added to the EU WFD as a monitoring matrix for substances that tend to accumulate there. As a result, after 18 years of the EU WFD, less than half of all European waterbodies reached a good ecological (40%) and chemical (38%) status. One of the primary pollution sources in aquatic ecosystems are wastewater treatment plants (WWTPs). Advanced wastewater treatment by ozonation is promising to remove most micropollutants. However, the knowledge about the possible improvement of the receiving waterbody is rare. The latter aspects were the main reasons for the start of the DemO3AC project in 2014. The study area was located in the federal state of North Rhine-Westphalia (Germany). The study area included the Wurm River and its tributary, the Haarbach River. Both waterbodies act as receiving waterbodies for WWTPs. One of them is the Aachen-Soers WWTP (receiving waterbody: Wurm River), upgraded by full stream ozonation as an advanced effluent treatment. Therefore, the extensive investigation program within the DemO3AC project included an investigation of the ecological and chemical status of both receiving waterbodies and the investigation of a possible improvement of the Wurm River after implementing advanced effluent treatment. The current study was a part of the DemO3AC project and covered the sediment toxicity and a possible impact of the ozonation on aquatic organisms in the receiving waterbody. Time-resolved sampling campaigns allowed investigations under different hydrological conditions, mainly determined by the weather. The first sampling campaign took place in June 2017 during a prolonged dry period with low water flow in the receiving waterbodies. The second sampling campaign was performed exactly one year later (June 2018) after a long rainy period and corresponding high-water levels. Full-stream ozonation at the Aachen-Soers WWTP had been in operation for half a year. Furthermore, a wide range of organic micropollutants was investigated in the effluent of the studied WWTPs to assess a possible hazard emerging from contaminants released into the receiving waterbody. The study design was developed based on the holistic approach to assessing the ecotoxicological pollution of surface waterbodies. It included the detection of chemical compounds combined with effect-based methods to identify possible drivers of toxicity. The sediment's ecotoxicological assessment included studies on endocrine-disrupting activity, genotoxic and embryotoxic potentials. These endpoints were evaluated using in vitro and in vivo bioassays. In addition, sediments’ chemical profiling was performed using modern analytical chemistry techniques. The genotoxic potential was investigated using the Ames fluctuation assay with Salmonella typhimurium bacterial strains TA98, TA100, YG1041, and YG1042, sensitive to different classes of compounds, and the Micronucleus assay as a eukaryotic assay with mammalian cells. A unique feature of the present study was the implementation of non-standard Salmonella typhimurium bacterial strains YG1041 and YG1042 in the Ames fluctuation assay. Moreover, a comprehensive genotoxicity ranking of chemical compounds identified in sediments was used and combined with statistical analysis to identify the drivers of genotoxicity. The results of this study were published in Shuliakevich et al. (2022a) (see also Annex 1), describing the mutagenic potential of all sampling sites, which was primarily driven by polycyclic aromatic hydrocarbons, nitroarenes, aromatic amines, and polycyclic heteroarenes. In addition, the rainwater overflow basin was identified as a significant source for particle-bound pollutants from untreated wastewater, suggesting its role as a possible source of genotoxic potential. The present study showed high sensitivity and applicability of non-standard Salmonella typhimurium bacterial strains YG1041 and YG1042 in the Ames fluctuation assay to assess the different classes of mutagenic compounds. A combination of effect-based methods and a chemical analysis was shown as a suitable tool for a genotoxic assessment of freshwater sediments. The sediments' endocrine-disruptive activity was investigated using the cell-based reporter gene CALUX® assay. A simultaneous launch of the full-scale effluent ozonation at the Aachen-Soers WWTP was used for investigation of the entrance of the ozonated effluent into the Wurm River and the endocrine-disrupting activity in the water phase. A particular focus of the present study was the unique investigation of PAHs as possible drivers of the endocrine-disrupting activity in sediments of the Wurm River. The results of this study were laid down in the publication by Shuliakevich et al. (2022b) (see also Annex 2), describing variations in endocrine-disrupting activity in the Wurm River under different weather conditions. Briefly, under stable hydrological conditions in June 2017, the estrogenic and the antiandrogenic activities in sediments of the Wurm River were within the range of 0.03-0.1 ng E2 equivalents (eq.)/g dry weight sediment equivalents (dw SEQ) and 3.0-13.9 µg Flu eq./g dw SEQ, respectively. After extensive rain events in June 2018, the sediments' estrogenic and antiandrogenic activities were detected within the range of 0.06-0.2 ng E2 eq./g dw SEQ and 1.7-39.2 µg Flu eq./g de SEQ, respectively. Increased endocrine-disruptive activity (up to 0.2 ng E2 eq./g dw SEQ in ERα- and 39.2 µg Flu eq./g dw SEQ in anti-AR-CALUX® assays) in sediments downstream of the rainwater overflow basin suggested it as a possible source of pollution. A unique result of the second study was finding a positive correlation between measured particle-bound antiandrogenic activity and detected polyaromatic hydrocarbons (PAHs) ...