Effects of treated wastewater on the ecotoxicity of small streams – Unravelling the contribution of chemicals causing effects

Abstract

Wastewater treatment plant effluents are important point sources of micropollutants. To assess how the discharge of treated wastewater affects the ecotoxicity of small to medium-sized streams we collected water samples up- and downstream of 24 wastewater treatment plants across the Swiss Plateau and the Jura regions of Switzerland. We investigated estrogenicity, inhibition of algal photosynthetic activity (photosystem II, PSII) and growth, and acetylcholinesterase (AChE) inhibition. At four sites, we measured feeding activity of amphipods (Gammarus fossarum) in situ as well as water flea (Ceriodaphnia dubia) reproduction in water samples. Ecotoxicological endpoints were compared with results from analyses of general water quality parameters as well as a target screening of a wide range of organic micropollutants with a focus on pesticides and pharmaceuticals using liquid chromatography high-resolution tandem mass spectrometry. Measured ecotoxicological effects in stream water varied substantially among sites: 17β-estradiol equivalent concentrations (EEQbio, indicating the degree of estrogenicity) were relatively low and ranged from 0.04 to 0.85 ng/L, never exceeding a proposed effect-based trigger (EBT) value of 0.88 ng/L. Diuron equivalent (DEQbio) concentrations (indicating the degree of photosystem II inhibition in algae) ranged from 2.4 to 1576 ng/L and exceeded the EBT value (70 ng/L) in one third of the rivers studied, sometimes even upstream of the WWTP. Parathion equivalent (PtEQbio) concentrations (indicating the degree of AChE inhibition) reached relatively high values (37 to 1278 ng/L) mostly exceeding the corresponding EBT (196 ng/L PtEQbio). Decreased feeding activity by amphipods or decreased water flea reproduction downstream compared to the upstream site was observed at one of four investigated sites only. Results of the combined algae assay (PSII inhibition) correlated best with results of chemical analysis for PSII inhibiting herbicides. Estrogenicity was partly and AChE inhibition strongly underestimated based on measured steroidal estrogens respectively organophosphate and carbamate insecticides. An impact of dissolved organic carbon on results of the AChE inhibition assay was obvious. For this assay more work is required to further explore the missing correlation of bioassay data with chemical analytical data. Overall, the discharge of WWTP effluent led to increased estrogenicity, PSII and AChE inhibition downstream, irrespective of upstream land use.

The Combined Algae Test for the Evaluation of Mixture Toxicity in Environmental Samples

“…All concentration–response curves of the individual chemicals (Supplemental Data, Table S2) are given in the Supplemental Data, Section S8 and Figure S18, and all EC10 and EC50 values are listed in the Supplemental Data, Table S3. The newly measured EC50s were in excellent agreement with previous studies (Tang and Escher 2014; Kienle et al 2019; Figure S19). For all PSII inhibitors, EC10 2h IPAM and EC10 24h IPAM were very similar, but the EC10 24h growth was 10.8 ± 5.6 times higher than the EC10 24h IPAM (Supplemental Data, Table S3).…”

“…The contribution of other chemicals to growth inhibition is also evidenced by the fact that overall a smaller fraction of effect could be explained by the 38 chemicals with effect data ( Figure 5), with 43% (minimum 3%, maximum 95% and 95%CI 20-66%) of 24h growth-DEQ bio . That PSII-herbicides dominate the mixture effects in algae of wastewater samples has already been previously demonstrated (Tang 2014;Kienle 2019). In a surface water quality assessment study in the Netherlands (de Baat 2018), the PSII-herbicides Desethylterbuthylazine, Dimethenamid and Linuron exceeded water quality standards, but the first two did not contribute to photosynthesis inhibition.…”

“…The combined algae test (Escher et al 2008) has been in use for more than a decade in water quality monitoring (Escher et al 2009; Vermeirssen et al 2010; Margot et al 2013; Tang et al 2013; Di Paolo et al 2016; Neale et al 2017; Kienle et al 2019) and for investigation of transformation processes (Mestankova et al 2011). It is a 96‐well‐plate–based assay that combines the quantification of photosynthesis inhibition with inhibition of growth rate and can differentiate between such herbicides that directly act on photosystem II (PSII) and chemicals and herbicides with other modes of action.…”

Stream microbial communities and ecosystem functioning show complex responses to multiple stressors in wastewater

“…However, maximum concentrations for single compounds at specific locations exceeded 1 μg/L for all classes except insecticides (Table SD2), and fungicide concentrations more than doubled on average downstream at the 2013 sites. Estrogenic activity barely exceeded 1 ng/L estradiol equivalents even downstream of the WWTPs (Kienle et al., 2019). Nutrient levels also increased downstream, with DIN increasing from a median 3.1 mg/L upstream to 5.0 mg/L below the WW input (Table SD3).…”

Monitoring of emerging contaminants of concern in the aquatic environment: a review of studies showing the application of effect-based measures

“…29 Sampling at WWTPs and rivers using river sediments or water samples was a common practice with some studies sampling at river sites that are proximal to WWTP. [29][30][31] This is because WWTPs are discharge points for chemicals that may inuence the composition of adjacent or nearby surface water sources. On the contrary, there are also studies reporting bioeffect of individual and cocktail mixture of pharmaceuticals using reconstituted analytical grade samples of the pharmaceuticals in specic matrices such as water.…”