Wastewater treatment efficacy evaluated with in vitro bioassays

Abstract

Bioassays show promise as a complementary approach to chemical analysis to assess the efficacy of wastewater treatment processes as they can detect the mixture effects of all bioactive chemicals in a sample. We investigated the treatment efficacy of ten Australian wastewater treatment plants (WWTPs) covering 42% of the national population over seven consecutive days. Solid-phase extracts of influent and effluent were subjected to an in vitro test battery with six bioassays covering nine endpoints that captured the major modes of action detected in receiving surface waters. WWTP influents and effluents were compared on the basis of population- and flow-normalised effect loads, which provided insights into the biological effects exhibited by the mixture of chemicals before and after treatment. Effect removal efficacy varied between effect endpoints and depended on the treatment process. An ozonation treatment step had the best treatment efficacy, while WWTPs with only primary treatment resulted in poor removal of effects. Effect removal was generally better for estrogenic effects and the peroxisome proliferator-activated receptor than for inhibition of photosynthesis, which is consistent with the persistence of herbicides causing this effect. Cytotoxicity and oxidative stress response provided a sum parameter of all bioactive chemicals including transformation products and removal was poorer than for specific endpoints except for photosynthesis inhibition. Although more than 500 chemicals were analysed, the detected chemicals explained typically less than 10% of the measured biological effect, apart from algal toxicity, where the majority of the effect could be explained by one dominant herbicide, diuron. Overall, the current study demonstrated the utility of applying bioassays alongside chemical analysis to evaluate loads of chemical pollution reaching WWTPs and treatment efficacy.

Effect‐Based Trigger Values for Mixtures of Chemicals in Surface Water Detected with In Vitro Bioassays

“…( B ) Extrapolated number of cytotoxic chemicals in surface water (Equation 5). ( C ) Relationship between number of detected bioactive chemicals and fraction of bioanalytical equivalent concentrations explained by the detected chemicals in 128 surface water samples (Neale et al 2020a) and 20 samples from wastewater‐treatment plants (Neale et al 2020c). All data are in Supplemental Data, Tables S2 and S3.…”

“…( A ) Distribution of inhibitory concentration causing 10% reduction in cell viability (IC10) in water samples collected during rainfall in small agricultural streams; (Neale et al 2020a) and ( B ) in wastewater‐treatment plant influent (color) and effluent (gray; Neale et al 2020c). In both figures, the dotted lines correspond to the proposed effect‐based trigger (EBT) for cytotoxicity EBT‐IC10 of REF 10.…”

“…Application of the new effect‐based triggers (EBTs) in field studies (circles [Neale et al 2020a] and squares and diamonds [Neale et al 2020c]) and previous data collections (gray symbols [Escher et al 2018b]). Red dashed lines indicate new EBT bioanalytical equivalent concentration (BEQ), black dotted lines indicate previously proposed EBT‐BEQ with the read‐across method (Escher et al 2018b).…”

“…Iceberg modeling compares the mixture effects predicted from the concentrations of detected chemicals and effect data of the detected chemicals with the measured effects (Escher et al 2020c). In the present study, we reused data from iceberg modeling of a highly diverse set of surface water quality data (tables S7-S9 in Neale et al [2020a], summarized in Supplemental Data, Table S2) and data from wastewater-treatment plants (WWTPs; Table S9 in Neale et al [2020c], summarized in Supplemental Data, Table S3), where more than 600 chemicals were analyzed with the same analytical method, and all bioassay data were measured with AREc32, PPARγ-BLA, and AhR-CALUX after SPE. The number of analyzed chemicals was smaller in those 2 case studies than in Supplemental Data, Table S1, and hence a smaller number of chemicals had been considered in the iceberg modeling (Neale et al 2020a(Neale et al , 2020c.…”

“…The same holds for PPARγ, where the EBT-rosiglitazone-EQ differentiated well between treated and untreated wastewater, with 2 wastewater samples exceeding the EBT ( Figure 8B). Both were from WWTPs that applied primary treatment only (P1 and P2 in Neale et al [2020c]). All surface water samples had acceptable water quality, with exception of 2 that were from the Danube River at Novi Sad, in areas impacted by wastewater (König et al 2017).…”