Seamless forward assessment of toxic risks in river networks for mixtures of chemicals originating from wastewater treatment plant effluents

Chemicals in the aquatic environment can be harmful to biota and may cause toxic risks to the aquatic ecosystems. A high number of these chemicals originate from point sources (households, manufacturing and industries). A subset of the substances is permanently released and the load is proportional to the number of people connected to wastewater treatment plants (WWTPs), while other substances show higher variable emission patterns. Especially at low discharges of the receiving waters  the toxic risk may increase due to reduced dilution.

We test the hypothesis that the accumulated urban discharge fraction (UDF) in a river network is a robust proxy for the toxic risk induced by discharged chemicals from point sources.

To prove this hypothesis we combined available catchment data like stream network organisation and spatially related WWTPs, the amount of wastewater and discharge data as well as data from a European reference mixture data set containing concentrations of chemicals regularly found  in European wastewater treatment plant effluents (Beckers et al. 2023). Based on these data we calculated mixing concentrations and toxic units for 80 chemicals, among them pesticides, biocides and pharmaceuticals, besides other typical wastewater-related compounds, such as sweeteners and corrosion inhibitors.

Measured data (WFD, 2015 - 2021) at 87 stations in the Federal State of Thuringia (Germany) were compared with the modelled concentrations and showed highly significant correlations for pharmaceuticals and no correlation with pesticides. We conclude, that our modelling approach using UDF as a proxy supports the identification of different sources of compounds occurring jointly as mixtures in aquatic systems and by this supports a source oriented pollution and risk management.

References

Beckers, L.-M., Altenburger, R., Brack, W., Escher, B.I., Hackermüller, J., Hassold, E., Illing, G., Krauss, M., Krüger, J., Michaelis, P., Schüttler, A., Stevens, S. and Busch, W. (2023) 'A data-derived reference mixture representative of European wastewater treatment plant effluents to complement mixture assessment', Environment International, 179, 108155, available: http://dx.doi.org/https://doi.org/10.1016/j.envint.2023.108155.