Decision-Support Tool in QGIS for Pharmaceutical Emission Modelling, Risk Assessment and Mitigation Measures

Human pharmaceuticals are essential in healthcare, but their discharge from wastewater treatment plants (WWTPs) poses a growing risk to aquatic ecosystems due to their biological activity at low concentrations. The amended EU Urban Wastewater Treatment Directive (UWWTD) in 2025 mandates quaternary treatment for large WWTPs (>150,000 population equivalents (PE)) to remove micropollutants and requires a risk-based prioritization for mid-sized plants (10,000-150,000 PE). A significant implementation gap has been identified, as the UWWTD does not yet specify a unified risk assessment methodology. In addition, numerous small WWTPs, frequently situated in vulnerable low-flow waters, are not directly addressed despite their cumulative impact and lack of monitoring data.

To address this issue and support decision-making, the APRIORA project developed an improved monitoring concept and a complementary, spatially high-resolution tool to provide estimates of pharmaceutical concentrations and related environmental risks in QGIS. This deterministic, steady-state model calculates annual per-capita loads discharged by each WWTP based on pharmaceutical sales data and WWTP-connected inhabitants. Substance-specific excretion and removal rates are incorporated either based on available monitoring data or literature. Point source emissions are transferred to the river network, and concentrations in different river sections are estimated using flow data. The regionalized yearly average flow data can be either integrated from external sources, or modelled using an integrated hydrological model in the QGIS plugin. Elimination processes occurring in the receiving waters, such as biodegradation, photodegradation and sorption to sediment particles, are neglected to ensure a conservative estimate. The resulting Predicted Environmental Concentrations (PECs) are used for calculating risk quotients (RQ). The modelling approach was piloted in five catchments (Germany, Finland, Latvia, Poland, Sweden).

To support the development of cost-effective mitigation strategies on a catchment scale, the tool allows for scenario assessment. Mitigation measures include: (I) upgrading the treatment type at a WWTP (e.g. from tertiary to quarternary treatment with higher removal efficiency), (II) relocating emissions by merging effluents of smaller WWTPs into larger facilities, and (III) redirecting the discharge point to a larger or less-sensitive receiving water body. The effectiveness of selected mitigation measures is directly visualized in mitigated risk maps. Testing mitigation measures for diclofenac in a German catchment showed that upgrading the three largest WWTPs (>10,000 PE) to quaternary treatment effectively reduced risks directly downstream.  However, this measure alone did not mitigate risks in numerous other sections, underscoring the limited effect of focusing solely on mid-sized plants in rural areas with scattered, smaller WWTPs (Figure 1).

This easy implementable tool is designed for environmental authorities providing a consistent, spatially explicit methodology for prioritizing interventions to close the gap between regulatory requirements and practical water resource management. Beyond pharmaceuticals, the modelling approach is transferable to other substances where point-source emissions can be quantified, e.g., PFAS from industrial sites.

Acknowledgement - The authors thank the IBSR funding programme – co-founded by the European Union (ERDF) – and the APRIORA project.