A national-scale assessment of hospital contributions to chemical loads in wastewater and the implications for wastewater-based epidemiology

Wastewater-based epidemiology (WBE) is an established approach for assessing population health through the quantification of pharmaceuticals and lifestyle chemicals in wastewater. As hospitals are a potential point source for these chemical indicators (CIs), assessment of population health within hospitals may be possible via WBE while hospitals’ chemical contributions have the potential to impact community wide WBE assessments. Untreated hospital wastewater and corresponding community influent wastewater were collected from six sites across Wales through a national sampling campaign capturing 18 % of the Welsh population and 23 % of hospital in-patients nationally in summer 2023. Using liquid chromatography and targeted mass spectrometry, the mass loads of over 50 CIs were quantified. An exploratory analysis of sewer catchment parameters and hospital parameters identified possible trends. From these insights, further examination of data from published literature demonstrated a statistically significant inverse relationship between catchment population and hospitals’ average contribution to influent wastewater flow. This suggests that hospitals located in smaller wastewater catchments may have more influence on the total CI load in influent wastewater. Across all CIs assessed, antimicrobials were the only chemical class to have a substantial influence on influent wastewater composition. The median percent contribution of sulfamethoxazole, trimethoprim, and fluconazole across studied sites ranged from 5 to 50 %, 6–66 %, and 2–33 %, respectively. Hospital contributions of antimicrobials can meaningfully impact the conclusions from WBE assessments of community antimicrobial use. These findings may help identify priority sites for future interventions to reduce antimicrobial loads in wastewater environments and their potential contribution to antimicrobial resistance.