Mass Flux Analysis Reveals the Presence and Fate of Antimicrobials in Hospital Effluent, Wastewater Treatment Plant, and River Environments

Background: Hospitals are recognized as important point sources of antimicrobials; however, their contributions to antimicrobial contamination at the watershed scale remain poorly understood. Methods: Seasonal monitoring was conducted between December 2024 and May 2026 at two hospitals, a wastewater treatment plant (WWTP), and receiving river waters in the Yodo River Basin, Japan. Seventeen antimicrobials were quantified, and concentration profiles and mass fluxes were integrated to evaluate source contributions. Results: Ampicillin, levofloxacin, azithromycin, clarithromycin, and vancomycin were the predominant antimicrobials. Hospital wastewater was identified as the dominant source of ampicillin and vancomycin, whereas levofloxacin and clarithromycin were largely influenced by diffuse watershed inputs. Several antimicrobials persisted through wastewater treatment and were continuously detected in WWTP effluent and downstream river waters. Conclusions: This watershed-scale assessment demonstrates that antimicrobial contamination is driven by both hospital-derived point sources and broader watershed inputs. These findings provide a scientific basis for integrated hospital wastewater and WWTP management to mitigate environmental antimicrobial resistance (AMR) within the One Health framework.