Fate and Ecological Risk Assessment of Antiviral Drugs in Multiprocess Wastewater Treatment Plants and Adjacent Watersheds: A Case Study in Shenzhen, China

Abstract The pervasive use of antiviral drugs (ATVs) for treating viral infections (e.g., HIV, hepatitis, and influenza) has led to their widespread detection in aquatic environments. However, their incomplete removal in wastewater treatment plants (WWTPs) and associated ecological risks remain poorly quantified, particularly in megacities with high population density and medical facility density post-COVID-19. This study analyzed influent, effluent, and process-unit samples from 16 WWTPs and surface water samples from two major river basins via UPLC–ESI–MS/MS to systematically evaluate the occurrence, removal dynamics, and ecological risks of eight priority ATVs. Ecological risk quotients (RQs) were calculated using measured environmental concentrations (MECs) and predicted no-effect concentrations (PNECs) for aquatic organisms. Acyclovir (ACV) was ubiquitously detected in all WWTPs (197–21,334 ng/L) and rivers (139–431 ng/L), with WWTP removal rates varying drastically by process (15.6–99.9%). Oseltamivir (OS) dominated influents (18,251–21,334 ng/L) but was absent in surface waters, suggesting rapid environmental transformation. Risk assessment identified high-risk RQs (>1) for ACV and OS in effluents, threatening algae and fish. Hybrid processes (e.g., A2O+MBR) outperformed single-stage systems, yet overall ATV removal remained suboptimal (avg. 48.6%). This work underscores the urgent need for process optimization and regulatory frameworks to mitigate ATV-driven ecological hazards.