Impact of COVID-19 policy easing on the fate, removal and ecological risk of anti-epidemic pharmaceuticals in a typical WWTP in South China

China's termination of the stringent “dynamic zero-COVID” policy in December 2022 triggered a shift in pharmaceutical consumption patterns, profoundly altering the load and fate of these compounds in wastewater treatment plants (WWTPs). To investigate the resulting transformations in pharmaceutical behavior and ecological risks, this study conducted monitoring at a typical AAO-process WWTP in Dongguan, collecting full-process wastewater samples according to hydraulic retention time during both the strict containment (September 2022) and the post-liberalization phases (July 2023). LC-MS/MS quantification of 30 target pharmaceuticals (encompassing antivirals, antibiotics, antifungals, and glucocorticoids) revealed a therapeutic shift from antivirals to conventional antibiotics in post-policy influent, exemplified by a 95.5% decline in the antiviral ritonavir (1051 to 47.7 ng/L) contrasted with 1.6–5.3-fold surges in antibiotics (azithromycin: 601 to 954 ng/L; clindamycin: 135 to 713 ng/L). The average removal efficiency declined from 58.7% in 2022 (excluding the extreme negative removal of ritonavir) to 45.3% in 2023, likely resulting from reduced influent concentrations and enhanced desorption of accumulated pharmaceuticals from sludge following the policy shift. Removal occurred predominantly in the AAO bioreactors, with minor contributions from the primary clarifier. Molecular characterization further indicated that lipid- and protein-like dissolved organic matter components were strongly correlated with pharmaceutical removal in anaerobic-anoxic tank. Notably, ritonavir and clindamycin posed continued high ecological risks (RQ > 1) in effluent even after policy relaxation. These results offer mechanistic insights into pharmaceutical fate under changing policy contexts and support the development of targeted strategies to enhance removal efficiency and mitigate ecological risks in WWTPs in the post-pandemic era. • Pharmaceutical residues in WWTP influent shifted from antivirals to antibiotics post-policy. • Anaerobic and anoxic reactors dominated pharmaceutical removal. • Lipid/protein-like DOM strongly correlated with pharmaceutical removal. • Ritonavir and clindamycin in effluent posed high risk.