Unraveling antibiotic fate in a highly urbanized estuary: Spatiotemporal patterns, multi-media partitioning, and...

Estuaries accumulate various pollutants, particularly antibiotics, yet significant gaps remain in understanding their multi-media partitioning mechanisms and prioritization. This study comprehensively examined spatiotemporal dynamics, partitioning mechanisms, ecological risks of antibiotics within a highly urbanized estuarine environments (the Pearl River Estuary), and identified priority antibiotics. Surface water, bottom water, and sediment samples contained 21, 18, and 20 antibiotics, respectively, with total concentrations spanning 2.0-54.7 ng/L, 1.7-49.1 ng/L, and 0.29-70.4 ng/g. Spatial gradients revealed decreasing antibiotic concentrations from riverine to marine environments. Antibiotic hydrophobicity and environmental parameters (e.g. pH, salinity, dissolved oxygen, and total organic carbon) regulated the antibiotic distribution. Seasonal variations significantly altered antibiotic levels in surface waters, whereas concentrations in bottom waters and sediments exhibited relative stability across seasons. Mass inventory data revealed that sediments may act as a sink for antibiotics (80.9-86%), with the plume diffusion zone being the predominant repository for these compounds. According to the ToxPi framework, two antibiotics were identified as high-priority antibiotics in the dry (anhydroerythromycin and trimethoprim) and wet seasons (anhydroerythromycin and oxytetracycline). This study emphasizes the necessity of surveilling high-priority antibiotics to guide environmental management and reduce ecological and health risks in the marine environment.