Spatiotemporal distribution, driving factors, and ecological risks of antibiotics in the wastewater of urban-scale sewers.

This study systematically investigated the spatiotemporal distribution, driving factors, and ecological risks of antibiotics in urban sewer systems. Only veterinary antibiotics (VAs) and human/veterinary antibiotics (H/VAs) were widely detected, with mean concentrations of 52.6 and 378 ng/L, respectively. Seasonal variations were evident: H/VAs were significantly higher in summer than in winter and spring, whereas VAs were higher in winter than in spring. Spatially, VAs concentrations in the urban sewer sewage followed an approximately normal distribution, suggesting that the presence of non-point sources of pollution (such as antibiotics transmitted through the food chain). In contrast, the concentrations of H/VAs exhibited a right-skewed, non-normal distribution. Source apportionment analysis indicates that the sources of H/VAs in the sewer sewage are likely to include hospital wastewater, mixtures of hospital and domestic sewage, as well as non-point sources of pollution similar to those of VAs. Simulations using a level-III fugacity model identified sedimentation removal and biodegradation as the primary removal pathways for antibiotics within the sewer systems. Significant positive correlations between the population normalized daily mass loads (PNDLs) of H/VAs (e.g., Gatifloxacin, Nalidixic acid, and Fleroxacin) and those of VAs indicate that certain H/VAs and VAs may be used in livestock production and subsequently transferred to sewers via the food chain. Significant negative correlations between heavy metals and antibiotics implied co-sorption onto sewer sediments. Ecological risk assessment revealed Ofloxacin posed medium risks (0.1 ≤ RQ < 1) in sewers near hospitals. Overall, this study provides key insights into emerging trends of antibiotic occurrence within sewer systems and offers valuable evidence for establishing priority lists in wastewater management.