The perspective of antibiotics occurrence in the impounded lake under the world-class water transfer project

Antibiotics have been widely used for decades to prevent and treat bacterial infections, and they are now ubiquitous in freshwater environments, posing potential threats to public health and aquatic life. However, knowledge of the spatial variability of antibiotics in navigable and impounded lakes remains limited, especially in the context of expanding water-transfer projects. Here, we evaluated the occurrence and spatial distribution of antibiotics in surface water from Wabu Lake, a key impounded and navigable lake along China's Yangtze River-Huai River Water Transfer Project. A total of 32 antibiotics from four classes were detected, with fluoroquinolones (FQs) showing the highest concentrations. Across the lake, antibiotic levels followed the pattern: southern zone > northern zone > central zone. Variations in antibiotic distribution were mainly associated with nitrogen/phosphorus-related variables and land use, with nutrient-related variables showing the strongest direct effect. Source apportionment suggested that antibiotics primarily originated from domestic and medical wastewater (38.3%), aquaculture wastewater (13.7%), livestock wastewater (10.9%), and secondary effluents from peri-urban wastewater treatment plants (37.2%). Ecological risk assessment indicated that antibiotics posed potential ecological risks in Wabu Lake, and ciprofloxacin (CIP) presented a high risk to algae. These findings provide a reference for controlling antibiotic pollution in similar lakes located along water-transfer project routes.