Source-related patterns and ecological risk prioritization of antibiotics in a large lake-river system: insights from...

Antibiotic mixtures in large floodplain lake basins are shaped by overlapping anthropogenic inputs, environmental mixing, and compound-specific toxicity, complicating source interpretation and risk prioritization. We measured 10 antibiotics in 158 samples collected during a high-water-period campaign from 26 to 30 August 2023 in the Poyang Lake basin, including 42 lake-water samples and 116 wastewater samples from sewage treatment plants, hospitals, livestock and aquaculture facilities, and pharmaceutical industries. Mean total antibiotic concentration in lake water was 73.9 ng L^-1, dominated by oxytetracycline, chlortetracycline, and tetracycline. Exploratory socio-economic correlation analyses showed category-dependent patterns with economic activity, production intensity, and sector-related antibiotic use. Receptor-side positive matrix factorization resolved three compositional patterns accounting for 46.0%, 11.8%, and 42.1% of modeled antibiotic mass: an oxytetracycline-rich mixed pattern, a sulfamethazine-chlortetracycline-doxycycline mixed pattern, and a chlortetracycline-dominated tetracycline-rich pattern. Source-profile comparison and non-negative least squares fitting indicated mixed and spatially variable compositional consistency with the four wastewater categories rather than evidence for a single dominant source. In the primary Monte Carlo analysis, oxytetracycline, chlortetracycline, and enrofloxacin had the highest probabilities of exceeding a risk quotient of 1 (16.3%, 16.3%, and 14.8%, respectively), while mixture-level summed risk quotients exceeded 1 in 65.1% of simulations. Weighting by predicted no-effect concentrations further increased the relative priority of ciprofloxacin in wastewater profiles and shifted lake-water priorities from oxytetracycline toward enrofloxacin and ofloxacin. These results show that concentration-based composition does not directly represent ecological-risk priority and support source-sensitive, risk-oriented management of antibiotic mixtures in large floodplain lake basins.