Dynamic distribution characteristics and ecological risks of antibiotics in typical subtropical tidal river

Antibiotics have garnered increasing global concern due to their frequent detection and persistence in the environment, which can lead to ecological risks, biological resistance, posing a potential threat to ecosystem and human health. This study investigated the occurrence of antibiotics in a typical tidal channel located in the lower reaches of the Dongjiang River during both wet and dry seasons. Additionally, high-frequency continuous dynamic monitoring was conducted over a full tidal cycle at a tidal-influenced section. The total concentrations of antibiotics ranged from 11.46 to 940.53 ng/L in the wet season and from 15.08 to 322.31 ng/L in the dry season. Fluoroquinolones, particularly ciprofloxacin, were the predominant antibiotics detected. Concentrations were significantly higher in the wet season compared to the dry season. Spatially, antibiotic levels exhibited a pattern with higher concentrations in the upstream and downstream regions and lower concentrations in the middle section. Furthermore, antibiotic concentrations showed a clear tidal influence, with the lowest levels observed during ebb tide and the highest during flood tide. Ecological risk assessment indicated that antibiotics posed higher ecotoxicological risks in the wet season than in the dry season, with fluoroquinolones representing the highest risk category. The potential for antimicrobial resistance was relatively high for ciprofloxacin, moderate for ofloxacin and norfloxacin, suggesting that these compounds should be prioritized in risk management strategies. In contrast, human health risks associated with antibiotic exposure were found to be negligible. These findings offer valuable insights into the behavior and management of antibiotic pollution in tidal rivers.