Antibiotics in northern China's largest shallow wetland lake: Occurrence, bioaccumulation, ecological risk, and indicator screening.

Antibiotics are widespread in aquatic environments due to their extensive use in human healthcare and animal husbandry. However, research on the occurrence and bioaccumulation of antibiotics in aquatic organisms within shallow wetland lakes remains limited. This study investigated the occurrence and bioaccumulation of ten commonly used antibiotics in the Baiyang Lake, northern China's largest shallow wetland lake. The results indicated that sulfonamides and fluoroquinolones were the predominant antibiotics in surface water, whereas fluoroquinolones and macrolides were more prevalent in sediment. Fluoroquinolones demonstrated significant potential for bioaccumulation in targeted aquatic organisms, including both animals and plants (Carassius auratus and Phragmites australis). The bioaccumulation of antibiotics in Carassius auratus was correlated with their solubility, whereas in Phragmites australis, this was associated with their octanol-water partition coefficients and molecular weights. Ecological risk assessment indicated that most antibiotics posed minimal to low risk levels. However, four antibiotics were exceptions: clarithromycin (12.5 %) and sulfamethoxazole (6.25 %) presented a high risk in surface water samples, while norfloxacin (25.0 %) and ciprofloxacin (25.0 %) posed a high risk in sediment samples. Norfloxacin, ciprofloxacin, and roxithromycin were identified as key indicator antibiotics for enhancing the local monitoring and control of antibiotic contamination based on four criteria: (1) high concentrations, (2) frequent detection, (3) capacity for bioaccumulation, and (4) ecological risk levels. This study contributes to a deeper understanding of the status of antibiotic contamination, bioaccumulation characteristics, and ecological risk in Baiyang Lake, thereby supporting efforts to monitor and regulate antibiotic pollution.