[Distribution Characteristics， Sources， and Risk Assessment of Antibiotics in the Surface Water of Zaohe River]

In recent years， with the increasing use of antibiotics， various antibiotics are discharged into aquatic environments and pose serious hazards to the safety of aquatic ecosystems and human health. To investigate the pollution status in the Zaohe River in Xi'an， the residues of 15 antibiotics in the surface water of the Zaohe River were detected using high performance liquid chromatography-tandem mass spectrometry （HPLC-MS/MS）， the sources of antibiotics were analyzed by the PCA-MLR model， and the ecological risk of typical antibiotics were evaluated by the risk quotient （RQ） method. The results showed that eight antibiotics belonging to four categories were detected at six sampling sites （two sampling sites in the upstream， midstream， and downstream of Zaohe River， respectively）， and the concentration ranged from 1.08 to 71.27 ng·L^-1 with detection frequencies ranging from 16.67% to 100%. The detection frequencies of ciprofloxacin （CIP）， roxithromycin （ROX）， and ofloxacin （OFX） were all 100%. The concentration of CIP was highest， followed by that of ROX. The concentration of antibiotics was higher in the dry season than that in the wet season. The main antibiotics were macrolides （Mas） in the wet season and fluoroquinolones （FQs） in the dry season. The PCA-MLR analysis indicated that antibiotics detected in Zaohe River mainly came from waste and wastewater discharged from hospitals， wastewater treatment plants， feed mills， livestock， and aquaculture plants. Redundancy analysis showed that there was a significant negative correlation between pH and ROX. The concentrations of norfloxacin （NOR） and ciprofloxacin （CIP） were significantly positively correlated with electrical conductivity （EC） and total nitrogen （TN）， while negatively correlated with water temperature. Ecological risk assessment based on the risk quotient showed that ROX and CIP posed high risk to green algae； NOR， OFX， and aureomycin （CTC） posed medium risk； and tetracycline （TC） and oxytetracycline （OTC） posed low risk. CIP， NOR， TC， OTC， and sulfamethoxazole （SMX） posed low risk to daphnia. All the antibiotics in water samples posed insignificant risk to fish. The health risk assessment results indicated that none of the antibiotics in the water samples presented potential health risks to humans. The resistance risk assessment results showed that ROX， CIP， and NOX had low resistance risk. Our results could provide scientific basis for the prevention and control of antibiotic pollution in the Zaohe River in Xi'an.