[Occurrence Characteristics， Ecological Risks， and Main Sources of Antibiotics in Rivers in Tongzhou District，...

China is a major producer and consumer of antibiotics. Because humans and animals have difficulty fully metabolizing antibiotics and the limited degradation efficiency of antibiotics in current wastewater treatment plants， antibiotic pollution is common in rivers in China， threatening the health of river ecosystems. Tongzhou District， Beijing， is the sub-center of Beijing， and all of the rivers flowing through the main urban area of Beijing converge in this district. A total of 16 antibiotics in the rivers of Tongzhou District， Beijing， were used as research objects， an analysis of the antibiotic concentration and spatial distribution characteristics was performed based on the geographic information system （GIS）， the ecological risk of the antibiotics and its uncertainty were evaluated by the coupling risk quotient method and Monte Carlo method， and the main sources of antibiotics were identified using the principal component analysis method. The results showed that the total concentrations of the 16 target antibiotics ranged from 69.52 to 1 913.05 ng·L^-1. Ofloxacin （OFL） had the highest concentration among all antibiotics， with an average concentration of 279.95 ng·L^-1， accounting for 50.07% of the total antibiotic concentration. Spatially， the concentrations of most of the antibiotics were relatively high in the Beiyun River and relatively low in the Wenyu River and Yunchaojian River. Compared to the Hai， Yangtze， Yellow， Pearl， Huai， and Liao Rivers， the concentrations of antibiotics in the rivers in Tongzhou District were low. The results of the ecological risk assessment showed that the ecological risk levels of sulfadimethoxine （SDM） and OFL were higher than those of the other antibiotics. The upper limits of the 90% confidence interval of the probability distribution of ecological risk for these antibiotics were 132.04 and 86.58 times the threshold of the high-risk class， respectively， and the probability of SDM leading to high ecological risk was higher than 95%. The results of source identification showed that the main sources of antibiotics were effluents of wastewater treatment plants， aquaculture， and livestock farming. Among these， effluent of wastewater treatment plants was the most dominant source， explaining 41.38% of the antibiotics. This study comprehensively explored the occurrence， ecological risks， and major sources of antibiotics in the rivers in Tongzhou District， Beijing， which is of great significance for targeted antibiotic pollution control and ecosystem health protection.