Solid-phase extraction and ultra-high performance liquid chromatography-electrostatic field orbit hydrazine mass spectrometry were used to detect and analyze the contamination of nine antibiotics including sulfonamides, tetracyclines, macrolides, quinolones, and lincomycin in the third drain of Ningxia. Correlations between the antibiotic concentration and water quality indexes were explored, and the ecological risks were evaluated. The results showed that seven antibiotics were detected in the third drain and its confluent stream, with the total concentrations of 14.91-153.48 ng·L-1 and ND-39.37 ng·L-1, respectively. The detection ratios of clarithromycin, levofloxacin, ciprofloxacin, and lincomycin were 100% in the third drain. The highest-concentration antibiotic was levofloxacin (0.84-94.12 ng·L-1), followed by lincomycin (11.15-48.13 ng·L-1). Based on the spatial distribution analysis, after flowing through Pingluo County, total antibiotic concentrations in the third drain increased significantly and showed an increasing trend. The maximum concentration appeared in the Huinong section and showed a decreasing trend downstream. The total concentration of antibiotics before flowing into the Yellow River was 20.26 ng·L-1. Correlation analysis showed that levofloxacin was significantly positively correlated with NH4+-N and TN (P<0.01), erythromycin was significantly correlated with TN, and clarithromycin was significantly correlated with both NH4+-N and TN (P<0.05), which indicated that water quality index was closely related to antibiotic concentration. The results of the ecological risk assessment showed that levofloxacin and clarithromycin in the third drain posed certain ecological risks.
Keywords: antibiotics; ecological risk; pollution characteristic; the third drain; water quality index.