Occurrence and risk assessment of antibiotics in the Xi'an section of the Weihe River, northwestern China.

Fifteen antibiotics, including seven sulfonamides (SAs); three macrolides (MLs); three quinolones (QNs); one lincosamide, lincomycin (LIN); and one tetracycline (TC), were detected in the surface water of the Xi'an section of the Weihe River by using high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS). The detection rates were 12.50-100%, and the detected concentrations were in the range of nd-270.60 ng/L. The average detected concentrations of the SAs, MLs, QNs, LIN and TC were 113.68, 111.79, 20.55, 23.81 and 25.66 ng/L, respectively. Among these, SAs and MLs were the dominant antibiotics detected in the Weihe River. Compared with those in other water bodies in China and abroad, the antibiotic residues in the Weihe River were at a moderate contamination level. The SAs concentration distribution followed upstream > midstream > downstream, while the MLs concentration distribution was midstream < downstream < upstream. The correlation analysis and principal component analysis (PCA) indicated that domestic sewage, livestock discharge, and aquaculture and pharmaceutical wastewater are the main sources of antibiotic residues in the Weihe River. In addition, the detected ciprofloxacin (CFX), ofloxacin (OFX) and sulfamethoxazole (SMX) pose high ecological risk in the short and long term.