Occurrence, removal, and ecological risk of antibiotics and antibiotic resistance genes in township wastewater treatment plants in the upper reaches of the Yangtze River, China.

The excessive use of antibiotics contributes significantly to environmental pollution and the widespread presence of antibiotic resistance genes (ARGs), which poses a serious threat to aquatic ecosystems and human health. Despite being a critical source of antibiotics and ARGs in the environment, research exploring their occurrence and removal characteristics in township wastewater treatment plants (WWTPs) remains limited. This study investigated the abundance and removal efficiencies of 39 antibiotics and 8 ARGs in influent and effluent samples from 40 township WWTPs located in the upper reaches of the Yangtze River. Antibiotics were detected in both influents and effluents, with detection frequencies (DFs) ranging from 2.44% to 100%. In contrast, all targeted ARGs exhibied 100% DFs in both influents and effluents. The average concentrations of antibiotics in influents and effluents were 370.67 ng/L and 242.06 ng/L, respectively, and the ARGs concentrations were 9.88 × 10 and 7.10 × 10 copies/mL, respectively. Among the antibiotics analyzed, macrolides and fluoroquinolones accounted for over 70% of the total antibiotic concentrations in both influent and effluent samples. Additionally, sul1 and sul2 were identified as the predominant ARGs, constituting more than 99% of the total abundance in both influent and effluent samples. Notably, significant correlations between the ARGs and their respective antibiotics were not consistently observed. The average removal efficiencies for total antibiotics and ARGs by township WWTPs were 34.70% and 93.30%, respectively. Furthermore, all calculated ecological risk values (risk quotient, RQ) for individual antibiotics in effluent samples were below one, except for oxytetracycline, which had RQ values greater than one in three effluents. The total RQs, representing the sum of individual RQs, indicated that 11 effluents presented a high risk (27.50%), while 17 effluents exhibited a moderate risk (42.50%). These findings suggest that township WWTPs may represent a significant source of antibiotics and ARGs in the environment, necessitating further process improvements for their effective elimination.