Antibiotics Sources, Concentrations, and Risk of Antimicrobial Resistance Selection in the Three Gorges Reservoir Basin, China

The widespread use of antibiotics in humans and animals raises significant environmental concerns. However, few approaches can simultaneously quantify their transfer from humans and animals and track their fate in soils and rivers. In this study, we developed the MARINA-Antibiotics model (Model to Assess River Inputs of pollutaNts to seAs for Antibiotics) to quantify the sources and concentrations of 30 widely used antibiotics, as well as assess their associated environmental risks, and implemented this model in the Three Gorges Reservoir Area in 2020. The risk of antimicrobial resistance was evaluated by calculating the risk quotient based on the minimum selective concentration. Our findings revealed that 11 tons of antibiotics entered cropland via manure application. High and medium risk quotients indicated potential risks from ciprofloxacin, enrofloxacin, sulfapyridine, tetracycline, doxycycline, and ofloxacin in cropland. In total, 13 tons were discharged into rivers, primarily through point sources (99%). In rivers, degradation and sedimentation accounted for 90% of antibiotic removal. Tetracyclines and fluoroquinolones contributed the highest loads to the sediments. The risk of promoting AMR was low for most antibiotics except for ciprofloxacin and enrofloxacin. This study improves our understanding of antibiotic sources and spatial patterns in watershed environments, providing valuable insights for clean water management.