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.