Fine particulate matter as a key factor promoting the spread of antibiotics in river network

The extensive utilization of antibiotics has resulted in their frequent detection, contributing to an increased abundance of antibiotic resistance genes in rivers and posing a significant threat to environmental health. Particulate matter plays a crucial role as the primary carrier of various pollutants in river ecosystem. Its physicochemical properties and processes of sedimentation and re-suspension can influence the migration and transformation of antibiotics, yet the mechanisms of this impact remain unclear. In this study, we investigated the distribution characteristics at the micro-scale of particles in the upstream plain river network of the Taihu basin and the adsorption behaviors of antibiotics in particulate matter. The results revealed that particles were predominantly in the size range of 30 to 150 μm in the river network and highest total antibiotic concentrations in 0 to 10 μm particle size fractions. Adsorption experiments also confirmed that the smaller the suspended particle size, the stronger the adsorption capacity for antibiotics. Spatially, both the average particle size and total antibiotic concentrations were lower downstream than upstream. The distribution mechanism of antibiotic in river network sediments was significantly influenced by frequent resuspension and settling of fine particles with a stronger capacity to adsorb antibiotics under hydrodynamic conditions. This ultimately facilitated the release of antibiotics from sediment into the water, resulting in lower antibiotic concentrations in downstream sediments relative to upstream These findings suggest that fine particles serve as the primary carriers of antibiotics, and their sorting and transport processes can significantly influence the distribution of antibiotics in water-sediment systems. This study enhances our understanding of the migration mechanisms of antibiotics in river networks and will prove beneficial for the development of management strategies aimed at controlling antibiotic dissemination.