Riverine antibiotic occurrence and potential ecological risks in a low-urbanized and rural basin of the middle Yangtze River: Socioeconomic, land use, and seasonal effects.

This study firstly investigated the effects of season, land use, and socioeconomic on the spatiotemporal changes of riverine antibiotic concentrations in a low urbanized and rural watershed. In the dry and wet seasons, water samples were collected and analyzed for 15 antibiotics. The results indicated that 14 antibiotics, excluding leucomycin, were detected. Monsoon led to significantly lower total antibiotic concentrations in the wet season (22.0ngL) than in the dry season (51.2ngL). Total antibiotic concentrations were dominated by amoxicillin (below limit of detection (<LOD)-34.7ngL)), erythromycin-HO (<LOD-14.7ngL), roxithromycin (<LOD-27.9ngL), and trimethoprim (<LOD-6.34ngL). The total antibiotic concentrations were usually higher in the downstream areas of urban land than in the river reaches of forest land and agricultural land. At county or city scales, total antibiotic concentrations in the dry season were significantly correlated with the rural population, public budget, husbandry product and output, effluent volume, fishery product and output, and hospital number, which generally depend on land use in the basin. Amoxicillin poses a high ecological risk to aquatic algae, whereas erythromycin-HO, ofloxacin, and norfloxacin pose medium ecological risks. However, trimethoprim poses a medium ecological risk to mollusks. These results provide improved insights into the characteristics of antibiotic occurrence and ecological risks in the waters of low-urbanized and rural areas in China and can be extrapolated worldwide.