Spatial distribution and drivers of antibiotics and resistance genes in a key Yellow River tributary.

Antibiotics, various environmental factors, and suspended particulate matter exert a significant influence on the occurrence and dissemination of antibiotic resistance genes (ARGs). However, current research on the mechanisms underlying environmental factor-driven ARG dissemination in sediment-laden rivers, particularly the role of suspended particulate matter, remains incomplete. This study systematically examined the distribution and interaction mechanisms among environmental factors, antibiotics, and ARGs in the Fenhe River Basin, a vital river traversing urban and agricultural areas of Shanxi province, China. The research aims to fill the knowledge gap regarding the driving role of environmental factors in ARG spread within sediment-laden river systems. Surface water samples were collected from six sites across the basin, and the characteristics and relationship among antibiotics, ARG mobile genetic elements, and environmental factors were analyzed. Results showed that macrolide antibiotics were dominant, with azithromycin reaching the highest concentration (584 ng/L, 23% of total antibiotics). Spatially, antibiotic and ARG levels peaked in the midstream; sulfonamide resistance genes sul2 and sul1 were the most abundant ARGs. Tetracycline resistance genes correlated positively with tetracyclines, macrolide antibiotics, and sulfonamide antibiotics, while QepA showed negative correlations with quinolone antibiotics and tetracyclines. Mobile genetic elements (e.g., intI-1LC) promoted ARG propagation. Thirteen environmental factors showed variable correlations with ARGs: sand content positively correlated with 78% of ARGs, while flow velocity and pH negatively correlated with 72% of ARGs. This study clarifies the combined effects of urban-agricultural activities on ARGs in multisediment-laden rivers, offering insights for river ecological risk management.