Occurrence characteristics, cross-media behavior, and influencing factors of antibiotics and ARGs in typical rivers around the Bohai Sea.

To investigate the cross-media behavior and key drivers of antibiotics and antibiotic resistance genes (ARGs) in typical rivers around the Bohai Rim region, this study analyzed 26 rivers discharging into the Bohai Sea using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and high-throughput quantitative fluorescence PCR. A total of 36 antibiotics were identified in the water samples and 33 in the sediments, with total concentrations ranging from n.d. to 1515.134 ng/L in water and n.d. to 85.926 ng/g in sediment. Tetracyclines were the dominant antibiotic class in both media. Additionally, 50 types of ARGs were detected in the water and 52 in the sediments, with absolute abundances ranging from n.d. to 1.04 × 105 copies/L in water and up to 2.13 × 105 copies/g in sediment. Gene abundances were generally higher in sediments, with macB and intI1 emerging as the predominant genes. Compared with pre-COVID-19 data, no significant increase in antibiotic concentrations or ARG abundances in the rivers was observed. Furthermore, the findings revealed that ARGs were highly mobile between the water and sediment phases, with non-corresponding antibiotics exerting a notable influence on this movement, while the effects of environmental physicochemical factors appeared minimal. This study provides key scientific insights for developing effective strategies to prevent antibiotic pollution and control the cross-media transmission of ARGs in the Bohai Sea region.