Driving factors for the distribution of i/eARGs in livestock and poultry manure and related wastewater across China.

Antibiotic resistance genes (ARGs), as emerging pollutants, have become a growing environmental concern owing to their wide distribution, durability, and potential adverse effects on humans, animals and the surrounding environments. Livestock and poultry manure and related wastewater (LPMW), the major reservoir of antibiotics, has higher abundance of extracellular ARGs (eARGs) compared with other environments. This review summarizes the abundance of intracellular ARGs (iARGs) and eARGs in LPMW in China. The absolute abundance of iARGs and eARGs in LPMW were 103-1012 and 102-1010 copies/mL or copies/g, respectively, with sul1, sul2, tetQ, tetW, tetG, ermB, ermF, blaTEM and blaampc as the main detected i/eARGs types. Subsequently, the study summarized the intrinsic molecular and biological properties, extrinsic drivers, and methodological influences that may influence the abundance of i/eARGs. Discrepancies in the absolute abundance of i/eARGs could be due to factors such as genetic location, sample sources, antibiotic residues and manure treatment methods. Besides, the efficiencies of extracellular DNA(eDNA) extraction methods commonly used for LPMW samples were compared and quantitative methods of i/eARGs were evaluated, which could also introduce subjective bias into i/eARGs abundance. Limitations related to the current eDNA extraction methods and quantitative methods, the establishment of the safety thresholds for eARGs, in situ monitoring methods, and the role of phages in the spread of ARGs were discussed as future prospects. This review highlights the importance of environmental risk assessment for i/eARGs, lay theoretical basis for the effective removal of i/eARGs for further researches and provides advice for future governance and regulatory measurement.