Transport of antibiotic resistance genes in the landfill plume: Experiment and numerical modeling

Antibiotic resistance genes (ARGs) in the landfill site would potentially seep into groundwater by leachate infiltration, which poses great threat of ARGs dissemination through groundwater flow. However, the transport characteristics of ARGs in the landfill plume are still unclear, impeding the risk management and remediation of landfill sites. This study carried out a series of column experiments to investigate the transport of various ARGs in the landfill plume and its influencing factors. Besides, a numerical model was also developed to simulate the transport of ARGs in the porous media, which could determine the attachment and decay rates of ARGs in various scenarios. Experimental results showed that high contents of organic matter and corresponding antibiotics in the landfill plume promoted the transport of antibiotic-resistant bacteria (ARB) and reduced the decay rates of intracellular ARGs (iARGs) in the porous media. Inorganic ions such as Cl^- and SO₄^2- inhibited the mobility of ARB, while they had little influence on iARGs decay. Extracellular ARGs (eARGs) in plasmids exhibited higher decay rate in pore water, leading to shorter transport distance in porous media. In the landfill plume, sul1 had higher mobility than aadA and ermB, which was tightly correlated with its lower decay rate in groundwater and the smaller bacterial host. The decrease of particle size greatly inhibited the transport of ARGs in porous media due to the attachment of ARB on sand surface, while the attached ARGs would easily detach from sand surface during background water flushing. This study could guide the accurate risk assessment of ARGs in the landfill plume as well as the optimization of management strategy for landfill site.