The Effect of Polystyrene with Different Aging States on the Transport of Intracellular ARGs in Agricultural Soils

Antibiotic resistance genes (ARGs) transport in porous media directly determines its environmental dissemination and associated ecological risks, and has therefore become a major concern in environmental research. Aging of microplastics (MPs) can markedly alter their surface properties, thereby affecting the environmental behavior of coexisting contaminants. To elucidate the effects of differently aged polystyrene (PS) on the transport of intracellular antibiotic resistance gene (iARG) host bacteria, a saturated quartz sand column system was established using Escherichia coli MG1655 carrying the RP4 plasmid as the model strain. The effects of pristine PS, chemically aged PS (CAPS), and biologically aged PS (BAPS) on bacterial transport were systematically compared. The results showed that all three types of PS inhibited iARG transport, with stronger inhibition observed for smaller particle sizes. Compared with pristine PS, CAPS further reduced bacterial transport, whereas BAPS exhibited the strongest inhibitory effect and delayed the breakthrough peak. These findings indicate that PS aging, particularly biological aging, can further suppress iARG transport in porous media by enhancing particle interfacial interactions and local retention. This study advances the understanding of how aged MPs influence ARG transport and environmental fate, and provides a theoretical basis for assessing the potential environmental risks of ARG dissemination in the presence of microplastics.