Effects Of Polystyrene Microplastics On The Transport Of Resistant Plasmids In Saturated Porous Media

Microplastic（MPs）pollution is a globally recognized environmental issue.In natural environments,MPs undergo aging processes that significantly alter their surface physicochemical properties,including the presence of amino,carboxyl,and aldehyde groups.These changes affect the migration and adsorption of MPs and other pollutants,ultimately impacting the transport and transformation of environmental contaminants.Antibiotic resistance plasmids（ARPs）play a decisive role in the spread of antibiotic resistance genes.This study investigates the migration behavior of functionalized polystyrene microplastics（PSMPs）and their effects on ARPs.The main findings are:Adsorption kinetics and isotherms for PS-Bare,PS-COOH,and PS-NH₂ on ARPs follow pseudo-second-order and Freundlich models,reaching adsorption equilibrium in 120minutes with maximum capacities of 2.26、2.17和128.40 mg g^-1,respectively.Adsorption of ARPs is affected by pH,ionic strength,and ion type.Overall,adsorption decreases as pH increases in the 3.0-8.0 range.Divalent cations promote adsorption more than monovalent cations.The adsorption of ARPs increases with ionic strength for PS-Bare and PS-COOH but decreases for PS-NH₂.Functionalization significantly alters the physicochemical properties of PSMPs,affecting their migration and deposition in porous media.FT-IR and Zeta potential results show that PS-NH₂ has a high amino content,resulting in a positive surface charge that forms strong electrostatic interactions with media surfaces,inhibiting migration and increasing deposition.PS-COOH has a high carboxyl content,lowering its Zeta potential and creating stronger repulsive forces that promote migration.Both PS-Bare and PS-COOH have negatively charged surfaces,so cations inhibit their migration,with higher ionic strength and valence having stronger inhibitory effects.Co-transport experiments of PSMPs and ARPs show that under low ionic strength conditions,PS-Bare and PS-COOH have over 90%recovery of adsorbed ARPs,which still exhibit high mobility.In contrast,due to electrostatic attraction,ARPs adsorbed on PS-NH₂are completely deposited in the sand column.PSMPs provide some protection for ARPs against enzymatic degradation,with the order of protection strength being PS-Bare>PS-COOH>PS-NH₂.This research provides new insights and scientific evidence for assessing the environmental risks and mitigation strategies for plastic particles and antibiotic resistance genes.