Effects of physicochemical factors on transport and retention of polystyrene microplastics (PS-MPs) in homogeneous and heterogeneous saturated porous media.

Microplastics (MPs) as an emerging environmental contaminant pose significant ecological and health risks. This study investigated polystyrene microplastics (PS-MPs) transport and release in saturated heterogeneous porous media using quartz sand columns (eight configurations: homogeneous and heterogeneous) and Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Experimental results showed increased PS-MPs retention in homogeneous media with smaller medium particles, larger PS-MPs (PS100, PS1000, PS5000), and higher ionic strength (1-10 mM NaCl/CaCl₂). Heterogeneous media exhibited earlier breakthrough with two-peak phenomena due to preferential flow. Higher ionic strength and divalent cations (Ca²⁺) enhanced retention by reducing electrostatic repulsion. Breakthrough peaks for PS-MPs in heterogeneous media followed 0.1 μm > 5 μm > 1 μm, influenced by pore structure-induced flow disturbances. PS-MPs demonstrated re-release potential, particularly under water chemistry changes and media heterogeneity. These findings clarify PS-MPs behavior in subsurface environments, aiding risk assessment for aquifer contamination. Key factors include ionic conditions, particle size interactions, and media heterogeneity, emphasizing the need to address preferential flow paths in contaminant transport models. These findings help to understand the transport and release behavior of PS-MPs in saturated porous media and provide important references for assessing the transport risks of PS-MPs in subsurface aquifer environments.