Retention and transport behavior of microplastic particles in water-saturated porous media

Microplastic (MP) pollution has become a global concern given its wide occurrence and potential ecological risks. The retention/transport features of MPs in porous media govern the fate and risks of MPs in subsurface environments. Polystyrene (PS) microspheres are employed as representative MPs to explore the migration behaviors in water-saturated quartz sand columns. The hydrodynamic size mainly determines the deposition and size exclusion straining of MPs in porous media, and further the attachment efficiency. PS50 (PS with 50 nm diameter) shows a total migration rate greater than 85% in each of the studied conditions. In contrast, PS500 commonly exhibits slower migration velocities and higher attachment efficiencies than those of PS50 and PS100. The ionic strength, pH, and dissolved organic matter content of the solution show obvious effects on the retention/transport of PS MPs. The influences of solution chemical properties are consistent with the prediction of Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The results in this study clarify the size-dependent migration characteristics of MPs in porous media and provide a basis for risk assessment of MPs in terrestrial environments.