Plasma-treated polystyrene microplastics for enhanced transport studies in porous media: A surfactant-free approach

Microplastics (MPs) are increasingly recognized as persistent contaminants in soils and groundwater systems worldwide. Polystyrene MPs are highly hydrophobic and show strong homoaggregation, which affects their mobility in porous media. Most laboratory transport studies therefore use chemical dispersants, such as Tween 20, to achieve a uniform distribution of particles during transport experiments. However, these additives coat plastic surfaces and alter plastic–soil interactions, making it difficult to assess environmentally realistic transport behavior. Here, we introduce a surfactant-free approach based on controlled radio-frequency oxygen plasma treatment to modify MP surface properties. Oxygen plasma-treated polystyrene particles (