Effects of Soil Components on Microplastics Transport and Retention in Natural Soils: Various Microplastics Types and Sizes

Microplastics (MPs) have emerged as a global concern, yet the interactions between MPs and natural soils remain poorly understood. This study aimed to investigate the transport and retention behaviors of different microplastics polymers in diverse soil environments, elucidating the critical role of soil physicochemical properties in MPs mobility. We conducted column experiments examining the transport and retention of three microplastics types (polyvinyl chloride, polymethyl methacrylate, and polypropylene) across three distinct soil types (desert, red, and black soils). Particle sizes ranging from 1–2 μm, 2–5 μm, and 10–15 μm were selected, with a focus on the impacts of soil components such as metal oxides and natural organic matter. MPs mobility generally decreased with increasing particle size, following the order PVC > PMMA > PP in desert soil (maximum transport mass recovery: 29.7%). The microplastics transport mass recovery approached 0% in red soil, primarily due to the high specific surface area and abundant metal oxides, which synergistically enhanced electrostatic attraction and physical retention. A non-monotonic trend observed in black soil was attributed to the interplay between natural organic matter (NOM) adsorption. Soil physicochemical properties significantly influenced MPs mobility, correlating with the soil texture, metal oxide, and organic carbon. Metal oxide typically enhanced MPs retention through decreased electrostatic repulsion and surface roughness, with the maximum observed increase in transport mass recovery being 53.2%. NOM removal exhibited biphasic effects on MPs transport, characterized by an initial promotional phase in low-NOM desert soil and an inhibitory phase in high-NOM black soil. The extended FDLVO theory and numerical modeling matched the experimental results well. The results showed that, soil physicochemical properties, particularly metal oxides and natural organic matter, significantly influenced microplastics transport and retention, with particle size, polymer type, and soil composition playing critical roles in determining microplastics mobility in natural environments.

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