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Transport and retention of polyethylene microplastics in saturated porous media: Effect of physicochemical properties
Summary
Researchers studied how polyethylene microplastics move through water-saturated sand and gravel, testing the effects of particle size, water chemistry, and flow speed. They found that smaller microplastics traveled farther through the porous material, while higher salt concentrations and lower flow rates increased particle retention. The findings help explain how microplastics may spread through groundwater systems under real-world conditions.
Microplastics (MPs) are persistent contaminants of global concern due to their widespread occurrence in ecosystems (surface and sub-surface media) and potential ecological and human health risks. Their mobility in subsurface environments (e.g., soil, groundwater) is governed by complex interactions among particle properties, water chemistry, and porous media, yet limited research has examined these processes under groundwater relevant conditions. Understanding the influence of physicochemical factors of environmental-sized MPs is critical for evaluating contamination risks and developing groundwater protection strategies. Therefore, this study investigates the transport and retention of environmental-seized (150–180 µm) polyethylene microplastics (PE-MPs) in saturated porous media through laboratory-controlled sand column experiments. The effects of pH (5, 7, 9) and ionic strength (0.1, 1, and 10 mM NaCl) were systematically evaluated. Results demonstrate that elevated pH (pH 9) enhances PE-MP migration by reducing electrostatic attraction between MPs and sand surfaces, thereby decreasing retention. Similarly, lower ionic strength (0.1 mM) promotes breakthrough by limiting charge screening, which reduces particle deposition. In contrast, lower pH and higher ionic strength increase retention, indicating the strong role of water chemistry in controlling MP fate in porous systems. These findings provide new mechanistic insights into microplastic transport in groundwater relevant environments. The outcomes advance understanding of PE-MPs mobility in porous media and highlight key physicochemical factors influencing their environmental behavior. This study provides a scientific foundation for developing strategies to mitigate microplastic pollution in natural aquifers, stormwater management, and engineered infiltration systems (e.g., bioretention media) and supports evidence based decision making by engineers and policymakers.