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Transport of Nanoplastics in Saturated Zeolite: Effects of Flow Rate and Hydro-Chemical Conditions
Summary
Column experiments showed that zeolite — a mineral common in natural soils — retains polystyrene nanoplastics through electrostatic attraction and physical straining, with retention decreasing at higher pore-water flow rates. Understanding how soil mineralogy and hydrology jointly govern nanoplastic transport is fundamental to predicting where these particles accumulate in the environment and how likely they are to reach groundwater and food-crop root zones.
Aluminosilicates are commonly present in natural soils, contributing to their texture and composition. The fate and transport of nanoplastics within natural sediments containing aluminosilicates have not been comprehensively studied yet. To investigate the interactions between nanoplastics and sediments, polystyrene nanoplastics (PS-NPs) were injected into columns filled with zeolite under the condition of different flow rates, pH values, and ionic strengths (IS). Results show that zeolite inhibited polystyrene nanoplastics (PS-NPs) transport to different extents under different conditions. The limitation of PS-NPs transport was mainly governed by (1) the PS-NPs–zeolite interaction energy obtained via the Derjaguin–Landau–Verwey–Overbeek calculation, (2) the amphoteric sites on zeolite surface (they will possess positive charges attracting negative PS-NPs when pH < pHpzc), and (3) surface roughness leading to physical straining phenomena. In addition, the flow rate of pore water played an essential role during the PS-NPs transport. The retention of PS-NPs decreased at higher flow rates, likely due to a reduction in particle-collector contact efficiency. This study uncovers the migration mechanism of PS-NPs within zeolite, providing insights into the behavior of nanoparticles in natural porous media.