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The initiation and resuspension characteristics of (micro)plastics from varied depositional environments under hydraulic disturbance
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Scientists found that microplastics settled in riverbeds and lakebeds can get stirred back up into the water when currents reach a certain speed, and how easily this happens depends on the plastic's type, shape, and the kind of sediment it's buried in. This matters because it means microplastics we thought were "trapped" in waterway sediments can re-enter the water we drink, fish from, and rely on for ecosystems, making pollution harder to predict and contain than previously thought.
Resuspension of (micro)plastics in sediments leads to their dispersion and increases environmental risks. Little is known about the initiation or resuspension characteristics of (micro)plastics from diverse sedimentary sources. Here, we investigated (micro)plastics resuspension under hydraulic disturbance and identified the main driving factors. Water tank and stirring experiments were used to determine the critical flow rate for resuspension and evaluate its characteristics. Powders of polypropylene (PP) (150 μm) and polyethylene terephthalate (PET, 150 μm), and fibers of PP (6 mm) and PET (6 mm) were used as (micro)plastics, and coarse sand, fine sand (FS), lotus pond soil, FS + 1% humic acids, and FS + 5% humic acids were used as the sediments. Resuspension required a flow rate of at least 0.33 m s− 1. The highest resuspension concentration was obtained for PP powders from coarse sand, but this concentration decreased as the sediment’s particle size decreased and as its total organic carbon (TOC) increased. Both PET powders and PET fibers had high resuspension concentrations from sediments with fine sands and high TOC contents. The sediment group with PET fibers exhibited significantly lower turbidity than that with PP fibers. The particle size and TOC content of sediments affected the initiation and resuspension characteristics of (micro)plastics. The resuspension of low-density (micro)plastics was driven by buoyancy, whereas that of high-density (micro)plastics was driven by sediment transport and water shear stress. (Micro)plastic fibers likely indirectly affected their own resuspension by modifying the resistance of the sediments to disturbance.
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