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Entrainment and vertical mixing of aquatic microplastics in turbulent flow: The coupled role of particle size and density
Summary
Researchers conducted laboratory flume experiments to study how turbulence affects the vertical mixing and entrainment of microplastic particles of different sizes and densities. Both particle size and polymer density significantly influenced mixing behavior, with smaller and denser particles more responsive to turbulent structures, informing models of microplastic transport in rivers and coastal waters.
Diversity in microplastics' characteristics, including their size, affects their transport and distribution in aquatic systems. Furthermore, turbulent induced mixing is often considered dominant in the dispersion of sediments and contaminants in marine and freshwater systems, which is also affected by particle size. The aim of this study is to investigate the effect of microplastics' size and polymer density on their mixing behaviour in response to turbulent structures. Using sediment analogy, several parameters are defined to describe entrainment patterns of microplastic particles of common polymers. Our results indicate that the level of mixing of microplastics in turbulent flow can vary several orders of magnitude. While large particles' vertical motion may be dominated by gravitational settling or rising, the motion of fine microplastics is mainly governed by the ambient turbulent flow. Our findings provide a plausible explanation for the presence of fine microplastics in remote areas.
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