Abstract
Marine Microplastics (MPs) exhibit a wide range of properties due to their variable origins and the weathering processes to which they are exposed. MP’s versatile properties are connected to their dispersal, accumulation, and deposition in the marine environment. MP transport and dispersion are often explained by analogy with sediments. For natural sediments, one of the key features linked to transport and marine morphology is particle size. There is, however, no size classification defined for MP particles and MPs constitute all plastic particles sized smaller than the threshold of 5 mm. In this study, based on existing knowledge in hydrodynamics and natural sediment transport, the impact of MP size on turbulent entrainment, particle settling, and resuspension is described. Moreover, by analyzing several quantitative studies that have provided size distribution, size-selective accumulation of MPs in various regions of the marine environment is reported on. The preferential presence of MPs based on their size in different marine compartments is discussed based on the governing hydrodynamic parameters. Furthermore, the linkage between polymer properties and MP shape and size is explored. Despite the evident connection between hydrodynamic transport and MP size presented, classification of MP size presents challenges. MP size, shape, and density appear simultaneously in the definition of many hydrodynamic parameters described in this study. Unlike mineral sediments that possess a narrow range of density and shape, plastics are manufactured in a wide variety of densities and marine MPs are versatile in shape. Classification for MP size should incorporate particle variability in terms of polymer density and shape.
Highlights
Plastics are used for a wide spectrum of products and their production has increased drastically over the past decades
Once plastic debris reaches a body of Microplastic Size Impact on Mobility water, water acts as a transport vehicle and distributes and spreads the particles
For nearshore surface water samples, the peak size bin was reported to be small, D50 extended beyond this size showing a wider spread of size distribution. This is attributed to the impact of size in hydrodynamic processes outlined in section “Microplastic Size Impact on Hydrodynamic Parameters.”
Summary
Plastics are used for a wide spectrum of products and their production has increased drastically over the past decades. Microplastic Size Impact on Mobility water, water acts as a transport vehicle and distributes and spreads the particles Due to their slow decomposition processes, plastics can last in aquatic environments for centuries, if not millennia. Tanaka and Takada (2016), among others, presented shapes for MPs, from fragments and FIGURE 1 | Range of physical processes that affect the transport and distribution of marine MPs (modified from Karimpour et al, 2021a): (1) advection; (2) entrainment by turbulent structures; (3) sinking of negatively buoyant or biofouled MPs, and vertical forces including drag force, Fd, gravity, Fg, and buoyant force, Fb; (4) rising of positively buoyant or defouled MPs; (5) transport by wind; (6) coastal beaching and wash off; (7) transport with sediment gravity flow.
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