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Settling and rising velocities of microplastics: Laboratory experiments and lattice Boltzmann modeling
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This study measured how different types of microplastics sink or float in water, testing how particle size, density, water temperature, salinity, and bacterial growth affect their movement. Biofilm growth on microplastics significantly changed their behavior, slowing sinking speeds and even causing some buoyant particles to reverse direction and sink. Understanding how microplastics move through water is important for predicting where they end up in the environment and how they might enter drinking water sources.
Microplastics (MPs) have become pervasive in marine ecosystems, potentially causing environmental degradation, impacting ecological function, and posing a serious public health risk. Despite the widespread distribution of MPs, their vertical transport within a water column has limited understanding, representing a key knowledge gap in the development of water quality models to minimize these risks. In this study, 6152 individual particles of six common types of MPs were observed through water column experiments to examine a range of drivers of the vertical velocity of MPs, including particle density and size, biofilm growth, water temperature, and salinity. The experimental results revealed that the vertical velocity of MPs obeyed Stokes' law under laminar conditions; increasing salinity decreased the settling tendency of the particles. Moreover, biofilm attachment induced notable alterations in particle characteristics within 60 days, resulting in slower settling velocities (up to a 21.9% change for non-buoyant MPs) and even a reversed vertical direction (up to several times for buoyant particles). Furthermore, a lattice Boltzmann model could predict the vertical velocity of MPs with reasonable accuracy, especially for small particles. This work facilitates the development of sophisticated models/formulas that integrate particle morphology, hydrodynamics, and biological factors to enhance the understanding of MP transport through the river-to-coastal continuum.
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Shifting settling regimes of aquatic microplastics
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Researchers conducted laboratory settling experiments and modeling to understand how physical properties of microplastics influence their settling velocity and transport behavior in aquatic environments. They found that biofilm colonization significantly increases settling rates, suggesting that biofouling is a key factor controlling microplastic fate and distribution in rivers and lakes.
An experimental study on microplastic settling velocities in different water environments: Which factors shape the settling process?
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Researchers experimentally investigated how biofilm formation and weathering processes affect the settling velocities of microplastics across different water matrices, identifying the key physical and biological factors shaping how particles sink in aquatic environments.
Non-buoyant microplastic settling velocity varies with biofilm growth and ambient water salinity
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Researchers investigated how biofilms (thin layers of bacteria that grow on plastic surfaces), water salinity, and suspended clay affect how fast microplastics sink in water, finding that biofilm growth alone increased sinking speed by up to 130% within just hours. These findings show that current models predicting where microplastics end up in rivers and oceans are too simplistic, and that biological and chemical conditions must be factored in for accurate predictions.
Assessing the Settling Velocity of Biofilm-Encrusted Microplastics: Accounting for Biofilms as an Equivalent to Surface Roughness
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This study investigated how biofilm growth on microplastics affects their sinking behavior in water. Researchers found that treating the biofilm as a form of surface roughness helps accurately predict how quickly biofouled plastic particles settle, with polyethylene particles sinking sooner than polypropylene ones. The findings improve our understanding of how microplastics move through water columns once marine organisms begin colonizing their surfaces.
Microplastic-specific biofilm growth determines the vertical transport of plastics in freshwater
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Researchers studied biofilm growth on five different microplastic polymer types in freshwater over 63 days to understand how biological colonization affects sinking behavior. The study found that biofilm growth is polymer-specific and can significantly alter the density of microplastic particles, which in turn determines whether they sink or float, influencing their vertical transport through freshwater systems.
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