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A Quantitative Relationship between Settling and Wettability for Weathered Microplastics in Aquatic Systems
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This study examined how the wettability — essentially how water-friendly the surface is — of weathered microplastics affects how fast they sink in water. Researchers found that more wettable plastic particles settle faster, and developed a physics-based drag model incorporating this surface property to improve predictions of microplastic movement through water bodies. More accurate models of microplastic settling are essential for predicting where particles accumulate in rivers, lakes, and oceans, and for assessing exposure risks to aquatic life and humans.
Settling plays a crucial role in determining the residence time, distribution, transport, and ultimate fate of microplastics (MPs) in aquatic environments. The settling dynamics of particles are influenced by their macroscale shape, mesoscale roundness, and microscale surface properties, along with ambient fluid flow conditions. Variations in the wettability of submillimeter MPs affect molecular interactions at the particle-water interface, altering the microscopic flow field and subsequently modifying drag forces during settling. This study examines the impact of wettability on the settling behavior of aged acrylonitrile butadiene styrene MPs by measuring their settling velocities and contact angles. It was shown that increased wettability promotes the settlement of the MPs. A drag model incorporating the Eötvös number─a dimensionless ratio of buoyancy energy to contact angle-derived surface energy─is developed to quantify the relationship between interfacial chemistry and hydrodynamic resistance. Unlike the conventional models, our model considers wettability as a key factor controlling the settling of MP particles. The model was validated using independently measured data and four sets of published data for the MPs. Results demonstrate that the model significantly improves the accuracy of the settling predictions for weathering spherical MPs. Additionally, by integrating the shape factor, it effectively accounts for the settling behavior of irregularly shaped MPs using published data sets. This improvement enhances predictability for MP transport pathways, helping assess MP accumulation zones and potential ecological risks in marine and freshwater systems.
More Papers Like This
AQuantitative Relationshipbetween Settling and Wettabilityfor Weathered Microplastics in Aquatic Systems
AI summary Read the abstract
Researchers quantified the relationship between surface wettability and settling velocity for weathered microplastics in aquatic systems, demonstrating that wettability-driven changes at the particle-water interface alter drag forces and thus residence time and distribution in the water column.
AQuantitative Relationshipbetween Settling and Wettabilityfor Weathered Microplastics in Aquatic Systems
AI summary Read the abstract
Researchers quantified the relationship between surface wettability and settling velocity for weathered microplastics in aquatic systems, demonstrating that wettability-driven microscale changes at the particle-water interface modify drag forces and thus govern the transport and fate of submillimeter plastic particles.
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.
Weathering alters the settling dynamics of polyethylene microplastics: Integrating morphology-dependent drag coefficient with numerical simulations.
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When plastic waste breaks down in water from sun, waves, and chemical exposure, the resulting microplastic pieces actually sink more slowly than fresh, unweathered particles, mainly because they shrink in size. This matters because slower-sinking microplastics stay suspended in water longer, meaning they can drift farther, linger near the surface, and potentially be ingested by fish and other wildlife (and eventually us) for longer periods before settling out.
Settling Velocities of Small Microplastic Fragments and Fibers
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Researchers precisely measured the settling speeds of over 4,000 small microplastic particles in water and found that existing prediction models designed for larger microplastics do not work well for these tiny fragments and fibers. The settling speed depends on each particle's size, density, and shape, with the smallest particles sinking extremely slowly. Understanding how quickly microplastics settle in water is important because it determines how far they travel and how long they remain available to be consumed by aquatic organisms that humans may eventually eat.
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