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Viscoelastic and shear-thinning effects of aqueous exopolymer solution on disk and sphere settling
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Using a gel-like polymer to mimic natural aquatic conditions, researchers found that the gel's non-Newtonian properties significantly slow the settling speed of particles compared to plain water. This suggests microplastics in natural waters rich in organic matter may sink more slowly than lab studies in clean water would predict.
In this study, xanthan gum is used as a model exopolymer to demonstrate potential effects of non-Newtonian properties of natural aquatic systems on settling dynamics of particles. Rheological measurements combined with settling experiments using visualization methods revealed that instantaneous velocity fluctuations and a flow pattern formed around a particle are the effects of solution viscoelasticity and shear-thinning properties and that the average settling velocity depends on the exopolymer concentration and particle size. Our study showed that in the considered conditions a disk-shaped particle settles preferably in vertical position with a negative wake behind. The understanding of these processes is essential in technology and engineering and is necessary to improve prediction accuracy of large-scale sedimentation processes and biogeochemical cycles in the ocean involving settling of minerals, marine snow, microplastics, and locomotion of microorganisms.
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Settling of microplastics in mucus-rich water column: The role of biologically modified rheology of seawater
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Laboratory experiments showed that naturally occurring exopolymers secreted by marine algae and bacteria convert seawater into a non-Newtonian fluid that slows the sinking of microplastic particles, altering how and where they accumulate in the ocean water column. Understanding these biologically driven settling dynamics is important for predicting microplastic distribution and exposure risk for marine organisms at different depths.
Effects of biologically modified seawater on settling behaviour of microplastics
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Researchers found that during algal blooms, exopolymers secreted by microorganisms significantly increased seawater viscosity and changed how microplastic particles sank through the water column. This finding means that the sinking behavior of microplastics in real ocean conditions — especially during bloom events — is far more complex than laboratory tests with clean seawater suggest.
Effects of rheologically stratified seawater during algal bloom on sinking dynamics of microplastics
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This study investigated how algal blooms affect the sinking behavior of microplastics in seawater by examining the role of exopolymers secreted by microorganisms during bloom events, which make the water more viscous and gel-like. In bloom-affected, rheologically modified seawater, microplastics sank differently than in normal conditions, with some particles being retarded and others accelerated depending on their properties. Understanding these dynamics is important because algal blooms are becoming more frequent globally, and how microplastics sink determines how long they remain in the water column where marine life is exposed to them.
Effect of exopolymer gels on the viscoelasticity of mucus-rich saltwater and settling dynamics of particles
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Researchers investigated how exopolymer gels produced during algal blooms affect the rheological properties of mucus-rich saltwater and the settling dynamics of particles, using xanthan gum as a model exopolymer in sodium chloride solutions. They found that colloidal exopolymers created a stronger internal structure than particulate gels and increased drag coefficients on sinking particles up to sixfold, suggesting colloidal exopolymers retard particle settling in marine environments more effectively.
Dataset on sinking of solid particles in non-ionic and single-salt aqueous dispersions of xanthan gum and carrageenan and rheological properties of these dispersions
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Researchers measured the settling velocities of six plastic particle shapes — including spheres, disks, and rods — in non-Newtonian xanthan gum and carrageenan solutions representing viscous aquatic environments, finding that ionic conditions and polymer type systematically alter sinking rates in ways relevant to predicting microplastic fate in coastal and marine waters.
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When a large batch of papers lands in the Atlas, we read through it and send a short write-up of what stood out.