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The transport behaviour of microplastics in longitudinal mixing and hyporheic exchange under varied flow conditions
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Researchers studied how microplastics move through river systems, examining both downstream transport and how particles interact with riverbeds through hyporheic exchange. Understanding these transport behaviors helps predict where microplastics accumulate in river sediments.
Microplastics is an emerging pollutant that are increasingly detected in major rivers around the world. They are potentially harmful to the natural environment due to their toxicity and potential for bioaccumulation. Yet much of the plastics today remain “missing” as transport and sink mechanisms of plastics and microplastics has not been properly studied. This study develops a novel method to track microplastic movement where spherical Polyethylene (PE) microplastics of size ranging from 40 to 46µm is stained using Nile Red. The dispersion behaviour of microplastics is subsequently studied by predicting the longitudinal dispersion coefficient from the standard Advection-Dispersion (ADE) Model at uniform flow discharges, and with the addition of a weir. Stable fluorescence detection of the microplastics in the water is achieved. This method proves to be successful in tracking the temporal concentration distribution of microplastics in the flow, producing a similar dispersion curve to conventional dye tracers. A comparison of the microplastics coefficients with that of Rhodamine WT further reveals that Polyethylene microplastics disperses in a similar manner as Rhodamine in the water column. This marks the potential of using Rhodamine WT as a proxy to study the dispersion characteristics of microplastics in natural rivers.
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Significance of Hyporheic Exchange for Predicting Microplastic Fate in Rivers
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Researchers modeled the role of hyporheic exchange — water flow between rivers and streambed sediments — in driving microplastic delivery and retention in riverbeds, finding that this process significantly increases the rate at which small and positively buoyant microplastics are transported into streambed sediments. The study highlights hyporheic exchange as an underappreciated mechanism controlling microplastic fate in freshwater environments.
An Experimental Method to Quantitatively Assess the Transport of Microplastic Particles in Fluvial Systems
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Researchers developed an experimental method to quantitatively measure how microplastic particles behave when transported through fluvial (river) systems, including both surface flow and subsurface hyporheic zones. The study provides much-needed empirical data on microplastic transport mechanisms in rivers, which are key pathways for delivering plastic pollution to the ocean.
Microplastic accumulation in riverbed sediment via hyporheic exchange from headwaters to mainstems
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Researchers developed a model showing that hyporheic exchange between river surface water and sediment causes long-term microplastic retention, with headwater residence times averaging 5 hours per kilometer but increasing to 7 years per kilometer during low-flow conditions.
Longitudinal and Vertical Transport of Microplastic Within Sediment in Rivers and Transitional Water Environments
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Researchers investigated the longitudinal and vertical transport of microplastics within sediments in rivers and transitional water environments, developing models to quantify how sediment presence affects microplastic mobility and their transport toward coastal areas.
Hyporheic exchange processes of pore-scale microplastics
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Researchers studied how microplastics move through the hyporheic zone, the region where river water mixes with groundwater beneath the streambed. They found that denser plastic particles sank through sediment pores toward groundwater, while lighter plastics rose to the surface, and both behaved differently from dissolved substances. These findings raise concerns that microplastics may be contaminating groundwater systems through processes that are not well captured by current water quality models.
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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.