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Microplastics transport in subsurface environments: Mechanisms and multi-scale modeling
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Tiny plastic particles are seeping through soil into groundwater—the same water many of us drink—and this review of existing research shows scientists still struggle to predict exactly how they move underground. Because these particles behave differently than the chemicals or germs we usually track in water, current safety models may miss how far and fast they travel, which matters since they can carry other pollutants along with them. Better tracking models, which the researchers propose building, could eventually help protect drinking water supplies from this hidden contamination.
Microplastics (MPs) are persistent contaminants in soils, the vadose zone, and groundwater, where they may act both as pollutants and vectors for co-contaminants. Although their sources and occurrence in subsurface environments have been increasing documented, the translation of this knowledge into mechanistic and predictive transport models remains limited. Unlike occurrence-oriented reviews, this review adopts a model-oriented perspective and examines how MP source characteristics, particle properties, and transport mechanisms can be represented across pore, column, vadose-zone, and field scales. We synthesize recent advances in three interconnected areas: (a) source and occurrence patterns relevant to model boundary conditions; (b) physical, geochemical, and biological processes controlling MP transport, retention, and remobilization; and (c) numerical modeling approaches, including continuum transport models, variably saturated vadose-zone models, and pore-scale simulations. We show that MPs cannot be treated simply as dissolved solutes or conventional colloids because their broad size distribution, irregular morphology, density contrast, deformability, and aging-dependent surface properties produce non-Fickian transport, size-dependent straining, interfacial trapping, and dynamic attachment-detachment behavior. Recent models increasingly extend advection-dispersion-reaction frameworks by incorporating particle-specific retention, dual-domain exchange, air-water interfacial processes, and multi-scale parameterization, while lattice-Boltzmann, computational-fluid-dynamics, and discrete-element simulations provide mechanistic constraints on particle-pore interactions. However, major gaps remain in representing unsaturated and preferential-flow conditions, bio-mediated transport, field-scale parameterization, and the upscaling of micro-CT and pore-scale observations. We therefore propose a focused multi-scale modeling framework that links source terms, process-based model closures, targeted experiments, and data-driven parameterization to improve prediction and risk assessment of MP contamination in subsurface environments.
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Scientists studied how tiny plastic particles move through soil toward underground water sources that we use for drinking water. They found that plastic particles travel very differently depending on how wet or dry the soil is - sometimes getting trapped, other times moving quickly through the ground. This research helps us better understand how microplastics might contaminate our groundwater supplies, which is important for protecting drinking water quality.
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Researchers developed a mathematical model to predict how microplastics move through soil and into groundwater, accounting for particle size, shape, and water flow conditions. The model shows that smaller and rounder microplastics travel farther and deeper into groundwater systems, which is important for predicting contamination risks to drinking water wells.
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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.