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Description
The pervasive production and consumption of plastics in daily life have resulted in the accumulation of vast quantities of fragmented and primary microplastics (MPs) in the natural environment. These contaminants pose a severe challenge in the 21st century, infiltration soil and water resources and bioaccumulating across the food web, thereby threatening human and ecosystem health. Soil porous media act as a critical reservoir and transport pathway, facilitating migration of MPs into groundwater systems and marine environments. Consequently, elucidating the mechanisms of MP transport and retention in soil is urgent for predicting contaminant distribution and developing remediation strategies.
However, the transport of MPs in porous media is a complex process governed by coupled factors, including MP-MP aggregation, MP-skeleton interactions, particle irregularity, and local hydrodynamics. These complexities present significant challenges for quantitative analysis based solely on experimental observation. To address this, a coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) is employed to investigate MP behaviors in inhomogeneous soil matrices. The multi-sphere method is utilized to simulate allistic irregular shapes, while the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory is integrated to resolve intermolecular forces, specifically Van der Waals attraction and electrical double layer repulsion.
This study quantitatively investigates the synergistic effects of inter-particle interactions, shape, and size. Results indicate that increased attraction promotes the formation of larger agglomerates. These aggregates possess sufficient cohesive strength to resist hydrodynamic shear, leading to enhanced retention via mechanical straining in narrow pore throats. Conversely, system dominated by high electrostatic repulsion exhibit the longest transport distances due to favorable dispersion and inhibition of agglomeration. Furthermore, larger MPs are prone to deposition via inertial impaction and straining. The irregularity of MPs significantly increases the probability of straining compared to spherical particles. These numerical findings provide a mechanistic understanding of MP dynamics in heterogeneous soils, essential for assessing environmental risk and soil contamination profiles.
| Country | China |
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