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Modeling of Microplastics Migration in Soil and Groundwater: Insights into Dispersion and Particle Property Effects

Environmental Science & Technology 2024 20 citations ? Citation count from OpenAlex, updated daily. May differ slightly from the publisher's own count. Score: 65 ? 0–100 AI score estimating relevance to the microplastics field. Papers below 30 are filtered from public browse.
Yaqiang Wei, Yuling Chen, Xinde Cao, Tian-Chyi Jim Yeh, Jiao Zhang, Zi Zhan, Yuedong Cui, Hui Li

Summary

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.

Migration of microplastics (MPs) in soil-groundwater systems plays a pivotal role in determining its concentration in aquifers and future threats to the terrestrial environment, including human health. However, existing models employing an advection-dispersion equation are insufficient to incorporate the holistic mechanism of MP migration. Therefore, to bridge the gap associated with MP migration in soil-groundwater systems, a dispersion-drag force coupled model incorporating a drag force on MPs along with dispersion is developed and validated through existing laboratory and field-scale experiments. The inclusion of the MP dispersion notably increased the global maximum particle velocity (vmaxp) of MPs, resulting in a higher concentration of MPs in the aquifer, which is also established by sensitivity analysis of MP dispersion. Additionally, increasing irrigation flux and irrigation areas significantly accelerates MP migration downward from soil to deep saturated aquifers. Intriguingly, vmaxp of MPs exhibited a nonlinear relationship with MPs' sizes smaller than 20 μm reaching the highest value (=1.64 × 10-5 m/s) at a particle size of 8 μm, while a decreasing trend was identified for particle sizes ranging from 20 to 100 μm because of the hindered effect by porous media and the weaker effect of the drag force. Moreover, distinct behaviors were observed among different plastic types, with poly(vinyl chloride), characterized by the highest density, displaying the lowest vmaxp and minimal flux entering groundwater. Furthermore, the presence of a heterogeneous structure with lower hydraulic conductivity facilitated MP dispersion and promoted their migration in saturated aquifers. The findings shed light on effective strategies to mitigate the impact of MPs in aquifers, contributing valuable insights to the broader scientific fraternity.

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