Weathering alters the settling dynamics of polyethylene microplastics: Integrating morphology-dependent drag coefficient with numerical simulations

초록

Weathering alters the physical properties of microplastics and can modify their transport behavior in aquatic systems, but its impact on settlement dynamics remains under-quantified. This study investigates how physico-chemical weathering affects the morphology and settling behavior of polyethylene microplastics by integrating laboratory experiments with numerical simulations. Particles underwent four laboratory-simulated weathering scenarios combining mechanical stirring, ultraviolet irradiation, and hydrogen peroxide treatment. Weathering resulted in substantial mass loss (∼25%) and systematic geometric changes, indicating size reduction accompanied by partial shape regularization. A numerical model based on an ad hoc Maxey–Riley formulation with a morphology-dependent drag coefficient was validated against independent experimental data (R2 = 0.90). Modeling results show that weathering reduced the terminal settling velocity by 5.2–7.1% relative to pristine particles. Mechanical stirring produced the largest reduction (6.7%) through particle size reduction and the associated mass loss, whereas hydrogen peroxide partially offset this reduction (+1.6%) through shape regularization. Ultraviolet irradiation had a negligible effect (<0.5%). These secondary effects were associated with slight shape regularization, partially compensating for the velocity reduction. When particle shape was explicitly incorporated into the corrected Reynolds number, settling velocities collapsed into a single scaling relationship (R2 > 0.99). These findings demonstrate that weathering causes slower settling of particles through size reduction, while shape-induced drag acts as a secondary but important factor in improving predictions of microplastic transport. © 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

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