ORIGINAL RESEARCH article
Front. Environ. Sci.
Sec. Biogeochemical Dynamics
Volume 13 - 2025 | doi: 10.3389/fenvs.2025.1639535
This article is part of the Research TopicLife in the "Plastisphere": Linking the Biodiversity of Microbial Communities to the Risk of Micro-(nano-)plastics and Related New ContaminantsView all 6 articles
Retention and Remobilization of Aged Polystyrene (PS) Microplastics in a Porous Medium under Wet-Dry Cycling
Provisionally accepted
- 1Sun Yat-Sen University School of Marine Sciences, Zhuhai, China
- 2Nanjing Forestry University, Nanjing, China
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Understanding the aging processes of microplastics (MPs) in environmental matrices and their behavior under dynamic wet-dry cycles in unsaturated zones (e.g., vadose and intertidal zones) is critical for accurate environmental risk assessment. This study investigates the impact of aging on the retention and remobilization dynamics of polystyrene (PS) microplastics in unsaturated porous media. We employed light-aged PS MPs and conducted column experiments using sea sand under cyclic drying-wetting conditions. Results demonstrate that aging significantly altered MP physicochemical properties, increasing surface negative charge and hydrophilicity. During drying (unsaturated conditions), aging suppressed the remobilization of retained MPs. Aged MPs exhibited markedly lower release recovery than pristine MPs, with remobilization governed by mobile air-water interfaces (AWI), where hydrophobicity served as the key determinant. MPs were remobilized via AWI detachment forces once water saturation (Sw) fell below a critical threshold (~0.6). Under cyclic wetting-drying with continuous MP input, aging substantially enhanced long-term retention and promoted a more uniform spatial distribution of PS MPs. After five cycles, the total retained fraction of aged MPs (32-day aging) reached 76.88%, consistently exceeding that of pristine MPs (72.83%). Although aging intensified electrostatic repulsion during wetting phases, it significantly reduced AWI-driven remobilization efficiency during drying due to increased hydrophilicity. Crucially, these retention-promoting mechanisms (reduced AWI remobilization) outweighed retention impedance from electrostatic repulsion during wetting, resulting in greater overall retention of aged MPs. This study elucidates the complex regulatory role of aging in MP remobilization and retention under dynamic unsaturated conditions, highlighting how shifting hydrology alters dominant retention mechanisms. These findings provide essential insights for assessing the environmental persistence and migration risks of aged microplastics.
Keywords: Microplastics, Aging, Drying-wetting cycle, unsaturated porous media, air-water interface
Received: 02 Jun 2025; Accepted: 30 Jun 2025.
Copyright: © 2025 Xi, Xu, Yao, Sun, Zhao, Huang and Li. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence:
Qing Huang, Nanjing Forestry University, Nanjing, China
Yan Li, Sun Yat-Sen University School of Marine Sciences, Zhuhai, China
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