Gray Austin, Gore Beija, Gaesser Megan, Rodriguez Sequeira Luisana, Thibodeau Tessa, Montgomery Allison, Purvis Sam, Ouimet Kathryn, Dura Tina, Mayer Kathleen
Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States.
Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States.
Environ Toxicol Chem. 2025 Jul 1;44(7):2017-2028. doi: 10.1093/etojnl/vgaf116.
Inland riverine systems are major conduits of microplastics (MPs) to coastal environments. Plastic materials that pass through riverine systems are subjected to various degradation processes that facilitate their fragmentation into MPs. Low-order streams, a critical yet understudied part of river networks, significantly influence the fate and transport of MPs. Here, we investigate the in situ degradation of common macroplastic polymers (e.g., low-density polyethylene, polyethylene terephthalate, and polystyrene) and their fragmentation into MPs in urban and forested streams. We deployed macroplastic items and a natural biodegradable polymer (cellulose) into a stream habitat for 52 weeks. We found that regardless of stream type (forested or urban), macroplastic polymers produced MPs in 2 weeks, with polystyrene having the highest fragmentation rate (8 particles/week). We explored several degradation indices (carboxyl index, hydroxyl index, and vinyl index), which revealed that photooxidation played a role in macroplastic degradation over time. Another driver of degradation was biofilm formation observed on the surface of all items, mainly composed of diatoms. Finally, we found that field-aged macroplastics can leach plastic-derived dissolved organic. Our study narrows the knowledge gap regarding MP degradation and fragmentation in freshwater by providing real-time in situ data on the rate of polymer fragmentation in a low-order riverine system.
内河系统是微塑料进入沿海环境的主要通道。流经内河系统的塑料材料会经历各种降解过程，这些过程促使它们破碎成微塑料。低阶溪流是河网中一个关键但尚未得到充分研究的部分，对微塑料的归宿和运输有重大影响。在此，我们研究了常见宏观塑料聚合物（如低密度聚乙烯、聚对苯二甲酸乙二酯和聚苯乙烯）在城市和森林溪流中的原位降解及其破碎成微塑料的过程。我们将宏观塑料物品和一种天然可生物降解聚合物（纤维素）放置在溪流栖息地中52周。我们发现，无论溪流类型（森林或城市）如何，宏观塑料聚合物在2周内就产生了微塑料，其中聚苯乙烯的破碎率最高（每周8个颗粒）。我们探索了几种降解指标（羧基指数、羟基指数和乙烯基指数），结果表明光氧化随着时间的推移在宏观塑料降解中发挥了作用。另一个降解驱动因素是在所有物品表面观察到的生物膜形成，主要由硅藻组成。最后，我们发现经过野外老化的宏观塑料会释放出源自塑料的溶解有机物。我们的研究通过提供低阶河流系统中聚合物破碎率的实时原位数据，缩小了关于淡水环境中微塑料降解和破碎方面的知识差距。
