Guangdong Provincial Key Laboratory of Water Quality Improvement and Ecological Restoration for Watersheds, Institute of Environmental and Ecological Engineering, Guangdong University of Technology, Guangzhou, 510006, China; Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
Water Res. 2021 Dec 1;207:117782. doi: 10.1016/j.watres.2021.117782. Epub 2021 Oct 21.
Aging of microplastics (MPs) (i.e., degradation and weathering) is ubiquitous in the environment. The MP aging process is thought to be limited to light and static areas, while aging in dark and fluctuating anoxic-oxic areas is poorly understood. Here, we provide initial evidence for aging of polystyrene microplastics (PS-MPs) under different anoxic/oxic conditions in sediments, and we further explored these mechanisms using sediment column experiments and pure-culture experiments. The results showed that PS-MPs in alternating anoxic-oxic sediments displayed the highest degree of aging. In the in-situ experiment, both the weight losses and O/C ratios of PS-MPs aged under alternating anoxic-oxic conditions were ∼2 times higher than those aged under static oxic and static anoxic conditions during 2-month experiments. In a 2-month column experiment, the PS-MPs in the alternating anoxic-oxic group showed weight losses and O/C ratios that were, respectively, triple and double the corresponding values for the static oxic and static anoxic groups. Column and pure-culture experiments demonstrated that dark production of ·OH which showed a positive correlation with a Fe redox process could explain enhanced MP aging under the alternating anoxic-oxic conditions. These findings provide a basis for risk assessment and management of MPs in the natural environment, such as in intertidal zones and paddy fields, and also have implications for engineering of optimized MP degradation processes.
微塑料（MPs）的老化（即降解和风化）在环境中普遍存在。人们认为 MP 的老化过程仅限于光照和静态区域，而对黑暗和波动的缺氧-需氧区域的老化过程了解甚少。在这里，我们提供了 MPs 在沉积物中不同缺氧/需氧条件下老化的初步证据，并进一步通过沉积物柱实验和纯培养实验来探索这些机制。结果表明，在交替缺氧-需氧沉积物中，聚苯乙烯微塑料（PS-MPs）的老化程度最高。在现场实验中，在 2 个月的实验中，PS-MPs 在交替缺氧-需氧条件下的老化导致的重量损失和 O/C 比值分别比在静态需氧和静态缺氧条件下老化时高出约 2 倍。在为期 2 个月的柱实验中，交替缺氧-需氧组的 PS-MPs 的重量损失和 O/C 比值分别是静态需氧组和静态缺氧组的 3 倍和 2 倍。柱实验和纯培养实验表明，黑暗中产生的·OH 与 Fe 氧化还原过程呈正相关，可以解释在交替缺氧-需氧条件下增强的 MP 老化。这些发现为在自然环境中（如潮间带和稻田）评估和管理 MPs 的风险提供了依据，同时也为优化 MP 降解过程的工程设计提供了参考。
