Department of Earth Sciences, College of Science, Shiraz University, Shiraz 71454, Iran; Centre for Environmental Studies and Emerging Pollutants (ZISTANO), Shiraz University, Shiraz, Iran.
Meteorology and Air Quality Group, Wageningen University & Research, P.O. Box 47, 6700, AA Wageningen, the Netherlands.
Chemosphere. 2023 May;322:138150. doi: 10.1016/j.chemosphere.2023.138150. Epub 2023 Feb 16.
Soils are an important source of microplastics (MPs) to the atmosphere but the fluxes and mechanisms involved in MPs entrainment are not well understood. In the present study, a series of horizontally aligned sediment traps have been deployed at different heights within 1 m above the ground for a two-month period at various locations in an arid region (Sarakhs, Iran). MPs were isolated from sediments and were quantified and characterised according to size, colour, shape and polymer composition by established techniques. Most MPs were <250 μm in length, fibres were the most important shape, black and blue-green were the dominant colours, and polymer abundance decreased in the order polyethylene > nylon > polypropylene > polystyrene > polyethylene terephthalate. The distributions of sediment mass (range <0.01-9 g) and number of MPs (range = 0 to 21) were heterogeneous, both between sites and at the different heights sampled, and yielded median, vertically-averaged horizontal fluxes for the region of about 450 g m d and 2600 MP m d, respectively. However, when data were pooled, the number of MPs normalised to sediment mass exhibited a significant inverse relationship with sediment mass, an effect attributed to the presence of ambient suspended MPs and sediment that are diluted by the suspension of soil and deposited MPs at higher wind speeds. The mechanisms of MP saltation and entrainment were not ascertained but a theoretical framework for threshold shear velocity based on regularly-shaped particles and density considerations is presented. Further experimental work is required to verify this framework, and in particular for fibrous MPs with different aerodynamic properties to soil particles.
土壤是大气中微塑料（MPs）的重要来源，但 MPs 夹带的通量和机制尚不清楚。在本研究中，在伊朗干旱地区的不同地点，在离地 1 米的不同高度部署了一系列水平排列的沉积物捕集器，为期两个月。通过已建立的技术，从沉积物中分离出 MPs，并根据大小、颜色、形状和聚合物组成对其进行定量和特征描述。大多数 MPs 的长度<250 μm，纤维是最重要的形状，黑色和蓝绿色是占主导地位的颜色，聚合物丰度按聚乙烯>尼龙>聚丙烯>聚苯乙烯>聚对苯二甲酸乙二醇酯的顺序减少。沉积物质量（范围<0.01-9 g）和 MPs 数量（范围= 0 到 21）的分布不均匀，无论是在不同地点之间还是在不同高度的采样点之间，并且该地区的中值、垂直平均水平通量分别约为 450 g m d 和 2600 MPs m d。然而，当数据汇总时，标准化为沉积物质量的 MPs 数量与沉积物质量呈显著负相关，这一效应归因于环境悬浮 MPs 和沉积物的存在，这些 MPs 和沉积物在较高的风速下被悬浮土壤和沉积 MPs 稀释。尚未确定 MPs 跳跃和夹带的机制，但提出了一个基于规则形状颗粒和密度考虑的理论框架，用于确定剪切速度阈值。需要进一步的实验工作来验证该框架，特别是对于具有不同空气动力学特性的纤维状 MPs 和土壤颗粒。
