Addition of microplastics (MP) to soil has the potential to increase soil water repellency. However, coating of MP with soil abundant substances e.g., iron compounds, can reduce this effect. Here, we tested if pre-coating or in situ coating of MP with ferrihydrite (Fh) reduces soil water repellency. We applied hotspots of pristine and coated MP (20–75 μm, PS and PET) to sand and imaged capillary rise via neutron radiography. Capillary rise experiments in wetting–drying cycles were conducted using water and Fh suspension. Pristine MP hotspots were not wettable. Capillary rise of water into coated MP hotspots differed in wettability depending on polymer type. While coated PS was still non-wettable, water imbibed into the coated PET hotspot. Capillary rise of Fh suspensions in wetting and drying cycles also showed varying results depending on polymer type. MP hotspots were still non-wettable and local water content increased only marginally. Our results indicate that Fh coating of MP changes MP surface wettability depending on polymer type and therefore counteracts the hydrophobic properties of pristine MP. However, MP coating is likely to be slowed down by the initial hydrophobicity of pristine MP. Dynamics of MP coating and increasing wettability are key factors for biotic and abiotic degradation processes.

中文翻译：

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水铁矿涂层可降低微塑料引起的土壤防水性

在土壤中添加微塑料 (MP) 有可能提高土壤的防水性。然而，用土壤丰富的物质（例如铁化合物）涂覆 MP可以减少这种影响。在这里，我们测试了用水铁矿 (Fh) 预涂覆或原位涂覆 MP 是否会降低土壤防水性。我们将原始和涂层 MP（20-75 μm、PS 和 PET）的热点应用到沙子上，并通过以下方式对毛细管上升进行成像：中子射线照相。使用水和 Fh 悬浮液进行润湿-干燥循环中的毛细管上升实验。原始 MP 热点不可润湿。水进入涂覆的 MP 热点的毛细管上升的润湿性因聚合物类型而异。虽然涂覆的 PS 仍然不可润湿，但水会吸收到涂覆的 PET 热点中。Fh 悬浮液在润湿和干燥循环中的毛细管上升也显示出不同的结果，具体取决于聚合物类型。MP 热点仍然不可润湿，局部含水量仅略有增加。我们的结果表明，MP 的 Fh 涂层会根据聚合物类型改变 MP 表面润湿性，从而抵消原始 MP 的疏水性。然而，MP 涂层可能会因原始 MP 的初始疏水性而减慢。