Department of Crop & Soil Sciences, Washington State University, Pullman, WA 99164, and Puyallup, WA 98371, USA.
Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
Sci Total Environ. 2024 Feb 20;912:168883. doi: 10.1016/j.scitotenv.2023.168883. Epub 2023 Nov 30.
Land-applied biosolids can be a considerable source of microplastics in soils. Previous studies reported microplastics accumulation in soils from biosolid application, however, little is known about the contribution of atmospherically deposited microplastics to agricultural soils. In this study, we quantified and characterized microplastics in soils that have been amended with biosolids over the past 23 years. We also collected atmospheric deposition samples to determine the amount and type of plastics added to soils through atmospheric input over a period of about 2 years. Soil samples were taken from a replicated field trial where biosolids have been applied at rates of 0, 4.8, 6.9, and 9.0 t/ha every second crop. The biosolids were anaerobically digested and dewatered, and were applied by spreading onto the soil surface. Soil and atmospheric samples were extracted for microplastics by Fenton's reaction to remove organic matter followed by flotation in a zinc chloride solution to separate plastic from soil particles. Samples were analyzed for microplastics by optical microscopy and Laser Direct Infrared Imaging Analysis (LDIR). The mean number of microplastics identified from biosolids samples was 12,000 particles/kg dry biosolids. The long-term applications of biosolids to the soil led to mean plastics concentrations of 383, 500, and 361 particles/kg dry soil in the 0-10 cm depth for low, medium, and high biosolids application rates, respectively. These plastic concentrations were not significantly different from each other, but significantly higher than those found in non biosolids-amended soil (117 particles/kg dry soil). The dominant plastic types by number found in biosolids were polyurethane, followed by polyethylene, and polyamide. The most abundant plastics in soil samples were polyurethane, polyethylene terephthalate, polyamide, and polyethylene. Atmospheric deposition contributed to 15 particles/kg dry soil per year and was mainly composed of polyamide fibers. This study shows that long-term application of biosolids led to an accumulation of microplastics in soil, but that atmospheric deposition also contributes a considerable input of microplastics.
土地施用生物固体可能是土壤中微塑料的一个重要来源。以前的研究报告称，在施用生物固体的土壤中积累了微塑料，但人们对通过大气输入添加到农业土壤中的大气沉积微塑料的贡献知之甚少。在这项研究中，我们量化和描述了过去 23 年中用生物固体改良的土壤中的微塑料。我们还收集了大气沉积样本，以确定在大约 2 年的时间内通过大气输入添加到土壤中的塑料的数量和类型。土壤样本取自一个重复田间试验，在该试验中，以 0、4.8、6.9 和 9.0 吨/公顷的速率每两季作物施用一次生物固体。生物固体经过厌氧消化和脱水，然后通过铺展到土壤表面进行施用。土壤和大气样本通过 Fenton 反应提取微塑料，以去除有机物，然后在氯化锌溶液中浮选，将塑料与土壤颗粒分离。通过光学显微镜和激光直接红外成像分析 (LDIR) 对样品进行微塑料分析。从生物固体样品中鉴定出的微塑料平均数量为 12000 个/公斤干生物固体。长期向土壤中施用生物固体导致低、中、高生物固体施用量下 0-10cm 深度干土中塑料浓度分别为 383、500 和 361 个/公斤。这些塑料浓度彼此之间没有显著差异，但明显高于未施用过生物固体的土壤（117 个/公斤干土）。生物固体中数量最多的塑料类型是聚氨酯，其次是聚乙烯和聚酰胺。土壤样品中最丰富的塑料是聚氨酯、聚对苯二甲酸乙二醇酯、聚酰胺和聚乙烯。大气沉降每年贡献 15 个/公斤干土，主要由聚酰胺纤维组成。这项研究表明，长期施用生物固体导致土壤中微塑料的积累，但大气沉降也对微塑料的输入有相当大的贡献。
