土壤环境中微塑料的分异机制研究

With the development of facility agriculture, the residual plastic film pollution in the farmland soil is increasingly aggravated. The residual plastic films may be broken down and become small sized plastic particles, known as microplastics, smaller than 5 mm, by mechanical fragmentation, photochemical and biological degradation in the farmland soils. Microplastics can also enter the farmland soils by aerial deposition, irrigation water contaminated with microplastics, from residues of plastic covers used in agricultural or horticultural products, or by sewage sludge deposition. Microplastics are ubiquitous in the farmland soils. Soil aggregates are the basic unit of soil structure。Different fractions of the soil aggregates have different ways of interacting with microplastics due to their structural differences. There are also small and systematic differences in the properties of different MPs, which may lead to regular differences in some specific geochemical processes. However, little is known about the fractionnation characteristics and its formation mechanisms of MPs in farmland soils. Based on our previous research, the objectives of this research are to investigate the dynamic behavior of homo/heteroaggregation and the differences of the soil structure effects of microplastics in soils, using the stable carbon isotope technique, by means of laboratory incubation experiment and field sampling, respectively. The biochemical and physicochemical interactions among soil aggregate structure, soil organic matter fractions and MPs in soils will be discussed. With the dynamic change of microplastics leaching in soils, the transportation patterns of microplastics by soil organisms, and the specific distribution of microplastics in soils, the fractionnation mechanisms of microplastics in soil will be uncovered. Such information will provide a scientific basis for the environmental behaviors and ecological effects microplastics in soils.

随着设施农业的发展，农田塑料残膜污染日趋加剧。在太阳辐射、土壤生物和人为翻耕等作用下，土壤中的塑料残膜降解或碎裂形成“微塑料/MPs”。同时，由于污水灌溉、污泥施用和大气干/湿沉降等途径，MPs已成为农田土壤中普遍存在的环境污染物之一。土壤团聚体是土壤结构的基本单元。不同粒级土壤团聚体因其组成结构不同与MPs作用方式存在差异，不同MPs之间微小而系统的特性差异，在一些特定的地球化学过程中也产生规律的分异。然而，土壤环境中MPs的分异机制知之甚少。本项目基于前期的研究基础，通过室内模拟试验和野外采样观测，利用同位素示踪技术，研究土壤环境中MPs的聚集动态及其土壤结构效应，探讨土壤环境中MPs-土壤团聚体-土壤有机碳的耦合作用；结合土壤环境中MPs的淋滤特性，生物输移过程以及农田土壤MPs的特异性分布，阐明土壤环境中MPs的分异机制，为准确地评估土壤中MPs的环境行为与生态风险提供科学依据。

本项目基于前期研究的基础，通过室内模拟实验和野外采样观测，研究了土壤环境中 MPs 的聚集动态及其土壤结构效应， 探讨了土壤环境中 MPs-土壤团聚体-土壤有机碳的耦合作用；结合土壤环境中 MPs 的淋滤特性，生物输移过程以及不同类型和土地利用方式下农田土壤 MPs 的特异性分布，阐明了土壤环境中 MPs 的分异机制。主要研究结果如下:（1）探讨了微塑料与土壤组分（土壤孔隙水、黏土矿物和有机质等）的相互作用，以及其存在形态对土壤理化性质的影响。微塑料聚集存在明显的离子特异性效应，对土壤有机质吸附具有异质特性，土壤矿物质与微塑料相互作用形成有机-矿质复合体， 不同土壤环境中多因素耦合条件下，微塑料聚集体与环境污染物（如，疏水性有机污染物和重金属等）相互作用影响其环境行为。微塑料与土壤组分相互作用，影响土壤理化性质及其土壤结构效应，以及其本身的存在形态。（2）阐明了农田土壤中微塑料的特异性分布特征。农业土壤微塑料主要来源于农用塑料薄膜使用、农业用水灌溉、污泥堆肥及施用、垃圾填埋和大气沉降等。薄膜、纤维、碎片和微珠等微塑料的主要成分为聚丙烯、聚苯乙烯和聚乙烯等。不同土地利用方式下的微塑料差异明显。耕作层微塑料丰度高于犁底层。土壤微塑料在耕作、淋溶、生物扰动和重力作用下发生水平和垂直方向迁移。（3）阐明了不同土壤环境条件下微塑料在不饱和多孔介质中的行为。通过比较不同土壤环境因子条件下微塑料在不饱和多孔介质中的穿透曲线和滞留分布曲线，结合Derjaguin-Landau-Verwey-Overbeek（DLVO）理论、舒尔采-哈迪准则和双点位迁移模型，阐明了土壤pH、电解质种类、腐殖酸和表面活性剂对微塑料在不饱和多孔介质迁移行为影响的作用机制。