污泥和猪粪长期施用土壤中微塑料积累与根际传递机制

Microplastics pollution has been studied globally and intensively in ocean and inland water during the past years, meanwhile their pollution in farmland soil is gradually recognized recently. Sewage sludge and organic manure applications in farmlands were regarded as the main source of microplastics in the soils. However, the knowledge gaps still exist in the mechanisms on microplastics accumulation in farmland soils and whether the accumulated microplastics could be taken up by plant root and translocated to the shoot parts of the plants. The aim of this project is to understand the microplastics accumulation and plant transfer processes in red soil and paddy soil receiving long-term applications with sewage sludge and pig manure. A novel method would be developed for the separation and identification of multiple microplastics from the soils with different characteristics. Based on this developed method and the long-term experimental stations, studies on the mechanisms on microplastics accumulation in the farmland soils and their accumulating rate would be conducted using field investigation at multiple scale levels. Meanwhile, another study would be conducted on the movement of microplastics from the surface soil to the underground, and accumulation in rhizosphere affected by bioturbation, root growth and microplastics weathering using the method of fluorescence dye. Then solution culture and soil culture experiments would be further conducted to examine the entry of microplastics from rhizosphere into plant root and further translocation to the shoot parts of the plants, and to analyze the factors affecting microplastics distribution in the different parts of the plants. The results may help to understand the risks associated with microplastics pollution in farmland soil through food chain and provide the methodology and theoretical foundation for the pollution control.

微塑料污染不仅在海洋和淡水环境中受到全球重视，而且在农地土壤中也开始受到关注。污泥和有机肥施用被认为是农地土壤中微塑料的主要来源，但目前对农地土壤中微塑料的积累过程，以及土壤中的微塑料是否能进入作物根，再传递到地上部分还不得而知。本项目拟围绕污泥和猪粪长期施用可能带来的土壤微塑料污染问题，以红壤和水稻土为目标土壤，在完善适用不同性质土壤中多种类型微塑料的分离与分析方法基础上，利用长期定位试验观测基地，通过田间多尺度调查、荧光标记微塑料示踪试验、水培和土培试验等方法途径，探明农地土壤微塑料的积累过程，并量化积累速率；揭示生物扰动、根系生长和微塑料老化等驱动影响下微塑料从表层土壤向植物根部迁移和汇聚过程，阐明土壤微塑料进入根际及在根系吸收、向地上部传递的机制和影响因素，为农地土壤微塑料污染规律认识、食物链风险评估与控制提供方法学和理论依据。

本项目围绕污泥和猪粪长期施用可能带来的土壤微塑料污染问题，以红壤和水稻土为目标土壤，分别建立并完善了适用不同性质土壤、污泥和畜禽堆肥的微塑料的分离与分析方法，包括多组合物理分离-密度浮选-连续流动分离法提取土壤中微塑料，以及多筛筛分-淘洗法分离提取污泥和有机肥中的微塑料。在此基础上，利用长期定位试验观测基地，通过田间多尺度调查等方法途径，探明了长期施肥和污泥、地膜使用的农地土壤中微塑料的积累过程与积累速率，初步估算污泥、残膜和猪粪带来的微塑料年积累量分别为3.2~12.1、8.2和1.2个/kg（干土重）。采用土壤中宇宙试验揭示了生物扰动、根系生长和微塑料老化等因素影响下，微塑料从表层土壤向植物根部迁移和汇聚过程，发现生物扰动促进了微塑料向深层土壤的迁移，其中蚯蚓可通过粘附作用促进轻质微塑料在土壤中的迁移，而作物根系的存在则更易于将微塑料保持在根际土层。阐明了土壤微塑料进入根际及在根系吸收、向地上部传递的机制和影响因素，发现亚微米级和微米级的塑料颗粒都可以穿透小麦和生菜根系进入植物体，并在蒸腾拉力的作用下，通过导管系统随液体流进入作物地上部；在植物新生侧根边缘存在狭小的缝隙，塑料颗粒可以通过该“通道”跨过屏障而进入根部木质部导管并进一步传输到茎叶组织。建立了基于稀土配合物掺杂标记的植物体内微塑料的示踪与精确定量方法，为研究微/纳塑料颗粒在复杂生物介质中积累、传输和分布提供了一种崭新、简便、通用的方法。项目共发表第一/通讯作者学术论文11篇（第一标注论文9篇），其中SCI收录5篇；培养研究生4名。研究成果可为农地土壤微塑料污染规律认识、食物链风险评估与控制提供方法学和理论依据。