可降解与不可降解微塑料颗粒在土壤中的变化及其对典型有机污染物归趋与生物有效性的影响

Microplastics can enter soil through several pathways. However, the current research about the change and risk of microplastics in soil has mainly concentrated on agricultural mulch (PVC), whereas the research on other kinds of traditional non-degradable, especially degradable plastics is rather scarce. This greatly limits the accurate risk assessment of microplastics in soil. Due to the special chemical compositions and properties of microplastics and the complexity of soil particle structure, there are many unknown scientific problems in related research field, which cannot be easily predicted and explained by traditional theories and needs clarification by experimental study and the innovation of theory and approach. Hence, the present project plans to select several degradable microplastics with non-degradable plastics as comparison, and the following researches are being considered: 1) to study the change of these microplastics in several typical soils in short and long terms and the possible effects of microplastics on the structure of soil microorganisms as well as the mutual effects of the microorganisms on the change of microplastics; 2) to study the sorption and the related micro-level mechanisms of two typical organic pollutants (polycyclic aromatic hydrocarbons and phthalates) on microplastics and the mixture of soil and microplastics; 3) to study the release or desorption and the bioavailability to earthworm accumulation of these sorbed compounds (endogenous and exogenous sources, respectively) and the key controlling structure or step therein. The results of this project will provide scientific bases for the risk assessment of microplastics and promote to obtain deep-insight of the knowledge and the progress of related theory.

微塑料颗粒可通过多种途径进入土壤环境。当前针对微塑料颗粒在土壤环境中的变化及其风险的研究主要集中在农用薄膜，对其它传统塑料、特别是可降解塑料的研究则非常缺乏，极大限制了对微塑料颗粒环境风险的正确评估。由于微塑料颗粒组成和性质的独特性及土壤结构的复杂性，该领域尚存在很多科学未知问题，难以用传统理论加以预测和解释，需要系统实验研究及理论与手段的创新。因此，本项目拟选择若干典型可降解微塑料颗粒，以传统不可降解塑料为对比，研究其在我国几种典型类别土壤中的短期与长期的变化、对土壤微生态结构的影响及微生物对其变化的反作用；研究其对两类典型有机污染物（多环芳烃与邻苯二甲酸酯）的吸附规律及其微观机理；研究微塑料颗粒吸附态内源与外源污染物的解吸与释放、对蚯蚓富集的生物有效性及其关键控制微观结构或环节。本项目结果将为完善微塑料颗粒的环境风险评估提供科学依据，并可带动环境科学相关研究领域的认识深入和理论进步。

土壤是微塑料一个重要的汇，但是相比于海洋系统，微塑料在土壤中的环境行为及其对土壤生态系统的危害研究较少。本项目系统探究了微塑料对有机污染物的吸附、微塑料及其载带的增塑剂对土壤微生物、典型动植物的影响。结果发现，极性微塑料的吸附能力高于非极性微塑料；疏水性分配是主要吸附机理，氢键等极性作用在极性微塑料的吸附中不可忽略。微塑料改变了根际和非根际土壤微生物多样性、敏感菌属（科）、网络结构特征及氮循环功能基因的丰度，这些变化因微塑料材质和添加量而有所差异。叶面暴露聚苯乙烯纳米塑料会显著降低生菜的干重（～27.3%）、株高（～27.3%）和叶面积（～19.2%））及营养品质（微量元素和必需氨基酸）并诱导氧化应激。微观机理研究结果表明纳米塑料可通过叶片气孔吸收，并可向下转移到植物根部。植物对增塑剂—邻苯二甲酸酯（PAEs）中性分子的吸收强于对代谢产物（mPAEs）阴离子的吸收。亲水性的mPAEs主要存储在细胞可溶性组分中，分子量较小的PAE—邻苯二甲酸二丁酯(DnBP)相对均匀地分布在细胞壁和细胞可溶性组分中，而疏水性更强的邻苯二甲酸二异辛酯主要富集在根的细胞壁上。质外体途径和共质体途径均参与了小白菜对(m)PAEs的吸收和转运。细胞代谢和排泄14C-DnBP及其代谢物可能是植物减轻PAEs介导的毒性的一种机制。蚯蚓消化液可加速微塑料结合态菲和六溴环十二烷的解吸，提高了结合态污染物对蚯蚓富集的生物有效性，微塑料粒径对结合态污染物生物有效性有显著影响。微塑料尤其是含增塑剂的微塑料降低鸡肠道微生物的多样性，显著增加放线菌门丰度和肠道通透性，不利于生长，改变组织质量并且高污染水平微塑料造成卵巢发育不良；通过转录组和代谢组学发现，微塑料改变了与脂质合成代谢、氨基酸代谢等相关过程的基因表达及代谢物水平。