改性纳米铁协同植物修复重金属污染河道底泥的行为作用机理与修复效应研究

The river sediment contaminated by heavy metals poses a threat to the ecological security of water environment, which needs to be remediated immediately. The synergy remediation technique, combining the modified nanoscale zero-valent iron (nZVI) with phytoremediation, was proved to be more efficient than the single using of modified nZVI or phytoremediation. However, the related mechanisms are unclear. Therefore, this project will take the heavy metal contaminated sediment from Xiangjiang River in Changsha as the research object, and aims to investigate the synergy mechanisms and the remediation effects during remediation of heavy metal polluted sediment by plants accompanied with modified nZVI. Main research contents include: (1) The effects of modified nZVI on the responses of plant organism, cells and gene to heavy metal stress will be investigated in order to elucidate the mechanisms of plant responses behaviours synergized by modified nZVI. (2) The synergy effects of modified nZVI and plants on the transfer and transformation of heavy metals in river sediment will be deeply studied. (3) On that basis, the remediation effects of the synergy remediation technique will be illustrated according to the studies on the response of microbial community sucession and aquatic plant toxicity analysis. As a result, the process mechanisms in the remediation of river sediment by the synergy remediation technique using modified nZVI and phytoremediation will be understood scientifically in terms of 2 aspects (synergy mechanism and remediation effects). The study will lay a foundation for the remediation of heavy metal polluted sediment by the synergy remediation technique, which provide a new pathway for the remediation of heavy metal polluted river sediment.

河湖底泥重金属污染威胁着水生态环境安全，亟需治理。目前已证实改性纳米铁（nZVI）协同植物修复法比单独使用改性nZVI或植物的效果好，但相关机理尚不清楚。为此，本项目拟以湖南省湘江长沙段重金属污染底泥为对象，研究改性nZVI协同植物修复重金属污染河道底泥的行为作用机理与修复效应，包括：通过探讨改性nZVI对植物机体、细胞与基因应答重金属能力的影响，剖析改性nZVI协同植物应答底泥重金属胁迫行为的作用机理；深入研究污染河道底泥修复过程中改性nZVI与植物对底泥重金属迁移转化与归趋行为的协同影响；在此基础上，分析底泥微生物群落演替、水生植物毒性以揭示改性nZVI与植物对底泥生态的协同修复效应。最终从协同修复机理、修复效应两方面科学认识改性nZVI协同植物修复污染河道底泥的过程机理。本研究可为发展改性nZVI协同植物修复重金属污染河道底泥关键技术与理论奠定重要基础，为河湖底泥污染治理提供新途径。

重金属污染底泥修复新方法与理论一直是水环境领域研究的热点问题之一。本项目从改性nZVI协同植物应答底泥重金属胁迫的作用机理、改性nZVI协同植物修复污染底泥对重金属迁移转化与归趋行为的协同影响机理、改性 nZVI 协同植物对重金属污染底泥生态修复效应等三个方面展开研究，对实现该技术修复重金属污染底泥有重要意义。主要结论：1.选取苎麻、黑麦草等为代表植物，明确了改性nZVI对重金属胁迫下植物生长发育、耐毒性的影响并剖析了其内在作用机制。发现低浓度改性nZVI可通过减少活性氧自由基，增加抗氧化酶活性及植物抗氧化物质的积累来缓解重金属对植物细胞造成氧化损伤；高浓度（5000 mg/kg以上）则促使植物内聚集ROS、抗氧化酶活性降低、细胞严重氧化损伤而抑制植物生长。改性nZVI显著提高了根际细菌群落多样性和丰富度，优势菌群利于重金属重新分配到更稳定的铁矿物相中，加速底泥有机物分解。2.发现了植物根际分泌物柠檬酸CA对重金属有螯合作用，可促进生成重金属吸附性强的羟基氧化铁。低浓度CA促进改性nZVI吸附重金属，但高浓度致使螯合物酸溶，且会削减改性nZVI表面铁氧化物有效官能团对重金属的吸附。3.探讨了修复过程改性nZVI作用下植物根、茎、叶及亚细胞中重金属的分布特征，阐明改性nZVI和重金属在植物体内的吸收转运机制：改性nZVI通过作为载体携带、促开植物通道、增强细胞内吞等作用促成污染物从根部转运至地上部分，而不是依赖促进植物生长、活化重金属等途径。与碳基材料以增强植物生长来强化修复这一机理不同，且20 mg/L以下微塑料共存反增强材料联合植物修复作用。4.多层面考察了改性nZVI与植物协同修复底泥生态效应，发现随着改性nZVI氧化，pH升高，铁氧化物增多，底泥有机质分解，促进了重金属向稳定态转变。明确了改性nZVI的引入不仅增加了铁还原菌相对丰度，还使底泥Eh值降低而长期处于还原态势，促进Fe(III)矿物质还原为Fe2+（其对有效态重金属吸附或共沉降），降低重金属移动性。改性nZVI的引入还促使硝化螺旋菌门、放线菌门、酸杆菌门成为优势菌来强化修复作用，减少湿地中污染物累积，降低了具较多致病菌的螺旋体菌门细菌丰度，微生态修复效应好。