应用于地下水污染原位修复的修饰型纳米零价铁的胶体稳定性、反应活性和微生物毒性三要素的内在关联机制研究

Nanoscale zero-valent iron (nZVI) technology is becoming the most widely studied and used nanotechnology in in-situ groundwater remediation. Due to its large specific surface area, high reactivity and the other unique physicochemical properties, nZVI suspended in the aqueous phase can be conveniently injected into contaminated groundwater to overcome fatal shortcomings of many conventional technologies for effective in-situ remediation. While the use and development of nZVI are understandably heralded as a promising environmental nanotechnology, fundamental questions remain on its long-term stability, reactivity and health risks in the environment. Meanwhile, the application of nZVI with varying physicochemical properties in the environment would enlarge the complexity and uncertainty of the above mentioned problems. In this proposal, systematic experimental designs are outlined to investigate the influence of different surface modifiers and the isolated natural organic matter (NOM) fractions on colloidal stability, reactivity and microbial toxicity of nZVI particles under geochemical conditions relevant to in-situ groundwater remediation. Firstly, the physiochemical properties and surface chemistry of various types of nZVI will be characterized and analyzed to determine the mechanisms for the colloidal stability under varying conditions. Then, the interfacial reactions between the different types of nZVI and inorganic/organic pollutants and the kinetics of the reactions will be respectively investigated to gain insights into the mechanisms underlying the reactions between nZVI and the pollutants. Additionally, the dosage of nZVI for the acute/chronic microbial toxicity will be determined and the potential mechanisms of the microbial toxicity will be analyzed. Overall, a correlation among the colloidal stability, reactivity and microbial toxicity of nZVI modified with different surface modifiers and the NOM fractions will be identified. It is expected that the results of this project will provide a theoretical support for the application of nZVI technology in environmental remediation and the assessment of the environmental and health risks.

纳米零价铁是地下水污染原位修复领域研究和使用最广泛的纳米材料。因其比表面积大，反应活性高以及独特的物化特性，纳米零价铁可以用胶体悬浮液形式直接注入受污染地下水中，实现简易高效原位修复。尽管纳米零价铁技术应用前景广阔，但其使用过程中的长期稳定性、反应活性和潜在的环境与健康风险等重要科学问题亟待解决（并且工程应用中不同修饰型纳米零价铁表面物化特性各异更增加了问题的复杂性和不确定性）。针对上述问题，本项目将系统考察不同表面修饰剂、天然有机物筛分结构对纳米零价铁胶体稳定性、反应活性和微生物毒性三要素的影响及其规律；着重探究不同表面改性纳米零价铁的物化特性、团聚及沉淀行为，与无机/有机污染物的界面反应机理和动力学，急性和慢性致毒剂量及致毒机理；最终揭示纳米零价铁胶体稳定性、反应活性和微生物毒性三要素之间的内在关联机制。期望在纳米零价铁地下水修复技术的应用及其环境与健康风险评估方面提供理论支撑。

纳米零价铁，因其比表面积大，反应活性高以及独特的物化特性，被广泛的应用于地下水污染原位修复领域。尽管纳米零价铁技术应用前景广阔，但其使用过程中的长期稳定性、反应活性和潜在的环境与健康风险等重要科学问题亟待解决。关于纳米零价铁胶体稳定性，反应活性以及微生物毒性三要素的研究早期主要集中在单一要素方面的研究，而很少有研究深入剖析三要素之间的内在关联。因此，本项目系统考察了纳米零价铁胶体稳定性、反应活性和微生物毒性三要素之间的内在关联及其作用机制。研究发现用以提高纳米零价铁胶体稳定性的表面修饰剂（如聚电解质）既可能促进也可能抑制纳米零价铁的反应活性，取决于表面修饰剂的浓度。低浓度的表面修饰剂会提高纳米零价铁的胶体稳定性，抑制团聚，增大纳米零价铁比表面积，从而有更多的反应活性位。然而高浓度的表面活性剂反而会抑制纳米零价铁与污染物的反应，原因在于表面修饰剂不但会占用纳米零价铁活性点位，并且其所提供的静电排斥及空间位阻效应也会抑制污染物向纳米零价铁表面的迁移。另外，研究发现纳米零价铁对大肠杆菌具有明显的致毒性(与浓度和暴露时间有关)，可以导致细胞膜破裂，浸入细胞内部，但是表面修饰剂会大大降低纳米零价铁对大肠杆菌的致毒性。原因在于表面修饰剂提供的静电排斥作用和位阻效应会极大的降低纳米零价铁在大肠杆菌表面上的吸附。此外，研究发现水中的钙离子和天然有机物（如腐殖酸、富里酸）可以吸附在纳米零价铁表面，改变纳米零价铁表面的物理化学特性，进而影响到颗粒与颗粒、颗粒与污染物以及颗粒与大肠杆菌之间的接触，因此对纳米零价铁胶体稳定性、反应活性及微生物毒性均会产生影响（促进或抑制）。本项目研究成果对纳米零价铁地下水原位修复技术应用及其风险评估具有重要的参考意义。