Nanoscale zerovalent iron (nZVI) impact on soil microbial communities

将纳米级颗粒释放到环境中以清除污染是一项新兴技术。最前沿的是纳米零价铁（nZVI）的开发，以清理被氯化有机化合物污染的环境。nZVI的工作原理是从污染物中去除氯原子，通常会产生毒性较小且持久性较低的化合物。nZVI最常用于清洁地下水，然而，随着将nZVI部署到土壤基质中而不粘在土壤或其本身上的方法的发展，对污染土壤的应用现在显示出希望。由于其尺寸，nZVI颗粒有可能在与土壤中微生物相关的规模上相互作用，直接通过与微生物细胞接触，或间接通过改变土壤微生物生存的化学环境。重要的是要评估nZVI是否对土壤微生物产生有害影响，因为微生物具有重要的功能;这些功能包括生物地球化学循环，从而为植物提供营养和分解有机污染物。因此，该提案将测试nZVI对两个重要微生物群体的影响;一个参与分解主要污染物多氯联苯（PCBs），另一个负责共生改善植物生长，从而增强和稳定土壤。本研究的背景将是一个两步土壤清理方案。第一步涉及使用nZVI来减少PCB中的氯数量，从而降低其毒性。第二个生物步骤涉及使用原生土壤微生物分解nZVI生产的单一或脱氯产品，随后种植土壤以稳定场地并刺激有益的污染物分解微生物。对于实验室实验，我们将使用商业生产的不同尺寸和配方的nZVI。因此，我们将解决nZVI的商业应用，同时定义一系列nZVI反应性的环境影响。在我们的研究过程中，我们将回答以下问题：1。nZVI是否会影响负责分解污染物的土壤微生物群落的数量、活性和多样性？2. nZVI会影响植物-微生物共生吗？具体而言：（i）豆科植物与负责在植物根部形成固氮根瘤的共生根瘤菌的共生;和（ii）形成“真菌根”并以多种方式有益于植物宿主的共生丛枝菌根真菌，包括改善磷营养。3. nZVI对土壤微生物群落的影响是否取决于nZVI的反应性及其环境行为？我们将使用基于核酸的指纹方法评估微生物群落的多样性，并通过量化它们分解添加的污染物化学品的速率来测量它们的活性。对共生的影响将通过以下方式确定：（i）计算根瘤的数量及其固氮速率;（ii）丛枝菌根真菌的根定殖程度和植物磷水平。我们将通过改变颗粒的大小（更大的表面积=更高的反应性）和配方（添加表面活性剂以阻止它们聚集）来操纵nZVI反应性。我们将通过电子显微镜观察nZVI颗粒在土壤中的行为。此外，我们将申请使用同步加速器“超级显微镜”，在牛津郡的一个新的设施，以评估其潜力，看看在未受干扰的土壤情况下的nZVI团聚。

The release of particles of nanometre scale to the environment for the clean up of pollution is an emerging technology. At the forefront is the development of nanoscale zerovalent iron (nZVI) to clean up environments that have become polluted with chlorinated organic compounds. The nZVI works by removal of chlorine atoms from the pollutant, usually resulting in the production of a less toxic and less persistent compound. nZVI has been most commonly used for clean up of ground water, however, application to contaminated soil is now showing promise with the development of ways to deploy nZVI into the soil matrix without it sticking to the soil, or itself. Because of their dimensions, nZVI particles have the potential to interact at a scale relevant to microbes living in the soil, either directly through contact with microbial cells, or, indirectly through altering the chemical environment in which soil microbes live. It is important to assess whether nZVI has detrimental impacts on soil microbes because of the important functions the microbes carry out; these include biogeochemical cycling with resulting provision of nutrients to plants and the breakdown of organic pollutants. Thus, this proposal will test the impacts of nZVI on two important microbial groups; one involved in the decomposition of a major class of pollutants, the polychlorinated biphenyls (PCBs), and the other responsible for symbiotic improvement of plant growth and thus for enhancing and stabilising soils. The context of the study will be a two-step soil clean up scenario. The first step involves the use of nZVI to reduce the number of chlorines in the PCBs, which reduces their toxicity. The second, biological, step involves use of native soil microbes to decompose the nZVI-produced mono or dechlorinated products with subsequent planting of the soil to stabilise the site and stimulate beneficial pollutant decomposing microbes. For laboratory experiments, we will use commercially produced nZVI of different sizes and formulation. In consequence, we will address nZVI commercial applications whilst defining the environmental impact for a range of nZVI reactivities. In the course of our research we will answer the following questions: 1. Does nZVI impact on the numbers, activity and diversity of soil microbial communities responsible for the breakdown of pollutants? 2. Does nZVI impact on plant-microbe symbioses? Specifically: (i) legume symbiosis with symbiotic rhizobia bacteria responsible for formation of nitrogen-fixing nodules on plant roots; and, (ii) symbiotic arbuscular mycorrhizal fungi which form a 'fungus root' and benefit the plant host in many ways, including improvement of phosphorus nutrition. 3. Does the nZVI impact on soil microbial communities depend on the reactivity of nZVI and its environmental behaviour? We will assess the diversity of microbial communities using a nucleic-acid based fingerprinting method and measure their activity by quantifying the rate at which they decompose an added pollutant chemical. The impact on symbiosis will be determined by: (i) counting numbers of root nodules and the rate at which they fix nitrogen; and, (ii) the extent of root colonisation by arbuscular mycorrhizal fungi and plant phosphorus levels. We will manipulate nZVI reactivity by varying the size of the particles (bigger surface area = higher reactivity) and formulation (addition of a surfactant to stop them from agglomerating). We will see how the nZVI particles behave in soil by using an electron microscope. Also, we will apply to use the synchrotron 'super-microscope', a new facility in Oxfordshire, to assess its potential to look at nZVI agglomeration in an undisturbed soil situation.