Molecular-scale mechanisms of antimony binding to soil organic matter

锑是一种有毒的类金属，由于其在工业和技术产品中的广泛使用，越来越多地释放到环境中。因此，锑化合物被环境保护机构视为优先污染物。尽管土壤中锑的输入量很高（约26,000吨/年），但只有少数研究调查了土壤中锑的种类和控制其环境命运的因素。泥炭土壤中锑的低流动性表明，土壤有机质对锑的络合作用是土壤锑循环的关键因素。然而，关于Sb与固有复杂的溶解性和颗粒性土壤OM的分子尺度相互作用的信息是缺失的。因此，本项目旨在研究Sb与土壤OM结合的分子尺度机制。在项目的第一部分，我们使用基于同步加速器的Sb K-edge x射线吸收光谱（XAS）来探索Sb在缺氧和缺氧条件下与土壤OM的结合机制，重点研究了Sb与羧基/羟基和巯基以及有机配合铁（三元Sb配合物）的结合。我们还利用富集稳定Sb同位素示踪剂的方法阐明了Sb- om配合物的动力学稳定性。本项目第二部分研究了英国Peak District泥炭土壤中锑的形态和分布，这些有机土壤长期受到大气中锑沉降的影响，因此受到广泛的锑污染。借助XAS，我们探索了这些土壤中主要的锑固存机制。这些测量是通过扫描电子显微镜-能量色散x射线能谱（SEM-EDX）和x射线光电子能谱（XPS）分析来补充的，以研究Sb的微观分布和形态，以及它与其他可能控制其形态形成的元素（例如铁和S）的关联。综上所述，该项目将提高我们对Sb-OM相互作用的机理理解，并阐明OM在受人为释放和大气沉积Sb影响的有机土壤中作为Sb吸附剂的作用。

Antimony (Sb) is a toxic metalloid which is increasingly released into the environment owing to its use in a vast range of industrial and technological products. Antimony compounds are therefore considered as priority pollutants by environmental protection agencies. Despite high Sb inputs to soils (ca. 26,000 t/a) only few studies have examined the speciation of Sb in soils and factors controlling its environmental fate. The low mobility of Sb observed in peat soils suggests that Sb complexation by soil organic matter (OM) represents a key element in the soil Sb cycle. Yet, information on molecular-scale interactions of Sb with inherently complex dissolved and particulate soil OM is missing. Therefore, this project aims at the investigation of molecular-scale mechanisms of Sb binding to soil OM. In the first part of the project we use synchrotron-based Sb K-edge X-ray absorption spectroscopy (XAS) to explore the mechanisms of Sb binding to soil OM under both oxic and anoxic conditions, focusing on Sb binding by carboxyl/hydroxyl and thiol groups as well as organically complexed Fe (ternary Sb complexes). We also elucidate the kinetic stability of the Sb-OM complexes using an enriched stable Sb isotope tracer approach. In the second part of this project, we study the speciation and distribution of Sb in peat soils of the Peak District, U.K. These organic soils have been impacted by long-term atmospheric deposition of Sb and are thus extensively contaminated with Sb. With the help of XAS we explore major Sb sequestration mechanisms operating in these soils. These measurements are complemented by scanning electron microscopy – energy-dispersive X-ray spectroscopy (SEM-EDX) and X-ray photoelectron spectroscopy (XPS) analyses to study the micro-scale distribution and speciation of Sb and its association with other elements potentially controlling its speciation (e.g., Fe and S). In summary, this project will improve our mechanistic understanding of Sb-OM interactions and clarify the role of OM as a sorbent for Sb in organic soils impacted by anthropogenically released and atmospherically deposited Sb.