Arai Yuji, Lanzirotti A, Sutton S R, Newville Matthew, Dyer J, Sparks D L
Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware 19717-1303, USA.
Environ Sci Technol. 2006 Feb 1;40(3):673-9. doi: 10.1021/es051266e.
The arsenic (As) solid-state speciation (i.e., oxidation state, precipitates, and adsorption complexes) is one of the most important factors controlling dissolved As concentrations at As contaminated sites. In this case study, two representative subsurface samples (i.e., oxidized and semi-reduced sites) from former lead arsenate contaminated soils in the northeastern United States were chosen to investigate the effects of aging on As retention mechanisms using multiscale spectroscopic techniques. X-ray powder diffraction (XRD), synchrotron based microfocused (micro) XRD, in situ micro-synchrotron based X-ray fluorescence spectroscopy (SXRF), and micro-X-ray absorption near edge structure (XANES) spectroscopy were used to compliment the final bulk X-ray absorption spectroscopy (XAS) analyses. In the sample from an oxic area, As is predominantly (approximately 71%) present as As(V) adsorbed onto amorphous iron oxyhydroxides with a residue (approximately 29%) of an original contaminant, schultenite (PbHAsO4). Contrarily, there is no trace of schultenite in the sample from a semi-reduced area. Approximately 25% of the total As is present as adsorbed phases on amorphous iron oxyhydroxide and amorphous orpiment (As2S3). The rest of the fractions (approximately 46%) were identified as As(V)-Ca coprecipitates. This study shows that aging effects can significantly alter the original chemical constituent (schultenite) in soils, resulting in multi and site-specific As solid-state speciation. The variability in spatial and temporal scale may be important in assessing the environmental risk and in developing in situ remediation technologies.
砷（As）的固态形态（即氧化态、沉淀物和吸附络合物）是控制砷污染场地中溶解态砷浓度的最重要因素之一。在本案例研究中，选取了美国东北部原砷酸铅污染土壤中的两个代表性地下样品（即氧化场地和半还原场地），采用多尺度光谱技术研究老化对砷保留机制的影响。利用X射线粉末衍射（XRD）、基于同步加速器的微聚焦（micro）XRD、基于原位微同步加速器的X射线荧光光谱（SXRF）和微X射线吸收近边结构（XANES）光谱对最终的体相X射线吸收光谱（XAS）分析进行补充。在来自有氧区域的样品中，砷主要（约71%）以吸附在无定形羟基氧化铁上的五价砷形式存在，还有原污染物砷酸铅矿（PbHAsO4）的残余物（约29%）。相反，在来自半还原区域的样品中没有砷酸铅矿的痕迹。总砷的约25%以吸附相形式存在于无定形羟基氧化铁和无定形雌黄（As2S3）上。其余部分（约46%）被鉴定为五价砷 - 钙共沉淀物。本研究表明，老化效应可显著改变土壤中的原始化学成分（砷酸铅矿），导致多种特定场地的砷固态形态。空间和时间尺度的变异性在评估环境风险和开发原位修复技术方面可能很重要。
