Environmental Sciences and Engineering Ph.D. Program, The University of Texas at El Paso, Texas 79968, USA.
Appl Spectrosc. 2012 Jun;66(6):719-27. doi: 10.1366/11-06336.
The bioavailability and mobility of arsenic (As) in soils depends on several factors such as pH, organic matter content, speciation, and the concentration of oxides and clay minerals, among others. Plants modify As bioavailability in the rhizosphere; thus, the biogeochemical processes of As in vegetated and non-vegetated soils are different. Changes in As speciation induced by the rhizosphere can be monitored using micro-focused synchrotron-based X-ray fluorescence (μXRF) combined with μX-ray absorption near-edge spectroscopy (μXANES). This research investigated As speciation in the rhizosphere of mesquite (Prosopis juliflora-velutina) plants grown in a sandy clay loam treated with As(III) and As(V) at 40 mg kg(-1). Rhizosphere soil and freeze-dried root tissues of one-month-old plants were analyzed by bulk XAS. Bulk XAS results showed that As(V) was the predominant species in the soil (rhizosphere and non-vegetated), whereas As(III) was dominant in the root tissues from both As(V) and As(III) treated plants. μXAS and μXRF studies of thin sections from resin embedded soil cores revealed the As(III)-S interactions in root tissues and a predominant As-Fe interaction in the soil. This research demonstrated that the combination of bulk XAS and μXAS techniques is a powerful analytical technique for the study of As speciation in soil and plant samples.
土壤中砷（As）的生物有效性和迁移性取决于多种因素，如 pH 值、有机质含量、形态、氧化物和粘土矿物的浓度等。植物会改变根际中砷的生物有效性；因此，植被和非植被土壤中砷的生物地球化学过程是不同的。可以使用基于同步加速器的微焦点 X 射线荧光（μXRF）与微 X 射线吸收近边光谱（μXANES）结合来监测根际引起的砷形态变化。本研究调查了在浓度为 40mg/kg 的砷（III）和砷（V）处理的沙壤土中种植的刺槐（Prosopis juliflora-velutina）植物根际中砷的形态。使用批量 XAS 分析了一个月大的植物的根际土壤和冻干根组织。批量 XAS 结果表明，砷（V）是土壤（根际和非植被）中主要的存在形态，而砷（III）则是砷（V）和砷（III）处理植物的根组织中主要的存在形态。对树脂包埋土壤芯的薄片进行的 μXAS 和 μXRF 研究表明，在根组织中存在砷（III）-S 相互作用，而在土壤中则存在主要的砷-铁相互作用。本研究表明，批量 XAS 和 μXAS 技术的结合是研究土壤和植物样品中砷形态的强大分析技术。
