Speciation of Arsenic under Dynamic Conditions
Speciation of Arsenic under Dynamic Conditions
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DOI：
10.1002/elsc.200800012
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发表时间：
2008-12-01
影响因子：
2.7
通讯作者：
Jahn, R.
中科院分区：
文献类型：
--
作者：
Ackermann, J.;Vetterlein, D.;Jahn, R.
在周期性淹没的土壤中，可能会出现还原条件，这有利于铁（氢）氧化物的溶解。 Fe（氢）氧化物，例如针铁矿，是砷酸盐（As-V）的重要吸附剂，砷酸盐是有氧条件下土壤中的主要砷形态。因此，Fe（氢氧化）氧化物在还原条件下的溶解可导致As-V的移动和还原，从而增加砷的生物利用度。人们对这些过程的时间动态以及可能形成的亚砷酸盐 (As-III) 的再吸收或沉淀知之甚少。在受控实验室条件下，对掺有 As-V 的石英针铁矿有机质基质进行模拟洪水事件后，氧化还原电位和砷形态随时间的变化进行了检查。在 6 周的时间内，每周使用微吸 CLIPS 对底物溶液进行取样，并分析 pH、As-III 和 As-V、Fe、Mn 和 P 浓度。氧化还原电位和基质电位在承载基底的圆柱体中原位测定。在不添加有机物的实验过程中，氧化还原电位以及As-III和As-V浓度之比保持不变。随着有机物的加入，氧化还原电位降低，底物溶液中的 As-III 浓度增加，而底物溶液中的总 As 浓度急剧下降。针铁矿 (1 g/kg) 本身的添加导致底物溶液中总砷的减少（几乎 50%）。就植物的潜在砷可用性以及由此导致的向食物链的转移而言，结果很难评估。底物溶液中总砷浓度越低（通过降低氧化还原电位来确定），植物对砷的吸收就越少。然而，这种效应可以通过溶液中的 P/As-V 摩尔比向有利于 As-V 的方向移动来补偿，这预计会增加 As 的吸收。
In periodically flooded soils, reductive conditions can occur, which favor the dissolution of Fe (hydr)oxides. Fe (hydr)oxides such as goethite are important sorbents for arsenate (As-V), which is the dominant As species in Soils under aerobic conditions. Hence, the dissolution of Fe (hydr)oxides under reductive conditions can result in the mobilization and reduction of As-V and, thus, in an increase in the bioavailability of arsenic. The temporal dynamics of these processes and possible re-sorption or precipitation of arsenite (As-III) formed are poorly understood. Under controlled laboratory conditions, the temporal change in the redox potential and arsenic speciation with time after a simulated flooding event ill a quartz-goethite organic matter substrate, spiked with As-V, was examined. During a period of 6 weeks, substrate solutions were sampled weekly using micro-suction CLIPS and analyzed for pH, As-III and As-V, Fe, Mn and P concentrations. Redox potentials and matric potentials were determined in situ in the substrate-bearing cylinders. The redox potential and the ratio between As-III and As-V concentrations remained unchanged during the experiment without organic matter application. With organic matter applied, the redox potential decreased and the As-III concentrations in the Substrate Solution increased while the total As concentrations in the substrate solution strongly decreased. An addition of goethite (1 g/kg) per se led to a decrease of the total As in the substrate Solution (almost 50%). In respect to the potential As availability for plants, and consequently, the transfer into the food chain, the results are difficult to evaluate. The lower the total As concentrations in the Substrate solution, determined with decreasing redox potential, the least plant AS uptake will occur. This effect may however be compensated by a shift of the molar P/As-V ratio in the Solution in favor of As-V which is expected to increase the As uptake.