Investigation on speciation and behavior of antimony in paddy soil

在水田中，淹水和非淹水的循环会引起土壤和土壤水中氧化还原状态的变化。通过室内实验和田间观测，研究了氧化还原敏感型水稻土中Sb的形态和迁移特性。[实验室实验]将干燥的水稻土样品浸泡在Sb(III)或Sb(V)溶液中，土壤表面暴露在空气中(未淹水)，土壤表面被Sb溶液覆盖(淹水)。浸泡7d后，用高效液相-电感耦合等离子体质谱系统测定土壤水中总Sb的含量及Sb(III)和Sb(V)的形态。结果表明，在非淹水条件下，Sb(III)溶液对土壤吸附Sb的分配比低于淹水条件下的土壤，接近于Sb(V)溶液的土壤吸附分配比。此外，非淹水条件下土壤水中Sb(V)浓度与总Sb浓度的比值大于淹水条件下的。在非淹水条件下，Sb(III)被氧化为Sb(V)。[野外观测]2005年7月在一块稻田采集土壤水(淹水条件)。结果表明，土壤中Sb(V)的浓度控制着土壤水中Sb的总浓度。研究结果表明：夏季(洪水期)，土壤中的Sb(主要来源于大气颗粒物)积累；冬季(非洪水期)，由于土壤对Sb(V)的吸附降低，土壤中Sb(V)的氧化作用增强，土壤中Sb(V)的迁移能力增强。

In paddy fields, the cycle of flooded and non-flooded periods causes changes of redox states in soil and soil water. This work investigated the speciation and mobility of antimony in paddy soil, which are redox-sensitive, by both laboratory experiments and field observations.[Laboratory Experiment] Dried paddy soil samples were immersed in Sb(III) or Sb(V)solutions under conditions where the soil surface was exposed to the air (non-flooded) and where the soil surface was covered by the antimony solution (flooded). After 7 days immersion, the total antimony concentrations and the speciation of Sb(III) and Sb(V) in the soil waters were evaluated by a HPLC-ICP-MS system. As a result, in the non-flooded condition, the distribution ratio of antimony adsorption to soil obtained in the experiment using Sb(III) solution was lower than in the flooded condition and close to the value obtained in the experiment using Sb(V) solution. Moreover, the ratio of Sb(V) concentration to the total Sb concentration in the soil water was larger in the non-flooded condition than in the flooded condition. Then it was suggested that the oxidation of Sb(III) to Sb(V) would be promoted in the non-flooded condition.[Field Observation] Soil water was collected at a paddy field in July 2005 (flooded condition). It was shown that the concentration of Sb(V) controlled the total concentration of Sb in the soil water.The results of this work suggests a scenario as follows :In summer (flooded period), antimony (e.g.originated in airborne particulate matter) would be accumulated in paddy soil.In winter (non-flooded period), oxidation of the accumulated antimony in soil would be promoted and the mobility of antimony in soil would increase because of lower adsorption of Sb(V) to soil.