Investigation on speciation and behavior of antimony in paddy soil

在稻田中，淹水与非淹水的周期性变化引起土壤和土壤水的氧化还原状态的变化。通过室内实验和田间观测，研究了锑在氧化还原敏感性水稻土中的形态和迁移特征。[实验室实验]在土壤表面暴露于空气（非淹没）和土壤表面被锑溶液覆盖（淹没）的条件下，将干燥的水稻土样品浸入Sb（III）或Sb（V）溶液中。浸泡7 d后，采用HPLC-ICP-MS系统测定了土壤沃茨中总锑含量及Sb（III）和Sb（V）的形态分布。结果表明，在非淹水条件下，Sb（III）溶液对土壤吸附的分配比低于淹水条件下的分配比，接近Sb（V）溶液对土壤吸附的分配比。土壤水中Sb（V）浓度占总Sb浓度的比例在非淹水条件下大于淹水条件下。在非淹没条件下，Sb（III）氧化为Sb（V）的反应会得到促进。[现场观察] 2005年7月在稻田采集土壤水（淹水条件）。结果表明，Sb（V）的浓度控制着土壤水中Sb的总浓度，夏季（淹水期），Sb（V）在水稻土中积累;冬季（非淹水期），Sb（V）在土壤中的吸附量降低，促进了土壤中积累的Sb的氧化，增加了Sb在土壤中的移动性。

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.