Investigation on speciation and behavior of antimony in paddy soil

在水田中，淹水期和非淹水期的循环引起了土壤和土壤水分氧化还原状态的变化。本文通过室内实验和田间观察，研究了水稻土中氧化还原敏感的锑的形态和迁移。【实验室实验】在土壤表面暴露在空气中（未淹水）和土壤表面被锑溶液覆盖（淹水）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系统测定土壤水体中总锑浓度和Sb（III）、Sb(V)的形态。结果表明，在非淹水条件下，Sb（III）溶液对土壤吸附锑的分配比低于淹水条件，接近Sb(V)溶液对土壤吸附锑的分配比。未淹水条件下土壤中Sb(V)浓度与总Sb浓度之比大于淹水条件下。结果表明，在非淹水条件下，Sb（III）氧化为Sb(V)会得到促进。【田间观察】2005年7月在某水田（淹水状态）采集土壤水分。结果表明，Sb(V)的浓度控制着土壤水中Sb的总浓度。研究结果表明：在夏季（汛期），水稻土中的锑（例如来自空气中的颗粒物）会积累。在冬季（非淹水期），由于Sb(V)在土壤中的吸附较低，促进了土壤中积累的锑的氧化，增加了锑在土壤中的流动性。

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.