Behavior of Radioiodine in Soil

表层土壤的各种成分是已知的（母质岩石、粘土矿物、有机质、微生物等）。研究了各主要组分对土壤表层放射性碘吸附的贡献。进行了碘离子（I^-）和碘酸离子（IO_3^-）从水中吸附到土壤中的放射性示踪实验。土壤样品采集于森林（福井县）、农田、水田和海岸（茨城县）。用示踪液孵育一定天后，分离土样。从两相的放射性特征出发，计算了土壤系统对放射性碘的吸附比。土壤对I^-的吸收通过风干处理显著减少，在与水平衡之前加热土壤。氯仿烟雾灭菌或伽马射线辐照也降低了分布比。通过测量土壤的粒度分布、含水量、有机质和微生物的数量以及土壤溶液的pH值，以及其他化学或物理分析来估计土壤的性质。结果表明，微生物对放射性碘作为无机和有机物质在土壤表层的吸附有很大的影响。

A variety of components of surface soil is known (parent rocks, clay minerals, organic matters, microorganisms and so on). The contribution of the main component to the sorption of radioiodine in surface soil has been investigated. Radiotracer experiments on the sorption of I^- (iodide) and IO_3^- (iodate) from water to soil have been carried out. Soil samples were collected in forest (Fukui Pref.), field, paddy field and seashore (Ibaraki Pref.). After incubating with tracer solution in a definite days, the soil samples were separated. From radioactivities of two phases the distribution ratio of radioiodine sorption to soil system were calculated. The sorption of I^-by soil was markedly reduced through treatments of air-drying, heating the soil prior to equilibration with water. The sterilization by chloroform fume or irradiation of gamma-ray also reduces the distribution ratio. The measurement of particle size distribution, quantities of water contents, organic matter and microorganisms and pH of soil solution, and other chemical or physical analysis have been carried to estimate the soil properties. Conclusively, the microorganisms has much influence on the sorption of radioiodine as inorganic and organic matter in surface soil.