Radiocesium interception potential of agricultural soils in northeast Japan

The health risks associated with the long-term intake of radiocesium from food have been of great concern since the Fukushima Daiichi Nuclear Power Station accident in 2011. Therefore, evaluating the phytoavailability and mobility of radiocesium in soil and determining the ability of soil to fix radiocesium are important research topics. The capacity and selectivity for ¹³⁷Cs sorption in soil is evaluated on the basis of the radiocesium interception potential (RIP). Here, we measured the RIP of 925 farmland soil samples collected from Fukushima Prefecture and surrounding regions and plotted the values on a soil classification map and a surface geological map. The RIP values ranged from 73 to 12700 mmol kg⁻¹, and a wide range was also observed among samples with identical soil types and geological features; however, the RIP values were significantly low for Andosols (P ≤ 0.05). In addition, soils that did not contain vermiculite, illite and smectite had low RIP values. All measured RIP values were negatively correlated with the total C content and phosphate absorption capacity and positively correlated with the clay, silt, and exchangeable K and Ca content (P ≤ 0.01). However, the relationship between the RIP and the measured soil properties, except for the exchangeable K content, is strongly dependent on the soil classification and clay mineral composition. Therefore, the soil properties that most significantly influence the RIP values are probably differences in the soil parent materials, which influence the soil classification and clay mineral composition.

自2011年福岛第一核电站事故以来，通过食物长期摄入放射性铯所带来的健康风险一直备受广泛关注。因此，评估放射性铯在土壤中的植物有效性与迁移性，以及土壤固持放射性铯的能力，均为重要的研究课题。土壤对¹³⁷铯的吸附容量与选择性，可通过放射性铯截留潜能（radiocesium interception potential, RIP）进行评估。本研究采集了来自福岛县及周边区域的925份农田土壤样本，测定其放射性铯截留潜能值，并将测定结果绘制于土壤分类图与表层地质图中。本次测定的RIP值区间为73至12700 mmol·kg⁻¹，即便土壤类型与地质特征相同的样本，其RIP值也存在较大差异；但火山灰土（Andosols）的RIP值显著偏低（P≤0.05）。此外，未含有蛭石、伊利石与蒙脱石的土壤，其RIP值普遍偏低。所有测定得到的RIP值与土壤总碳含量、磷酸盐吸附容量呈显著负相关，而与黏粒、粉粒、交换性钾及交换性钙含量呈显著正相关（P≤0.01）。但除交换性钾含量外，RIP值与其余测定土壤性质之间的关联，强烈依赖于土壤分类与黏土矿物组成。因此，对RIP值影响最为显著的土壤性质，本质上或许是土壤母质的差异；而母质差异正是决定土壤分类与黏土矿物组成的关键因素。