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，经食物长期摄入放射性铯所引发的健康风险始终受到广泛关注。因此，评估放射性铯在土壤中的植物有效性与迁移性，明确土壤固持放射性铯的能力，已成为重要的研究课题。土壤对¹³⁷Cs的吸附容量与选择性，可通过放射性铯截留势（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份农田土壤样品，测定其放射性铯截留势，并将测定值绘制于土壤分类图与地表地质图中。本次研究测得的放射性铯截留势取值范围为73~12700 mmol·kg⁻¹，即便土壤类型与地质特征一致的样品，其放射性铯截留势也存在较大波动；但火山灰土（Andosols）的放射性铯截留势显著偏低（P ≤ 0.05）。此外，不含蛭石、伊利石与蒙脱石的土壤，其放射性铯截留势普遍较低。所有测定得到的放射性铯截留势值，均与土壤总碳含量及磷酸盐吸附容量呈显著负相关，而与土壤黏粒、粉粒、交换性钾及交换性钙含量呈显著正相关（P ≤ 0.01）。不过，除交换性钾含量外，放射性铯截留势与其余测定土壤性质之间的相关性，均强烈依赖于土壤分类与黏土矿物组成。因此，对放射性铯截留势影响最为显著的土壤因素，大概率源于土壤母质的差异——这种差异会进一步影响土壤分类与黏土矿物组成。