University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan.
Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan.
Environ Pollut. 2023 Oct 1;334:122147. doi: 10.1016/j.envpol.2023.122147. Epub 2023 Jul 8.
Radionuclides released and deposited because of the 2011 Fukushima Dai-ichi Nuclear Power Plant accident caused an increase in air dose rates in Fukushima Prefecture forests. Although an increase in air dose rates during rainfall was previously reported, the air dose rates in the Fukushima forests decreased during rainfall. This study aimed to develop a method to estimate rainfall-related changes in air dose rates, even in the absence of soil moisture data, in Namie-Town and Kawauchi-Village, Futaba-gun, Fukushima Prefecture. Moreover, we examined the relationship between preceding rainfall (Rw) and soil moisture content. The air dose rate was estimated by calculating the Rw in Namie-Town from May to July 2020. We found that the air dose rates decreased with increasing soil moisture content. The soil moisture content was estimated from Rw by combining short-term and long-term effective rainfall using half-live values of 2 h and 7 d and considering the hysteresis of water absorption and drainage processes. Furthermore, the soil moisture content and air dose rate estimations showed a good agreement with coefficient of determination (R) scores >0.70 and >0.65, respectively. The same method was tested to estimate the air dose rates in Kawauchi-Village from May to July 2019. At the Kawauchi site, variation in estimated value is relatively large due to the presence of water repellency in dry conditions, and the amount of Cs inventory was low, so estimating air dose from rainfall remained a challenge. In conclusion, rainfall data were successfully used to estimate soil moisture and air dose rates in areas with high Cs inventories. This leads to the possibility of removing the influence of rainfall on measured air dose rate data and could contribute to the improvement of methods currently used to estimate the external air dose rates for humans, animals, and terrestrial forest plants.
由于 2011 年福岛第一核电站事故释放和沉积的放射性核素，福岛县森林中的空气剂量率增加。尽管先前有报道称降雨期间空气剂量率会增加，但福岛森林中的空气剂量率在降雨期间会降低。本研究旨在开发一种方法，即使在缺乏土壤湿度数据的情况下，也能估算福岛县相马市和川内村的空气剂量率与降雨相关的变化。此外，我们还研究了前期降雨量（Rw）与土壤湿度之间的关系。通过计算 2020 年 5 月至 7 月期间相马市的 Rw，估算空气剂量率。结果表明，空气剂量率随土壤湿度的增加而降低。通过将半衰期分别为 2 小时和 7 天的短期和长期有效降雨量结合起来，并考虑吸水和排水过程的滞后性，用 Rw 来估算土壤湿度。此外，土壤湿度和空气剂量率的估算值与决定系数（R）得分分别>0.70 和>0.65 具有很好的一致性。该方法还用于估算 2019 年 5 月至 7 月期间川内村的空气剂量率。在川内村，由于干燥条件下存在拒水性，估计值的变化较大，而且 Cs 库存较低，因此仍难以通过降雨来估算空气剂量。总之，成功地利用降雨数据估算了高 Cs 库存地区的土壤湿度和空气剂量率。这为去除降雨对测量空气剂量率数据的影响提供了可能性，并有助于改进目前用于估算人类、动物和陆地森林植物的外部空气剂量率的方法。
