Changes in air dose rates due to soil moisture content in the Fukushima prefecture forests

• Published in: Environmental pollution (1987) 2023-10, Vol.334, p.122147-122147, Article 122147
• Main Authors: Nakanishi, Miyu, Onda, Yuichi, Takahashi, Junko, Kato, Hiroaki, Iida, Hikaru, Takada, Momo
• Format: Article
• Language: English
• Subjects: Air dose rate; Effective rainfall; Hysteresis; Shielding effect; Soil moisture content
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2023.122147

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 (R2) 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 137Cs 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 137Cs 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. [Display omitted] •Soil moisture content and air dose rate were estimated using effective rainfall.•Air dose rate changes were estimated using measured soil moisture content changes.•Magnitude of soil shielding effect was elevated by preceding rainfall.•This method might reveal influences besides rainfall on air dose rate changes.