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

Miyu Nakanishi; Yuichi Onda; Junko Takahashi; Hiroaki Kato; Hikaru Iida; Momo Takada

doi:10.1016/j.envpol.2023.122147

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

Environ Pollut. 2023 Oct 1:334:122147. doi: 10.1016/j.envpol.2023.122147. Epub 2023 Jul 8.

Authors

Miyu Nakanishi¹, Yuichi Onda², Junko Takahashi³, Hiroaki Kato³, Hikaru Iida⁴, Momo Takada⁵

Affiliations

¹ University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan. Electronic address: na73mi26@gmail.com.
² Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan. Electronic address: onda@geoenv.tsukuba.ac.jp.
³ Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan.
⁴ University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan.
⁵ National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, 305-8567, Japan.

PMID: 37429488
DOI: 10.1016/j.envpol.2023.122147

Abstract

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.

Keywords: Air dose rate; Effective rainfall; Hysteresis; Shielding effect; Soil moisture content.

MeSH terms

Animals
Cesium Radioisotopes / analysis
Forests
Fukushima Nuclear Accident*
Humans
Japan
Radiation Monitoring* / methods
Soil
Soil Pollutants, Radioactive* / analysis
Water

Substances

Cesium-137
Soil
Soil Pollutants, Radioactive
Cesium Radioisotopes
Water