Soil dust and bioaerosols as potential sources for resuspended 137Cs occurring near the Fukushima Dai-ichi nuclear power plant

Masakazu Ota; Shogo Takahara; Kazuya Yoshimura; Azusa Nagakubo; Jun Hirouchi; Naho Hayashi; Tomohisa Abe; Hironori Funaki; Haruyasu Nagai

doi:10.1016/j.jenvrad.2023.107198

Soil dust and bioaerosols as potential sources for resuspended ¹³⁷Cs occurring near the Fukushima Dai-ichi nuclear power plant

J Environ Radioact. 2023 Aug:264:107198. doi: 10.1016/j.jenvrad.2023.107198. Epub 2023 May 11.

Authors

Masakazu Ota¹, Shogo Takahara², Kazuya Yoshimura³, Azusa Nagakubo², Jun Hirouchi², Naho Hayashi², Tomohisa Abe³, Hironori Funaki³, Haruyasu Nagai⁴

Affiliations

¹ Research Group for Environmental Science, Nuclear Science and Engineering Center, Japan Atomic Energy Agency, 2-4 Shirakata, Tokai, Ibaraki, 319-1195, Japan. Electronic address: ohta.masakazu@jaea.go.jp.
² Risk Analysis Research Group, Nuclear Safety Research Center, Japan Atomic Energy Agency, 2-4 Shirakata, Tokai, Ibaraki, 319-1195, Japan.
³ Environmental Monitoring Group, Collaborative Laboratories for Advanced Decommissioning Science, Japan Atomic Energy Agency, 45-169, Sukakeba, Kaihama, Haramachi, Minamisoma, Fukushima, 975-0036, Japan.
⁴ Nuclear Science and Engineering Center, Japan Atomic Energy Agency, 2-4 Shirakata, Tokai, Ibaraki, 319-1195, Japan.

PMID: 37178632
DOI: 10.1016/j.jenvrad.2023.107198

Abstract

One of the current pathways to radiation exposure, caused by the radionuclides discharged during the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, is the inhalation of resuspended ¹³⁷Cs present in the air. Although wind-induced soil particle resuspension is recognized as a primary resuspension mechanism, studies regarding the aftermath of the FDNPP accident have suggested that bioaerosols can also be a potential source of atmospheric ¹³⁷Cs in rural areas, although the quantitative impact on the atmospheric ¹³⁷Cs concentration is still largely unknown. We propose a model for simulating the ¹³⁷Cs resuspension as soil particles and bioaerosols in the form of fungal spores, which are regarded as a potential candidate for the source of ¹³⁷Cs-bearing bioaerosol emission into the air. We apply the model to the difficult-to-return zone (DRZ) near the FDNPP to characterize the relative importance of the two resuspension mechanisms. Our model calculations show that soil particle resuspension is responsible for the surface-air ¹³⁷Cs observed during winter-spring but could not account for the higher ¹³⁷Cs concentrations observed in summer-autumn. Higher ¹³⁷Cs concentrations are reproduced by the emission of ¹³⁷Cs-bearing bioaerosols (fungal spores) that replenishes the low-level soil particle resuspension in summer-autumn. Our model results show that the accumulation of ¹³⁷Cs in fungal spores and large emissions of spores characteristic of the rural environment are likely responsible for the presence of biogenic ¹³⁷Cs in the air, although the former must be experimentally validated. These findings provide vital information for the assessment of the atmospheric ¹³⁷Cs concentration in the DRZ, as applying the resuspension factor (m^-1) from urban areas, where soil particle resuspension would dominate, can lead to a biased estimate of the surface-air ¹³⁷Cs concentration. Moreover, the influence of bioaerosol ¹³⁷Cs on the atmospheric ¹³⁷Cs concentration would last longer, because undecontaminated forests commonly exist within the DRZ.

Keywords: Atmospheric concentration; Bioaerosol; Fukushima Dai-ichi Nuclear Power Plant accident; Radiocesium; Resuspension; Soil particle.

MeSH terms

Cesium Radioisotopes / analysis
Dust
Fukushima Nuclear Accident*
Japan
Nuclear Power Plants
Radiation Monitoring* / methods
Soil
Soil Pollutants, Radioactive* / analysis

Substances

Soil
Dust
Cesium-137
Cesium Radioisotopes
Soil Pollutants, Radioactive