[M-AG33] Dynamics of radionuclides emitted from Fukuchima Dai-ichi Nuclear Power Plant in the environment

[MAG33-15] Incease of radioactive cesium resuspension to the atmosphere with
bioaerosols in a polluted area in Fukushima

*Kazuyuki Kita¹, Naho Hayashi¹, Koutaro Minami¹, Mao Kimura¹, Yasuhito Igarashi², Kouji Adachi², Teruya Maki³, Masahide Ishizuka⁴, Hiroshi Okochi⁵, Jun Furukawa⁶, Kazuhiko Ninomiya⁷, SHINOHARA ATSUSHI⁷ (1.Faculty of Science, Ibaraki University, 2.Meteorological Research Institute, 3.Kanazawa University, 4.Kagawa University, 5.Waseda University, 6.Tsukuba University, 7.Osaka University)

Keywords:FDNPP accident, radiocesium, bioaerosol

Radionuclides emitted in the Fukushima dai-ichi nuclear power plant (FNDPP) accident in March 2011 have been
deposited on the soil, ocean and vegetation. Re-suspension of radioactive cesium (Cs) from the soil and vegetation
to the atmosphere may be one of significant path in the diffusion of radionuclides after the accident.
We have measured the concentration of atmospheric Cs-134/137 radioactivity at a mountainous region in
Fukushima, where deposition density of Cs-134/137 is relatively high. Atmospheric suspended particles have been
collected on a sheet of quartz fiber filter with high-volume air samplers mounted at a playground site and forest
site, and gamma-ray emission from them were measured with Ge detector to obtain the atmospheric activity concentration
of Cs-134/137. A small part of each filter was used to measure chemical composition and microscope
particle observation.
This observation showed that major part of the sampled course particles were carbonaceous, probably biogenic
particles, such as spores and bacteria in summer and autumn, between June and October, indicating that a large
amount of bioaerosol could be emitted from forest around Fukushima.
The atmospheric Cs radioactivity concentration significantly increased in this period. It was higher in the forest
than that at the playground in these seasons. The measured concentration of atmospheric Cs-134/137 was
positively correlated with amount of carbonaceous particles in these seasons. Bioaerosol sampling and genome
analyses showed that major coarse particles in these seasons were probably spores of fungi and stain. We counted
the spores collected on the sample filters to evaluate their number density, and found the number density was positively
correlated with the atmospheric Cs radioactivity concentration. We collected fungi at Namie to sample its
spores. About half of Cs-137 in the spores was removed by pure water, being consistent with similar experiment for
the atmospheric particle samples. These results indicated that spore emission from fungi significantly contributes
to the resuspension of radioactive Cs to the atmosphere in summer and autumn. Water solubility of atmospheric
Cs-137 in these seasons suggests possibility of its circulation between the atmosphere and biosphere.