First successful isolation of radioactive particles from soil near the Fukushima Daiichi Nuclear Power Plant

The Fukushima Daiichi Nuclear Power Plant (F1NPP) accident in 2011 released radionuclides into the atmosphere in both aerosol and gaseous form. Subsequent studies of contamination in the environment have focused on the bulk radioactivity in samples. Comparatively little is known about the relative contribution and patterns of soluble versus particulate deposition of the radionuclides. We investigated a sample of heavily contaminated surface soil from a site 20 km northwest of the F1NPP and isolated four radioactive particles from the surrounding soil. These particles had a maximum particle area equivalent diameter of 6.4 μm and a maximum 137Cs radioactivity of 67.5 ± 0.1 Bq per particle. They were larger than the particles identified in aerosol samples shortly after the accident at a location 170 km southwest of the F1NPP. Two of the particles were spherical and two were fragmental. Silicates were a major component of the Fukushima radioactive particles. These characteristics clearly differ from the so-called hot particles observed at the Chernobyl accident in 1986. Clarifying the physical and chemical properties of the radionuclides released from the F1NPP accident is important for assessing the potential long-term impacts to humans.