In Fukushima Daiichi Nuclear Power Plant accident occurred in March 2011, radioactive contamination to the environment occurred on a global scale. Although the influence on the living area is decreasing because it is more than six years since the accident, when space radioactivity measured is used as an index, the infl uence still remains. In this study, radioactive cesium and radioactive iodine, which are main radionuclides sprayed, were measured in soil collected at the Tama River riverbed, and compared with the data already published four years ago in our laboratory. Radioactive iodine was not detected in this measurement, but radioactive cesium (Cs-134, Cs-137) was detected. On the other hand, when comparing this research result with that in 2013, it became clear that its abundance was smaller than the decrease based on the physical half-life.

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