Radiocaesium in the environment of Fukushima.

It has been 10 years since the accident at Fukushima Daiichi nuclear power plant in 2011. Large quantities of ¹³¹I, ¹³⁴Cs, and ¹³⁷Cs were released into the environment, and 80% of ¹³⁷Cs still remains. In addition to the decrease by attenuation, the transfer of ¹³⁷Cs to plants, animals, and humans is decreasing due to movement and changing fractions with elapsed time. The activity concentration of ¹³⁷Cs in the atmosphere has decreased drastically, and the internal radiation dose due to inhalation is negligible. The activity concentration of ¹³⁷Cs in agricultural plants is decreasing due to decontamination of soil, application of potassium, and lower levels in irrigation water. The activity concentration of ¹³⁷Cs in wild animals is decreasing, and shows seasonal variation in wild boars. The activity concentration of ¹³⁷Cs in offshore seawater has decreased to 0.01 Bq l^-1. Therefore, the radiation dose is <1 mSv of the additional radiation dose.