• Results from a continuous survey from April, 2015 to March, 2018 showed that the radioactive Cs concentration in rivers continued to decrease even in 2018, after 7 years had passed since the accident.
• The speed of decrease was approximately ten times the physical half-life of ¹³⁷Cs.

Fig.1　Changes in the concentration of dissolved and suspended Cs observed in the Ota and Ukedo Rivers

The solid lines show the exponentially approximated decrease in concentration, and the dotted lines show the decrease due to physical half-life

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Reference

1. Nakanishi, T. and Sakuma, K. (2019): Trend of ¹³⁷Cs concentration in river water in the medium term and future following the Fukushima nuclear accident, Chemosphere, vol. 215, 272-279. https://doi.org/10.1016/j.chemosphere.2018.10.017