• 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

Related articles

• How is the cesium concentration in river water changing over time? 【Northern Fukushima prefecture】
• How is the cesium concentration in river water changing over time? 【Southern Fukushima prefecture】
• Does radioactive cesium move from the ground surface to underground or into groundwater? 【Movement in underground water】
• Does radioactive cesium move from the ground surface to underground or into groundwater? 【Vertical movement in soil】
• Does the concentration in river water change before and after forest fire? How did it change by time?

Reference

1. T. Nakanishi and K. Sakuma, “Trend of 137Cs concentration in river water in the medium term and future following the Fukushima nuclear accident”, Chemosphere (2019), 215, 272-279.
2. 長尾ほか(2019), 福島における放射性セシウムの環境動態研究の現状（平成30年度版）, JAEA-Research 2019-002, 235p.