Fig.1　¹³⁷Cs concentrations in riverwater down the Kido dam in 2014

• When water level is low, the concentration of ¹³⁷Cs (particulate state and dissolved state) in river water was lower than 0.1Bq/L.
• When water level is high, the concentration of ¹³⁷Cs in dissolved states increases to about 1 Bq/L, that is lower than maximum permissible value of drinking water (10 Bq/L).
• The concentration of radioactive cesium in the dissolved state is lower than 0.1 Bq/L even during high flow periods. The concentration of radioactive cesium tends to decrease with decreasing turbidity. Therefore most of radioactive cesium in river water is in the particulate state, and it is presumed that the concentration of radioactive cesium will decrease with time (see also; Q Is there a continuous input of cesium contamination to rivers from forests)

According to the Ministry of Environment, radioactive materials were lower than 0.1 Bq/L in any other rivers in Fukushima Prefecture.
Reference:　”Results for Monitoring of Radioactive Materials in Public Water in Fukushima Prefecture” Homepage of the Ministry of Environment

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Reference

1. 鶴田忠彦, 新里忠史, 中西貴宏, 土肥輝美, 中間茂雄, 舟木泰智, 御園生敏治, 大山卓也, 操上広志, 林誠二, 齊藤宏, 北村哲浩, 飯島和毅(2017): 福島における放射性セシウムの環境動態研究の現状; 根拠となる科学的知見の明示をより意識した情報発信の一環として, JAEA-Review 2017-018, 86p. https://doi.org/10.11484/jaea-review-2017-018