The concentration of cesium dissolved in river water (dissolved cesium) is far below the limits for drinking water (1 Bq/L).
However, with shipping restrictions still imposed on some freshwater fish species and freshwater fish caught in some areas, studies are ongoing to investigate the situation of river water in detail.

Fig.1　Relationship between the river basin situation and the concentration of cesium dissolved in river water

The average cesium deposition amount in the river basin in (b) is higher than that in (a), and therefore the cesium concentration in river water is higher in (b).
The ratio of land with buildings in (d) is higher than that in (c), and therefore the cesium concentration in river water is higher in (d).

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  Fig.2　Concentration of Cs-137 dissolved in river water in relation to average Cs-137 deposition amount in the river basin

  The larger the cesium deposition amount in the river basin is, the higher the concentration of cesium dissolved in river water is.

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  Fig.3　Concentration of Cs-137 dissolved in river water in relation to the ratio of the land area with buildings

  The higher the ratio of the land area with buildings is (i.e., more flatlands), the higher the concentration of cesium dissolved in river water is.

(Research results from the National Institute for Environmental Studies and others)

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Reference

1. Tsuji, H., Ishii, Y., Shin, M., Taniguchi, K., Arai, H., Kurihara, M., Yasutaka, T., Kuramoto, T., Nakanishi, T., Lee, S., Shinano, T., Onda, Y. and Hayashi, S. (2019): Factors controlling dissolved ¹³⁷Cs concentrations in east Japanese Rivers, Science and The Total Environment, vol. 697, 134093.https://doi.org/10.1016/j.scitotenv.2019.134093