The concentration of radioactive cesium in sea water(upper figures) and marine sediment(lower figures) has been decreasing. Similar results are reported by other institutes (e.g., NRA, 2017).

Fig.1　Changes in concentration of radioactive cesium in seawater (Upper figures) and marine sediment (Lower figures) offshore of Fukushima Prefecture
Reference： Report on Inspection of Radioactive Materials in Marine Products (March 2011-January 2015) (Fisheries Agency)

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Reference

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