The distribution of radioactive caesium in river water at the Tama River watershed six years after the Fukushima Daiichi Nuclear Power Plant accident

Following the Fukushima Dai-ichi Nuclear Power Plant accident, radioactive caesium was detected in the Tama River watershed in the Kanto region of Japan. Radioactivity analysis was conducted on river water samples collected in 2017 to determine the distribution of dissolved and suspended radioactive caesium in the Tama River watershed. The activity concentrations of 137 Cs in the dissolved and suspended phases were below 1.17 mBq L −1 and 3.30 mBq L −1 , respectively. A significant correlation was observed between the activity concentration of 137 Cs in the river water and several water quality parameters. We obtained useful insights into the migration of 137 Cs in river water within a watershed within urban areas.