SPECIATION OF CESIUM ISOTOPES IN RIVER WATER: A CASE STUDY IN THE UKEDO RIVER.

137Cs in river systems can be taken up by aquatic animals. In this paper, total 137Cs concentration in the Ukedo River system and 137Cs presence in dissolved, acid-soluble and -insoluble fractions in river water samples were determined. Total 137Cs concentration had the maximum value of 2.08 Bq kg-1 below the Ogaki Dam in May 2012. In the base flow condition, > 87% of 137Cs existed in the dissolved state, and the acid-soluble state and the insoluble state were <13% and the undetectable level, respectively. After the heavy rain event, the particulate fraction (acid-soluble state + insoluble state) was elevated to 65%, which corresponds to twice as much as that in the base flow condition. Particulate 137Cs, especially the acid-soluble Cs, can play a role when taken into the food chain in aquatic ecosystems.