U and radiocesium in river bank soil and river sediment in Fukushima Prefecture, after the Fukushima Daiichi Nuclear Power Plant accident.

Almost 8 years after the Japanese Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, data for U and U/U have mainly remained limited to only a few heavily contaminated samples. In the present study, activities of U, Cs, and Cs, along with U, U, U, in 15 river bank soil and 10 river sediment samples, were measured by ICP-MS/MS and γ spectrometry. The Cs activities and Cs/Cs activity ratios (decay-corrected to March 11, 2011) in these 15 river bank soil samples were from 74.8 to 3.88 × 10 Bq kg and from 0.944 to 1.02, respectively; and in these 10 river sediment samples were from 87.1 to 1.86 × 10 Bq kg and from 0.904 to 0.990, respectively. The U activities and U/U atom ratios in these soil samples were in the respective ranges of (0.139-17.6) × 10 Bq kg and (0.259-3.83) × 10; and in these sediment samples were in the respective ranges of (0.884-27.0) × 10 Bq kg and (1.12-5.04) × 10. For one river sediment core sample, Cs and U activities decreased with the depth indicating Cs and U accumulated in the river sediment with time. Unlike Cs, no clear evidence of FDNPP accident-derived U has been found in this study, although further monitoring is encouraged to establish the background database on U/U for its potential application as a tracer in environmental studies.