Accumulation of accident-derived radiocesium in lake and coastal sediments at 300-700 km distance from Fukushima area

The accumulation of accident-derived radiocesium was investigated in nine water bodies located 300-700 km from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP). ¹³⁴Cs from the accident was detected in surface sediment of five water bodies. The ¹³⁴Cs concentration, corrected to the time of the accident in 2011, was generally lower than that of ¹³⁷Cs, and its spatial pattern does not fully correspond to that of ¹³⁷Cs. These results suggest that radiocesium derived from both FDNPP and past global fallout can be separately observed and that the contributions of both sources are non-uniform within these sites. The ¹³⁴Cs inventory in surface sediments is smaller than its deposition, suggesting that almost all deposited ¹³⁴Cs remains within the catchment and/or a part has been discharged from the saline and brackish water bodies. (authors)