Remobilisation of radiocaesium from bottom sediments to water column in reservoirs in Fukushima, Japan

Funaki, Hironori ; Tsuji, Hideki*; Nakanishi, Takahiro   ; Yoshimura, Kazuya  ; Sakuma, Kazuyuki   ; Hayashi, Seiji*

Reservoir sediments generally act as a sink for radionuclides derived from nuclear accidents, but under anaerobic conditions, several radionuclides remobilise in bioavailable form from sediment to water columns, which may contribute to a long-term contamination in aquatic products. This study systematically investigated the Cs activities between sediment and pore water, which is a direct evidence of the remobilisation of bioavailable Cs from sediments, in two highly contaminated reservoirs affected by the Fukushima Dai-ichi Nuclear Power Plant accident. Our results strongly indicate a competitive ion exchange process between Cs and NH via a highly selective interaction with the frayed edges sites of phyllosilicate minerals to be the major reason for the variability of the Kd values between sediment and pore water, even in the Fukushima case.