Exchange of radiocesium between sediment and pore water in the coastal seabed off Fukushima

Otosaka, Shigeyoshi  ; Fukuda, Miho*; Aono, Tatsuo*

Behavior of dissolved radiocesium near the seafloor is discussed from the distributions of Cs in seawater, seabed sediment and pore water collected from the area around Fukushima. The Cs concentrations in the pore water, collected from 2015 to 2017, ranged between 33 and 1186 mBq/L, and were 1040 times higher than those in seawater on the sediment surface. The Cs concentration in the overlying water did not show clear differences regardless of the pore size of the filter used for filtration. From these results, it was confirmed that radiocesium in the seabed sediment was dissolved in pore water and diffused to the benthic layer. The apparent distribution coefficient between pore water and sediment was [0.94.2]10 L/kg, with no difference depending on the year of sampling. These results indicated that an equilibrium of Cs between pore water and sediment has established during the observation period.