Behavior of Radiocesium in Sediments in Fukushima Coastal Waters: Verification of Desorption Potential through Pore Water

Abstract

Concentrations of 137Cs in seawater, seabed sediment, and pore water collected from the area around Fukushima were investigated from 2015 to 2018, and the potential of coastal sediments to supply radiocesium to the bottom environment was evaluated. The 137Cs concentration in the pore water ranged from 33 to 1934 mBq L–1 and was 10–40 times higher than that in the overlying water (seawater overlying within 30 cm on the seabed). At most stations, the 137Cs concentrations in the overlying water and the pore water were approximately proportional to those in the sediment. The conditional partition coefficient between pore water and sediment was [0.9–14] × 102 L kg–1, independent of the year of sampling. These results indicated that an equilibrium of 137Cs between pore water and sediment has been established in a relatively short period, and 137Cs in the pore water is gradually exported to seawater near the seabed. A simple box model estimation based on these results showed that 137Cs in the sediment decreased by about 6% per year by desorption/diffusion of 137Cs from the seabed.

Modelling the kinetic reactive transport of pollutants at the sediment-water interface. Applications with atmospheric fallout radionuclides

“…Thus, in some lacustrine and marine sediment cores sampled shortly after the Chernobyl accident in areas affected by its radioactive fallout, it was observed that 134 Cs had penetrated into the sediment up to 10-20 cm depth (e.g., Petersen et al, 1990;Kramer et al, 1991;Robbins and Jasinski, 1995;Holby and Evans, 1996). Similar observations have been documented in some sedimentary systems affected by the Fukushima accident (e.g., Yoshimura et al, 2014;Otosaka et al, 2020). Diffusion models provided apparently satisfactory descriptions of the data, but in some cases, the required diffusion coefficients had unreliable values (Holby and Evans, 1996).…”

Behavior of Radiocesium (137Cs) on the Coastal Seafloor near the Fukushima Daiichi Nuclear Power Plant Inferred from Radiocesium Distributions in Long Cores

“…However, 10 years after the accident, the 137 Cs supply from the deep layers might slow the 137 Cs concentration decrease in the surface sediment in this area. The slow decrease in 137 Cs concentrations at present is thought to be due to desorption of 137 Cs from sediment (Otosaka et al, 2020). Besides, higher 137 Cs concentrations in the surface layer of some cores (Nos.…”

Evaluation of the impact of the 137Cs supply from rivers to coastal waters off Fukushima on the 137Cs behavior in seabed sediment

“…The parameters for the sediment and 137 Cs are shown in Table 1. The desorption rate from seabed sediment (s -1 ), defined as the product of the kinetic coefficient for desorption from suspended matter (s -1 ) and the correction factor (-) in Kamidaira et al [15], was set to the same order as the value obtained by monitoring [19]. The other parameters are based on Kamidaira et al [15].…”