Status and future of radiocesium in the seafloor off Fukushima
福島沖の海底における放射性セシウムの現状と将来
Shigeyoshi Otosaka
AORI, The University of Tokyo
Shigeyoshi Otosaka
AORI, The University of Tokyo
Is the equilibrium portion of Cs-137 in porewater bioavailable fractions in sediments? After many years, will all radiocesium in sediments be strongly incorporated into sediment particles?
As shown in Fig. 6, a certain proportion of radiocesium is incorporated in the organic fraction, which is relatively easily decomposed (probably bioavailable) even several years after the accident. This may indicate that some of the radiocesium is in equilibrium with the bioavailable fraction in the surface sediment. For this reason, we think that the bioavailable radiocesium will apparently remain in sediment in the future. It will be necessary to clarify which fraction of the sediment supports the high concentration of radiocesium in the pore water. Thank you for your question.
Dear Shigeyoshi, apart from the abukuma in sendai bay, do we have a precise idea of the contribution of particulate matter from the small rivers?
Thank you, Sabine, for your question.
The impact of small rivers on the initial distribution is relatively small (<5% of total deposition). However, i think that the continuous influx of radiocesium from the land will increase the relative contribution over time.
A detailed survey by NRA found that the impact of the inflow from small rivers (Ukedo, Mano, and Tomioka Rivers) on the concentration of radiocesium in seabed sediments was limited to a few kilometers from the river mouth. The relative impact is considered small.
It has also been reported that the concentration near the estuary temporarily increases during flooding, but it will return to “normal” levels within a year due to the desorption of radiocesium from suspended particles and the horizontal transport of suspended matter.
I think that further investigation is needed for the detailed desorption process and the identification of the carriers of radionuclide.