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  1. Takami MORITA on March 5, 2021 at 2:31 am

    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?

    • Shigeyoshi Otosaka on March 5, 2021 at 8:53 pm

      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.

  2. sabine charmasson on March 9, 2021 at 5:56 pm

    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?

    • Shigeyoshi Otosaka on March 10, 2021 at 5:30 pm

      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.