58. The Concentrations of Technetium-99 in Sargassum thunbergii along the Coast of the Japanese Islands
Shigeki Hirano
Keywords: algae, 99Tc
Technetium-99 is already present in the terrestrial and the marine environment as a result of nuclear weapon tests carried out in the past. It is very important to study the distribution of the nuclide in the marine environment in regards to increasing number of power plants all over the world because of its high yield in nuclear fission, its long half-life, its high solubility and stability in water media, and its high concentration factor (CF) by brown algae.
We have been determining the concentration of the nuclide in algae collected along the coast of the Japanese Islands to assess an internal exposure to Japanese through marine foods. The concentratuon of the nuclide was also determined in seawater collected on the coast of Flitachinaka City.
It was found that the present level of the nuclide was very low in algae collected in most areas of Japan and this level was attributed to global fallout. However, it was found that a relatively high concentration of the nuclide was detected in samples collected in Hitachinaka City which neighbors Tokai Village where there are many nuclear facilities in operation. The concentration of the nuclide in the algae was in the range of 50 to 1,500 mBq/kg wet. It was found that the level of the nuclide in the algae in Kitaibaraki City was the same as that in other areas, except Hitachinaka City, despite the fact that Kitaibaraki City is also near Tokai. There is a down current along the coast of those areas so that northern sites are free from the influence of the emission of waste from Tokai. The level of the nuclide in the algae collected in Chiba Prefecture was low and the waste from Tokai did not reach this far and the concentration of the nuclide in the algae was below TO mBq/kg wet.
The concentration of the nuclide in seawater was not detected in most samples obtained along the coast of the Japanese Islands. However, in Hitachinaka City, the concentrations of the nuclide were detected several times through the year and the values varied from below the detection limit, 10mBq, to 23OmBq/m3.