Concentration factors for Cs-137 in marine algae from Japanese coastal waters

Concentration factors (CF: Bq.kg-1 in wet algae/Bq.kg-1 in filtered seawater) for Cs-137 in Japanese coastal algae, were investigated during 1984-1990. Cs-137/Cs(stable) atom ratios were also examined to clarify the distribution equilibrium of Cs-137 in marine algae and sea water. The CFs in marine algae were within the range of 5.4 approximately 92, and the geometric mean of CF was 28 +/- 2 (standard error) in Japanese coastal species. The CFs in edible species were within the range of 5.4 approximately 67, and the geometric mean of CF was 26 +/- 4 (standard error). The values of Cs-137/Cs atom ratios in marine algae and sea water indicated that Cs-137 reached an equilibrium state in partition between algae and sea water. Therefore, the CF value obtained in the present study can be regarded as an equilibrated value. Our results showed that the CF for Cs-137 in Japanese coastal algae were consistent with the Japanese guideline CFs, but were smaller than the recommended value by IAEA.