Comparison of coastal area sediment-seawater distribution coefficients (K-d) of stable and radioactive Sr and Cs

摘要

Values of the sediment-seawater distribution coefficient (K-d) in Japanese coastal areas were compared for stable and radioactive Sr and Cs, respectively, in order to clarify whether or not the constant exchangeable fraction in sediment of 20% for the ocean margin (the IAEA recommended method) for all elements was reasonable. Global fallout origin Sr-90 and Cs-137 concentrations in sediment and seawater were obtained from open data sources as collected in 1964-2010 and 319 and 1506 K-d values were calculated, respectively. When the values were classified into about 10 y intervals from the 1960's to 2000's, K-d values of the two most recent decades did not show any difference for Sr-90 and Cs-137. The geometric means of the most recent K-d values in 2000-2010 were 1.2 x 10(2) L kg(-1) for Sr-90 and 5.8 x 10(2) L kg(-1) for Cs-137. The stable Sr and Cs concentration data in sediment and seawater samples collected in 2000-2011 were used to calculate stable Sr and Cs K-d values based on the IAEA's recommended method and values were compared. It was found that the stable Sr K-d (geometric mean = 5.3) was much less than that of K-d-Sr-90, while stable Cs K-d (geometric mean = 1.7 x 10(3)) was higher than that of K-d-Cs-137. Thus, it was judged to be unsuitable to estimate the K(d)s of these radionuclides by apply a factor of 0.2 to the total concentration of Sr and Cs in Japanese coastal sediment, assuming 20% was the exchangeable fraction. It is likely that applying the constant exchangeable fraction percentage to all elements will sometimes lead to overestimated or underestimated values. (C) 2016 Elsevier Ltd. All rights reserved.