Association of fallout-derived 137Cs, 90Sr and 239,240Pu with natural organic substances in soils

Activity concentrations and associations of fallout-derived Cs, Sr and Pu in soils were investigated. The activity concentrations of Cs-137, Sr-90 and Pu-239,Pu-240 in volcanic ash soil were much higher than those in granite soil. They decreased with increasing depth in the soil. The activity ratios of Pu-239,Pu-240/Cs-137 and Sr-90/Cs-137 tended to increase slightly with increasing soil depth. Alkali extraction experiments with 0.1 M NaOH solution showed that the percentage activities of the fallout radionuclides found in the organic acid fractions were in the order Pu-239,Pu-240 > Sr-90 > Cs-137. The concentrations of Cs-137 and Pu-239,Pu-240 reacted with humic fractions were higher than those with fulvic fractions. In contrast to Cs-137 and Pu-239,Pu-240,Sr-90 reacted more with fulvic fractions than with humic fractions. These results provide information about the effects of organic substances on the retention and migration of Cs-137,Sr-90 and Pu-239,Pu-240 in soils under natural conditions. (C) 1999 Elsevier Science Ltd. All rights reserved.