Vertical distribution of 90Sr and 137 Cs in uncultivated soil in three localities of central Bohemia

The purpose of this work was study the vertical distribution of 90Sr and 137Cs in uncultivated soils. The radionuclide contents in different soil layers and the cumulative deposition of radionuclides at the study sites were to be established with a view to possible identification of their sources. The present paper investigated the vertical distribution of 90Sr and 137Cs in uncultivated soil samples in central Bohemia and inventory of these radionuclides at representative sampling sites. These data provide the information about the availability, movement and environmental behaviour of these important radionuclides in the study region. The cumulative deposition of 90Sr at sites 1, 2 and 3 were found of 700, 1390 and 970 Bq/m2, respectively, The cumulative deposition of 137Cs at sites 1, 2 and 3 were found of 260, 510 and 10000 Bq/m2, respectively. The obtained values of 9Sr are about 47% lower than the value of UNSCEAR inventories, but our average value of 137Cs (3590 Bq/m2) agree with the cumulative deposition of 137Cs from the atmospheric nuclear tests in northern 40 grad - 50 grad temperate zone according UNSCEAR inventories. The radioactive decay should have reduced the reported 90Sr and 137Cs inventories in the northern hemisphere to 2190 Bq/m2 and 3580 Bq/m2, respectively. The concentration of 90Sr and 137 Cs increased proportionally to the SOM content in soil, but the difference of the degree of correlation among 90Sr and 137CS could be explained by the fact that SOM held 137Cs more strongly than 90Sr. 137Cs showed very low mobility in soil profiles in undisturbed soils, therefore, it was concentrated in the upper 10 cm of the soils. Although the concentration of 90Sr increased with organic content through an anion exchange reaction, which is enhanced by SOM keeping high cationic exchange capacity, the retention of Sr was relatively weak in contrast to Cs. It is related with high mobility of Sr that is a member of group II in the periodic table and acts like Ca. The fact that the peak 90Sr concentration usually could be found below 10 cm of the soil profile is a proof, whereas some 85% of the 137Cs was found within 10 cm from the surface soil layers. It is well known that calcium plays an important role in the adsorption process. (authors)