Vertical distribution and bioavailability of 137Cs in organic and mineral soils

The vertical distribution and bioavailability of ¹³⁷Cs in Histosols and mineral soils with different physicochemical properties from the southeast of Bavaria (Germany) more than ten years after the Chernobyl accident were the focus of this study. The vertical distribution of ¹³⁷Cs was low in the investigated soils. About 85–98 % of the total ¹³⁷Cs was located in the upper 10 cm of the mineral soils. Slightly higher ¹³⁷Cs percentages were observed in deeper soil layers of the peat soils. Although the organic matter is assumed to enhance ¹³⁷Cs mobility in soils, ¹³⁷Cs was also located in the upper 10 cm of the peat soils (73–85 %). The highest ¹³⁷Cs‐activities were found in the humus layers of forest soils, where 45–93 % of the total ¹³⁷Cs soil inventories were observed. To determine the bioavailability of radiocesium, the soil‐to‐plant transfer of ¹³⁷Cs and additionally added ¹³⁴Cs was investigated under controlled conditions. The results revealed that the ^134+137Cs soil‐to‐plant transfer factors as well as the percentages of NH₄‐exchangeable ^134+137Cs were much higher for the peat soils and humus layers than for the mineral soils. Nevertheless, the migration of ¹³⁷Cs from the humus layers to the underlying soils was low. Considering the high bioavailability and low migration of radiocesium in the humus layers, it is suggested that radiocesium is involved in a shortcut element cycle in the system humus layer‐plant uptake‐litter. Furthermore, the organic matter has to be taken into account for radiocesium immobilization.