Financial support: This work was carried out as a part of the EC-project “Long term dynamics of radionuclides in semi-natural environments: derivation of parameters and modeling” in the EC-framework “Nuclear Fission Safety”. Research Contract # F14P-CT95-0022. European Commission - Nuclear Fission Safety Programme.

Keywords: ¹³⁷Cs plant uptake, radioactive traces, radiocaesium, radiopotassium.

The uptake of radionuclides by plant roots constitutes the main pathway for the migration of radiocaesium from soil to humans, via food chain. In this study we assessed radiocaesium uptake by plant in order to piece together information on factors affecting uptake processes, particularly K supply and differential uptake among different plant species. Soil contaminated by the Chernobyl accident and forage from a semi-natural alpine grassland, situated in Tarvisio, Italy, were sampled during 1999. Under field conditions, ¹³⁷Cs uptake for Graminaceae and Taraxacum officinale seem to behave in a comparable way. Higher ⁴⁰K soil activity concentration leads to a lower ¹³⁷Cs plant uptake, suggesting an inhibitory pattern of potassium on radiocaesium plants uptake. For forage samples, a similar tendency was observed. We analyzed the influence of the ratio of ¹³⁷Cs/ ⁴⁰K in soil on ¹³⁷Cs plant uptake. Under field conditions, the ratio observed varied in a range of 0.5 to 1.3. For most of the species, at higher ⁴⁰K soil concentration a lower ¹³⁷Cs uptake was observed, a fact that reflects the resulting effect of the complexity of factors controlling ion absorption from soil.