Modelling speciation and distribution of radionuclides in agricultural soils

Abstract

The behaviour of radionuclides (and thus their plant availability) in cultivated soils principally depends on soil solution composition and the presence of adsorbing surfaces. Both properties vary with soil type, soil cultivation and climatic conditions. We give an overview of the relevant soil processes and the basic sorption modelling concepts with the emphasis on surface complexation on minerals and humic matter. For estimating speciation and distribution of radionuclides, geochemical codes can be employed. We show an example how modelling can be carried out by using the well-known code PHREEQC and introducing the reference soil concept. Using the example of the UNISECS model, we discuss issues of parametrisation and validation as well as the sources of uncertainty. For selected nuclides, we evaluate the dependence of the distribution coefficient (Kd) on the most important soil parameters.