Predicting soil-to-plant transfer of radionuclides with a mechanistic model (BioRUR) J. Casadesus a , T. Sauras-Yera b, * , V.R. Vallejo b,c a Servei de Camps Experimentals, Universitat de Barcelona, Avda Diagonal 645, 08028 Barcelona, Spain b Departament de Biologia Vegetal, Facultat de Biologia, Universitat de Barcelona, Avda Diagonal 645, 08028 Barcelona, Spain c Centro de Estudios Ambientales del Mediterraneo, Charles Darwin 14, Parc Tecnolo `gic, 46980 Paterna, Valencia, Spain Accepted 18 October 2007 Available online 7 February 2008 Abstract BioRUR model has been developed for the simulation of radionuclide (RN) transfer through physical and biological compart- ments, based on the available information on the transfer of their nutrient analogues. The model assumes that radionuclides are transferred from soil to plant through the same pathways as their nutrient analogues, where K and Ca are the analogues of Cs and Sr, respectively. Basically, the transfer of radionuclide between two compartments is calculated as the transfer of nutrient mul- tiplied by the ratio of concentrations of RN to nutrient, corrected by a selectivity coefficient. Hydroponic experiments showed the validity of this assumption for root uptake of Cs and Sr and reported a selectivity coefficient around 1.0 for both. However, the application of this approach to soil-to-plant transfer raises some questions on which are the effective concentra- tions of RN and nutrient detected by the plant uptake mechanism. This paper describes the evaluation of two configurations of Bio- RUR, one which simplifies the soil as an homogeneous pool, and the other which considers that some concentration gradients develop around roots and therefore ion concentrations at the root surface are different from those of the bulk soil. The results show a good fit between the observed Sr transfer and the mechanistic simulations, even when a homogeneous soil is considered. On the other hand, Cs transfer is overestimated by two orders of magnitude if the development of a decreasing K profile around roots is not taken into account. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Radionuclides; Plant uptake mechanisms; Modelling 1. Introduction Soil-to-plant transfer of radionuclides is not only determined by the concentration of radionuclides in the soil so- lution, at least in the case of Cs (Shaw, 1992, 1993; Smolders et al., 1996) and Sr (Lembrechts et al., 1990; Veresoglou et al., 1995). It has empirically been established that the uptake of Cs by roots is largely affected by the concentration of K in the root medium (Menzel, 1954; Cline and Hungate, 1960; Shaw and Bell, 1989; Shaw 1992; Smolders et al., 1996), while root uptake of Sr is affected by Ca concentration (Menzel, 1954; Lembrechts et al., 1990; Veresoglou * Corresponding author. Tel.: þ34 934021462; fax: þ34 934112842. E-mail address: msauras@ub.edu (T. Sauras-Yera). 0265-931X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2007.10.013 Available online at www.sciencedirect.com Journal of Environmental Radioactivity 99 (2008) 864e871 www.elsevier.com/locate/jenvrad