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Radionuclide transfer factor from soil to plant in tropical and subtropical environments: statistical analysis for different plant/soil combinations
VELASCO, R. H.; JURI AYUB, J.; SANSONE, U.
Conferencia; International Conference on Environmental Radioactivity; 2007
Soil to plant transfer factor (TF) is recognized as a key parameter in assessment of human exposure to radionuclides via the food chain. For each particular radionuclide, TF exhibits pronounced variability; differences of two orders of magnitude could be observed between samples obtained at similar sites and for the same plant. Consequently, it is desirable to dispose enough replicated TF values to acquire reliable average values and the associated error for their adequate application in radiological assessment models. In the present study, more than 2700 TF values from terrestrial ecosystems belonging lo tropical and subtropical environments were analysed with the end to determine general patterns or behaviour tendencies. The study was carried out in the framework of an IAEA research agreement with the GEA-IMASL with the purpose of contributing to the new version of the IAEA - Handbook of Parameter Value for Predicting of Radionuclide transfer in temperate environment. Clustering of TF values was performed considering the different combinations of identified soil and plant groups. Different radionuclides were considered, mostly radioisotopes of Cs and Sr but also of Mn, Zn, Po, Pb, Th, U and K. For each cluster a descriptive statistical analysis was carried out including the calculus of mean, geometric mean, standard deviation geometric standard deviation and range. When the number of available TF values is significant, we found that TF statistical distribution can be approximated by a lognormal distribution. Consequently, for the TF comparative analysis among clusters the geometric mean value was used. In subtropical environments TF values for 137Cs and 90Sr are mostly less than 1. In tropical environments, frequently, TF for these radionuclides are greater than 1 and values greater than 5 are occasionally found.