Variability of 137Cs and 40K soil-to-fruit transfer factor in tropical lemon trees during the fruit development period

In this investigation we evaluate the soil uptake of Cs-137 and K-40 by tropical plants and their consequent translocation to fruits, by calculating the soil-to-fruit transfer factors defined as F-v = [concentration of radionuclide in fruit (Bq kg(-1) dry mass)/concentration of radionuclide in soil (Bq kg-1 dry mass in upper 20 cm)]. In order to obtain F, values, the accumulation of these radionuclides in fruits of lemon trees (Citrus limon B.) during the fruit growth was measured. A mathematical model was calibrated from the experimental data allowing simulating the incorporation process of these radionuclides by fruits. Although the fruit incorporates a lot more potassium than cesium, both radionuclides present similar absorption patterns during the entire growth period. F-v ranged from 0.54 to 1.02 for K-40 and from 0.02 to 0.06 for Cs-137. Maximum F-v values are reached at the initial time of fruit growth and decrease as the fruit develops, being lowest at the maturation period. As a result of applying the model a decreasing exponential function is derived for F-v as time increases. The agreement between the theoretical approach and the experimental values is satisfactory. (C) 2011 Elsevier Ltd. All rights reserved.