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

Abstract

In this investigation we evaluate the soil uptake of 137Cs and 40K by tropical plants and their consequent translocation to fruits, by calculating the soil-to-fruit transfer factors defined as Fv = [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 Fv 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. Fv ranged from 0.54 to 1.02 for 40K and from 0.02 to 0.06 for 137Cs. Maximum Fv 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 Fv as time increases. The agreement between the theoretical approach and the experimental values is satisfactory.