Soil-to-plant transfer factors of U and Th in rice from Ezillo paddy fields, Ebonyi State, Nigeria.

The uptake of radionuclides by plants and their subsequent relocation to the human body through ingestion is one major pathway of human internal exposure. Thus, the present study was conducted to examine the levels of natural radionuclides, U and Th, in soil of Ezillo paddy fields (field 1 and field 2) at depths 0-4 cm and 4-8 cm, their transfer and accumulation in rice grains. The mean concentrations of both radionuclides in the soil were clearly greater than the UNSCEAR estimated worldwide average while that of the rice with values of 11.7 ± 4.3 and 3.0 ± 1.3 Bq/kg in field 1 and 8.5 ± 4.2 and 4.3 ± 1.6 Bq/kg in field 2 for U and Th respectively, were well below the worldwide average. The radionuclide transfer factors (TFs) across both depths ranged from 0.03 to 0.67 and 0.01 to 1.20 for U and Th respectively. The overall geometric means and geometric standard deviations of the TF estimated in field 1 were respectively 0.22 and 1.52 for U and 0.18 and 4.21 for Th (soil); 0.43 and 1.80 for U and 0.18 and 3.79 for Th (soil) whereas in field 2 the values were respectively 0.12 and 2.62 for U and 0.06 and 4.15 for Th (soil); 0.11 and 1.85 for U and 0.12 and 4.15 for Th (soil). The nuclide concentrations in the rice and the present TFs are within the ranges of values in the literature.