Soil-to-plant transfer factors of 238U and 232Th in rice from Ezillo paddy fields, Ebonyi State, Nigeria

Abstract

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, 238U and 232Th, 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 238U and 232Th 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 238U and 232Th respectively. The overall geometric means and geometric standard deviations of the TF estimated in field 1 were respectively 0.22 and 1.52 for 238U and 0.18 and 4.21 for 232Th (soil,0-4cm); 0.43 and 1.80 for 238U and 0.18 and 3.79 for 232Th (soil,4-8cm) whereas in field 2 the values were respectively 0.12 and 2.62 for 238U and 0.06 and 4.15 for 232Th (soil,0–4cm); 0.11 and 1.85 for 238U and 0.12 and 4.15 for 232Th (soil,4-8cm). The nuclide concentrations in the rice and the present TFs are within the ranges of values in the literature.