Soil-to-plant transfer factors of 238U and 232Th 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-238 and Th-232, 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-238 and Th-232 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-238 and Th-232 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-238 and 0.18 and 4.21 for Th-232 (soil(,0-4 cm)); 0.43 and 1.80 for U-238 and 0.18 and 3.79 for Th-232 (soil(,4-8 cm)) whereas in field 2 the values were respectively 0.12 and 2.62 for U-238 and 0.06 and 4.15 for Th-232 (soil(,0-4 cm)); 0.11 and 1.85 for U-238 and 0.12 and 4.15 for Th-232 (soil(,4-8 cm)). The nuclide concentrations in the rice and the present TFs are within the ranges of values in the literature.

Automated summary

The study examined the levels of U-238 and Th-232 in soil of Ezillo paddy fields, as well as their transfer and accumulation in rice grains. The concentrations of these radionuclides in soil were higher than the worldwide average, while their levels in rice were below the global average. The transfer factors of radionuclides across different soil depths were within the ranges reported in literature.