Distribution of 226Ra, 232Th, and 40K in rice plant components and physico-chemical effects of soil on their transportation to grains

Radioactivity distribution and transfer factor (TF) in plants are crucial parameters used to assess radioactive contamination in the environment and its risks to humans. In this study, the activities of 226Ra, 232Th, and 40K were successfully measured via gamma-ray spectrometry on rice plant components (root, straw, husk, and grain) and on corresponding soil samples collected from paddy fields in Penang, Malaysia. Soil physico-chemical characteristics (pH, cation exchange capacity, electrical conductivity, organic matter, and soil texture) were also analyzed for their estimated effects on soil–grain TF. A major fraction of the total 226Ra and 232Th activities measured as 47% and 57%, respectively, were concentrated in the roots, whereas only about 9% and 8% were distributed in the grains, correspondingly. 40K activity accumulation was about 59% in the straw and 7% in the grains. Rice soil–grain TFs were observed in the ranges of (0.06–0.36) × 10−1 for 226Ra, (0.04–0.14) × 10−1 for 232Th, and (0.74–4.72) × 10−1 for 40K. Results showed that the selected radionuclide distributions in rice are dependent on component type, and their grain concentrations are not linearly related to their soil concentrations. These findings indicated that uptake predominantly depends on soil physico-chemical characteristics.