Soil to tobacco component transfer factors for natural radionuclides K-40, Ra-226, and Th-232 and the risk assessment of tobacco leaf in smoking

This study determined the activity concentrations and corresponding transfer factors (TF) of K-40, Ra-226, and Th-232 in three tobacco components (root, stem, and leaf). The radiation hazard index parameters were assessed for the tobacco leaf. The activity concentrations in the soil were 589-762, 32-43, and 49-59 Bq kg-dw(-1) (dry weight) for K-40, Ra-226, and Th-232, respectively. The average activity concentrations of K-40, Ra-226, and Th-232 were 447, 5.41 and 5.69 Bq/kg-dw for the root, 670, 9.64 and 7.61 Bq kg-dw(-1) for the stem, and 793, 6.79 and 6.15 Bq kg-dw(-1) for the leaf, respectively. The TF values were 0.42-1.42, 0.10-0.49 and 0.06-0.23 for K-40, Ra-226, and Th-232, respectively. The stem and leaf K-40 TF values were significantly higher than the root values. The stem Ra-226 TF values were significantly higher than the root values. The Ra-226 and Th-232 activity concentrations and TFs of tobacco components had a significant positive correlation. Based on the activity concentrations of the tobacco leaves, the annual inhalation effective dose to the lungs for an adult smoker was 0.32-0.81 mSv y(-1) (average 0.60 mSv y(-1)). The Excess Lifetime Cancer Risk (ELCR) caused by smoking was an average of 2.39 x 10(-3).