Soil-to-plant transfer factors of natural radionuclides (226Ra and 40K) in selected Thai medicinal plants

A soil-to-plant transfer factor (TF) is an important parameter that could be used to estimate radionuclides levels in medicinal plants. This work reports concentrations of natural radionuclides (Ra-226 and K-40) and TFs in six Thai medicinal plants grown in central Thailand using an HPGe gamma ray spectrometer. Either root, leaf, or flower parts of each medicinal plant were selected for use in the investigation according to their practical uses in traditional medicine. The results showed that due to K being essential in plants, K-40 had higher arithmetic means of activity concentrations and geometric means of TFs (geometric standard deviations in parentheses) of 610 +/- 260 Bq kg(-1) dry weight (DW) and 2.0 (1.4), respectively, than Ra-226, which had the activity concentrations and TFs of 4.8 +/- 2.6 Bq kg(-1) DW and 0.17 (1.8), respectively. The results also showed that the leaves of medicinal plants had higher activity concentrations and TFs than root and flower parts, probably due to higher metabolic activities in leaves. Furthermore, there was good agreement between the results from the current work and other similar reports on medicinal plants. The information obtained from this work could strengthen knowledge of natural radionuclides in plants and particularly increase available TF data on Thai medicinal plants.