Commentary to the paper Assessment of annual effective dose from natural radioactivity intake through wheat grain produced in Faisalabad, Pakistan

Abstract

Tufail et al. [1] studied and reported the concentrations of naturally occurring radionuclides (K, Ra and Th) in wheat grains. The method that was used was gamma-ray spectroscopy. Determining the activity concentration of Th by gamma-ray spectroscopy is, however, not possible. The two gammas from Th (63.8 and 141 keV) exhibit very low intensities (0.26 and 0.02%, respectively) and cannot hence be separated from the background using the set-up described in the paper. It is, hence, probable that the authors used the gammas from thorium series radionuclides of Ac, Pb or Tl. The activity of Ac follows that of Ra whereas the activity the latter two that of Th (and/or Ra). In short, they did not measure Th. The authors listed the activity concentrations of Th in wheat reported by e.g. Scheibel et al. [2] and PieterzakFlies et al. [3] and found that ‘‘activity values for K and Th in Indian wheat grain samples are quite comparable to that of studied samples’’. This is true with respect to Scheibel et al. [2], who employed the same erroneous method in analyzing Th as the authors did. The survey carried out by Pieterzak-Flies et al. [3] is, however, rigorous and the analyzing methods used are correct. The authors failed to recognize the activity concentration reported by Pieterzak-Flies et al. [3] was expressed as mBq kg, not as Bq kg. Market basket study of K, U and Th in foods sold in Pakistan has been carried out previously by Akhter et al. [4]. The ICP-MS method used for determining Th in this study was correct and the reported values were in-line with e.g. values compiled in UNSCEAR 2000. The effective dose to Pakistani adult population from Th from all food was 0.8 lSv a which is in gross contrast to the value reported by Tufail et al. [1] which was 43.1 lSv a from wheat consumption only. I would like to point out that this commentary also applies to several other papers on this topic (that I find fruitless to list here). Regrettably, it is a common mistake to assume full equilibrium of natural decays series’ radionuclides in biological samples, such as food. Radium uptake by vegetation is much more efficient than that of actinoids. This applies also to intake by livestock. Caution must therefore be exercised when calculating results of the natural decay series.