br Living organisms are continuously exposed to background i
Living organisms are continuously exposed to background ionizing radiation emitted from either natural or man-made radiation sources. Effects from radiation usually fall under the category of stochastic effects (Flynn and Theodore,
2002). Cancer and genetic effects are the two most common possible negative effects linked with exposure to radiation.
The great interest expressed worldwide for the study of the relation of smoking with cancer, particularly lung can-cer, has led to extensive surveys and investigations in many countries. In general, the toxicity in tobacco was consid-ered earliest mainly due to the presence of chemi-toxins like nicotine, tars, aromatic hydrocarbons, sterols and many other materials leading to mutagenicity and carcinogenicity (Mahabir et al., 2010). Although, there may be other cancer inducing mechanisms in humans, one of the causative fac-tors is radioactive elements present in tobacco 936563-96-1 used for the manufacture of cigarettes.
Like all soils, the soil in which tobacco plants are grown is radioactive (Grupen, 2010). In addition, tobacco plants are frequently fertilized with phosphate fertilizers to ful-fil their requirement of nutrients, which may significantly increase the radionuclide content in soil. This is because the phosphates used for the manufacturing of phosphate fertilizers are derived from a rock mineral named ‘apatite’ containing high levels of uranium and other radioactive ele-ments (Abbady, 2005). The most important radionuclides are radium, thorium and their decay products, which can easily transfer from soil to plants through root uptake. In the radium decay chain, the radioactive gas 222Rn occurs as well as the relatively long-lived radioisotopes 210Pb and
210 Po. These radionuclides can accumulate on the surfaces of tobacco leaves as the plant grows, and can remain their throughout the cigarette-manufacturing process. Due to the presence of the natural radionuclides in fresh tobacco leaves, in an amount exceeding that normally found in general foods for human usage, cigarette smoking is one practice of radiological concern (Kilthau, 1996). The con-tents of naturally occurring radioisotopes in manufactured tobacco vary with the source. The difference may result from production locality, culture and curing (Shousha and Ahmad, 2012). Therefore, continuous measurement of natu-ral radioactivity concentration and calculating gamma dose rates in tobacco leaves and their derivative products are very important issues in order to evaluate accompanying radiological hazards.
The purpose of this paper is first, to determine the activity concentrations of naturally occurring radionuclides 226 Ra (238U), 232Th and 40K as well as the artificial radionu-clide 137Cs in different brands of tobacco leaves before cigarette production by means of gamma-ray spectrometry. Second, to estimate the annual effective dose received from cigarette tobacco and the excess lifetime cancer risk caused by gamma-radiation exposure.
Table 1 Activity concentrations in different types of tobacco leaves (Bq kg−1 ).
Materials and methods
In this work, four brands of imported tobacco plants (leaves) commonly used in the manufacture of cigarettes in Algeria, commercially named: Basma (TAB1) type from Greece, Burley (TAB2) and Havane (TAB3) brands from Italy, and the last one Burley (TAB4), which is from Brazil, were examined for their radioactivity content using gamma-ray spectroscopy. At the Chrono-Environnement lab-oratory, the collected samples were dried at a temperature of 40 ◦ C, ground and mixed to obtain a homogeneous mixture, and then were packed and sealed in cylindri-cal polyethylene containers of 50 cm3 (SG50) for four weeks before measuring, in order to assure the secu-lar equilibrium between radium and thorium, and their progenies.
For qualitative identification as well as quantitative determination of the specific activity of gamma-emitting radionuclides present in tobacco samples, a high-resolution gamma-ray spectrometer equipped with a planar BEGe (Broad Energy Germanium) detector (Canberra, model BE 3825) was used. The system has a relative efficiency of 20% and an energy resolution (FWHM) of 0.38 keV at 5.9 keV, 0.628 keV at 122 keV and 1.724 keV at 1332.5 keV. The detec-tor was connected to a Digital Signal Analyser (DSA-LX) Unit (16K channel signal analyser, V1.0) from Canberra. It is shielded with 15 cm of lead (including 2 cm made of archae-ological lead) to reduce the contribution of environmental radioactivity to its background. The lead shielding was sur-rounded with an inner layer of copper (0.2 cm thick) to reduce the contribution from Pb X-rays. The control of the acquisition parameters and the analysis of the collected spectra are carried out using GENIE-2000 computer software (Canberra, V3.3).