Polonium in cigarette smoke and radiation exposure of lungs

Polonium (Po), the most volatile of naturally-occurring radionuclides in plants, was analysed in three common brands of cigarettes produced in Portugal. The analyses were carried out on the unburned tobacco contained in cigarettes, on the ashes and butts of smoked cigarettes and on the mainstream smoke. Po in tobacco displays concentrations ranging from 3 to 37 mBq g, depending upon the cigarette brand. The Po activity remaining in the solid residue of a smoked cigarette varied from 0.3 to 4.9 mBq per cigarette, and the Po in the inhaled smoke varied from 2.6 to 28.9 mBq. In all brands of cigarettes tested, a large fraction of the Po content is not inhaled by the smoker and it is released into the atmosphere. Part of it may be inhaled by passive smokers. Depending upon the commercial brand and upon the presence or absence of a filter in the cigarette, 5 to 37 % of the Po in the cigarette can be inhaled by the smoker. Taking into account the average Po in surface air, the smoker of one pack of twenty cigarettes per day may inhale 50 times more Po than a non smoker. Cigarette smoke contributes with 1.5 % to the daily rate of Po absorption into the blood, 0.39 Bq d, and, after systemic circulation it gives rise to a whole body radiation dose in the same proportion. However, in the smoker the deposition of Po in the lungs is much more elevated than normal and may originate an enhanced radiation exposure. Estimated dose to the lungs is presented and radiobiological effects of cigarette smoke are discussed.