Radioactivity of cigarettes and the importance of (210)Po and thorium isotopes for radiation dose assessment due to smoking

Tobacco and tobacco smoke are very complex mixtures. In addition to various chemical and organic compounds they also contain natural radioactive elements (radionuclides). In this work, the natural radionuclide activity concentrations ((234)U, (238)U, (228)Th, (230)Th, (232)Th, (226)Ra, (210)Pb and (210)Po) of nine different cigarette samples available on the Slovenian market are reported. In addition to (210)Po, the transfer of thorium isotopes from a cigarette to a smoker's body and lungs have been determined for the first time. Cigarette smoke and exhaled air from smokers' lungs were collected from volunteer smokers (C-4 brand) to determinate what quantity of (210)Po and thorium isotopes is transferred from the tobacco to the smoker's lungs. Cigarette ash and smoked filters were also collected and analysed. Among the determined isotopes, (210)Pb and (210)Po showed the highest activity concentrations. During the smoking of one cigarette approximately 22% of (210)Po (and presumably its predecessor (210)Pb), 0.6% of (228)Th, 24% of (230)Th, and 31% of (232)Th are transferred from the cigarette and retained in the smoker's body. The estimated annual effective dose for smokers is 61 μSv/year from (210)Po; 9 μSv/year from (210)Pb; 6 μSv/year from (228)Th; 47 μSv/year from (230)Th, and 37 μSv/year from (232)Th. These results show the importance of thorium isotopes in contributing to the annual effective dose for smoking.