Our results show that 210Po and 210Pb activity in tobacco of conventional cigarettes sold in Switzerland, the 1R6F reference cigarette and Heets® cigarette, are very similar for all brands and within the range of 210Po activities determined in other similar studies.9, 22 In addition, our results show that 210Po and 210Pb are in secular radioactivity equilibrium in tobacco fillers. 210Pb is less radiotoxic than 210Po due to the emission of a low energy β-particle; however, its long physical half-life of 22.3 years (compared to 138.4 days for 210Po) makes its presence in lungs a health hazard because it will continually produce the very radiotoxic bismuth-210 (210Bi; high energy β-particle > 1MeV) and 210Po radionuclides. Consequently, we may assume that the presence of 210Pb in the mainstream smoke and subsequently in the lungs will induce deleterious impact on health.
Conventional cigarettes transfers a fraction of 13.6% of the total 210Po cigarette activity in the mainstream smoke. This fraction is within the range of other studies, in which a percentage of transfer between 6% and 20% has been determined22, 23 and very close to the most recent study24 using a smoking machine to determine 210Po and 210Pb in the mainstream smoke (13% for 210Po). We also found that a fraction of 7% of total 210Pb is transferred to the mainstream smoke. This percentage is very similar to the 8% value found by Schayer et al.24 Thus, our results back up most of the data in the literature on conventional cigarettes and radioactive concentrations of 210Pb and 210Po. Building on this, our study presents the first data on the IQOS® system and the 210Po and 210Pb radiotoxic components in smoke aerosol. We found that the Heets® cigarette contains the same 210Po and 210Pb activities than the other conventional cigarette brands sold in Switzerland. However, the IQOS® system transfers only 2% of the total 210Po activity from a Heets® cigarette and about 1.5% of its 210Pb activity to the mainstream aerosol. In this respect, IQOS® seems to be a worthy option to users regarding their exposure to radiotoxic 210Po and 210Pb. Nevertheless, our study on the homogeneous heating of tobacco establishes also that the percentage loss of 210Po and 210Pb from tobacco are equivalent, regardless the conventional cigarette brand, 1R6F reference cigarette or Heets® cigarette. These results demonstrate that IQOS® system heats only a small fraction of the tobacco content at 300°C, evaluated here at 15%. This fraction represents clearly the tobacco fraction in close contact with the electrical resistance. In this respect, the IQOS® system may not deliver a satisfactory pulse of nicotine to users, leading to an over-consumption of Heets® cigarettes, with similar health deleterious effect than conventional cigarettes. In our study, the smoking regime used to generate emissions from IQOS® was the HCI regime used for conventional cigarettes. However, studies in IQOS® users observed a larger mean puff volume (around 60-65 mL) and a shorter puff intervals (about 10-12 s) compared to the HCI standardized regime (puff volume of 55 mL and puff interval of 30 s).25–27 This use-behavior difference in IQOS® smoker influences the aerosol generated, and might underestimate user exposure to 210Po and 210Pb.26 Phillips-Waller et al. compared HnB IQOS®, Juul®, E-cigarette and conventional smoking in their ability to deliver nicotine and rated the satisfaction of the smoker after overnight abstinence of smoking and vaping.28 Results show that IQOS® delivered less nicotine than conventional smoking and received less favorable ratings than Juul® (effect on the urge to smoke), which may be correlated with very partial heating of the tobacco. In addition, Meehan-Atrash et al. found nearly no free-base nicotine in aerosol from HnB IQOS® using a sophisticated 1H-NRM method.29 However, a greater fraction of free-base nicotine (αfb) is associated with a faster nicotine absorption kinetic and physiological response. The very low concentrations of free-base nicotine in IQOS® aerosol confirmed the limited absorption of nicotine compared to conventional cigarettes, and thus the assumption to consume more Heets® to obtain a satisfying dose of nicotine.
For members of the public, there is no surprise that tobacco products contain toxic chemicals. However, most individuals are not aware that tobacco products contain radioactive particles, which lodge in the lungs when inhaled. As radioactivity is most feared,30, 31 this knowledge could be an incentive for smoking cessation. The WHO Framework Convention on Tobacco Control recommends information on smoking associated risks, such as information campaigns, as a key measure to reduce tobacco demand.32 A recent systematic review reports little evidence and no significant effect of biomedical risk assessment on smoking cessation33. However, showing to smokers that they had developed atherosclerotic plaques34, or motivational intervention with feedback on a combination of, including spirometry, exhaled carbon monoxide and pulmonary symptoms discussion, have increased significantly the smoking cessation rate.35 In a similar way, we can expect that providing smokers with their personal level of urine 210Po radioactivity level, together with a relevant explanation and a motivational intervention, will increase their motivation for smoking cessation. This is particularly important in view of the significant increase in HTP users during the Covid-19 pandemic, as observed by Gallus et al. in a very recent study in Italy.36 Work is in progress in our laboratory and hospital to study the role of fear of radioactivity in tobacco products (210Po) in the smoking cessation rate.
Our results confirmed previous studies showing the presence of 210Po and 210Pb in the mainstream of tobacco smoke. They also demonstrated that the mainstream smoke of the IQOS® system contains 210Po and 210Pb, although at lower level compared to conventional smoking. This lower percentage of 210Po and 210Pb in the smoke is related to the small fraction of tobacco really heated at a temperature of 300°C and not to specific counter-measures, such as tobacco acid-washing, associated with the 210Po in tobacco concern. Consequently, tobacco smoke from conventional and Heets® cigarettes commit an effective radiation dose to the lung of users that may further result in cancer. Providing that knowledge of radioactivity induced by tobacco products is effective to increase motivation to quit among smokers, this intervention could be cost-effective and have a major public health impact.