Abstract Background：Since the accident at Fukushima Daiichi Nuclear Power Station in March 2011, public concern about radiation hazards has been increasing in Japan. However, there is little information available on radioactive materials in tobacco smoke. This study was to investigate and report on polonium in tobacco smoke with a review of previous articles. Methods：Two words—“polonium” and “smoke” (or “cigarettes” or “tobacco”) were entered as search items in PubMed. A total of 70 articles, including nine review articles, were obtained. By investigating the
nine review articles as well as new articles (from the last five years), the article summarizes and discusses the toxicity and origin of polonium in tobacco and the relationships between lung cancer, polonium, and passive smoking. Results：No increase of articles on this topic was found after the Chernobyl disaster in 1986. The half-life of polonium-210 is 138.4 days, the longest of the polonium isotopes that exist in the natural world. The principal resource in which polonium-210 is found is food, especially fish. The isotope emits alpha rays and decays to a stable Pb-206. As alpha rays cannot penetrate the keratin layer of human skin, internal exposure is more significant than external exposure. Polonium-210 can be found in passive smoke as well, and reach the bronchopulmonary apparatus, shows up especially in the bifurcations of the segmental bronchi after being absorbed into the lung, where it emits alpha rays that induce carcinogenicity by DNA damage. Its carcinogenicity is 100 times greater than that of other types of radiation and is strengthened in association with other non-radioactive carcinogenic substances like tobacco-specific N-nitrosamine. There is evidence that in the last 40 years a histotype change in lung cancers has been noticed, shifting from squamous cell carcinoma to adenocarcinoma. According to internal documents of tobacco manufacturers, they have been aware of the presence of polonium-210 in smoke since 1960 but have concealed its existence intentionally. Conclusion：The fact that polonium-210 is found in tobacco smoke is very important but has not been widely noticed by mass media. Therefore, in Japan, the measurement and spreading of awareness about polonium-210 exposure is an urgent task.