The alpha-radioactive
polonium 210 (Po-210) is one of the most powerful carcinogenic agents of tobacco
smoke and is responsible for the histotype shift of
lung cancer from squamous cell type to
adenocarcinoma. According to several studies, the principal source of Po-210 is the
fertilizers used in tobacco plants, which are rich in
polyphosphates containing radio (Ra-226) and its decay products, lead 210 (Pb-210) and Po-210. Tobacco leaves accumulate Pb-210 and Po-210 through their trichomes, and Pb-210 decays into Po-210 over time. With the combustion of the cigarette
smoke becomes radioactive and Pb-210 and Po-210 reach the bronchopulmonary apparatus, especially in bifurcations of segmental bronchi. In this place, combined with other agents, it will manifest its carcinogenic activity, especially in patients with compromised mucous-ciliary clearance. Various studies have confirmed that the radiological risk from Po-210 in a smoker of 20 cigarettes per day for a year is equivalent to the one deriving from 300 chest X-rays, with an autonomous oncogenic capability of 4
lung cancers per 10000 smokers. Po-210 can also be found in passive
smoke, since part of Po-210 spreads in the surrounding environment during tobacco combustion. Tobacco manufacturers have been aware of the alpha-radioactivity presence in tobacco
smoke since the sixties.