This is an article from 2006 that I found while trying to research the actual ingredients in cigarettes. Robert N. Proctor writes in the New York Times:
When the former KGB agent Alexander V. Litvinenko was found to have been poisoned by radioactive polonium 210, there was one group that must have been particularly horrified: the tobacco industry.
The industry has been aware at least since the 1960s that cigarettes contain significant levels of polonium. Exactly how it gets into tobacco is not entirely understood, but uranium “daughter products” naturally present in soils seem to be selectively absorbed by the tobacco plant, where they decay into radioactive polonium.
High-phosphate fertilizers may worsen the problem, since uranium tends to associate with phosphates. In 1975, Philip Morris scientists wondered whether the secret to tobacco growers’ longevity in the Caucasus might be that farmers there avoided phosphate fertilizers.
How much polonium is in tobacco? In 1968, the American Tobacco Company began a secret research effort to find out. Using precision analytic techniques, the researchers found that smokers inhale an average of about .04 picocuries of polonium 210 per cigarette. The company also found, no doubt to its dismay, that the filters being considered to help trap the isotope were not terribly effective. (Disclosure: I’ve served as a witness in litigation against the tobacco industry.)
A fraction of a trillionth of a curie (a unit of radiation named for polonium’s discoverers, Marie and Pierre Curie) may not sound like much, but remember that we’re talking about a powerful radionuclide disgorging alpha particles — the most dangerous kind when it comes to lung cancer — at a much higher rate even than the plutonium used in the bomb dropped on Nagasaki. Polonium 210 has a half life of about 138 days, making it thousands of times more radioactive than the nuclear fuels used in early atomic bombs.
Read More in the New York Times