It's also a naturally occuring substance in tobacco (taken up from the soil). That doesn't preclude cigarettes from being a convenient vehicle for the delivery of a lethal amount...
I know.
Polonium-210, which emits alpha particles, is a natural contaminant of tobacco. For an individual smoking two packages of cigarettes a day, the radiation dose to bronchial epithelium from Po210 inhaled in cigarette smoke probably is at least seven times that from background sources, and in localized areas may be up to 1000 rem or more in 25 years...
Polonium is also present in chewing tobacco, benignly referred to as smokeless tobacco....
http://www.webspawner.com/users/radioactivethreat/index.html