[Tobacco Smoke as Another Source of Radiation]
Actual cause of the lung cancer ,associated with cigarette smoking, is Radioactivity ??
Per [Tobacco Smoke | Radiation Protection | US EPA]:
(more at http://www.epa.gov/radiation/sources/tobacco.html )
Radioactivity may be one of the key factors in lung cancer among smokers....†.
The tobacco leaves used in making cigarettes contain radioactive material, particularly lead-210 and polonium-210. ...
The radionuclide content of tobacco leaves depends [on fertilizer use]...
"... phosphate fertilizers, favored by the tobacco industry,
contain radium and its decay products (including lead-210 and polonium-210).
When phosphate fertilizer is spread on tobacco fields year after year,
the concentration of lead-210 and polonium-210 in the soil rises... ..."
...So what about other plants (foods)?
† See http://www.epa.gov/radiation/sources/tobacco.html#footnote
See also:
http://www.epa.gov/radiation/understand/perspective.html
and
http://www.epa.gov/radiation/topics.html.