Tobacco companies have known for 40 years that tobacco contains radioactive polonium-210 but never disclosed their research to the public after failing to find a way to remove the substance from cigarettes, The Age reported Sept. 7.

"Documents show that the major transnational cigarette manufacturers managed the potential public-relations problem of PO-210 in cigarettes by avoiding any public attention to the issue," according to a new study.

"The internal debate, carried on for the better part of a decade, involved most cigarette manufacturers and pitted tobacco researchers against tobacco lawyers. The lawyers prevailed," said Monique Muggli, a researcher at the Mayo Clinic and one of the study authors. "Internal Philip Morris documents suggest that as long as the company could avoid having knowledge of biologically significant levels of PO-210 in its products, it could ignore PO-210 as a possible cause of lung cancer."

The polonium-210 found in cigarettes comes from high-phosphate fertilizers used to grow tobacco plants; experts say that smoking a pack and a half of cigarettes daily exposes smokers to radiation equivalent to getting 300 chest x-rays annually.

Polonium-210 is the same substance used to fatally poison Russian dissident Alexander Litvinenko in 2006.

The study authors recommended that cigarette packs include a warning that cigarettes are a major source of radiation exposure. Research suggests that the polonium-210 found in cigarettes causes 1 percent of all lung cancer cases in the U.S.

The study was published in the September 2008 issue of the American Journal of Public Health.