UCLA researchers who analyzed dozens of previously unexamined internal documents from the tobacco industry say tobacco companies developed “deep and intimate” knowledge about the cancer-causing potential of radioactive alpha particles in cigarette smoke but deliberately kept it from the public for more than four decades. The researchers wrote a paper about their findings that was published online on 27 September in the peer-reviewed journal Nicotine & Tobacco Research.

Although this is not the first study to reveal that big tobacco knew quite a lot about radioactivity in cigarette smoke and kept that knowledge hidden, it adds to the weight of research on the subject. It could also be timely in the light of recent new legislation that gives the regulators more clout to make tobacco companies remove radioactive substances from their tobacco products. The idea that cigarettes may be radiation hazards could also have a considerable public health impact.

The authors write that the documents reveal “the industry was well aware of the presence of a radioactive substance in tobacco as early as 1959”.

The documents that the researchers examined came to light in 1998 as the result of a legal settlement, the landmark 1998 Tobacco Master Settlement Agreement. They show that the industry was aware of radioactivity in cigarettes five years earlier than previously thought.

The documents also reveal, say the authors, that the tobacco companies, concerned about the link to lung cancer, began detailed studies on the potential effect of radioactivity on smokers as early as the 1960s.

“Furthermore, the industry was not only cognizant of the potential ‘cancerous growth’ in the lungs of regular smokers, but also did quantitative radiobiological calculations to estimate the long-term lung radiation absorption dose of ionizing alpha particles emitted from cigarette smoke,” they write.

First author Hrayr S. Karagueuzian, an adjunct professor of cardiology who conducts research at University of California Los Angeles’ (UCLA’s) Cardiovascular Research Laboratory, part of the David Geffen School of Medicine at UCLA, told the press that:

“They knew that the cigarette smoke was radioactive way back then and that it could potentially result in cancer, and they deliberately kept that information under wraps.”

“Specifically, we show here that the industry used misleading statements to obfuscate the hazard of ionizing alpha particles to the lungs of smokers and, more importantly, banned any and all publication on tobacco smoke radioactivity,” he added.

Alpha particles do not dissolve: they bind with resins in the cigarette smoke and instead of dispersing in the lung tissue, they get stuck and collect at the branching off points of the airways forming what Karagueuzian calls “hot spots”. Studies of lung autopsies of smokers who died of lung cancer have shown that tumors grew from locations where the hot spots reside.

Karagueuzian said we used to think lung cancer was only caused by the chemicals in cigarettes:

“But the case of the these hot spots, acknowledged by the industry and academia alike, makes a strong case for an increased probability of long-term development of malignancies caused by the alpha particles. If we’re lucky, the alpha particle-irradiated cell dies. If it doesn’t, it could mutate and become cancerous,” he explained.

The radioactive substance that Karagueuzian and colleagues say the industry knew about in 1959 was identified in 1964 as polonium-210, an isotope of polonium, a rare, highly radioactive and unstable element: all its isotopes are radioactive. Polonium -210 emits alpha particles which can cause cancer.

Karagueuzian said you will find this isotope in all commercially available domestic and foreign cigarette brands. It gets into the cigarettes from two sources: as a byproduct of the decay of naturally occurring radon gas in the atmosphere that the tobacco plant absorbs as it grows, and from the high-phosphate chemical fertilizers that the tobacco growers use. Smokers then inhale it into their lungs when they smoke the cigarettes.

The authors describe how tobacco companies became increasingly worried about the potential risk of cancer from inhaling polonium-210. They outline the research their scientists performed to find out how the isotope might affect smokers: one study even measured how much total radiation would enter the lung of a smoker who smoked two packs a day for twenty years.

Using their own independent calculations and data from other published industry and academic sources, the authors found their figures were very similar to those that the tobacco companies arrived at nearly 25 years earlier.

Using figures from the Environmental Protection Agency (EPA) on lung cancer risk from being exposed to radon gas in homes where that is a problem, they calculated the estimated lung cancer risk from exposure to a similar level of alpha particle radiation as found in the cigarettes.

Karagueuzian explained:

“The gathered data from the documents on the relevant radiobiological parameters of the alpha particles – such as dose, distribution and retention time – permitted us to duplicate the industry’s secretly estimated radiation absorbed dose by regular smokers over a 20- or 25-year period, which equaled 40 to 50 rads.”

“These levels of rads, according to the EPA’s estimate of lung cancer risk in residents exposed to radon gas, equal 120 to 138 deaths per 1,000 regular smokers over a 25-year period,” he added.

The paper also reveals other things that the tobacco companies hid, such as refusing to use a method called acid-wash discovered in 1959 and then another in 1980, that could have removed polonium-210 from tobacco, even though they knew about the lung cancer risk.

Acid wash could have removed the radioisotope from the tobacco leaves, and although the companies used cost and possible environmental impact as reasons not to take up the method, the researchers say they found evidence suggesting there was another reason:

“The industry was concerned that the acid media would ionize the nicotine, making it more difficult to be absorbed into the brains of smokers and depriving them of that instant nicotine rush that fuels their addiction,” said Karagueuzian.

He said the study makes a strong case for the US Food and Drug Administration to make the tobacco companies remove alpha particles from tobacco products. This is now possible because the new Family Smoking Prevention and Tobacco Control Act, passed in June 2009, gives the FDA wider powers to regulate and remove harmful substances (except nicotine) from tobacco products.

“Such a move could have a considerable public health impact, due to the public’s graphic perception of radiation hazards,” said Karagueuzian.

Funds from the University of California Tobacco-Related Disease Research Program paid for the study, and the authors report no conflicts of interest.

Written by Catharine Paddock PhD