It was going to happen eventually - that the latest polonium scare would end up being tied to a different kind of radiation scare 40 years in the past.
Like a lot of people after the death of Alexander Litvinenko, I did a bit of a Google to get more familiar with a poison that is "a trillion times more toxic than cyanide". I vaguely recalled how the Curies gave the element its name but little else. References to smoking and polonium kept popping up - but with very little evidence of what researchers had actually said.
Polonium in cigarette smoke is something that has popped up about every ten years since the publication of a paper in the journal Science in early 1964. It's strange because very little in the way of new work actually seems to drive the stories about polonium in smoke.
The problem with the story of polonium and smoke is similar to the problem people have today with assessing the risk of polonium on planes and in hotels and sushi bars. That word "significant" keeps coming up and in relation to tiny numbers. The trouble is, the inability to visualise what tiny numbers mean lead people to the wrong conclusions. You can see the logic that Proctor is applying. Litvinenko was poisoned by a tiny amount of polonium. There is a tiny amount of polonium in cigarette smoke. There is, in fact, a tiny amount of polonium in the food we eat. Oh crap. We're in trouble.
Only kidding: there is a yawning gap between the numbers involved.
It's Robert Proctor, a professor of the history of science at Stanford University, who we can thank for raising the issue of polonium in tobacco once again. He wrote an opinion column, "Puffing on polonium", for the New York Times about a much larger source of polonium-210 than what is apparently available to shady hitmen. "The [tobacco] industry has been aware at least since the 1960s that cigarettes contain significant levels of polonium...about a quarter of a curie of one of the world’s most radioactive poisons is inhaled along with the tar, nicotine and cyanide of all the world’s cigarettes smoked each year. Pack-and-a-half smokers are dosed to the tune of about 300 chest X-rays," he wrote. It's that word "significant" again.
I wondered, if that is the case, and polonium could so easily be the cause of lung cancer, why are the references to it pretty much reserved to fringe sites on the Web? It turns out that, over the course of the last 40 years, no-one has been able to draw any firm conclusions. The only clue as to whether polonium is really a primary cause of lung cancer in smokers is the way that the research largely fizzled out 20 years ago. That would seem to make the answer to the question "is polonium in smoke the culprit behind lung cancer?" a no - if it was a promising line of research, people would have continued to go after it. But so much in this story is inconclusive, even where the polonium comes from.
The trail started in 1964. Working at the Harvard School of Public Health, researchers Edward Radford and Vilma Hunt uncovered a possible radioactive link between cigarette smoking and lung cancer: polonium-210. Radford and Hunt estimated that the smoke produced by a single cigarette had enough polonium-210 to emit 0.1picoCurie of radiation. That is about 100 million times lower than what is considered to be the lethal dose for humans if polonium-210 is inhaled.
A later study by Thomas Kelley of Bio-Research Consultants in Massachusetts, again published in Science estimated that around 0.03 to 0.04picoCurie found their way into smokers. For some reason, Proctor points to "secret" research carried out "using precision analytic techniques" by the American Tobacco Company in 1968 to come up with roughly the same figure of 0.04picoCurie.
Controversy raged between academics as to whether lung cancer could be ascribed to the radiation in cigarette smoke or the various other nasties - there are, after all, quite a few to choose from. Radford and Hunt claimed that the levels of polonium in the urine of three smokers were six times higher than those of non-smokers, but there was no direct link between emitters of alpha radiation and lung cancer in smokers. Even though the levels of polonium were higher in smokers, it was difficult to see how the amounts involved could provoke tumours unless the radiation were confined to key parts of the body, a theory that Radford and Hunt entertained.
The other question, asked a little more quietly, was where was the polonium coming from? In Science in July 1965, LP Gregory of the New Zealand National Radiation Laboratory reported the results of a survey of the amount of polonium-210 found in various types of leaf tobacco. Curiously, New Zealand had half the polonium content of American tobacco, and less than a third that of Rhodesian leaves. There were about 0.4 picoCurie per gram of polonium in the US tobacco, on average.
A 1984 document from Philip Morris indicated that the cigarettes you really wanted to avoid if you were worried about polonium-210 came from Central and South America - they contained twice as much as US makes.
After looking at Gregory's work TC Tso, Naomi Harley and LT Alexander at the US Department of Agriculture in Beltsville, Maryland and the Atomic Energy Commission decided to grow their own samples and found, in 1966, that most of the polonium and its precursors were absorbed from the soil. Although the researchers did not finger fertiliser as the source of the radiation there were clear differences in the content of polonium-210 and its radon-226 in the nutrients they used to grow the tobacco.
Some people thought there was a strong link between polonium and superphosphate fertilisers, although there was a problem with the theory. The case for superphosphate being the source was that the deposits mined for the fertiliser tended to be comparatively rich in uranium. It's the decay series of uranium that leads to polonium-210 and lead-210, which is often found in tobacco as well. It was a theory that attracted radiochemist Edward Martell.
In November 1974, TS Laszlo at Philip Morris wrote in favour of the idea of the company making a few thousand cigarettes from tobacco grown without superphosphate fertiliser at the request of radiochemist Edward Martell, who "appeared to be very eager to discuss his theory and findings in annoying and repetitive details". Martell claimed that the polonium originated in phosphates: Philip Morris considered, at least briefly, whether using tobacco grown without superphosphates might be a bit safer than the regular stuff for making gaspers. Later on, in the 1980s, they'd hatch a scheme to get chimps to smoke specially polonium-enriched cigarettes to try to work out whether they promoted cancers. However, it's not clear that the project got off the ground. The problem that many of the researchers found when trying to finger polonium as the prime carcinogen was that, even among heavy smokers, it was hard to find enough polonium. The only possible answer, if polonium were to blame, was if the element concentrated in key parts of the lung. The evidence there was inconclusive.
Among others, according to the documents released as the result of recent class actions, Philip Morris's scientists were also perplexed by the source of the polonium-210 - finding that superphosphates could not explain the presence of the element in tobacco alone.
Slowly, the trail of research into polonium and smoking ran cold - very little seems to exist after the mid-1980s from what I can find. It was just one of those bits of research that ran out of angles, but without concluding that polonium was unlikely to be the major source of cancers in smokers.
I can understand the anti-smoking lobby wanting to use radiation as a way to convince smokers they should give up. Yet, if it were that simple, the tobacco companies could have easily dealt with the issue - the reality is that smoking's role in cancer is much more complex. That is something that helped the tobacco companies for years, and now is the rope from which they will hang - there is nothing that can create a 'safe' cigarette.
Just imagine how pleased the tobacco suppliers might have been were radiation from polonium-210 the main culprit. It might have made the Stauffer Chemical Company rich, as that operation obtained a patent on a method to cut the polonium and lead content in tobacco tenfold. But, life is never that simple. Unfortunately, you are going to see a lot more claims about radioactive fags and their role in lung cancer. Just wait until they get started on the polonium in your food - all thanks to non-organic superphosphate fertilisers.