Puffing on Polonium
By ROBERT N. PROCTOR
WHEN the former K.G.B. agent Alexander V. Litvinenko was found to have been poisoned by radioactive polonium 210 last week, there was one group that must have been particularly horrified: the tobacco industry.
The industry has been aware at least since the 1960s that cigarettes contain significant levels of polonium. Exactly how it gets into tobacco is not entirely understood, but uranium “daughter products” naturally present in soils seem to be selectively absorbed by the tobacco plant, where they decay into radioactive polonium. High-phosphate fertilizers may worsen the problem, since uranium tends to associate with phosphates. In 1975, Philip Morris scientists wondered whether the secret to tobacco growers’ longevity in the Caucasus might be that farmers there avoided phosphate fertilizers.
How much polonium is in tobacco? In 1968, the American Tobacco Company began a secret research effort to find out. Using precision analytic techniques, the researchers found that smokers inhale an average of about .04 picocuries of polonium 210 per cigarette. The company also found, no doubt to its dismay, that the filters being considered to help trap the isotope were not terribly effective. (Disclosure: I’ve served as a witness in litigation against the tobacco industry.)
A fraction of a trillionth of a curie (a unit of radiation named for polonium’s discoverers, Marie and Pierre Curie) may not sound like much, but remember that we’re talking about a powerful radionuclide disgorging alpha particles — the most dangerous kind when it comes to lung cancer — at a much higher rate even than the plutonium used in the bomb dropped on Nagasaki. Polonium 210 has a half life of about 138 days, making it thousands of times more radioactive than the nuclear fuels used in early atomic bombs.
We should also recall that people smoke a lot of cigarettes — about 5.7 trillion worldwide every year, enough to make a continuous chain from the earth to the sun and back, with enough left over for a few side-trips to Mars. If .04 picocuries of polonium are inhaled with every cigarette, 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.
Is it therefore really correct to say, as Britain’s Health Protection Agency did this week, that the risk of having been exposed to this substance remains low? That statement might be true for whatever particular supplies were used to poison Mr. Litvinenko, but consider also this: London’s smokers (and those Londoners exposed to secondhand smoke), taken as a group, probably inhale more polonium 210 on any given day than the former spy ingested with his sushi.
No one knows how many people may be dying from the polonium part of tobacco. There are hundreds of toxic chemicals in cigarette smoke, and it’s hard to sort out how much one contributes compared to another — and interactive effects can be diabolical.
In a sense, it doesn’t really matter. Taking one toxin out usually means increasing another — one reason “lights” don’t appear to be much safer. What few experts will dispute is the magnitude of the hazard: the World Health Organization estimates that 10 million people will be dying annually from cigarettes by the year 2020 — a third of these in China. Cigarettes, which claimed about 100 million lives in the 20th century, could claim close to a billion in the present century.
The tobacco industry of course doesn’t like to have attention drawn to the more exotic poisons in tobacco smoke. Arsenic, cyanide and nicotine, bad enough. But radiation? As more people learn more about the secrets hidden in the golden leaf, it may become harder for the industry to align itself with candy and coffee — and harder to maintain, as we often hear in litigation, that the dangers of tobacco have long been “common knowledge.” I suspect that even some of our more enlightened smokers will be surprised to learn that cigarette smoke is radioactive, and that these odd fears spilling from a poisoned K.G.B. man may be molehills compared with our really big cancer mountains.
Robert N. Proctor is a professor of the history of science at Stanford University.
While cigarette smoke is not an obvious source of radiation exposure, it contains small amounts of radioactive materials which smokers bring into their lungs as they inhale. The radioactive particles lodge in lung tissue and over time contribute a huge radiation dose. Radioactivity may be one of the key factors in lung cancer among smokers†.
How many people are exposed to radioactivity in cigarettes?
According to the American Lung Association, there are about 48 million adult smokers in the U.S., and 4.8 million adolescent smokers. This means that the U.S., population, directly exposed to radioactivity in cigarette smoke, is approximately 53 million.
According to the Centers for Disease Control and Prevention, 80 percent of adult tobacco users started smoking as teens; 35 percent had become daily smokers by age 18. Thirty nine percent of adult smokers smoke one pack of cigarettes per day, and 20% smoke more than a pack a day.
Smoking is the number one cause of preventable death in the U.S., with 443,000 deaths, or 1 of every 5 deaths, in the United States each year. And, there are 123,000 lung cancer deaths annually attributed to smoking cigarettes. Nearly 1 of every 5 deaths is related to smoking, more than alcohol, car accidents, suicide, AIDS, homicide, and illegal drugs combined.
In addition to smokers, those exposed to secondhand or side-stream smoke have been shown to risk disease as well. In some studies, it has been found that side-stream or secondhand smoke is two to five times more concentrated in some carcinogens than the mainstream smoke inhaled by a smoker. Each year, approximately 3,400 nonsmoking adults die of lung cancer as a result of breathing the smoke of others’ cigarettes. Environmental tobacco smoke also causes an estimated 46,000 deaths from heart disease in people who are not current smokers. Secondhand smoke contains over 4,000 chemical compounds, including 69 known carcinogens such as formaldehyde, lead, arsenic, benzene, and radioactive polonium 210.
How does radioactive material get into a cigarette?
The tobacco leaves used in making cigarettes contain radioactive material, particularly lead-210 and polonium-210. The radionuclide content of tobacco leaves depends heavily on soil conditions and fertilizer use.
Soils that contain elevated radium lead to high radon gas emanations rising into the growing tobacco crop. Radon rapidly decays into a series of solid, highly radioactive metals (radon decay products). These metals cling to dust particles which in turn are collected by the sticky tobacco leaves. The sticky compound that seeps from the trichomes is not water soluble, so the particles do not wash off in the rain. There they stay, through curing process, cutting, and manufacture into cigarettes.Lead-210 and Polonium-210 can be absorbed into tobacco leaves directly from the soil. But more importantly, fine, sticky hairs (called trichomes) on both sides of tobacco leaves grab airborne radioactive particles.
For example, 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,
What happens when I smoke a cigarette?
Research indicates that lead-210 and polonium-210 are present in tobacco smoke as it passes into the lung. The concentration of lead-210 and polonium-210 in tobacco leaf is relatively low, however, this low concentration can accumulate into very high concentrations in the lungs of smokers.
As it passes into the lungs, the smoke impacts the branches of the lung passages, called bronchioles, where the branches split. Tar from tobacco smoke builds up there, and traps lead-210 and polonium-210 against the sensitive tissues of the bronchioles. Studies show filters on ordinary commercial cigarette remove only a modest amount of radioactivity from the smoke inhaled into the lungs of smokers. Most of what is deposited is lead-210, but polonium-210 (whose half life is about 138 days) quickly grows in as the lead-210 (half life = 22.3 years) decays and becomes the dominant radionuclide. Over time, the concentration of polonium-210 directly on tissues of the bronchioles grows very high, and intense localized radiation doses can occur at the bronchioles.
†There is very little information concerning radioactivity in cigar, pipe, or smokeless tobacco, or on the potential health effects from radioactivity in tobacco products other than cigarettes.
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