Friday, December 01, 2006

Polonium 210, Russian Spies and Safe Tobacco.

Probably for the first time ever, the element polonium 210 has hit the headlines, in connection with its use as a poison to kill Alexander Litvinenko, an outspoken critic of the Putin regime. Polonium was discovered by Marie Curie (and her husband Pierre), among the products heroically obtained from extracting four tons of uranium ore (pitchblende), working for four years in an unheated shed, boiling the rock in vats of concentrated acids. At that time, only uranium and thorium were known to be radioactive, and the far more intensely radioactive radium and polonium were revealed and isolated by the procedure of fractional crystallization, probably the most laborious in chemistry. Marie named polonium after her native Poland. Polonium 210 has a half life of about 138 days, and emits five thousand times the amount of radiation as an equal quantity of radium does. Put differently, one milligram of polonium 210 (210Po) emits as much radiation as 5 grams of radium. Polonium is an alpha emitter (i.e. when the nucleus undergoes radioactive decay it releases alpha particles), and so it must be inhaled, swallowed or injected to exert any toxic effects, since alpha particles are stopped by the skin and do not penetrate thus into the body. Only one decay out of every 100,000 results in the emission of a gamma ray along with an alpha particle, while the rest are pure alpha decays. This makes the material more difficult to detect than many other radioactive isotopes, and this is most sensitively done using an alpha spectrometer to measure alpha particles rather than by measuring gamma rays.
The decay of polonium releases a considerable amount of energy and half a gram of the material will quickly reach a temperature of 500 degrees Celsius. A quantity of 210Po equal to just a few curies (one curie is equal to one gram of radium and hence is equal to around 0.2 milligrams of 210Po) is observed to emit a blue glow from gamma rays exciting surrounding air molecules. One gram of 210Po produces 140 Watts of power, and accordingly it has been used as a heat source to power thermoelectric cells in satellites. Because polonium is a highly radioactive and toxic element it is very difficult to handle, and even microgram (millionths of a gram) quantities of 210Po are extremely dangerous, requiring specialized equipment and strict containment procedures. Alpha particles emitted by 210Po will damage internal organic tissue easily if polonium is ingested, inhaled or injected. The maximum permitted body burden for ingested polonium is reckoned at just 1,100 becquerels (0.03 microcurie - 30 billionths of a Curie), which is equivalent to a particle weighing only 6.8 × 10-12 gram (6.8 millonths of a microgram). Weight for weight, polonium is 250 billion times as toxic as prussic acid (hydrogen cyanide).
I discovered only the other day that there is a relation between polonium and lung cancers caused by smoking cigarettes. Indeed, 210Po is the one individual component of cigarette smoke shown to cause cancers by inhalation. In studies of laboratory animals, lung tumours were found to develop at levels far lower than the dose received by a heavy smoker. The history is that lung cancer rates among men climbed from being a rare disease that occurred at a rate of 4 in every 100,000 people per year, to 72/100,000 by 1980, making it the number one fatal cancer, despite an almost 20% decrease in levels of smoking during that same period. This coincided with a tripling in the levels of 210Po found in American tobacco, a result of tobacco growers using superphosphate fertilizers. Calcium phosphate ores tend to concentrate uranium, which decays to radon which then breaks down to 210Po (a "daughter product"). Indeed, soils associated with phosphate ores have uranium concentrations from 50 - 1000 parts per million (ppm), and far in excess of the the 2 - 3 ppm usually found. The 210Po becomes attached to the sticky hairs on the underside of tobacco leaves and when the resulting cigarette is smoked, the intense heat of the burning tip volatalises it, and so it is inhaled. Apparently the filters, while effective against chemical carcinogens do not hold-back the radioactive components.
The lungs of a heavy smoker (which may mean only 15 cigarettes per day - I used to smoke a lot more than this until I gave up twenty years ago, and un-filtered cigarettes at that!) become coated with a radioactive lining which irradiates the sensitive lung tissue. Smoking two packs (40 a day) gives an alpha particle radiation dose of around 1,300 millirems per year, over six-times the dose received by the average American from breathing in radon (200 millirems). Furthermore, 210Po is soluble in body fluids and is thus percolated through every tissue and cell giving levels of radiation much higher than that received from radon. The circulating polonium causes genetic damage and premature death from diseases that are reminiscent of those encountered by the early radiation pioneers: e.g. cancers of the liver and bladder, liver cirrhosis, leukemia, stomach ulcers and cardiovascular conditions. Marie Curie herself died of cancer.
C. Everett Coup, surgeon general for the United States of America, has stated categorically that radiation, rather than tar accounts for at least 90% of all smoking related lung cancers. Now, that is a huge statistic: nine cases out of ten! Indeed, the Center for Disease Control has concluded that: "Americans are exposed to far more radiation from tobacco than from any other source." Although 30% of all cancer deaths can be related to tobacco smoking, nonetheless the National Cancer Institute has no active funding for research into radiation from smoking as a cause of cancer. This may be in order to prevent panic amongst the public over radiation, but surely, the solution is simple, if people are not going to quit smoking (which is the absolute safeguard), then wouldn't simply growing the plants on soil fertilized "organically" say, rather than using phosphate fertilizers, solve much of the problem?
Once again, I imagine the underlying reason is economics: that tobacco, like most plants, grows better when "pushed" by chemical fertilizers, and greater crop yields mean greater profits. It is as simple as that, and the lives of smokers are expendable, since there is always a new generation (or new market in the developing world) to take their place in the ranks once they have been cut down. "Safer", "polonium-free" tobacco would cost money, and is therefore unattractive both to growers and to cigarette manufacturers.


Professor Chris Rhodes said...

Hi dave,
yes, that's a good point. I guess the "healthiest" way would be if everybody gave up smoking (I gave up about 20 years ago!) but that would not please either the tobacco growers or cigarette manufacturers! If sure that some detergent-based washing process could be found which effectively physically dislodges the polonium (and radium) cation particles from the "hairy" undersides of the tobacco leaves, and renders the product safer, but it would add cost - though less than that of potential lawsuits!
I agree, organic farming does use more land - hence part of the attraction of "super" fertilisers, to get more crop per hectare. It is less of a problem with foodstuffs though, since most of the radioactive material will simply pass-through! However, smoking contaminated tobacco is a particular problem, because the radiocative particles get lodged in the lungs where they expose tissue to a steady dose of alpha particles, and these cause the more serious kind of DNA damage (double stand breaks) that is less readily repaired and can lead to cancer.

Anonymous said...

Would it be possible to clean the phosphate fertilizer? Uranium extraction from phosphates has been done, it is even marginally economical and expected to become truly economical with rising uranium prices.

But the actual problem are the long lived daughter products Radium-226 and Thorium-230. Would it be feasible to extract them, too? Once you get hold of them, you could fairly easily get rid of them by transmutation in a nuclear reactor.

Professor Chris Rhodes said...

I'm sure you could extract the uranium, but it is cost that probably explains why this is not done. For most crops it doesn't matter too much, but those that are smoked result in the immobilsation of radioactive (alpha-emitters) in lung tissue. Maybe the U.S. Surgeon General could badger the government to pass law on the kind of fertiliser used for tobacco growing, since he is aware of the health hazard from superphospahte fertiliser in this regard. I'm not sure there is enough of the "useful" radioactive elements to make commerical extraction worthwhile. Compared to uranium ores, the amount of uranium in phosphates is pretty low, and so until there is a depletion of current uranium minerals and a big run on the stock market for uranium, I doubt this will happen on a commercial scale. Thanks for some useful input! Chris.

Anonymous said...

There are a couple of problems with the idea that we could somehow clean the radioactive dust off the tobacco leaves.

The first is that it's physically kind of out of the question. Give the leaves any kind of bath and you've got to dry them out again-- and hope your detergent doesn't stay on the leaves. Costly, clumsy and damaging to the quality of the leaf.

But second, that's only the surface dust you're removing. The Po-210 gets taken up by the leaf preferentially through its calcium receptors. So every cell of the leaf may well have polonium inside it.

Best either to stop smoking or to smoke only certified organic tobacco.

Professor Chris Rhodes said...

Thanks Adelen,

good to know there's so much help out there. I gave up "cold turkey" about 20 years ago.

Actually what I did was to use the technique of setting a date to stop about three weeks in advance, and I found that my mind began to prepare itself and I started to cut down naturally from 30 to about 3 a day.

I believe this is a form of CBT?

So, when the day came although the first three days were bad from time to time, it wasn't all that hard in fact.


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Unknown said...

How can polonium reach 500 degrees? Is there anything that makes it happen? Or something that will allow it to reach 500 degrees? Or it is naturally 500 degrees?

Unknown said...

If polonium is 500 degrees, how can we contain it? Is there any special container? If polonium is to be put in plastic container, it will melt for sure... So what is the name of container that is used to contain polonium?

Professor Chris Rhodes said...

Hi Isaac,

when polonium is used in actual devices (e.g. for space applications), it is contained in a double walled stainless steel capsule. Presumably if the temperature is 500 degrees C, the element must be in a molten state.



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