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Q&A: Polonium-210


27 November 2006

Polonium-210 is reported to have caused the fatal poisoning of former Russian spy, Alexander Litvinenko. Litvinenko died on the evening of Thursday 23 November at University College Hospital, London, UK. He fell ill on 1 November within hours of meetings in a central London hotel and, later, a sushi bar. Chemistry World asked John Emsley, author of Elements of murder: a history of poison, what is known about polonium-210 poisoning.

 

How would one get hold of polonium-210?   

With difficulty, unless you had access to a nuclear facility or were an authorized user, such as those who use it to generate thermoelectric power. (Polonium-210, half life 138 days, releases a lot of heat energy and a gram of the element can reach a temperature of 500 Celsius, which is why it has been used as an energy source in space). Around 100 grams a year of polonium-210 are manufactured in nuclear reactors, and this is done by bombarding bismuth with neutrons.   

 

How much constitutes a fatal dose?   

The maximum safe body burden of polonium is only 7 picograms. Polonium occurs naturally in the environment due to radioactive decay of radon, and we all have traces of polonium in us. Polonium-210 is regarded as one of the most dangerous substances known because it ejects alpha-particles, which are helium nuclei, and these wreak havoc with every organ of the body in which the polonium resides. (Inside a living cell they can trigger cancer if they damage DNA.)   

In theory, a mere microgram of polonium-210, which is no larger than a spec of dust, would deliver a fatal dose of radiation. Polonium is only slowly excreted - it has a biological half life of around a month - and this ensures its alpha-particles continue to wreak havoc.     

 

How would polonium-210 be used to kill someone?     

Clearly it has to be added to the food or drink of the intended victim but that does not present a problem because so little is needed. There are soluble compounds of polonium and the easiest way to deliver a fatal dose would be in a cup of tea, as has been suggested. 

 

What would poisoners have to watch out for?     

Because alpha-particles are easily stopped by nothing more substantial than a sheet of paper, handling a polonium compound does not present a serious risk to a secret agent. No doubt such a person would have some method of concealing the poison (James Bond style) before using it. 

 

I hear it could kill victims a bit too quickly if you get it all wrong   

This appears to have been what happened to Litvinenko, and there may be those who know how to link the dose of polonium-210 to deliver a particular outcome, but they used too much, perhaps a milligram or more. Forensic analysis might eventually reveal how much polonium-210 there was in his body. From the day he was poisoned, Litvinenko would begin to excrete polonium which might explain its presence at various locations.   

 

Has anybody else been poisoned in this way in the past?     

Not deliberately to my knowledge. Ironically, Irčne Joliot-Curie, the daughter of Marie Curie who first isolated polonium, died because of it but her exposure was accidental. It happened when a sealed capsule of polonium exploded in her laboratory bench many years earlier. It was this which finally led to her death from leukemia in 1956 although the accident had occurred a decade earlier.   

 

How was it tested for, why did it take this long to figure it out, and how could it have been confused with thallium?   

It appears that the doctors at University College Hospital first assumed that Litvinenko had been poisoned with thallium because all his hair fell out and that is the tell-tale symptom of poisoning by this metal and occurs after about 10 days. However, analysis showed there were only trace amount of thallium in his blood so it was then assumed he'd been poisoned with thallium-201 a radioactive form with a half life of 3 days. He was radioactive, and eventually it was deduced that he had been poisoned with polonium-210, which can be identified from the radiation it emits. Hair loss is also a symptom of exposure to high levels of radiation. 

Also of interest

The dark side of chemistry

The elements of murder: a history of poison

Atomic history

Before the fall-out: from Marie Curie to Hiroshima

Madame Curie reigns supreme

Obsessive genius: the inner world of Marie Curie