The murder of former Russian spy Alexander Litvinenko was one of the most high-profile assassinations of the decade. It particularly captured the public imagination because Litvinenko was killed using polonium-210, a rare but deadly substance that was thought to have been slipped into Litvinenkoâ€™s tea. Now a UK public inquiry has issued its findings on the case. But what is polonium?
Rare and radioactive
Polonium is a radioactive element that occurs naturally in tiny amounts (which are harmless to us). It was discovered in 1898 by Marie Curie, during her research on pitchblende, an ore of uranium. It has the chemical symbol â€śPoâ€ť and Curie named it after Poland, her native country. If you look at a periodic table, youâ€™ll find polonium at the bottom of the group headed by oxygen and sulfur.
There are around 30 different isotopes of polonium ranging in atomic mass from 194 to 218, only differing from each other in their neutron number. The important one is polonium-210, which happens to be the one discovered by Curie.
Uranium atoms slowly decay into other atoms, eventually ending up as lead but with polonium as one stop on the way. Because of this radioactive decay, polonium atoms are continually being formed and decomposed so the element does not naturally accumulate in any significant amount.
Although polonium-210 was first isolated from uranium ores, today it can be artificially made by bombarding atoms of the metal bismuth with neutrons. According to an expert who testified to the Litvinenko enquiry, only one place in the world had a polonium â€śproduction lineâ€ť â€“ a closed nuclear facility in Sarov, just under 500 miles south-east of Moscow â€“ and the sample used in the murder was highly likely to have come from here.
Polonium is one of the most toxic substances known. According to some sources, it is up to a trillion times more toxic than hydrogen cyanide. It is radioactive because it emits alpha particles (helium ions). Because these are easily absorbed by other materials, even by a few thin sheets of paper or by a few centimetres of air, polonium has to be inside your body to damage you.
Itâ€™s this radiation that has made minuscule traces of polonium useful in anti-static brushes, which are used to remove static charge from sensitive equipment. The fact that its alpha particles are so easily absorbed also make it hard to detect by radiation detectors such as Geiger counters, so polonium is probably easier to smuggle than some other lethal agents.
If polonium is known to have entered the body very recently, there is a chance of removing it by gastric aspiration (sucking out the stomach contents) or lavage (washing the stomach out with water). Chelating chemical agents, the sort that are used to treat heavy metal poisoning, can also remove polonium from the body if administered very quickly. But once it gets into the blood, it is likely to cause acute radiation syndrome and you will die of multiple organ failure.
Effect on the body
The alpha radiation breaks apart the chemical bonds in living cells, damages DNA and creates lots of very reactive free radical ions that can do further damage. One specific result is a reduction in your white blood cell count which, apart from anything else, can make you more susceptible to infection and requires blood and platelet transfusions.
The liver, kidneys, spleen and bone marrow are particular targets and are massively damaged by the alpha-radiation. The rapid damage to the gastrointestinal tract causes nausea and vomiting. Bone marrow failure can result in days. One other target is hair follicles, which is why Litvinenko lost his hair before he died.
Alexander Litvinenko is not the first casualty of polonium. In 1956, Marie Curieâ€™s scientist daughter IrĂ¨ne Joliot-Curie died of leukaemia that she is believed to have contracted through exposure to polonium years before. There have also been claims that Palestinian leader Yasser Arafat may have been exposed to it in a similar way to which Litvinenko was.