Polonium poisoning – in a cup of tea

Jan 29 2008 by Andrew Flynn, Huddersfield Daily Examiner

The death of former KGB agent Alexander Litvinenko by radiation poisoning is still damaging relations between the UK and Russia. Here Dr ROGER JEWSBURY, of the School of Applied Sciences at the University of Huddersfield looks at the poison that brought such a terrible death

THE continuing diplomatic tension between Russia and this country, resulting in closure of the offices of the British Council, whose activities are educational and cultural, stems from the death of Alexander Litvinenko in London just over a year ago.

Litvinenko was poisoned by radioactive polonium-210, an unusual choice but one which has enabled scientists to forensically investigate the trail of the poisoning. Polonium-210 is found naturally in uranium ores, as it is formed as part of the route by which atoms of uranium decay to lead, although as explained later this was not the source of the polonium which killed Litvinenko.

Each different element has a particular number of particles in its nucleus called protons.

The number of known elements is limited to about 100 or so, because as the number of protons increases in the nucleus, the element becomes increasing unstable.

Unstable elements usually decay by emitting alpha, beta or gamma radiation. Of these, alpha radiation is the least penetrating, travelling only a few centimetres in air and unable to penetrate skin or paper.

Alpha radiation, however, causes the most damage. Polonium-210 emits only alpha radiation, so if a polonium compound is ingested, the radiation will cause damage within the body but will not be immediately apparent outside the body.

Polonium is a metal, so in order to be used as a poison it would have been administered as a soluble compound similar in form to table salt.

To be fatal, all that would be needed would be about ten millionths of a gram, a speck almost too small to be seen with the naked eye.

Once ingested, the polonium salt would enter the blood and be transferred to the organs and tissues of the body. This small weight of polonium corresponds to an enormous number of atoms and one thousand million of these will decay each second, emitting deadly alpha particles.

This radiation will kill cells, having the most effect on those that regenerate the most rapidly. The loss of white blood cells from bone marrow is a major contributor to death in a matter of weeks, but other organs are also affected, so there is little that can be done for the patient.

The polonium does not remain in the body and whilst the victim is alive, is lost slowly via faeces, urine and to smaller extent sweat. Over a period of about a month, half the polonium ingested would be lost by excretion – if the victim survived that long.

Whenever an alpha particle is detected, it corresponds to the decay of a single atom and this extreme sensitivity means that the analytical scientist can detect very small amounts of polonium-210, enabling the tracing of the route of the poisoning.

The evidence suggests that the polonium was added to a cup of tea served in the bar of the Millennium Hotel. Later, after it had been washed, the pianist drank out of the same cup and also showed evidence of polonium ingestion.

The bar is only one of a number of sites in London where polonium-210 has been detected.

The trail of radioactivity goes further still. Seats in two planes which flew between Moscow and London have shown contamination, as has a house in Hamburg.

It is by the comparison of the location of polonium contamination with the movement of suspects that the police have identified Andrei Lugovoy as a suspect.

It is not possible to separate polonium-210 in a pure state from the uranium with which it is linked, but the polonium-210 used to poison Mr Litvinenko has been shown to be pure. Pure polonium-210 is made by a reaction involving neutrons, which requires access to a nuclear reactor, possibly implicating the Russian authorities, which may be why they are so concerned about continuing requests by the UK Crown Prosecution Service to interview Mr Lugovoy.