Polonium-210 and a murder most foul

Wednesday, 17 February 2016

Britain blames the Russian president, Vladimir Putin, for the murder of the former Russian security service officer, Alexander Litvinenko, in London with the radioactive element, polonium-210, in 2006.  Professor Ian Shaw explores the intrigue surrounding the case and explains why polonium-210 is so horrifically toxic.

On November 23rd, 2006 Alexander Litvinenko died in University College Hospital, London.  On the face of it this is sad, but not unusual until we delve into the circumstances of his death.  

Litvinenko was only 44 years old when he died; he had no recent history of illness, but became gravely ill very quickly and died within 23 days of hospitalisation. What's more, he had been an officer of the Federal Security Service of the Russian Federation (FSB), the successor of the KGB, before being arrested in Russia in March 1998 for accusing his superiors of ordering the assassination of the Russian tycoon, Boris Berezovsky. He was acquitted in November 1999, re-arrested and acquitted again in 2000.  

He justifiably felt unsafe in his home country and fled to Britain where he was granted asylum. In 2000 he was convicted in absentia by the Russian courts and given a three-year prison sentence.

You might think that he would have chosen a quiet life in the freedom of his adopted country; but no, he became a journalist and consultant to the British intelligence service – MI6. 

He wrote two books after moving to Britain, Blowing up Russia: terror from Within and Lubyanka Criminal Group. These books cast serious aspersions on the Russian system and accused it of stopping at nothing to get Putin into power.  Perhaps understandably, this upset his Russian 'friends', particularly Vladimir Putin.

His final public words from his deathbed in University College Hospital were, 'You may succeed in silencing one man but the howl of protest from around the world, Mr. Putin, will reverberate in your ears for the rest of your life.' 

This is the stuff of a gripping John le Carré novel, but read on; the plot thickens…

The symptoms leading up to Litvinenko's death - rapid hair loss and immune system collapse – are clues to what might have caused his demise. Thallium, a highly toxic element causes hair loss which led the initial investigators down the wrong path, but they found no trace of thallium anywhere. Combined rapid hair loss and immune system failure are associated with radiation exposure; some shrewd toxicological thinking pointed to the horrifically toxic radioactive element polonium-210 as the culprit in this, as yet, unexplained death.

The poisoning agent was clinched when British government scientists found polonium-210 in Litvinenko's urine a few days before he died.

It is believed that the polonium-210 was administered in a cup of tea given to Litvinenko by two of his FSB acquaintances (Andrei Lugovoy and Dmitri Kovtun) in a bar in the Millennium Hotel in Mayfair, London. They left polonium-210 traces in Hamburg (where Kovtun had been before travelling to Britain), on the aeroplane Kovtun travelled in, and many places as he crossed London with the polonium-210 in a glass vial.  

Polonium-210 is radioactive, it emits alpha particles of a particular energy that is characteristic of the element – the murderers presumably did not know how easy it would be to prove the presence of polonium-210.  

Litvinenko probably only took a few sips of the polonium-laced tea to achieve the fatal dose. Since polonium is excreted in sweat, tears and urine he too left traces wherever he went. This complex jigsaw of polonium-210 residues was important in the forensic case presented in the Litvinenko hearing at the Royal Courts of Justice, London in January 2015. 

So why is polonium-210 so toxic? Polonium salts (e.g. polonium citrate) are readily absorbed from the intestine and are rapidly distributed around the body. When polonium-210 enters cells the alpha particles it emits wreak havoc with cell components.  

Alpha particles are large – in an atomic scale context – and charged, and when they hit important molecules in cells (eg DNA) they fragment them.  It's a bit like throwing golf balls in a greenhouse; you will inevitably break the glass. The molecular fragments no longer have their key biological functions, and the cell dies.  

It only takes a few polonium-210 ions per cell to kill it.  In fact the lethal dose of polonium-210 for a human is thought to be only about 10 picograms (a picogram is one million millionth of a gram) - this is a vanishingly small lethal dose and makes polonium-210 one of the most toxic substances known (it is 25,000 times more toxic than potassium cyanide).  Once absorbed into the body, polonium is only slowly excreted - it takes a month to excrete half of a polonium dose.  This slow excretion exacerbates its toxicity.

Just 23 days after he sipped that fateful cup of tea in a posh London Hotel, Litvinenko died. During those painful 23 days he lost all of his hair, his immune system collapsed, and he suffered multiple organ failure. This was the first case of polonium-210 fatal acute toxicity ever recorded.

Interestingly, it is likely that Litvinenko's murderers did not appreciate the incredible toxicity of their murder weapon or the ease with which it could be detected and identified - from the polonium-210 contamination found wherever they had been they were clearly not as careful as they should have been. Traces of polonium-210 were even found on the hands of people the murderers had shaken hands with.

Litvinenko's autopsy was carried out at the Royal London Hospital, Whitechapel and is reputed to be one of the most dangerous autopsies ever carried out. The pathologists wore double protective suits with filtered air supplies to prevent their contamination with lethal polonium-210.

Litvinenko was buried in Highgate Cemetery, London on 7th December, 2006. Enough polonium-210 remained in his body to kill at least several people, and so to prevent polonium-210 leaching from his body into the surrounding soil, he was buried in a lead-lined, hermetically-sealed coffin. 

Radioactive isotopes eventually decay to form stable elements – polonium-210 decays to lead. Therefore, polonium-210 gradually loses its toxicity as it forms very much less toxic, non-radioactive lead. This means that one day Litvinenko's remains will be safe – let's hope his lead-lined coffin lasts long enough. But will this be enough to protect future generations?

The radioactive half-life of polonium-210 is 138 days; therefore, after 10 years there will be only about one millionth of a percent of the original polonium-210 remaining in his corpse. The lead coffin should last at least 10 years, and so there is no need to worry about a Litvinenko polonium legacy poisoning future generations.

Ian Shaw is professor of toxicology at the University of Canterbury.