Litvinenko – Seven Years on
We are approaching the seventh anniversary of the poisoning and death of Alexander Litvinenko. He was poisoned on 1st November 2006 dying of acute radiation sickness 22 days later. The radionuclide that he was poisoned with was Polonium 210 which is a radioactive element first discovered and characterised by Marie Curie and her husband Pierre in 1898. She also died as a result of her long-term exposure to radioactive elements – from anaemia at the age of 66. Incidentally she was the first woman to win a Nobel Prize and remarkably won two (one for chemistry and one for physics). As a point of historical interest Pierre Curie did not die of radiation sickness despite his party trick of dimming the lights around the dinner table and pulling out of his jacket pocket a glowing phial of radioactive liquid to the delight and bewilderment of his audience. Instead, he was run over by a horse and cart on the streets of Paris. It would be inappropriate to comment that it’s never the bus that you are looking at that runs you over; so I won’t.
Now Polonium 210 is a radionuclide that occurs in nature as a part of the decay chain of Uranium 238, which is the most abundant form of Uranium, the others being Uranium 235 and 234. Incidentally U235 is the isotope used in nuclear power stations and atom bombs, but only 0.7% of Uranium found in nature is U235. Therefore Uranium ore has to be refined to extract and concentrate the Uranium, which then has to be ‘enriched’ to separate out and concentrate the U235. The Uranium left over from this enrichment process is called Depleted Uranium and, being a very dense metal, is used to make armour piercing shells.
Back to our main thrust, Uranium 238 is the most abundant naturally occurring radionuclide of Uranium. It can be found in rocks, soil and water and is more concentrated in certain geographic areas. When Uranium 238 undergoes spontaneous radioactive decay it ejects an alpha particle. This alpha particle is, as all of your radiation geeks out there know, a helium nucleus; two protons and two neutrons. So ejection of the alpha particle changes the atomic mass of the Uranium and also changes its atomic number. Since atomic number (number of protons) determines the element, Uranium 238 looses four atomic mass units to transmute into Thorium 234, which is itself an unstable radionuclide. So in turn it, decays; emitting a beta particle to form Protactinium 234. Remarkably the Uranium 238 decay chain has fourteen individual decay events, one after the other from one unstable radionuclide to the next until finally we end with Lead 206 which is not an unstable radionuclide so no further radioactive decay events occur.
The thirteenth radionuclide on the decay chain is our old friend Polonium 210. But don’t worry the concentration of Polonium found in soil and water as a result of natural U238 decay are tiny. Interestingly the sixth in the decay chain is Radon 222, a naturally occurring, radioactive Radon gas. So if you live in an area with a relatively high concentration of Uranium 238 in the earth beneath your feet then Radon gas will be seeping from the soil into the atmosphere.
Radon 222 is an alpha particle emitter. Alpha particles cannot travel significant distances through the air before they collide with air molecules and cause ionisation. They do not penetrate solid materials well at all and the dead layer of cells at the surface of the skin is usually enough to prevent alpha particles that are external to the body doing any harm.
So Radon gas in the external environment should not present much of a health risk right? Wrong! The problem with Radon is that it is a gas. It is released into the atmosphere and can then be inhaled. As you NEBOSH Diploma Unit B fans will know the lungs do not have a layer of dead cells lining their internal membranes. This is not your epidermis. The thin delicate membranes lining the lung are immediately adjacent to the air inhaled. When Radon 222 does it thing and undergoes spontaneous decay the alpha particle emitted is straight into living tissue. But far worse, the decay product of Radon 222 is Polonium 218; another radionuclide (we are in the Uranium 238 decay chain remember). In fact there are five radionuclides after Radon 222 that all have short half-lives. All of these ‘daughter’ products are solids by nature and attach themselves to dust or surfaces in the lungs.
So if you live in a high Radon area you are inhaling radioactive Radon gas, and also the radioactive daughter products of the decay of Radon that have attached themselves to dust particles in the air. Double Whammy – or Quintuple Whammy – if you prefer. Have an alpha particle; have another one; have a beta particle; have another; had enough yet – course not; have another alpha particle – you know you want one!
The end result is cell damage, DNA damage, cell mutation, early cell death, cancer. The principle health risk is an increased risk of lung cancer. Note the words ‘increased risk’, not surety, but increased risk. If you live in a high Radon area there is a greater risk that you will contract a fatal lung cancer compared to you living in a low-Radon area. Various epidemiological studies show that Radon gas inhalation is the second biggest case of fatal lung cancers; the top cause being smoking. This does not mean that you are at a similar risk of contracting lung cancer if you live in a high Radon area as you are if you smoked 20 a day. It simply means that Radon gas inhalation is the number two cause of fatal lung cancers.
The risks from smoking alone are high; in the UK 28,000 premature deaths from lung cancer occur each year as a result of smoking. Premature deaths from lung cancer caused by Radon gas inhalation are estimated at 1,100 per year. So simplistically you are 25 times more likely to die of lung cancer if you smoke than if you inhale high concentration of Radon (and before you leave a comment I know that this is a gross simplification). There is very strong evidence that smoking in combination with Radon gas exposure significantly increase the risk of lung cancer – there is a synergistic effect between the two. A smoker living in high Radon concentrations has a lifetime risk of one in three of contracting lung cancer (compared to less than one in 200 for a non-smoker in low Radon concentrations).
And just to take us back to the beginning; a high Radon gas concentration in the context of the last sentence is 800 Becquerels per cubic metre (800 decay events per second per cubic metre). It is estimated that Litvinenko was poisoned with 2 gigabecquerels (2 x 109 decay events per second) of radioactivity.
You’ve got to love a bit of ionising radiation haven’t you? That’s why I have spent the last 16 years of my life living on Dartmoor and the previous nine in and around the Derbyshire Peak District. Don’t know what I mean; then take a look at this Radon Map of the UK published by UKRadon.
What the hell; anyone got a cigarette?
Jim Phelpstead BSc, PhD, CMIOSH
Working in health and safety for 18 years Jim is a long-standing RRC Associate Tutor, who loves the great outdoors.