November 21, 2006

scientists respond to the news that Russian ex-spy might have been poisoned with radioactive thallium

At this time Mr Alexander Litvinenko was being treated in intensive care in a London hospital.

Some information about thallium: Thallium-201 is a 3 day half-life gamma emitter It is used medically for blood flow imaging Thallium-201 has also been used for radionucleide imaging in the investigation of cardiac ischaemia

Dr Andrea Sella, Lecturer in Chemistry, UCL, said:

“Thallium is one of the “heavy metals”. It is not widely used or very commonly available. It has a number of uses as a dopant in electronic applications and other high tech materials, and is an occasional additive for specialist glass. You used to get it in rat poison but no longer as it’s been misused enough times to merit attention from the authorities.

“Thallium is highly toxic. In essence you can think of it as a wolf in sheep’s clothing – it is of the same size and has the same charge as potassium, one of the key elements involved in neurotransmission and cell transport processes. Thallium therefore binds in the same places as potassium (and to some extent sodium), but once there, gets “stuck” – in other words it jams/blocks ion channels and other transport systems which cells use for transporting materials and ions across membranes, and equally crucially for neurotransmission. This is a complete disaster for an organism- there are catastrophic effects – neurological and whole host besides.

“Radioactive Thallium-201, usually in the form of the chloride – is used as a cardiac imaging agent. It’s a radioactive isotope with a half life of a little over 3 days so it disappears pretty fast. It’s a gamma emitter which guarantees that the radioactivity is visible outside the body. So it’s less likely to cause much radiation damage to people – in order to give someone radiation poisoning you would normally give them something that would be absorbed and that is precisely what is done with radiation therapy (such as K-capture therapy) which is designed to kill tissues locally.

“My gut feeling at the moment is that whoever did this wanted not only to do him harm, but also to send a spectacular message to others – mess with us and we make you die a lingering death. And to add radioactivity into the brew is an additional way of fuelling people’s fears.”

Professor Peter Weissberg, Medical Director, at the British Heart Foundation (BHF), said:

“The amount of thallium used in diagnostic cardiovascular medicine is safe and people who are awaiting a thallium scan of their heart should not be alarmed.

“The benefits of carrying out a thallium scan, in patients with suspected cardiac disease, far outweigh the risks of having a small amount of thallium in the bloodstream.”

John Henry, Professor of Accident and Emergency at St Mary’s Hospital, London, said:

“The levels of thallium present in this case are lower than expected. Mr Litvinenko also has signs and symptoms that are unexpected and do not normally occur with thallium poisoning, especially the fact that is bone marrow is not functioning and his white cell count has dropped to zero. Something other than thallium is involved. There are several possibilities as to what this something is. One is a that he was given thallium plus a second cytotoxic drug, the second is that he was given thallium plus a different radioactive compound, the third is that he was given radioactive thallium. At this stage radioactive thallium seems the most likely cause.”

Prof David Coggon, Professor of Occupational and Environmental Medicine, said:

“In general, the chemical toxicity would be no different for radioactive as compared with non-radioactive thallium. The former will, however, also pose an additional hazard from its radioactivity. The nature and risk of adverse effects from radioactivity will depend on where the thallium gets to in the body, in what quantities, how long it stays there, and what type of radiation is produced. Radiation doses have to be relatively high to cause short-term toxic effects, but lower levels can cause long-term effects such as an increased risk of cancer. How much of an increase in risk will depend on the dose.”

Off the record – a radiation expert also, said:

“If he had enough to give him radiation poisoning it should be detectable now, 20 days after. Patients having trace amounts for blood studies have to be careful going through airports because they set off alarms for 30 days afterwards.”