2022 Alexander Litvinenko - "Polonium-210 Poisoning" - revisiting an Ionactive 2006 blog article

Important Ionactive statement on this blog entry

For Christmas 2022 we thought we would look back over our blog archive (much of which is not on this website - our new website went live in 2018 and we left most of our old content to lay to rest). Given the recent Litvinenko 2022 drama, we thought we would revisit our own article on this subject which we issued 23 November 2006, at the same time as the incident was being discussed in the media (e.g. BBC - Radiation found after spy's death). Whilst this was an unprecedented event, and social media channels like Twitter were still in their infancy, we felt at the time we could lend some useful information to the debate, trying to make it understandable. We went further and did a first estimate (guess) on how much Po-210 activity may have been used (and this was long before anything official came out). It so happened that this estimate ended up on many other sites including Wikipedia - but most have since been removed as our older website and relevant links are redundant.

The rest of this blog article, containing "Alexander Litvinenko - "Polonium-210 Poisoning" from November 2006 is offered 'as is' and for general interest. I would like to think that Ionactive has improved both technically and in its ability to write about these subjects. That said, I am still pleased with this blog entry which appeared to gain a lot of interest at the time. Please note that much has changed since this article, Po-210 is not now routinely used as a commercial source (e.g. for static eliminators) as it was at the time. In addition security of radioactive materials around the world is much improved (driven mostly by 9/11 and July 7th 2005 terrorist events, but also this event in terms of investigation and forensic radiological analysis).

Once you have read this blog post you may be interested in our update 'Ionactive - further thoughts on our Polonium 210 (Po-210) Litvinenko activity and dose assessment' (posted 28 December 2022).

Mark Ramsay, Ionactive Consulting, 27 December 2022

Alexander Litvinenko - "Polonium-210 Poisoning"

Published 24 November 2006 by Mark Ramsay (Ionactive Consulting). (c) 2006 and 2022.

Polonium 210 (Po-210) has been identified as the likely source of 'radiation poison' which may have lead to the death of Alexander Litvinenko. The BBC is currently running a story on this event.

Ionactive Consulting Comment

Polonium 210 (Po-210) is an alpha emitter (a type of ionising radiation) with a half life of about 140 days (meaning its activity will reduce by half every 140 days). In simple terms the 'activity' (given the units of Bq or Becquerel) is a measure of how radioactive a substance is - the more Bq the more radioactive. It is important to note that the Bq is not like a measure of mass (e.g. g, kg). Therefore when one is asked 'how much radiation was Alexander Litvinenko given' it is not simply a question of the physical quantity.

Specific Activity

However, what we do know is that Po-210 has a very high specific activity - this means the amount of activity per unit mass (or Bq/g). This means that a fraction of a micro-g of pure Po-210 contains an incredibly large activity. It is difficult speculate how Po-210 may have been delivered to the victim, but what is clear is that the physical mass of the material needed would be small - essentially unnoticeable if put in a drink or placed in food. [There is about 166500 GBq or 166500000000000Bq in a 1 g of pure Po-210].

Where is Po-210 found?

Po-210 can be found in cigarette tobacco, drinking water and indeed food (at very low concentrations). In fact we all have very low concentrations of Po-210 in our bodies. Those that are exposed to naturally occurring radon gas (particularly in Cornwall or other granite bearing areas) are exposed to Po-210 - its a 'daughter' produced by the decay of radon gas. Furthermore, Po-210 is also found in industrial applications such as static eliminators and heat sources for low power generation applications . Indeed, it is a combination of Po-210 being an alpha emitter and having a high specific activity which actually produces enough decay heat to power small electrical generators.

Po-210: an internal hazard not an external hazard

The fact that Po-210 is an alpha emitter means that it is relatively harmless whilst outside the body - indeed it could sit on the skin with little resulting harm. This is common to most alpha emitters (unless they emit other radiations which are more penetrating). In the case of Po-210 it does have some weak gamma rays but the energy of these is so low as not to be of concern (also their probability of emission is very low). It is for this reason that Po-210 is difficult to detect when it is 'in something' or 'under something' or 'mixed with something'. In all cases once the alpha emitter is in a substance the detection of the emitted alpha particles becomes difficult - it would not be detected by simply waving a 'radiation counter' over a contaminated area. In order to detect the alpha particles (e.g. in urine) one would probably have to undertake a process called 'alpha / gamma spectrometry' where the urine would be evaporated down to dryness in controlled conditions. This would then allow the alpha particles (and weak gamma rays) to be detected with sensitive instrumentation and the 'signature' of Po-210 would be seen.

Po-210: physical form and entry route is important

The radiation hazard comes from the inhalation or ingestion of Po-210 since this brings the alpha particles into the region of specific cells in the body (where they can deliver their 'radiation dose'). These cells would include those from the lung, blood, spleen, kidney, liver and bone marrow (the exact location would to some extent depend on how the Po-210 was delivered). However, it's not just the 'radioactive nature' of the Po-210 which dictates its effects - it's also the chemical nature and physical form. For example, its degree of solubility (i.e. chemical form) will have a bearing on how long the material might stay in the body and do harm. Its physical form (particle size) might have an influence on the damage it can do if inhaled (since certain sizes would be inhaled deep into the lung where they would transfer to the blood, where as other sizes would be exhaled). This is one of the reasons why the Health Protection Agency is being cautious at this time - there are many factors to be considered.

Po-210: activity & dose

The media have tended to ask the question 'how much radiation was Alexander Litvinenko given?' or 'what was the dose?'. We must be clear about what we mean by 'dose of radiation'. What he was given was a certain 'activity (Bq)' of Po-210 - it is only when this has entered the body and been incorporated into the various organs / tissues of the body that it can deliver the 'critical damaging dose'. What seems to be clear of course is that enough activity was taken into the body to provide a massive dose of radiation to major organs in the body.

Harm: Low doses vs high doses

When talking about ionising radiation many tend to think of it as a 'cancer enhancing agent'. Indeed at low doses (and by this we mean anything from background radiation, radon, medical diagnostic x-rays and similar), we talk about the enhanced / excess life time fatal cancer risk which can be attributed to a certain exposure (dose) of ionising radiation. What is certain is the uncertainty that this dose will actually cause a cancer. All we know is that as the dose increases the risk / probability of the fatal cancer being caused by the ionising radiation also increases. It is something we live with and it's a simple fact of life - driving a car, taking the bus, smoking and drinking beer are all 'risky'.

However it seems that the radiation dose delivered by the Po-210 incorporated into Alexander Litvinenko has not followed the above expected pattern (stochastic) radiation effect. Instead it looks like the much less common and more serious 'deterministic' radiation effect which manifests itself in almost immediate and obvious clinical symptoms (hair loss, sickness, organ failure and possibly death). It should be pointed out that this effect is very uncommon - even in accident situations involving sources of ionising radiation. It only occurs after massive doses of radiation have been delivered to the body in a short period of time. There is a whole body and organ specific threshold below which the deterministic effect does not occur.

Unfortunately in this case it seems clear that the threshold has been reached.
The basic unit of radiation exposure is the Gray or 'Gy'. If one were to assume that a whole body could be irradiated uniformly by an external source of radiation (e.g. from an x-ray machine), then effects similar to that noted of the victim would be apparent somewhere between 3-5 Gy (which is a massive dose of ionising radiation by any standards). However, the dose calculation for Alexander Litvinenko will be a lot more complicated as we are not dealing with a nice uniform radiation field interacting with the body. Instead we are dealing Po-210 being incorporated into the body and irradiating cells at very close distance. Many have noted that alpha particles are more damaging than other types of ionising radiation (such as x-rays). For stochastic radiation effects (e.g. cancer induction) it is true that alpha particles can produce around 20 times more damage than x-rays for the same given quantity of absorbed dose (Gy). For deterministic effects exposure to the alpha particles will produce similar damage to x-rays but the severity will be greater per unit absorbed dose (i.e. like the stochastic effect). However there is not a factor of 20 difference in damage potential (i.e. like there is for stochastic effects), it is more like 2-4 for the large doses expected to have killed the victim.

How much Po-210 was used?

This is very difficult to establish and Ionactive does not have enough information to predict this with any certainty. However what we can do is provide some pointers as to how this might be worked out. Firstly, we start by looking at the stochastic effect (to simply rule it out). For these effects we can look to the literature to provide us with 'dose per unit intake' - that is the 'dose of radiation per Bq of Po-210'. Even this is not that simple because the values used depend on if the Po-210 was inhaled or ingested and also on the chemical nature of the Po-210 (i.e. what it was chemically attached to). For example, we can look at the ingestion coefficient and find that 833000 Bq would be needed to provide an effective whole body dose of 1 Sv (ICRP 72, worse case assumption for a member of the public). [For this paragraph please assume that 1Sv = 1Gy].

Therefore, one might consider that a small activity in the order of 4000000 Bq would be enough (in mass terms about 0.025 micrograms of Po-210). However, this calculation is only related to stochastic effects at low exposures and is not designed to work with large exposures. In other words, whilst the calculation might tell us that the victim would have certainly died (eventually) from a radiation induced cancer, it does not tell us anything about how he might have died from a deterministic radiation exposure. To summarise - the activity / mass calculated in this paragraph would not be enough to produce the deterministic effects seen in Alexander Litvinenko. Dose calculations based on stochastic dose coefficients - especially where alpha particles are involved is not valid.

Ionactive suspects the actual dose calculations will be based on computer models and by going back to first principles of internal radiation dosimetry (the science that looks at exposures produced by radioactive material in the body). In order to calculate the actual dose some assumptions (some perhaps later proved by analysis) will be required - these include the route of entry (e.g. inhalation or ingestion), the chemical form of the Po-210 compound (e.g. oxide, nitrate), the specific activity (Bq/g), the bio kinetics (i.e how and where the Po-210 is incorporated into the body and for how long) and so on.

However we can still have a stab at estimating an intake based on some very basic concepts and assumptions. For this we need to define a few terms.

(1) Unit of absorbed dose: Gray (Gy) [Units of J/kg]

(2) Units of decay energy: eV (electron volt) where 1 eV = 1.6 x 10-19 J

(3) Energy of Po-210 Alpha decay: 5.4 MeV

Here are some assumptions:

(i) Assume mass of body: 70Kg

(ii) Assume that Po-210 incorporates into all vital organs of body [likely]

(iii) Assume dose must be at least 10 Gy (to produce known effects in the victim during the 20 known days of exposure)

(iv) Assume that there is substantial retention of the Po-210 in the body over at least 20 days (i.e. worst case)

(v) Assume that the Alpha particle is 4 times as effective as x-rays in producing deterministic effects (at high doses). [This may not be accurate, but as noted above for a deterministic effect at high exposures, the alpha particle is not 20 times more damaging than x-rays and 4 seems a reasonable assumption].

Given 1Gy = 1 J/Kg, to give a 70Kg body at least 10 Gy (this will ensure bone marrow depression and gastrointestinal effects) will need 700 J. Each alpha decay can provide 5.4 MeV of energy which is 8.6 x 10-13 J. Therefore the total number of alpha particles required to give this energy will be 8 x 1014. If we assume the dose was delivered over 20 days then the activity required to do this would be around 462 MBq (462000000 Bq). [This is based on the fact that 1Bq of P-210 will produce 1 alpha per second].

However, since we have assumed that the alpha particle will produce around 4 times as much damage as an x-ray, we can say that ¼ of the activity will provide the same level of dose - i.e. 115.5 MBq.

The 115.5 MBq is probably a lower end estimate. If the required dose were to be delivered over 10 days then this would require at least 231 MBq. Alternatively (or in addition), if perhaps half the Po-210 were to be excreted over 20 days then significantly more activity were be required in order to deliver the same dose.

Sticking with our estimate of 115.5 MBq: this would have a mass in the region of 0.7 micrograms. What is therefore clear is that the mass of Po-210 required to kill an individual by the deterministic radiation effect is miniscule (put it this way, if a grain of sugar represented Po-210 then there would be about 900 deterministic doses in the grain). In actual fact the exact mass (or activity) is totally irrelevant / academic. 1g of Po-210 delivered in food would be clearly devastating and totally undetectable by the victim. Further more, to deliver this tiny mass, the actual mass of 'mixture' delivered would need to be significantly more (i.e. who can manipulate micro g quantities with ease).

Additional Ionactive content

During the preparation of this 2022 rendering of our 2006 article we also came across a later Ionactive article in December 2006 "Polonium 210 (Po-210) - Reaction" (7 December 2006). It seemed appropriate to feature this also in this blog - which now follows.

Polonium 210 (Po-210) - Reaction

Published 07 December 2006 by Mark Ramsay (Ionactive Consulting). (c) 2006 and 2022.

The last couple of weeks have been very interesting at Ionactive towers. Busy as usual, but we also had the polonium 210 (Po-210) incident to consider. Clearly this was a most unfortunate event and we must not forget that someone died here – Alexander Litvinenko. However it has to be said that as morbid as this might sound, it takes a situation like this to get the radiation protection community champing at the bit – trying to work out what the radiation exposure was or what mass of Po-210 was delivered to the victim. Indeed this has been evident in some of the private professional forums we belong to – some of the discussions have been impressive.

Ionactive keeps out of the limelight

We received many requests to appear on news programmes but turned down most – 5 minutes in the lime light is much less important than our client work. The usual suspects (you know who you are) did appear in the media with varying levels of success (our humble opinion of course).

Unfortunately we are less impressed with the media and how technical accuracy has taken second place to ‘the radiation poisoning story’. We are not actually blaming the media here – far from it. So who do we blame?

Telling it how it (really) is

Well – the radiation protection community in the UK must take some of the blame for the media misinterpreting some of the facts. The Health Protection Agency (HPA) press releases have been a useful information resource – but do they really do the trick (and have the media read them?).

We also think the professional radiation protection societies in the UK have kept their heads down - they might have supplied information behind the scenes - but where was the public press release?

Ionactive Po-210 Statement

For better or worse Ionactive did pop its head above the parapet and issue a news article: Polonium-210 Poisoning [see above]. The news article may not be that eloquent and certainly not worthy (or interesting enough) for a Sunday supplement. However we felt the radiation protection community needed to say more and so we attempted to put some facts together – perhaps suitable for the reader with more than just a casual interest.

After reading a number of press reports and watching the news it was clear that phrases such as ‘radiation found on plane’ were being banded about. Our article attempts to clarify what radiation means in the context of Po-210 – if one understands this then one will understand that the above statement is nonsense unless clarified. Of course (background) radiation (in all its forms) will be found on a plane - and more so once it’s at cruising height (cosmic radiation). This is not meant to sound pedantic or arrogant – the terms really must be used in the correct context otherwise the media (and hence the public) get the wrong idea. Only tonight (07/12/2006) the BBC report ‘radiation found in hotel workers’ – what does that really mean since we all have radioactive material in us (at low concentrations of course). In the HPA statement issued today (07/12/2006) a statement reads '...appear to have been exposed to low levels of Polonium-210...' (regarding staff working in The Pine Bar of the Millennium Hotel). Does this mean 'came into contact with', 'found internally' - and what is low? Is it not right that any amount of 'lethal radiation' (to use the words in one national news paper) is just that - lethal? (better not fly then, have your teeth x-rayed or smoke!).

How much Po-210 does it take to kill?

In our article we make a number of assumptions – some clearly sensible and others more or less plucked out of thin air (but still with some merit). Many want to know ‘how much radiation did it take to kill Alexander Litvinenko’ (note, even this question is nonsense – it should be ‘how much Po-210’). For a bit of fun (radiation protection is our life after all) we attempted to calculated this figure and came up with a value of 0.7 micro-g (i.e. a mass of Po-210 that would not be seen by the naked eye but could kill in 20 days if ingested - via a chemical delivery which would allow the radioactive material to be distributed around the body).

It is therefore rather amazing (and perhaps a fluke but we would rather not suggest this), the US Health Physics Society (HPS) came up with the same value! There is no way humble Ionactive would argue with such an acclaimed body of experts – but as it happens we don’t need to as we agree! You can read the HPS article by following the link: HPS Po-210 Information Sheet (link & article does not appear to be available as of 2022). Even this article has a couple of errors, but we feel it is better than most official information provided from the UK direct.

Ionactive and Po-210 on the WWW

Releasing our Po-210 article has also been a lesson in website / search engine optimisation (meaning: how to appear at the top of web searches). Whilst it was certainly not our aim to seek high rankings, our Po-210 article has increased visits to the site significantly. For example, looking at our own web stats reveals that the following search terms (on goggle) have turned up our site near the top of the listings:

  • polonium-210 poisoning
  • alexander litvinenko and the effects of polonium 210
  • polonium 210 effects on the body
  • dose calculation for po-210 (No 1 position !?)
  • Po-210

Po-210 incident - what we can learn

We hope the UK radiation protection community, the media and indeed the public will learn from this unfortunate incident (now being classed as murder). We do not believe the risk of a dirty bomb incident has gone away – what we have seen is a small demonstration of how we, the media and the public might react to such an event. To call a dirty bomb a MAD weapon (Mass Assured Disruption) looks like being a certain understatement based on the last couple of weeks.

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