Death by polonium?

po clearanceLast year I posted a piece that, in addition to 2 other short bits, briefly discussed the possibility that Yassar Arafat might have been poisoned with polonium-210 (Po-210) in 2004, including the apparent finding of elevated levels of the nuclide in Arafat’s remains. At the time I was dubious that there would be enough Po-210 left after so many years to reliably detect or to quantify the amount that might have been administered (or even to differentiate between the Po-210 that is naturally a part of our biochemistry versus what might have been administered as a poison. It looks as though I might have been wrong to dismiss the idea – here’s the latest news on the topic.

Earlier this week Al Jazeera America published a story on their website discussing the further testing that was done on Arafat’s belongings, his remains, and his gravesite. Al Jazeera included a link to the forensic report by the University Center of Legal Medicine in Lausanne and Geneva in Switzerland. To cut to the chase, the authors of the report felt that their “results moderately support the proposition that (Arafat’s) death was the consequence of poisoning with polonium-210.” The work appears to have been undertaken with care and appears to have no flaws that would invalidate the authors’ conclusions – what I’d like to do in this week’s posting is to discuss some of the tests that were run, what was found, and the science behind them.

Where Po-210 comes from and where it’s used

For starters, Po-210 is found in nature – as U-238 decays towards stable lead (Pb-206) it passes through a number of intermediate radionuclides. Radium (Ra-226) is one, radon (Rn-222) is another, and Po-210 is in the decay chain as well as the decay product of Pb-210. So any piece of rock or dirt will have some Po-210 – but that’s not where commercial Po-210 comes from. There’s far too little Po-210 in nature to make it worthwhile to go to the trouble of separating it out; instead, a chunk of bismuth (Bi-209 to be precise) is placed in a nuclear reactor where it captures a neutron and forms Bi-210. With a half-life of only about 5 days, the Bi-210 decays by beta emission to form Po-210.

World-wide production of Po-210 is about 100 grams annually (about 16,600 TBq or nearly 450,000 curies), almost all produced in Russia. Although it used to be used as a neutron source, as a source of heat to keep delicate electronic components warm, and as a power source for satellites (polonium is so intensely radioactive that a 1-gram source will heat itself up to over 500˚ C, producing up to 140 watts of energy in a radioisotopic thermal generator, or RTG). Today, however, Po-210 is used only as a static eliminator for industries that manufacture thin films, strands, and powders.

There is also Po-210 naturally in our bodies – we all inhale traces of dust as well as radon (which decays to form Po-210), not to mention bits of dust that drift into our food. Minute traces of Po-210 are also found in fruits and vegetables that we eat – the bottom line is that everybody has some level of polonium in his or her body. Smokers have even more polonium than the rest of us because tobacco (and other broad-leaved plants) contains elevated amounts of the nuclide. So smokers will have higher levels of Po-210 in their bodies; their excreta (urine and feces) will also have higher levels of polonium. Why all of this is important is that we have to remember that Arafat’s body would be expected to have traces of Po-210 from natural sources and, if he smoked, it would be expected to have even more. Thus, the question the Swiss scientists had to answer was not “Did we find Po-210 in Arafat’s body” but, rather, “Did we find significantly more than can be accounted for from natural uptake (inhalation and ingestion), from radon that might have deposited Po-210 in the grave, or from smoking or other sources?” And, of course, “Is there enough Po-210 left to even measure?”

Measuring Po-210

Measuring Po-210 is fairly straightforward – radiochemistry is a fairly well-established discipline and radiochemists are very good at extracting polonium from samples and identifying it. They also do a great job with other nuclides, including Pb-210 that can act as a parent to the Po-210. There’s a laboratory term – the lower limit of detection (LLD) – that refers to the lowest level of any nuclide that can be unambiguously identified in laboratory testing. Any detection that’s less than the LLD is problematic; it could be instrument or laboratory error, or even a statistical anomaly while any detection higher than this level is probably an actual detection.

The Swiss scientists sampled Arafat’s belongings – clothing that he wore in his last weeks of life as well as a few other items – and they did find traces of Po-210 in items that came in contact with his body fluids. They compared these levels to similar items bought new in the store to see if these items (cotton clothing for example) normally had elevated levels of polonium. They concluded that the levels of polonium in Arafat’s personal effects were higher than normal – that they were apparently contaminated with polonium. Not only that – and more important – the levels they found were higher than the LLD.

In addition to measuring Arafat’s clothing, which could have been contaminated somehow, the scientists wanted to find out how much polonium was in Arafat’s body. To do this they had to exhume his body. But they also had to account for the polonium naturally present in the soil as a possible source of any polonium they might find; before even opening the grave they sampled for radon and calculated how much this might have added to the remains they were about to sample. Only with this information could they determine whether or not what they found was more than expected. And what they found was that there appeared to be higher-than-expected levels of polonium in Arafat’s body at the time he died. Smokers can have higher levels of polonium in their bodies, but not enough to account for the samples – and Arafat didn’t smoke at the end of life anyway. The bottom line is that the examination of Arafat’s body and grave revealed more Po-210 than could be explained by natural radioactivity. Based on their analytical results the scientists estimated that Arafat might have been dosed with approximately 1 GBq (about 27 mCi) of Po-210 – comparable to the 1-3 GBq with which Alexander Litvenenko, the former Russian spy who was poisoned with Po-210, is estimated to have ingested prior to his death in November 2006.

 

Medical symptoms

So laboratory results suggest that Arafat was dosed with a large amount of polonium – it’s reasonable to wonder if his symptoms were consistent with what would be expected from this level of polonium ingestion.

The answer isn’t really clear-cut. Arafat came down with acute nausea a few hours after eating a meal – nausea is one of the symptoms of acute radiation sickness. Over the next few weeks his platelet counts dropped steadily which is also consistent with radiation sickness. The last week or so, Arafat showed signs of liver and kidney damage as well as damage to the gastrointestinal tract; all of these are also consistent with what the medical literature reports for polonium poisoning. Finally, Arafat died a little more than a month after the proposed poisoning date – similar to the length of time Litvenenko survived after his poisoning.

On the other hand, other blood cell counts didn’t change in the manner expected of a person who died of radiation sickness. He also kept his hair, unlike Litvenenko – these are inconsistent with polonium poisoning. The bottom line is that the medical examinations and Arafat’s symptoms could point towards polonium poisoning, but there could be other explanations as well.

 

The report’s conclusions

The Swiss team considered a number of factors, some of which seem to support the possibility of foul play and some of which did not. They also considered a number of possible explanations for the symptoms and lab results that seemed to support the hypothesis of polonium poisoning. After considering all of the laboratory information and medical symptoms they concluded that “the results moderately support the proposition that (Arafat’s) death was the consequence of poisoning with polonium-210.”

I will not weigh in on the group’s conclusions because they were the ones who performed the study and who evaluated the evidence. And I certainly won’t speculate on who might have planned and done the deed – if that’s what happened – I’m a scientist and, as such, it’s best that I avoid speculating about criminal, terrorist, or political motivations. All I am really competent to comment on is the science and the manner in which it was used.

What I can say is that there didn’t seem to be any gaping holes in their approach, in their work, or in their interpretation of the data. It doesn’t seem as though they missed anything or that they steered the results towards a pre-determined conclusion. As of now, I guess you’d say that the jury is still out – the Swiss report doesn’t conclude definitively that Arafat was poisoned, just that it seems more plausible than the alternative. Having said that, it’s possible that they made a mistake somewhere – there are two reports yet to come in (one Russian and one French) and we’ll have to see what they conclude.

 

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4 Responses to “Death by polonium?”

  1. Raymond Firehock November 18, 2013 at 9:41 AM #

    Interesting. I assume not only the Russians but the Israelis (as well as other unsavory folks) could conjure up enough polonium for such a hit. Getting into his food and no one else’s sounds a bit tricky from afar.

    I note the judgment that there are “no gaping holes” evident in the analysis. That sounds like a cop-out. Are there any holes that are major but less than “gaping”?

    • Dr. Y November 18, 2013 at 6:19 PM #

      Pretty much anybody with a nuclear reactor CAN make Po-210, the question is whether or not they have. And I really can’t hazard a guess at the answer to that one since that question is as much political as scientific. Getting the material into food or drink is certainly possible – consider not only Litvenenko, but all of the women whose dates (or acquaintances) manage to drug them at the bar or at parties.

      With regards to hedging my argument – certainly (although I prefer to think of it as “scientific caution”). The parts that I know well hold together and I can’t see any serious flaws in the work. But there are areas in which I am not schooled in the details and I prefer not to make a blanket statement in such a case.

  2. Raymond Hoover CHP November 18, 2013 at 3:33 PM #

    First, when I ran the calculations on how much Po-210 Litvenenko ingested I came up with about 320 mCi, which I remember as being consistent with most of the estimates I saw at the time.

    Second, the fact that they found measurable amounts of Po-210 in the recent analysis does not show that Arafat died of Po-210 poisoning. Po-210 undergoes about 3 half-lives in a year. After 20 years the amount of Po-210 remaining would have decreased by about a million. This means the remaining Po-210 would have been in the nanoCurie range. Unlikely to have been detectable. Which means any Po-210 seen in the body would have had to come from a parent isotope Ra-226, or Pb-214 perhaps). Did the researchers look for these.

    Finally I would argue that any Po-210 outside the body is irrelevant since there would be essentially no exchange between the body and the outside of the body.

    I was interested to see that the researchers did sample for radon in the grave, but what were the results? The external Po-210 could have been due to Radon in the grave, since radon is a fairly short-lived while a couple of the daughters are longer lived hence at equilibrium you would see some Po-210.

    Enjoyed the article.

    • Dr. Y November 18, 2013 at 6:37 PM #

      Let’s see…320 mCi is about 11 GBq (if I got the unit conversion right), which is about an order of magnitude higher than the Swiss estimate from their data. But even the lower dose is enough to be fatal.

      With regards to detection after so many half-lives,I was dubious on this matter as well. But if we start with 1 GBq and decay it through a factor of 10 million then there’s still 100 Bq remaining – 1 Bq is left after 30 half-lives. I found a couple of references in which the LLD for alpha-emitters is given to be on the order of 1 mBq (about 0.03 pCi) – even if this is off by an order of magnitude, it looks as though there would still be enough Po-210 to be detectable. Given that the company I used to work for routinely measured environmental contamination levels on the order of 1 pCi/gm or less (and this was 20 years ago), a detection limit of 0.027 pCi in a modern lab seems plausible.

      The authors did discuss the search for Pb-210, which has a long enough half-life to have lasted virtually undiminished and which occurs in nature – they corrected for this by looking for “unsupported” Po-210 (that is, Po-210 beyond what could be explained by the Pb-210 that was found).

      You’re correct that Po-210 outside the body is irrelevant at the time of death – but after several years most of the soft tissues have decayed and their contents released into the soil. But elevated levels of Po-21- were also reported in bone and in stains from body fluids in personal effects (e.g. a small urine stain in underwear).

      So – all good points, and all reasons that I was skeptical when the plan to explore this possibility was first announced. I have to admit that, when I started reading the report, I fully expected to find glaring errors, wishful thinking, poor science, etc. – it was only grudgingly that I had to acknowledge that these major errors seemed to have been avoided.

      At this point I think the question is still open – I agree with the authors that their work did not find conclusively that Arafat was poisoned with Po-210, but neither did it rule out the possibility.

      And finally – I’m glad you enjoyed the article; I certainly enjoyed reading it!

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