By Dr. Ferenc Dalnoki-Veress – President Yasser Arafat, the former president of the Palestinian National Authority, passed away under strange circumstances in 2004 and the cause of his death has never been satisfactorily explained. The doctors who examined him in 2004 were perplexed. They looked for any toxins in his body that could explain the observed symptoms but found none. They also considered the possibility of radiological poisoning such as thallium, a radioactive element, but after measuring his urine and blood found none present. The doctors also did not benefit from knowing that two years later in 2006, a lethal silent killer, an isotope known as polonium-210 (hereafter, Po-210) would be used to kill an Ex-KGB agent Alexandr Litvenenko.
Po-210 has a half-life of 138 days which means that after 138 days, half of the original amount will have decayed to a stable isotope known as lead-206, after additional 138 days the original amount is one quarter what it was, and so on. When the isotope decays it releases particles which shoot out like bullets and harm surrounding tissue leading to massive cell death. Presumably, if the investigators in 2004 had known about the possibility of Po-210 as a toxin, then they could have most certainly proved or disproved the hypothesis that a lethal dose of Po-210 was the cause of President Arafat’s death without any lingering doubts as there are now. Unfortunately, hindsight is twenty-twenty. However, this does not mean that determining the cause of death is impossible; it is just immensely difficult today, twenty half-lives later. The first rule about radioactivity is that a substance doesn’t just decay into nothing, it decays into another isotope, and always leave some evidence of its presence behind. To make matters worse, while Po-210 when used as a dangerous poison is produced in nuclear research reactors, it is also present in minute quantities in nature. So that if most of the Po-210 from the initial poison has already decayed away it will become difficult to distinguish it from the Po-210 that is present naturally.
In 2011, Al Jazeera launched an investigation into the death of President Arafat with the support of his widow Suha Arafat. Al Jazeera’s investigator, Clayton Swisher, received from Suha Arafat access to Arafat’s French and Palestinian medical files, and a green duffel bag containing Arafat’s final possessions. Swisher reportedly delivered the effects to the Lausanne University Hospital for testing in January 2012. Arafat’s belongings from the French hospital, the clothes he wore, his tooth brush, anything that touched his body were provided to a well-respected forensics team from the Institut de Radiophysique (IRA) in Lausanne, Switzerland for careful analysis.
If President Arafat would have been given a lethal dose of Po-210 in 2004, nine years ago then a portion of the toxin would have been excreted from his body through sweat and urine. Finding Po-210 on the clothes President Arafat wore would be tell-tale sign that he was poisoned. This measurement would have been relatively easy immediately after he died, but now twenty half-lives later the quantity that can be found is so low that it is almost identical to the quantity of Po-210 that is naturally present in the environment. This means that investigators must have very sensitive detectors and must carry out careful sample preparation so that very small fluctuations above the environmental level of Po-210 can be measured.
There were two stages to the investigation into President Arafat’s death. The original belongings of President Arafat were analyzed by the Swiss group in early 2012, which revealed enough evidence for the French prosecutor to launch a detailed murder investigation. President Arafat passed away November 11 2004 at the Percy Military Hospital west of Paris so the criminal investigation has been launched in France. As part of the investigation, President Arafat’s grave was exhumed and samples were taken from the corpse on Nov 2012. The samples were given to three independent forensic teams: Russian, French and the Swiss team that also investigated the original belongings in 2012.
No detailed results have been released by the Russian and French teams and the report released by the Swiss team and published by Aljazeera concerns both the first phase of the investigation of President Arafat’s belongings and the second one, the samples from his body. The 108 page report is a comprehensive, careful, clear, transparent scientific analysis, and the team should be commended on their rigour (TEPCO please learn from the Swiss!). However, as in all scientific analysis it also leads to further questions, surprises and unfortunately further doubts as well.
Analysis of Arafat’s belongings
Ironically, it is my opinion that the original analysis of President Arafat’s belongings holds the strongest evidence for a lethal Po-210 poisoning. Just last month, the British Journal Lancet published (behind paywall) a letter from the Swiss group summarizing the results of the Po-210 investigation on President Arafat’s belongings hyperlinked to an extensive appendix where for the first time the percentage of supported Po-210 was published.
To better understand the concept of half-life, picture the depletion of Po-210 due to radioactive decay to lead-206 (Pb-206) as a leak of a liquid through a spout at the bottom from a bucket. As the Po-210 decays the bucket is accumulating into a second Pb-206 bucket which has no spout because it is stable. In this analogy the wider the spout the shorter the half-life since the bucket will decrease quickly. If only Po-210 would be present then the quantity of Po-210 should follow the half-life of Po-210, that is after one half-life has passed only half the amount of Po-210 would be present. This would be called unsupported Po-210. Now, picture a third bucket that feeds into the Po-210 bucket, then as the Po-210 bucket is emptying it is being partly replenished by the third bucket. In fact, the third bucket exists in nature and is known as the isotope Pb-210 (see Figure 1 below). The isotope Pb-210 is present in small quantities and is a natural decay product of one of the isotopes of the radioactive gas Radon which is present in dwellings around the world. The fraction of Po-210 that is coming from Pb-210 decay is known as supported Po-210 because the Po-210 is constantly being replenished by Pb-210.
Figure 1: The series decay of Pb-210 to Pb-206 pictured as a series of buckets where the width of the spout is analogous to the half-life of the isotopes. Pb-210 has a 22 year half-life and so is pictured as a thick width spout, whereas Po-210 has a 138 day half-life and is pictured as having a considerably wider spout. The figure also demonstrates the notion of supported and unsupported Po-210. If the Po-210 is supported then the Po-210 that is decaying to Pb-206 is being replenished by the decay of Pb-210. If the Po-210 is unsupported then the Pb-210 bucket is essentially not there and the Po-210 decays to Pb-206 consistent with its 138 day half-life.
One would expect that if President Arafat would have been poisoned purely with Po-210 then only unsupported Po-210 would be present. However, just as there is natural Po-210 present in the environment there is also natural Pb-210 in the environment which influences the amount of Po-210 that is measured. The strongest evidence for Po-210 poisoning would be a large quantity of Po-210 on a sample, significantly above the level expected for the sample if no poisoning had occurred (the blank, or background level of Po-210) and if the majority of the sample demonstrates unsupported Po-210.
In fact, buried deep in the appendix of last month Lancet article, the Swiss group published that they found that a urine stain of a sample of underwear had a Po-210 quantity significantly above what would be expected. Most importantly, in a bomb-shell that the media missed, it was only 42% supported. Moreover, another urine stain found a high quantity of Po-210 as well, this time with only 10% supported indicating that it was as if there was almost no third bucket at all replenishing the Po-210. These results are discussed at length in the report released by Aljazeera this week. It is important to note that other samples randomly taken without visual cues as to the presence of urine showed a much lower level of Po-210 and can be seen as a “blank” measurement.
Being prudent scientists the Swiss group cannot discount the “voluntary mishandling of the specimens between the time of President Arafat’s death and the time the bag was presented”. However, they correctly temper this statement by saying that this type of tampering with evidence would require “very specific knowledge” and the “precise and selective contamination of clothing is a very difficult task”. The measurement of unsupported Po-210 significantly higher than expected from the blank is the first evidence and in my opinion the strongest evidence for Po-210 poisoning.
Analysis after exhumation
President Arafat’s body was exhumed in Nov 27, 2012, and the forensics teams approached the corpse carefully in order to understand the state of the body. The team took skeletal samples from Arafat’s body, the surrounding soil and the burial shroud. They conducted a genetic analysis to verify the authenticity of the skeletal remains, and conducted a toxicological analysis but found that there were no chemicals inconsistent with the medical reports. They hypothesized that the soil samples taken close to the body would have been contaminated with Po-210 by the presence of body fluids, whereas the soil samples away from the body could be considered as “blank” samples of soil. In fact, in further analysis they found a 15-fold increase in Po-210 concentration in the soil in a dark high humidity spot directly underneath the corpse compared to the soil sample away from the body. This is the second supporting evidence for Po-210 poisoning.
The team also took a sample from the Iliac crest and the scalp. The Illiac crest is the top part of the pelvic bone known as the Ilium. This sample was chosen because it tends to be covered on skeletonized remains with decayed tissue that has turned to a layer of wax (0.5-3 mm thick) insulating the bone from further environmental contaminants and sealing in the radioactive contaminants. When analyzing the level of Po-210 from these samples the level of contamination was not significantly different from the burial shroud which was also analyzed. However, the scalp showed a level of Po-210 more than twice as much as the highly contaminated soil underneath the body. Further analysis was conducted on bone fragments from the vertebrae, ribs, sternum and femur for the Po-210 concentration, and compared to other forensic reference samples of different ages at time of death. It was found that there was a significant increase above the reference level, especially in the ribs, for Po-210 contamination (see Figure 14 from Swiss report, pg 46, reproduced below as Figure 2).
Figure 2: Po-210 activities of all measured bones from President Arafat’s grave, as well as comparable reference bones from reference bones. Full triangles: President Arafat’s bones. Open circles: bones of forensic interest (CURML). Open squares: IRA reference bones collected at autopsy. This caption is taken verbatim from Figure 14, pg 46 of the Swiss report. See also B. Schrag et al., Dating human skeletal remains using Sr-90 and Pb-210: case studies, Forensic Science International (2013, accepted for publication).
The exact data of the reference forensic samples were not given but I estimate that the Po-210 concentration from the ribs exceeded the reference samples by as much as an order or magnitude. Non-bone samples such as altered tissue which has turned to wax from various parts of the body and burial shroud were also analyzed and most of the samples were found to have significant quantities of Po-210. This can be seen as the third evidence supporting the hypothesis of Po-210 poisoning.
Finally, the Swiss group assisted by the Paul Scherrer Institute (PSI) used mass spectrometry to measure the fraction of (Pb-207/Pb-206). This isotope ratio would not be expected to vary much for the illiac crest, vertebrae and ribs in the body. However, if a significant amount of Po-210 would have decayed to Pb-206, then an increase in Pb-206 would register as a decrease in the (Pb-207/Pb-206) ratio compared to the reference samples. In fact, a lower (Pb-207/Pb-206) ratio was observed in the rib specimens, which is exactly the specimen which also registered with a high Po-210 contamination. This is the fourth evidence supporting the hypothesis that President Arafat was poisoned with Po-210 toxin.
Not the end of the story
However, this is not the end of the story. When carefully analyzing the Po-210 concentration from the grave specimens the Swiss team found that while the level of Po-210 was higher than the reference samples, the Pb-210 was also higher. Recall, that Pb-210 eventually decays to Po-210, so if Pb-210 is present it would replenish the Po-210 that is decreasing with the 138 day half-life. At face value seeing highly supported Po-210 would lead one to conclude that some unknown environmental contaminant is the actual cause of the observation of Po-210 and lead one to have serious doubts about some of the exhumation results. However, as the Swiss group points out there may be alternative explanations for the high amount of Pb-210.
One possibility which they have investigated was that by thoroughly washing the bone fragments to remove external contaminants they may have washed away a significant fraction of the Po-210 present in the bone. In further analysis they confirmed that the solution they used to clean the bones preferentially extracted polonium rather than lead. This would have meant that they may have underestimated the concentration of Po-210 present in the samples. However, when analyzing the non-bone samples which have not been cleaned, the fraction that is supported is not significantly below 100% and does not demonstrate the same unsupported Po-210 as the urine sample stain.
The team then considered an alternative explanation which is the presence of a Pb-210 contaminant in the original Po-210 toxin. The presence of even a low level contaminant would not be observable when the Po-210 concentration is high, but when the Po-210 is significantly reduced the presence of a Pb-210 contaminant may be observed. It is well known that purchased sources tend not to be radiopure and often have isotopic contaminants. To test this possibility the Swiss group purchased a Po-210 source from the Czech Metrology Institute to determine the Pb-210 presence in a commercially purchased source which they determined at a level of 1 part in 10 million. The presence of this contaminant can significantly change the fraction of supported Po-210 consistent with observation.
Furthermore, the team points out that when the results were first released commentators suggested that the reason for the Po-210 contamination was because of the fact that Arafat was a “passive” smoker. However, the high level of Po-210 found in his urine cannot be attributed to smoking since daily excretion of Po-210 for a heavy smoker would be 4500 times less than observed.
The report published by the Swiss group is a thorough forensic analysis and this status report only discusses some of the main points associated with the radiological investigation. The interested reader is encouraged to study the appendix to the Swiss report where the full analysis techniques and procedures are documented. The main results from the paper are summarized in the table below.
|High Po-210 in Arafat Urine Stain||Unsupported Po-210 was found in a urine stain significantly above expected background level|
|High Po-210 in Soil sample taken from underneath corpse||A soil sample taken directly beneath the corpse in the area of the abdomen expected to be contaminated by bodily fluids was found to be highly contaminated with Po-210 at least 15 times higher Po-210 than an identical soil sample away from the corpse.|
|Bone fragments found to be highly contaminated with Po-210||Many bone fragments (especially from the ribs) were found to be highly contaminated with Po-210 compared to similar samples from forensic reference samples.|
|(Pb-207/Pb-206) measurement of bones indicated a higher Po-206 quantity in high activity samples||The (Pb-207/Pb-206) ratio was measured using mass spectrometric techniques at PSI and indicated a lower value for the high Po-210 samples, such as the ribs. This suggests that a significant quantity of Po-210 has decayed to Pb-206 which indicates an initial presence of Po-210.|
Table 1: Summary of the main points of evidence that support the hypothesis that President Arafat was poisoned with a lethal dose of Po-210.
I conclude that the weight of the evidence moderately supports the hypothesis that President Arafat was poisoned with Po-210 in 2004. However, the high supported Po-210 concentration in the bones and non-bone fragments (evidence #3) does cause the nature of the Po-210 to be questioned. It is hoped that the forthcoming reports from the other two independent groups will shed further light on the hypothesis.
Dr. Ferenc Dalnoki-Veress is a scientist in residence and adjunct professor at the Monterey Institute of International Studies.