Making a Poisoner: Half-life in a scientific detective story.

    Former Palestinian Liberation Organization leader Yasser Arafat died in November 2004 in a French hospital, where he was flown after falling ill in October 2004. After suggestions that Arafat was poisoned with the radioisotope Polonium (210Po), an autopsy was begun in February 2012.

    The previous Litvinenko assassination has been reconstructed as a single oral dose of 109 Bq (= 1 GBq) of 210Po., which resulted in death in <30 days, accompanied by characteristic toxicity and acute radiation syndrome. Of this dose, 10% would have been absorbed into the blood system, and thence into the kidneys and urine, where it would be excreted initially at a rate of (0.5% / day)(108 Bq) =  5 x 105 Bq / day. The biological half-life is 30 ~ 70 days could introduce  a factor of no more than two prior to death within < 30 days.

1) The evidence in the Arafat case was the presence of  210Po in his urine-stained underwear. Suppose a typical urine stain in underwear derives from 1 ml urine. At the above excretion rate of (5 x 105 Bq / day) / (500 ml urine / day) = 103 Bq / ml, any one such stain would contain 103 Bq. As in the Litvinenko case, Arafat died in < 30 days during which time he would have excreted a maximum of (30)(0.5% / day) = 6% of the single initial dose.

2) 210Po has a physical half-life of 138.4 days, and there are 19 half-lives between death in October 2004 and testing in February 2012. The physical decay factor is (0.5)19 = 2 x 10-6

3) A 1 ml urine stain would therefore be expected to decay to (103 Bq)(2 x 10-6) = 2 x 10-3 Bq = 2 mBqAuthors of an autopsy report in The Lancet concluded “it is reasonable to expect an activity in the order of magnitude of 1-10 mBq….” in the observed stains in Arafat's underwear, under the conditions and assumptions above.

4) The background = ~3 mBq, and suspicion of poisoning would arise at >10 mBq. The two most highly contaminated stains in Arafat's underwear showed 60 ~ 181 mBq, his toothbrush 21 mBq

Conclusions: A 109 Bq (= 1 GBq) oral dose would be expected to decay to below background levels, by biological and physical processes, in the interval between death and autopsy. The reported residual levels are as much as 90 times that. The poisoning scenario is (very) unlikely to underestimate dose by as much as a factor of 10, and if it did expect classical acute radiation syndrome manifested, as with Litvinenko. News media took “contamination well above background” as proof of poisoning, however the higher the estimate above background, the poorer the fit to a poisoning model, as versus (deliberate) contamination. A dose of 1 GBq is 100 times the LD50 lethal oral dose of 10 MBq, if the poisoner wanted to be subtle.

5) 210Po is produced artificially by neutron bombardment of Bismuth (210Bi) in specialized reactors. However, it also occurs in nature, for example in cigarette tobacco and cotton. Arafat’s brand of underwear, tested new out of the package, had as much as 20 mBq.


All text material © 2016 by Steven M. Carr