Issue Date: January 29, 2007
THE PUTATIVE polonium poisoning of former Soviet spy Alexander Litvinenko has aroused great interest in the radiation protection community (C&EN, Dec. 4, 2006, page 15).
As a long-retired radiation protection person, I dusted off my International Committee on Radiological Protection (ICRP) manuals to do a few calculations and look up some data. Although, as frequently stated, the polonium-210 half-life is 138 days, its effective half-life in the body is 25 days when ingested. The target organs are the kidneys and spleen, not bone marrow, as suggested in the article.
The article also states that 0.1 µg is the equivalent of about 3 quadrillion atoms of Po-210. This is correct, but it must be compared with the total number of atoms in a typical human body, which I estimate to be roughly 4E27 (4 followed by 27 zeroes).
Another factor to be considered is the fraction of the Po-210 that actually remains in the whole body after ingestion. From ICRP data, this fraction is 0.06. Most of the Po-210 is presumably rapidly eliminated in urine and feces. From another calculation, 0.1 µg of Po-210 has a radioactivity of 4,500 µCi compared with Po-210's permissible body burden of 0.4 µCi. This means the body can tolerate a constant level 0.4 µCi for 50 years without increased cancer risk.
The next question is how long would it take for an ingested 4,500 µCi of Po-210 to be reduced in the body to 0.4 µCi? The answer to this question is 150 days. What this all means as to the acute radiation hazard of Po-210 I do not know.
However, if ever I suspect that someone has just given me a dose of Po-210, I would immediately take a large swallow of Pepto-Bismol. Since bismuth and polonium have similar chemical reactions, most of any ingested polonium in the gut would rapidly be replaced by the bismuth in Pepto-Bismol, and the Po-210 would be harmlessly eliminated. Historically, we remember that Madame Curie used bismuth as a carrier for polonium.
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