How Polonium Poisons

The polonium-210 poisoning of former Soviet spy Alexander Litvinenko has health physicists dusting off Cold War-era tomes on the biological effects of radioactive isotopes. Data are scarce, especially for human exposure to the isotope, but scientists still have a good idea of how polonium may have led to Litvinenko's death on Nov. 23, 22 days after his alleged poisoning in London.

²¹⁰Po, once used in triggers for fission bombs, is an α-particle emitter with a half-life of 138 days. It decays into stable ²⁰⁶Pb by spitting out an α-particle—a helium nucleus—with 5.3 MeV of energy. That's a million times the energy of a typical chemical bond. Even so, α-particles are readily stopped by a single sheet of paper, so ²¹⁰Po generally becomes dangerous only if it gets inside the body.

If Litvinenko ingested even 1 µg of ²¹⁰Po, perhaps as a citrate or chloride salt, roughly 3 quadrillion atoms of the isotope would have entered his system, enough potentially for tens or even hundreds of ²¹⁰Po atoms to reach every cell of his body. Even as he began excreting the poison, most of the polonium atoms would have insinuated themselves into cells by associating with proteins. From those perches, the radioactive nuclei would have shot out α-particles that wreak biochemical carnage.

Wherever these α-particles go, they deposit a huge amount of energy in a tiny region, says radiation researcher Roger W. Howell of the University of Medicine & Dentistry of New Jersey, in Newark. As each α-particle cuts a path through a several-cell distance, Howell and others say, it leaves a devastating trail of ionization and radical formation, destroying proteins and severing DNA along the way.

Litvinenko died just a few weeks following his poisoning probably because the α-particles decimated the especially fragile stem cells in his bone marrow that are required for the constant proliferation of red blood cells and key immune system cells, explains veteran radiation scientist Albert L. Wiley Jr. of the Radiation Emergency Assistance Center/Training Site, in Oak Ridge, Tenn.

It will take sleuthing by detectives and a detailed autopsy report to determine more precisely what happened before, during, and after Litvinenko's poisoning, Wiley notes.