Note that investigators of Litvinenko's poisoning are talking not just about food and drink but now cigarettes. From the getgo backgrounders on polonium have informed us that inhalation is one way this deadly poison gets in the body. They've not mentioned that ingested polonium is liable to go straight through you--making sushi a dubious candidate vehicle for poisoning somebody with polonium. Note what the EPA says about this more familiar alpha-emitting heavy metal:
About 99 percent of the uranium ingested in food or water will leave a person's body in the feces, and the remainder will enter the blood. Most of this absorbed uranium will be removed by the kidneys and excreted in the urine within a few days. A small amount of the uranium in the bloodstream will deposit in a person's bones, where it will remain for years.I'd say the smart money is on the cigarettes. Your victim carries them everywhere and spies obviously have a thing about them. Even if your spy's a yuppie, best think noire, not nori.
Follow up: Litvinenko ingested the polonium that killed him by drinking a cup of tea, the Times (UK) is reporting. Despite what I wrote above, the report sounds kinda sensible, in that it says the poisoner had to use a hot beverage to avoid tipping off his victim, and had to let it cool before he added the polonium, because it's radiation would be continuously delivering heat to the water. Water doesn't get hot easily, compared to metals and other common materials, and so immediately my thought was "Wow, that's a lot of polonium! Well, then, maybe bets are off: The EPA is unlikely to know or care about acute exposures that intense, which essentially can't happen by accident, in which case their point about ingestion overlooks the forest for the trees under Litinenko's dosing." The water heating makes perfect sense, since water is a very efficient absorber of alpha particles, and polonium radiates alphas. Except it's so efficient that, in the nuclide biz, one learns not even to worry about alphas penetrating the dead layer of cells in your skin, and so it seems like only Litivinenko's gut-lining cells would have been killed off. This can kill you? A hole in your intestine--from a burst appendix, for example--will kill you because it lets bacteria go lunch on your vital organs. But "infection" isn't a word a remember from any of the Litvinenko news I've read. My intuition is that Litvinenko's gut would have to become darn perforated, darn fast, to leak much polonium into his chest, assuming business as usual. Peristalsis and other business might well have shut down, I guess, as his intestinal epithelial cells dissolved under the barrage of alphas. Could sloughing of these cells have exposed Litvinenko's intestinal capillaries, through which the polonium atoms or atomic-clusters he ate might have traveled around his body widely?