Polonium, $22.50 Plus Tax

THE trail of clues in the mysterious death of Alexander V. Litvinenko may lead to Moscow, as the former spy claimed on his deathbed. But solving the nuclear whodunit may prove harder than Scotland Yard and many scientists at first anticipated.

The complicating factor is the relative ubiquity of polonium 210, the highly radioactive substance found in Mr. Litvinenko’s body and now in high levels in the body of an Italian associate, who has been hospitalized in London. Experts initially called it quite rare, with some claiming that only the Kremlin had the wherewithal to administer a lethal dose. But public and private inquiries have shown that it proliferated quite widely during the nuclear era, of late as an industrial commodity.

“You can get it all over the place,” said William Happer, a physicist at Princeton who has advised the United States government on nuclear forensics. “And it’s a terrible way to go.”

Today, polonium 210 can show up in everything from atom bombs, to antistatic brushes to cigarette smoke, though in the last case only minute quantities are involved. Iran made relatively large amounts of polonium 210 in what some experts call a secret effort to develop nuclear arms, and North Korea probably used it to trigger its recent nuclear blast.

Commercially, Web sites and companies sell many products based on polonium 210, with labels warning of health dangers. By some estimates, a lethal dose might cost as little as $22.50, plus tax. “Radiation from polonium is dangerous if the solid material is ingested or inhaled,” warns the label of an antistatic brush. “Keep away from children.”

Peter D. Zimmerman, a professor in the war studies department of King’s College, London, said the many industrial uses of polonium 210 threatened to complicate efforts at solving the Litvinenko case. “It’s a great Agatha Christie novel,” he said. “She couldn’t have written anything weirder than this.”