Polonium-210: Science Meets Spydom

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Polonium-210: Science Meets Spydom

by Elisheva Coleman

Martin Hayhow/AFP/Getty Images; Roland Magunia/AFP/Getty Images
Through the first three weeks of November 2006, doctors at London's University College Hospital struggled vainly to save Alexander Litvinenko (left), as the former KGB spy's organs failed one after another.

Through the first three weeks of November 2006, doctors at London's University College Hospital struggled vainly to save Alexander Litvinenko, as the former KGB spy's organs failed one after another. Litvinenko, a dogged critic of Vladimir Putin's Russian government, had clearly been poisoned, but without knowing what toxin was at work, the doctors treating him were flailing in the dark. It wasn't until November 24, the day after Litvinenko died, that the poison was identified as polonium-210, an extremely rare, radioactive element. Because the element is so obscure, hard to obtain and perfectly suited to poisoning, investigators believe that the murderers must have been well-connected and scientifically knowledgeable. The polonium-210 revelation places science squarely at the center of this unfolding political intrigue.

Periodic Table Poison

Polonium, element number 84 on the periodic table, was discovered by Marie and Pierre Curie in 1898. Like radium, its more famous and abundant sister element, trace amounts of polonium occur naturally in pitchblende—a type of uranium ore. Because of those traces, pitchblende is more radioactive than the uranium derived from it. The Curies solved this scientific conundrum by isolating the highly radioactive elements polonium and radium from pitchblende samples.

Axel Schmidt/AFP/Getty Images

Polonium, element number 84 on the periodic table, was discovered by Marie and Pierre Curie in 1898.

No less than 25 isotopes of polonium are known to exist, but Po-210, with 84 protons and 126 neutrons, is by far the most common. Calling polonium-210 common, however, is a matter of perspective; one ton of uranium ore contains a miniscule 100 micrograms (millionths of a gram) of the stuff. Polonium "is one of the rarest elements on the earth's crust and also one of the most exotic," chemist Andrea Sella of University College in London told the New York Times.

Obscure Element

Since it's so rare in nature, most of the polonium in existence is made artificially, in nuclear reactors. Polonium-210 is made by bombarding bismuth, a stable, metallic element, with neutrons. When the normal bismuth isotope, Bi-209, absorbs a neutron, it becomes Bi-210, which is radioactive. Bi-210 undergoes beta decay, exchanging a neutron for a proton and emitting an electron, to become Po-210.

Russia is the world's foremost producer of polonium-210, exporting about 100 grams of the substance per year. Most of that is bought by manufacturers of devices to neutralize static electricity. Static electricity results from an overabundance of electrons, which carry negative charges. Alpha particles, the type of radiation emitted by polonium-210, are positively charged, so they attract stray electrons to quell static.

Scott Barbour/Getty Images

News outlets recently reported that it is possible to purchase a lethal dose of Po-210 on the Internet.

Scott Barbour/Getty Images

Experts interviewed in early reports on the Litvinenko case claimed that polonium-210 was accessible only to individuals with connections to nuclear facilities. More recently, news outlets, including the New York Times, have reported that the substance is actually not so hard to come by. By one estimate, it's possible to buy a lethal dose of Po-210 on the Internet, in the form of an anti-static-electricity fan, for $22.50. Still, a would-be poisoner would have to have considerable chemical know-how, and access to sophisticated lab equipment, to be able to extract the polonium from the fan. Doing so without poisoning himself would require even greater expertise.

Evidence that polonium-210 is easier to obtain than first believed has widened the circle of possible suspects. Nonetheless, the substance points to a killer with a sophisticated science background, and possibly connections to high-level Russian nuclear facilities. It is also a highly creative choice—Litvinenko's is the first intentional poisoning in history to be attributed to polonium-210.

Alpha Assassins

Alpha particles are the least penetrating, most easily blocked form of radiation. On its face, this fact sounds like it should make polonium fairly innocuous—and to an extent, that is true. Alpha particles can't penetrate skin unless it's cut, so being near the stuff isn't particularly dangerous. Once it gets inside the body, however, all bets are off.

Alpha particles don't travel far, but they do possess enormous amounts of energy. In a controlled setting, energy from polonium-210 decay is given off as heat, and can be harnessed by a thermoelectric cell to generate electricity. One gram of Po-210 can produce 140 watts of energy, and during the 1970s, the Soviet Union used the isotope to power short-mission spacecraft. (Polonium-210 is useless for long missions because it has such a short half-life, just 138 days.)

While skin blocks alpha particles, if polonium-210 is ingested, inhaled, or injected, the radiation rips through cells to do massive internal damage. The same feature that makes alpha particles easier to block than other forms of radiation, namely their mass, also makes them particularly insidious to human tissue. (An alpha particle has a weight of 4 atomic mass units (amus), whereas beta and gamma rays have practically no mass.) When a hefty alpha particle barrels into DNA, it does considerable damage. The radiation can also damage DNA indirectly, by splitting water molecules to form free radicals, which attack DNA.

As polonium travels through the bloodstream and spreads into tissues, the first casualties are fast-growing cells in hair, bone marrow, blood and the digestive tract. These rapidly dividing cells are especially vulnerable because they copy their DNA frequently, giving alpha particles more targets. Genetic damage is also immediately disruptive in actively dividing cells, since the effects of damaged genes often don't register until the cell tries to replicate.

No Antidote

Litvinenko fell ill on November 1, hours after he had tea with two business associates, Andrei Lugovoi and Dmitry Kovtun, both fellow former KGB agents. Officials suspect that the poisoning occurred at that meeting. Litvinenko's first symptoms were gastrointestinal, leading doctors to believe that polonium was slipped into his food or drink. Since a lethal dose of polonium is tiny—one millionth of a gram, according to Nick Priest, a radiation expert at Britain's Middlesex University—it could have been dissolved in "any volume [of liquid] from a litre down to a few drops," he told the BBC.

Natasja Writsz/Getty Images

After Litvinenko was admitted to the hospital, his hair fell out and his immune system largely shut down as radiation destroyed his bone marrow and white blood cells.

After Litvinenko was admitted to the hospital, his hair fell out and his immune system largely shut down as radiation destroyed his bone marrow and white blood cells. In time, radiation damage began to affect slower-growing cells as well, and his liver and digestive organs began to fail. The direct cause of the ex-spy's death was a heart attack, suffered on the night of November 23. He died the following day.

Throughout Litvinenko's ordeal, doctors struggled to identify the poison, but they realized early on that fingering the substance would make little difference in their ability to help him. At first, doctors linked Litvinenko's symptoms to thallium, a heavy metal used in several high-profile murders. Rapid hair loss is a hallmark of thallium poisoning, and the metal also causes gastrointestinal distress—but it does not attack bone marrow, which ultimately disqualified it as the toxic agent. Once it became clear that radiation was involved, doctors knew there was little they could do beyond treating Litvinenko's symptoms. There is no known way to rid the body of radioactive particles; treatment is limited to fending off infection and trying to support the body while it repairs itself.

Unsolved Mystery

To date, Litvinenko's killer is still on the loose, and investigators have few promising leads. Detectives are taking advantage of the fact that transporting radioactive material often leaves a trail, in the form of minute traces that can be detected with radiation-sensing equipment. Although polonium-210 is easy to contain, since a simple vial stops its alpha particles, a person who has the isotope in his system will excrete it in tears, sweat and other bodily fluids. The polonium trail has led investigators from London to Moscow-bound British Airways planes to, most recently, Germany. (Moscow has, so far, remained off-limits to British investigators.) German officials found polonium traces in several spots in Hamburg, where Kovtun, one of the men at the November 1 meeting, stopped on his way from Moscow to London. One of the Hamburg hot spots was a couch in Kovtun's ex-wife's apartment, where the KGB agent-turned-business-consultant spent the night. No charges have been brought against Kovtun, and unconfirmed reports that he has been hospitalized in Russia with radiation poisoning have left doubts over whether he was an assassin or another victim.

Some nuclear experts hope that investigators might be able to use sensitive scientific tests to discover where the murderous polonium-210 was produced. Radioactive material made in reactors generally carries "nuclear fingerprints," contaminants of other radioactive substances that were processed in the reactor. Assembling a profile of these contaminants could help detectives pinpoint the facility that produced the polonium; that information might lead them to the perpetrator. It's not clear, however, whether there is enough material in the scattered polonium traces to run such tests.

Ultimately, despite all the high-tech science involved in the mystery, some experts think solving it will hinge on old-fashioned detective work. Investigators "will do the best they can technically," William Happer, a physicist at Princeton University, told the New York Times. "But my guess is that it will take an informant." Pitted against the shadowy world of international spydom, even science may be out of its league.

Radioactive Decay Table

Radiation comes from unstable atomic nuclei, which degenerate into stable nuclei by emitting subatomic particles. We call those particles radiation. There are three categories of radioactive decay, defined by the type of particle given off.

Type of Radiation	Particle Emitted	Change in Nucleus	Blocked By
Alpha Decay	Helium Nucleus—2 Protons, 2 Neutrons	M - 4, Z - 2	Sheet of Paper
Beta Decay (minus)	Electron, Anti-Neutrino (neutron converts to proton)	Z + 1	Aluminum Plate
Beta Decay (plus)	Positron, Neutrino (proton converts to neutron)	Z - 1	Aluminum Plate
Gamma Decay	Gamma Ray (photon)	No Change	Thick Lead Sheet
M = Mass Number, Z = Atomic Number

Bibliography

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McNeil Jr., Donald G. "A Rare Material and a Surprising Weapon." New York Times, November 25, 2006, page A9.

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