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A highly active alpha particle emitter, Polonium-210 is a fatal toxin, even at very small doses.
Polonium-210 (210Po) made headlines in 2006 as the poison used to murder former Russian spy Alexander Litvinenko. Litvinenko was a KGB agent who later became an FSB (Federal Security Service) agent when Russia replaced the collapsed KGB in the early 1990s. He was given orders to assassinate an influential Russian business tycoon (whom he knew well), orders he disobeyed and then publicly exposed, among other KGB and FSB activities, on the international stage. His disclosures embarrassed the Kremlin and then-director of the FSB, Vladamir Putin. The Kremlin charged Litvinenko with treason and imprisoned him for nine months. After his release in 2000, in the wake of numerous death threats, Litvinenko and his family fled to the United Kingdom where they were granted political asylum.1
Litvinenko continued to aggressively denounce the Kremlin and Vladamir Putin, whom he accused of drug trafficking and pedophilia, perhaps naively enjoying a false sense of security inside the UK. Then, on November 1, 2006, he was mysteriously poisoned. Litvinenko’s rapid deterioration was chronicled by the international media, and he ultimately suffered for an excruciating 22 days before lapsing into a coma and dying on November 23. The toxin was identified just hours before his death as 210Po, an extremely rare substance. It is one million times more lethal than cyanide, and an amount the size of a grain of salt will kill a human being. Toxicology reports show that Litvinenko ingested more than ten times the lethal dose of the poison, indicating the resolve of his assassin to silence him once and for all.1
210Po—Radioactive and Rare
Polonium, atomic number 84, is a rare earth metal. It was discovered by Marie and Pierre Curie in 1898 while separating uranium from Bohemian pitchblende. The Curie’s found that the unrefined pitchblende was more radioactive than the isolated uranium, meaning it contained another radioactive component. They named this new element polonium, after their native land of Poland. The metal has over 25 isotopes, more than any other known element, and all are radioactive.2
210Po has unique properties that make it suitable for commercial use. The radiation emitted from one gram of the isotope generates 140 watts of heat energy, making it a desirable alternative for powering spacecraft (this is still in the research and development stages). It is currently used commercially to neutralize static electricity in machinery and to remove dust from photograph film and camera lenses.3 Production occurs in a nuclear reactor and is extremely costly, time-consuming, dangerous, and very highly regulated. A mere 100 grams are manufactured annually, mainly in Russia.1
210Po is present in the environment as a byproduct of radioactive uranium and radon decay. Although considered rare, trace amounts are ubiquitous. We are exposed to minute quantities present in soil, air, water, food, and dust.3 It is important to note that polonium itself is not the toxin, but rather the alpha particles it emits during the decay process. Alpha particles are a colorless, odorless, and tasteless form of ionizing radiation. They are very weighty and heavily charged, and can only travel a short distance (a few centimeters in air) before losing momentum. Their energy is released upon impact and therefore incapable of penetrating barriers like paper, clothing, or skin. Thus, 210Po is not dangerous in the environment per se, but is toxic if actually taken into the body.4
Inhalation of the isotope may occur during occupational exposure or while smoking cigarettes, since atmospheric 210Po settles onto tobacco leaves.3 Deposition in the lung depends on particle size and solubility. The majority of particles are removed from the respiratory tract by mucociliary clearing and then subsequently swallowed. At that point, 210Po is reintroduced to the body as ingesta.5
Ingestion may also occur while eating in contaminated areas or through consumption of contaminated foodstuffs. For example, caribou meat, a dietary staple in northern Canada, has a high concentration of 210Po due to its presence in the lichens they eat.6 In general, only a small fraction of the isotope is absorbed following ingestion, with as much as 90% being quickly excreted from the body in the feces.3
Dermal or parenteral exposure to 210Po is unlikely. While dust or aerosolized particles may deposit on skin and clothing, alpha particles cannot penetrate these barriers since most of their energy is lost on impact. The particles can, however, enter through open wounds and absorb subcutaneously.7 Parenteral access does not typically occur accidentally or occupationally, but is a common route of entry in medical procedures and in clinical research.2
Once 210Po is taken in, the whole body is essentially targeted. The administered dose and individual tissue sensitivity determines the extent of damage throughout the body.2 Unlike most heavy metals, 210Po accumulates in soft tissue rather than bone.8 There is species variation with regard to distribution, but for the most part, the kidneys, liver, and spleen contain the highest concentrations. In blood, the majority of the isotope is found in the red blood cells, bound to hemoglobin. Its binding to the globin component rather than heme indicates an affinity for proteins. Very little is found in aggregates with plasma or erythrocyte lipids. Deposition seems to depend somewhat on route of entry, with a much higher concentration in the blood after oral administration and in the kidney and spleen after intravenous administration.8
210Po is primarily eliminated in feces and urine. Older data asserts that following oral administration, 90% of the ingested isotope is rapidly excreted in the feces.8 This conflicts with newer experimental findings which put the fecal excretion rate at 55–69% and renal elimination at 20–38%. The newer study also found that the biological half-life of polonium-210 varies from 15–50 days depending on the species.5 The isotope may be eliminated through the sweat glands as well, although clearance by this route is minimal.9
Following the Trail
210Po has a radiological half-life of 139 days. It disperses over time, contaminating the environment and leaving a trail behind, a unique property called “creeping.”2 This quality, coupled with the availability of detection and quantification devices, allowed authorities to retrace Litvinenko’s footsteps on November 1, 2006, in order to establish where he was poisoned.
He began the day with a bus ride into London, where he stopped at a shop for a paper and bottle of water. He then met Italian nuclear waste and security consultant Mario Scaramella for sushi. Tests indicated no 210Po on the bus, the ticket, or in the shop where he bought the paper and water. There were, however, traces of the poison found in the sushi restaurant, but not at the table where he and Scaramella ate.1
Litvinenko then met with Boris Berezovsky, the man he refused to assassinate years before. He warned Berezovsky of yet another assassination order, information provided by Scaramella. Samples taken from Berezovsky’s office tested positive for trace amounts of 210Po.1
Next, Litvinenko went to the Millennium Hotel where he met Andrei Lugovoi, a former KGB agent, and Dmitri Kovtun to discuss possible business ventures. Litvinenko drank tea during the meeting. Samples from the bar showed levels of 210Po that were “off the charts.”1 Litvinenko’s tea cup was contaminated, as were many of the hotel employees. For these reasons, investigators believe this is where he was poisoned.10
The evidence points to Lugovoi and Kovtun. Traces of 210Po were detected virtually everywhere they went: their planes to London; the hotels where they stayed; the sushi restaurant (Litvinenko met them there two weeks prior to meeting with Scaramella); Berezovsky’s office (the two men had paid him a visit); and the London stadium seat where Lugovoi sat during a Russian football match. Furthermore, both men tested positive for 210Po exposure upon returning to Russia and were subsequently hospitalized. Despite this evidence, both Lugovoi and Kovtun vehemently deny the allegations and insist they were framed.1
210Po Symptoms and Diagnosis
The clinical manifestations of 210Po poisoning are those of radiation sickness. Dose-dependent effects follow those of acute radiation syndrome (ARS). In non-lethal doses (<1 sievert), the individual is typically asymptomatic or has very mild clinical manifestations. Approximately 1–10% of individuals experience intermittent nausea and vomiting, and there may be a slight decrease in white blood cells after two to four weeks. Highly toxic doses (4.5 sieverts) cause nausea, vomiting, anorexia, and lethargy within hours, with a latent period of days to weeks before the onset of more severe symptoms. Loss of bone marrow, white blood cells, and platelets results in infection, bleeding, and bruising. Hair loss occurs in two to three weeks. If left untreated, 50% of individuals will die. At 10 sieverts, 100% of individuals will die within two weeks. At >20 sieverts, clinical manifestations occur almost instantly. Symptoms include projectile vomiting, explosive bloody diarrhea, headache, fainting, confusion, agitation, and burning sensations. Cardiovascular symptoms and neurological deficits ensue, followed by shock, seizures, coma, and death in two to three days.4
Ultimately, the damage caused by 210Po alpha particles is due to total body irradiation. This results in extraction of electrons, disruption of cellular structure and activity, fragmentation of nuclei, chromosomal damage, as well as tumor induction. Some cells are more sensitive than others to these injuries, particularly bone marrow, lymphocytes, and enterocytes. Extremely high levels of ionizing radiation overwhelm the mechanisms of cell repair, and mass cell death occurs throughout the body, as seen in the case of Alexander Litvinenko.11
Diagnosis of 210Po poisoning is often delayed by the presence of non-specific gastrointestinal maladies that mimic food poisoning or the flu. Consequently, appropriate treatment is not always pursued at the onset of symptoms. Suspected exposures are confirmed through diagnostics. Fecal specimens are often used to determine exposure and, to a lesser extent, clearance rates. A more likely test for tracking the elimination rate of the isotope is a 24-hour urine assay. Quantification in urine cannot, however, predict the total systemic dose received or tissue concentrations. This is also true for fecal specimens.5 Analysis of blood is more useful for this purpose. A simple radiochemical and counting technique is used to measure the concentration of 210Po in the sample, which correlates to total body burden. The concentration of the decay product (lead) is also quantifiable and aids in determination of total body concentration.12
Chronic low-dose exposure to 210Po can likewise be determined from radiochemical analysis of urine. The results are then compared to previously established tolerance levels. This type of testing occurs when there is a risk of occupational exposure. Employees are tested monthly and the results used to direct modifications in usage or handling protocols.5
210Po is quantifiable in hair samples. It is secreted by the sweat glands and then retained in the hair follicle. Like blood, urine, and fecal specimen analysis, alpha particles are counted radiochemically in order to determine total body burden and clearance rates. It is a practical method for chronic low-dose monitoring rather than acute poisoning. However, as is the case with urine and fecal analysis, concentrations cannot predict activity in specific tissues.9
210Po is a highly active alpha particle emitter, but is only toxic if it enters the body. If entry does occur, the toxic effects are often fatal, even at very small doses. Much of the initial dose is quickly excreted in the feces and urine, but the remainder is preferentially distributed to the soft tissues of the body. The kidney, liver, and spleen receive the highest concentrations, while the skeletal system receives very little, atypical for a heavy metal. Exposure to 210Po is confirmed through diagnostics. Fecal and hair samples are good indicators of exposure. A 24-hour urine assay is effective for determining clearance rate, and blood analysis can predict total body burden. Clinical manifestations of 210Po poisoning are essentially identical to acute radiation syndrome (ARS), often mimicking food poisoning or the flu. Delays in diagnosis may occur for this reason. As soon as 210Po is identified as a possible toxin, medical management should follow as indicated for ARS. Measures should be taken immediately to prevent cross-contamination from the patient’s self, clothing, and bodily fluids.
There is no known antidote for 210Po poisoning. While chelating agents may potentially increase clearance rates, they are not antidotes. Furthermore, chelation therapy is not always initiated quickly enough to prevent significant morbidity or death. Death occurs after total body irradiation, massive cell death, infection, and complete organ failure.
The murder of Alexander Litvinenko did little for diplomatic relations between the United Kingdom and Russia, but it did bring a rare earth metal into the spotlight. Litvinenko’s murder is still considered unsolved, though Scotland Yard believes Andrei Lugovoi carried out the assassination at the command of the FSB. Diplomatic relations between the UK and the Kremlin have suffered, suggesting the effects of Litvinenko’s death could reverberate for years to come and influence the course of international affairs. Questions still remain that may never be answered, and it is unlikely that justice will ever be delivered.
- "Who killed Alexander Litvinenko?" Dateline. NBC News. Ann Curry. NBC, New York. 08 July 2007.
- Roessler, Gen. "Why 210Po?" Health Physics News XXXV(2007): 1, 3-9.
- Peterson, John. "Radiological and Chemical Fact Sheets." Mar 2007. Argonne National Laboratory, Environmental Sciences Division. 12 Jan 2009 <http://www.evs.anl.gov/pub/doc/ANL_ContaminantFact Sheets_All_070418.pdf>.
- Donaldson, Liam. Great Britain. Department of Health.Information to health professionals regarding the radioactive material ‘polonium-210’ resulting from a radiological incident occurring in November 2006. London: National Health Service Central Alerting System, 2006.
- Cohen, Norman. United States. Department of Energy, Office of Scientific and Technical Information. “Primate polonium metabolic models and their use in estimation of systemic radiation doses from bioassay data.” Final report. Washington, D.C.: U.S. Government Printing Office, 1989.
- Bliss, Tracy. Canada. Health Canada. "Effects of polonium-210 alpha radiation on human and animal systems.” Canadian Government Publishing, 2004.
- "Polonium-210: basic facts and questions." Dec 2006. The World Health Organization's Department of Public Health and Environment. 12 Jan 2009
- Thomas, R.G & J.N. Stannard. Radiation Research Supplement. Vol. 5. Oak Ridge: Radiation Research Society, 1964.
- Lykken, Glen & Hassan Alkhatib. "Analysis of hair for polonium-210 particle emissions." The American Association of Radon Scientists and Technologists. 1993. 12 Jan 2009 <http://www.aarst.org/proceedings/1993/1993_32_Analysis_of_Hair_ For_Polonium- 210%20-%20Particle_Emissio.pdf>.
- Bennetto, Jason. "Litvinenko inquiry closes in on suspected killers." The Independent 06 Jan 2007 12 Jan 2009
- Kennish, Steven & Stuart Currie. "Polonium-210 poisoning." STUDENTBMJ Vol. 15. Sep 2007 324-325. 12 Jan 2009 <http://student.bmj.com/search/pdf/07/09/sbmj324.pdf>.
- J.B. & R.B. McGandy. "Measurement of Polonium-210 in Human Blood." Nature 211. 20 Aug 1966 842-843. 12 Jan 2009
Caroline DiCarlo has a B.S. in Forensic Toxicology from John Jay College of Criminal Justice and received her M.S. in Veterinary Medical Science with a concentration in Forensic Toxicology from the University of Florida. She is currently pursuing her Doctor of Veterinary Medicine degree from the University of Illinois and plans to pursue a career in veterinary forensic science in the future.