SharePoint
Aide
IRSN, Institut de radioprotection et de sûreté nucléaire

Search our site :

ok

Contact us :

ok
En Fr

Enhancing Nuclear Safety


NewsRoom
Send Print
28/11/2006

Impact of polonium-210 on human health

Reminder of events

On November 23, 2006, Alexander Litvinenko died of heart failure at London's University College Hospital (UCH). His health problems began in early November, a few days after he had met with several of his contacts at his hotel and in a Japanese restaurant in London. He was admitted to UCH on November 17, 2006 with recurrent bouts of vomiting, irregular heartbeat, kidney problems, a very significant drop in his white blood cell count. He also suffered total hair loss within a week. His throat was also inflamed, with the result that he had stopped eating 18 days earlier. Roger Cox, a British professor at the Health Protection Agency (HPA), declared that polonium-210 had been detected in Mr. Litvinenko's urine. Furthermore, the authorities in charge of investigations announced that radioactive traces had been found in various places where the deceased had been seen.

Polonium-210 : characteristics and origins

Discovered by Marie Curie in 1898, polonium-210 (210Po), a decay product of uranium-238, is a naturally-occurring radionuclide found in trace form in every environmental compartment, along with radon-222 and lead-210, its precursor nuclides.

It is the most abundant of polonium's 29 isotopes and has a radioactive half-life of 138.4 days.
Its specific activity is very high: 1.66 x 1014 Bq per gram.
It emits 99.999% alpha particles, with an energy level of 5.304 MeV, and 0.001% gamma rays, representing an energy level of 0.80 MeV. It transforms into stable lead-206.

Radon-222, a radioactive gas and precursor of 210Po, is the reason why 210Po is found permanently suspended in the air in aerosol form. It is generally found in the air at a concentration of some 50 mBq/m3, although this can vary according to the degree of local radon exhalation and the existence of industrial activities favoring its emission (mining, phosphate industry, etc.). Volcanic activity is also responsible for a considerable amount of emissions.

Polonium-210 is also found in the top few centimeters of the soil. This is the result of radon-222 decay in the top layers of the soil and atmospheric fallout of the 210Po suspended in the air. Polonium-210 then binds almost irreversibly to particles of soil by coprecipitating with metal hydroxides or as a sulfide. It is not a very mobile element. Concentration levels in the soil vary from 10 to 200 Bq/kg (dry soil). Significantly higher concentrations (from 15,000 to 22,000 Bq/kg) can be found in uranium mine tailings.
It is also found in the world's oceans, either through direct emission into the water or via exchange mechanisms with volatile compounds in the air. It is generally insoluble and associated with a particulate or colloid phase. For this reason, it is found trapped in sediments, bound to other mineral phases, or as a sulfide precipitate.

Polonium-210 also has an artificial source, as it can be produced in a nuclear reactor by bombarding bismuth-209 with neutrons to obtain bismuth-210, which then turns into polonium-210 over a physical half-life of 5 days as a result of beta emission. Polonium can be used in industrial air ionizers to prevent the buildup of electrostatic charges that are generated, for example, when rolling paper, wire or metal foil.

Environmental behavior of polonium-210

Terrestrial plants take up 210Po mostly through their leaves. Little or no incorporation or translocation occurs after that and most of the polonium remains concentrated in the leaves(*).
In the case of animals, ingestion is the main route of entry. Concentration factors are relatively high but vary with the animals' habits (quantity ingested) and the target organs. For example, the concentration of 210Po ranges from 3.7 x 10-2 Bq/kg (fresh product) in ox muscle to 332 Bq/kg in caribou liver.

Aquatic organisms, especially plankton and invertebrates, can concentrate the 210Po contained in water in their soft tissues or, in the case of animals, in their internal organs. Fish have less ability to concentrate polonium, the lowest specific activity levels being observed in the flesh, i.e. the part destined for human consumption.

In seawater, 210Po has a strong affinity for suspended matter. Ingestion is the main route of entry in animals. Significant concentrations of polonium-210 are observed in marine animals, with certain organs, including the digestive gland in mollusks, the hepatopancreas in crustaceans and the liver in fish, exhibiting activity levels far above those observed in the surrounding environment. To illustrate this point, the 210Po concentration generally observed in mussels is between 150 and 600 Bq/kg (dry product). At just a few Bq/kg (dry product), concentrations are lower in fish. Polonium-210 therefore makes a large contribution to the radiation doses absorbed by humans through the consumption of fish and seafood.

(*) Polonium-210 is found particularly in tobacco leaves, which explains why it is found in greater quantities in smokers.

Behavior of polonium-210 in the human body

The alpha particles emitted by 210Po only travel a very short distance in the air (no more than a few centimeters). This radionuclide therefore only presents a health risk in the event of internal contamination (intake by ingestion, inhalation or injection) or direct contact with the skin.

As polonium-210 is found everywhere in the environment, humans are constantly exposed to contamination by inhalation and ingestion. The effective dose due to 210Po in the adult is approximately 0.07 mSv per year. Polonium-210 intake in humans is naturally excreted in varying quantities in the urine and feces, with uranium miners and smokers eliminating greater quantities than nonsmokers. Considering the balance between intake and excretion, the total activity found continuously in the average adult is estimated at some 30 Bq (or 0.18 picograms).

Polonium-210 is closely related to sulfur and selenium and its biological behavior resembles that of the rare earths. Following bodily intake, polonium-210 is carried rapidly to the soft tissues via the blood stream. The quantity absorbed following ingestion varies between 10% and 15% depending on the physical-chemical form of administration. In the blood and plasma, it exhibits a very strong affinity for red blood cells (90% of polonium-210 contained in the formed elements of the blood is related to the red corpuscles) and plasma proteins. About 30% of ingested or injected polonium-210 goes to the liver, spleen and kidneys. The bone marrow, lymph nodes and lungs – the lungs are the target organ for inhaled polonium-210 – display higher-than-average concentrations compared with other tissues (except for the liver, spleen and kidneys). The radionuclide is then eliminated in the feces and urine over a biological half-life of about 50 days (at the end of which, the body has excreted half the 210Po). Measurements have shown that, on average, the feces contain nine times more 210Po than the urine. Several studies have demonstrated that polonium-210 could also be found in exposed subjects' hair.

Throughout the period 1940 to 1970, many experiments were performed to study the fate and toxicity of polonium-210 in mice, rats, rabbits, cats, dogs, tamarins and baboons. The studies showed that after polonium-210 had been injected or ingested in citrate, chloride, colloidal hydroxide or nitrate form (polonium-210 seemed to be absorbed most effectively in nitrate form), the animals developed a number of clinical and biological signs, including weight loss, asthenia, lethargy, as well as liver, kidney, spleen, lung, pancreas and hematopoiesis dysfunctions, atrophy of the lymph nodes and hardening of the blood vessels (particularly in the kidneys and testicles). In addition to these symptoms, by the time of death – generally due to cardio-vascular collapse – almost all lymphocytes had disappeared. Within 20 days of intoxication, the median lethal dose (or LD50) was approximately 18 nanogram/kg body weight in the mouse, rabbit, cat and dog and 9 nanogram/kg body weight in the rat. This experimental data would suggest that acute toxic effects in human beings could be triggered by very slight quantities of polonium-210 (a few micrograms).

Several studies of rats, contaminated with an injection of a 210Po nitrate solution, showed that faster excretion could be achieved by rapid intramuscular or subcutaneous administration of chelating agents with thiol groups, such as HOEtTTC (N,N'-di(2-hydroxyethyl)ethylenediamine-N,N'-bisdithiocarbamate) and BAL (British Anti Lewisite or 2,3-dimercaptopropanol). On average, rats treated with the second compound (the reference treatment in France) survived 82 days, as opposed to 21 days for untreated rats. However, a study validating this data in humans has yet to be published.

There is little data available concerning accidental human exposure to polonium-210. The only familiar cases to date concern persons exposed following contact with a leaking Po-Be source. The only symptoms observed in these persons were some temporary functional disturbances – though with no clinical impact – to the liver (increased concentration of bilirubin in the plasma) and kidneys (reduced perfusion). The whole-body activity due to polonium-120 intake in these persons ranged from 0.034 to 2.41 nanograms.

Related publications :

  • Aposhian HV, Bruce DC. Binding of polonium-210 to liver metallothionein. Radiat Res. 1991 Jun;126(3):379-82.
  • Baratta EJ, Apidianakis JC, Ferri ES. Cesium-167, lead-210 and polonium-210 concentrations in selected human tissues in the United States. Am Ind Hyg Assoc J. 1969 Sep-Oct;30(5):443-8.
  • Berke HL, Dipasqua AC. Distribution and excretion of polonium-210. VIII. After inhalation by the rat. Radiat Res. 1964;51:SUPPL 5:133+.
  • Bruenger FW, Lloyd RD, Taylor GN, Miller SC, Mays CW. Kidney disease in beagles injected with polonium-210. Radiat Res. 1990 Jun;122(3):241-51.
  • Campbell JE, Talley LH. Association of polonium-210 with blood. Proc Soc Exp Biol Med. 1954 Oct;87(1):221-3.
  • Casarett LJ, Morrow PE. Distribution and excretion of polonium 210. XI. Autoradiographic studies after intratracheal administration in the rabbit. Radiat Res. 1964;51:SUPPL 5:175+.
  • Casarett LJ. Distribution and excretion of polonium 210. IX. Deposition, retention, and fate after inhalation by “nose only” exposure, with notes on mechanics of deposition and clearance and comparison of routes of administration. Radiat Res. 1964;51:SUPPL 5:148+.
  • Casarett LJ. Distribution and excretion of polonium-210. V. Autoradiographic study of effects of route of administration on distribution of polonium. Radiat Res. 1964;51:SUPPL 5:93+.
  • Cohen BS, Eisenbud M, Wrenn ME, Harley NH. Distribution of polonium-210 in the human lung. Radiat Res. 1979 Jul;79(1):162-8.
  • Fellman A, Ralston L, Hickman D, Ayres L, Cohen N. Polonium metabolism in adult female baboons. Radiat Res. 1994 Feb;137(2):238-50.
  • Finkel MP, Norris WP, Kisieleski WE, Hirsch GM. The toxicity of polonium 210 in mice. I. The thirty day LD50, retention, and distribution. Am Roentgenol Radium Ther Nucl Med. 1953 Sep;70(3):477-85.
  • Hill CR. Polonium-210 in man. Nature. 1965 Oct 30;208(9):423-8.
  • IRSN. Polonium 210 et environnement. Fiche Radionucléide et Environnement 2004.
  • Lanzola EE, Allegrini ME, Taylor DM. The binding of polonium-210 to rat tissues. Radiat Res. 1973 Nov;56(2):370-84.
  • Leggett RW, Eckerman KF. A systemic biokinetic model for polonuim. Sci Total Environ. 2001 Jul 25;275(1-3):109-25.
  • McInroy JF, Watters RL, Johnson JE. Polonium-210 absorption in rats: effects of biological modification. Nat New Biol. 1972 Mar 29;236(65):118-20.
  • Morrow PE, Dellarosa RJ. Distribution and excretion of polonium-210. VII. Fate of polonium colloid after intratracheal administration to rabbits Radiat Res. 1964;51:SUPPL 5:124+.
  • Morrow PE, Smith FA, Dellarosa RJ, Casarett LJ, Stannard JN. Distribution and excretion of polonium-210. II. The early fate in cats. Radiat Res. 1964;51:SUPPL 5:60-6.
  • Novak LJ, Panov D. Polonium-210 in blood and urine of uranium mine workers in Yugoslavia. Am Ind Hyg Assoc J. 1972 Mar;33(3):192-6.
  • Osborne RV. Lead-210 and polonium-210 in human tissues. Nature. 1963 Jul 20;199:295.
  • Parfenov YD, Poluboyarinova ZI. Polonium-210 metabolism in rabbits after a single intravenous and intratracheal injection. Int J Radiat Biol Relat Stud Phys Chem Med. 1973 May;23(5):487-93.
  • Parfenov YD. Polonium-210 in the environment and in the human organism. At Energy Rev. 1974;12(1):75-113.
  • Rencova J, Svoboda V, Holusa R, Volf V, Jones MM, Singh PK. Reduction of subacute lethal radiotoxicity of polonium-210 in rats by chelating agents. Int J Radiat Biol. 1997 Sep;72(3):341-8.
  • Rencova J, Volf V, Jones MM, Singh PK, Filgas R. Bis-dithiocarbamates: effective chelating agents for mobilization of polonium-210 from rat. Int J Radiat Biol. 1995 Feb;67(2):229-34.
  • Rencova J, Volf V, Jones MM, Singh PK. Mobilisation and detoxification of polonium-210 in rats by 2,3-dimercaptosuccinic acid and its derivatives. Int J Radiat Biol. 2000 Oct;76(10):1409-15.
  • Rencova J, Volf V, Jones MM, Singh PK. Relative effectiveness of dithiol and dithiocarbamate chelating agents in reducing retention of polonium-210 in rats. Int J Radiat Biol. 1993 Feb;63(2):223-32.
  • Samuels LD. Effects of polonium-210 on mouse ovaries. Int J Radiat Biol Relat Stud Phys Chem Med. 1966;11(2):117-30.
  • Soremark R, Hunt VR. Autoradiographic studies of the distribution of polonium-210 in mice after a single intravenous injection. Int J Radiat Biol Relat Stud Phys Chem Med. 1966;11(1):43-50.
  • Sproul JA, Baxter RC, Tuttle LW. Some late physiological changes in rats after polonium-210 alpha-particle irradiation. Radiat Res. 1964;51:SUPPL 5:373+.
  • Stannard JN, Baxter RC. Distribution and excretion of polonium 210. IV. On a multiple dose regimen. Radiat Res. 1964;51:SUPPL 5:80-92.
  • Stannard JN, Casarett GW. Concluding comments on biological effects of alpha-particle emitters in soft tissue as exemplified by experiments with polonium-210. Radiat Res. 1964;51:SUPPL 5:398+.
  • Stannard JN, Smith FA. Distribution and excretion of polonium 210. X. Species comparison. Radiat Res. 1964;51:SUPPL 5:166+.
  • Stannard JN. Distribution and excretion of polonium 210. I. Comparison of oral and intravenous routes in the rat. Radiat Res. 1964;51:SUPPL 5:49-59.
  • Stannard JN. Distribution and excretion of polonium 210. III. Long-term retention and distribution in the rat. Radiat Res. 1964;51:SUPPL 5:67-79.
  • Thomas RG, Stannard JN. Distribution and excretion of polonium-210. VI. After intratracheal administration in the rat. Radiat Res. 1964;51:SUPPL 5:106+.
  • Thomas RG, Stannard JN. Influence of physiochemical state of intravenously administered polonium-210 on uptake and distribution. Radiat Res. 1964;51:SUPPL 5:16-22.
  • Torvik R, Pfitzer E, Kereiakes JG, Blanchard R. Long term effective half-lives for lead-210 and polonium-210 in selected organs of the male rat. Health Phys. 1974 Jan;26(1):81-7

 

Back to all the news

Close

Send to a friend

The information you provide in this page are single use only and will not be saved.
* Required fields

Recipient's email:*  

Sign with your name:* 

Type your email address:*   

Add a message :

Do you want to receive a copy of this email?

Send

Cancel

Close

WP_IMPRIMER_TITLE

WP_IMPRIMER_MESSAGE

Back

Ok