Polonium-210 Information Sheet 


Bobby R. Scott, Ph.D.

Senior Scientist

Lovelace Respiratory Research Institute

2425 Ridgecrest Drive SE

Albuquerque, NM 87108 USA

February 19 22, 2007





Since the recent poisoning of former Russian spy Alexander Litvinenko via intentional exposure to the radionuclide polonium-210 in London, there has been much misinformation in the news and other media about what amount constitutes a lethal intake of polonium-210. This information sheet presents scientifically based results about polonium-210 toxicity to humans, including amounts expected to be lethal in a short amount of time.  This information sheet also includes background information on sources of exposure to polonium-210, its radiological characteristics, how it is absorbed, and where it is distributed in the human body. Radioactivity units used are older units relative to what is currently used.   This facilitates making comparisons to measurements reported in most of the earlier polonium-210 toxicity and environmental exposure studies.


Polonium-210 Sources and Radiological Characteristics




·        Is one of more than 24 known polonium isotopes, all of which are radioactive. Polonium was discovered in 1898 by Marie (http://www.aip.org/history/curie/ ) and Pierre Curie, pioneers in radiological research.  Polonium was named after Marie’s homeland of Poland (Latin: Polonia). The name was a political statement since Poland at the time was under Russian, Prussian, and Austrian domination and was not recognized as an independent country.

·        Is abbreviated as Po-210 and is a radioactive daughter of lead-210.

·        Is a very rare element in nature, and is present in uranium ores at about 100 micrograms per metric ton of ore.

·        Is associated with the radioactive decay of uranium-series radionuclides, leading to very low levels of polonium-210 being present in the air we breathe, the water we drink, and foods we ingest.

·        Average daily dietary intake ranges from about 1 to about 10 picocuries. One picocurie = 10-12 curies (an older unit of radioactivity). It takes 1 billion picocuries to make a milicurie (a unit often used in the United States for expressing the amount of radioactivity).  The curie unit of radioactivity was established in honor of Marie and Pierre Curie and related units (picocurie and milicurie) are used here to be consistent with units used in most previous publications on Po-210 toxicity and environmental exposures.

·        Can be produced in lethal amounts in nuclear reactors and is found in very small, nonlethal amounts in cigarettes (from about 0.2 to about 0.5 picocuries per cigarette).

·        Is contained in harmless amounts in dust that settles on our TV screens.

·        Is the most widely available of the polonium isotopes and has a physical half-life of 138 days (time for half of the initial radioactivity to decay away).  Its biological half-time for retention in the body (i.e., biological half-life) is much shorter (e.g., < 50 days).

·        Has a high specific activity (meaning a small mass contains a large amount of radioactivity) and mainly emits 5.3 million electron volt (an electron volt is a unit of energy) alpha particles, which in some physical forms can result in unintended spread of contamination.

·        Is difficult to detect by nonexperts.

·        Dissolves readily in dilute acids and is closely related chemically to bismuth and tellurium.

·        Is easily aerosolized.

·        Has the following applications:

-Is used in devices that eliminate static charges in textile mills and other places

-Is used on brushes (with sealed polonium-210) that remove accumulated dust from photographic films

·        Sources involving microgram or larger amounts of polonium-210 are very difficult to safely handle because of their high radioactivity per unit mass.  Specialized equipment and strict handling procedures are required for safe handling.


Polonium-210 Deposition, Uptake, and Distribution in Humans




·        Is contained throughout our bodies in small, essentially harmless amounts due to ingestion and inhalation exposure to naturally occurring sources and is eliminated via urinary and fecal excretion and via sweating.

·        Can occur in large concentrations in the liver, spleen, bone marrow, thymus, lymph nodes, and other sites (including the gastrointestinal tract, testes, and skin) after lethal ingestion or inhalation intakes.

·        Concentrations in human tissues due to natural sources generally amount to < 0.050 picocurie/g for bone and soft tissue.  For hair, the corresponding concentrations are < 0.1 picocurie/g, suggesting that body hair follicles may be an important excretion route in addition to the fecal and urinary routes.

·        Appears in the blood shortly after exposure via inhalation, ingestion, skin absorption, or through a wound.

·        Is quickly but not totally excreted from the body after entering the blood.

·        Its retention halftime in the body (i.e., biological half-life) is much shorter than its 138-day physical half-life.

·        When taken into the body in large amounts (based on radioactivity), the material should be easily detectable in excreta by experts who know how to look for alpha radiation sources.  However, using detection methods intended for gamma rays may lead to missing its presence.

·        Gastrointestinal uptake into the blood depends on polonium-210’s physical and chemical characteristics—polonium-210 has a great propensity to form colloids (aggregates larger than ordinary molecules but not visible to the unaided eye). 

·        Uptake via the gastrointestinal tract into blood is currently estimated to be about 10% of the deposited amount.

·        When inhaled in an insoluble or soluble form would be expected to be eliminated from the lung with an effective half-time of < 50 days.

·        Aggregates when inhaled are likely to break up over time because of high-specific activity, thereby enabling additional absorption into the blood.

·        Colloids being solublized by macrophages and/or lymphatic elements after inhalation exposure have a significant influence on the clearance and redistribution of the polonium-210.

·        Systemic uptake after inhalation can also occur because of its transport up the mucociliary escalator, resulting in polonium-210 being swallowed, then entering the gastrointestinal tract and being absorbed into the blood.

·        Is slowly absorbed into blood after deposition on the surface of the skin.  The rate of absorption depends on the solubility of the polonium-210 source.

·        Alpha radiation doses are larger for children than for adults for a given amount of radioactivity that enters the blood because of the smaller body masses for children.

·        Alpha radiation doses to the kidney, spleen, liver, bone marrow, lymph nodes, thymus, skin, and other organs can be substantial when large amounts of radioactivity enter the blood.  Large radiation doses to the respiratory tract can also occur in cases of inhalation exposure.

·        Quantities entering the blood represent the systemic burdens and can have units such as picocuries/kg-body-mass (picocuries per kilogram of body mass).


Polonium-210 Toxicity to Humans




·        Systemic burdens determine the risk of death via deterministic effects.  Deterministic effects are those serious threshold-type radiobiological effects associated with large radiation doses and the subsequent massive death of cells.  An example is lethal damage to the bone marrow or the gastrointestinal tract.  The bone marrow is the most sensitive target organ for lethal injury after intake of polonium-210, even though larger (possibly lethal) radiation doses likely occur in other organs than for the bone marrow.

·        Could in theory deliver a lethal radiation dose via any of the indicated modes (ingestion, inhalation, skin deposition, wound penetration) of internal incorporation into the body.  However, later damage resulting from skin deposition and absorption into blood could be minimized via washing of the contaminated skin.  Washing out the lung (i.e., lavage) could also reduce radiation doses to body organs after inhalation exposure.  In addition, the use of chelating agents that latch onto polonium-210 and speed its removal could hasten elimination from the body.

·        Lethal intakes can be evaluated on the basis of the amount of material that enters the blood. Here the systemic burden is expressed as picocuries/g-body-mass (picocuries per gram of body mass).  Use of this unit of radioactivity concentration makes it easy to compare toxic intakes with the published intakes we all normally have on a daily basis (picocurie quantities) from natural sources.





Polonium Effects on the Human Body


Amount of polonium-210 Detected in Blood (picocuries/g-body-mass)


Effect on the Body



Less than about 1

No different from that which occurs as a result of our dietary intake from natural sources

No harm expected

1 to about 300

No different from that which occurs as a result of our dietary intake from natural sources

No harm expected

300 to about 1,000

Induced cancers and life shortening are possible.

No deaths from deterministic effects would be expected.

1,000 to about 10,000

Severe damage to multiple body organs would be expected to accumulate slowly.  Moderate weight loss would be expected over time.

This systemic burden range is considered to contain the transition zone where the risk of death from deterministic effects increases from 0 to 100%.  Death in lethal cases would be expected to occur from about 300 to about 500 days after intake and relate to lethal injury to radiosensitive bone marrow along with severe injury to other organs. 

10,000 to about 30,000

Weight loss and severe damage to multiple organs (including the kidney, spleen, liver, bone marrow) would be expected to occur rather rapidly.  Moderate to severe loss of lymphocytes, WBCs, RBCs, and hemoglobin as well as significant weight loss would be expected.

Lethal for all.  Death from lethal injury to the radiosensitive bone marrow (along with severe injury to other organs) would be expected to occur from about 50 to about 250 days after intake.


Greater than  30,000

Weight loss and severe damage to multiple organs would be expected to occur rapidly.  Severe loss of lymphocytes, WBCs, RBCs, and hemoglobin as well as significant rapid weight loss would be expected.

Lethal for all.  Death via lethal damage to the radiosensitive bone marrow (along with severe injury to other organs) would be expected to occur within about 1 month after intake unless death from severe damage to a more radioresistant organ (e.g., large intestine) preceded death from bone marrow failure. 


WBC:  white blood cells

RBC:  red blood cells

Multiply numbers in column 1 by 10-6 to convert to millicuries per kilogram of body mass.  This unit is used in the figure that follows

Divide numbers in column 1 by 27 to convert to Becquerel per gram of body mass. One Becquerel represents 1 atomic disintegration for each second




image description


Current estimates for the lethality risk after human intake of polonium-210 as a function of the amount of polonium-210 that enters the blood (in millicuries per kilogram of body mass).  The data points are from published animal studies that used different mammalian species and the indicated curve is based on theoretical calculations for humans presented in a paper by B. R. Scott that is submitted to the Dose-Response Journal for publication. A logarithmic scale was used so that the threshold characteristic of the dose-response curve could be easily seen.


·        Medical countermeasures after large intake of polonium-210 would need to be directed at addressing multiple organ damage.  This would include severe damage to the kidney, liver, spleen, bone marrow, lung, lymph nodes, thymus, skin and components of the gastrointestinal tract (stomach, small intestines, large intestines).

·        Induced injury to all critical organs (including kidney, spleen, bone marrow, lung, gastrointestinal tract, skin) influences the time of death in cases of lethal intakes. Survival time is expected to decrease as the levels of damage to these organs collectively increase.


Comment:  The above findings apply to humans of all ages except for in utero exposure which has not been researched.




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This information sheet benefited from support from the Office of Science (BER), U.S. Department of Energy (DOE) Grant DE-FG02-03ER63657. The views and conclusions contained herein are those of the author and should not be interpreted as necessarily representing the official policies or endorsement, either express or implied, of the Lovelace Respiratory Research Institute or the DOE.  Comments related to this information sheet may be sent to the author at bscott@LRRI.org.