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
Introduction
Since the recent poisoning
of former Russian spy Alexander Litvinenko via intentional exposure to the
radionuclide polonium-210 in
Polonium-210 Sources and
Radiological Characteristics
Polonium-210:
·
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
·
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
·
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
Polonium-210:
·
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
Polonium-210:
·
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 |
Lethality |
|
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
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.
References
Argonne National Laboratory,
EVS, Human Health Fact Sheet, Polonium, August 2005 http://www.ead.anl.gov/pub/doc/polonium.pdf,
last accessed 1/22/07.
Cohen N. Primate Polonium
Metabolic Models and Their Use in Estimation of Systemic Radiation Doses from
Bioassay Data, Final Report prepared for Henry B. Spitz, Polonium Dosimetry
Project Manager, EG&G Mound Applied Technologies, P.O. Box 3000,
Miamisburg, Ohio 45343-0987, 1989.
Desuderi D, Meli MA, Feduzi
L, and Roselli C. 210Po and 210Pb
inhalation by cigarette smoking in
Moroz
BB and Parfenov YD. 1971. Effects of Polonium-210 on the Organism.
Rencová
J, Svoboda V, Holuša, Volf V, Jones MM, and Singh PK. Reduction of subacute lethal radiotoxicity of
polonium-210 in rats by chelating agents.
International Journal of Radiation Biology 72(3):341-348, 1997.
Scott BR. Health risk
evaluations for ingestion exposure of humans to polonium-210. Dose-Response (submitted).
Stannard JN and Casarett GW
(editors). Metabolism and Biological Effects of an Alpha Particle Emitter,
Polonium-210. Radiation Research Supplement 5, 1964.
Stannard JN. Radioactivity
and Health. A History. Baalman RW (ed.).
Wikipedia, the Free
Encyclopedia, Polonium, http://en.wikipedia.org/wiki/Polonium,
last accessed
Acknowledgements
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.