Public Health Statement for Strontium
PDF Versionpdf icon[78.3 KB]
This Public Health Statement is the
summary chapter from the Toxicological
Profile for strontium. It is one in a series of Public
Health Statements about hazardous substances and their health
effects. A shorter version, the ToxFAQsTM,
is also available. This information is important because this substance may harm you. The effects of exposure to any hazardous substance depend on the dose, the duration, how you are exposed, personal traits and habits, and whether other chemicals are present. For more information, call the ATSDR Information Center at 1-800-232-4636.
This public health statement tells you about strontium and the effects of exposure.
The Environmental Protection Agency (EPA) identifies the most serious hazardous waste sites in the nation. These sites make up the National Priorities List (NPL) and are the sites targeted for long-term federal cleanup activities. Strontium and strontium-90 have been found in at least 102 and 12 of the 1,636 current or former NPL sites, respectively. However, the total number of NPL sites evaluated for strontium and strontium-90 are not known. As more sites are evaluated, the sites at which strontium and strontium-90 are found may increase. This information is important because exposure to strontium and strontium-90 may harm you and because these sites may be sources of exposure.
When a substance is released from a large area, such as an industrial plant, or from a container, such as a drum or bottle, it enters the environment. This release does not always lead to exposure. You are exposed to a substance only when you come in contact with it. You may be exposed by breathing, eating, or drinking the substance, or by skin contact.
External exposure to radiation may occur from natural or man-made sources. Naturally occurring sources of radiation are cosmic radiation from space or radioactive materials in soil or building materials. Man-made sources of radioactive materials are found in consumer products, industrial equipment, atom bomb fallout, and to a smaller extent from hospital waste and nuclear reactors.
If you are exposed to strontium, many factors determine whether you'll be harmed. These factors include the dose (how much), the duration (how long), and how you come in contact with it. You must also consider the other chemicals you're exposed to and your age, sex, diet, family traits, lifestyle, and state of health.
What is strontium?
Strontium is a natural and commonly occurring
element. Strontium can exist in two oxidation states: 0 and
+2. Under normal environmental conditions, only the +2 oxidation
state is stable enough to be important. Pure strontium is
a hard, white-colored metal, but this form is not found in
the environment. Rather, strontium is usually found in nature
in the form of minerals. Strontium can form a variety of compounds.
Strontium compounds do not have any particular smell. There
are two types of strontium compounds, those that dissolve
in water and those that do not. Natural strontium is not radioactive
and exists in four stable types (or isotopes), each of which
can be written as 84Sr, 86Sr, 87Sr,
and 88Sr, and read as strontium eighty-four, strontium
eighty-six, etc. All four isotopes behave the same chemically,
so any combination of the four would have the same chemical
effect on your body.
Rocks, soil, dust, coal, oil, surface
and underground water, air, plants, and animals all contain
varying amounts of strontium. Typical concentrations in most
materials are a few parts per million (ppm). Strontium ore
is found in nature as the minerals celestite (SrSO4)
and strontianite (SrCO3). After the strontium is
extracted from strontium ore, it is concentrated into strontium
carbonate or other chemical forms by a series of chemical
processes. Strontium compounds, such as strontium carbonate,
are used in making ceramics and glass products, pyrotechnics,
paint pigments, fluorescent lights, medicines, and other products.
Strontium can also exist as radioactive
isotopes. 90Sr, or strontium ninety, is the most
hazardous of the radioactive isotopes of the chemical element
strontium. 90Sr is formed in nuclear reactors or
during the explosion of nuclear weapons. Each radioactive
element, including strontium, constantly gives off radiation,
and this process changes it into an isotope of another element
or a different isotope of the same element. This process is
called radioactive decay. 90Sr gives off beta particles
(sometimes referred to as beta radiation) and turns into yttrium
ninety (90Y); 90Y is also radioactive
and gives off radiation to form zirconium ninety (90Zr),
which is a stable isotope. The radioactive half-life is the
time that it takes for half of a radioactive strontium isotope
to give off its radiation and change into a different element. 90Sr has a half-life of 29 years.
90Sr has limited use and is
considered a waste product. The radioactive isotope 89Sr
is used as a cancer therapeutic to alleviate bone pain. 85Sr
has also been used in medical applications. .
Quantities of radioactive strontium,
as well as other radioactive elements, are measured in units
of mass (grams) or radioactivity (curies or becquerels). Both
the curie (Ci) and the becquerel (Bq) tell us how much a radioactive
material decays every second. The becquerel is a new international
unit known as the SI unit, and the curie is an older unit;
both are used currently. A becquerel is the amount of radioactive
material in which 1 atom transforms every second. One curie
is the amount of radioactive material in which 37 billion
atoms transform every second; this is approximately the radioactivity
of 1 gram of radium.
What happens to strontium when it enters the environment?
Stable and radioactive strontium compounds
in the air are present as dust. Emissions from burning coal
and oil increase stable strontium levels in air. The average
amount of strontium that has been measured in air from different
parts of the United States is 20 nanograms per cubic meter
(a nanogram is a trillion times smaller than a gram). Most
of the strontium in air is in the form of stable strontium.
Very small dust particles of stable and radioactive strontium
in the air fall out of the air onto surface water, plant surfaces,
and soil either by themselves or when rain or snow falls.
These particles of strontium eventually end up back in the
soil or in the bottoms of lakes, rivers, and ponds, where
they stay and mix with stable and radioactive strontium that
is already there.
In water, most forms of stable and radioactive
strontium are dissolved. Stable strontium that is dissolved
in water comes from strontium in rocks and soil that water
runs over and through. Only a very small part of the strontium
found in water is from the settling of strontium dust out
of the air.
Some strontium is suspended in water.
Typically, the amount of strontium that has been measured
in drinking water in different parts of the United States
by the EPA is less than 1 milligram for every liter of water
(1 mg/L). 90Sr in water comes primarily from the
settling of 90Sr dust out of the air. Some 90Sr
is suspended in water. In general, the amount of 90Sr
that has been measured in drinking water in different parts
of the United States by EPA is less than one tenth of a picocurie
for every liter of water (0.1 pCi/L or 0.004 Bq/L).
Strontium is found naturally in soil
in amounts that vary over a wide range, but the typical concentration
is 0.2 milligrams per kilogram (kg) of soil (or 0.2 mg/kg).
The disposal of coal ash, incinerator ash, and industrial
wastes may increase the concentration of strontium in soil.
Generally, the amount of 90Sr in soil is very small
and is only a fraction of the total concentration of strontium
in soil. Higher concentrations of 90Sr in soil
may be found near hazardous waste sites, radioactive waste
sites, and Department of Energy facilities located around
the United States. A major portion of stable and radioactive
strontium in soil dissolves in water, so it is likely to move
deeper into the ground and enter groundwater. However, strontium
compounds may stay in the soil for years without moving downward
into groundwater. In the environment, chemical reactions can
change the water-soluble stable and radioactive strontium
compounds into insoluble forms. In some cases, water-insoluble
strontium compounds can change to soluble forms.
How might I be exposed to strontium?
Strontium is found nearly everywhere
in small amounts, and you can be exposed to low levels of
strontium by breathing air, eating food, drinking water, or
accidentally eating soil or dust that contains strontium.
Food and drinking water are the largest sources of exposure
to strontium. Because of the nature of strontium, some of
it gets into fish, vegetables, and livestock. Grain, leafy
vegetables, and dairy products contribute the greatest percentage
of dietary strontium to humans. The concentration of strontium
in leafy vegetables, such as cabbage, grown in the United
States is less than 64 mg in a kg of the fresh vegetables
(i.e., 64 ppm). For most people, the intake of strontium will
90Sr is found nearly everywhere
in small amounts from past nuclear accidents and fallout from
nuclear explosions. You can be exposed to low levels of 90Sr
by eating food, drinking water, or accidentally eating soil
or dust that contains 90Sr. Food and drinking water
are the largest sources of exposure to 90Sr. Because
of the nature of 90Sr, some of it gets into fish,
vegetables, and livestock. Grain, leafy vegetables, and dairy
products contribute the greatest percentage of dietary 90Sr
to humans. The concentration of 90Sr in fresh vegetables
grown in the United States is less than 9 pCi (or 0.3 Bq)
in 1 kg of dried vegetables (in a hot oven). The intake of
radioactive strontium for most people will be small. You can
take in more 90Sr if you eat food that was grown
on a radioactive strontium-contaminated hazardous waste site.
How can strontium enter and leave my body?
Both stable strontium and radioactive
strontium enter and leave the body in the same way.
If a person breathes in vapors or dust
containing a chemical form of strontium that is soluble in
water, then the chemical will dissolve in the moist surface
inside the lungs and strontium will enter the bloodstream
relatively quickly. If the chemical form of strontium does
not dissolve in water easily, then particles may remain in
the lung for a time. When you eat food or drink water that
contains strontium, only a small portion leaves the intestines
and enters the bloodstream. Studies in animals suggest that
infants may absorb more strontium from the intestines than
adults. If a fluid mixture of a strontium salt is placed on
the skin, the strontium will pass through the skin very slowly
and then enter the bloodstream. If the skin has scratches
or cuts, strontium will pass through the skin much more quickly.
Once strontium enters the bloodstream,
it is distributed throughout the body, where it can enter
and leave cells quite easily. In the body, strontium behaves
very much like calcium. A large portion of the strontium will
accumulate in bone. In adults, strontium mostly attaches to
the surfaces of bones. In children, whose bones are still
growing, strontium may be used by the body to create the hard
bone mineral itself. As a result the strontium will be stored
in the bone for a long time (years). Because of the way bone
grows, strontium will be locally dissolved from bone and recirculate
through the bloodstream, where it may be reused by growing
bone, or be eliminated. This process accounts for the slow
removal of strontium from the body.
Strontium is eliminated from the body
through urine, feces, and sweat. Elimination through urine
may occur over long periods, when small amounts of strontium
are released from bone and do not get recaptured by bone.
When strontium is taken in by mouth, the portion that does
not pass through the intestinal wall to enter the bloodstream
is eliminated through feces during the first day or so after
How can strontium affect my health?
To protect the public from the harmful
effects of toxic chemicals and to find ways to treat people
who have been harmed, scientists use many tests.
One way to see if a chemical will hurt
people is to learn how the chemical is absorbed, used, and
released by the body. In the case of a radioactive chemical,
it is also important to gather information concerning the
radiation dose and dose rate to the body. For some chemicals,
animal testing may be necessary. Animal testing may also be
used to identify health effects such as cancer or birth defects.
Without laboratory animals, scientists would lose a basic
method to get information needed to make wise decisions to
protect public health. Scientists have the responsibility
to treat research animals with care and compassion. Laws today
protect the welfare of research animals, and scientists must
comply with strict animal care guidelines.
There are no harmful effects of stable
strontium in humans at the levels typically found in the environment.
The only chemical form of stable strontium that is very harmful
by inhalation is strontium chromate, but this is because of
toxic chromium and not strontium itself. Problems with bone
growth may occur in children eating or drinking unusually
high levels of strontium, especially if the diet is low in
calcium and protein. Ordinary strontium salts are not harmful
when inhaled or placed on the skin.
Animal studies showed that eating or
drinking very large amounts of stable strontium can be lethal,
but the public is not likely to encounter such high levels
of strontium. In these unusually high amounts, so much strontium
was taken into bone instead of calcium that growing bones
were weakened. Strontium had more severe effects on bone growth
in young animals than in adults.
It is not known whether stable strontium
affects reproduction in people. The effect of stable strontium
on reproduction in animals is not known. The Department of
Health and Human Services has determined that strontium chromate
is expected to be a carcinogen, but this is because of chromium.
There is no information that any other form of stable strontium
causes cancer in humans or animals.
The harmful effects of radioactive strontium
are caused by the high energy effects of radiation. Since
radioactive strontium is taken up into bone, bone itself and
the soft tissues nearby may be damaged by radiation released
over time. Because bone marrow is the essential source of
blood cells, blood cell counts may be reduced if the dose
is too high. This has been seen in humans who received injections
of radioactive strontium (89Sr) to destroy cancer
tissue that had spread to the bone marrow. Lowered blood cell
counts were also seen in animals that breathed or swallowed
radioactive strontium. Numerous problems occur when the number
of blood cells is too low. A loss of red blood cells, anemia,
prevents the body from getting sufficient oxygen, resulting
in tiredness. A loss of platelets may prevent the blood from
clotting properly, and may result in abnormal bleeding, especially
in the intestines. A loss in white blood cells harms the body's
ability to fight infectious disease.
Radiation damage may also occur from
exposure to the skin. Medically, radioactive strontium probes
have been used intentionally to destroy unwanted tissue on
the surface of the eye or skin. The eye tissues sometimes
become inflamed or abnormally thin after a long time. Thinning
of the lower layer of the skin (dermis) has also been reported
in animal studies as a delayed effect.
It is not known whether exposure to radioactive
strontium would affect human reproduction. Harmful effects
on animal reproduction occurred at doses that were more than
a million times higher than typical exposure levels for the
Radioactive strontium may cause cancer
as a result of damage to the genetic material (DNA) in cells.
An increase in leukemia over time was reported in individuals
in one foreign population who swallowed relatively large amounts
of 90Sr (and other radioactive materials) in river
water contaminated by a nuclear weapons plant. Cancers of
the bone, nose, and lung (in the case of a breathing exposure),
and leukemia were reported in animal studies. In addition,
skin and bone cancer were reported in animals that received
radiation at high doses to the skin. The International Agency
for Research on Cancer (IARC) has determined that radioactive
strontium is carcinogenic to humans, because it is deposited
inside the body and emits beta radiation. The EPA has determined
that radioactive strontium is a human carcinogen.
How can strontium affect children?
This section discusses potential health
effects from exposures during the period from conception to
maturity at 18 years of age in humans.
Children are exposed to stable strontium
in the same manner as adults: usually in small amounts in
drinking water and food. Young children who have more hand-to-mouth
activity or who eat soil may accidentally eat more strontium.
Infants and children with active bone growth absorb more strontium
from the gut than adults.
Excess stable strontium causes problems
with growing bone. For this reason, children are more susceptible
to the effects of stable strontium than adults who have mature
bone. Children who eat or drink unusually high levels of stable
strontium may have problems with bone growth, but only if
the diet is low in calcium and protein. Children who drink
milk, especially milk fortified with vitamin D, are not likely
to have bone problems from exposure to excess stable strontium.
The amount of stable strontium that is usually taken in from
food or water or by breathing is too low to cause bone problems
in children. No developmental studies in humans or animals
examined the effect on the fetus when the mother takes in
excess strontium. However, no problems are expected with fetal
bone growth because only small amounts of strontium are transferred
from the mother across the placenta to the fetus. Evidence
suggests that stable strontium can be transferred from the
mother to nursing infants through breast milk, but the presence
of calcium and protein in milk protects against bone problems
Children take in, use, and get rid of
radioactive strontium in the same ways as stable strontium.
Children are likely to be more vulnerable than adults to the
effects of radioactive strontium because relatively more goes
into bone when it is growing. Also, children are potentially
more vulnerable than adults to radiation damage because they
keep radioactive strontium in bone for a longer time.
Children would be expected to have the
same types of effects from exposure to radioactive strontium
as exposed adults. Children can be exposed to radioactive
strontium at levels higher than background without showing
increases in cancer rates. Evidence from one foreign population
showed that children who drank water containing unusually
high levels of radioactive strontium for 7 years showed an
increase in leukemia. High levels of radioactive strontium
cause more bone damage and higher bone cancer rates when animals
are exposed before birth or as juveniles rather than as adults.
In humans and animals, radioactive strontium can be transferred
into milk or across the placenta into the fetus.
How can families reduce the risk of exposure to strontium?
If your doctor finds that you have been
exposed to significant amounts of strontium, ask whether your
children might also be exposed. Your doctor might need to
ask your state health department to investigate. Public health
officials may publish guidelines for reducing exposure to
strontium when necessary.
It is possible that higher-than-normal
levels of stable strontium may occur naturally in soil in
some places or that higher levels of radioactive strontium
may be found in soil near hazardous waste sites. Some children
eat a lot of dirt. You should prevent your children from eating
dirt. Make sure they wash their hands frequently, and before
eating. If you live near a hazardous waste site, discourage
your children from putting their hands in their mouths or
from engaging in other hand-to-mouth activities.
Since strontium is so common in the environment,
and is naturally present in food and water, we cannot avoid
being exposed to it. For several reasons, having a balanced
diet with sufficient vitamin D, calcium, and protein will
be protective by reducing the amount of ingested strontium
that is absorbed.
Is there a medical test to determine whether I have been exposed to strontium?
All people have small amounts of stable
strontium in their bodies, mostly in bone. It can be measured
in the blood, hair, feces, or urine. The amount is usually
measured by its mass (grams). Measurements in urine can show
whether you have been exposed recently to larger-than-normal
amounts of strontium. Measurements in hair can reveal whether
you were exposed to high amounts of strontium in the past.
Most physicians do not test for strontium in their offices,
but can collect samples and send them to a special laboratory.
X-rays can show changes in bone that may occur from exposure
to high amounts of strontium, but these changes may have other
causes (a diet low in vitamin D or a high exposure to some
other trace metal).
If a person has been exposed to radioactive
strontium, special tests can be used to measure radioactive
strontium in blood, feces, or urine. These tests are most
useful when done soon after exposure, since radioactive strontium
quickly enters into bone and takes many years to be completely
removed from bone. Radioactive strontium can be measured by
its mass (in grams) or by its radiation emissions. These emissions,
which differ for the various isotopes of strontium, are used
to tell the amount of radioactive strontium (in curies or
bequerels) and the radiation dose that it gives to your body
(in sieverts or rem). In a procedure that is similar to being
x-rayed, specialized equipment can measure radioactive strontium
that has been incorporated into bone.
What recommendations has the federal government made to protect human health?
The federal government develops regulations
and recommendations to protect public health. Regulations
can be enforced by law. Federal agencies that develop regulations
for toxic substances include the Environmental Protection
Agency (EPA), the Occupational Safety and Health Administration
(OSHA), the Food and Drug Administration (FDA), and the U.S.
Nuclear Regulatory Commission (USNRC).
Recommendations provide valuable guidelines
to protect public health but cannot be enforced by law. Federal
organizations that develop recommendations for toxic substances
include the Agency for Toxic Substances and Disease Registry
(ATSDR), the National Institute for Occupational Safety and
Health (NIOSH), and the FDA.
Regulations and recommendations can be
expressed in not-to-exceed levels in air, water, soil, or
food that are usually based on levels that affect animals;
they are then adjusted to help protect people. Sometimes these
not-to-exceed levels differ among federal organizations because
of different exposure times (an 8-hour workday or a 24-hour
day), the use of different animal studies, or other factors.
Recommendations and regulations are also periodically updated as more information becomes available. For the most current information, check with the federal agency or organization that provides it. Some regulations and recommendations for strontium include the following:
EPA recommends that drinking water levels of stable strontium should not be more than 4 milligrams per liter of water (4 mg/L).
The Department of Energy (DOE) established derived air concentrations (DAC) for workplace exposure to radiation at DOE facilities. The DAC ranges from 0.000000002 microcuries per milliliter (μCi/mL) (2x10-9 μCi/mL of air = 70 μBq/mL of air) for radioactive particles remaining in the lung for 100 days to 0.000000008 μCi/mL (8x10-9 μCi/mL of air = 300 μBq/mL of air) for radioactive particles remaining in the lung for less than 10 days. The USNRC established an annual intake limit of 20 μCi (7 MBq) for on-the-job exposure to 90Sr in air.
EPA set standards for the concentration of 90Sr in community water supplies. The average annual concentration of 90Sr in water supplies should not exceed 8 pCi/L (0.3 Bq/L). EPA also established maximum contaminant levels (MCLs) in drinking water for radionuclide activities to protect against harmful effects of 90Sr. For beta particles like strontium, the MCL is 4 mrem per year (4x10-5 Sv per year). The USNRC set a workplace value of 31 μCi (1.1 MBq) for the amount of 90Sr that can be taken in by mouth in a year without any harmful effects.
Agency for Toxic Substances and Disease
Registry (ATSDR). 2004. Toxicological
profile for strontium. Atlanta, GA: U.S. Department of
Health and Human Services, Public Health Service.
Where can I get more information?
If you have questions or concerns, please contact your community or state health or environmental quality department or:
For more information, contact:
Agency for Toxic Substances and Disease Registry
Division of Toxicology and Human Health Sciences
4770 Buford Highway
Chamblee, GA 30341-3717
Phone: 1-800-CDC-INFO 888-232-6348 (TTY)
Email: Contact CDC-INFO
ATSDR can also tell you the location of occupational and environmental health clinics. These clinics specialize in recognizing, evaluating, and treating illnesses resulting from exposure to hazardous substances.