Health Effects from EPA.gov
Health effects are the central focus of EPA's Radiation
Protection Programs. Below is information that explains the topics that we
consider as we prepare regulations and guidance on protective limits.
Radiation and Health
How does radiation cause health effects?
Radioactive materials that decay spontaneously produce ionizing
radiation, which has sufficient energy to strip away electrons from atoms
(creating two charged ions)
or to break some chemical bonds. Any living tissue in the human body can be
damaged by ionizing radiation in a unique manner. The body attempts to repair
the damage, but sometimes the damage is of a nature that cannot be repaired or
it is too severe or widespread to be repaired. Also mistakes made in the natural
repair process can lead to cancerous cells. The most common forms of ionizing
radiation are alpha
particles, or gamma
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What kinds of health effects does exposure to radiation cause?
In general, the amount and duration of radiation exposure affects the
severity or type of health effect. There are two broad categories of health
effects: stochastic and non-stochastic.
Stochastic Health Effects
Stochastic effects are associated with long-term, low-level (chronic)
exposure to radiation. ("Stochastic" refers to the likelihood that
something will happen.) Increased levels of exposure make these health effects
more likely to occur, but do not influence the type or severity of the effect.
Cancer is considered by most people the primary health effect from radiation
exposure. Simply put, cancer is the uncontrolled growth of cells. Ordinarily,
natural processes control the rate at which cells grow and replace themselves.
They also control the body's processes for repairing or replacing damaged
tissue. Damage occurring at the cellular or molecular level, can disrupt the
control processes, permitting the uncontrolled growth of cells cancer This is
why ionizing radiation's ability to break chemical bonds in atoms and molecules
makes it such a potent carcinogen.
Other stochastic effects also occur. Radiation can cause changes in DNA, the
"blueprints" that ensure cell repair and replacement produces a
perfect copy of the original cell. Changes in DNA are called mutations.
Sometimes the body fails to repair these mutations or even creates mutations
during repair. The mutations can be teratogenic or genetic. Teratogenic
mutations are caused by exposure of the fetus in the uterus and affect only the
individual who was exposed. Genetic mutations are passed on to offspring.
Non-Stochastic Health Effects
Non-stochastic effects appear in cases of exposure to high levels of
radiation, and become more severe as the exposure increases. Short-term,
high-level exposure is referred to as 'acute' exposure.
Many non-cancerous health effects of radiation are non-stochastic. Unlike
cancer, health effects from 'acute' exposure to radiation usually appear
quickly. Acute health effects include burns and radiation sickness. Radiation
sickness is also called 'radiation poisoning.' It can cause premature aging or
even death. If the dose is fatal, death usually occurs within two months. The
symptoms of radiation sickness include: nausea, weakness, hair loss, skin burns
or diminished organ function.
Medical patients receiving radiation treatments often experience acute
effects, because they are receiving relatively high "bursts" of
radiation during treatment.
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Is any amount of radiation safe?
There is no firm basis for setting a "safe" level of exposure above
background for stochastic effects. Many sources emit radiation that is well
below natural background levels. This makes it extremely difficult to isolate
its stochastic effects. In setting limits, EPA makes the conservative (cautious)
assumption that any increase in radiation exposure is accompanied by an
increased risk of stochastic effects.
Some scientists assert that low levels of radiation are beneficial to health
(this idea is known as hormesis).
However, there do appear to be threshold exposures for the various
non-stochastic effects. (Please note that the acute affects in the following
table are cumulative. For example, a dose that produces damage to bone marrow
will have produced changes in blood chemistry and be accompanied by nausea.)
|Time to Onset
|changes in blood chemistry
|within 2 months
|destruction of intestinal lining
|damage to central nervous system
|loss of consciousness;
|hours to days
This page describes how scientists estimate cancer and other health risks
from radiation exposures.
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How do we know radiation causes cancer?
Basically, we have learned through observation. When people first began
working with radioactive materials, scientists didn't understand radioactive
decay, and reports of illness were scattered.
As the use of radioactive materials and reports of illness became more
frequent, scientists began to notice patterns in the illnesses. People working
with radioactive materials and x-rays developed particular types of uncommon
medical conditions. For example, scientists recognized as early at 1910 that
radiation caused skin cancer. Scientists began to keep track of the health
effects, and soon set up careful scientific studies of groups of people who had
Among the best known long-term studies are those of Japanese atomic bomb
blast survivors, other populations exposed to nuclear testing fallout (for
example, natives of the Marshall Islands), and uranium miners.
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Aren't children more sensitive to radiation than adults?
Yes, because children are growing more rapidly, there are more cells dividing
and a greater opportunity for radiation to disrupt the process. EPA's radiation
protection standards take into account the differences in the sensitivity due to
age and gender.
Fetuses are also highly sensitive to radiation. The resulting effects depend
on which systems are developing at the time of exposure.
Effects of Radiation Type and Exposure Pathway
Both the type of radiation to which the person is exposed and the pathway by
which they are exposed influence health effects. Different types of radiation
vary in their ability to damage different kinds of tissue. Radiation and
radiation emitters (radionuclides) can expose the whole body (direct exposure)
or expose tissues inside the body when inhaled or ingested.
All kinds of ionizing radiation can cause cancer and other health effects.
The main difference in the ability of alpha and beta particles and gamma and
x-rays to cause health effects is the amount of energy they can deposit in a
given space. Their energy determines how far they can penetrate into tissue. It
also determines how much energy they are able to transmit directly or indirectly
to tissues and the resulting damage.
Although an alpha particle and a gamma ray may have the same amount of
energy, inside the body the alpha particle will deposit all of its energy in a
very small volume of tissue. The gamma radiation will spread energy over a much
larger volume. This occurs because alpha particles have a mass that carries the
energy, while gamma rays do not.
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Non-Radiation Health Effects of Radionuclides
Radioactive elements and compounds behave chemically exactly like their
non-radioactive forms. For example, radioactive lead has the same chemical
properties as non-radioactive lead. The public health protection question that
EPA's scientists must answer is, "How do we best manage all the hazards a
(See Protecting Against Exposure)
Do chemical properties of radionuclides contribute to
radiation health effects?
The chemical properties of a radionuclide can determine where health effects
occur. To function properly many organs require certain elements. They cannot
distinguish between radioactive and non-radioactive forms of the element and
accumulate one as quickly as the other.
- Radioactive iodine
concentrates in the thyroid. The thyroid needs iodine to function normally,
and cannot tell the difference between stable and radioactive isotopes. As a
result, radioactive iodine contributes to thyroid cancer more than other
types of cancer.
- Calcium, strontium-90
have similar chemical properties. The result is that strontium and radium in
the body tend to collect in calcium rich areas, such as bones and teeth.
They contribute to bone cancer.
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Estimating Health Effects
What is the cancer risk from radiation? How does it
compare to the risk of cancer from other sources?
Each radionuclide represents a somewhat different health risk. However,
health physicists currently estimate that overall, if each person in a group of
10,000 people exposed to 1 rem of ionizing radiation, in small doses over a life
time, we would expect 5 or 6 more people to die of cancer than would otherwise.
In this group of 10,000 people, we can expect about 2,000 to die of cancer
from all non-radiation causes. The accumulated exposure to 1 rem of radiation,
would increase that number to about 2005 or 2006.
To give you an idea of the usual rate of exposure, most people receive about
3 tenths of a rem (300 mrem) every year from natural background sources of
radiation (mostly radon).
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What are the risks of other long-term health effects?
Other than cancer, the most prominent long-term health effects are
teratogenic and genetic mutations.
Teratogenic mutations result from the exposure of fetuses (unborn children)
to radiation. They can include smaller head or brain size, poorly formed eyes,
abnormally slow growth, and mental retardation. Studies indicate that fetuses
are most sensitive between about eight to fifteen weeks after conception.
They remain somewhat less sensitive between six and twenty-five weeks old.
The relationship between dose and mental retardation is not known exactly.
However, scientists estimate that if 1,000 fetuses that were between eight and
fifteen weeks old were exposed to one rem, four fetuses would become mentally
retarded. If the fetuses were between sixteen and twenty-five weeks old, it is
estimated that one of them would be mentally retarded.
Genetic effects are those that can be passed from parent to child. Health
physicists estimate that about fifty severe hereditary effects will occur in a
group of one million live-born children whose parents were both exposed to one
rem. About one hundred twenty severe hereditary effects would occur in all
In comparison, all other causes of genetic effects result in as many as
100,000 severe hereditary effects in one million live-born children. These
genetic effects include those that occur spontaneously ("just happen")
as well as those that have non-radioactive causes.
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Protecting Against Exposure
What limits does EPA set on exposure to radiation?
Health physicists generally agree on limiting a person's exposure beyond
background radiation to about 100 mrem per year from all sources. Exceptions are
occupational, medical or accidental exposures. (Medical X-rays generally deliver
less than 10 mrem). EPA and other regulatory agencies generally limit
exposures from specific source to the public to levels well under 100 mrem. This
is far below the exposure levels that cause acute
How does EPA protect against radionuclides that are also
In most cases, the radiation hazard is much greater than the chemical (toxic)
hazard. Radiation protection limits are lower than the chemical hazard
protection limits would be. By issuing radiation protection regulations, EPA can
protect people from both the radiation and the chemical hazard. However,
deciding which hazard is greater is not always straightforward. Several factors
can tip the balance:
- toxicity of the radionuclide
- strength of the ionizing radiation
- how quickly the radionuclide emits radiation (half-life)
- relative abundance of the radioactive and non-radioactive forms
Uranium-238 is both radioactive and very toxic. Its half-life of 4.5
billion years means that only a few atoms emit radiation at a time. A sample
containing enough atoms to pose a radiation hazard contains enough atoms to
pose a chemical hazard. As a result, EPA regulates uranium-238 as both a
chemical and a radiation hazard.
Radioactive isotopes of lead are both radioactive and toxic. In spite of
the severe effects of lead on the brain and the nervous system, the
radiation hazard is greater. However, the radioactive forms of lead are so
uncommon that paint or other lead containing products do not contain enough
radioactive lead to present a radiation hazard. As a result, EPA regulates
lead as a chemical hazard.
All information above comes from the EPA.gov website
and is copied using the Freedom of Information Act.