Radon
ATSDR Public Health Statement, December 1990
This Statement was prepared to give you information about radon and to
emphasize the human health effects that may result from exposure to
it. The Environmental Protection Agency (EPA) has identified 1,177
sites on its National Priorities List (NPL). Radon has been found
above background levels at five of these sites. However, we do not
know how many of the 1,177 NPL sites have been evaluated for radon.
As EPA evaluates more sites, the number of sites at which radon is
found may change. The information is important for you because radon
may cause harmful health effects and because these sites are potential
or actual sources of human exposure to radon.
When a radioactive chemical 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 as a radioactive chemical. This emission,
which is also called a release, does not always lead to exposure. You
can be exposed to a chemical only when you come into contact with the
chemical. You may be exposed to it in the environment by breathing,
eating, or drinking substances containing the chemical or from skin
contact with it.
If you are exposed to a hazardous substance such as radon, several
factors will determine whether harmful health effects will occur and
what the type and severity of those health effects will be. These
factors include the dose (how much), the duration (how long), the
route or pathway by which you are exposed (breathing, eating,
drinking, or skin contact), the other chemicals to which you are
exposed, and your individual characteristics such as age, sex,
nutritional status, family traits, life style, and state of health.
What is radon?
Radon is a naturally occurring colorless, odorless, tasteless
radioactive gas that is formed from the normal radioactive decay of
uranium. Uranium is present in small amounts in most rocks and soil.
It slowly breaks down to other products such as radium, which breaks
down to radon. Some of the radon moves to the soil surface and enters
the air, while some remains below the soil surface and enters the
groundwater (water that flows and collects underground). Uranium has
been around since the earth was formed and has a very long half-life
(4.5 billion years), which is the amount of time required for one-half
of uranium to break down. Uranium, radium, and thus radon, will
continue to exist indefinitely at about the same levels as they do
now.
Radon also undergoes radioactive decay and has a radioactive half-life
of about 4 days. This means that one- half of a given amount of radon
will be changed or decayed to other products every 4 days. When radon
decays, it divides into two parts. One part is called radiation, and
the second part is called a daughter. The daughter, like radon, is
not stable; and it also divides into radiation and another daughter.
Unlike radon, the daughters are metal and easily attach to dust and
other particles in the air. The dividing of daughters continues until
a stable, nonradioactive daughter is formed. During the decay
process, alpha, beta, and gamma radiations are released. Alpha
particles can travel only a short distance and cannot go through your
skin. Beta particles can penetrate your skin, but they cannot go all
the way through your body. Gamma radiation, however, can go all the
way through your body. Thus there are several types of decay products
that result from radon decay.
How might I be exposed to radon?
Since radon is a gas and radon daughters are often attached to dust,
you are exposed to them primarily by breathing them in. They are
present in nearly all air. However, background levels of radon in
outdoor air are generally quite low, about 0.003 to 2.6 picocuries of
radon per liter of air. A picocurie is a very small amount of
radioactivity equal to one quintillionth (1/1018) of an ounce of
radon. In indoor locations, such as homes, schools, or office
buildings, levels of radon and daughters are generally higher than
outdoor levels. Indoor radon levels are generally about 1.5
picocuries radon per liter of air. Cracks in the foundation or
basement of your home may allow increased amounts of radon to move
into your home. You may also be exposed to radon and daughters by
drinking water obtained from wells that contain radon. Average levels
of radon in groundwater are about 350 picocuries of radon per liter of
water. However, most radon in water is rapidly released into the air
and can be breathed in. In some areas of the country the amount of
uranium and radium in some rock types, such as phosphate or granite,
is high. In these areas radon levels in outdoor air or in groundwater
will generally be higher.
How can radon enter and leave my body?
Radon and its radioactive daughters can enter your body when you
breathe them in or swallow them. By far, the greater amounts are
breathed in. Most of the radon is breathed out again. However, some
radon and most of the daughters remain in your lungs and undergo
radioactive decay. The radiation released during this process passes
into lung tissue and is the cause of lung damage. Some of the radon
that you swallow with drinking water passes through the walls of your
stomach and intestine. After radon enters your bloodstream most
(greater than 90%) of the radon goes to the lungs where you breathe
most of it out. This occurs very shortly after it is taken in. Any
remaining radon undergoes decay. Radon that does not go to the lungs
goes to other organs and fat where it may remain and undergo decay.
There is very limited information on whether radon gas can penetrate
the skin, but some radon may be able to pass through the skin when you
bathe in water containing radon.
How can radon affect my health?
Long-term exposure to radon and radon daughters in air increases your
chances of getting lung cancer. When exposures are high, noncancer
diseases of the lungs may occur, such as thickening of certain lung
tissues. While noncancer health effects may occur within days or
weeks after exposure to radon, it will be several years before cancer
effects become apparent. This is known from studies of workers
exposed to radon in mines, primarily uranium miners, and from tests on
laboratory animals. Although radon is radioactive, it gives off
little gamma radiation. Therefore, harmful health effects from
external exposure (when the chemical does not come into direct contact
with your body) are not likely to occur. In addition, it is not known
if radon causes health effects other than to the lung. Also, the
effects of drinking water or eating food containing radon are not
known.
What levels of exposure have resulted in harmful health effects?
In studies of uranium miners, workers exposed to radon levels of 50 to
150 picocuries of radon per liter of air for about 10 years have shown
an increased frequency of lung cancer. Although there is some
uncertainty as to how much exposure to radon increases your chances of
getting lung cancer, the greater your exposure to radon, the greater
your chance of developing lung cancer. Even small exposures may
increase your risk of developing lung cancer, especially if you smoke
cigarettes. Tables 1-1 and 1-2 were derived from animal and human data
for short-term or long-term exposure. This information provides a
basis for comparison to radon levels that you might encounter in the
air. As seen in Tables 1-3 and 1-4, there is no information on the effects
of radon if you drink water or eat food containing radon.
Is there a medical test to determine whether I have been exposed to radon?
Radon in human tissues is not detectable by routine medical testing.
However, several of its decay products can be detected in urine and in
lung and bone tissue. These tests, however, are not generally
available to the public and are of limited value since they cannot be
used to accurately determine how much radon you were exposed to, nor
can they be used to predict whether you will develop harmful health
effects.
What recommendations has the federal government made to protect human health?
EPA recommends that all homes should be monitored for radon. If
testing shows levels less than 4 picocuries radon per liter of air,
then no action is necessary. For levels above this, follow-up
measurements should be taken. If follow-up levels are 20 picocuries
radon per liter of air or higher, the home owner should consider some
type of procedure to decrease indoor radon levels. The Mine Safety and
Health Administration (MSHA) uses a standard of 4 Working Level Months
(WLMs) per year for people who work in mines. (WLMs combine the
amount with length of exposure.)