EPA Facts about Radon
What is radon?
Radon is a naturally occurring radioactive gas
without color, odor, or taste that undergoes
radioactive decay and emits ionizing radiation.
Radon comes from the natural (radioactive)
breakdown of uranium and thorium in soil, rock,
and groundwater and is found all over the U.S.
The largest fraction of the public's exposure to
natural radiation comes from radon, mostly
from soil under homes. (There are three forms
of radon, but this document refers primarily to
radon-222 and its progeny.)
How does radon change in the
environment?
The primary source of radon is from uranium in
soils and rocks and in groundwater. Over time,
uranium decays into radium, which then decays
directly into radon. (See EPA Facts about Radium
and Uranium.) Uranium is present naturally in all
soil, although quantities differ from place to
place. Because radon is a gas and chemically
unreactive with most materials, it moves easily
through very small spaces, such as those
between particles of soil and rock, to the soil
surface. Radon is also moderately soluble in
water, and it can be absorbed by groundwater
flowing through rock or sand. Radon undergoes
radioactive decay, when it releases ionizing
radiation and forms "daughter" elements,
known as decay products. It is the release of
radiation from this decay process that leads to
exposure and health risks from radon.
During the decay process, radiation is released
in the form of alpha particles, beta particles, and
gamma rays. Alpha particles can travel only
short distances and cannot penetrate human
skin. However, when inhaled, they can
penetrate the cells lining the lungs. Beta
particles penetrate skin, but cannot pass
through the entire body. Gamma radiation can
travel all the way through the body. The health
risk associated with each type of radiation is a
function of how and what parts of the body are
exposed.
The time required for a radioactive substance to
lose 50 percent of its radioactivity by decay is
known as the half-life. The half-life of uranium-
238 is about 4.5 billion years. The half-life of
radon is 3.8 days.
How are people exposed to radon?
Outside air typically contains very low levels of
radon (about 0.4 picoCuries per liter [pCi/L] of
air). But it can build up to higher concentrations
in indoor air from soil under foundations of
homes, schools, and office buildings, where it
can seep into buildings. EPA estimates that the
national average annual indoor radon level in
homes is about 1.3 pCi/L of air. However, more
than 6 percent of all homes nationwide have
elevated levels at or above EPA's voluntary
action level of 4 pCi/L. Levels greater than 2,000
pCi/L of air have been measured in some homes.
Although radon in indoor air from soil gas
typically accounts for the bulk of the total radon
risk to individuals, people may also be exposed
to radon and its daughters through use of
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drinking water from groundwater that contains
radon. Radon gas escapes from the water and
goes into the air when water that contains
radon is used in the home for showering,
washing dishes, and cooking. Radon in domestic
water generally contributes only a small
proportion (about 1 to 2 percent) of the total
radon in indoor air. Radon levels in air and
groundwater will generally be higher in areas of
the country with rock types that contain high
amounts of uranium and radium, such as
phosphate or granite.
How does radon get into the body?
Radon and its radioactive daughters can enter
the body through inhalation and ingestion.
Inhaling radon is the main route of entry into
the body, with most of the radon being exhaled
again. However, some radon and its daughter
products will remain in the lungs, where
radiation released during the decay process
passes into the lung tissues, causing damage.
Radon is also produced in the body from parent
radium deposited in the body.
Is there a medical test to determine
exposure to radon?
Radon in human tissue is not detectable by
routine medical testing. However, several of its
decay products can be detected in urine, in lung
and bone tissue, and by breath tests. These
tests, however, are not generally available to the
public. They are also of limited value since they
cannot be used to determine accurately how
much radon a person was exposed to, nor can
these tests be used to predict whether a person
will develop harmful health effects.
How can radon affect people's health?
Exposure to radon and its daughters increases
the chance that a person will develop lung
cancer. The increased risk of lung cancer from
radon primarily results from alpha particles
irradiating lung tissues. Most of the damage is
not from radon gas itself, which is removed from
the lungs by exhalation, but from radon's short-
lived decay products (half-life measured in
minutes or less). When inhaled, these decay
products may be deposited in the airways of the
lungs, especially if attached to dust particles,
and subsequently emit alpha particles as they
decay further, resulting in damage to cells lining
the airways.
Radon is considered a known human carcinogen
based on extensive studies of exposure to
human beings. In two 1999 reports, the National
Academy of Sciences (NAS) concluded that
radon in indoor air is the second leading cause
of lung cancer in the U.S. after cigarette
smoking. The NAS estimated that the annual
number of radon-related lung cancer deaths in
the U.S., is about 15,000 to 22,000. NAS also
estimated that radon in drinking water causes
about 180 cancer deaths each year in the United
States. Approximately 89 percent of these
cancer deaths are caused by lung cancer from
inhalation of radon released to indoor air from
the water, and about 11 percent are a result of
cancers of internal organs, mostly stomach
cancers, from ingestion of radon in water.
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What recommendations has the U.S.
Environmental Protection Agency made
to protect human health?
Please note that the information in this section
is limited to recommendations EPA has made to
protect human health from exposure to radon.
General recommendations EPA has made to
protect human health at Superfund sites (the 10"
4 to 10~6 cancer risk range), which cover all
radionuclides including radon, are summarized
in the fact sheet "Primer on Radionuclides
Commonly Found at Superfund Sites."
EPA has established a limitation to exposure to
radon-222 and radon-220 decay products of less
than 0.02 Working Levels (WL) for uranium mill
tailings sites, where radon poses the major
health threat. These regulations under 40 Code
of Federal Regulations (CFR) Part 192.12(b) are
often Applicable or Relevant and Appropriate
Requirements (ARARs) at Superfund sites with
either radium- or thorium-contaminated soil.
In 1988, EPA and the U.S. Surgeon General
issued a health advisory recommending that all
homes below the third floor be tested for radon
and fixed if the radon level is at or above 4 pCi/L,
EPA's national voluntary action level. EPA and
the Surgeon General also recommend that
schools nationwide be tested for radon.
(Exposure to 5 pCi/L of radon-222, or 7.5 pCi/L
of radon-220, corresponds to an approximate
annual average exposure of 0.02 WL for radon
decay products in the home.) For more details,
see EPA's "A Citizen's Guide to Radon,"
September 1994, USEPA #402-K92-001, and
"Consumer's Guide to Radon Reduction," August
1992, USEPA 402-K92-003. For copies, contact
the National Radon Hotline (800) 767-7236 or
EPA's web site
http://www.epa.gov/iaq/pubs/index.html.
There is currently a proposed Maximum
Contaminant Level (MCL) for radon in drinking
water from community water systems using
groundwater. The Safe Drinking Water Act
directs EPA to set both an MCL for radon in
drinking water, as well a higher alternative
maximum contaminant level accompanied by a
multimedia mitigation program to address radon
risks in indoor air. This approach reflects radon's
unique characteristics: that radon released to
indoor air from soil under homes and buildings
in most cases is the main source of exposure,
with radon released from tap water being a
much smaller source of radon exposure. For
more information, contact the Safe Drinking
Water Hotline at (800) 426-4791 or visit EPA's
web site at
http://water.epa.gov/drink/index.cfm.
For more information about how EPA addresses
radon at Superfund sites
Contact Stuart Walker of EPA:
(703) 603-8748 or walker.stuart@epa.gov,
or visit EPA's Superfund Radiation Webpage:
http://www.epa.gov/superfund/resources/radiation/

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