EPA Facts About
lSSS£/ Radon

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4i mo^	July 2002

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 ground water 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 ground water. 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 ground water flowing through rock or sand.
Radon also undergoes radioactive decay, during which 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
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
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, over 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 drinking water
from ground water that contains radon. When water that contains
radon is used in the home for showering, washing dishes, and
cooking, radon gas escapes from the water and goes into the air.
Radon in domestic water generally contributes only a small
proportion (about 1 to 2%) of the total radon in indoor air. Radon
levels in air and ground water 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.

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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% of these cancer deaths are due to lung cancer
from inhalation of radon released to indoor air from the water, and
about 11 % are due to cancers of internal organs, mostly stomach
cancers, from ingestion of radon in water.

What recommendations has the Environmental
Protection Agency made to protect human
health?

National Radon Hotline (800) 767-7236 or EPA's web site
http://www.epa.gov/iaa/radon.

There is currently a proposed Maximum Contaminant Level
(MCL) for radon in drinking water from community water
systems using ground water. The Safe Drinking Water Act directs
EPA to set both a maximum contaminant level (MCL) for radon in
drinking water, as well as an alternative, higher alternative
maximum contaminant level (AMCL) 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 EPA's web site at http://www.epa.gov/safewater.

For more information about how EPA addresses radon at
Superfund sites, please contact either :

EPA 's Superfund Hotline
1-800-424-9346 or 1-800-535-0202
or EPA 's Superfund Radiation Webpage
http://www.eDa. eov/superfund/resources/radiation

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, which cover all radionuclides including
radon, are summarized in the Introduction section of this booklet.

For uranium mill tailings sites, at which radon poses the major
health threat, EPA has established a limitation to exposure to
radon decay products of less than 0.02 Working Levels (WL).
These regulations under 40 CFR Part 192.12(b) are often 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
picocuries per liter (pCi/L), EPA's national voluntary Action
Level. EPA and the Surgeon General also recommend that schools
nationwide be tested for radon. (Exposure to 4 pCi/1 of radon
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

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