Radon (chemical symbol Rn) is a naturally occurring radioactive
gas found in soils, rock, and water throughout the U.S. It has
numerous different isotopes, but radon-220, and -222 are the most
common. Radon causes lung cancer, and is a threat to health because
it tends to collect in homes, sometimes to very high concentrations.
As a result, radon is the largest source of exposure to naturally
occurring radiation.
Who discovered radon?
The German chemist Friedrich E. Dorn discovered radon-222 in
1900, and called it radium emanation. However, a scarcer isotope,
radon-220, was actually observed first, in 1899, by British scientists
R.B. Owens and Ernest Rutherford. The medical community nationwide
became aware of radon in 1984 That year a nuclear plant worker
in Pennsylvania discovered radioactivity on his clothing while
exiting his place of work through the radiation detectors. The
source of the radiation was determined to be radon decay products
on his clothing originating from his home.
Where does radon come from?
Radon-222 is the decay product of radium-226. Radon-222 and its
parent, radium-226, are part of the long decay chain for uranium-238.
Since uranium is essentially ubiquitous in the earth's crust,
radium-226 and radon-222 are present in almost all rock, soil,
and water.
Radon is a noble gas, which means it is essentially inert, and
does not combine with other chemicals. Radon is a heavy gas, which
accounts for its tendency to collect in basements. It has no color,
odor, or taste. Radon-222 is produced by the decay of radium,
has a half-life of 3.8 days, and emits an alpha particle as it
decays to polonium-218, and eventually to stable lead. Radon-220,
is the decay product of thorium – it is sometimes called
thoron, has a half-life of 54.5 seconds and emits an alpha particle
in its decay to polonium-216.
Does radon have any practical uses?
Radon has little practical use. Some medical treatments have
employed radon in small sealed glass tubes, called seeds, that
are specially manufactured to contain the exact amount of radioactivity
needed for the application.
Radon-222 is the radioactive decay product of radium-226, which
is found at low concentrations in almost all rock and soil. Radon
is generated in rock and soil, and it creeps up to the outside
air. Although outdoor concentrations of radon are typically low,
about 0.4 picocuries per liter (pCi/l) of air, it can seep into
buildings through foundation cracks or openings and build up to
much higher concentrations indoors.
The average indoor radon concentration is about 1.3 pCi/l of
air. It is not uncommon, though, for indoor radon levels to be
found in the range of 5 - 50 pCi/l, and they have been found as
high as 2,000 pCi/l. The concentration of radon measured in a
house depends on many factors, including the design of the house,
local geology and soil conditions, and the weather. Radon's decay
products are all metallic solids, and when radon decay occurs
in air, the decay products can cling to aerosols and dust, which
makes them available for inhalation into the lungs.
Radon easily dissolves in water. In areas of the country that
have high radium content in soils and rocks, local ground water
may contain high concentrations of radon. For example, underlying
rock such as granite, or phosphate rock, typically have increased
uranium and radium, and therefore radon. While radon easily dissolves
into water, it also easily escapes from water when exposed to
the atmosphere, especially if it is stirred or agitated. Consequently,
radon concentrations are very low in rivers and lakes, but could
still be high in water pumped from the ground. Some natural springs,
such as those at Hot Springs, Arkansas, contain radon, and were
once considered healthful.
Because radon is a chemically inert (unreactive) gas, it can
move easily through rock and soil and arrive at the surface. The
half-life of radon-222 is 3.8 days. As it undergoes radioactive
decay, radon-222 releases alpha radiation and changes to polonium-218,
a short-lived radioactive solid. After several more decay transformations,
the series ends at lead-206, which is stable.
Radon dissolves in water, and easily leaves water that is exposed
to the atmosphere, especially if the water is agitated. Consequently,
radon levels are very low in rivers and lakes, but water drawn
from underground can have elevated radon concentrations. Radon
that decays in water, leaves only solid decay products which will
remain in the water as they decay to stable lead.
How are people exposed to radon?
Most of the public's exposure to natural radiation comes from
radon which can accumulate in homes, schools, and office buildings.
EPA estimates that the national average indoor radon level in
homes is about 1.3 pCi/l of air. We also estimate that about 1
in 15 homes nationwide have levels at or above the level of 4
pCi/l, the level at which EPA recommends taking action to reduce
concentrations. Levels greater than 2,000 pCi/l of air have been
measured in some homes.
Radon is also found in the water in homes, in particular, homes
that have their own well rather than municipal water. When the
water is agitated, as when showering or washing dishes, radon
escapes into the air. However, radon from domestic water generally
contributes only a small proportion (less than 1%) of the total
radon in indoor air. Municipal water systems hold and treat water,
which helps to release radon, so that levels are very low by the
time the water reaches our homes. But, people who have private
wells, particularly in areas of high radium soil content, may
be exposed to higher levels of radon.
People may ingest trace amounts of radon with food and water,
However, inhalation is the main route of entry into the body for
radon and its decay products. Radon decay products may attach
to particulates and aerosols in the air we breathe (for example,
cooking oil vapors). When they are inhaled, some of these particles
are retained in the lungs. Radon decay products also cling to
tobacco leaves, which are sticky, during the growing season, and
enter the lungs when tobacco is smoked. Smoke in indoor environments
also is very effective at picking up radon decay products from
the air and making them available for inhalation. It is likely
that radon decay products contribute significantly to the risk
of lung cancer from cigarette smoke.
What does radon do once it gets into the body?
Most of the radon gas that you inhale is also exhaled. However,
some of radon's decay products attach to dusts and aerosols in
the air and are then readily deposited in the lungs. Some of these
are cleared by the lung's natural defense system, and swallowed
or coughed out. Those particles that are retained long enough
release radiation damaging surrounding lung tissues. A small amount
of radon decay products in the lung are absorbed into the blood.
Most of the radon ingested in water is excreted through the urine
over several days. There is some risk from drinking water with
elevated radon, because radioactive decay can occur within the
body where tissues, such as the stomach lining, would be exposed.
However, alpha particles emitted by radon and its decay product
in water prior to drinking quickly lose their energy and are taken
up by other compounds in water, and do not themselves pose a health
concern.
Almost all risk from radon comes from breathing air with radon
and its decay products. Radon decay products cause lung cancer.
The health risk of ingesting radon, in water for example, is dwarfed
by the risk of inhaling radon and its decay products. They occur
in indoor air or with tobacco smoke. Alpha radiation directly
causes damage to sensitive lung tissue. Most of the radiation
dose is not actually from radon itself, though, which is mostly
exhaled. It comes from radon's chain of short-lived solid decay
products that are inhaled and lodge in the airways of the lungs.
These radionuclides decay quickly, producing other radionuclides
that continue damaging the lung tissue.
There is no safe level of radon--any exposure poses some risk
of cancer. In two 1999 reports, the National Academy of Sciences
(NAS) concluded after an exhaustive review that radon in indoor
air is the second leading cause of lung cancer in the U.S. after
cigarette smoking. The NAS estimated that 15,000-22,000 Americans
die every year from radon-related lung cancer. Cigarette smoke
makes radon much more dangerous.
When people who smoke are exposed to radon as well, the risk
of developing lung cancer is significantly higher than the risk
of smoking alone. People who don't smoke, but are exposed to second
hand smoke, also have higher risk of lung cancer from radon indoors.
The NAS also estimated that radon in drinking water causes an
additional 180 cancer deaths annually. However almost 90% of those
projected deaths were from lung cancer from the inhalation of
radon released to the indoor air from water, and only about 10%
were from cancers of internal organs, mostly stomach cancers,
from ingestion of radon in water.
Is there a medical test to determine exposure to radon?
Several decay products can be detected in urine, blood, and lung
and bone tissue. However, these tests are not generally available
through typical medical facilities. Also, they cannot be used
to determine accurate exposure levels, since most radon decay
products deliver their dose and decay within a few hours. Finally,
these tests cannot be used to predict whether a person's exposure
will cause harmful health effects, since everyone's response to
exposure is different.
The best way to assess exposure to radon is by measuring concentrations
of radon (or radon decay products) in the air you breathe at home.
You cannot see, feel, smell, or taste radon. Testing your home
is the only way to know if you and your family are at risk from
radon. EPA and the Surgeon General recommend testing for radon
in all rooms below the third floor. EPA also recommends testing
in schools.
The
EPA Citizen's Guide to Radon describes commonly available
tests for measuring radon concentrations in the home. EPA recommends
reducing levels of radon in homes where radon concentrations exceed
the EPA radon action level of 4 picocuries per liter.
Radon testing is inexpensive and easy--it should only take a
few minutes of your time. Millions of Americans have already tested
their homes for radon. Various low-cost, do-it-yourself test kits
are available through the mail and in hardware stores and other
retail outlets. You can also hire a trained contractor to do the
testing for you.
What can I do to protect myself and my family from radon?
The first step is to test your home for radon, and have it fixed
if it is at or above EPA's Action Level of 4 picocuries per liter.
You may want to take action if the levels are in the range of
2-4 picocuries per liter. Generally, levels can be brought below
2 pCi/l fairly simply.
The best method for reducing radon in your home will depend on
how radon enters your home and the design of your home. For example,
sealing cracks in floors and walls may help to reduce radon. There
are also systems that remove radon from the crawl space or from
beneath the concrete floor or basement slab that are effective
at keeping radon from entering your home. These systems are simple
and don't require major changes to your home. Other methods may
be necessary.
People who have private wells should test their well water to
ensure that radon levels meet EPA's newly proposed standard.
What recommendations has the federal government made to protect
human health from radon?
In 1988, EPA and the U.S. Surgeon General issued a Health Advisory
recommending that all homes be tested below the third floor for
radon. They also recommended fixing homes with radon levels 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.
EPA has established a voluntary program to promote radon awareness,
testing, and reduction. The program sets an ‘Action Level'
of 4 picocuries per liter (pCi/l) of air for indoor radon. The
action level is not the maximum safe level for radon in the home.
Instead it is the point at which the cost to the homeowner for
fixing the problem (taking action) is warranted by the risk from
the radon. However, the lower the level of radon, the better.
Generally, levels can be brought below 2 pCi/l fairly simply.
In addition to working with homeowners, EPA is working with home
builders and building code organizations. The goals are to help
newly constructed homes be more radon resistant and to encourage
radon testing when existing homes are sold.
The 1988 Indoor Radon Abatement
Act authorizes EPA to provide grants to states to support
testing and reducing radon in homes. With various non-governmental
and public health organizations, EPA promotes awareness and reduction
of indoor radon. Partners include the American Lung Association,
the National Environmental Health Association, the American Society
of Home Inspectors, and the National Safety Council. The Radon
Publications page provides a list of EPA-sponsored publications
in English and Spanish.
EPA has also proposed a standard for the maximum amount of radon
that may be found in drinking from community water systems using
ground water.
