This is a fact sheet about a chemical that may be found in some public or
private drinking water supplies. It may cause health problems if found
in amounts greater than the health standard set by the United States
Environmental Protection Agency (EPA).
What is radon?
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 radon-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.
Radon in soil under homes is the biggest source of radon in indoor air, and presents a
greater risk of lung cancer than radon in drinking water. As required by the Safe Drinking Water Act, EPA has developed a
to reduce radon in drinking water that has a multimedia mitigation option to reduce radon in indoor air.
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
. Since uranium is essentially ubiquitous in the earth's crust, radium-226 and radon-222 are present
in almost all rock, soil, and water.
What are the properties of radon?
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.
Exposure to Radon
How does radon get into the environment?
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.
How does radon change in the environment?
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.
How does radon get into the body?
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.
Health Effects of Radon
How can radon affect people's health?
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.
Protecting People from Radon
How do I know if there is radon in my 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 is EPA doing about 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.
A report released September 15, 1998, by the National Academy of Sciences is the most
comprehensive accumulation of scientific data on the public health risks of radon in
drinking water. The report was required by the Safe Drinking Water Act (SDWA). The
NAS report (BEIR VI) issued earlier this year confirmed that radon is a serious public
health threat. This report goes on to refine the risks of radon in drinking water and
confirms that there are drinking water related cancer deaths, primarily due to lung cancer.
The report, in general, confirms earlier EPA scientific conclusions and analyses for
drinking water, and presents no major changes to EPA's 1994 risk assessment.
The Office of Ground Water Drinking Water has posted the press release of "Risk Assessment
of Radon in Drinking Water". There is also a link to NAS's Executive Summary on the report
(with initial EPA perspectives) at:
For general information on radon in drinking water, contact the Safe Drinking Water Hotline,
at (800) 426-4791. The Safe Drinking Water Hotline is open Monday through Friday, excluding
Federal holidays, from 9:00 a.m. to 5:30 p.m. Eastern Time.
EPA Map of Radon Zones
The Map was developed using five factors to determine radon potential: indoor radon measurements; geology;
aerial radioactivity; soil permeability; and, foundation type. Radon potential assessment is based on
geologic provinces. Radon Index Matrix is the quantitative assessment of radon potential. Confidence Index
Matrix shows the quantity and quality of the data used to assess radon potential. Geologic Provinces were
adapted to county boundaries for the Map of Radon Zones.
Sections 307 and 309 of the Indoor Radon Abatement Act of 1988 (IRAA) directed EPA to list and identify areas
of the U.S. with the potential for elevated indoor radon levels. EPA's Map of Radon Zones assigns each of the
3,141 counties in the U.S. to one of three zones based on radon potential:
counties have a predicted average indoor radon screening level greater than 4 pCi/L
per liter) (red zones)
counties have a predicted average indoor radon screening level between 2 and 4 pCi/L (orange
counties have a predicted average indoor radon screening level less than 2 pCi/L (yellow zones)
You can view your State's radon potential map by clicking on your State name below.
The purpose of this map is to assist National, State, and local organizations to target their resources and to implement
radon-resistant building codes. This map is not intended to be used to determine if a home in a given zone should be
tested for radon. Homes with elevated levels of radon have been found in all three zones. All homes should be tested
regardless of geographic location. Important points to note:
All homes should test for radon, regardless of geographic location or zone designation
There are many thousands of individual homes with elevated radon levels in Zone 2 and 3. Elevated levels can be found
in Zone 2 and Zone 3 counties.
All users of the map should carefully review the map documentation for information on within-county variations in radon
potential and supplement the map with locally available information before making any decisions.
The map is not to be used in lieu of testing during real estate transactions.
IMPORTANT: Consult the EPA Map of Radon Zones document (EPA-402-R-93-071) before using this map [call your
State Radon Contact
for a copy of the Map and the Zones document]. This document contains information on radon potential
variations within counties. EPA also recommends that this map be supplemented with any available local data in order
to further understand and predict the radon potential of a specific area. If you have questions about radon in water,
you should contact your State
Note: This fact sheet is part of a larger
publication adapted from U.S. EPA publication: EPA National Primary
Drinking Water Regulations.
Are there any water filters that reduce Radon in water?
According to the "Residential Water Processing by Water Quality Association", radon can be reduced by open aeration with outside venting, followed by an activated carbon filter. Also, use a good faucet aerator. All of our carbon filters are activated carbon.