Definition
Sources of Radon
What are the Health Effects From Exposure to Radon?
What is the
Average Level of Radon Found in a Home?
What's the debate on radon?
How do we know radon is a carcinogen?
Does the Auvinen Finnish Study Prove that Residential Radon Does
Not Cause Lung Cancer?
Why does it take so many cases to make residential radon
epidemiology (EPI) studies meaningful?
Why are residential EPI studies of radon so complicated?
Are there any residential EPI studies finding increased risk of
lung cancer due to radon?
When will we know for sure about Radon's Health Risk?
What is the National Academy of Sciences (NAS) doing now?
What is meta-analysis, and does the Lubin/Boice meta-analysis
prove that residential radon levels cause lung cancer?
RE: the meta-analysis - What has changed?
RE: the meta-analysis - How does this affect EPA's risk assessment?
Radon Hotline
Finding a "Qualified" Radon Service Professional
Radon is a gaseous radioactive element having the symbol
Rn, the atomic number 86, an atomic weight of 222, a melting point of -71ºC,
a boiling point of -62ºC, and (depending on the source, there are between 20 and
25 isotopes of radon - 20 cited in the chemical summary, 25 listed in the table
of isotopes); it is an extremely
toxic, colorless gas; it can be condensed to a transparent liquid and to an
opaque, glowing solid; it is derived from the radioactive decay of radium and is
used in cancer treatment, as a tracer in leak detection, and in radiography.
(From the word radium, the substance from which it is derived.)
Sources: Condensed Chemical Dictionary, and Handbook of Chemistry and
Physics, 69th ed., CRC Press, Boca Raton, FL, 1988.
EPA's Integrated Risk Information
System profile on Radon 222 [CASRN 14859-67-7] is located at: epa.gov/iris/subst/0275.htm
Conversion Factors for Radon Units (conversion_factors_rn.pdf)
Radon Decay Series Chart (radon_decay_units.pdf)
Earth and rock beneath home; well water; building materials.
No immediate symptoms. Radon in indoor air is
estimated to cause between 15,000 and 22,000 lung cancer deaths each year in the United States. Smokers are at higher risk of developing Radon-induced lung cancer. The
only health effect which has been definitively linked with radon exposure is
lung cancer. Lung cancer would usually occur years (5-25) after exposure. There
is no evidence that other respiratory diseases, such as asthma, are caused by
radon exposure and there is no evidence that children are at any greater risk of
radon induced lung cancer than adults.
Based on a national residential radon survey completed in 1991, the average indoor radon level is 1.3 picocuries per liter
(pCi/L) in the United States. The average outdoor level is about 0.4 pCi/L.
There is no debate about radon being a lung
carcinogen in humans. All major national and international organizations that
have examined the health risks of radon agree that it is a lung carcinogen. The
scientific community continues to conduct research to refine our understanding
of the precise number of deaths attributable to radon. EPA and the National
Cancer Institute (NCI) have independently placed that number at about 15,000
lung cancer deaths each year in the United States.
A few scientists have questioned whether low
radon levels, such as those found in residences, increase the risk of lung
cancer because some small studies of radon and lung cancer in residences have
produced varied results. Some have shown a relationship between radon and lung
cancer, some have not. However, the national and international scientific
communities are in agreement that all of these residential studies have been too
small to provide conclusive information about radon health risks. All major
scientific organizations continue to believe that approximately 10% of lung
cancers in the United States -- or about 15,000 lung cancer deaths annually --
are attributable to radon.
The World Health Organization (WHO) and the US
Department of Health and Human Services, as well as EPA, have classified radon
as a "Class A" known human carcinogen, because of the wealth of
biological and epidemiological evidence and data showing the connection between
exposure to radon and lung cancer in humans.
The World Health Organization, the National
Academy of Sciences and other scientific organizations agree that studies of the
miners are the best scientific information for estimating radon health risks in
homes. The Lubin/Boice meta-analysis paper also concludes that the miners
studies are the best data source for analyzing residential radon risk. Based on
the miner data, NCI has previously estimated that 15,000 people die of lung
cancer from residential radon each year in the U.S.
There have been many studies conducted by many
different organizations in many nations around the world to examine the
relationship of radon exposure and human lung cancer. The largest and most
recent of these was an international study, led by the National Cancer Institute
(NCI), which examined the data on 68,000 underground miners who were exposed to
a wide range of radon levels. The studies of miners are very useful because the
subjects are humans, not rats, as in many cancer research studies. These miners
are dying of lung cancer at 5 times the rate expected for the general
population. Over many years scientists around the world have conducted
exhaustive research to verify the cause-effect relationship between radon exposure
and the observed increased lung cancer deaths in these miners and
to eliminate other possible causes.
In addition, there is an overlap between radon
exposures received by miners who got lung cancer and the exposures people would
receive over their lifetime in a home at EPA's action level of 4 pCi/L, i.e.,
there are no large extrapolations involved in estimating radon risks in homes.
No, the Finnish study by itself is too small with
only 1055 subjects to provide any definitive proof. Scientists from the U.S.
Public Health Service Agencies recently reviewed the radon risk assessment and
the proliferation of small residential epidemiological studies like the Finnish
study. They concluded that residential epidemiology studies would need a minimum of
10,000 to 30,000 lung cancer cases plus twice a many controls to adequately
address this issue.
Clarification: The residential epidemiology study recently reported out of Finland, examined homes with
low radon levels; the median indoor radon level was 1.8 picoCuries per liter (pCi/L)
of air.
Dr. Jonathan Samet, chairman of the National
Academy of Sciences BEIR VI Committee, responded to the Finnish study stating,
"...by itself, the study is too small in size and consequently without
sufficient statistical power to characterize precisely the risk of lung cancer
associated with indoor radon. Consequently, the conclusions of the article are
overstated and the authors' judgment as to the implications of their findings,
"Indoor radon exposure does not appear to be an important cause of lung
cancer,"" is not supported by the evidence presented."
To have a reasonable certainty in the
conclusions, many thousands of cases are required to detect the increased risk
of lung cancer due to radon. This is because the more things that cause a
disease the harder it is to separate one cause from another, thus it takes many
cases to pinpoint the risk from each separate cause. The U.S. Public Health
Service radon experts estimate that 10,000 to 30,000 cases, and twice as many
controls would be needed to conduct a definitive epidemiologic study of
residential radon lung cancer risk. The residential studies conducted to date
have all included between 50 and 1500 cases and thus have been too small to
provide conclusive information.
Some years ago this same process was used to
detect an increased risk of lung cancer due to cigarette smoking. It took many
years of study to make the positive link between the cause and effect of smoking
and lung cancer. Most of the increased lung cancer risk is attributable to
smoking through mathematical modeling. The research process for smoking was very
laborious. However, radon's process is even more challenging because radon's
contribution to increased lung cancer risk (10%) is difficult to see against the
large background of lung cancer due to other causes, which include smoking,
asbestos, some heavy metals and other types of radiation; i.e., detecting
radon-related lung cancer is like trying to detect a 10% increase of sand on a
beach already full of sand.
Finally, it is difficult to accurately determine
radon exposures in residential settings since we are estimating past exposures
from current measurements. The number of required study participants increases
with the difficulty in determining the exposure.
There are many factors that must be considered
when designing a residential radon epidemiology study. It is very expensive and often
impossible to design a study that takes all the pertinent factors into
consideration. These factors include:
- Mobility: people move a
lot over their lifetime; it is virtually impossible to go back and test
every home where an individual has lived;
- Housing Stock Changes: over
time, older homes are often destroyed or remodeled, thus radon measurements
will be non-existent or highly varied; a home's radon level may change,
higher or lower, over time if new ventilation systems are installed, the
occupancy patterns are substantially different, or the home's foundation
shifts or cracks appear.
- Inaccurate Histories:
often a majority of the lung cancer cases (individuals) being studied are
deceased or too sick to be interviewed by researchers. This requires
reliance on second-hand information which may not be as accurate. These
inaccuracies primarily affect:
Residence History: a child or other relative may not be aware of all
residences occupied by the patient - particularly if the occupancy is
distant in time or of relatively short duration. Even if the surrogate
respondent is aware of a residence they may not have enough additional
information to allow researchers to locate the home.
Smoking History: smoking history historically has reliability
problems. Individuals may under-estimate the amount they smoke. Conversely,
relatives or friends may over-estimate smoking history.
- Other: complicating
factors other than variations in smoking habits include an individual's:
genetics, lifestyle, exposure to other carcinogens, and home heating,
venting and air conditioning preferences.
Yes, several residential epidemiology studies have found
an increased risk of lung cancer due to residential exposures (i.e. Sweden, New
Jersey ) These studies are also just pieces of a much bigger puzzle that is
being put together.
We already have a wealth of scientific data on
the relationship between radon exposure and the development of lung cancer. The
scientific experts agree that the occupational miner data is a very solid base
from which to estimate a risk range of 7,000-30,000 lung cancer deaths annually.
While residential radon epidemiology studies will improve what we know about radon, they
will not supersede the occupational data. EPA is funding efforts by the NAS.
Health authorities like the Centers for Disease Control (CDC), the Surgeon
General, the American Lung Association, the American Medical Association, and
others agree that we know enough now to recommend radon testing and to encourage
public action when levels are above 4 pCi/L. The most comprehensive of these
efforts is the National Academy of Science's Biological
Effects of Ionizing Radiation (BEIR VI) Report. As in the case of
cigarette smoking, it would probably take many years and rigorous scientific
research to produce the composite data needed to make an even more definitive
conclusion.
The NAS has prepared its latest analysis of
health research on radon, the Biological
Effects of Ionizing Radiation (BEIR VI) Report. This is the most
comprehensive review effort to date. The Committee was charged with:
- reviewing all current miner and residential
data, as well as all existing cellular-biological data,
- comparing the dose per unit exposure effects
of radon in mines and homes, and
- examining:
- interactions between radon exposure and smoking, and
- any exposure-rate effect (alteration of effect by intensity of exposure).
Meta-analysis is a statistical attempt to analyze
the results of several different studies to assess the presence or absence of a
trend or to summarize results. Lubin and Boice conclude that the results of
their meta-analysis are consistent with the current miner-based estimates of
lung cancer risk from radon which place the number of radon-related deaths at
approximately 15,000 per year in the United States.
Because meta-analysis has several inherent
limitations (such as the inability to adequately explore the consistency of
results within and between studies and to control for confounding factors)
meta-analysis is NOT able to PROVE that residential radon causes lung cancer,
but it does provide additional GOOD SUGGESTIVE EVIDENCE. It is one more link in
the "chain of evidence" connecting residential radon exposure to
increased lung cancer risk.
Since the investigators performing a
meta-analysis do not have access to the raw data on the individual study
subjects, the analysis is based on the published relative risks and confidence
intervals of the individual studies. Frequently, the impact of each study is
weighted based on some factor which the meta-analysis authors feel is relevant
to the reliability of each study's data. In the Lubin/Boice meta-analysis, the
results of each individual study were weighted so that each study contributed in
relation to the precision (relative lack of random or sampling errors) of its
estimate.
The Lubin/Boice meta-analysis
paper cites 5,000-15,000 lung cancer cases required for a single case-control
study to have sufficient power to detect an exposure-response equal to that
expected from miner studies. EPA has maintained that Public Health Service
investigators claim 10,000-30,000 cases would be required.
What has changed?
EPA asked Dr. Lubin this question. He indicated
that nothing had changed, that the "science" of sample size estimation
was something of a "black box," and that the number of cases required
probably should be higher than the 5,000-15,000 cited in the paper.
Relating to the Meta-Analysis -
No "inverse exposure-rate effect" was noted.
Does this indicate that the residential exposure effects are substantially
different from those seen in the miners?
How does this affect EPA's risk assessment?
An exposure-rate effect is the alteration of an
effect by intensity of an exposure. An inverse exposure-rate effect would be the
enhancement of an effect as the intensity of the exposure decreases (i.e.,
low-level chronic exposures would be riskier than high-level more acute
exposures). An "inverse exposure-rate effect" was observed in the
miner data. This means that for miners who received the same exposure, those
that received it over a longer period of time had a greater risk of lung cancer.
The "inverse exposure-rate effect" diminished in miners exposed below
50-100 WLM.
The finding that the "inverse exposure-rate
effect" does not seem to apply in residential situations will not change
EPA's risk assessment since EPA had not included the "inverse exposure-rate
effect" in their latest risk estimate (1992). Since the effect was noted in
1994, EPA has indicated that IF the "inverse exposure-rate effect" was
found to apply in residential situations, EPA's risk estimates would understate
the risk. Since the effect does not seem to apply in residential situations,
EPA's risk estimates remain valid.
If you have further questions about Radon, please call your
State Radon Contact or the National Radon Information Line at:
1-800-SOS-RADON
[1 (800) 767-7236]
or (if you have tested your home)
The Radon FIX-IT Program at:
1-800-644-6999 or www.radonfixit.org
To get a discounted Radon
Test Kit
 ,
go to the National Safety Council's
Environmental Health Center
If you are interested in finding a qualified radon service
professional to test or mitigate your home, or you need to purchase a radon
measurement device, you should:
- Contact your State
Radon Contact to determine what are, or whether there are, requirements associated with providing radon measurement and or radon
mitigations/reductions in your State. Some States maintain lists of
contractors available in their state or they have proficiency programs or
requirements of their own.
- Contact one or both of the two privately-run Radon
Proficiency Program (listed here alphabetically) who are offering proficiency
listing/accreditation/certification in radon testing and mitigation.
The National Environmental Health
Association (NEHA)
National Radon Proficiency Program
Administrative Office
P.O. Box 2109
24 Cardinal Ridge Road
Fletcher, NC 28732
Toll Free: (800) 269-4174 or
(828) 890-4117
Fax: (828) 890-4161
http://www.radongas.org/
e-mail: angel@radon.com |
The National Radon Safety
Board (NRSB)
P.O. Box 703
Athens, TX 75751
Toll Free:
(866) 329-3474
Fax: (903) 675-3748
http://www.nrsb.org
e-mail: info@NRSB.org |
| (Reference herein
to any specific commercial products, process, or service by trade name,
trademark, manufacturer, or otherwise, does not necessarily constitute
or imply its endorsement, recommendation, or favoring by the United
States Government.) |
EPA's Position on
These Two Privately-run Programs
|
