Radon And Cancer
Radon Gas
Radon is a chemically inert, naturally occurring radioactive gas without
odour, colour or taste. It is produced from radium in the decay chain of
uranium, an element found in varying amounts in all rocks and soil all over
the world. Radon gas escapes easily from the ground into the air and
disintegrates through short-lived decay products called radon daughters or
radon progeny. The short-lived progeny, which decay emitting heavily
ionizing radiation called alpha particles, can be electrically charged and
attach to aerosols, dust and other particles in the air we breathe. As a
result, radon progeny may be deposited on the cells lining the airways where
the alpha particles can damage the DNA and potentially cause lung cancer.
When radon gas itself is inhaled, most is exhaled before it decays. A small
part of the inhaled radon and its progeny may be transferred from the lungs
to the blood and finally to other organs, but the corresponding doses and
associated cancer risk are negligible compared to the lung cancer risk. Due
to dilution in the air, outdoor radon levels are usually very low. Radon can
also be found in drinking water, the concentration depending on the water
source, and this can sometimes present a hazard. Radon levels are higher
indoors, and much higher radon concentrations can be found in places such as
mines, caves and water treatment facilities. Health effects have been found
in, for example, miners. However, the lower concentrations - found, for
example, in normal buildings and to which large populations are exposed –
also confer health risks. For most people, by far the greatest exposure to
radon comes in the home.
Radon In Homes
The concentration of radon in a home depends on the amount of
radon-producing uranium in the underlying rocks and soils, the routes
available for its passage into the home and the rate of exchange between
indoor and outdoor air. Radon gas enters houses through openings such as
cracks at concrete floor-wall junctions, gaps in the floor, small pores in
hollow-block walls, and through sumps and drains.
Consequently, radon levels are usually higher in basements, cellars or other
structural areas in contact with soil.
Exchange of indoor air with the outside depends on the construction of the
house, ventilation habits of the inhabitants, and sealing of windows. The
radon concentration in houses directly adjacent to each other can be very
different. Radon concentrations within a home can vary with the time of the
year, from day to day and from hour to hour. Because of these fluctuations,
estimation of the annual mean concentration of radon in indoor air requires
reliable measurements of mean radon concentrations for at least three months
and preferably longer. Short term radon measurements give only limited
information. Radon radioactivity is measured in becquerels (Bq). One
becquerel corresponds to the transformation (disintegration) of one atomic
nucleus per second. Radon concentration in air is measured as the number
of transformations per second in a cubic metre of air (Bq/m3). The average
radon level outdoors varies between 5 and 15 Bq/m3, but both higher and
lower values have been observed.
Based on a series of surveys, the global mean indoor radon concentration is
estimated to be 39 Bq/m3, with marked variation between countries reported
by the United Nations Scientific Committee on the Effects of Atomic
Radiation (UNSCEAR). Very high radon concentrations (>1000 Bq/m3) have been
found in countries where houses are built on soils with a high uranium
content and/or high permeability of the ground. In specific geological
formations found, for example, in many European countries, radon released
from underground waters easily permeates through the rock to the surface and
into buildings. Overall, many countries around the world may have tens of
thousands of houses with indoor radon concentrations above levels considered
acceptable.
Health Effects Of Radon
The main health hazard from high radon exposure is an increased risk of lung
cancer. This has been substantiated in many studies of uranium miners. Based
on these studies, the International Agency for Research on Cancer (IARC), a
agency specializing in cancer, WHO (World Health Agency), and the US
National Toxicology Program have classified radon as a human carcinogen.
Scientists have also been
investigating whether levels of radon found in homes and other places are a
significant hazard to health. These studies are now complete and pooled
analyses of key studies in Europe, North America and China have confirmed
that radon in homes contributes substantially to the occurrence of lung
cancers world-wide. Recent estimates of the proportion of lung cancers
attributable to radon range from 6 to 15%. The pooling studies all agree on
the magnitude of the risk estimates. The recent pooled analysis of key
European studies estimated that the risk of lung cancer increases by 16% per
100 Bq/m3 increase in radon concentration. The dose-response relation seems
to be linear without evidence of a threshold, meaning that the lung cancer
risk increases proportionally with increasing radon exposure. From the
results of the same study, when a non-smoker is exposed to radon
concentrations of 0, 100 and 400 Bq/m3, the risk of lung cancer by age 75
years will be about 4, 5 and 7 in a 1000, respectively. However, for those
who smoke, the risk of lung cancer is about 25 times greater, namely 100,
120 and 160 in a 1000, respectively. Most of the radon-induced lung cancer
cases occur among smokers.
Radon In Drinking Water
In many countries, some homes obtain drinking water from groundwater sources
(springs, wells and boreholes). Underground water often moves through rock
containing natural uranium and radium that produce radon. This is why water
from deep drilled wells normally has much higher concentrations of radon
than surface water from rivers, lakes, and streams. Radon concentrations of
20 Bq/l and more, in some instances well above 100 Bq/l, have been measured
in individual water supplies in many countries. Calculations indicate that
some small risk exists due to radon in drinking water but the few
epidemiological studies conducted to date have not found an association
between radon in drinking water and cancer of the digestive and other
systems. However, more data are needed to better quantify the risk from
radon in drinking water.
Guidelines For Concentrations Of Radon In Air And Water
Most countries have adopted a radon concentration of 200–400 Bq/m3 for
indoor air as an Action or Reference Level above which mitigation measures
should be taken to reduce the level in homes. Other countries have chosen
higher or lower Action Levels. The choice of Action Levels generally has
been based on the concept of acceptable risk, i.e. these levels are thought
to represent population health risks
similar to other everyday risks. Concerning drinking water, the 2004 WHO
Guidelines for Drinking Water Quality and the European Commission recommend
that controls - for example repeat measurements - should be implemented if
radon in public drinking-water supplies exceeds 100 Bq/l. The United States
has proposed a Maximum Contaminant Level for radon of 150 Bq/l for private
water supplies. For public or commercial water supplies, the European
Commission recommends that remedial action be taken if the radon level
exceeds
1000 Bq/l. A tap water radon concentration of 1000 Bq/l contributes 100 to
200 Bq/m3 to indoor air and thus corresponds to the indoor air radon Action
Levels discussed above.
Dealing With Radon In Homes
Radon levels in indoor air can be lowered in a number of ways, from sealing
cracks in floors and walls to increasing the ventilation rate of the
building. The five principal ways of reducing the amount of radon
accumulating in a house are:
1. Improving the ventilation of the house and avoiding the transport of
radon from the basement into living rooms.
2. Increasing under-floor ventilation.
3. Installing a radon sump system in the basement.
4. Sealing floors and walls.
5. Installing a positive pressurization or positive supply ventilation
system.
Radon safety should be considered when new houses are built, particularly in
high radon areas. In Europe and the United States, the inclusion of
protective measures in new buildings has become routine for some builders
and - in some countries - has become a mandatory procedure. Passive systems
of mitigation have been shown to be capable of reducing indoor radon levels
by up to 50%. When radon
ventilation fans are added (active system) radon levels can be reduced
further.
What Is WHO Doing About Radon?
Recent studies of people exposed to radon have confirmed that radon in homes
is a serious health hazard that can be easily mitigated. As a result WHO has
established the International Radon Project in which over 20 countries have
formed a network of partners to identify and promote programs that reduce
the health impact of radon. The first meeting of the Project was held in
Geneva in January 2005 to develop a
strategy for dealing with this important health issue. The key objectives of
the Project are to:
1. Identify effective strategies for reducing the health impact of radon.
2. Promote sound policy options, prevention and mitigation program’s to
national authorities.
3. Raise public and political awareness about the consequences of exposure
to radon.
4. Raise the awareness of financial institutions supplying home mortgages to
the potential impact of elevated radon levels on property values.
5. Monitor and periodically review mitigation measures to ensure their
effectiveness.
6. Estimate the global health impact of exposure to residential radon and so
allow resources to be allocated effectively to mitigate the health impact of
radon.
7. Create a global database (including maps) of residential radon exposure.
The International Radon Project will be issuing detailed recommendations
on radon risk reduction that will target:
1. The installation of mitigation devices at the time of construction versus
retrofitting.
2. The incorporation of radon prevention and control measures in national
building codes.
3. Radon testing, mitigation and inspection of existing passive/active
systems at the time of sale for existing homes.
4. Control measures designed for medium and low radon exposure levels, which
contribute most to the overall radon lung cancer burden.
5. The role of tobacco smoking in radon risk reduction programs with a view
to the overall goal of healthy indoor air.
6. The use of both voluntary guidelines and enforceable regulations.
7. Financial support mechanisms to assist radon mitigation actions in cases
where such support is necessary to allow implementation of effective
protection from radon health hazards.
The International Radon Project will provide sound, science-based
information on radon control
measures and investigate the cost-effectiveness of alternative approaches.
The Project will also provide a
worldwide estimate of the number of lung cancers attributable to radon
exposure that can be used to
highlight the global scope of the problem. This estimate will also allow
assessment of progress made
through future prevention and mitigation programs.