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Radon and Cancer
Radon-222
is a naturally occurring chemically inert gas, which arises
from the decay chain of uranium in the earth’s crust.
Inhalation of air containing radon and its products results
in the exposure of cells in the bronchial epithelium and elsewhere
to ionising radiation, chiefly from alpha
-particles.
Surveys have indicated that radon accounts for an average
annual effective dose of 1.15 mSv worldwide, almost half the
total annual effective dose from all natural sources of radiation.
There is very wide variation in levels of radon exposure and
a number of populations are exposed to levels that are more
than a factor of ten higher than the overall average. The
majority of exposure to radon occurs indoors, especially in
homes, where the principal source is usually the subsoil,
although under some circumstances appreciable exposure may
occur from building materials or from radon dissolved in water.
There is conclusive evidence from studies
of underground
miners occupationally exposed to high concentrations of radon
in
air that radon is a cause of lung cancer. Extrapolation from
the
miners’ studies to the likely effects of environmental
exposure to
radon suggests that radon should be the second most important
cause of lung cancer in the general population after cigarette
smoking, and that the majority of radon-induced lung cancers
are
in those who smoke cigarettes or who have smoked them in the
past. Direct studies of the risk of lung cancer from residential
radon exposure are consistent with these conclusions. The
studies
of underground miners and also some direct studies suggest
that
high concentrations of radon in air do not cause a material
risk of
death from cancers other than lung cancer.
When a new house or other building
is being constructed, it
is usually possible, for a minimal cost, to ensure that the
radon
concentration inside the building will be very low. For existing
buildings it is also usually possible at some cost to reduce
the
radon concentrations. In terms of risk reduction, such measures
will have their biggest effect on smoking inhabitants.
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