n029  1046  07 Oct 80
 
BC-RADON
(ScienceTimes)
(Art en route to picture clients)
By WALTER SULLIVAN
c. 1980 N.Y. Times News Service
    NEW YORK - A number of radiation specialists are becoming
increasingly concerned that the most damaging exposure of some
Americans to radioactivity occurs in their own homes from
accumulations of radon, a short-lived decay product of radium that
seeps - sometimes infinitesimally and at other times significantly -
from stone walls and soil.
    Radon thus appears to be taking a prominent place alongside other
common sources of radiation exposure, ranging from cosmic rays and
medical X-rays to nuclear power plants and weapons tests. Some
scientists believe that radon adds a small increment to cancer
incidence, although efforts to document harm from such low levels of
radiation have not been persuasive so far.
    The Radiation Policy Council in the Executive Office of the
President has asked the Environmental Protection Agency to prepare,
by Nov. 18, a strategy for determining more precisely the extent of
public exposure to radon and its health effects. It will then be
decided whether to follow the lead of Sweden, the Soviet Union and
other countries in efforts to control exposures on a nationwide basis.
    The situation confronts the Department of Energy with a dilemma in
its effort to conserve energy by making homes as airtight as
possible, since that raises interior radon levels. These levels can
be reduced by several techniques, but some are costly.
    It has also been found that in homes where rock, especially granite,
is used as a reservoir for solar heat, air circulated through the
rock to heat the house at night can become heavily laden with radon.
    Virtually all naturally occurring materials emit radon, but in
greatly varying quantities. The form of primary concern is the
isotope radon 222, produced by the radioactive decay of radium 226.
There are enough atoms of radium 226 in one thimbleful of typical
rock or soil for two of them to decay every minute.
    The resulting radon 222 has a half life of 3.8 days. That is, in
that time half of a given amount decays. This sets in motion a rapid
succession of decay steps, two of which emit alpha rays, a
particularly damaging form of radiation that has been implicated as a
cause of lung cancer among uranium miners.
    Radon levels are higher indoors than out because the gas and its
radioactive ''daughters'' accumulate before they can decay. Outdoors,
they are rapidly dissipated. On the sidewalks of New York, radon
measurements are exceptionally low because the city is so thoroughly
''paved over'' with buildings, streets and sidewalks. This curbs the
escape of radon from rocks below, its primary source.
    In most homes, radon escaping from the large reservoir of
surrounding earth is far more extensive than that emitted by walls
and pavement.
    Recent readings in 21 homes in the metropolitan area indicated that
some contained unacceptably high levels of radon. Last week, however,
a spot check of several public places below ground level in New York
City that might be expected to have high levels showed that they did
not, possibly because of ventilation and sealing against entry from
below.
    Radon levels in basements are usually double what they are in living
areas because of seepage from the ground. They are presumably low in
upper story apartments, unless ventilated by air from the basement or
unless the apartments are composed of granite or other material that
emits much radon.
    In Sweden, for example, it is estimated that from 3,000 to 15,000
dwellings were built with concrete based on alum shale and made
bubbly for added strength. The shale is a relatively rich source of
radon. For centuries it has been mined as a source of dye, oil and
other products and the residue has been used for construction. That,
however, was outlawed last year, and the Swedes are using detectors
in automobiles to find homes with high radon levels.
    The percentage of American residences with unacceptable levels is
unknown. A recent survey in Canada led to an estimate that 10 percent
of homes there have excessive levels. Those levels can often be
reduced by such measures as better ventilation.
    Energy loss from ventilation in winter can be minimized by using the
heat of air leaving a house to warm air entering it. Heat exchangers
that do this are being introduced in Europe.
    Seepage of radon into basements can be curtailed by coating surfaces
with an epoxy or other sealant. Cracks in walls and floors, as well
as leaks around utility intakes, can also be sealed. Air filtration,
requiring sophisticated techniques, tends to be costly.
    In typical homes, with all windows closed, the indoor air is
replaced by outdoor air about once an hour. This is referred to as an
exchange rate of 1.0.
    The National Radiological Protection Board in Britain has estimated
that radon can be blamed for 15 cases of lung cancer each year for
every million inhabitants of homes with typical radon exposure and an
air exchange rate of 0.8. In homes made as airtight as feasible, with
a ventilation rate of only 0.2, the figure allegedly would rise to 58
per million. The total annual incidence of lung cancer in Britain is
650 per million.
    These estimates, presented last March at a workshop on radon in Port
Hope, Ontario, were largely based on statistics relating to lung
cancer among uranium miners. The latter were generally exposed to
radon levels higher than those in even the more heavily contaminated
homes.
    This extension of the statistics to low levels of exposure assumes
there is no ''threshold'' dose below which either no harm is done or
any damage is repaired by the body.
    
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