CA: A Cancer Journal for Clinicians, Vol 40, Issue 5 265-275, Copyright © 1990 by American Cancer Society
Potential lung cancer risk from indoor radon exposure
N. H. Harley and J. H. Harley
Institute of Environmental Medicine, New York University Medical Center, New York.
The contribution of radon daughter exposure to excess lung cancer in
underground miners is universally accepted. These miners received exposures
from tens to thousands of WLM in a relatively few years. Although the
miners were also exposed to other noxious agents in mines, the appearance
of the excess lung cancer mortality in several types of mines and the
increase with increasing exposure provide convincing evidence of the role
of radon as the carcinogen. It is conceivable that exposures to radon at an
average concentration of one to two pCi/liter, the levels for a majority of
homes, might not produce excess lung cancers. This would require that a
lifetime exposure at low concentrations produce a different response from
that of a few years at higher levels for the miners. This is unlikely but
not impossible. The current environmental epidemiology is of varying
quality. The better studies may give some answers in a few years. These
studies are more likely to establish an upper limit of risk than to provide
an exposure-response model. Present risk estimates cannot be used
accurately in estimating the overall lung cancer risk to the US population,
since there are no good data on average exposure and exposure distribution.
For example, the number of homes above the EPA guideline of four pCi/liter
may range from two million to 10 million. An estimate of the actual radon
exposure in the US may be forthcoming from a planned EPA survey, but these
data will not be available for a few years. In the conservative tradition
of radiation protection, indoor radon exposures in homes are estimated to
produce a number of excess lung cancers in the population. One estimate by
the NCRP is about 10,000 deaths per year in the US, for an average annual
estimated exposure of 0.2 WLM (about one pCi/liter). The National Academy
of Sciences (BEIR IV) estimates 13,000 deaths for the same exposure, and
the EPA's estimate is 5,000 to 20,000.