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RESIDENTIAL RADON AND LUNG CANCER: END OF THE STORY?
Jonathan M. Samet
Department of Epidemiology, Johns Hopkins University Bloomberg
School of Public Health, Baltimore, Maryland, USA
The earliest evidence of increased lung cancer risk associated with radon came largely
from studies of highly exposed underground miners. In the United States, concerns
about residential exposures became prominent in the early 1980s with the identification
of the Watras home, which had remarkably elevated radon concentrations. By then, the
problem of indoor radon was already recognized in Europe and the first epidemiological
studies on indoor radon had been reported. The concern about the risk of indoor radon
motivated a series of case-control studies of residential radon and lung cancer in the
United States, Canada, China, and a number of European countries. In 1999, the U.S.
National Research Council Committee on the Biological Effects of Ionizing Radiation
(BEIR VI) weighed the scientific evidence available at that time on this issue and
concluded that residential radon was an important contributor to the lung cancer burden
and that risks were appropriately estimated by a linear nonthreshold model. Since
individual case-control studies have not provided consistent direct evidence of excess
lung cancer risk at residential exposure levels, combined analyses of residential radon
studies have been undertaken in both North America and Europe. These combined
analyses, including the North American pooled analysis described in this issue,
represent an important complement to the findings of the miner studies and further
support the linear no-threshold model for cancer risk adopted by the BEIR VI Committee
and other groups.
In considering the findings of the pooled case-
control studies of indoor radon included in this
special issue of the Journal of Toxicology and
Environmental Health, we should turn back 20
years ago to the early 1980s, when concern about
indoor radon first swept the United States. The
problem surged to national attention with the
identification of the Watras home in the early
1980s, a home with an indoor radon concentration
orders of magnitude greater than the mean
concentrations found in the studies reported in this
issue. The contamination of indoor environments
by radon had been recognized earlier, particularly
in Scandinavia, and, in an article in Science in 1986, Nero and colleagues reported a
geometric mean indoor residential concentration for U.S. homes of 33 Bq/m3 (Nero et
al., 1986). The first large-scale national survey of residential radon levels was carried
out in Canada in 1977–1978 (McGregor et al., 1980).