Radon — an odorless, colorless gas that seeps from uranium in the soil — accounts for more than half of the ionizing radiation most people encounter in their lives. When inhaled, this radioactive gas can set the stage for lung cancer.
Much as researchers use atomic blasts to estimate the risks of CT scans and X-rays, they use cancer rates of uranium miners to calculate the toll from radon. Although nobody's basement has as much radon as a uranium mine, it's estimated that 20,000 Americans die of lung cancer from radon exposure each year, says R. William Field, a professor of occupational and environmental health at the University of Iowa in Iowa City. By comparison, smoking is thought to cause more than 130,000 lung cancer deaths each year.
Field estimates that the death rate from radon could be cut by more than half if all homes had radon levels of less than 2 picocuries per liter of air. The Environmental Protection Agency currently recommends that homeowners shoot for a level of 4 pc/L or less.
But not all experts are convinced that getting aggressive about radon would really save many lives. Tony Brooks, professor emeritus of radiation biology and biophysics at Washington State University–Tri-Cities in Richland, notes that the places in the U.S. with the most radon also tend to have the lowest rates of cancer, including lung cancer.