Dangers of radon exposure and smoking compound each other.

The National Research Council (NRC) has reported that smokers who are exposed to radon appear to be at greater risk for lung cancer. The effects of smoking and radon are more powerful when the two factors are combined. Indoor radon contributes to about 12 percent of lung cancer deaths each year in the United States.

The NRC report, Health Effects of Exposure to Radon (BEIR VI), is the sixth in a series on the biological effects of ionizing radiation. The report examines data from 11 major studies of underground miners exposed to radon, as well as new epidemiological data on lung cancer in the general population. NRC has developed two models to estimate the number of radon-related lung cancer deaths in the general population. Depending on which model is used, indoor radon contributes to 15,400 or 21,800 of the estimated 157,400 lung cancer deaths each year in the United States. The majority of radon-related deaths are among smokers; among nonsmokers, they number perhaps 2,100 or 2,900.

The U.S. Environmental Protection Agency (U.S. EPA) recommends that radon levels in homes be reduced to at least 4 picocuries per liter of air. Radon levels are higher than that in approximately six percent of U.S. homes. If the radon in these homes were reduced to meet U.S. EPA guidelines, about one third of radon-related lung cancer deaths could be prevented each year. Although the majority of preventable deaths would be among smokers, perhaps 1,000 nonsmokers also would avoid lung cancer.

Effects of Radon

Radon is produced from radioactive decay of uranium that occurs naturally in rocks and soil. Outside air contains very low levels of radon, but indoors the gas builds up to higher concentrations. Although radon is chemically inert and electrically uncharged, it is radioactive, which means that radon atoms in the air can spontaneously decay or change to other atoms. The resulting atoms are electrically charged and can attach themselves to tiny dust particles in the air. The radiation given off by these inhaled particles cannot travel far enough to reach cells in organs other than the lung, so it is likely that lung cancer is the only significant health hazard posed by radon.

The NRC report found that for both smokers and nonsmokers, the risk of developing lung cancer from radon is proportionate to the amount of exposure. Radon might pose some risk even at very low levels. No evidence exists that shows a threshold below which exposure is harmless. Biological data suggest that most cancers originate from damage to a single cell. Even a very small amount of radon can produce alpha particles that penetrate cells, causing irreparable damage.

Further Information

Copies of Health Effects of Exposure to Radon (HEIR VI) are available from the National Academy Press at the National Research Council, 2101 Constitution Ave., N.W., Washington, D.C. 20418. Orders can be placed by telephone at [phone] or [phone]. The report costs $75 plus shipping.