A three-year study by the National Research Council has found that the danger of indoor exposure to radioactive radon gas is much higher than previously believed and is especially hazardous for smokers.
The council, an arm of the prestigious National Academy of Sciences, said Tuesday that the lifetime risk of dying from lung cancer due to radon exposure is nearly three times greater than widely respected estimates made as recently as 1984.
The council estimated that among every 1 million people exposed to a relatively low dose of radon in a lifetime, there will be an average of 350 lung cancer deaths above those that will normally occur. The risk estimate is nearly three times higher than the 130 in a million estimated in 1984 by the highly regarded National Council on Radiation Protection and Measurements.
U.S. Environmental Protection Agency officials, who commissioned the study amid growing concern over radon levels found in homes throughout the nation, said the findings confirm their fears.
"A prestigious group of scientists independently looking at all this data . . . are coming to a conclusion that radon is a very serious problem and can have very significant risks at levels that we have widely seen in homes throughout America," said Richard Guimond, who heads the EPA's radon program.
Indeed, the study found that the risk of contracting lung cancer for people who are exposed each year to radon levels at or slightly above the maximum EPA exposure limits is 50% greater than the risk for a person who is exposed only to extremely low levels normally found in outdoor air.
The lung cancer risk to smokers associated with exposure to radon is substantially greater, than the risk to non-smokers," the report said. And, the council said radon exposure does not merely add to a smoker's risk, it multiplies it.
At the same time, however, the study said that people long exposed to radon can minimize lung cancer risks--much like smokers who stop smoking--if radon levels found in their homes are reduced.
The findings, released in Washington, come at a time when the EPA has warned that radon--which is odorless and invisible, is the No. 1 environmental health risk in the United States.
Radon gas is produced by the breakdown of uranium and radium found in soils throughout the nation. As the gas decays, it gives off radioactive alpha particles that can be inhaled and lodge in the the lungs where they continue to radiate.
Last August, the EPA said that based on a survey of 11,600 homes in 10 states, not including California, one out of five homes in the United States may have radon concentrations that exceed the limit set by the EPA. That limit is four picocuries per liter of air.
The EPA has said between 5,000 and 20,000 lung cancer deaths each year can be attributed to radon. The overwhelming majority of lung cancer, however, is caused by smoking.
All previous estimates of the risk to the general population, like the new one, are drawn from data collected on lung cancer deaths among uranium miners, who work in an environment heavily laden with radon gas. By calculating the length of the miners' exposure to known or estimated levels of radon and their mortality rate, scientists have attempted to characterize the risks posed to the general population.
The study was hailed by committee chairman Jacob I. Fabrikant of the University of California, Berkeley, as a "seminal" examination of lung cancer data recorded among uranium miners in the United States and elsewhere. For the first time, he said, the study relied not on previous analyses but fed the raw data into a sophisticated computer model that has only recently been developed.
"We have narrowed the uncertainties. . . . The numbers are becoming more and more precise and accurate," Fabrikant said in a telephone interview from Berkeley.
'It Firms Our Resolve'
The EPA said the findings backed up the agency's own risk estimates. "From our standpoint, it kind of firms our resolve that we're on the right track," Guimond said.
However, the results were not universally hailed. Naomi Harley of New York University Medical Center, who has studied radon since the 1950s, said she believes that the new study's assessment of risk is too high.
"It's just going to be an embarrassment," she said. Harley, who chaired the 1984 study by the National Council on Radiation Protection and Measurements, said that if the National Research Council's figures are right it will mean that one out of every five smokers will die from radon exposure.
"I find that hard to believe. In fact, I find it really unacceptable," she said in a telephone interview from New York.
Fabrikant defended the findings, however, saying they represent the most thorough review of raw data yet. He agreed, however, that the model may have to be adjusted in the future and to reflect actual death rates.
But Fabrikant said, the findings can only serve to buttress the EPA's warnings about the threat of radon in homes across America.
The good news, he said, is the committee's finding that the lowering of radon levels can reduce the risk of lung cancer.
'Constant Risk of Cancer'
"Previous studies of atomic bomb survivors have appeared to show a constant risk of cancer following radiation exposure," Gail Porter, a spokeswoman for the National Research Council in Washington, observed.
She said the new study found that 15 years after exposure to radon has ended, the risk of lung cancer from that exposure declines to half the original risk.
The EPA has recommended that home owners with levels ranging between 4 and 20 picocuries per liter take action to reduce the levels within a year or two, such as by ventilating crawl spaces beneath their homes.
There are several fairly inexpensive ways to test for the presence of radon in homes. The EPA's regional office in San Francisco has a list of companies that conduct the testing in California.