September 16, 1998

Radon More Dangerous in Air Than in Water, Study Finds

By WARREN E. LEARY

ASHINGTON -- Radon in drinking water poses few human health risks by itself, but it increases people's overall risk from the toxic gas when it escapes into the air and is inhaled, a National Research Council committee said in a report released on Tuesday.

The committee of experts, charged with evaluating the health consequences of waterborne radon and assessing the Environmental Protection Agency's methods of analyzing these risks in response to the Safe Drinking Water Act of 1996, said consuming water containing radon is much less a health risk than inhaling the radioactive gas.

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Radon, an odorless byproduct of the uranium and radium that are present in most soils, disperses quickly in open air. But it can dissolve into water and seep into basements, accumulating in high concentrations in unventilated areas. The panel convened by the National Research Council, the research branch of the National Academy of Sciences, said small amounts of radon in water could escape to the air whenever water was used, such as in showering or washing dishes. But radon going into the air of a house from water use usually makes up only a small fraction of the overall gas concentration indoors, the panel said.

"In general, more radon enters households through the soil beneath the home than through water supplies," said Dr. John Doull of the University of Kansas Medical Center, chairman of the panel. "Radon in water does increase people's overall exposure to the gas, but radon in indoor air is the biggest public health threat," he said in a statement.

The most likely health threat from consuming radon in water is stomach cancer, the committee said. In all, the panel estimated, only about 20 of the 13,000 stomach cancer deaths each year in the nation result from consuming radon-contaminated water.

Radon plays a bigger detrimental health role in lung cancer, it said. About 160,000 people, mostly tobacco smokers, die from lung cancer each year in the United States and some 19,000 of these deaths are attributable to a combination of smoking and breathing indoor radon. Of this last group, the committee estimated that about 160 deaths result from inhaling radon that escaped from contaminated household water.

As radon decays, it produces damaging particles that stick to dust and smoke inhaled into the lungs, causing cell damage that leads to cancer.

Ground water moves through rock containing uranium, which releases radon into the water. Radon is found in ground water tapped by wells, which supply half of the drinking water in the country, the report said. Well water usually has higher concentrations of radon than surface water such as lakes and streams.

The new study by the 12-member panel of experts generally agreed with the EPA's earlier risk projections, but there were some differences. The committee estimated that radon consumed in water causes 20 stomach cancer deaths a year, compared with an EPA estimate of 100 stomach, colon and liver cancer deaths. The committee said that when radon passed into the bloodstream from the stomach, it typically was eliminated from the body before it harmed other organs.

But the committee's estimate of risks from inhaling radon released from water were higher than those of the environmental agency. Using new models and updated biological data, the study estimated that inhaling radon from water caused 160 cancer deaths a year, compared to 86 such deaths estimated by the agency.

Dr. Thomas Borak of Colorado State University at Fort Collins, a member of the panel, said in an interview that it would be unusual for a water source alone to be the main health threat from radon. "Inhalation is the main problem," he said, "Most water supplies you see simply don't have enough radon in them to contribute much to inhalation risk."

In 1991, the EPA proposed a standard for radon in water, suggesting 300 picocuries per liter as the maximum contamination level. A picocurie is a unit by which radiation is measured. The agency said most household water in the nation was below this level, with only one in 14 Americans routinely consuming water with higher concentrations of radon. Of more than 60,000 water systems in the nation serving more than 25 consumers, 27,000 were estimated to be above the proposed standards.

William Diamond, director of standards and risk management in the EPA's Office of Water, said the new report is the most comprehensive ever on radon in water and most of its risk estimates were very close to ones produced by the agency in a 1994 assessment.

Congress has set up a schedule for the agency to enact radon-water regulations, Diamond said. The agency is to complete a new risk analysis by next February, publish a formal rule proposal in August 1999 and implement a final regulation by the year 2000, he said. States and water utilities would have three years or more from then before the rules take affect.

Under the Safe Drinking Water Act, states with water supplies contaminated with radon above certain levels are to be given options for mitigating health risks, using a combination of strategies that could allow lowering radon in water, lowering levels of the gas in the air or combinations of both to reduce overall dangers from the gas, experts said.

Copyright 1998 The New York Times Company