Date: Sept. 15, 1998
Contacts: Molly Galvin, Media Relations Officer
David Schneier, Media Relations Assistant
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Radon in Drinking Water Constitutes Small Health Risk

WASHINGTON -- Radon in household water supplies increases people's overall exposure to the gas, but waterborne radon poses few risks to human health, says a new report by a committee of the National Research Council.

Risk Assessment of Radon in Drinking Water, a congressionally requested study, found that drinking water which contains radon is much less of a health risk than inhaling radon. In fact, the risk of stomach cancer -- the most likely health threat from consuming radon in water -- is extremely small. The committee estimated that about 20 of the 13,000 stomach cancer deaths each year may result from consuming water that contains radon. No evidence suggests that radon causes any reproductive problems or birth defects, regardless of whether it is ingested or inhaled.

"In general, much more radon enters households through soil beneath the home than through water supplies," said committee chair John Doull, professor, department of pharmacology, toxicology, and therapeutics, University of Kansas Medical Center, Kansas City. "Radon in water does increase people's overall exposure to the gas, but radon in indoor air is the biggest public health threat. Nevertheless, the government and water suppliers should work together to develop strategies that limit potentially harmful amounts of radon in homes."

Small amounts of radon in water can escape into the air whenever the water is used -- for example, when showering or washing dishes. But because of the relatively small volume of water used in homes, the large volume of air into which radon is emitted, and the exchange of indoor air with outside air, radon in water typically adds only a small increment to overall indoor concentrations of the gas.

Estimating Risk

About 160,000 people -- mostly smokers -- die from lung cancer each year in the United States. Some 19,000 of these deaths are attributable to a combination of indoor radon and smoking. Of those, the committee estimated that about 160 deaths result from inhaling radon that is emitted from household water.

In 1991 and 1994, the Environmental Protection Agency (EPA) performed its own analyses of the risks posed by radon in drinking water. The Research Council committee's estimates of health risks from ingesting radon in water are lower than EPA's. EPA calculated that about 100 stomach, colon, and liver cancer deaths annually would result from ingesting radon -- compared to the committee's estimate of 20 stomach cancer deaths per year. Because radon can diffuse into the stomach wall and damage sensitive cells, it might cause stomach cancer in rare cases. However, once radon has entered the bloodstream through the stomach or small intestine, it is typically eliminated from the body through the lungs and will not target other organs.

Conversely, the committee's estimates of risks posed by inhaling radon released from water are higher than EPA's. EPA's analyses indicated that only 86 deaths each year may result from inhaling radon emitted from household water supplies, whereas the committee estimated 160 lung cancer deaths per year. The committee's risk estimates were different because it developed new models with updated biological data on the cancer-causing effects of ingesting radon. The committee also drew upon findings of a recent Research Council report on health risks posed by radon in air.

Radon is a gas produced from the radioactive decay of uranium that occurs naturally in rocks and soil. Although radon is chemically inert and electrically uncharged, it also is radioactive, which means that radon atoms can spontaneously decay and might damage cells when inhaled or ingested. Outside air contains very low levels of radon, but indoors the gas builds to higher concentrations. Radon is also found in ground water tapped by wells, which supply about half the drinking water in the United States. Ground water moves through rock containing natural uranium that releases radon into the water. Water from wells usually has higher concentrations of radon than does surface water such as lakes and streams.

National data on radon distribution across the United States indicates that the northern United States and some areas in southern states tend to have higher than average indoor radon, while New England states and some areas in the Southwest have higher concentrations of radon in water. The Appalachian and Rocky Mountain states and some areas in the Great Plains have higher than average radon in both water and indoor air.

To lessen the health risks posed by radon, mitigation efforts should focus on removing radon from indoor air, the committee said. Reducing radon in homes can be achieved by using ventilation systems. Except in rare situations where concentrations of radon in water are very high, bringing levels of radon down in water alone will generally not significantly reduce radon-related health risks for most individuals.

Setting Standards

Based on its own risk estimates, EPA proposed in 1991 that the standard for radon in drinking water -- known as the maximum contaminant level -- should be set at 11 becquerel per liter. A becquerel is a unit by which radiation is measured. Most household water falls below this level; only about one in 14 Americans routinely consume water with concentrations greater than 11 becquerel per liter. EPA is required to propose a new standard for radon in water next year, based in part on the findings of the Research Council report.

In addition, EPA is required to set an alternative maximum contaminant level, which provides options for mitigation in communities that have water with radon levels above the current standard. Radon will be regulated as a radionuclide in public water supplies, but a major portion of the associated risk occurs because of its contribution to the airborne radon concentration -- which is not regulated. The purpose of the alternative standard is to provide methods for reducing health risks by ensuring that radon expelled from household water uses will not raise levels of radon in indoor air to above that found naturally outdoors. To meet that goal, the Research Council committee's analysis recommends that EPA's alternative standard be set at 150 becquerel per liter of water.

Under the law, communities with water supplies containing concentrations of radon above EPA's alternative standard would have to bring those levels down in water. Most water mitigation technologies are capable of reducing radon to EPA's current standard. But states having water supplies containing levels of radon between these two standards could reduce health risk to their population by using a combination of strategies -- called a "multimedia approach" -- to lower the level of radon in water, lower the level of radon in homes that have high concentrations of the gas in the air, or both.

States that choose multimedia programs will need to develop plans to reduce public health risks to levels no greater than if the radon in water supplies were below EPA's current standard. To meet that requirement, state plans would have to identify and mitigate homes with high concentrations of indoor radon, the committee said. On their own, education and outreach programs designed to entice homeowners to reduce indoor radon would probably not be effective.

Moreover, state plans would need to include air monitoring programs to identify the homes with high concentrations of radon in air, and trained staff would be required to regularly evaluate the performance of ventilation equipment and other systems to ensure that multimedia programs meet federal requirements. Although reducing high concentrations of radon in a few homes rather than mitigating the water supply might meet public health standards, only residents in these homes would receive health benefits. The cost implications for homeowners, water utilities, and state governments of reducing radon in private homes should be considered, the committee said.

The study was funded by the Environmental Protection Agency. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, non-profit institution that provides independent advice on science and technology issues under a congressional charter. A committee roster follows.

Copies of Risk Assessment of Radon in Drinking Water are available at or by calling 202-334-3313  or 1-800-624-6242.  Reporters may obtain a pre-publication copy from the Office of News and Public Information at the letterhead address (contacts listed above).

Commission on Life Sciences
Board on Radiation Effects Research

Committee on Risk Assessment of Exposure to Radon in Drinking Water

John Doull, Ph.D., M.D. (committee chair)
Department of Pharmacology, Toxicology, and Therapeutics
University of Kansas Medical Center
Kansas City

Thomas B. Borak, Ph.D.
Department of Radiological Health Sciences
Colorado State University
Fort Collins

James E. Cleaver, Ph.D.
Professor of Dermatology
Department of Dermatology
University of California
San Francisco

Keith F. Eckerman, Ph.D.
Leader of the Dosimetry Group
Assessment Technology Section
Life Sciences Division
Oak Ridge National Laboratory
Oak Ridge, Tenn.

Linda C.S. Gundersen
Acting Associate Chief Geologist for Operations
U.S. Geological Survey
Reston, Va.

Naomi H. Harley, Ph.D.
Research Professor
Department of Environmental Medicine
Nelson Institute of Environmental Medicine
New York University School of Medicine
New York City

Charles T. Hess, Ph.D.
Professor of Physics and Astronomy
Department of Physics and Astronomy
University of Maine

Philip K. Hopke, Ph.D.
Professor of Chemistry
Department of Chemistry
Clarkson University
Potsdam, N.Y.

Nancy E. Kinner, Ph.D.
Professor of Civil Engineering
Civil Engineering, Environmental Research Group
Department of Civil Engineering
University of New Hampshire

Kenneth J. Kopecky, Ph.D.
Member, Division of Public Health Sciences
Fred Hutchinson Cancer Research Center

Thomas E. McKone, Ph.D.
Adjunct Professor
School of Public Health
University of California

Richard G. Sextro, Ph.D.
Staff Scientist
Indoor Environmental Program
Energy and Environment Division
Lawrence Berkeley National Laboratory
Berkeley, Calif.


Steven L. Simon, Ph.D. Study Director