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Radon in Drinking Water
Risk Assessment by the National Academy of Sciences
Background
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National and international health organizations, including the National Academy
of Sciences and the International
Agency for Research and Cancer, have established that there is sufficient evidence to determine
that radon is a
human carcinogen.
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In its 1994 Report to Congress, the Environmental Protection Agency (EPA)
estimated that approximately 19 million people are exposed to radon levels above the 1991 proposed maximum contaminant level (MCL) of 300
pCi/Lwater. EPA also estimates that the risk of developing a fatal cancer as a
result of exposure to radon at 300
pCi/Lwater is high (approximately 2 of every 10,000 individuals exposed).
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Exposure to radon in indoor air is the second leading cause of lung cancer,
second only to active cigarette
smoking. Approximately 15 million people are estimated by EPA to be exposed to residential
radon in air at levels
above EPA's voluntary indoor air action level of 4 pCi/Lair.
Requirements in the Safe Drinking Water Act (SDWA) 1996 Amendments
The 1996 amendments to the Safe Drinking Water Act direct EPA to arrange with the
National Academy of Sciences (NAS) to conduct a risk assessment of radon in drinking water, and an assessment of health risk reduction benefits associated with various mitigation measures to reduce radon in indoor air.
National Academy of Sciences Proposal
In February 1997, EPA approved funding for NAS to conduct a study and report on the
health risks associated with exposure to radon in drinking water and an assessment of the health risk reduction benefits associated with various mitigation measures to reduce radon levels in indoor air. The NAS report will be used by EPA to quantify the unit risk (risk per pCi/L) associated with exposure to radon in drinking water and expected health risk reduction benefits from state multimedia mitigation programs. EPA will use the NAS report in developing the Health Risk Reduction and Cost Analysis (to be published for public comment in February, 1999) and the proposed rule (August, 1999). EPA will also use the NAS report in developing guidelines for proposed state multimedia mitigation programs. NAS will not be selecting an MCL or performing other activities outside the scope of the proposal.
Proposed Activities
In May 1997, the NAS established the Committee on Risk Assessment of Exposure to Radon
in Drinking Water under the Board on Radiation Effects Research. The Committee members were chosen from multiple disciplines including radiation biology, radiation dosimetry, epidemiology and biostatistics, environmental radioactivity and pathway analysis, radioisotope metabolism, radiation health effects, risk analysis, policy, and management (including public health), water treatment methodologies, and radon-mitigation engineering.
The NAS committee will be holding a series of meetings open for public observation and
comment. The initial meeting was held on July 14-15, 1997 in Washington, DC. Upcoming meetings will be held on October 9-10 and December 2-3 in Washington, DC, November 6-7 in Irvine, CA, and January 5-6, 1998 (location to be announced).
The Committee will examine the development of waterborne radon risk assessments for both
inhalation and water ingestion and their attendant uncertainties reported by EPA, Committee on the Biological Effects of Ionizing Radiation (BEIR VI), National Council on Radiation Protection and Measurements, United Nations Scientific Committee on the Effects of Atomic Radiation, and other bodies. The NAS committee will modify an existing risk model if deemed appropriate or develop a new one if necessary. It will review the scientific data and technical methodologies used to mitigate exposures to radon and radon progeny. When appropriate, it will study and comment on the dose-response data, the models used to fit the data, and other methodologies employed to arrive at risk coefficients for radon.
To do its work the committee will use:
1. the best available, peer-reviewed science and supporting studies conducted in accordance with sound and objective scientific practices; and
2. data collected by accepted methods or best available methods (if the reliability of the
method and the nature of the decision justifies use of the data).
In its report, the NAS committee will provide estimates of cancer risks as a
result of ingestion and inhalation from exposure to radon in drinking water for the general
population and for subgroups within the general population. These subgroups will include infants, children, pregnant women, the elderly, individuals with a history of serious illness, or other subpopulations that are identified as likely to be at greater risk due to exposure to radon in drinking water than the general population.
The NAS committee will also assess the health risk reduction benefits associated with various mitigation measures to reduce radon levels in indoor air.
Product and Dissemination Plan
The NAS committee will produce a consensus report by July 1998 containing assessments of
health risks associated with radon in drinking water and health risk-reduction benefits associated with various mitigation measures. The report will be reviewed in accordance with NAS procedures before distribution. The report resulting from this effort will be available for distribution to the sponsor, federal agencies, state radiological control and public health units, interested professional societies, committee members, and to other relevant parties in accordance with NAS policy in collaboration with the NAS's Office of News and Public Information. Reports may be made available to the public without restrictions.
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