Risk Assessment of Radon in Drinking Water (1999) / Chapter Skim
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Executive Summary
Executive Summary
Pages 8-22
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From page 8... ...
A recent report by the National Research Council suggested that between 3,000 and 32,000 lung-cancer deaths annually (the most likely value for the number of deaths is 19,000) in the United States are associated with exposure to 222Rn and its short-lived decay products in indoor air, largely because radon substantially increases the lung-cancer risk for smokers.
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From page 9... ...
That report was to address the risks posed by human exposure to radon and consider both air and water sources, the costs of controlling or mitigating exposure to waterborne radon, and the risks posed by treating water to remove radon. The SAB review of the report questioned EPA's estimates of the number of community water supplies affected, the extrapolation of the risk of lung cancer associated with the high radon exposures of uranium miners to the low levels of exposure experienced in domestic environments and the magnitude of risk associated with ingestion.
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From page 10... ...
if the proposed MCL is less than the concentration of radon in water "necessary to reduce the contribution of radon in indoor air from drinking water to a concentration that is equivalent to the national average concentration of radon in outdoor air." Under the law, states may develop a multimedia mitigation progam which if approved by EPA would allow utilities whose water has radon concentrations higher than the MCL, but lower than the AMCL, to comply with the AMCL. The multimedia programs to mitigate radon in indoor air may include "public education; testing; training; technical assistance; remediation grants, loan or incentive programs; or other regulatory or non-regulatory measures." If a state does not have an EPA-approved multimedia mitigation program, a public water supply in that state may submit such a program to EPA directly.
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From page 11... ...
Thus, in most homes, the risk to the occupants posed by indoor radon is dominated by the radon from soil gas, which is not subject to regulation, and a change in the radon in drinking water would produce a minimal change in the risk posed by airborne radon. This problem led to the suggestion that mitigation of radon in indoor air be considered an alternative means of achieving risk reduction equal to or greater than that which would be achieved by reducing the concentration of radon in drinking water.
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From page 12... ...
Some smaller areas of the southern states also have higher than average indoor radon concentrations. Data on radon in water from public water supplies indicate that elevated concentrations of radon in water occur in the New England states, the Appalachian states, the Rocky Mountain states, and small areas of the Southwest and the Great Plains.
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From page 13... ...
After reviewing all the other ambient radon concentration data that are available from other specific sites, the committee concluded that the national average ambient radon concentration would lie between 14 and 16 Bq m-3. Transfer Coefficient The transfer coefficient is the average fraction of the initial average radon concentration in water that is contributed to the indoor airborne radon concentration.
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From page 14... ...
Unlike previous estimates of the radiation dose, the committee' s analysis also considered that each radioactive decay product formed from radon decay in the body exhibited its own behavior with respect to tissues of deposition, retention, and routes of excretion. The committee's estimates of cancer risk are based on calculations with riskprojection models for specific cancer sites.
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From page 15... ...
The actual risk from ingested radon could be as low as zero depending on the validity of the linear, no-threshold dose response hypothesis, however, the committee has estimated confidence limits on the ingestion risk (see chapter 4~. Inhalation Risk Lung cancer arising from exposure to radon and its decay products is bronchogenic.
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From page 16... ...
The committee's analysis indicates that most of the cancer risk posed by radon in drinking water arises from the transfer of radon into indoor air and the subsequent inhalation of the radon decay products, and not from the ingestion of the water. TABLE ES-1 Committee Estimate of Lifetime Risk Posed by Exposure to Radon in Drinking Water at 1 Bq m-3 Exposure Pathway Lifetime risk Male Female U.S.
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From page 17... ...
There are a number of factors underlying the analysis of the risk associated with radon in drinking water, in addition to the lifetime radiation risk factors described above. These include the amount of water ingested, the effective expo TABLE ES-2 Comparison of Individual Lifetime Risk Estimates Posed by Radon in Drinking Water at a Concentration of 1 Bq m-3 Committee 1991 EPA 1994 Revised EPA Exposure Pathway Analysisa Proposed Ruleb AnalysisC (A)
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From page 18... ...
Both the EPA and the committee analyses used a transfer factor of 1 x 10= for purposes of estimating the contribution radon dissolved in water makes to the overall indoor air radon concentration. The estimated number of cancer deaths per year from public exposure to radon are compared in table ES-3.
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From page 19... ...
With the exception of the results in research conducted in Florida, there are no comparative data on which to base estimates of the overall effects of radon-resistant construction methods on reducing concentrations of radon in indoor air radon concentrations. Mitigation of Radon in Water Several water treatment technologies have been used to effectively remove radon from water.
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From page 20... ...
The AMCL is defined such that the waterborne contribution of radon to the indoor air concentration is equal to the radon concentration in outdoor air, which is taken to be the national average ambient radon concentration. In the situations where radon concentrations in water are greater than the MCL but less than the AMCL, states or water utilities can develop a multi-media approach to health risk reduction.
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From page 21... ...
For such water supplies, it is unlikely that a public water system's multimedia mitigation program will be practical unless the water concentration of radon is only slightly above the MCL. In areas of medium and high indoor air radon potential, it is more feasible to mitigate a small number of high-indoor-concentration homes to provide an equivalent health-risk reduction at a cost less than the cost of mitigating the water.
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From page 22... ...
Furthermore, the mitigation of indoor-air radon concentrations in a small number of homes means risk reduction among only a few people who had high initial risk, rather than uniform risk reduction for a whole population served by the water utility. This approach raises questions of equity among the various groups that are being exposed to various levels of risk associated with radon.
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