Public Summary

Radiation is a natural part of the environment in which we live. All people receive exposure from naturally occurring radioactivity in soil, water, air and food. The largest fraction of the natural radiation exposure we receive comes from a radioactive gas, radon. Radon is emitted from uranium, a naturally occurring mineral in rocks and soil; thus, radon is present virtually everywhere on the earth, but particularly over land. Thus, low levels of radon are present in all the air we breathe. There are three forms of radon, but the use of the term radon in this report refers specifically to radon-222. Although it cannot be detected by a person's senses, radon and its radioactive by-products are a health concern because they can cause lung cancer when inhaled over many years. A recent report by the National Research Council suggested that between 3,000 and 32,000 lung-cancer deaths each year (the most likely value is given as 19,000 deaths) in the United States are associated with breathing radon and its radioactive by-products in indoor air, but these deaths are mainly among people who also smoke.

Most of the radon that enters a building comes directly from soil that is in contact with or beneath the basement or foundation. Radon is also found in well water and will enter a home whenever this water is used. In many situations such as showering, washing clothes, and flushing toilets, radon is released from the water and mixes with the indoor air. Thus, radon from water contributes to the total inhalation risk associated with radon in indoor air. In addition to this, drinking water contains dissolved radon and the radiation emitted by radon and its radioactive decay products exposes sensitive cells in the stomach as well as other organs once it is absorbed into the bloodstream. This report examines to what degree this ingested radon is a health risk and to what extent radon released



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--> Public Summary Radiation is a natural part of the environment in which we live. All people receive exposure from naturally occurring radioactivity in soil, water, air and food. The largest fraction of the natural radiation exposure we receive comes from a radioactive gas, radon. Radon is emitted from uranium, a naturally occurring mineral in rocks and soil; thus, radon is present virtually everywhere on the earth, but particularly over land. Thus, low levels of radon are present in all the air we breathe. There are three forms of radon, but the use of the term radon in this report refers specifically to radon-222. Although it cannot be detected by a person's senses, radon and its radioactive by-products are a health concern because they can cause lung cancer when inhaled over many years. A recent report by the National Research Council suggested that between 3,000 and 32,000 lung-cancer deaths each year (the most likely value is given as 19,000 deaths) in the United States are associated with breathing radon and its radioactive by-products in indoor air, but these deaths are mainly among people who also smoke. Most of the radon that enters a building comes directly from soil that is in contact with or beneath the basement or foundation. Radon is also found in well water and will enter a home whenever this water is used. In many situations such as showering, washing clothes, and flushing toilets, radon is released from the water and mixes with the indoor air. Thus, radon from water contributes to the total inhalation risk associated with radon in indoor air. In addition to this, drinking water contains dissolved radon and the radiation emitted by radon and its radioactive decay products exposes sensitive cells in the stomach as well as other organs once it is absorbed into the bloodstream. This report examines to what degree this ingested radon is a health risk and to what extent radon released

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--> from water into air increases the health risk due to radon already in the air in homes. Approximately half of the drinking water in the United States comes from ground water that is tapped by wells. Underground, this water often moves through rock containing natural uranium that releases radon to the water. Water from wells normally has much higher concentrations of radon than does surface water such as lakes and streams. Radon concentrations can be measured either in terms of a volume of air (becquerel of radon per cubic meter) or a volume of water (becquerel of radon per liter). The average concentration of radon in public water supplies derived from ground water sources is about 20 becquerel per liter (540 pCi). Some wells have been identified with high concentrations, up to 400 times the average. Surface water, such as in lakes and streams, has the lowest concentrations, about one-tenth that of most wells. Drinking-water quality in the United States is regulated by the Environmental Protection Agency (EPA) under the Safe Drinking Water Act (SDWA). Since radon is acknowledged as a cancer-causing substance, the law directs EPA to set a maximum contaminant level (MCL) for radon to restrict the exposure of the public to the extent that is possible, that is, as close to zero as is feasible. In 1991, EPA proposed an MCL for radon of 11 becquerel per liter (about 300 pCi per liter) for radon in drinking water. In 2000, the agency is required to set a new MCL based in part on this report. The law also directed EPA to set an alternative MCL (AMCL); an AMCL is the concentration of radon in water that would cause an increase of radon in indoor air that is no greater than the level of radon naturally present in outdoor air. Limiting public risk from radon by treating the water alone is not feasible because radon is also naturally present in the air. Thus, the AMCL is the tool that allows EPA to limit exposure to radon in water to a practical level, that is, allowing no more risk from the radon in water than is posed by the level of radon naturally present in outdoor air. The 1996 amendments to the Safe Drinking Water Act required EPA to fund the National Academy of Sciences (NAS) to determine the risk from radon in drinking water and also to determine the public-health benefits of various methods of removing radon from indoor air. In response to that agreement, the NAS established through its principal operating agency, the National Research Council, a committee which has evaluated various issues related to the risk from radon in drinking water and provides here the information needed by EPA to set the AMCL. The primary conclusion from the committee's investigation into the risk of inhaling radon as compared to drinking water containing dissolved radon is as follows: Most of the cancer risk resulting from radon in the household water supply is due to inhalation of the radioactive by-products that are produced from radon that has been released from the water into the air, rather than from drinking the water. (The risk from radon is higher among smokers because the combination

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--> of radon and smoke has a greater damaging effect than the sum of the individual risks.) Furthermore, the increased level of indoor radon that is caused by using water in the home is generally small compared with the level of indoor radon that originated in the soil beneath the home. Based on an analysis of the available data on radon concentrations outdoors and on the transfer from water to air, the Research Council committee arrived at these additional conclusions: The average outdoor air concentration over the entire United States is about 15 becquerel per cubic meter (405 pCi per cubic meter or 0.4 pCi per liter). The contribution to radon concentration in indoor air from household usage of water is very low—only about one ten-thousandth the water concentration. The reason the resulting airborne concentration is so low is because only about half of the radon in the household water supply escapes into the air and then it is diluted into the large volume of air inside the home. Combining this information, the committee has determined that the level of radon in drinking water that would cause an increase of radon in indoor air that is no greater than the level of radon naturally present in outdoor air is about 150 becquerel per liter (4,050 pCi per liter). This conclusion will affect the public and water utilities in the following ways: People who own their own wells are not legally obliged to do anything because the Safe Drinking Water Act does not regulate private wells. However, people who are served by private wells and who wish to minimize their risk should test their water and consider taking action to reduce the radon if the concentration in the water is above the AMCL. In addition, those people should also measure the indoor air concentration in their home and consider taking actions to reduce it if it is above EPA's recommended action levels. Lastly, as the earlier NRC report concluded, stopping smoking is the most effective way to reduce the risk of lung cancer and reduce the risks associated with radon. Water supplies serving 25 or more people or with 15 or more connections are considered to be public water supplies. Those supplies, along with some special cases such as schools, will be subject to radon regulation if they rely on groundwater. In this case, there are three possibilities: (a) The radon in the water is already below the MCL. This will apply to the majority of people in the United States—only about 1 of every 14 individuals routinely consumes water with concentrations greater than the 1991 proposed MCL (11 becquerel per liter or 300 pCi/L). For water below the MCL, nothing needs be done. (b) The radon in the water is greater than the AMCL. In this case, radon reduction (mitigation) would be required by law after the regulation is final. Data available to the committee indicate that there are several types of water mitigation technology that could effectively reduce the radon concentration to the MCL. (c) The radon in the water is between the MCL and the AMCL. In this case, the concentration

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--> must be reduced to the MCL or, if there is an approved state plan, the risk to the population served by the water supply can be reduced by activities that reduce radon in air and/or water. The committee discussed a variety of methods to reduce radon entry into homes and the concentrations in the indoor air and in water. Ventilation systems can be used to reduce radon concentrations in indoor air to acceptable levels. Periodic testing would be needed to ensure the continued successful operation of individual air treatment systems. New homes can be constructed using methods to reduce airborne radon (radon resistant construction). However, there is not enough evidence at the present time to be certain these techniques are effective. Several water-treatment technologies to remove radon from water are very effective, however, they do not address the largest risk to the occupants of the house, namely radon in air. The EPA mandate is to reduce public risk caused by exposure to radon. For those communities where the public water supply contains radon at concentrations between the MCL and the AMCL, the law will allow individual states to reduce the risk to their population through multimedia measures to mitigate radon levels in indoor air. A state may develop and submit a multimedia program to mitigate radon levels in indoor air for approval by the EPA Administrator. The Administrator shall approve a state program if the health risk reduction benefits expected to be achieved by the program are equal to or greater than the health risk reduction benefits that would be achieved if each public water system in the state complied with the MCL. If the program is approved, public water systems in the state may comply with the alternative maximum contaminant level in lieu of the MCL. State programs may rely on a variety of mitigation measures, including public education, home radon testing, training, technical assistance, remediation grant and loan or other financial incentive programs, or other regulatory or nonregulatory measures. As required by SDWA, EPA is developing guidelines for multimedia mitigation programs. If there is no approved state multimedia mitigation program, any public water system in the state may submit a program for approval by the EPA Administrator, according to the same criteria, conditions and approval process that would apply to a state program. In this scenario, water utilities can minimize the level of risk to their consumers—even if the water they provide is higher than the MCL (but lower than the AMCL)—by reducing airborne radon in some of the community's homes. Because the risk caused by inhaled radon is so much greater than that caused by radon that is swallowed in water, reducing the airborne radon in only a few homes may reduce public risk enough for the water utility to be in compliance with the multimedia program requirements. With regard to multimedia programs, the committee's report provides discussion of risk-reduction methods at the community level and of ways to evaluate the effectiveness of reducing radon-related risk within a community or region

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--> served by a water utility. One risk reduction technique is public education programs to encourage radon mitigation from indoor air. The previously conducted education and outreach programs reviewed by the committee were largely unsuccessful; therefore, the committee concluded that public education and outreach programs alone would be insufficient to achieve a measurable reduction in health risk. A multimedia mitigation program will reduce radon risks in indoor air in lieu of reduction to the MCL in drinking water. The specific design of each community water utility's program will depend on many factors. At the same time, complicated risk-reduction programs like those discussed here have many potential difficulties. For example, for water utilities that provide water that contains radon at levels between the MCL and the AMCL, the feasibility of using a multimedia mitigation program will depend on whether there are homes with relatively high indoor radon concentrations. Only in those homes is it feasible to reduce the air concentration sufficiently such that an expensive, large-scale water mitigation program in the region is not needed to satisfy the multimedia program requirements. The key issue is determining how many buildings must have air mitigation systems to obtain a reduction in public risk equal to that which could be achieved by reducing radon in the water supplied to the community. Moreover, air monitoring programs will be needed to identify the homes whose indoor air must be mitigated and effective outreach programs will be needed to educate the public about the need to modify these homes to reduce indoor radon so that the water utility can demonstrate the risk reduction needed for compliance. Finally, consideration needs to be given to how the costs of mitigation of private homes will be apportioned among homeowners and the water utilities or state government. Another potential problem is the present-day scarcity of trained personnel (particularly in the water utilities) that could design or maintain home air mitigation systems and carry out the tests needed to ensure continued performance of these systems. Finally, the committee recognizes that the reduction in risk by multimedia programs will not be distributed equally among the public. The mitigation of indoor-air radon in a small number of homes means risk reduction among only a few people who had high initial risk, rather than a uniform risk reduction for a whole population served by the water utility. The various analyses conducted allowed the committee to estimate the risk and annual number of fatalities caused by radon in water and to compare it with the risk caused by radon in air. The figure presented here summarizes the cancer risk posed by inhaling radon in air (with and without the addition of radon from using water in the home) and the risk posed by drinking water that contains dissolved radon. Specifically, in 1998 in the United States, there will be about 160,000 deaths from lung cancer, mainly as a result of smoking tobacco. Of those, about 19,000 are estimated to result from inhaling radon gas in the home;

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--> though most of these deaths will be among people who smoke. Of the 19,000 deaths, only 160 are estimated to result from inhaling radon that was emitted from water used in the home though most of these deaths would also among smokers. As a benchmark for comparison, about 700 lung-cancer deaths each year can be attributed to exposure to natural levels of radon while people are outdoors. The committee determined that the risk of stomach cancer caused by drinking water that contains dissolved radon is extremely small and would probably result in about 20 deaths annually compared with the 13,000 deaths from stomach cancer that arises from other causes. Except in situations where concentrations of radon in water are very high, reducing the radon in water will generally not make a large difference in the total radon-related health risks to occupants of dwellings. Using techniques to reduce airborne radon and its related lung-cancer risk makes good sense from a public-health perspective. However, there are concerns about the equity of the multimedia approach. The committee concludes that evaluating whether a multimedia approach to radon reduction will achieve an acceptable risk reduction in a cost-effective and equitable manner will be a complex process. It will require significant cooperation among EPA, state agencies, water utilities and local governments, especially because many of the communities affected by the radon regulation will be very small and they will need assistance in making decisions concerning the advantages or disadvantages of a multimedia program. Thus, each public water supply will find it necessary to study its own circumstances carefully before deciding to undertake a multimedia mitigation program instead of treating the water to reduce the radon dissolved in it.

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