Multimedia Approach to Risk Reduction
The 1996 Safe Drinking Act Amendments permits states to develop a multimedia approach to reduce the health risk associated with radon if the maximum contaminant level (MCL) were so stringent as to make the contribution of waterborne radon to the indoor radon concentration less than the national average concentration in ambient (outdoor) air. Under those circumstances, an alternative maximum contaminant level (AMCL) would be defined as the radon concentration in water that results in a contribution of waterborne radon to the indoor air concentration equal to the national average ambient radon concentration. The Administrator of the Environmental Protection Agency (EPA) is required to publish guidelines, including criteria, for establishing multimedia approaches to mitigate radon levels in indoor air that will result in an equivalent or greater reduction in the health risk posed by radon in the area served by a public water supply that contains radon in concentrations greater than the MCL but less than or equal to the AMCL.
The objective of this chapter is to describe the considerations involved in performing a quantitative evaluation of the health-risk reductions that would be achieved by reducing the concentration of radon in the water relative to those achieved through such multimedia activities as mitigating homes to reduce their average indoor radon concentrations. To consider how the multimedia approach to risk reduction might be applied, the committee provides several scenarios that suggest how the risks posed by radon in the indoor air of a home from soil gas can be compared with the risks posed by radon in the drinking water of that dwelling.
Derivation of the Alternative Maximum Contaminant Level (AMCL)
The AMCL for radon is defined as the concentration of radon in water that will contribute to indoor air a radon concentration equal to the national average ambient-air concentration. In effect, the AMCL is defined implicitly by the following relationship:
where TF represents the water-to-indoor-air transfer factor, and Mambient is the national average ambient-air concentration. Note that Mambient is a single number that is unknown but that can be estimated with some degree of uncertainty (see chapter 2). The AMCL is also a single number that is to be determined. The role of the transfer factor, TF, in this relationship is less clear, because it is not simply a single number. In fact, the TF is subject to both variability (that is, variation from dwelling to dwelling and over time for a given dwelling) and uncertainty (that is, the distribution of TF over the population of all dwellings is unknown). The legislation that mandates the derivation of an AMCL does not specify how the TF is to be derived. The committee chose to interpret TF as the mean transfer factor (MTF) that is, as a single numerical quantity that, like Mambient, is unknown but can be estimated with uncertainty:
The AMCL derived from this relationship has the property that water with radon at the AMCL will, on average over the population of dwellings (that is, over the distribution of TFs), contribute a concentration of Mambient to indoor air. It does not, however, imply that in any given dwelling, the contribution to the airborne radon concentration from water at the AMCL will equal Mambient.
The available data regarding ambient-air concentrations and transfer factors are limited but adequate for estimation of MTF and Mambient , and the committee determined that the best estimate of the AMCL that can be derived from the available data is the ratio of the estimated arithmetic means:
There are, of course, uncertainties in the estimates of both MTF and Mambient, so it is necessary to assess the magnitude of uncertainty that they induce in the estimation of the AMCL. If the uncertainties are relatively small, the value of AMCLest is unlikely to differ greatly from the true value defined implicitly by equation 9.2. In view of the limited nature of the data available for estimation of MTF and Mambient, the committee chose not to attempt to represent the uncertainties in those estimates with probability distributions. Instead, the committee defined upper and lower bounds that, in its opinion, are highly likely to contain the true values.
As described in chapter 2, the national average ambient air concentration was estimated to be 15 Bq m-3 with a high level of certainty that the value lies between 14 and 16 Bq m-3. Therefore, the uncertainty in the estimation of Mambient was represented by lower and upper bounds of 14 and 16 Bq m-3, respectively.
Regarding the mean transfer factor, MTF, the committee noted that the compiled measurement data had an estimated mean and standard error of 0.9 × 10-4 and 0.1 × 10-4, respectively, on the basis of 154 observations, whereas the estimate derived from modeling was either 0.9 or 1.2 × 10-4 (see chapter 3). The committee's best estimate of the mean transfer factor was 1 × 10-4.
The uncertainty in the estimation of MTF was represented by lower and upper bounds of 0.8 × 10-4 and 1.2 × 10-4, respectively. Therefore, on the basis of estimates of mambient (15 Bq m-3) and mTF (1 X 10-4 ) given above, the committee estimates the AMCL to be 150,000 Bq m-3. The uncertainty of AMCLest arising from the uncertainties in estimation of Mambient and MTF was estimated by considering the extremes of the bounds that were defined for the two input values. By propagating the upper and lower bounds on the numerator and denominator, the lower bound of the AMCLest is 117,000 Bq m-3, and the upper bound is 200,000 Bq m-3.
EPA will set the MCL value on the basis of the committee's risk assessment in this report and its own policy considerations. However, for the examples in this chapter, it is necessary to assume a value of the MCL. It will be assumed that the MCL will be 25,000 Bq m-3 of water. The committee makes no recommendation or endorsement of a specific value and is using this assumption only in order to provide a framework for the following discussion of potential risk-reduction scenarios for implementing a multimedia mitigation program.
Equivalent Risk-Reduction Scenarios
To estimate the health-risk reductions that are obtained by treating water to remove radon or mitigating homes to reduce indoor 222Rn, it is necessary to consider all the associated risks. For example, the processing of water to remove radon would probably then require that the water be disinfected under the proposed rules (EPA 1992b). Disinfection could be performed through illumination with ultraviolet light for small systems or the addition of chlorine or ozone for larger systems. The risks arising from exposure to disinfection byproducts were discussed in chapter 8 and are estimated to be smaller than the risks arising from airborne radon. Thus, the incremental risk posed by disinfection byproducts will not be included in the risk-reduction analysis. The cancer risks to the body associated with ingested radon (2 × 10-9 Bq-1 m3) are small but not negligible when compared with the risk to the lungs posed by the airborne decay products arising from radon released by water used in the home (1.6 × 10-8 Bq-1 m3). Thus, the committee has assumed a mitigation of airborne radon equal to 113% of the airborne radon would provide an equivalent health-risk reduction to account for
the risk of radon in the drinking water. This concept will be illustrated in the following scenarios.
Scenario 1: High Radon Concentrations in Water
In scenario 1, the radon concentration in drinking water exceeds the AMCL. The water utility will be required to install treatment equipment to reduce the concentration of radon in the water to at least the AMCL. The incremental cost of further treating the water so that it achieves the MCL will generally be sufficiently small that the multimedia-mitigation approach would probably not be considered. Some additional considerations arise from the increased quantity of radon being removed from the water, such as increased gamma-ray exposure to the water-treatment workers from a GAC bed or the airborne radon released to the atmosphere by an aeration system at the water-treatment plant. In general these factors would not produce sufficient cost differences between meeting the AMCL and meeting the MCL to constitute an incentive to consider a multimedia mitigation program. Thus, the only cases where it is of practical interest to consider implementation of a multimedia program is for water systems in which the radon concentration in the water is between the MCL and the AMCL.
To provide a perspective on how the risk reductions could be compared, we provide an illustrative calculation. Suppose that a water supply contains radon at 125,000 Bq m-3. If the water is treated to reach the assumed MCL, it would provide an average reduction of 125,000–25,000 = 100,000 Bq m-3. Multiplying this value by the transfer coefficient of 10-4 yields a decrement of 10 Bq m-3 in radon concentration in the air in each dwelling. For a water supply that provides water to 1,000 homes each with the same average number of occupants, the committee assumed that there were to be three persons per home. The total reduction in radon resulting from the mitigation of the water to reach the MCL would be 10 Bq m-3 per dwelling × 1,000 dwellings, or a cumulative reduction within the community of 10,000 Bq m-3. Taking into account the additional ingestion risk, it would require a reduction of 11,300 Bq m-3 in indoor airborne radon to provide the equivalent health-risk reduction.
This risk-reduction analysis could be based on the actual number of occupants in the homes so that the health-risk reductions would be applied to defined populations. However, enumeration of the people in each home presents a potential problem in that the number of individuals in a given dwelling can vary. Homes are sold to new families. Children grow up and move away, and there is the question of the presence or absence of smokers in a home. Because the lung cancer risk posed by radon is significantly higher for smokers than for nonsmokers, a greater health-risk reduction would be obtained by preferentially mitigating the homes of smokers relative to the homes of nonsmokers. Thus, a potential difficulty in demonstrating the continuing benefits of mitigation of homes for health risk reduction is the variability in the number and nature of occupants of
the dwelling. The committee has examined health-risk reduction only for an average dwelling within the community.
It is necessary to consider that each home contains the average number of individuals and the same fraction of smokers. If 113 homes were found with high concentrations of airborne radon (concentrations in excess of 150 Bq m-3, the EPA guidance concentration) and these were mitigated so that the average long-term 222Rn reduction in each home were 100 Bq m-3, then the mitigation of these dwellings would provide the same level of risk reduction as reducing the radon in the drinking water to the MCL (100 Bq m-3 per dwelling × 113 dwellings = 11,300 Bq m-3). If a typical home mitigation costs $1,500, the mitigation of the 113 homes costs about $170,000 plus the estimated cost of home testing (1,000 homes in the community × $75 per home = $75,000), for a total of at least $245,000, which includes the cost of distributing detectors, collecting them, and analyzing the resulting data.
Because of the nature of water-quality regulations, there would be a requirement for continued monitoring to ensure continuing compliance with the equivalent health-risk reduction. Thus, there are O&M costs which would involve annual measurements in the mitigated homes and replacement of fans that fail. The typical mean time to failure for the fans is estimated to be about 10 years. Thus, some fans would probably have to be replaced each year. In this scenario, all the homes with concentrations above 150 Bq m-3 are to be found and mitigated. To obtain a high level of participation, it would be necessary to attempt to measure the activity concentration in each home with a long-term detector that leads to the high estimated costs to perform the radon survey. The cost to mitigate the water in a community of about 3,000 individuals is estimated by EPA (1991b) to be $78,000 plus annual O&M costs of $3,000. Mitigation of radon in indoor air in the 113 homes is substantially more than the cost of buying and operating the system to aerate the water to remove the radon. Thus, the water-supply utility would not choose to adopt the multimedia approach to risk reduction rather than fully mitigate the water to the MCL. However, the American Water Works Association estimate (Kennedy/Jenks 1991a) for the acquisition of an appropriate water-treatment system is $275,000 plus annual O&M costs of $23,000, so multimedia mitigation might be considered as a cost-effective alternative.
Scenarios 2–4: Effects of Distribution of Radon in Indoor Air
On the basis of previously described scenario, an important consideration in deciding on the feasibility of the multimedia approach relative to the water-treatment approaches is whether a subpopulation of dwellings can be identified that would provide the needed equivalent health-risk reduction when their airborne radon concentrations were reduced sufficiently. Rather than mitigate all the homes that exceed 150 Bq m-3, it would be more cost-effective to mitigate only enough homes to achieve the target level of risk reduction. The prevalence of
high-concentration homes will depend on the geology of the area. EPA has separated the United States into three regions of different radon potential (Marcinowski and White 1993). To examine the feasibility of the selective-mitigation approach, we examine the concentration distributions for each of the different radon-potential areas of the United States. In 1989–1990, the EPA conducted the National Residential Radon Survey, NRRS (Marcinowski and others 1994) which provided a statistically valid survey of the distribution of indoor radon concentrations in homes. Each home in the survey was classified by the EPA radon potential region associated with its location. The results are summarized in figure 9.1 for these 3 regions and the entire United States. The lines in the figure were obtained by fitting a lognormal distribution to measured concentrations from each of the three regions.
Scenario 2: Low Radon Potential
To illustrate the problem of finding homes to mitigate, suppose our water supply is in a region of low radon potential. By taking the parameters of the
Geometric Mean (Bq m-3)
Geometric Standard Deviation
lognormal distribution fitted to the low radon potential region data, five sets of values for the hypothetical 1,000 homes were estimated using a random number generator. Based on the average values of the 5 sets of values, only 2.5% of the homes exceed the 150 Bq m-3 indoor-air guidance value suggested by EPA. Thus, only 25 homes would be likely candidates for mitigation of airborne radon. These highest concentration dwellings have an average radon concentration of about 215 Bq m-3. If all were mitigated and the indoor airborne 222Rn concentration were reduced to 75 Bq m-3, a concentration that has been found to be generally achievable with active mitigation systems, it would produce about 3,500 Bq m-3 in total radon-concentration reduction.1 Thus, the multimedia approach could be considered only if the 222Rnconcentration in the water were below 60,000 Bq m-3 [(60,000–25,000)(10-4)(1,000) = 3,500], and it would require that all the high-concentration homes could be found and mitigated. For lower concentrations of radon in the water that still exceed the MCL, it would be possible to identify a subset of dwellings that would provide sufficient reduction in airborne radon in enough dwellings to provide an equivalent or greater health-risk reduction. However, it appears likely that the costs of identifying and mitigating enough of dwellings to provide the equivalent health-risk reduction would exceed the costs of processing the water to reduce the radon concentration to the MCL.
Scenarios 3 and 4: Medium and High Radon Potential
For the medium-and high-potential regions, sets of values were generated in a similar manner. For these regions, the fractions of dwellings with more than 150 Bq m-3 are about 11% and 20%, respectively, on the basis of the NRRS distributions. The average concentration in the dwellings with concentrations of 150 Bq m-3 or more is 250 Bq m-3 in the medium-potential region and 270 Bq m-3 in the high-potential region. Thus, the problems of finding high-concentration dwellings and reducing their indoor airborne 222Rn concentrations are much smaller than in the low-potential region because there will now be 110 and 200 homes, respectively, that exceed the EPA guidance value and are candidates for mitigation. In the medium-regions, there would be over 19,250 Bq m-3 that could be mitigated; in the high-potential area, 39,000 Bq m-3 would be available. Thus, the mitigation of a fraction of the homes that exceed the current EPA guidance level would actually produce a larger health risk reduction than mitigation of the water would provide even if the radon concentration in the water supply approached the AMCL.
The ability to obtain the required health-risk reduction by mitigating fewer homes might make the multimedia approach more financially attractive. For the medium-potential region, mitigating the 38 homes with the highest concentra-
tions would provide the 11,300 Bq m-3. For the high-potential region, mitigation of the 23 highest-concentration homes would provide the required health-risk reduction. However, in both cases, to obtain the absolute minimum number of dwellings to be mitigated would require that 100% of the dwellings in the community be monitored to ensure finding the highest concentration homes. It is unlikely that such a high level of participation can be achieved, so alternative strategies would need to be adopted. Because there are more high-concentration dwellings to find, an extensive but not exhaustive survey of the community could identify enough high concentration homes to provide the needed health-risk reduction at a cost that would be less than the cost of implementing and maintaining a water-treatment facility.
One cost-effective approach to solicit participation would be to send a notice to ratepayers with their water bills asking whether they know what their indoor radon concentration is, and that if it is above 150 Bq m-3 in the home, they might be eligible for mitigation at no cost. The solicitation could also indicate that if the owner were interested in participating, a free test kit would be provided. It is essential that long-term monitoring of radon concentrations be performed in order to provide a reliable estimate of the risk reduction potential. This approach might provide a utility with an initial indication of the availability of high-concentration homes that could be used in developing a health-risk reduction plan. It is the committee's judgment that such an approach is unlikely to identify all the homes that would have to be mitigated to provide an equivalent health-risk reduction, but it would provide a cost-effective way to test the possibility of using the multimedia approach in a utility's operating region.
Scenario 5: Use of New Radon-Resistant Construction
As discussed in chapter 8, the effectiveness of radon-resistant construction is highly uncertain. The committee feels that it is not now possible to quantitatively assign radon-risk reduction potential to such construction practices. In many areas of the country, home construction is not contributing a substantial number of new dwellings to the community. To take credit for using radon-resistant techniques, new houses would have to be connected to existing water supplies. If in the future, the extent of radon reduction in new radon-resistant homes could be reliably estimated, then the following framework could be used to incorporate it into a multimedia mitigation program.
Radon-resistant construction will reduce the indoor radon concentration to a fixed fraction of the value it would have been if conventional construction practices had been used. Thus, it is necessary to estimate what the concentrations would have been in the new homes if they had not been built to be radon-resistant. The potential for radon in these homes will depend on the geology of the area. Assuming that the geology of the area is reasonably uniform, so that existing homes are on geologically comparable soils, a statistically valid survey
of long-term average indoor radon concentrations in existing homes would provide the baseline distribution of indoor radon concentrations for the area. Long-term measurements of the radon concentrations in new radon-resistant homes would provide the distribution of radon concentrations in these homes, and the difference between the two distributions would yield the quantitative estimate of the health-risk reduction provided by the construction of new radon-resistant homes. Although the current approaches to radon-resistant building codes are being applied in the EPA high-radon potential areas, only about 20% of the homes in such a region would be expected to exceed the 150 Bq m-3 guidance level as previously discussed. Newer methods to estimate the indoor radon potential are likely to provide a basis for refining the regions in which radon-resistant building codes will have the greatest applicability (Price 1997 and references therein). However, it will still be essential to conduct a baseline survey to provide a sound basis for estimating the radon risk reduction potential.
The incremental cost of adding radon-resistant components to new homes is estimated to be $400 per home, so the payment of incentives to new-home contractors to make homes radon-resistant could be economically competitive with water treatment. Thus, the development of a scientifically based estimate of the effectiveness of radon-resistant construction in reducing indoor radon concentrations is critical to being able to use this approach to provide equivalent radon-risk reduction. It is important to note that overall reduction in indoor radon concentrations are not likely to exceed a factor of 2 to 3 (based on the FRI research described earlier), so these techniques may not always result in indoor radon concentrations below the EPA 150 Bq m-3 guideline.
Scenario 6: Multicommunity Mitigation
Because the objective of the multimedia-mitigation strategy is to provide equivalent or greater public-health benefit (health-risk reduction) for a lower cost, a scenario could be developed in which a water utility operates wells in several communities or separate production and distribution systems within a single community. Suppose that one community has water with a radon concentration between the MCL and the AMCL and another community has low radon concentrations in its water but high radon concentrations in its indoor air. Could the water utility mitigate the air concentrations in dwellings in the low-water-radon community to produce the equivalent health-risk reduction that would have been obtained by lowering the water concentration of 222Rn in the other community?
The philosophy of maximizing the public-health by using the assumption of linearity in the risks that arise from exposure to radon and its decay products would support this tradeoff as providing cost-effective equivalent risk reduction. On that basis, the committee cannot eliminate this type of risk trading from consideration because it will produce equivalent or better health benefits. How-
ever, important questions of equity in the treatment of the-two communities must be taken into consideration in the decision as to how to proceed.
A similar scenario can be envisioned in which some homes in a community are served by a public water supply and others have private wells. Under the provisions of the Safe Drinking Water Act (SDWA), the utility would be required only to provide water that meets the radon MCL to the homes that it serves. It is possible that the homes served by private wells would have some of the highest indoor-air radon concentrations. In a holistic view of achieving a comparable or greater health-risk reduction for the community, it might be best to remediate the air in the homes with the highest radon concentrations even if they are not served by the utility. However, that would present a dilemma for the utility because it would be mitigating homes to which it does not provide water. Such dwellings are outside the normal jurisdiction of the SDWA and therefore potentially outside the purview of a multimedia program. A policy decision would be needed as to whether such dwellings could be included in a multimedia mitigation program and would raise an important equity question, in that water ratepayers would be charged for the mitigation of homes that are not being served by their utility and whose occupants are not contributing to the payment of the costs of the radon-abatement program.
Scenario 7: Use of Outreach, Education, and Incentives
Another possible approach to reducing the indoor air concentrations of radon is to enlist homeowners in the identification and mitigation of homes with high radon concentrations. As previously described, home-mitigation programs will be practical only in areas of medium or high indoor-air radon potential or in communities with radon concentrations in the water supply that are close to the MCL. In this case, the utility might involve the community via a public-education program and potentially provide incentives for mitigation of those homes. The committee was asked to comment on the body of evidence regarding the effectiveness of such programs and on how the health-risk reductions could be evaluated in such cases. With respect to outreach and education programs, there is some experience that can be examined.
Communicating risk to the public such that individuals are motivated to change their behaviors and reduce their exposure to the hazard is a well-known problem. The report, Improving Risk Communication (National Research Council 1990b), addresses many of the issues relevant to that process. In particular, the report gives an example of comparing radon with other types of risk: ''radon risk can equal or exceed the 2% risk of death in an auto accident . . . for anyone who lives 20 years at levels exceeding about 25 picocuries per liter.'' This statement places an unfamiliar risk (radon exposure in homes) in juxtaposition to a more familiar risk (death in an auto accident). Though such techniques may help people understand the magnitude of an unfamiliar risk, it can also be misleading because
it does not specify the respective or acceptable levels of exposure, leaves out potentially relevant nonlethal consequences, and uses language (picocuries per liter) unfamiliar to most people. The comparison above is an example of an expert's message that is precise and accurate but is too complex, or uses unfamiliar technical jargon, such that only another expert would likely understand it. In contrast, simplified messages that nonexperts can understand usually present only selected information, thus, they can be challenged as inaccurate, incomplete, or manipulative.
There have been limited studies of the effectiveness of communicating the risk of radon to the public though little has been peer-reviewed and openly published. A useful summary of state programs to determine the effectiveness of radon programs in mitigating individual risk was prepared by the Conference of Radiation Control Program Directors (1996). Following various types of state outreach programs, CRCPD determined through surveys that a total of 73% of the participants recognized radon, 52% considered radon to be unhealthy, and 44% defined radon correctly. Only 10% of the survey participants tested for radon in their homes, and only 16% of those who thought radon was unhealthy tested their homes. Surveys revealed that radon tests took place for other reasons. For example, 26% of the tests were associated with real-estate transactions though 18% of the tests were carried out despite that residents did not believe radon was unhealthy. The CRCPD surveys indicated that states with radon testing as part of their real-estate transactions requirements also had high-awareness. Furthermore, the surveys indicated that home mitigation was lower for homes with indoor air concentrations less than the EPA-recommended action level of 150 Bq m-3.
It is clear from the CRCPD surveys that certain state radon programs were more effective in communicating risk to the public and that Maine had the greatest success. In Maine, a total of 5% of all homes have been mitigated and 30% of homes with radon levels above average have been mitigated. Of homes that had radon in water at over 370,000 Bq m-3, more than 75% have been mitigated, even though the state of Maine has recommended for the last 20 years that homeowners should mitigate water at levels greater than 740,000 Bq m-3. Factors in Maine which seem to be related to that success include partnering between state agencies and local groups and authorities, and effective use of the media. Wyoming also had high awareness; similar partnering activities were used there as well as using the media to promote radon awareness including outdoor advertising on billboards, direct mail, newspapers, and television publicity. The District of Columbia and Texas had the largest increases in radon awareness at 6% each. The District of Columbia distributed radon information in English and four other languages.
Mitigation of residences for high radon levels varied among the states from 3.6% in Pennsylvania to 0.3% in Hawaii. The states with the highest mitigation rates also were the top 25% of states in terms of public radon awareness. These states provided advice and assistance by telephone as well as printed materials,
brochures, and do-it-yourself guides. Three factors were important to influencing the number of households that mitigated radon: educating the public about mitigation and ensuring availability of qualified contractors, a radon-awareness campaign, and promoting the widespread testing of residential radon levels.
Several studies have described the problems of communicating risk to the general public; a broad review of radon-related risk communication was done by the EPA's Science Advisory Board (1995). A telephone survey was used to assess information about homeowners with indoor air concentrations greater than 740 Bq m-3 (Field and others 1993). Of these homeowners, only 19% identified lung cancer as a possible health outcome of high radon exposure, and fewer than one-third remembered the value measured in their home to within 370 Bq m-3, even within the first 3 months after receiving their test results. In another study 99 homeowners were randomly selected in a community. In this group, 64% expressed concern about radon but only 7% tested their homes (Kennedy and others 1991). These findings tend to show that knowledge about the hazard does not necessarily lead to actions to reduce the risk. A survey of 275 adults showed that 92% had heard of radon and believed it to be a health risk though only 4% believed that they were exposed to high levels of radon gas (Mainous and Hagen 1993). The phenomenon of believing that exposure happens only to others appears common. In this study, younger and less-educated people were more likely to perceive radon as presenting a health risk and women were found to be 3.5 times as likely as men to perceive radon as a risk. Finally, Sandman (1993) showed that among 3,329 homeowners, the likelihood of radon testing was predicted by the degree of general knowledge about radon and a decision to test was related to each individual's perception of the seriousness of the risk.
Three states have detailed results of testing and mitigation programs. New Jersey examined the short-term home radon-test results, including real-estate tests, by month from 1991 to 1997 (J. Lipoti, State Radiation Protection Program of NJ, private communication). Non-real-estate tests make up about 25% of all the tests for radon in houses. When high radon was found in a test, especially airborne concentrations in excess of 3,700 Bq m-3, free radon packets were sent to homeowners within a I mile radius. Roughly one fourth of the homes that received packets used them. These tests were done from January 1996 through April 1997. Another investigation was of the fraction of homes testing high for radon that were not mediated by state-certified contractors. These homes were not reported to have been mitigated. For houses found to have indoor radon concentrations greater than 150 Bq m-3, the percent of dwellings not mitigated ranged from 64 to 72% during the period 1992–1996.
New York state tested radon awareness, testing, and remediation with a survey (NYDH 1997b). The survey included information about ethnic background, age, education, and income and involved more than 1,000 interviews. Of 993 respondents, 152 had tested for radon and 12 had radon concentrations in excess of 150 Bq m-3. Of those in the high-radon group, nine undertook mitiga-
tive action and four tested again after mitigation. Those who did not test mainly thought that radon was not high in their home, that radon did not pose a problem in their areas, or that radon risk was exaggerated. When asked to specify their information source, most reported that they had heard about radon on television (27–30%) or from news stories (84–85%). Respondents in high-radon counties showed an increased knowledge about radon over those in low-radon counties by between 50 and 100%. When asked what radon caused, respondents noted headache, asthma, birth defects, lung cancer, and other cancers. Of the 993 respondents who had heard of radon, 86–90% were aware that radon can be unhealthy.
New York state (NYDH 1997a) also performed a mitigation survey. The study sample included 1,522 homes, of which 1,095 had indoor-air radon at over 370 Bq m-3 and 427 homes with air concentrations of 150–370 Bq m-3. The subjects in the study were interviewed to ensure that they were at least 18 years old. Of the 1,113 higher-radon-concentration respondents, only 665 (60%) indicated that they had had radon mitigation performed. Mitigation increased with respondent education level from 45% to 65%, increased with household income from 38% to 70%, and increased with household radon level from 47% to 79%. A total of 393, or 59%, of the mitigated homes were retested for radon after mitigation. Respondents where homes were not mitigated had a major concern about the cost of the mitigation. Actions taken included opening windows and doors (51 of 148), sealing or caulking cracks and openings (74 of 148), installing a powered system (9 of 148), installing a system to draw radon (34 of 148), and spending less time in the area with radon (22 of 148). Active mitigation systems were more prevalent for higher radon levels, from 370 to 1,850 Bq m-3. The reasons for performing the mitigation for the people who were most strongly concerned for their own health, concerned for children's health, and the publicity on health effects. Reasons for not performing mitigation were mainly that radon concentration was not too high and that mitigation was too expensive.
Another question is the potential effectiveness of incentives. The costs of a multimedia program could be reduced if homeowners and the utility shared the cost of mitigation. Sweden has a program of partial incentives. It has 8.8 million inhabitants and about 4.1 million dwellings (1.9 million detached houses and 2.2 million multifamily houses). The average radon concentration in Swedish dwellings is 108 Bq m-3. Sweden has a legally enforceable limit for radon in existing dwellings of 400 Bq m-3 and a recommendation to reduce radon concentrations that are above 200 Bq m-3. The new-building limit is 200 Bq m-3. Indoor radon concentrations have been measured in about 350,000 dwellings with the cost of the measurement usually paid by the homeowner. About 45,000 homes with radon concentrations above 400 Bq m-3 have been found. Based on these measurements, it is projected that about 150,000 dwellings, most of them detached houses, have radon over 400 Bq m -3 and about 500,000 have radon over 200 Bq m-3. Of the measured homes with high concentrations (>400 Bq m-3), some 20,000–25,000 have been mitigated. Homeowners can receive a grant for
half the cost of remedial work up to 15,000 Swedish krone (SEK) (about $2,000). The homeowners must be able to show that the initial radon concentration exceeds 400 Bq m-3; the measurements must be made in accordance with the protocol for radon measurements in dwellings (issued by the Swedish government), and the intended remedial measures must be approved by the local authorities (288 municipalities). The application is handled by the regional authorities (25 regions). The board for housing and planning has the overall responsibility for the grants. A homeowner who is not satisfied with the decision of the regional authority can complain to the board. During the last 2 y, about 1,900 grants have been paid, at a cost of about 20,000,000 SEK (2.7 million dollars). The Swedish authorities have had advertising campaigns to raise public interest in the radon issue and special campaigns for the grants.
Pennsylvania had a low-interest loan program to encourage homeowners to mitigate their dwellings once they determined that their homes had high concentrations of radon. However, very few of the eligible homeowners took advantage of the program.
The programs described above indicate that public apathy about the potential risks of exposure to radon has generally remained despite numerous and sometimes costly public education efforts. On the basis of these reported results, the committee concludes that an education and outreach program would be insufficient to provide a scientifically sound basis for claiming equivalent health-risk reductions and that an active program of mitigation of homes would be needed to demonstrate health-risk reduction. Nevertheless, education or other programs to deliver basic information about radon could be a useful part of a program to attract homeowners as eventual participants in a mitigation program. Incentives could be used to further increase participation, however, there does not appear to be clear quantitative evidence of the effectiveness of such programs.
Scenario 8: Outreach for Other Health Risks
It has been suggested that because the only effect of indoor radon is lung cancer and the primary cause of lung cancer is smoking, equivalent health-risk reductions could be obtained by an education and outreach program that persuades people to quit smoking. Irrespective of the question of the effectiveness of outreach and education programs, this substitution of causality is a policy issue that is beyond the scope of the committee's charge and expertise.
Equity and Implementation Issues and Risk Reduction
Implementation of a multimedia mitigation program presents several potentially major problems for a utility. There are important equity issues that the committee sees as the most critical. Equity issues exist in trading the risks of the
entire community against the risks to the occupants of the houses being mitigated. The benefits of the risk-reduction program will go only to the people in the homes that are mitigated rather than to all those who use the water supply and are exposed to radon in the drinking water, so there are questions of fairness that will need to be addressed by the state that establishes the multimedia mitigation program and the utility that implements it. It can be shown statistically that there would be a net public-health benefit to the community if the highest-concentration homes, particularly in the medium-and high-potential areas of the country were mitigated. However, it might be difficult to convince residents whose homes are not treated that the net health benefits to the community, the net economic benefits to the utility, and the benefits to the water-users justify their small increased risk associated with the radon in the water.
Another problem is related to the accounting of the health-risk reduction and the potential natural variability of the indoor concentration of radon. Few homes have been continuously monitored over long periods, but where they have been (Steck 1992), a substantial variability can be observed even in the absence of any changes in construction or in the normal mode of living in the homes. That variability means that there could be increases or decreases in the health-risk reduction obtained by the mitigation of any specific dwelling. It is difficult to assess how much such variability would affect the total aggregate indoor-radon reduction obtained by the mitigation of a number of dwellings. Thus, the committee recommends that a margin of safety be designed into any multimedia mitigation plan. The committee suggests that there be a 10–20% excess in the cumulative amount of indoor radon mitigation performed to ensure that there will always be an equivalent or higher health-risk reduction.
The committee has presented a scenario in which the risks in one community have been traded for the risks in another with a resulting identical or improved public-health effect and a commensurate economic benefit to both communities. Thus, from the viewpoint of public health, it would be reasonable to take the cost-effective solution. However, residents in the community whose water is going untreated, in exchange for reduced risks to those living in what were high-airborne-concentration homes in the other community, are not likely to be in favor of such a solution even if it does result in a smaller increase in their water costs than would occur if their water were treated. Thus, non-economic considerations such as equity, fraction of homes mitigated, and other related matters are expected to play a large role in the evaluation of multimedia mitigation programs and might ultimately constitute the deciding factor in whether such a program is undertaken. In any planning process, a carefully designed program of public education will be essential to provide a perspective on the tradeoffs in the risks being proposed and the health and economic costs and benefits that will be produced by the various alternatives. Because of the sensitivity of the equity issue, the assistance of risk communication experts will be needed in both the planning and implementation stages of public education programs.
Water utilities have traditionally been involved in treating groundwater at the wellhead, or just before its entry into the distribution system. Rarely is water treated by a utility at the tap of the individual home or business because SDWA requirements dictate that water quality be acceptable when water leaves the treatment plant and enters the distribution system, as well as when it arrives at the consumer's tap. Where a decrease in water quality is expected (for example, because of microbial regrowth in the distribution system), a remedy is used to maintain standards (for example, a disinfectant is introduced to prevent regrowth).
If a multimedia approach to the radon problem involves mitigation of air in specifically targeted homes, water utilities will have to oversee the installation, operation, and maintenance of mitigation systems in individual homes. Utilities might have some experience installing, operating and maintaining point-of-entry systems for water in homes, but they are unlikely to have any experience with air mitigation. It is not clear how a water utility, especially a small one, will address this demand for expertise in air mitigation. Many small utilities would have to contract out the installation of the system and then determine how they will monitor the continuing performance at every home. The installation, operation, and maintenance of the airborne-radon reduction systems in individual homes and businesses presents a substantial problem in routinely gaining access to the areas where the treatment units are so that they can be monitored and maintained as required.
Historically, within EPA and many state governments, the personnel addressing issues of airborne and waterborne radon are in different departments, divisions, or even agencies. This division of responsibilities has hindered coordination of policy and response to radon-related issues. The problem is compounded by the fact that waterborne-radon concentrations will be regulated, whereas airborne-radon concentrations are not (only guidelines are provided for indoor-air concentrations). If multimedia approaches to radon are implemented, there will be a need for interaction between the government entities charged with the regulation of radon in water and those familiar with airborne-radon mitigation. It is clear that multimedia approaches to radon mitigation will be varied, and this will require substantial cooperation within and among EPA, the state agencies involved in airborne-and waterborne-radon mitigation and monitoring, water utilities, and local governments. Thus, major problems in policy implementation will need to be addressed.
Another potential problem can be illustrated by a related example. The Water Pollution Control Act Amendments of 1972 mandated that all communities, at a minimum, achieve secondary treatment of their wastewater. In 1977, Congress modified that requirement to allow communities discharging into marine waters to apply for a waiver of secondary treatment if they could demonstrate that it would cause no adverse effect on the environment. The waiver was intended, in part, to relieve rural villages with very small wastewater discharges in such places as Alaska, of the burden of building and operating secondary treatment
facilities. When the first round of waiver applications were submitted, most were from large cities that were well organized and could afford to prepare the required environmental-impact assessment. A similar phenomenon could happen with the proposed multimedia approach to radon mitigation, especially if a state chose not to submit such a program to EPA. In this case, the law allows individual public water supplies within a state to submit their own multimedia mitigation programs. It is likely that many very small water utilities whose water contained radon concentrations exceeding the MCL but not the AMCL could not muster the resources or mount the effort required to propose such a program formally. EPA, state agencies, and perhaps the water associations should develop mechanisms to assist small public water supplies in decision-making regarding multimedia mitigation programs.
In the 1991 proposed rule for radon in drinking water, EPA outlined a set of monitoring requirements for establishing and maintaining compliance with the MCL. The agency recommended that systems that must treat their water for radon be required to sample annually to demonstrate compliance. If the water did not meet the MCL, the sampling frequency would be increased to quarterly until the average of four consecutive samples was less than the MCL. The goal of compliance monitoring is to ensure that there is a continued measurable health-risk reduction due to the removal of radon from drinking water. If a multimedia approach were used in which the air in specifically targeted homes is mitigated for radon, the water utility would have to monitor the indoor airborne-radon concentrations in the mitigated dwellings to ensure a continued measurable health-risk reduction. The monitoring requirement should be similar for any new houses built to be radon-resistant. The committee recommends that air-compliance monitoring be required in each home whose air is mitigated and that these compliance requirements be equivalent to the requirements established in the final rule that regulates radon in drinking water.
A number of important issues will need to be considered by any state agency or local water utility before it proposes the implementation of a multimedia mitigation program. The ease with which dwellings with high indoor radon concentrations can be found within the utility's service area is important because it will mean that houses that can be potentially mitigated can be more easily identified. In addition there will be a large health-risk reduction associated with each mitigated house. At the same time, the smaller number of houses that are mitigated to obtain the same or greater health-risk reduction as would occur from treating the water will also increase the equity issues in that fewer individuals will benefit from the multimedia mitigation program relative to the number being asked to share the remaining risk. Public education will certainly be needed to obtain a community's commitment to the multimedia program and here again,
experts in risk communication must be an integral part of the planning and implementation team. The committee believes that the equity questions that are generated by the program of risk-trading could represent the most important barrier to the implementation of a cost-effective program that yields maximum public-health benefits.
EPA and the state agencies responsible for water quality will continue to be faced with the problem that the health risks arising from the presence of radon in drinking water are essentially associated with the water's contribution to the indoor air concentration. With an average transfer coefficient of 10-4, the increment of indoor radon that emanates from water will generally be smaller than the average concentration of radon already present in the dwellings from other sources. Thus, even if water treatment is required, the reduction of radon in water will not substantially reduce the total radon-related health risks that are faced by the occupants of the dwellings being served by the water utility.