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12 Conclusions and Recommendations This chapter presents a summary of the most important conclusions and recommendations developed from this study. The presentations in this chapter are organized as follows: the central conclusions and recommendations of the committee, including those which address the charge to the committee; the context for regulation of TENORM; risk-assessment issues underlying the regulation of TENORM; risk-management issues underlying regulations for TENORM; the comparability of guidances and regulations applicable to TENORM; and issues related to natural background radiation. CENTRAL CONCLUSIONS AND RECOMMENDATIONS OF THE COMMITTEE 1. This committee finds that the differences between the Environmental Protection Agency (EPA) proposed and current guidelines for TENORM and similar guidelines developed by other organizations have no scientific or technical basis. There are some differences between various federal agencies in how they perform risk assessment, but the differences in their guidelines represent differences in policies for risk management. 2. This committee has not found a substantial body of relevant and appropriate scientific information that has not been used in the development of contemporary risk analysis for TENORM for purposes of developing and implementing guidelines. We emphasize that properties of TENORM do not differ from properties of other radionuclides in a way that would necessitate the development of different approaches to risk assessment. This committee has noted research needs related to improved understanding of the basis for high 243
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244 GUIDELINES FOR EXPOSURE TO TENORM dose to low-dose extrapolation, particularly in the current use of the linear no- threshold model for cancer induction. We also call for research related to the improvement of exposure- and dose-assessment models through validation of parameters, for better standardization of measurement methods for TENORM, for better understanding of the effects of the chemical form and physical structure of TENORM on dose, and for greater insight into and documentation of the various uses and dispersal of TENORM. 3. The ALARA (as low as reasonably achievable) objective is the most important factor in guiding agency actions aimed at radiation protection much more important than established regulatory limits or goals. To the extent that the ALARA objective is applied consistently to all exposure situations, all guidances and regulations would be consistent, provided that it is recognized that risks that are ALARA can vary considerably with the particular exposure situation. CONTEXT FOR REGULATION OF TENORM 1. All natural media earth, air, and water and biota, including humans, contain naturally occurring radionuclides to some degree. Annual doses received by residents of the United States from all sources of natural radiation in the environment average about 3 mSv and are quite variable estimated to range over a factor of about 4 for external sources and 20 for radon. 2. TENORM can be formed whenever NORM are moved from inaccessible locations to sites where there is a greater possibility of human exposure and whenever human activities process earth materials in a way that concentrates NORM. TENORM radionuclide concentrations and volumes vary greatly because of the diversity of sites, materials, and processes and because of the substantial variations in leachability, sorption, and biologic availability. Increases in radiation exposure from TENORM sources are typically local, rawer than global, concerns. RISK ASSESSMENT ISSUES UNDERLYING TENOR1VI REGULATION 1. The committee notes that for radiation sources related to TENORM, including indoor radon, all regulatory and advisory groups have assumed about the same risk coefficients. This reflects a general acceptance by the scientific community of the linear no-threshold risk-extrapolation approach as a plausible and useful means of developing public-health regulations. The committee does
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CONCLUSIONS AND RECOMMENDATIONS 245 not question the current suitability of the linear no-threshold model for regulatory purposes or the need for additional research as a basis for change in this model. 2. Exposure and dose or risk assessments used in developing standards should be reasonably realistic; that is, they should not be intended to greatly overestimate or underestimate actual effects for the exposure situations of concern. 3. For the purpose of developing guidelines, it is appropriate to develop stylized methods of exposure and dose or risk assessments for assumed reference conditions, provided that the assumed conditions are reasonably representative of the exposure situations of concern. 4. The chemical and physical forms of radionuclides in TENORM can greatly influence their environmental mobility and biologic availability. Exposure assessment for TENORM should consider such factors as bioavailability, leachability, and radon-emanation rates. Those factors are potentially important for developing guidelines for TENORM, and further research to understand them better should be undertaken. 5. Risk assessments for TENORM should also consider exposures to nonradioactive chemical agents that are often associated with TENORM. RISK-MANAGEMENT ISSUES UNDERLYING TENORM GUIDELINES 1. All standards and guidances for radiation exposure are based fundamentally on judgments about the acceptability of health risks to the public or judgments about the achievability of health risks to the public. The latter, embodied in the ALARA principle, has been the most important consideration in controlling radiation exposures of the public for specific practices or sources, provided that the dose limit for all controlled sources is met. 2. Other considerations that may be important in developing guidances for radiation protection are the justification of practices (positive net benefits, the measurability of radioactivity in the environment at levels corresponding to the quantitative criteria in standards, and the magnitude and variability of natural background radiation and naturally occurring radionuclides in various environmental media.
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246 GUIDELINES FOR EXPOSURE TO TENORM 3. The committee notes that neither EPA, which has primary responsibility for setting federal radiation standards, nor any other federal agency with responsibility for regulating radiation exposures has developed standards applicable to all exposure situations that involve TENORM. Instead, federal regulation of TENORM is fragmentary, and many potentially important sources of public exposure to TENORM are not regulated by any federal agency. 4. The committee strongly cautions against generalizing numerical guidance derived for a specific situation to another situation without sufficient thought as to the applicability to the new circumstance. For example, the soil- cleanup criteria developed under the Uranium Mill Tailings Radiation Control Act have been extended to many other situations by state and federal regulatory agencies, but many sources of TENORM have mineralogic characteristics and processing histories that differ greatly from those of uranium mill tailings, and therefore have different radon-emanation coefficients, leachability, and bioavailability. COMPARABILITY OF GUIDANCES AND REGULATIONS POTENTIALLY RELATED TO TENORM 1. The implied health risks for the different radiation guidances and regulations potentially applicable to TENORM vary over several orders of magnitude. 2. Although consistency among the many guidances and regulations for radionuclides is desirable, there are valid reasons not to expect it, including agency differences in statutory and judicial mandates for standards, in the regulatory bases of standards, in the applicability of standards, in the population groups of primary concern to the standards, and in the considerations of natural background in setting standards. Furthermore, the various guidances for TENORM were developed at different times, and the basic assumptions about radiation risk have changed. 3. The committee concludes that different guidances and regulations should not be compared unless their bases and their applicability are well understood and the quantitative criteria are interpreted properly. Otherwise, misleading conclusions about the meaning and importance of differences in implied risks might result.
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CONCLUSIONS AND RECOMMENDATIONS 247 4. We conclude that the large differences in implied health risks among the various guidelines and regulations do not necessarily mean that the different standards are inconsistent with regard to the determination of an acceptable risk to the public. The principle that exposures should be maintained ALARA, economic and social factors being taken into account, appears to be the most important factor in determining risks actually experienced for any controllable exposure situation. 5. The more stringent mitigation levels for indoor radon recommended by EPA, compared with those of most other countries and the National Council on Radiation Protection and Measurements (NCRP) and the International Commission on Radiological Protection (ICRP), do not result from differences in scientific opinion about risks posed by exposure to indoor radon. Rather, they result primarily from such factors as differences in average radon levels in homes, differences in judgments based on cost-benefit analysis about levels of radon that are reasonably achievable after mitigation, and differences in whether the guidances focus primarily on reduction of risks to individuals receiving the highest exposures or on reduction of population risks. 6. In most cases, EPA's current guidances on acceptable exposures to TENORM other than indoor radon also are somewhat more restrictive than the guidances developed by some of the states, the NCRP, and the Health Physics Society. However, direct comparisons of these guidances are difficult and potentially misleading, because of such factors as differences in whether exposures to natural background are included, the difference between a regulatory limit and a goal, and the use of a dose criterion in some cases but activity concentrations of particular radionuclides in others. 7. The committee does not view the current differences in how the agencies develop and carry out their recommendations, although perhaps confusing, as necessarily resulting in important differences in protection of public health. However, the committee does caution that, as the regulations are developed and acted on, continued attention to the factors that affect radiation dose and risk for specific TENORM situations is crucial for consistently protective, cost-effective radiation control. In addition, further study on issues of cost-benefit and other nonscientific concerns could be important in regulating TENORM, given the magnitude and variability of natural background. 8. The committee has considered the disagreement between EPA and the Nuclear Regulatory Commission over the adequacy of the Commission's standards for unrestricted release of contaminated sites. The committee believes that the disagreement is a matter of policy with no scientific or technical basis.
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248 GUIDELINES FOR EXPOSURE TO TENORM The difference between EPA's proposed annual dose constraint of 0.15 mSv and the Commission's dose constraint of 0.25 mSv cannot reasonably be regarded as significant, particularly when the Commission also requires that the ALARA objective be applied in reducing doses below 0.25 mSv. Furthermore, the difference between 0.15 mSv and 0.25 mSv normally cannot be distinguished reliably in a dose assessment. The disagreement over the need for a separate groundwater-protection standard consistent with existing standards for radioactivity in drinking water also is a matter of differences in policies for risk management. 9. EPA and the Nuclear Regulatory Commission have worked together to produce a valuable document on risk harmonization that effectively summarizes their similarities and differences in the approach to radiation protection. The committee commends the agencies for having done so and recommends that they pursue this approach further. The committee recognizes the different objectives and histories of the two agencies, but it is good public policy to reconcile the existing differences in approaches to risk management with an eye to better, more timely, and more efficient compliance activities by the regulated community, and greater acceptance by Congress and the public. ISSUES RELATED TO BACKGROUND RADIATION 1. The committee concludes that background radiation levels of NORM are highly relevant to regulation of TENORM because the radionuclides being regulated as TENORM are identical with those in nature. Arguments concerning small differences in the target regulatory level at small fractions of the natural background tend to pale into insignificance in comparison with natural background levels and their local and regional variations. 2. Considering only external photon exposure, the committee notes that EPA's proposed 0.15-mSv (15-mrem) standard is equivalent to an incremental increase in the concentration of radium-226 in soil of about the usual natural background level of 0.04 Bq/g (1 pCi/g). In view of the ubiquitousness of 226Ra in soil and the substantial local variation in natural background, it is likely to be difficult to implement a 0.15-mSv (15-mrem) soil-cleanup standard for radium, particularly when the contamination is only marginally above the local background. That is especially the case if potential exposures to indoor radon are included in complying with the standard. 3. As a practical matter, the implications of existing levels and variability of natural radionuclide concentrations and doses received by humans should receive careful consideration in the regulation of TENORM.
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