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Executive Summary INTRODUCTION Naturally occurring radionuclides are found throughout the earths crust, and they form part of the natural background of radiation to which all humans are exposed. Many human activities such as mining and milling of ores, extraction of petroleum products, use of groundwater for domestic purposes, and living in house& alter the natural background of radiation either by moving naturally occurring radionuclides from inaccessible locations to locations where humans are present or by concentrating the radionuclides in the exposure environment. Such alterations of the natural environment can increase, sometimes substantially, radiation exposures of the public. Exposures of the public to naturally occurring radioactive materials (NORM) that result from human activities that alter the natural environment can be subjected to regulatory control, at least to some degree. The regulation of public exposures to such technologically enhanced naturally occurring radioactive materials (TENORM) by the US Environmental Protection Agency (EPA) and other regulatory and advisory organizations is the subject of this study by the National Research Council's Committee on the Evaluation of EPA Guidelines for Exposures to Naturally Occulting Radioactive Materials. The committee has used the term technologically enhanced naturally occurring radioactive materials to refer to He materials of concern to this study and has defined this term as follows: Technologically enhanced naturally occurring radioactive materials are any naturally occurring radioactive materials not subject to regulation under the Atomic Energy Act whose radionuclide concentrations or potential for human exposure have
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2 GUIDELINES FOR EXPOSURE TO TENORM been increased above levels encountered in the natural state by human activities. The exclusion of NORM subject to Atomic Energy Act jurisdiction from the definition of TENORM means that this study is not concerned with evaluating guidelines developed by EPA or other federal agencies that apply to NORM associated with the production and use of nuclear fuels, including uranium and thorium mill tailings, naturally occurring radionuclides released to the environment during operations of nuclear fuel-cycle facilities, or natural uranium or thorium in the form of source material. The most important radionuclides in TENORM as defined in this study include the long-lived, naturally occurring isotopes of radium, thorium, and uranium and their radiologically important decay products (such as radon), as well as potassium- 40. PURPOSE AND SCOPE OF STUDY This study resulted from considerations by EPA and other organizations of guidelines for controlling exposures of the public to TENORM. Specifically, there has been a concern that EPA and other organizations have arrived at different numerical values for guidelines for essentially the same exposure situations but that the reasons for the differences, especially the extent to which they were based on scientific and technical considerations, were not apparent. In light of that concern, the National Research Council committee was asked to address the following questions: · Whether the differences in the guidelines for TENORM developed by EPA and other organizations are based upon scientific and technical information, or on policy decisions related to risk management. · If the guidelines developed by EPA and other organizations differ in their scientific and technical bases, what the relative merits of the different scientific and technical assumptions are. . Whether there is relevant and appropriate scientific information that has not been used in the development of contemporary risk analysis for NORM.
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EXECUTIVE SUMMARY 3 In view of the concern about guidelines for TENORM and their scientific and technical bases, the committee has considered approaches to risk assessment for NORM only in regard to their use in developing and implementing guidelines for controlling radiation exposures of the public. The committee has not addressed other issues of risk assessment for NORM that may arise in attempting to estimate real risks posed by actual exposures of individuals or populations. The guidelines evaluated in this study include those for indoor radon and those for any other TENORM. Those two types of NORM generally have been regulated separately. After a thorough review of the subject, we have concluded that the differences between regulatory agencies' and other organizations' guidances for the control of TENORM have little basis in science but reflect differences in risk-management approaches and organizational . . mlsslons. This study is not concerned with evaluations of nonscientific issues of importance to the development of guidelines for NORM, such as costs and policy judgments in risk management. However, in evaluating whether differences in guidelines for NORM developed by EPA and other organizations are based on scientific and technical information, the committee found it necessary to identify important policy judgments in risk management that have influenced development of the guidelines, even though the merit of any such judgments is not considered. The EPA's current guidelines for indoor radon, however, are easily identified. In the case of TENORM other than indoor radon, it was not a simple matter for the committee to define what the current EPA guidelines are. Some existing guidelines clearly are outdated and do not represent EPA's current views on suitable approaches to regulating TENORM; proposals for revising some of them have been published, but the proposals have not been issued in final form, so there is uncertainty about what the new guidelines might be. Some guidelines are in the form of legally enforceable regulations, but EPA's preferred approach to regulating TENORM in some cases is indicated only by policy statements, and there are no published guidelines for some important exposure situations. Thus, judgment was required by the committee in selecting EPA guidelines for TENORM other than indoor radon to be emphasized in the comparisons with similar guidelines developed by other organizations. In general, the committee has emphasized the most recent statements by EPA concerning guidelines for TENORM other than indoor radon, regardless of their form or status. However, the committee also has attempted to discuss all EPA guidelines, in whatever form, in an effort to provide a reasonably complete picture of EPA's current policies.
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4 GUIDELINES FOR EXPOSURE TO TENORM RESPONSES TO COMMITTEE CHARGE The following sections summarize the committee's responses to the three parts of its charge. Technical Basis for Differences in Guidelines for TENORM The committee has reviewed existing or proposed guidelines for TENORM developed by EPA and similar guidelines developed by other regulatory or advisory organizations in the United States and elsewhere. The other organizations whose guidelines have been considered are the National Council on Radiation Protection and Measurements (NCRP), the International Commission on Radiological Protection (ICRP), other federal agencies, state agencies and organizations, regulatory authorities in other nations, and other national and international advisory organizations. In keeping with its charge, the committee paid particular attention to the bases of the various guidelines developed by the different organizations. There clearly are differences in the numerical values of the most recent guidelines for TENORM developed by EPA and some of the guidelines for similar exposure situations developed by other organizations. Differences are found in the guidelines for indoor radon and for TENORM other than indoor radon. Furthermore, where there are differences, EPA guidelines tend to be more restrictive, that is to correspond to lower levels of exposure and therefore presumably lower risks to the public. Whether the differences between the EPA guidelines and those developed by other organizations are significant is entirely a matter of judgment. On the basis of its review, the committee finds that the differences between EPA guidelines for TENORM and similar guidelines developed by other organizations are not based on scientific and technical information. This conclusion is based primarily on the following considerations: . All organizations that have developed guidelines for indoor radon have assumed approximately the same risk associated with exposure to radon and its short-lived decay products based on epidemiologic data obtained from studies of underground miners and extrapolation of these data to exposures to radon in indoor residences. · All organizations that have developed guidelines for TENORM other than indoor radon have assumed approximately the same risk
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EXECUTIVE SUMMARY associated with uniform irradiation of the whole body based on epidemiologic data obtained primarily from studies of the Japanese atomic-bomb survivors and extrapolation of these data to the low doses of concern in environmental exposures. . All organizations that have developed guidelines for TENORM have assumed a linear, no-threshold dose-response relationship at low levels of exposure. 5 Thus the committee finds that differences in the guidelines for TENORM developed by EPA and other organizations are based essentially on differences in policy judgments for risk management. That is not to say that EPA and other organizations have used the same methods and assumptions in estimating risks posed by radiation exposure. For indoor radon, different organizations have assumed somewhat different lifetime risks of lung cancer associated with exposure to short-lived radon decay products in air based, for example, on differences in the assumed risk-projection models, and the risk estimates have changed over time. EPA also has given greater attention than other organizations to the dependence of lung-cancer risk on an individual's smoking history. Similarly, for radionuclides other than radon, EPA has used methods and assumptions that differ from those normally used by other organizations in estimating risks associated with chronic lifetime exposure. As a result, EPA's current estimate of the risk posed by external exposure is slightly higher than the risk estimate currently used by most other organizations, but EPA's risk estimates for internal exposure to the important long-lived alpha-emitting radionuclides in TENORM are, in some cases, substantially lower than risk estimates obtained with the methods and assumptions of other organizations. An example is the risk from ingestion or inhalation of thorium. However, the differences between EPA guidelines for TENORM and the guidelines developed by other organizations are not a reflection of differences in the methods and assumptions for risk assessments for radon and other naturally occurring radionuclides. That is, EPA's current approach to risk assessment, as it differs from the approaches normally used by other organizations, was not an important factor in developing the numerical values of its current guidelines for TENORM.
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6 Relative Merits Assumptions GUIDELINES FOR EXPOSURE TO TENORM of Different Scientific and Technical Given that the differences between the guidelines for TENORM developed by EPA and other organizations are not, in the committee's opinion, based on scientific information, the second question in the charge to the committee is moot. However, the committee has considered the differences between EPA's current methods and assumptions for risk assessment and the approaches normally used by other organizations, even though these differences have not had a substantial influence on the development of guidelines for TENORM. The committee's views on the approaches to risk assessment are summarized later. Development of Contemporary Risk Analysis for NORM The third part of the charge to the committee was to consider whether there is relevant and appropriate scientific information that has not been used in the development of contemporary risk analysis for NORM, especially risk analysis for purposes of developing and implementing guidelines for radiation exposure. A particular concern expressed to the committee is that some of the important radionuclides are parents of long decay chains involving a complex mixture of radioisotopes of different chemical elements and that exposures to such mixtures might necessitate novel approaches to methods of risk estimation. The committee is not aware of any evidence that the properties of NORM differ from the properties of any other radionuclides in ways that would necessitate the development of different approaches to risk assessment. In regard to radiological properties, if one accepts the view currently held by all regulatory and advisory organizations involved in radiation protection that estimates of absorbed dose in tissue are the fundamental physical quantities that determine radiation risks for any exposure situation, there is no plausible rationale for any differences in risks due to ionizing radiation arising from naturally occurring and any other radionuclides, because absorbed dose in tissue depends only on the radiation type and its energy, not on the source of the radiation. The decay chains of some naturally occurring radionuclides are considerably more complex than the decay chains of other radionuclides with regard to the number of decay products and chemical elements involved. However, contemporary methods of risk assessment that estimate doses and risks related to ingestion or inhalation of radionuclides by assuming that decay
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EXECUTIVE SUMMARY 7 products produced in the body are redistributed and retained in the body according to the metabolic behavior characteristic of particular chemical elements take the added complexity into account by using the same methods that are applied to other radionuclides with many fewer decay products. Thus, in general, there should be no difference between NORM and other radioactive materials with regard to suitable approaches to estimating doses and risks related to external or internal exposure. However, because naturally occurring radionuclides are ubiquitous in the exposure environment, there might be more opportunity than there is with many human-made radionuclides to use observational data on natural levels in different environmental comparknents (such as soil, water, air, plants, and animals) and the fluxes between compartments to calibrate exposure-pa~way models for TENORM. On the other hand, the ability to use such natural analog data for exposure pathway analysis must be tempered by the recognition that the physical and chemical forms of TENORM could be substantially different from those for the same elements in the natural environment. In that case, observations on He behavior of radionuclides in natural systems might not be relevant to the exposure situation of concern. OTHER CONCLUSIONS AND RECOMMENDATIONS During this study, the committee considered other issues related to the development of guidelines for TENORM. The committee's views on some of these issues are summarized below. Policy Judgments for Risk Management The committee has concluded that the differences between EPA guidelines for TENORM and similar guidelines developed by other organizations are based essentially on differences in policy judgments for risk management, rather than differences in scientific and technical information. An evaluation of the relative merit of the differences in policy judgments for risk management was not part of this study, but the committee needed to identify these judgments in reaching the conclusion that the differences in the guidelines do not reflect differences in scientific and technical information. From its considerations of the various guidelines for TENORM developed by EPA and other organizations, the committee believes that the differences often are based, at least in part, on two factors that are strictly matters of policy:
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8 GUIDELINES FOR EXPOSURE TO TENORM · Differences in judgments about acceptable risks related to exposure to TENORM. · Differences in judgments about levels of TENORM in the environment, doses, or risks that are reasonably achievable. Judgments about what is reasonably achievable in controlling exposures to TENORM take into account such factors as the costs of reducing exposures in relation to the benefits in reduced health risks to the public and other societal concerns. A particularly important consideration in regulating TENORM is the pre-existing levels of naturally occurring radionuclides in the environment and associated human exposures. An additional factor that has been important in developing guidelines for TENORM is a judgment about the extent to which existing guidelines for particular exposure situations can be transferred to other situations. For example, some organizations have developed guidelines for TENORM in soil based on the concentration limits in current EPA guidelines for cleanup of soil contaminated with radium at uranium mill tailings sites developed under the Atomic Energy Act. TransferabilitY of standards developed for a specific class of TENORM waste is limited bY the extent that the physical and chemical properties of the TENORM in issues as well as projected exposure pathways are substantially similar to those considered for uranium mill tailings. Other policy judgments for risk management also have been important causes of the differences between EPA guidelines and guidelines developed by other organizations. Some guidelines are concerned primarily with reducing risks to individuals who receive the highest exposures, and others with reducing risks to whole populations. Some guidelines include exposures to natural background, and others do not. Finally, in accordance with legislative mandates, some EPA guidelines apply only to a particular environmental medium (such as air) or a particular exposure pathway (such as drinking water), whereas guidelines developed by most other organizations, especially those expressed in terms of dose or risk, apply to all environmental media and all exposure pathways combined. The importance of differences in policy judgments for risk management in determining differences in guidelines for TENORM is illustrated by the following three examples. First, the EPA guideline for mitigation of radon in homes, 150 Bq/m3 (4 pCi/L), is lower than mitigation levels recommended by NCRP and ICRP. The differences result from differences in the primary focus of the guidelines. NCRP and ICRP were concerned primarily with mitigation of risks to individuals who receive the highest exposures, and their recommended action
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EXECUTIVE SUMMARY 9 levels were based primarily on judgments about the maximum tolerable risk, with some consideration of the feasibility of achieving concentrations below the action levels. EPA also was concerned with limiting individual risks but emphasized reducing exposures in the greatest number of homes possible, on the basis of judgments about levels that were reasonably achievable in most homes. Second, EPA has issued proposed guidance on radiation protection of the public that includes a limit on annual dose equivalent of 1 mSv from all controlled sources combined, including TENORM, naturally occurring radionuclides from the nuclear fuel cycle, and human-made radionuclides but excluding radon. In contrast, NCRP has recommended an annual dose equivalent of 5 mSv as a remedial-action level for all natural sources, including natural background and TENORM but excluding radon. EPA's annual dose limit of 1 mSv for all controlled sources combined normally should be considerably more restrictive than NCRP's recommended remedial-action level of 5 mSv for all natural sources. The difference between the two guidelines is due entirely to differences in policy judgments for risk management because EPA and NCRP assumed the same risk per unit dose. The most important difference is in the judgments about the maximum tolerable risk posed by exposure to TENORM. EPA regards TENORM other than indoor radon as a type of controlled source that should be regulated in the same manner as human-made sources, whereas NCRP essentially regards sources of TENORM, even if they are controllable, as a form of natural background that should be controlled differently from human- made sources. The other important difference in policy judgments is that EPA's dose limit excludes the dose from undisturbed natural background, whereas NCRP's remedial-action level includes the dose from background. The third example concerns guidelines for cleanup of radioactively contaminated sites. The Nuclear Regulatory Commission has issued regulations that specify that sites are acceptable for unrestricted use if the annual dose equivalent from all exposure pathways, including the use of groundwater as a source of drinking water, does not exceed 0.25 mSv. EPA has objected to the Nuclear Regulatory Commission standards on two grounds. First, EPA believes that the annual dose from all exposure pathways should be limited to 0.15 mSv to achieve an acceptable level of risk. Second, in addition to the dose constraint for all exposure pathways, concentrations of radionuclides in groundwater should be limited in accordance with current standards for public drinking-water supplies unless compliance with drinking-water standards is not feasible. The difference of opinion between EPA and the Nuclear Regulatory Commission about the adequacy of the Nuclear Regulatory Commission's cleanup standards for contaminated sites is strictly a matter of differences in policy judgments for risk management. Those judgments include the
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10 GUIDELINES FOR EXPOSURE TO TENORM determination of a limit on acceptable risk and therefore dose for this exposure situation and the determination of whether separate requirements are needed for protection of groundwater resources. Consistency of Radiation Guidelines Many diverse guidelines have been developed by EPA and other organizations for TENORM and human-made radionuclides. The fundamental purpose of the guidelines is to limit risks to exposed individuals and populations. However, when the various guidelines are compared, the levels of acceptable risk corresponding to the numerical criteria in the guidelines appear to be inconsistent. The committee has considered the issue of consistency of radiation guidelines with regard to risk and offers the following observations. First, although the desire for consistency of guidelines with regard to levels of acceptable risk is understandable, the committee has identified several important reasons why such a consistency should not be expected: · Differences in statutory and judicial mandates for guidelines, especially the fundamental difference between a regulatory limit, as embodied in some guidelines, and a regulatory goal that can be relaxed on the basis of other considerations as embodied in other guidelines. · Differences in the primary bases of guidelines, especially judgments about acceptable risk versus judgments about risks that are reasonably achievable. · Differences in the applicability of guidelines, especially guidelines that apply to all sources of exposure combined versus guidelines that apply only to specific sources or practices, or to particular environmental media and comparisons of guidelines that apply to quite different sources or practices. · Differences in the population groups of primary concern, especially individuals who receive the highest exposures versus whole populations. · Differences in the considerations of natural background. The committee believes that it is important to understand those factors when comparing different guidelines.
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EXECUTIVE SUMMARY 11 Second, the numerical criteria in the guidelines, whether they are in the form of limits or goals, do not appear to be the most important factor in determining acceptable risks to individuals or populations. Rather, without regard for the substantial differences in risks corresponding to the various guidelines and without regard for the different factors that result in these differences, as described above, the principle that exposures of individuals and populations should be maintained as low as reasonably achievable (ALARA), economic and social factors being taken into account, appears to be the most important factor in determining risks actually experienced for any exposure situation that is subject to regulatory control. Therefore, to the extent that the ALARA objective is applied consistently to all exposure situations, all guidelines would be consistent with regard to the risks actually achieved, even though the risks that are ALA MA can depend significantly on the particular exposure situation. Importance of Natural Background for Guidelines for TENORM Regulation of TENORM is a unique problem among all radioactive materials in that the radionuclides of concern occur naturally in all environmental media. Therefore, guidelines for TENORM must correspond to levels of naturally occurring radionuclides in the environment at which it is practical to distinguish the radionuclides resulting from human activities from those in the undisturbed natural background. Furthermore, determinations of practical levels for identifying and controlling TENORM must take into account the variability of natural levels in different environmental media, as well as the average values. Importance of Knowledge of Sources of TENORM Sources of TENORM other than indoor radon result from a wide variety of human activities, and the physical and chemical properties of the radioactive materials that result from those activities vary widely. Furthermore, some sources are discrete and thus localized, whereas others are diffuse and very large in volume. Especially when guidelines for TENORM might be expressed in terms of concentrations in environmental media (such as soil), rather than dose or risk, development of the guidelines should take into account the properties of the various sources of concern. It would be inappropriate to apply a guideline developed for a particular exposure situation to other
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12 GUIDELINrES FOR EXPOSURE TO TENORM situations when there are important differences in the properties of the radioactive materials. In addition, exposure-pathway analysis for TENORM generally should take into account the leachability, sorption, and biologic availability of the particular physical and chemical forms of the materials. In some cases, the characteristics of TENORM differ substantially from the characteristics of naturally occurring materials in their undisturbed state. Differences in Approaches to Radiation Risk Assessment As part of this study, the committee considered the approaches currently used by EPA in estimating cancer risks posed by radiation exposure, as documented in Federal Guidance Report No. 13 (Part 1, interim version), in comparison with the approaches used by most other organizations whose guidelines were evaluated. Most other organizations estimate cancer risks on the basis of methods developed by ICRP either the current methods represented in ICRP Publications 60 and 72 and supporting documents or, in the case of other federal agencies and state organizations, the methods represented in ICRP Publications 26 and 30, which have been superseded by Publications 60 and 72. The issue of differences in approaches to risk assessment is of concern only for radionuclides other than radon because the risks posed by exposure to radon can be estimated, with some uncertainty, from epidemiologic data without the need to estimate the dose to radiosensitive tissues per unit exposure and the risk per unit dose for different types of radiation. In addition, for external exposure, the differences between risks estimated by EPA and the risks estimated by other organizations and based on ICRP methods generally are insignificant. For internal exposure, EPA's approach to risk estimation differs from approaches based on current or outdated ICRP methods in three important respects. · First, EPA's risk models take into account the age dependence of the absorbed dose rate in body tissues and the age dependence of the radiogenic risks, whereas risks calculated with ICRP methods are based on calculated committed effective doses or effective dose equivalents, which are not intended to provide accurate representations of cancer risks for individual organs and tissues of the body. The difference between the two approaches is particularly important for long-lived radionuclides with long retention times in the body.
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EXECUTIVE SUMMARY Second, EPA's assumptions about mortality for all cancers and for other competing causes of death, which are used in estimating radiogenic risks, are based on data on the U.S. population, which differ from the data used by ICRP, and there are other differences in the risk estimates for particular cancers. · Third, the other federal agencies and state governments that normally estimate risks based on the outdated ICRP methods do not take into account age-specific dosimetric and biokinetic models and current models for the redistribution and retention of radioactive decay products in the body. 13 The differences between EPA's risk estimates for internal exposure and estimates obtained with ICRP methods are particularly important for the long- lived, alpha-emitting radionuclides found in TENORM (such as thorium). If EPA's risk estimates are compared with estimates based on the outdated ICRP methods normally used by other federal agencies and state governments, the differences are well in excess of a factor of 10 in some cases. In comparison with current ICRP methods based on age-specific committed effective doses, the differences can be as large as a factor of 5. EPA's risk estimates are lower in all cases. The EPA uses its methodologically more rigorous approaches to risk assessment only in assessing risks for purposes of reaching decisions on rule- making, including decisions on the feasibility of establishing guidelines and the effects of alternative guidelines. However, when guidelines are expressed in terms of dose, as is often the case, EPA uses standard ICRP calculations of committed effective dose equivalents for adults, based on the methods and data in ICED Publications 26 and 30, for purposes of demonstrating compliance with the guidelines to maintain a stable and uniform framework for the regulated community. The committee generally supports the current EPA approaches to estimating risks posed by radiation exposure. They should be appropriate for the current US population, and the methods for estimating risks posed by internal exposure are methodologically more rigorous than those used by other organizations on the basis of current or outdated ICRP methods incorporating committed doses. EPA's current methods of risk assessment as they differ from the methods used by most other organizations-especially for long-lived, alpha- emitting radionuclides have not had a direct influence on the development of guidelines for TENORM expressed in terms of dose. That is mainly because guidelines expressed in terms of dose apply to both external and internal exposure, EPA's risk estimate for external exposure is nearly the same as
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14 GUIDELINES FOR EXPOSURE TO TENORM ICRP's, and external exposure often is important in scenarios for TENORM. Furthermore, policy judgments for risk management and a desire for consistency in regulation have been more important for the development of guidelines for TENORM than any differences in estimated risks based on different methods. However, if EPA chose to develop guidelines for TENORM in the form of concentrations in environmental media, its current methods for risk assessment could be used to derive the guidelines from an assumed limit on acceptable dose or risk. Such an approach could be suitable for TENORM, because only a few radionuclides are of concern. However, the analysis of exposure pathways and dose would need to account for the various physical and chemical forms of radionuclides that may be encountered in the environment. Use of Linear' No-threshold Dose-Response Hypothesis At the present time, there is considerable debate over the validity of the linear, no-threshold dose-response hypothesis for low levels of exposure. It remains as an assumption used in developing all radiation guidelines, including those for TENORM, in spite of the current debate over the validity of this hypothesis, including the possibilities that there is an effective threshold for radiation risks and that there are beneficial effects at low doses. The committee does not have any new insights into the validity of the linear, no-threshold dose-response hypothesis. However, the committee understands that it is used because it represents a prudent approach to health protection of the public in the absence of definitive information on radiation risks at the dose levels of concern for routine exposures. The committee also notes that the central issue here is the risks due to incremental increases in dose above background, not the risks due to the incremental increases themselves. Directions for Further Research on TENORM The committee has noted a number of subjects on which additional scientific information would be beneficial in developing guidelines for TENORS. Although models for exposure and dose assessment generally are well developed, the models for TENORM, especially the models for exposure assessment, possibly could be improved through validation of parameters. Much information on exposure-pathway models for naturally occurring radionuclides was obtained in studies on uranium mill tailings, but this information may be inappropriate for other exposure situations involving substantially different physical and chemical forms of radionuclides. Differences in chemical and
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EXECUTIVE SUMMARY 15 physical forms of TENORM also could affect the estimates of dose from ingestion and inhalation of radionuclides. There is need for improved methods for locating and measuring discrete and diffuse TENORM in the environment, especially if guidelines for TENORM correspond to levels in the environment that are only marginally above the levels of natural background. Finally, given the importance of the linear, no-threshold dose-response hypothesis, an understanding of radiation carcinogenesis and the validity of the hypothesis remains an important scientific need for radiation protection, specifically for estimating the probabilities of adverse human health effects at the levels of natural background.
Representative terms from entire chapter: