Evaluation of Guidelines for Exposures to Technologically Enhanced Naturally Occurring Radioactive Materials (1999) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-15
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From page 1... ...
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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From page 2... ...
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.
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From page 3... ...
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.
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From page 4... ...
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.
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From page 5... ...
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.
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From page 6... ...
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.
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From page 7... ...
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.
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From page 8... ...
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.
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From page 9... ...
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.
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From page 10... ...
· 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.
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From page 11... ...
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.
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From page 12... ...
· 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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From page 13... ...
· 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 longlived, alpha-emitting radionuclides found in TENORM (such as thorium)
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From page 14... ...
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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From page 15... ...
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.
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