This report provides methods to interpret and apply occupational uranium monitoring data. The methods are based on current international radiation protection guidance, current information on the chemical toxicity of uranium, and best available biokinetic models for uranium. Emphasis is on air monitoring data and three types of bioassay data: the concentration of uranium in urine; the concentration of uranium in feces; and the externally measured content of uranium in the chest. Primary Reference guidance levels for prevention of chemical effects and limitation of radiation effects are selected based on a review of current scientific data and regulatory principles for setting standards. Generic investigation levels and immediate action levels are then defined in terms of these primary guidance levels. The generic investigation and immediate actions levels are stated in terms of radiation dose and concentration of uranium in the kidneys. These are not directly measurable quantities, but models can be used to relate the generic levels to the concentration of uranium in air, urine, or feces, or the total uranium activity in the chest. Default investigation and immediate action levels for uranium in air, urine, feces, and chest are recommended for situations in which there is little information on the form of uranium taken into the body. Methods are prescribed also for deriving case-specific investigation and immediate action levels for uranium in air, urine, feces, and chest when there is sufficient information on the form of uranium to narrow the range of predictions of accumulation of uranium in the main target organs for uranium: kidneys for chemical effects and lungs for radiological effects. In addition, methods for using the information herein for alternative guidance levels, different from the ones selected for this report, are described. v FOREWORDThis report provides a detailed description of uranium biokinetics and bioassays applicable to evaluation of health risks from potential intakes in an occupational setting. The report addresses both the radiotoxicity and chemical (renal) toxicity of uranium. For reference occupational exposure scenarios, predictions of the time-dependent concentration of uranium in tissues and bioassay are based on biokinetic models currently recommended by the International Commission on Radiological Protection (ICRP). The ICRP's models and default assumptions for uranium were based primarily on data for human subjects exposed to uranium in controlled studies or in occupational or environmental settings. In addition, the ICRP considered an extensive database for uranium in laboratory animals. Sensitivity studies examine the robustness of these models and assumptions to ensure that radiation doses and accumulation of uranium in the kidneys are not underestimated. For example, analyses indicate that a default 5 µm activity median aerodynamic diameter particle size can lead to an underestimation of radiation dose as well as the concentration of uranium in the kidneys if inhal...
Scientific data are reviewed to evaluate the risks of radioiodine uptake and to compare those risks with the benefits and risks of low milligram doses of stable potassium iodide (KI). The limit of 25 rad to the thyroid due to radioiodine uptake is adopted as the "break-even" point above which 130-mg KI doses should be administered. The biological and radiological kinetics of radioiodine for protracted uptakes were derived from the Medical Internal Radiation Dose Committee (MIRD) model (MIRD75). Resulting calculations yielded estimates of dose commitment rates to the thyroid as a function of thyroidal uptake. The extrapolated value of the 1-hr inhalation curve for 131I with 30% uptake compares well with the established MPCa value and intercepts the origin. The calculated KI-blocking efficiency as a function of time after radioiodine uptake agrees well with previously reported experimental data. The prevention or "blocking" of 25 rad to the thyroid was the criterion used to define critical values of radioiodine in the thyroid. Critical values are functions of isotope, the duration of uptake and the elapsed time between inhalation and assay of thyroid content. The presence of radioiodine in the thyroid in amounts greater than the critical value indicates that more than 25 rad to the thyroid can be averted, and KI should be administered in the absence of contraindications. Critical average concentrations are implicitly defined by the method of calculation used in the derivation. Critical average concentrations are presented as criteria for KI administration when assays of the radioiodine content of the thyroid are unavailable. Illustrative applications of critical values and critical average concentrations are presented in the Appendix.
The time required for the complete decay of a radioactive source can be quantified by specifying an acceptable probability and using an original derivation. The physical phenomenon of complete decay may be used as the technical basis to change regulations and permit, with public acceptance, the inexpensive disposal of short half-lived radioactive waste into municipal landfills. Current regulations require isolation of trash from the biosphere for 30 years during the post-closure control period for municipal landfills. Thirty years is sufficient time for complete decay of significant quantities of short-lived radionuclides, and there is a large decay capacity in the nation's landfills. As the major generators of low-level radioactive waste with relatively short half-lives, the academic, medical, and research communities likely would benefit most from such regulatory relief. Disposal of such waste is prohibited or costly. The waste must be specially packaged, stored, transported, and disposed in designated repositories. Regulatory relief can be initiated by citizens since the Administrative Procedures Act gives citizens the right to petition for regulatory change.
A method is described for deriving two levels of action-an investigation level (IL) and an immediate action level (IAL)-for different forms and mixtures of the natural uranium (U) isotopes U,U, and U in air in the workplace. An IL indicates the need to confirm the validity of moderately elevated measurements of airborne U and adequacy of confinement controls and determine whether work limitations are appropriate. An IAL indicates that safeguards should be put into place immediately, including removal of workers from further exposure until conditions are acceptable. Derivations of ILs and IALs are based on latest radiation protection guidance, information on chemical toxicity of U, and biokinetic models for U. An action level (IL or IAL) is the more restrictive of two derived values, the action level based on U as a chemical hazard and the action level based on U as a radiation hazard.
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