A biokinetic model for trivalent or hexavalent chromium in adult humans.

Chromium exists in several oxidation states, with the trivalent state (Cr(III)) being the dominant naturally occurring form. Chromium in other oxidation states tends to be converted to the trivalent oxide in the natural environment and in biological systems. Chromium(III) has been shown to be an essential nutrient for humans and several non-human species. Chromium(VI), the second most stable form of chromium, is an important environmental contaminant that is mostly of industrial origin and is associated with lung cancer and nose tumours in chromium workers. This paper proposes a biokinetic model for chromium that addresses the distinctive behaviours of Cr(III) and Cr(VI) following uptake to blood of an adult human. The model is based on biokinetic data derived from relatively short-term studies involving administration of chromium tracers to adult human subjects or laboratory animals, supplemented with data on the long-term distribution of chromium in adult humans as estimated from autopsy measurements. The model is part of a comprehensive update of biokinetic models of the International Commission on Radiological Protection, used to project or evaluate radiation doses from occupational intake of radionuclides.

ICRP Publication 141: Occupational Intakes of Radionuclides: Part 4.

The 2007 Recommendations (ICRP, 2007) introduced changes that affect the calculation of effective dose, and implied a revision of the dose coefficients for internal exposure, published previously in the Publication 30 series (ICRP, 1979a,b, 1980a, 1981, 1988) and Publication 68 (ICRP, 1994b). In addition, new data are now available that support an update of the radionuclide-specific information given in Publications 54 and 78 (ICRP, 1989a, 1997) for the design of monitoring programmes and retrospective assessment of occupational internal doses. Provision of new biokinetic models, dose coefficients, monitoring methods, and bioassay data was performed by Committee 2 and its task groups. A new series, the Occupational Intakes of Radionuclides (OIR) series, will replace the Publication 30 series and Publications 54, 68, and 78. OIR Part 1 (ICRP, 2015) describes the assessment of internal occupational exposure to radionuclides, biokinetic and dosimetric models, methods of individual and workplace monitoring, and general aspects of retrospective dose assessment. OIR Part 2 (ICRP, 2016), OIR Part 3 (ICRP, 2017), this current publication, and the final publication in the OIR series (OIR Part 5) provide data on individual elements and their radioisotopes, including information on chemical forms encountered in the workplace; a list of principal radioisotopes and their physical half-lives and decay modes; the parameter values of the reference biokinetic models; and data on monitoring techniques for the radioisotopes most commonly encountered in workplaces. Reviews of data on inhalation, ingestion, and systemic biokinetics are also provided for most of the elements. Dosimetric data provided in the printed publications of the OIR series include tables of committed effective dose per intake (Sv per Bq intake) for inhalation and ingestion, tables of committed effective dose per content (Sv per Bq measurement) for inhalation, and graphs of retention and excretion data per Bq intake for inhalation. These data are provided for all absorption types and for the most common isotope(s) of each element. The online electronic files that accompany the OIR series of publications contains a comprehensive set of committed effective and equivalent dose coefficients, committed effective dose per content functions, and reference bioassay functions. Data are provided for inhalation, ingestion, and direct input to blood. This fourth publication in the OIR series provides the above data for the following elements: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), actinium (Ac), protactinium (Pa), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), and fermium (Fm).

Action levels for airborne uranium in the workplace: chemical and radiological assessments.

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 234U, 235U, and 238U 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.

ICRP Publication 137: Occupational Intakes of Radionuclides: Part 3.

Abstract ­: The 2007 Recommendations of the International Commission on Radiological Protection (ICRP, 2007) introduced changes that affect the calculation of effective dose, and implied a revision of the dose coefficients for internal exposure, published previously in the Publication 30 series (ICRP, 1979, 1980, 1981, 1988) and Publication 68 (ICRP, 1994). In addition, new data are now available that support an update of the radionuclide-specific information given in Publications 54 and 78 (ICRP, 1988a, 1997b) for the design of monitoring programmes and retrospective assessment of occupational internal doses. Provision of new biokinetic models, dose coefficients, monitoring methods, and bioassay data was performed by Committee 2, Task Group 21 on Internal Dosimetry, and Task Group 4 on Dose Calculations. A new series, the Occupational Intakes of Radionuclides (OIR) series, will replace the Publication 30 series and Publications 54, 68, and 78. OIR Part 1 has been issued (ICRP, 2015), and describes the assessment of internal occupational exposure to radionuclides, biokinetic and dosimetric models, methods of individual and workplace monitoring, and general aspects of retrospective dose assessment. OIR Part 2 (ICRP, 2016), this current publication and upcoming publications in the OIR series (Parts 4 and 5) provide data on individual elements and their radioisotopes, including information on chemical forms encountered in the workplace; a list of principal radioisotopes and their physical half-lives and decay modes; the parameter values of the reference biokinetic model; and data on monitoring techniques for the radioisotopes encountered most commonly in workplaces. Reviews of data on inhalation, ingestion, and systemic biokinetics are also provided for most of the elements. Dosimetric data provided in the printed publications of the OIR series include tables of committed effective dose per intake (Sv Bq−1 intake) for inhalation and ingestion, tables of committed effective dose per content (Sv Bq−1 measurement) for inhalation, and graphs of retention and excretion data per Bq intake for inhalation. These data are provided for all absorption types and for the most common isotope(s) of each element. The electronic annex that accompanies the OIR series of publications contains a comprehensive set of committed effective and equivalent dose coefficients, committed effective dose per content functions, and reference bioassay functions. Data are provided for inhalation, ingestion, and direct input to blood. This third publication in the series provides the above data for the following elements: ruthenium (Ru), antimony (Sb), tellurium (Te), iodine (I), caesium (Cs), barium (Ba), iridium (Ir), lead (Pb), bismuth (Bi), polonium (Po), radon (Rn), radium (Ra), thorium (Th), and uranium (U).

Effective Dose Rate Coefficients for Immersions in Radioactive Air and Water.

The Oak Ridge National Laboratory Center for Radiation Protection Knowledge (CRPK) has undertaken a number of calculations in support of a revision to the United States Environmental Protection Agency (US EPA) Federal Guidance Report on external exposure to radionuclides in air, water and soil (FGR 12). Age-specific mathematical phantom calculations were performed for the conditions of submersion in radioactive air and immersion in water. Dose rate coefficients were calculated for discrete photon and electron energies and folded with emissions from 1252 radionuclides using ICRP Publication 107 decay data to determine equivalent and effective dose rate coefficients. The coefficients calculated in this work compare favorably to those reported in FGR12 as well as by other authors that employed voxel phantoms for similar exposure scenarios.

Assessment and interpretation of internal doses: uncertainty and variability.

Internal doses are calculated on the basis of knowledge of intakes and/or measurements of activity in bioassay samples, typically using reference biokinetic and dosimetric models recommended by the International Commission on Radiological Protection (ICRP). These models describe the behaviour of the radionuclides after ingestion, inhalation, and absorption to the blood, and the absorption of the energy resulting from their nuclear transformations. They are intended to be used mainly for the purpose of radiological protection: that is, optimisation and demonstration of compliance with dose limits. These models and parameter values are fixed by convention and are not subject to uncertainty. Over the past few years, ICRP has devoted a considerable amount of effort to the revision and improvement of models to make them more physiologically realistic. ICRP models are now sufficiently sophisticated for calculating organ and tissue absorbed doses for scientific purposes, and in many other areas, including toxicology, pharmacology and medicine. In these specific cases, uncertainties in parameters and variability between individuals need to be taken into account.

COMPARISON OF MONOENERGETIC PHOTON ORGAN DOSE RATE COEFFICIENTS FOR STYLIZED AND VOXEL PHANTOMS SUBMERGED IN AIR.

As part of a broader effort to calculate effective dose rate coefficients for external exposure to photons and electrons emitted by radionuclides distributed in air, soil or water, age-specific stylized phantoms have been employed to determine dose coefficients relating dose rate to organs and tissues in the body. In this article, dose rate coefficients computed using the International Commission on Radiological Protection reference adult male voxel phantom are compared with values computed using the Oak Ridge National Laboratory adult male stylized phantom in an air submersion exposure geometry. Monte Carlo calculations for both phantoms were performed for monoenergetic source photons in the range of 30 keV to 5 MeV. These calculations largely result in differences under 10 % for photon energies above 50 keV, and it can be expected that both models show comparable results for the environmental sources of radionuclides.

ICRP Publication 134: Occupational Intakes of Radionuclides: Part 2.

Abstract ­: The 2007 Recommendations of the International Commission on Radiological Protection (ICRP, 2007) introduced changes that affect the calculation of effective dose, and implied a revision of the dose coefficients for internal exposure, published previously in the Publication 30 series (ICRP, 1979, 1980, 1981, 1988b) and Publication 68 (ICRP, 1994b). In addition, new data are available that support an update of the radionuclide-specific information given in Publications 54 and 78 (ICRP, 1988a, 1997b) for the design of monitoring programmes and retrospective assessment of occupational internal doses. Provision of new biokinetic models, dose coefficients, monitoring methods, and bioassay data was performed by Committee 2, Task Group 21 on Internal Dosimetry, and Task Group 4 on Dose Calculations. A new series, the Occupational Intakes of Radionuclides (OIR) series, will replace the Publication 30 series and Publications 54, 68, and 78. Part 1 of the OIR series has been issued (ICRP, 2015), and describes the assessment of internal occupational exposure to radionuclides, biokinetic and dosimetric models, methods of individual and workplace monitoring, and general aspects of retrospective dose assessment. The following publications in the OIR series (Parts 2­5) will provide data on individual elements and their radioisotopes, including information on chemical forms encountered in the workplace; a list of principal radioisotopes and their physical half-lives and decay modes; the parameter values of the reference biokinetic model; and data on monitoring techniques for the radioisotopes encountered most commonly in workplaces. Reviews of data on inhalation, ingestion, and systemic biokinetics are also provided for most of the elements. Dosimetric data provided in the printed publications of the OIR series include tables of committed effective dose per intake (Sv per Bq intake) for inhalation and ingestion, tables of committed effective dose per content (Sv per Bq measurement) for inhalation, and graphs of retention and excretion data per Bq intake for inhalation. These data are provided for all absorption types and for the most common isotope(s) of each element. The electronic annex that accompanies the OIR series of reports contains a comprehensive set of committed effective and equivalent dose coefficients, committed effective dose per content functions, and reference bioassay functions. Data are provided for inhalation, ingestion, and direct input to blood. The present publication provides the above data for the following elements: hydrogen (H), carbon (C), phosphorus (P), sulphur (S), calcium (Ca), iron (Fe), cobalt (Co), zinc (Zn), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), and technetium (Tc).

ICRP Publication 130: Occupational Intakes of Radionuclides: Part 1.

Abstract ­: This report is the first in a series of reports replacing Publications 30 and 68 to provide revised dose coefficients for occupational intakes of radionuclides by inhalation and ingestion. The revised dose coefficients have been calculated using the Human Alimentary Tract Model (Publication 100) and a revision of the Human Respiratory Tract Model (Publication 66) that takes account of more recent data. In addition, information is provided on absorption into blood following inhalation and ingestion of different chemical forms of elements and their radioisotopes. In selected cases, it is judged that the data are sufficient to make material-specific recommendations. Revisions have been made to many of the models that describe the systemic biokinetics of radionuclides absorbed into blood, making them more physiologically realistic representations of uptake and retention in organs and tissues, and excretion. The reports in this series provide data for the interpretation of bioassay measurements as well as dose coefficients, replacing Publications 54 and 78. In assessing bioassay data such as measurements of whole-body or organ content, or urinary excretion, assumptions have to be made about the exposure scenario, including the pattern and mode of radionuclide intake, physical and chemical characteristics of the material involved, and the elapsed time between the exposure(s) and measurement. This report provides some guidance on monitoring programmes and data interpretation.

Parameter uncertainty analysis of a biokinetic model of caesium.

Parameter uncertainties for the biokinetic model of caesium (Cs) developed by Leggett et al. were inventoried and evaluated. The methods of parameter uncertainty analysis were used to assess the uncertainties of model predictions with the assumptions of model parameter uncertainties and distributions. Furthermore, the importance of individual model parameters was assessed by means of sensitivity analysis. The calculated uncertainties of model predictions were compared with human data of Cs measured in blood and in the whole body. It was found that propagating the derived uncertainties in model parameter values reproduced the range of bioassay data observed in human subjects at different times after intake. The maximum ranges, expressed as uncertainty factors (UFs) (defined as a square root of ratio between 97.5th and 2.5th percentiles) of blood clearance, whole-body retention and urinary excretion of Cs predicted at earlier time after intake were, respectively: 1.5, 1.0 and 2.5 at the first day; 1.8, 1.1 and 2.4 at Day 10 and 1.8, 2.0 and 1.8 at Day 100; for the late times (1000 d) after intake, the UFs were increased to 43, 24 and 31, respectively. The model parameters of transfer rates between kidneys and blood, muscle and blood and the rate of transfer from kidneys to urinary bladder content are most influential to the blood clearance and to the whole-body retention of Cs. For the urinary excretion, the parameters of transfer rates from urinary bladder content to urine and from kidneys to urinary bladder content impact mostly. The implication and effect on the estimated equivalent and effective doses of the larger uncertainty of 43 in whole-body retention in the later time, say, after Day 500 will be explored in a successive work in the framework of EURADOS.

Proposed biokinetic model for phosphorus.

This paper reviews data related to the biokinetics of phosphorus in the human body and proposes a biokinetic model for systemic phosphorus for use in updated International Commission on Radiological Protection (ICRP) guidance on occupational intake of radionuclides. Compared with the ICRP's current occupational model for systemic phosphorus (Publication 68, 1994), the proposed model provides a more realistic description of the paths of movement of phosphorus in the body and greater consistency with experimental, medical, and environmental data regarding its time-dependent distribution. For acute uptake of (32)P to blood, the proposed model yields roughly a 50% decrease in dose estimates for bone surface and red marrow and a six-fold increase in estimates for liver and kidney compared with the model of Publication 68. For acute uptake of (33)P to blood, the proposed model yields roughly a 50% increase in dose estimates for bone surface and red marrow and a seven-fold increase in estimates for liver and kidney compared with the model of Publication 68.

Biokinetic models for radiocaesium and its progeny.

The International Commission on Radiological Protection (ICRP) is preparing a series of reports that will provide updated biokinetic and dosimetric models and dose coefficients for occupational intake of radionuclides. The biokinetic modelling scheme continues a trend in ICRP reports towards physiologically realistic descriptions of the time-dependent behaviour of absorbed radionuclides and their radioactive progeny. This paper proposes systemic biokinetic models for caesium isotopes and their ingrowing chain members and examines the dosimetric implications of the proposed models. Comparisons of D68 = tissue dose per unit input to blood based on current ICRP models for workers (ICRP Publication 68, 1994) with DP = corresponding values based on the proposed biokinetic models (but using the dosimetry models of Publication 68) yields the following ranges of the ratios DP:D68 for the tissues addressed in Publication 68: 0.5-25 for (130)Cs (T1/2 = 29.2 min), 0.6-9.5 for (134m)Cs (2.9 h), 0.7-1.7 for (131)Cs (9.69 d), 0.7-1.1 for (134)Cs (2.06 y), 0.5-1.9 for (137)Cs (30.2 y) and 0.2-3.7 for (135)Cs (2.3 × 10(6) y). The large differences in the derived dose coefficients for some tissues and caesium isotopes, particularly short-lived isotopes, result mainly from differences in predictions of the time-dependent distributions of caesium in the body. For example, the proposed model and the current ICRP model for occupational intake of caesium predict peak kidney contents of ∼22% and ∼0.4%, respectively, following intravenous injection of stable caesium. Based on the proposed models for caesium and its progeny, the only dosimetrically significant chain members of caesium isotopes with half-life ≥10 min are (137m)Ba, which represents 32-85% of the estimated tissue doses from injected (137)Cs, and (134)Cs, which represents 4-53% of the estimated tissue doses from injected (134m)Cs.

A biokinetic model for zinc for use in radiation protection.

The physiology of the essential trace element zinc has been studied extensively in human subjects using kinetic analysis of time-dependent measurements of administered zinc tracers. A number of biokinetic models describing zinc exchange between plasma and tissues and endogenous excretion of zinc have been derived as fits to data for specific study groups. More rudimentary biokinetic models for zinc have been developed to estimate radiation doses from internally deposited radioisotopes of zinc. The latter models are designed to provide broadly accurate estimates of cumulative decays of zinc radioisotopes in tissues and are not intended as realistic descriptions of the directions of movement of zinc in the body. This paper reviews biokinetic data for zinc and proposes a physiologically meaningful biokinetic model for systemic zinc for use in radiation protection. The proposed model bears some resemblance to zinc models developed in physiological studies but depicts a finer division of systemic zinc and is based on a broader spectrum of data than previous models. The proposed model and the model for zinc currently recommended by the International Commission on Radiological Protection yield reasonably similar estimates of total-body retention and effective dose for internally deposited radioisotopes of zinc but much different systemic distributions of activity and much different dose estimates for some individual tissues, particularly the liver.

The biokinetics of ruthenium in the human body.

The International Commission on Radiological Protection (ICRP) is updating its biokinetic and dosimetric models for workers and subsequently will revisit its models for members of the public. This paper summarises the biokinetic database for ruthenium and proposes a new biokinetic model for systemic ruthenium. In contrast to the ICRP's current model, the proposed model depicts recycling of ruthenium between tissues and blood and a non-uniform distribution of systemic ruthenium. The paper also points out inconsistencies between the ICRP's respiratory model for RuO(4) vapour and reported data, and inconsistencies between the ICRP's default gastrointestinal (GI) uptake value and data for some forms of ruthenium. Dosimetric implications of the proposed systemic model and the findings for inhaled RuO(4) vapour and GI uptake of ruthenium are examined.

A biokinetic model for manganese.

The International Commission on Radiological Protection (ICRP) is updating its biokinetic models used to derive dose coefficients and assess bioassay data for intake of radionuclides. This paper reviews biokinetic data for manganese and proposes a biokinetic model for systemic manganese in adult humans. The proposed model provides a more detailed and physiologically meaningful description of the behavior of absorbed manganese in the body than the current ICRP model. The proposed model and current ICRP model yield broadly similar estimates of dose per unit activity of inhaled or ingested radio-manganese but differ substantially with regard to interpretation of bioassay data. The model is intended primarily for use in radiation protection but can also serve as a baseline model for evaluation of potentially excessive intakes of stable manganese in occupational settings.

New developments in internal dosimetry models.

This paper describes new biokinetic and dosimetric models, especially those being developed by ICRP which will be used in the forthcoming documents on Occupational Intakes of Radionuclides. It also presents the results of a working group within the European project CONRAD which is being continued within EURADOS. This group is implementing the new models, performing quality assurance of the model implementation (including their description) and giving guidance to the scientific community on the application of the models for individual dose assessment.

A physiological systems model for iodine for use in radiation protection.

This paper summarizes the biokinetic database for iodine in the human body and proposes a biokinetic model for systemic iodine for use in dose assessments for internally deposited radioiodine. The model consolidates and extends existing physiological systems models describing three subsystems of the iodine cycle in the body: circulating inorganic iodide, thyroidal iodine (trapping and organic binding of iodide and synthesis, storage and secretion of thyroid hormones), and extrathyroidal organic iodine. Thyroidal uptake of inorganic iodide is described as a function of stable iodine intake (Y, µg day(-1)) and thyroidal secretion of hormonal iodine (S, µg day(-1)). Baseline parameter values are developed for reference adults with typical iodine intake. Compared with the current systemic biokinetic model of the International Commission on Radiological Protection (ICRP) for occupational intake of radioiodine, the proposed model predicts higher absorbed doses to the thyroid per unit uptake to blood for very short-lived iodine isotopes, similar absorbed doses to thyroid for iodine isotopes with half-life of at least a few hours, and substantially higher estimates of absorbed dose to stomach wall, salivary gland and kidneys for most iodine isotopes. Absorbed dose estimates for intravenous administration of radioiodine-labeled thyroid hormones based on the proposed model differ substantially in some cases from current ICRP values.