[Show abstract][Hide abstract] ABSTRACT: The Techa River (Southern Urals, Russia) was contaminated as a result of radioactive releases by the Mayak plutonium production facility during 1949-1956. The persons born after the onset of the contamination have been identified as the "Techa River Offspring Cohort" (TROC). The TROC has the potential to provide direct data on health effects in progeny that resulted from exposure of a general parent population to chronic radiation. The purpose of the present investigation is the estimation of (90)Sr intake from breast milk and river water in the period from birth to 6 months of life, necessary for an infant dose calculation. The investigation is based on all available data concerning radioactive contamination due to global fallouts and Mayak releases in the Southern Urals where extensive radiometric and radiochemical investigations of human tissues and environmental samples were conducted during the second half of the twentieth century. The strontium transfer factor from mother's daily diet to breast milk was estimated as 0.05 (0.01-0.13) d L(-1). Based on this transfer factor and data on (90)Sr water contamination, the average total (90)Sr intake for an infant born in the middle Techa River region was found to be equal to 60-80 kBq in 1950-1951. For the same period, calculations of (90)Sr intake using ICRP models gave values of 70-100 kBq. From 1952 onwards, the differences in intakes calculated using the two approaches increased, reaching a factor of 2-3 in 1953. The Techa River data provide the basis for improving and adapting the ICRP models for application to Techa River-specific population.
[Show abstract][Hide abstract] ABSTRACT: The dosimetry of radon-220, often known as thoron, and its decay products has received less attention than has that of radon-222. Dose coefficients used by international bodies such as UNSCEAR and ICRP and by the UK's former National Radiological Protection Board are based on calculations from the 1980s. We present calculations for thoron decay products using the most recent ICRP models. These indicate that the effective dose is dominated by the doses to lung and that, under the present models, these doses are somewhat higher than under the previous consensus. Conversely, the present models give doses to organs outside the respiratory tract that are somewhat lower than those previously calculated. Dose coefficients for children are somewhat higher than those for adults. However, breathing rates for children are lower than those for adults and there are no great differences in annual doses.
[Show abstract][Hide abstract] ABSTRACT: The death of Alexander Litvinenko on 23 November 2006 has brought into focus scientific judgements concerning the radiotoxicity of polonium-210 ((210)Po). This paper does not consider the specific radiological circumstances surrounding the tragic death of Mr Litvinenko; rather, it provides an evaluation of published human and animal data and models developed for the estimation of alpha radiation doses from (210)Po and the induction of potentially fatal damage to different organs and tissues. Although uncertainties have not been addressed comprehensively, the reliability of key assumptions is considered. Concentrating on the possibility of intake by ingestion, the use of biokinetic and dosimetric models to estimate organ and tissue doses from (210)Po is examined and model predictions of the time-course of dose delivery are illustrated. Estimates are made of doses required to cause fatal damage, taking account of the possible effects of dose protraction and the relative biological effectiveness (RBE) of alpha particles compared to gamma and x-rays. Comparison of LD(50) values (dose to cause death for 50% of people) for different tissues with the possible accumulation of dose to these tissues suggests that bone marrow failure is likely to be an important component of multiple contributory causes of death occurring within a few weeks of an intake by ingestion. Animal data on the effects of (210)Po provide good confirmatory evidence of intakes and doses required to cause death within about 3 weeks. The conclusion is reached that 0.1-0.3 GBq or more absorbed to blood of an adult male is likely to be fatal within 1 month. This corresponds to ingestion of 1-3 GBq or more, assuming 10% absorption to blood. Well-characterised reductions in white cell counts would be observed. Bone marrow failure is likely to be compounded by damage caused by higher doses to other organs, including kidneys and liver. Even if the bone marrow could be rescued, damage to other organs can be expected to prove fatal.
[Show abstract][Hide abstract] ABSTRACT: The International Commission on Radiological Protection (ICRP) has published dose coefficients for the ingestion or inhalation of radionuclides in a series of reports covering intakes by workers and members of the public, including children and pregnant or lactating women. The calculation of these coefficients divides naturally into two distinct parts-the biokinetic and dosimetric. This paper describes in detail the methods used to solve the biokinetic problem in the generation of dose coefficients on behalf of the ICRP, as implemented in the Health Protection Agency's internal dosimetry code PLEIADES. A summary of the dosimetric treatment is included.
[Show abstract][Hide abstract] ABSTRACT: Publication 100 of the International Commission on Radiological Protection (ICRP) provides a Human Alimentary Tract Model (HATM) to replace the gastrointestinal (GI) model described in Publication 30. The HATM will be used for future calculations of dose coefficients and bioassay predictions, first in a series of publications on occupational intakes of radionuclides, and subsequently in revision of dose coefficients for public exposures. This paper compares dose coefficients calculated using the new model with current values calculated using the GI model for a range of radionuclides. Colon doses are lower using the HATM in all cases considered, in some cases by significant factors. Stomach doses tend to be lower, but are in some cases higher under HATM. The extent to which these changes in doses to gut tissues impacts upon the effective dose varies among nuclides, but there is a tendency for lower effective doses. Special-case applications of the HATM are also described, considering retention on teeth or in the walls of the small intestine. Although the effect of such retention on the regional tissue dose can be large, the effective dose is not greatly changed.
[Show abstract][Hide abstract] ABSTRACT: The accidental or deliberate dispersal of radioactive aerosols into the public environment may require urgent assessments of radiation dose to be made to aid decisions on whether treatment should be implemented, or to reassure the public that doses are acceptably low. However, rapid assessments will be difficult due to lack of information on factors such as the particle size distribution and biokinetic characteristics of the aerosol. A procedure is described that relates the amount of activity of a radionuclide in the body and excreta to time after intake for a specified dose, taking into account the likely variations in aerosol size and differences in the biokinetic behaviour of the same or different chemical forms of the radionuclide. The implementation of the procedure for an intake of caesium-137 and a dose level of 1 mSv is described and the information presented graphically. Figures for other specified dose levels can be produced by simply scaling the data by an appropriate factor. The figures can also be used to assess the most appropriate monitoring procedure and indicate the uncertainty in the assessed dose according to the parameter and parameter values used. This approach is proposed for rapid decisions on public reassurance when potentially large numbers of people are involved. It is not intended as a substitute for individual dose assessment.
[Show abstract][Hide abstract] ABSTRACT: Reliable estimates of tissue doses to individuals exposed as a result of radioactive releases to the Techa River are essential prerequisites for epidemiological analyses. This paper describes progress made in collaborative studies, sponsored by the European Union, between the Urals Research Center for Radiation Medicine and the UK Health Protection Agency to provide dose estimates to Techa River populations following in utero exposures and infant exposures resulting from breast-feeding. Studies have concentrated on the assessment of internal doses from 90Sr as the main contributor to internal doses to the Techa River populations.
[Show abstract][Hide abstract] ABSTRACT: The biokinetic and dosimetric model of the gastrointestinal (GI) tract applied in current documents of the International Commission on Radiological Protection (ICRP) was developed in the mid-1960s. The model was based on features of a reference adult male and was first used by the ICRP in Publication 30, Limits for Intakes of Radionuclides by Workers (Part 1, 1979). In the late 1990s an ICRP task group was appointed to develop a biokinetic and dosimetric model of the alimentary tract that reflects updated information and addresses current needs in radiation protection. The new age-specific and gender-specific model, called the Human Alimentary Tract Model (HATM), has been completed and will replace the GI model of Publication 30 in upcoming ICRP documents. This paper discusses the basis for the structure and parameter values of the HATM, summarises the uncertainties associated with selected features and types of predictions of the HATM and examines the sensitivity of dose estimates to these uncertainties for selected radionuclides. Emphasis is on generic biokinetic features of the HATM, particularly transit times through the lumen of the alimentary tract, but key dosimetric features of the model are outlined, and the sensitivity of tissue dose estimates to uncertainties in dosimetric as well as biokinetic features of the HATM are examined for selected radionuclides.
[Show abstract][Hide abstract] ABSTRACT: Several approaches are available for bioassay interpretation when assigning Pu doses to Mayak workers. First, a conventional approach is to apply ICRP models per se. An alternative method involves individualised fitting of bioassay data using Bayesian statistical methods. A third approach is to develop an independent dosimetry system for Mayak workers by adapting ICRP models using a dataset of available bioassay measurements for this population. Thus, a dataset of 42 former Mayak workers, who died of non-radiation effects, with both urine bioassay and post-mortem tissue data was used to test these three approaches. All three approaches proved to be adequate for bioassay and tissue interpretation, and thus for Pu dose reconstruction purposes. However, large discrepancies are observed in the resulting quantitative dose estimates. These discrepancies can, in large part, be explained by differences in the interpretation of Pu behaviour in the lungs in the context of ICRP lung model. Thus, a careful validation of Pu lung dosimetry model is needed in Mayak worker dosimetry systems.
[Show abstract][Hide abstract] ABSTRACT: Assessments of potential internal exposures of the child following radionuclide intakes by the mother require consideration of transfers during lactation as well as during pregnancy. Current ICRP work on internal dosimetry includes the estimation of radiation doses to newborn infants from radionuclides ingested in mothers' milk. Infant doses will be calculated for maternal intakes by ingestion or inhalation of the radionuclides, radioisotopes of 31 elements, for which fetal dose coefficients have been published. In this paper, modelling approaches are examined, concentrating on models developed for iodine, caesium, polonium, alkaline earth elements and the actinides. Comparisons of model predictions show maximum overall transfer to milk following maternal ingestion during lactation of about 30% of ingested activity for 131I, 20% for 45Ca and 137Cs, 10% for 90Sr, 1% for 210Po and low values of less than 0.01% for 239Pu and 241Am. The corresponding infant doses from milk consumption are estimated in preliminary calculations to be about two to three times the adult dose for 45Ca and 131I, 70-80% of the adult dose for 90Sr, about 40% for 137Cs, 20% for 210Po, and <0.1% for 239Pu and 241Am. Infant doses from radionuclides in breast milk are compared with doses to the offspring resulting from in utero exposures during pregnancy.
[Show abstract][Hide abstract] ABSTRACT: This paper discusses the biokinetic and dosimetric models adopted in ICRP Publication 88 for the evaluation of fetal doses resulting from maternal intakes of radioiodine. The biokinetic model is used to simulate the behaviour of iodine in both the mother and the fetus. Such simulations provide the basis for the estimation of the dose to the embryo and determine the distribution of maternal iodine at the beginning of the fetal period. The model considers iodine to accumulate in the fetal thyroid from the 11th week. The dose to the fetus delivered following birth is evaluated with the biokinetic and dosimetric models described in ICRP Publication 67. Although a substantial fraction of the emitted energy of electrons and photons is less than 10 keV, conventionally assumed to be non-penetrating radiation, these emissions can escape the small fetal thyroid. Absorbed fractions for both self-dose and crossfire were evaluated for the requirements of radioiodine dosimetry in ICRP Publication 88.
[Show abstract][Hide abstract] ABSTRACT: The International Commission on Radiological Protection (ICRP) has recently published dose coefficients (dose per unit intake, Sv Bq(-1)) for the offspring of women exposed to radionuclides during or before pregnancy. These dose estimates include in utero doses to the embryo and fetus and doses delivered postnatally to the newborn child from radionuclides retained at birth. This paper considers the effect on doses of the time of radionuclide intake and examines the proportion of dose delivered in utero and postnatally for different radionuclides. Methods used to calculate doses to the fetal skeleton are compared. For many radionuclides, doses are greatest for intakes early in pregnancy but important exceptions, for which doses are greatest for intakes later in pregnancy, are iodine isotopes and isotopes of the alkaline earth elements, including strontium. While radionuclides such as 131I deliver dose largely in utero, even for intakes late in pregnancy, others such as 239Pu deliver dose largely postnatally, even for intakes early during pregnancy. For alpha emitters deposited in the skeleton, the assumption made is of uniform distribution of the radionuclide and of target cells for leukaemia and bone cancer in utero; that is, the developing bone structure is not considered. However, for beta emitters, the bone structure was considered. Both approaches can be regarded as reasonably conservative, given uncertainties in particular in the location of the target cells and the rapid growth and remodelling of the skeleton at this stage of development.
[Show abstract][Hide abstract] ABSTRACT: The International Commission on Radiological Protection has recently issued Publication 88, giving dose coefficients for the embryo, fetus and newborn child from intakes of selected radionuclides of 31 elements by the mother, either before or during pregnancy. The biokinetic models used for calculating these doses were based upon the available human data and the results of animal experiments. This paper summarises the approach used for the development of biokinetic and dosimetric models. It also compares the estimates of dose received by the offspring with those received by the reference adult. The main findings are that, in general, doses to the offspring are similar to or lower than those to the reference adult. For a few radionuclides, however, the dose to the offspring can exceed that to the adult. The reasons for these variations in comparative doses are examined.
[Show abstract][Hide abstract] ABSTRACT: An international programme of work is currently under way to develop methods for calculating doses to infants from ingestion of radionuclides present in mothers' milk. This paper considers the special case of the alkaline earth elements. Models have been developed for 45Ca, 90Sr and 226Ra and the sensitivity of results to various changes in parameter values is discussed. A complication when calculating doses from intakes of radium is that the International Commission on Radiological Protection has previously recommended that doses from decay products of radium should be calculated using element-specific biokinetic models (so-called independent biokinetics). An extension of this method to the models for breastfeeding is proposed. Preliminary estimates of the doses received by the infant for a number of maternal intake scenarios show that doses to the infant can exceed the corresponding adult dose, such as for 45Ca (ratio = 3.1) while, in other cases such as 90Sr, the infant dose can be a significant fraction of the adult dose.
[Show abstract][Hide abstract] ABSTRACT: Committee 2 of the International Commission on Radiological Protection (ICRP) has the responsibility for calculating radiation doses from intakes of radionuclides for all age groups in the population. Publication 88 of the ICRP, which has recently been published, describes the development of models used for calculating radiation doses to the embryo and foetus following intakes of radionuclides by the mother. It also gives radiation doses to the offspring for intakes of radionuclides by the mother either before or during pregnancy. The approaches used in the development of the biokinetic and dosimetric models are summarised here together with a comparison of the doses to the offspring with those to the reference adult.
[Show abstract][Hide abstract] ABSTRACT: To measure the transfer of cerium from mother to fetus in experimental animals and estimate doses to the human fetus following intakes of radioisotopes of Ce.
Cerium-141 in chloride solution was administered intravenously to rats at different stages of pregnancy (days 9.5, 12.5 or 18.5), and retention in the embryo/fetus and associated tissues was measured 3 days later in each case. Retention in rat fetal tissues on day 21.5 (shortly before birth) was also measured after administration of 141Ce chloride 1 month prior to conception or 141Ce citrate on day 18.5. Cerium-141 chloride was administered to guinea pigs on day 50 for measurements of fetal retention on day 57 (shortly before birth).
Retention of 141Ce in the rat embryo/fetus, measured at 3 days after administration to the mother, increased from about 0.00002% of injected activity per embryo/fetus on day 12.5 to about 0.014% on day 21.5 of gestation. However, the relative concentrations of 141Ce in the embryo/fetus and mother (CF:CM ratio) were between 0.005 and 0.01 in each case. After 141Ce administration prior to conception, retention by the rat fetus on day 21.5 was substantially lower than after short-term administration. Comparison of retention of 141Ce on day 21.5 after administration on day 18.5 as either chloride or citrate showed similar levels in maternal tissues but greater transfer to the fetus (CF:CM ratio of 0.03). Retention in the guinea pig fetus in late gestation at 7 days after administration of (141)Ce chloride was about 0.05% injected activity per fetus, corresponding to a CF:CM ratio of about 0.02.
These results and other published animal data have been used to specify CF:CM ratios for use in the calculation of doses to the human fetus. The values used were 0.05 for intakes during pregnancy and 0.01 for intakes prior to conception. Doses to the offspring after maternal ingestion of 141Ce or 144Ce are largely due to irradiation from activity in the maternal colon and are insensitive to CF:CM. After inhalation, however, absorption of Ce to blood is much greater and doses to the offspring are dominated by the contribution from activity in the fetus, and therefore dependent on the CF:CM ratio used.
International Journal of Radiation Biology 04/2002; 78(3):227-35. DOI:10.1080/09553000110097226 · 1.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Data on the gastrointestinal absorption of 12 elements have been reviewed. In each case, absorption is expressed as the fraction of the ingested element absorbed to blood, referred to as the f 1 value, applying to intakes of unspecified chemical form by average population groups. The level of confidence in individual absorption values has been estimated in terms of lower and upper bounds, A and B, such that there is judged to be roughly a 90% probability that the true central value is no less than A and no greater than B. Ranges are proposed for intakes by adults, 10-year-old children and 3-month-old infants. Uncertainty in f 1 values (B/A) ranged from 10% to factors of 100-400. The lowest uncertainties were for the well absorbed elements, H, I and Cs, for which there are good data, and the greatest uncertainties were for less well absorbed elements for which few data are available, particularly Zr and Sb. Ranges were generally wider for children and infants than for adults because of the need to allow for the likelihood of increased absorption with only limited data in support of the proposed values. The largest ranges were for 3-month-old infants, reflecting lack of knowledge on the time-course and magnitude of possible increased absorption in the first few months of life. For each age group, ICRP values of absorption tend towards the upper bound of the ranges, indicating a degree of conservatism in the calculation of ingestion dose coefficients. Examination of the effect of the proposed confidence intervals for f 1 values on uncertainties in dose coefficients for ingested radionuclides showed that there was no direct relationship. For some radionuclides, uncertainties in effective dose were small despite large uncertainties in f 1 values while for others the uncertainties in effective doses approached the corresponding values for uncertainty in f 1 values. These differences reflect the relative contributions to effective dose from cumulative activity in the contents of the alimentary tract, which in many cases is insensitive to uncertainties in f 1 , and cumulative activity of the absorbed radionuclide in systemic tissues, which is proportional to f 1 . In general, uncertainties in effective dose for children and infants exceeded those in adults as a result of greater uncertainties in f 1 values for the younger age groups. However, this effect was reduced in some cases by shorter retention times of absorbed nuclides in body tissues and organs.
[Show abstract][Hide abstract] ABSTRACT: An overview is given of the models recommended by the International Commission on Radiological Protection (ICRP) for assessing intakes and doses, and summarises biokinetic data obtained after the deposition of different chemical compounds of thorium in the rat lung. The results emphasise the importance of using material-specific data rather than default reference values for absorption into blood. The limitations of external monitoring of the chest or urine analysis are discussed, and comments made on alternative strategies for radiological protection of the worker.