Individual Dose Estimates Research Articles

Protracted Radiation Exposure and Cancer Mortality in the Techa River Cohort

In the 1950s many thousands of people living in rural villages on the Techa River received protracted internal and external exposures to ionizing radiation from the release of radioactive material from the Mayak plutonium production complex. The Extended Techa River Cohort includes 29,873 people born before 1950 who lived near the river sometime between 1950 and 1960. Vital status and cause of death are known for most cohort members. Individualized dose estimates have been computed using the Techa River Dosimetry System 2000. The analyses provide strong evidence of long-term carcinogenic effects of protracted low-dose-rate exposures; however, the risk estimates must be interpreted with caution because of uncertainties in the dose estimates. We provide preliminary radiation risk estimates for cancer mortality based on 1,842 solid cancer deaths (excluding bone cancer) and 61 deaths from leukemia. The excess relative risk per gray for solid cancer is 0.92 (95% CI 0.2; 1.7), while those for leukemia, including and excluding chronic lymphocytic leukemia, are 4.2 (CI 95% 1.2; 13) and 6.5 (CI 95% 1.8; 24), respectively. It is estimated that about 2.5% of the solid cancer deaths and 63% of the leukemia deaths are associated with the radiation exposure.

Application of biosphere models in the BIOMOSA project: A comparative assessment of five European radioactive waste disposal sites

The BioMoSA (Biosphere Models for Safety Assessment of Radioactive Waste Disposal) project was part of the EC fifth framework research program. The main goal of this project was the improvement of the scientific basis for the application of biosphere models in the framework of long-term safety studies of radioactive waste disposal facilities. Another aim of the project was to provide operators and regulatory bodies with guidelines for performance assessments of repository systems. The study focused on the development and application of site-specific models and a generic biosphere tool BIOGEM (BIOsphere GEneric Model), using the experience from National programs and the IAEA BIOMASS reference biosphere methodology. The models were applied to 5 typical locations in Europe, resulting in estimates of the annual individual doses to the critical groups and the ranking of the importance of the pathways for each of the sites. The results of the site-specific and generic models were then compared. Uncertainty in the results was estimated by means of stochastic calculations which allowed a comparison of the overall model uncertainty with the variability across the different sites considered.

Individual dose estimation—our experience with the Karunagappally study in Kerala, India

A radiation cohort consisting of four panchayats and a control area consisting of two panchayats was identified in the high background radiation area of Karunagappally after measuring air kerma values of indoor and outdoor radiation levels in 75,052 houses in the area. Radioactivity in the soil was estimated from 181 samples collected from seven panchayats. Thoron-in-breath analysis was done in 87 subjects living in low, medium and high radiation level areas. Occupancy factor of 7711 subjects in different age groups was also estimated. Annual effective dose of individuals was calculated assuming the cosmic ray component of 0.227 and 0.252 mGy/year indoor and outdoor, respectively. Risk analysis will be attempted after measuring the individual dose of a sample population in the area.

Occupational radiation dose estimation for Finnish aircraft cabin attendants.

The objective of this study was to develop a method for assessing dose radiation on the basis of individual flight history and to estimate whether this method is applicable for cabin attendants without flight log data. Questionnaire data were collected to determine attendants' flight history covering up to three decades. Finnair timetables and an expert panel of pilots were used to determine one to four representative flights in five route categories. The cumulative career and annual doses were calculated on the basis of the flight histories and route-specific exposure data. Questionnaire data were obtained from 544 flight attendants. The mean number of active workyears was 10.5 (range 0-30) years, and the mean cosmic radiation dose was 3.2 (range 0-9.5) mSv per active workyear. The mean cumulative career dose for all the cabin attendants was 34.0 (range 0-156.8) mSv. If no flight log data are available, survey data are needed for individual dose estimation when possible radiation effects on cabin crew are evaluated in epidemiologic studies. This method provides a crude procedure for assessing cosmic radiation exposure among attendants when survey data are missing.

Cosmic radiation and cancer mortality among airline pilots: results from a European cohort study (ESCAPE).

Cosmic radiation is an occupational risk factor for commercial aircrews. In this large European cohort study (ESCAPE) its association with cancer mortality was investigated on the basis of individual effective dose estimates for 19,184 male pilots. Mean annual doses were in the range of 2-5 mSv and cumulative lifetime doses did not exceed 80 mSv. All-cause and all-cancer mortality was low for all exposure categories. A significant negative risk trend for all-cause mortality was seen with increasing dose. Neither external and internal comparisons nor nested case-control analyses showed any substantially increased risks for cancer mortality due to ionizing radiation. However, the number of deaths for specific types of cancer was low and the confidence intervals of the risk estimates were rather wide. Difficulties in interpreting mortality risk estimates for time-dependent exposures are discussed.

Studies of mortality of atomic bomb survivors. Report 13: Solid cancer and noncancer disease mortality: 1950-1997.

This continues the series of general reports on mortality in the cohort of atomic bomb survivors followed up by the Radiation Effects Research Foundation. This cohort includes 86,572 people with individual dose estimates, 60% of whom have doses of at least 5 mSv. We consider mortality for solid cancer and for noncancer diseases with 7 additional years of follow-up. There have been 9,335 deaths from solid cancer and 31,881 deaths from noncancer diseases during the 47-year follow-up. Of these, 19% of the solid cancer and 15% of the noncancer deaths occurred during the latest 7 years. We estimate that about 440 (5%) of the solid cancer deaths and 250 (0.8%) of the noncancer deaths were associated with the radiation exposure. The excess solid cancer risks appear to be linear in dose even for doses in the 0 to 150-mSv range. While excess rates for radiation-related cancers increase throughout the study period, a new finding is that relative risks decline with increasing attained age, as well as being highest for those exposed as children as noted previously. A useful representative value is that for those exposed at age 30 the solid cancer risk is elevated by 47% per sievert at age 70. There is no significant city difference in either the relative or absolute excess solid cancer risk. Site-specific analyses highlight the difficulties, and need for caution, in distinguishing between site-specific relative risks. These analyses also provide insight into the difficulties in interpretation and generalization of LSS estimates of age-at-exposure effects. The evidence for radiation effects on noncancer mortality remains strong, with risks elevated by about 14% per sievert during the last 30 years of follow-up. Statistically significant increases are seen for heart disease, stroke, digestive diseases, and respiratory diseases. The noncancer data are consistent with some non-linearity in the dose response owing to the substantial uncertainties in the data. There is no direct evidence of radiation effects for doses less than about 0.5 Sv. While there are no statistically significant variations in noncancer relative risks with age, age at exposure, or sex, the estimated effects are comparable to those seen for cancer. Lifetime risk summaries are used to examine uncertainties of the LSS noncancer disease findings.

40 YEARS OF FOLLOW-UP IN THE SEMIPALATINSK HISTORICAL COHORT STUDY

The aim of the collaborative study is to contribute to the assessment and documentation of long term health effects, primarily cancer, due to local fallout from atmospheric nuclear weapons testing conducted between 1949 and 1962 at the Semipalatinsk test site (STS), Kazakhstan. The Semipalatinsk cohort study had been set up already in the 1960s comprises follow-up information for an exposed and a comparison group of a total of 19,545 people. Cohort members include inhabitants of ten highly exposed settlements adjacent to the STS during the period of atmospheric nuclear weapons testing at STS and six settlements in the Kokpektinsky rayon of the Semipalatinskaya oblast which can be considered as virtually non (or very low) exposed group. For both groups, follow-up data were included from 1960 to end of 1999. A preliminary individual dose estimation due to external and internal radiation exposure was conducted by SRIRME. It took into account technical details of the nuclear device, meteorological data at time of the test, place of residence, and age at exposure of each person. The estimated mean dose in the exposed group was 640 mSv. Cause of death data were obtained based on death registration acts. Relative risks in terms of age-adjusted rate ratios were calculated as measures of effect. When comparing exposed and non-exposed group, overall rate ratios of 2.42 (2.10; 2.80)95%CI for mortality due to all solid tumours were found. For men and women, the rate ratios are 2.21 (1.84; 2.65) 95%CI and 2.79 (2.22; 3.51) 95%CI, respectively. The obtained results suggest significant increases in cancer mortality in the exposed group. Although dose estimates require further validation and refinement, the data from the Semipalatinsk historical cohort study remain a valuable source of information for radiation risk estimates relevant for radiation protection and the follow-up of the cohorts should be continued and extended in future. The results indicate the importance of further epidemiological investigation in order to address both the local lack of information and related health care issues.

Use of CR-39 solid state nuclear track detector in neutron personnel monitoring

Neutron sources like 241 Am –Be, 239 Pu –Be, 252 Cf and 14.6 MeV neutron generator are being used in oil exploration industries as well as in research institutions. While handling these neutron sources, personnel may be exposed to neutrons. Also personnel working in reactors, accelerators may receive dose from neutrons. These exposed individuals need to be monitored regularly for measurement of neutron doses. The individual neutron doses can be estimated by using Kodak NTA films and CR-39 Solid State Nuclear Track Detector with a polyethylene radiator to increase sensitivity in front in holder. Nearly 1450 personnel are being monitored regularly throughout the country on a quarterly basis. In India, the monitoring system adopted for individual neutron dose estimation having energy from 100 keV and above is described in this paper. Background counts of 0.20 mSv could be measured with CR-39 SSNTD foil system and it has been successfully introduced for Fast Neutron Personnel Monitoring for the country.

Re-evaluation of thyroid doses in Russia after the Chernobyl accident

Immediately after the Chernobyl accident, the team of Medical Radiological Research Center (MRRC) specialists carried out wide-scale measurements of iodine-131 content in the thyroid gland of 27 887 inhabitants of the Kaluga region. This initial information was presented only as official reports to governmental structures. Similar work was done by local specialists for 1441 inhabitants of the Bryansk region. The data of direct measurements provided us the basis for further individual thyroid dose estimations, where we exploited the developed model and personal interviews. This paper presents the results of updated dose evaluations, including the additional factors, such as dynamics of fallout and data on the pasture period. According to new estimations, the median of individual dose values in the Kaluga database (seven districts) vary from 30 mGy for children to 8 mGy for adults (geometric standard deviation of about 2.6). In the database of Bryansk (five raions), the median dose values are ranging from 140 mGy for children to 30 mGy for adults (geometric standard deviation of about 2.7). The obtained data were used for the validation of the semi-empirical model for thyroid dose reconstruction. This allowed the reconstruction of the mean doses for the settlements where I-131 measurements were not performed. The collective thyroid doses for the Bryansk and Kaluga regions were estimated as 72 600 and 3400 persons-Gy (for population of 1 137 100 and 213 500 inhabitants).

Conceptus radiation dose and risk from chest screen-film radiography.

The objectives of the present study were to (a) estimate the conceptus radiation dose and risks for pregnant women undergoing posteroanterior and anteroposterior (AP) chest radiographs, (b) study the conceptus dose as a function of chest thickness of the patient undergoing chest radiograph, and (c) investigate the possibility of a conceptus to receive a dose of more than 10 mGy, the level above which specific measurements of conceptus doses may be necessary. Thermoluminescent dosimeters were used for dose measurements in anthropomorphic phantoms simulating pregnancy at the three trimesters of gestation. The effect of chest thickness on conceptus dose and risk was studied by adding slabs of lucite on the anterior and posterior surface of the phantom chest. The conceptus risk for radiation-induced childhood fatal cancer and hereditary effects was calculated based on appropriate risk factors. The average AP chest dimension (d(a)) was estimated for 51 women of childbearing age from chest CT examinations. The value of d(a) was estimated to be 22.3 cm (17.4-27.2 cm). The calculated maximum conceptus dose was 107 x 10(-3) mGy for AP chest radiographs performed during the third trimester of pregnancy with maternal chest thickness of 27.2 cm. This calculation was based on dose data obtained from measurements in the phantoms and d(a) estimated from the patient group. The corresponding average excess of childhood cancer was 10.7 per million patients. The risk for hereditary effects was 1.1 per million births. Radiation dose for a conceptus increases exponentially as chest thickness increases. The conceptus dose at the third trimester is higher than that of the second and first trimesters. The results of the current study suggest that chest radiographs carried out in women at any time during gestation will result in a negligible increase in risk of radiation-induced harmful effects to the unborn child. After a properly performed maternal chest X-ray, there is no need for individual conceptus dose estimations.

Studies on the extended Techa river cohort: cancer risk estimation.

Initial population-based studies of riverside residents were begun in the late 1950s and in 1967 a systematic effort was undertaken to develop a well-defined fixed cohort of Techa river residents, to carry out ongoing mortality and (limited) clinical follow-up of this cohort, and to provide individualized dose estimates for cohort members. Over the past decade, extensive efforts have been made to refine the cohort definition and improve both the follow-up and dosimetry data. Analyses of the Techa river cohort can provide useful quantitative estimates of the effects of low dose rate, chronic external and internal exposures on cancer mortality and incidence and non-cancer mortality rates. These risk estimates complement quantitative risk estimates for acute exposures based on the atomic bomb survivors and chronic exposure risk estimates from worker studies, including Mayak workers and other groups with occupational radiation exposures. As the dosimetry and follow-up are refined it may also be possible to gain useful insights into risks associated with 90Sr exposures.

Elemental phosphorus slag exposure study in Southeastern Idaho, USA

Phosphorus slag containing elevated concentrations of radionuclides in the uranium series with radium-226 ranging from 750 to 1100 Bq/kg has been used in Southeastern Idaho communities as a construction material. An exposure study was conducted in the region to identify residences that incorporated phosphorus slag in the construction material, to determine the dose from the slag to residents, and to find slag in public structures and roads. Measurements were made with calibrated, commercial “Micro Rem” instruments and with commercial Al 2O 3 TL dosimeters. A total of 1472 residences were surveyed, and we estimate that less than 12% of the residences in Soda Springs contain slag; while no houses in Pocatello or Fort Hall were found to have slag in the construction. Individual dose estimates for nine individuals in this study exceeded 1 mSv/year above background, while the highest estimated individual dose was 1.32 mSv/year. Few of the public structures surveyed were found to contain slag. A significant fraction of the public roads, however, contained slag: 27% in Pocatello, 23% in Soda Springs, and 20% in Fort Hall.

Stable chromosome aberrations in atomic bomb survivors: results from 25 years of investigation.

Frequencies of stable chromosome aberrations from more than 3,000 atomic bomb survivors were used to examine the nature of the radiation dose response. The end point was the proportion of cells with at least one translocation or inversion detected in Giemsa-stained cultures of approximately 100 lymphocytes per person. The statistical methods allow for both imprecision of individual dose estimates and extra-binomial variation. A highly significant and nonlinear dose response was seen. The shape of the dose response was concave upward for doses below 1.5 Sv but exhibited some leveling off at higher doses. This curvature was similar for the two cities, with a crossover dose (i.e. the ratio of the linear coefficient to the quadratic coefficient) of 1.7 Sv (95% CI 0.9, 4). The low-dose slopes for the two cities differed significantly: 6.6% per Sv (95% CI 5.5, 8.4) in Hiroshima and 3.7% (95% CI 2.6, 4.9) in Nagasaki. This difference was reduced considerably, but not eliminated, when the comparison was limited to people who were exposed in houses or tenements. Nagasaki survivors exposed in factories, as well as people in either city who were outside with little or no shielding, had a lower dose response than those exposed in houses. This suggests that doses for Nagasaki factory worker survivors may be overestimated by the DS86, apparently by about 60%. Even though factory workers constitute about 20% of Nagasaki survivors with dose estimates in the range of 0.5 to 2 Sv, calculations indicate that the dosimetry problems for these people have little impact on cancer risk estimates for Nagasaki.

Re: Researchers should talk to workers Am. J. Ind. Med. 2000. 37:668

Dr. McDonald errs in his reply to my earlier letter "Researchers Should Talk to Workers," stating that the Amandus et al. [1987] study did not rely on McDonald's exposure estimates. Amandus [1987] states "the eight hour TWA fiber-exposure for jobs was estimated from the short term samples employing a scheme derived by McDonald et al. [1986a,b]." As this sentence indicates, Amandus et al. used Dr. McDonald's formula for the individual dose estimates. While it may be, as Dr. McDonald claims, that the Amandus team decided separately to rely on this exposure estimate, this does not obviate the fact that Amandus et al. did indeed rely on the McDonald et al. exposure scheme. Dr. McDonald's publications make no mention of his "numerous discussions with past and present employees." The only "employee" thanked for assistance in the 1986 study that was the focus of my original letter was Earl D. Lovick, the W.R. Grace Co. plant manager, an accountant by training [McDonald, 1986]. Moreover, in his sworn testimony Lovick said that he reviewed the exposure estimates with top executives at corporate headquarters, none of whom ever worked in the mine or mill. If Dr. McDonald's discussions with employees contributed to his estimates, then he should have cited (and perhaps thanked) them in his original paper. Dr. McDonald's interviews should have revealed a variety of problems with the Company's estimates. One worker, for example, testified that dust samples that were "too heavy to count" were thrown out [Egilman, 2000]. Dr. McDonald's assertion that fiber estimates which included the observations of workers would mean that tremolite was less hazardous than previously thought reveals other problems with his data. For example, Dr. McDonald underreported the occurrence of lung cancer at Libby. He reported 21 cases, but as of 1984, Grace knew of 32 asbestos lung cancers (R.C. Walsh to H.A. Eschenbach, October 18, 1983). The protocol explains why six of those lung cancers were omitted, but that still leaves 26 lung cancers that should have been included in the published papers. Since data on the higher number of lung cancers was available at the time of the study, I am hard-pressed to understand why this was omitted from the published paper. Neither Dr. McDonald nor the Grace Company has made the raw data from the tremolite studies public. Given the number and seriousness of the flaws in the McDonald et al. study, no conclusions about the toxicity of tremolite can be drawn from the Libby studies.

Internal Dose Estimates for Workers Exposed to Plutonium by Performing In Vivo Measurements of 241Am

Individual dose estimates for workers chronically exposed to plutonium is an important task in the investigation of possible health effects from internal plutonium depositions. Systemic and total body deposition of plutonium is usually estimated from urinalysis. However, this technique used alone results in uncertainty in individual dose assessment, by about an order of magnitude. Direct in vivo measurements of 241Am content in lungs, skeleton and liver by whole-body counting allows one to improve the result of dose assessment. First of all the improvement is due to the additional qualitative information about the route of intake (sorting out subjects with contaminated wounds) and solubility of plutonium aerosol particles (estimating the lung/skeleton ratio). This paper develops an algorithm for performing quantitative estimates of individual doses for workers, using the results of in vivo measurements of 241Am by whole-body counting. The algorithm applies the new ICRP Publication 66/67 models and takes into account such parameters as the 241Pu/239Pu ratio, effective aging time of mixed fission products and actinides, particle size distribution of plutonium aerosols and some other parameters. The uncertainties in individual dose assessment due to application of these parameters were analysed. It was shown that regular in vivo measurements of 241Am in the lungs allow the detection of single intake of plutonium at a level of the order of one ALI and can be a good monitoring programme for individuals involved in operations with plutonium treated in nuclear fuel cycle.

Biological Dosimetry of Chernobyl Cleanup Workers: Inclusion of Data on Age and Smoking Provides Improved Radiation Dose Estimates

We report the results of a study of chromosome translocations in 126 Russian subjects who participated in the cleanup activities at Chernobyl and another 53 subjects, from other places in Russia, who were not exposed at Chernobyl. In agreement with our earlier study, we find increased translocation frequencies among the exposed compared to Russian controls. We describe statistical methods for estimating the dose of ionizing radiation determined by scoring chromosome translocations found in circulating lymphocytes sampled several years after exposure. Two statistical models were fitted to the data. One model assumed that translocation frequencies followed an overdispersed Poisson distribution. The second model assumed that translocation frequencies followed a negative binomial distribution. In addition, the effects of radiation exposure were modeled as additive or as multiplicative to the effects of age and smoking history. We found that the negative binomial model fit the data better than the overdispersed Poisson model. We could not distinguish between the additive and the multiplicative model with our data. Individual dose estimates ranged from 0 (for 43 subjects) to 0.56 Gy (mean 0.14 Gy) under the multiplicative model and from 0 to 0.95 Gy (mean 0.15 Gy) under the additive model. Dose estimates were similar under the two models when the number of translocations was less than 4 per 100 cells. The additive model tended to estimate larger doses when the number of translocations was greater than 4 per 100 cells. We also describe a method for estimating upper 95% tolerance bounds for numbers of translocations in unexposed individuals. We found that inclusion of data on age and smoking history was important for dose estimation. Ignoring these factors could result in gross overestimation of exposures, particularly in older subjects who smoke.

FISH-based analysis of stable translocations in a Techa River population

Purpose: Measurements of symmetrical translocations by fluorescence in situ hybridization (FISH) were performed for retrospective biodosimetry in a Techa River population exposed to external (gamma -rays) and internal (90Sr, 137Cs) irradiation. Materials and methods: Chromosome analyses were carried out on peripheral lymphocytes from 73 radiation-exposed residents from settlements along the Techa River (Southern Urals, Russia) located 7-148 km downstream from the site of release of liquid radioactive waste from the plutonium production facility Mayak. Thirty-nine unexposed persons from non-contaminated areas were used as controls. Whole-chromosome painting probes for chromosomes 1, 4 and 12 were used simultaneously with a pancentromeric probe. Results: A significantly elevated mean translocation frequency compared with controls was found for the total study group and for either of two subgroups of inhabitants residing in villages of the upper regions of the Techa River (7-60 km) during 1950 to 1951, or in villages of the lower regions (78-148 km) until the time of blood sampling. Within the first subgroup, subjects born between 1937 and 1949 showed higher translocation frequencies than those born between 1914 and 1936. Collective biodosimetry estimates for the various groups were between 0.24 and 0.54 Gy. Individual dose estimates for seven subjects with at least five translocations ranged between 0.77 and 1.80 Gy and compared well with doses reconstructed on the basis of 90Sr whole-body counts (WBC) and electronic paramagnetic resonance (EPR) measurements. Individual translocation frequencies from 40 subjects with existing WBC data and calculated cumulative red bone marrow doses below 0.6 Gy fall within the 95% prediction limits of the calibration curve. Conclusions: FISH-based translocation measurements can provide useful information for a retrospective biodosimetric interpretation. However, with the analysed number of cells, individual estimates required for a reliable evaluation of this highly variable exposure situation can be obtained only for a minority of subjects. In addition, influence of a temporal decline on the yield of stable translocations cannot be fully excluded.

Analysis of symmetrical translocations for retrospective biodosimetry in radiation workers of the Mayak nuclear-industrial complex (Southern Urals) using FISH-chromosome painting

Purpose: Frequencies of symmetrical translocations were determined by fluorescence in situ hybridization (FISH) for retrospective biodosimetry in workers occupationally exposed to external gamma -rays and internal plutonium at the Mayak nuclear-industrial complex (Southern Urals, Russia). Materials and methods : Chromosome analyses were carried out on peripheral lymphocytes from 75 Mayak workers who had received their main exposures between 1948 and 1963. Cumulative external gamma -ray doses between 0.02 and 9.91 Sv and plutonium burdens ranging between 0.26 and 18.5kBq are reported. As controls, 33 unexposed persons from noncontaminated areas of the Southern Urals were used. Wholechromosome painting probes for chromosomes 1, 4 and 12 were used simultaneously with a pancentromeric probe. Results : Compared with the control group, a significantly elevated translocation frequency was found for the total study group and for either of two subsets with (48 subjects) and without (27 subjects) plutonium incorporation. The dicentric frequency was not significantly different from the control level. In the pooled data set, translocation frequencies showed a significant dependence on cumulative external gamma -ray doses. Plutonium uptake had no substantial influence. Individual dose estimates for 21 cases exhibiting at least five translocations ranged between 0.5 and 1.8 Gy, which is substantially lower than the workers' registered personal doses. Conclusion : At 35-40 years after protracted exposure to low-dose rate external gamma -rays, the postulated lifetime stability of translocations cannot be confirmed. Apparently, the natural loss of translocation-bearing peripheral lymphocytes cannot be fully compensated so that a temporal decline even of transmissible aberrations takes place. As a consequence, individual retrospective biodosimetry estimates cannot be obtained reliably from the remaining fraction of translocations.

DNA content proportionality and persistence of radiation-induced chromosomal aberrations studied by FISH

Chromosome aberrations induced by radiation have been used for the purpose of dosimetry for a long time. Translocations are especially useful for retrospective dosimetry, since they are assumed to be stable. The method of chromosome painting (FISH) has facilitated objective scoring of aberrations considerably. Translocation frequencies, obtained by FISH, for retrospective dosimetry rely on the main assumptions of neutral selection value and that the distribution of aberrations over the chromosomes is a known function of the DNA content of the chromosomes. Data scrutinising the two above-mentioned assumptions indicate deviations from both. Other factors potentially causing problems for retrospective dosimetry, such as inter-individual variations in background and induction patterns, are discussed. Finally, a brief analysis of the statistical power of dosimetry studies shows that establishing low doses (≈ 0.25 Gy) with good precision requires a great effort, which is probably unrealistic for individual dose estimates in epidemiological studies.

Ingestion of Nevada Test Site Fallout

This paper summarizes individual and collective dose estimates for the internal organs of hypothetical yet representative residents of selected communities that received measurable fallout from nuclear detonations at the Nevada Test Site. The doses, which resulted from ingestion of local and regional food products contaminated with over 20 radionuclides, were estimated with use of the PATHWAY food-chain-transport model to provide estimates of central tendency and uncertainty. The thyroid gland received much higher doses than other internal organs and tissues. In a very few cases, infants might have received thyroid doses in excess of 1 Gy, depending on location, diet, and timing of fallout. 131I was the primary thyroid dose contributor, and fresh milk was the main exposure pathway. With the exception of the thyroid, organ doses from the ingestion pathway were much smaller (< 3%) than those from external gamma exposure to deposited fallout. Doses to residents living closest to the Nevada Test Site were contributed mainly by a few fallout events; doses to more distantly located people were generally smaller, but a greater number of events provided measurable contributions. The effectiveness of different fallout events in producing internal organ doses through ingestion varied dramatically with seasonal timing of the test, with maximum dose per unit fallout occurring for early summer depositions when milk cows were on pasture and fresh, local vegetables were used. Within specific communities, internal doses differed by age, sex, and lifestyle. Collective internal dose estimates for specific geographic areas are provided.