Lung cancer mortality among male nuclear workers of the Mayak facilities in the former Soviet Union

An analysis of lung cancer mortality in a cohort of 1,669 Mayak workers who started their employment in the plutonium and reprocessing plants between 1948 and 1958 has been carried out in terms of a relative risk model. Particular emphasis has been given to a discrimination of the effects of external gamma-ray exposure and internal alpha-particle exposure due to incorporated plutonium. This study has also used the information from a cohort of 2,172 Mayak reactor workers who were exposed only to external gamma rays. The baseline lung cancer mortality rate has not been taken from national statistics but has been derived from the cohort itself. For both alpha particles and gamma rays, the results of the analysis are consistent with linear dose dependences. The estimated excess relative risk per unit organ dose equivalent in the lung due to the plutonium alpha particles at age 60 equals, according to the present study, 0.6/Sv, with a radiation weighting factor of 20 for alpha particles. The 95% confidence range is 0.39/Sv to 1.0/Sv. For the gamma-ray component, the present analysis suggests an excess relative risk for lung cancer mortality at age 60 of 0.20/Sv, with, however, a large 95% confidence range of-0.04/Sv to 0.69/Sv.     

Bone cancers in Mayak workers

Bone cancer mortality risks were evaluated in 11,000 workers who started working at the "Mayak" Production Association in 1948-1958 and who were exposed to both internally deposited plutonium and external gamma radiation. Comparisons with Russian and U.S. general population rates indicate excess mortality, especially among females, plutonium plant workers, and workers with external doses exceeding 1 Sv. Comparisons within the Mayak worker cohort, which evaluate the role of plutonium body burden with adjustment for cumulative external dose, indicate excess mortality among workers with burdens estimated to exceed 7.4 kBq (relative risk = 7.9; 95% CI = 1.6-32) and among workers in the plutonium plant who did not have routine plutonium monitoring data based on urine measurements (relative risk = 4.1; 95% CI = 1.2-14). In addition, analyses treating the estimated plutonium body burden as a continuous variable indicate increasing risk with increasing burden (P < 0.001). Because of limitations in current plutonium dosimetry, no attempt was made to quantify bone cancer risks from plutonium in terms of organ dose, and risk from external dose could not be reliably evaluated.     

Lung cancer risk of Mayak workers: modelling of carcinogenesis and bystander effect

Lung cancer mortality in the period of 1948-2002 has been analysed for 6,293 male workers of the Mayak Production Association, for whose information on smoking, annual external doses and annual lung doses due to plutonium exposures was available. Individual likelihoods were maximized for the two-stage clonal expansion (TSCE) model of carcinogenesis and for an empirical risk model. Possible detrimental and protective bystander effects on mutation and malignant transformation rates were taken into account in the TSCE model. Criteria for non-nested models were used to evaluate the quality of fit. Data were found to be incompatible with the model including a detrimental bystander effect. The model with a protective bystander effect did not improve the quality of fit over models without a bystander effect. The preferred TSCE model was sub-multiplicative in the risks due to smoking and internal radiation, and more than additive. Smoking contributed 57% to the lung cancer deaths, the interaction of smoking and radiation 27%, radiation 10%, and others cause 6%. An assessment of the relative biological effectiveness of plutonium was consistent with the ICRP recommended value of 20. At age 60 years, the excess relative risk (ERR) per lung dose was 0.20 (95% CI: 0.13; 0.40) Sv(-1), while the excess absolute risk (EAR) per lung dose was 3.2 (2.0; 6.2) per 10(4) PY Sv. With increasing age attained the ERR decreased and the EAR increased. In contrast to the atomic bomb survivors, a significant elevated lung cancer risk was also found for age attained younger than 55 years. For cumulative lung doses below 5 Sv, the excess risk depended linearly on dose. The excess relative risk was significantly lower in the TSCE model for ages attained younger than 55 than that in the empirical model. This reflects a model uncertainty in the results, which is not expressed by the standard statistical uncertainty bands.     

Radiation Effects on Mortality from Solid Cancers Other than Lung,Liver, and Bone Cancer in the Mayak Worker Cohort: 1948–2008

Radiation effects on mortality from solid cancers other than lung, liver, and bone cancer in the Mayak worker cohort: 1948–2008. The cohort of Mayak Production Association (PA) workers in Russia offers a unique opportunity to study the effects of prolonged low dose rate external gamma exposures and exposure to plutonium in a working age population. We examined radiation effects on the risk of mortality from solid cancers excluding sites of primary plutonium deposition (lung, liver, and bone surface) among 25,757 workers who were first employed in 1948–1982. During the period 1948–2008, there were 1,825 deaths from cancers other than lung, liver and bone. Using colon dose as a representative external dose, a linear dose response model described the data well. The excess relative risk per Gray for external gamma exposure was 0.16 (95% CI: 0.07 – 0.26) when unadjusted for plutonium exposure and 0.12 (95% CI 0.03 – 0.21) when adjusted for plutonium dose and monitoring status. There was no significant effect modification by sex or attained age. Plutonium exposure was not significantly associated with the group of cancers analyzed after adjusting for monitoring status. Site-specific risks were uncertainly estimated but positive for 13 of the 15 sites evaluated with a statistically significant estimate only for esophageal cancer. Comparison with estimates based on the acute exposures in atomic bomb survivors suggests that the excess relative risk per Gray for prolonged external exposure in Mayak workers may be lower than that for acute exposure but, given the uncertainties, the possibility of equal effects cannot be dismissed.     

The association of inbreeding with lung fibrosis incidence in Beagle dogs that inhaled 238PuO2 or 239PuO2

Studies of health effects in animals after exposure to internally deposited radionuclides were intended to supplement observational studies in humans. Both nuclear workers and Beagle dogs have exhibited plutonium-associated lung fibrosis; however, the dogs' smaller gene pool may limit the applicability of findings to humans. Data on Beagles that inhaled either plutonium-238 dioxide ((238)PuO(2)) or plutonium-239 dioxide ((239)PuO(2)) were analyzed. Wright's Coefficient of Inbreeding was used to measure genetic or familial susceptibility and was assessed as an explanatory variable when modeling the association between lung fibrosis incidence and plutonium exposure. Lung fibrosis was diagnosed in approximately 80% of the exposed dogs compared with 23.7% of the control dogs. The maximum degree of inbreeding was 9.4%. Regardless of isotope, the addition of inbreeding significantly improved the model in female dogs but not in males. In female dogs, an increased inbreeding coefficient predicted decreased hazard of a lung fibrosis diagnosis. Lung fibrosis was common in these dogs with inbreeding affecting models of lung fibrosis incidence in females but not in males. The apparent protective effect in females predicted by these models of lung fibrosis incidence is likely to be minimal given the small degree of inbreeding in these groups.     

Evaluation of respiratory and cutaneous doses of chlorothalonil during re-entry in greenhouses

Five female workers were monitored for 5 consecutive days during re-entry into a greenhouse containing ornamental plants. Skin contamination (excluding hands) was evaluated with nine pads of filter paper placed on the skin. Hand contamination was assessed by washing with 95% ethanol. Respiratory exposure was evaluated by personal air sampling. The respiratory dose was based on a lung ventilation of 15 l/min. The doses absorbed were estimated assuming 10% skin absorption and 100% lung retention. Dislodgeable foliar residue was determined on days of re-entry to evaluate the decay of chlorothalonil. Chlorothalonil was analysed in the different matrices by GC-MS. Respiratory exposure was less than skin contamination, being 11.4+/-5.1% (mean+/-SD) of total exposure. The estimated total absorbed dose did not exceed the acceptable daily intake of 0.03 mg/kg body mass. The hands and unexposed skin of all workers were always found to be contaminated. Greater precautions are therefore needed to reduce skin exposure (clean gloves and suitable clean clothing every day).     

Cerebrovascular diseases in nuclear workers first employed at the Mayak PA in 1948–1972

Incidence and mortality from cerebrovascular diseases (CVD) (430–438 ICD-9 codes) have been studied in a cohort of 18,763 workers first employed at the Mayak Production Association (Mayak PA) in 1948–1972 and followed up to the end of 2005. Some of the workers were exposed to external gamma-rays only while others were exposed to a mixture of external gamma-rays and internal alpha-particle radiation due to incorporated ²³⁹Pu. After adjusting for non-radiation factors, there were significantly increasing trends in CVD incidence with total absorbed dose from external gamma-rays and total absorbed dose to liver from internal alpha radiation. The CVD incidence was statistically significantly higher among workers with total absorbed external gamma-ray doses greater than 0.20 Gy compared to those exposed to lower doses; the data were consistent with a linear trend in risk with external dose. The CVD incidence was statistically significantly higher among workers with total absorbed internal alpha-radiation doses to liver from incorporated ²³⁹Pu greater than 0.025 Gy compared to those exposed to lower doses. There was no statistically significant trend in CVD mortality risk with either external gamma-ray dose or internal alpha-radiation dose to liver. The risk estimates obtained are generally compatible with those from other large occupational studies, although the incidence data point to higher risk estimates compared to those from the Japanese A-bomb survivors. Further studies of the unique cohort of Mayak workers chronically exposed to external and internal radiation will allow improving the reliability and validating the radiation safety standards for occupational and public exposure.     

Mortality from solid cancers other than lung,liver, and bone in relation to external dose among plutonium and non-plutonium workers in the Mayak Worker Cohort

Exposure to ionizing radiation has well-documented long-term effects on cancer rates and other health outcomes in humans. While in vitro experimental studies had demonstrated that the nature of some radiation effects depend on both total dose of the radiation and the dose rate (i.e., the pattern of dose distribution over time), the question of whether or not the carcinogenic effect of radiation exposure depends on the dose rate remains unanswered. Another issue of interest concerns whether or not concomitant exposure to external gamma rays and inhaled plutonium aerosols has any effect on the external exposure effects. The analyses of the present paper focus on the risk of solid cancers at sites other than lung, liver, and bone in Mayak workers. Recent findings are reviewed indicating that there is no evidence of plutonium dose response for these cancers in the Mayak worker cohort. Then the evidence for differences in the external dose effects among workers with and without the potential for exposure to alpha particles from inhaled plutonium is examined. It is found that there is no evidence that exposure to plutonium aerosols significantly affects the risk associated with external exposure. While the Mayak external dose risk estimate of an excess relative risk of 0.16 per Gy is somewhat lower than an appropriately normalized risk estimate from the Life Span Study of Japanese atomic bomb survivors, the uncertainties in these estimates preclude concluding that the external dose excess relative risks of this group of solid cancers differ in the two cohorts.     

Cerebrovascular diseases in the cohort of workers first employed at Mayak PA in 1948-1958

The incidence of and mortality from cerebrovascular diseases (CVD) have been studied in a cohort of 12,210 workers first employed at one of the main plants of the Mayak nuclear facility during 1948-1958 and followed up to 31 December 2000. Information on external γ-ray doses is available for virtually all of these workers (99.9%); the mean total γ-ray dose (± SD) was 0.91 ± 0.95 Gy (99th percentile 3.9 Gy) for men and 0.65 ± 0.75 Gy (99th percentile 2.99 Gy) for women. In contrast, plutonium body burden was measured only for 30.0% of workers; among those monitored, the mean cumulative liver dose from plutonium α-particle exposure (± SD) was 0.40 ± 1.15 Gy (99th percentile 5.88 Gy) for men and 0.81 ± 4.60 Gy (99th percentile 15.95 Gy) for women. A total of 4418 cases of CVD, including 665 cases of stroke, and 753 deaths from CVD, including 404 deaths from stroke, were identified in the study cohort. Having adjusted for non-radiation factors, there were statistically significant increasing trends in CVD incidence but not mortality with both total external γ-ray dose and internal liver dose. Much of the evidence for increased incidence in relation to external dose arose for workers with cumulative doses above 1 Gy. Although the dose response is consistent with linearity, the statistical power to detect non-linearity at external doses below 1 Gy was low. CVD incidence was statistically significantly higher among workers with a plutonium liver dose above 0.1 Gy. There was a statistically significant increasing trend in incidence with increasing internal dose, even after adjusting for external dose, although the trend estimates differed between workers at different plants. The risk estimates for external radiation are generally compatible with those from other large occupational studies, although the incidence data point to higher risk estimates compared to those from the Japanese A-bomb survivors.     

Cancer mortality risk among workers at the Mayak nuclear complex

At present, direct data on risk from protracted or fractionated radiation exposure at low dose rates have been limited largely to studies of populations exposed to low cumulative doses with resulting low statistical power. We evaluated the cancer risks associated with protracted exposure to external whole-body gamma radiation at high cumulative doses (the average dose is 0.8 Gy and the highest doses exceed 10 Gy) in Russian nuclear workers. Cancer deaths in a cohort of about 21,500 nuclear workers who began working at the Mayak complex between 1948 and 1972 were ascertained from death certificates and autopsy reports with follow-up through December 1997. Excess relative risk models were used to estimate solid cancer and leukemia risks associated with external gamma-radiation dose with adjustment for effects of plutonium exposures. Both solid cancer and leukemia death rates increased significantly with increasing gamma-ray dose (P < 0.001). Under a linear dose-response model, the excess relative risk for lung, liver and skeletal cancers as a group (668 deaths) adjusted for plutonium exposure is 0.30 per gray (P < 0.001) and 0.08 per gray (P < 0.001) for all other solid cancers (1062 deaths). The solid cancer dose-response functions appear to be nonlinear, with the excess risk estimates at doses of less than 3 Gy being about twice those predicted by the linear model. Plutonium exposure was associated with increased risks both for lung, liver and skeletal cancers (the sites of primary plutonium deposition) and for other solid cancers as a group. A significant dose response, with no indication of plutonium exposure effects, was found for leukemia. Excess risks for leukemia exhibited a significant dependence on the time since the dose was received. For doses received within 3 to 5 years of death the excess relative risk per gray was estimated to be about 7 (P < 0.001), but this risk was only 0.45 (P = 0.02) for doses received 5 to 45 years prior to death. External gamma-ray exposures significantly increased risks of both solid cancers and leukemia in this large cohort of men and women with occupational radiation exposures. Risks at doses of less than 1 Gy may be slightly lower than those seen for doses arising from acute exposures in the atomic bomb survivors. As dose estimates for the Mayak workers are improved, it should be possible to obtain more precise estimates of solid cancer and leukemia risks from protracted external radiation exposure in this cohort.     

Risk of cerebrovascular disease incidence in the cohort of Mayak production association workers first employed during 1948-1958

Incidence of cerebrovascular diseases (CVD) has been studied in a cohort of 12210 workers first employed at one of the main plants (reactors, radiochemical or plutonium) of the Mayak nuclear facility during 1948-1958 and followed up to the end of 2000. Information on external gamma doses is available for virtually all (99.9%) of these workers; the mean (+/- one standard deviation) total gamma dose was 0.91 +/- 0.95 Gy (99% percentile 3.9 Gy) for men and 0.65 +/- 0.75 Gy (99% percentile 2.99 Gy) for women. Plutonium body burden was measured only for 30.0% of workers. Amongst those monitored, the mean (+/- standard deviation) cumulative liver dose from plutonium alpha exposure was 0.40 +/- 1.15 Gy (99% percentile 5.88 Gy) for men and 0.81 +/- 4.60 Gy (99% percentile 15.95 Gy) for women 4418 cases (first diagnosis) of CVD were identified in the studied cohort. A statistically significant increasing trend in CVD incidence with total external gamma dose was revealed after adjustment for non-radiation factors and internal exposure from incorporated plutonium-239. Excess relative risk per Gy was 0.464 (95% confidence interval 0.360-0.567). Incidence of CVD was statistically significantly higher for the workers chronically exposed to external gamma rays at a dose above 1.0 Gy A statistically significant increasing trend in CVD incidence with internal liver dose from plutonium alpha exposure was observed after adjustment for non-radiation factors and external exposure. ERR per Gy was 0.155 (95% confidence interval 0.075-0.235). CVD incidence was statistically significantly higher among workers with a plutonium liver dose above 0.1 Gy, although the trend estimates differed between workers at different plants. The incidence risk estimates for external radiation are generally compatible with estimates from the study of Chernobyl clean-up workers, although the incidence data point to higher risk estimates compared to those from the Japanese A-bomb survivors.     

Determinants of restrictive lung function in asbestos-induced pleural fibrosis

We evaluated whether restrictive lung function among asbestos-exposed individuals with pleural fibrosis was caused by radiographically inapparent parenchymal inflammation and/or parenchymal fibrosis. All 24 study participants were sheet metal workers who were nonsmokers with normal parenchyma on posteroanterior chest radiograph. These subjects had either normal pleura (n = 7), circumscribed plaques (n = 9), or diffuse pleural thickening (n = 8). After controlling for age, years in the trade, and pack-years of smoking, we found that sheet metal workers with diffuse pleural thickening had a lower forced vital capacity (P less than 0.001), total lung capacity (P less than 0.01), and CO-diffusing capacity of the lung (P less than 0.05) than those with normal pleura. Similarly, sheet metal workers with circumscribed plaques were found to have a reduced forced vital capacity; however, because of the small number of study subjects, this difference (regression coefficient = -11.0) was only marginally significant (P = 0.06). Although circumscribed plaque and diffuse pleural thickening were both associated with a lymphocytic alveolitis and a higher prevalence of parenchymal fibrosis on high-resolution computerized tomography (HRCT) scan, neither a lymphocytic alveolitis nor the finding of parenchymal fibrosis on HRCT scan influenced the relationship between pleural fibrosis and restrictive lung function. We conclude that pleural fibrosis is associated with restrictive lung function and abnormally low diffusion that appears to be independent of our measures of parenchymal injury (chest X-ray, bronchoalveolar lavage, and HRCT scan).(ABSTRACT TRUNCATED AT 250 WORDS)     

mFISH analysis reveals complexity of chromosome aberrations in individuals occupationally exposed to internal plutonium: a pilot study to assess the relevance of complex aberrations as biomarkers of exposure to high-LET alpha particles

We recently demonstrated that a significant proportion of apparently stable insertions induced after exposure to a mean of one alpha particle/cell, detected using three-color FISH, were part of larger unstable complexes when visualized by 24-color FISH. Interestingly, regardless of the long-term persistence capability of the cell, the complexity of each alpha-particle-induced complex appeared to be specific to the nuclear traversal of a single alpha particle. To assess whether aberrations of a similar complexity are observed in vivo and also to examine the usefulness of detecting such aberrations as a biomarker of chronic exposure to alpha particles, we have carried out a limited pilot study of Russian workers with large body burdens of alpha-particle-emitting plutonium. We found unstable cells containing non-transmissible complex aberrations in all of the plutonium-exposed subjects analyzed by mFISH. In addition, all of the complexes seen were consistent with those previously observed in vitro. Non-transmissible complex aberrations were more common than transmissible-type complexes, consistent with ongoing/chronic exposure, and insertions were dominant features of both types of complex. Accordingly, this preliminary study supports the proposal that aberration complexity and non-transmissibility are the major cytogenetic features of alpha-particle exposure that could potentially be exploited as a specific indicator of chronic exposures to high-LET alpha particles.     

Lung cancer mortality among nuclear workers of the Mayak facilities in the former Soviet Union. An updated analysis considering smoking as the main confounding factor

A new analysis of lung cancer mortality in a cohort of male Mayak workers who started their employment in the plutonium and reprocessing plants between 1948 and 1958 has been carried out in terms of a relative risk model. The follow-up has been extended until 1999, moreover a new dosimetry system (DOSES2000) has been established. Particular emphasis has been given to a discrimination of the effects of external -exposure and internal -exposure due to incorporated plutonium. This study has also utilized and incorporated the information from a cohort of Mayak reactor workers, who were exposed only externally to -rays. The influence of smoking as the main confounding factor for lung cancer has been studied. The baseline lung cancer mortality rate was not taken from national statistics but was derived from the cohort itself. The estimated excess relative risk for the plutonium -rays was 0.23/Sv (95%CI: 0.16–0.31). The resulting risk coefficient for external -ray exposure was very low with a statistically insignificant estimate of 0.058/Sv (95%CI: –0.072–0.20). The inferred relative risk for smokers was 16.5 (95%CI: 12.6–20.5).     

Occupational exposure and respiratory health of workers at small scale industries

Certain occupations like welding, painting, and vehicle repairing are associated with regular exposure to dust, exhausts, fuels, fumes, PM, and vapors of welding, solvents, and paint. Many studies have proved a reduction in lung functions due to exposure to these agents. The present study aims to assess and compare respiratory symptoms and pulmonary functions among exposed and non-exposed persons as well as suggests controls respectively. A cross-sectional case study was carried out among small scale industry workers having matched demographic and anthropometric parameters. Medical Research Council (MRC) questionnaire and Micro Direct computerized automated spirometer were used for recording respiratory ailments and pulmonary function tests (PFT) respectively. The percentages of mechanics, welders and painters were 40.9, 31.8, and 27.3 respectively. The highest reported respiratory symptom was chest tightness and whistling among exposed (22.7%) and unexposed (10%). Among study exposed cases, the occupational exposure was found as often (22.7%), sometimes (68.2%) and never (9.1%) while the reported use of airway protection (masks) was very low. Overall respiratory health of the exposed versus controls was reported as excellent (54.5% vs 73.4%), good (27.3% vs 23.3%) and average (18.2% vs 3.3%) respectively. The exposed group on contrary to control one has decreased mean values for FEV1 (3.12 vs 3.50), FVC (4.12 vs 4.43), FEV1/ FVC % (79.60 vs 80.79) and PEF (414.77 vs 523.16). The present study reveals that exposed workers are at increased risk of developing respiratory symptoms and decreased pulmonary functions as compared to unexposed. Such exposure research studies are instrumental in health status evaluation of workers. However, this area has been neglected by the researchers in Saudi Arabia. It is, thus, strongly recommended to carry out prospective studies to substantiate the study results including large sample size, background pollutants concentrations and biological monitoring. Control strategies should be adopted to reduce the vapor concentration in the ambient air, protect and promote respiratory health of workers.     

Uncertainties on lung doses from inhaled plutonium

In a recent epidemiological study, Bayesian uncertainties on lung doses have been calculated to determine lung cancer risk from occupational exposures to plutonium. These calculations used a revised version of the Human Respiratory Tract Model (HRTM) published by the ICRP. In addition to the Bayesian analyses, which give probability distributions of doses, point estimates of doses (single estimates without uncertainty) were also provided for that study using the existing HRTM as it is described in ICRP Publication 66; these are to be used in a preliminary analysis of risk. To infer the differences between the point estimates and Bayesian uncertainty analyses, this paper applies the methodology to former workers of the United Kingdom Atomic Energy Authority (UKAEA), who constituted a subset of the study cohort. The resulting probability distributions of lung doses are compared with the point estimates obtained for each worker. It is shown that mean posterior lung doses are around two- to fourfold higher than point estimates and that uncertainties on doses vary over a wide range, greater than two orders of magnitude for some lung tissues. In addition, we demonstrate that uncertainties on the parameter values, rather than the model structure, are largely responsible for these effects. Of these it appears to be the parameters describing absorption from the lungs to blood that have the greatest impact on estimates of lung doses from urine bioassay. Therefore, accurate determination of the chemical form of inhaled plutonium and the absorption parameter values for these materials is important for obtaining reliable estimates of lung doses and hence risk from occupational exposures to plutonium.     

Epidemiological studies of cataract risk at low to moderate radiation doses: (not) seeing is believing

The prevailing belief for some decades has been that human radiation-related cataract occurs only after relatively high doses; for instance, the ICRP estimates that brief exposures of at least 0.5-2 Sv are required to cause detectable lens opacities and 5 Sv for vision-impairing cataracts. For protracted exposures, the ICRP estimates the corresponding dose thresholds as 5 Sv and 8 Sv, respectively. However, several studies, especially in the last decade, indicate that radiation-associated opacities occur at much lower doses. Several studies suggest that medical or environmental radiation exposure to the lens confers risk of opacities at doses well under 1 Sv. Among Japanese A-bomb survivors, risks for cataracts necessitating lens surgery were seen at doses under 1 Gy. The confidence interval on the A-bomb dose threshold for cataract surgery prevalence indicated that the data are compatible with a dose threshold ranging from none up to only 0.8 Gy, similar to the dose threshold for minor opacities seen among Chernobyl clean-up workers with primarily protracted exposures. Findings from various studies indicate that radiation risk estimates are probably not due to confounding by other cataract risk factors and that risk is seen after both childhood and adult exposures. The recent data are instigating reassessments of guidelines by various radiation protection bodies regarding permissible levels of radiation to the eye. Among the future epidemiological research directions, the most important research need is for adequate studies of vision-impairing cataract after protracted radiation exposure.     

Plutonium microdistribution in the lungs of Mayak workers

The degree of nonuniform distribution of plutonium in the human lung has not been determined; thus current dosimetric models do not account for nonuniform irradiation. A better scientific basis is needed for assessing the risk of developing radiation-induced disease from inhaled alpha-particle-emitting radionuclides. We measured the distribution of plutonium activity in the lung by autoradiography and related the activity to specific compartments of the lung. The study materials were lung specimens from deceased workers employed by the Mayak Production Association. The approach to analyzing these lung samples used contemporary stereological sampling and analysis techniques together with quantitative alpha-particle autoradiography. For the first time, plutonium distribution has been quantified in the human lung. The distribution of long-term retained plutonium is nonuniform, and a significant portion of plutonium was retained in pulmonary scars. In addition, a large fraction of plutonium was present in the parenchyma, where it was retained much longer than was estimated previously. The sequestration of plutonium particles in scars would greatly reduce the radiation exposure of the critical target cells and tissues for lung cancer. Thus the prolonged retention of plutonium in lung scars may not increase the dose or risk for lung cancer.     

Influence of dose rate on survival time for 239PuO2-induced radiation pneumonitis or pulmonary fibrosis in dogs.

Beagle dogs were exposed once or repeatedly to 0.75-microns-diameter monodisperse aerosols of 239PuO2 by pernasal inhalation. The dogs that were exposed once received alveolar depositions (+/- standard deviation) of 3.9 +/- 1.9 kBq/kg body mass and accumulated doses of 23 +/- 8 Gy to the lung before death at 5.4 +/- 1.7 years after exposure. Dogs exposed repeatedly received a total alveolar deposition of 5.3 +/- 0.9 kBq/kg body mass during 7 to 10 semiannual exposures and accumulated doses of 22 +/- 5 Gy to the lung before death at 4.9 +/- 0.7 years after first exposure. Clearance of the plutonium from the lung in the dogs exposed repeatedly was slower than in the dogs exposed once. All dogs in the repeated-exposure study and all but one dog in the single-exposure study died from radiation effects. Pulmonary fibrosis accounted for 72% of the radiation-related deaths in the single-exposure study and 87% in the repeated-exposure study. The remaining dogs died with pulmonary cancer. Based on total cumulative radiation dose, the times after exposure to death from radiation pneumonitis and pulmonary fibrosis were not significantly different for single and repeated exposures. Thus dose rate does not appear to be an important factor in predicting death from radiation pneumonitis or pulmonary fibrosis for dogs inhaling 239PuO2.     

The relative biological effectiveness of alpha-radiation during human lung exposure to irradiation

The assessment of the relative biological effectiveness (RBE) for alpha-radiation was held in the cases of inhalation of radon progeny and incorporation of plutonium in lungs. It is based on simulation of lung cancer radiation risk for different types of radiation. Specific radiation risk models developed according to the results of direct epidemiological studies are used for the simulation. These include two published risk models for uranium miners and nuclear workers of the Mayak facilities in the former Soviet Union. Additionally two lung cancer risk models are developed and described for the following cases: population indoor radon exposure and low-linear-energy-transfer reference radiation exposure. By the results of lifetime lung cancer risk simulation the RBE values range from 11 to 12 and from 1.7 to 4.9 for the cases of plutonium incorporation and of radon progeny exposure accordingly. The significant uncertainty of radiation risk models results in significant variation of RBE assessments. Rough estimations of RBE values 90% confidence interval are from unit fraction to 25 and from 2 to 50 for the cases of radon progeny exposure and plutonium incorporation accordingly.