Risks of circulatory diseases among Mayak PA workers with radiation doses estimated using the improved Mayak Worker Dosimetry System 2008

The new Mayak Worker Dosimetry System 2008 (MWDS-2008) was published in 2013 and supersedes the Doses-2005 dosimetry system for Mayak Production Association (PA) workers. It provides revised external and internal dose estimates based on the updated occupational history data. Using MWDS-2008, a cohort of 18,856 workers first employed at one of the main Mayak PA plants during 1948–1972 and followed up to 2005 was identified. Incidence and mortality risks from ischemic heart disease (IHD) (International Classification of Diseases (ICD)-9 codes 410–414) and from cerebrovascular diseases (CVD) (ICD-9 codes 430–438) were examined in this cohort and compared with previously published risk estimates in the same cohort based on the Doses-2005 dosimetry system. Significant associations were observed between doses from external gamma-rays and IHD and CVD incidence and also between internal doses from alpha-radiation and IHD mortality and CVD incidence. The estimates of excess relative risk (ERR)/Gy were consistent with those estimates from the previous studies based on Doses-2005 system apart from the relationship between CVD incidence and internal liver dose where the ERR/Gy based on MWDS-2008 was just over three times higher than the corresponding estimate based on Doses-2005 system. Adjustment for smoking status did not show any effect on the estimates of risk from internal alpha-particle exposure.     

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.     

Assessment of radiation exposure of murine rodents at the EURT territories

The study provides data on contemporary levels of radiation exposure of organs and tissues of murine rodents (several species of mice and voles) inhabiting the East-Ural Radioactive Trace. The estimation procedure involves the most advanced approach based on application of appropriate voxel phantom and biokinetic model. Input data for dose assessment are the results of measurements of skeletal ⁹⁰Sr activity concentration. Maximal internal dose to skeleton, accumulated during 45 days, is 303 mGy. Median internal dose rates on the last day before trapping were 0.83, 0.092 and 0.023 mGy/day for animals trapped at the sites with initial (1957) ⁹⁰Sr surface contamination >37 MBq/m², 18.5–37 MBq/m² and 0.074–18.5 MBq/m² respectively. Taking to account internal and external exposures, upper boundary of the ICRP Derived Consideration Reference Level (DCRL) is exceeded on the territory with maximal level of the initial ⁹⁰Sr surface contamination. On the territory with 18.5–37 MBq/m², whole body mean dose rates to murine rodents exceed the lower boundary of DCRL. On the areas with lower level of surface contamination, even the 90-th percentile of dose rate is below the DCRL.     

Ischemic Heart Disease in Workers at Mayak PA: Latency of Incidence Risk after Radiation Exposure

We present an updated analysis of incidence and mortality from atherosclerotic induced ischemic heart diseases in the cohort of workers at the Mayak Production Association (PA). This cohort constitutes one of the most important sources for the assessment of radiation risk. It is exceptional because it comprises information on several other risk factors. While most of the workers have been exposed to external gamma radiation, a large proportion has additionally been exposed to internal radiation from inhaled plutonium. Compared to a previous study by Azizova et al. 2012, the updated dosimetry system MWDS-2008 has been applied and methods of analysis have been revised. We extend the analysis of the significant incidence risk and observe that main detrimental effects of external radiation exposure occur after more than about 30 years. For mortality, significant risk was found in males with an excess relative risk per dose of 0.09 (95% CI: 0.02; 0.16) while risk was insignificant for females. With respect to internal radiation exposure no association to risk could be established.     

Cerebrovascular Diseases in Workers at Mayak PA: The Difference in Radiation Risk between Incidence and Mortality

A detailed analysis of cerebrovascular diseases (CeVD) for the cohort of workers at Mayak Production Association (PA) is presented. This cohort is especially suitable for the analysis of radiation induced circulatory diseases, due to the detailed medical surveillance and information on several risk factors. The risk after external, typically protracted, gamma exposure is analysed, accounting for potential additional internal alpha exposure. Three different endpoints have been investigated: incidence and mortality from all cerebrovascular diseases and incidence of stroke. Particular emphasis was given to the form of the dose-response relationship and the time dependence of the radiation induced risk. Young attained age was observed to be an important, aggravating modifier of radiation risk for incidence of CeVD and stroke. For incidence of CeVD, our analysis supports a dose response sub-linear for low doses. Finally, the excess relative risk per dose was confirmed to be significantly higher for incidence of CeVD compared to CeVD mortality and incidence of stroke. Arguments are presented for this difference to be based on a true biological effect.     

Low level radiation exposure the radiobiologist's challenge in the next millennium

A formal definition for low level exposure does not exist. This has arbitrarily been defined here as exposures from 0 to 5 cGy. The health implications of exposures within this dose range are highly controversial since the effects are exclusively stochastic. As such, the effects can only be detected in large populations. The Oxford Survey of Childhood Cancers (OSCC) established leukaemia as a predominant effect. After the chernobyl nuclear disaster, studies in European countries have correlated perinatal mortality with radioactive contaminations which could only have raised the radiation burdens by levels which are currently regarded as negligible. The reported risk indices for childhood leukaemia arising from low level exposures are generally comparable to those ascertained for high exposures, thus posing an enigma to radiobiologists. This paper reviews the progress in various areas of radiobiological research and attempts to make a synthesis of the facts with the view to provide an explanation. The purpose is also to stimulate an understanding of multifactorial biological mechanisms. Environmental radiation exposures must be expected to be concomitant with other toxic agents which must be taken into account in risk assessment. The challenge in the future will be to realise this goal.     

Remote effects at cell and subcell level in the hemopoietic system after chronic radiation exposure in man

The parameters characterizing the state of hemopoietic cells obtained from chronically exposed residents of the Techa riverside villages studied at late time after the exposure included: the level of somatic mutations in the TCR gene, the level of chromosome aberrations, the intensity of peripheral blood lymphocyte apoptosis. Exposed versus unexposed subjects (controls) showed an increased frequency of CD3-CD4+ T-lymphocytes, chromosome aberrations of stable type (translocations) and unstable type (dicentrics, rings), and also increased intensity of lymphocyte apoptosis. The findings of tests using a standard additional gamma-irradiation (1 Gy) accompanied by 24-hour incubation indicated that the rate of apoptosis of lymphocytes was significantly higher in exposed individuals in comparison with unexposed ones. It was suggested basing on the obtained data that at late time the chronic (for over 50 years) exposure at RBM doses from 0.01 to 3.22 Sv was a factor inducing the damage to the genetic apparatus of hemopoietic cells. Evidently, the initial chronic low-intensity irradiation in the above-indicated dose range activates adaptive processes at the cellular level in hemopoietic cells. Late time after the onset of exposure the adaptation reserves are depleted in chronically exposed persons which brings about its failure in the case of a challenge by additional external exposures.     

Radiation and nonradiation factors in thyroid pathology development for Chernobyl cleanup workers--residents of Mayak PA affected zone

Thyroid state study was been carried out for Chernobyl NPP accident liquidators living in Ozyorsk, the city, located in the nuclear facility affected zone (Mayak PA). In total 531 individuals were examined. Thyroid assessment was made basing on physical examination, on ultrasound study and on hormones measurement of thyroid stimulating hormone, free thyroxine and thyroid peroxidase antibody. Screening revealed thyroid pathology for 27% of clean-up workers. As a result of the study carried the following conclusions were made: thyroid disease prevalence among the Ozyorsk residents participated in the breakdown elimination after Chernobyl accident was not differ from the individuals who didn't take part in this work; the prevalence of thyroid disease in liquidators was significantly connected with non radiation risk factors: with gender (for women compared to men), RR = 4.0, 95% CI 2.9-5.5; with age (over 60 years old vs under 60 years old), RR for women was 1.7; 95% CI 1.0-3.0 and for men -1.9; 95% CI 1.1-3.2; with hereditary predisposition, RR for autoimmune thyroiditis was 3.3, 95% CI 1.4-7.9.     

Lung cancer in Mayak workers: interaction of smoking and plutonium exposure

Lung cancer mortality among 5058 male workers of the Mayak Production Association has been analyzed with emphasis on the interaction of smoking and radiation exposure by using the two-step clonal expansion (TSCE) model of carcinogenesis. The cohort consists of all Mayak workers with known smoking status, who were employed in the period 1948–1972, and who either had the plutonium concentration in urine measured or who worked in the reactors, where plutonium exposure was negligible. Those who died during the first two years after the first urine sampling were excluded. The follow-up extended until the end of 1998. During this time, 2176 workers died, including 244 lung cancer cases. Mayak workers were exposed to external (gamma and neutron) radiation, and in the radiochemical and plutonium plants to plutonium. In the preferred TSCE model, internal radiation and smoking act on the clonal expansion of pre-carcinogenic clones. Assuming a plutonium radiation weighting factor of 20, the excess relative risk per lung dose was estimated to be 0.11 (95% CI: 0.08; 0.17) Sv⁻¹. Most of the lung cancer deaths are found to be due to smoking. The second main factor is the interaction of smoking and internal radiation. The model is sub-multiplicative in relative risks due to smoking and radiation. In a multiplicative version of the TSCE model, internal radiation acts on initiation and transformation rates. This model version agrees with conventional epidemiological risk models, because it also suggests a higher risk estimate than the preferred TSCE model. However, it fits the data less well than the preferred model. An erratum to this article can be found at     

External radiation exposure of residents living close to the Mayak facility: main sources,dose estimates,and comparison with earlier assessments

Radiation and Environmental Biophysics -     

External radiation exposure of residents living close to the Mayak facility: main sources,dose estimates,and comparison with earlier assessments

In 1951 and 1952 specialists from the Mayak production association investigated the radiological situation in the area of the Metlinski reservoir that was located 5-7 km from the site of liquid radioactive waste (LRW) discharge. Based on their measurements of both the specific radioactivity in the water and the dose-rate above the water surface, the gamma-field above the water surface in 1951 was demonstrated to be mainly due to (95)Zr+(95)Nb. The dose-rate at the shore of the reservoir was calculated for the period 1949-1951. In November and December 1951, the gamma-field at the shore was mainly due to (140)Ba+(140)La. For the period 1949-1951, the external exposure of the Metlino population due to the decay of these radionuclides was about 200 R (2 Sv), most of the dose having been produced in 1951. The contribution of (137)Cs to external doses did at that time probably not exceed a fraction of several percent. This finding is in contradiction to the assumptions made in the most recent TRDS-2000 system that was developed to reconstruct the doses to the residents of the Techa river. The results presented here demonstrate that the reconstruction of external doses received by the Metlino population as well as by the Techa river residents can be improved for the most critical period between 1949 and 1954.     

Assessment of genome damage in occupational exposure to ionising radiation and ultrasound

The mutagenic effects of low doses of radiation on occupationally exposed subjects were studied on lymphocyte culture using two methods: analysis of structural chromosome aberrations and micronucleus assay. The results obtained in subjects exposed to ionising radiation alone were compared to those exposed to both ionising radiation and ultrasound. A correlation between the total number of chromosome aberrations and distribution of micronuclei in the genome of somatic cells show higher deviation in the group exposed to X-ray and ultrasound than in the group exposed to X-rays alone. The degree of genome damage in occupational exposure to X-rays and ultrasound were discussed.     

Radiation-induced taste aversion: effects of radiation exposure level and the exposure-taste interval

Radiation-induced taste aversion has been suggested to possibly play a role in the dietary difficulties observed in some radiotherapy patients. In rats, these aversions can still be formed even when the radiation exposure precedes the taste experience by several hours. This study was conducted to examine whether increasing the radiation exposure level could extend the range of the exposure-taste interval that would still support the formation of a taste aversion. Separate groups of rats received either a 100 or 300 R gamma-ray exposure followed 1, 3, 6, or 24 h later by a 10-min saccharin (0.1% w/v) presentation. A control group received a sham exposure followed 1 h later by a 10-min saccharin presentation. Twenty-four hours following the saccharin presentation all rats received a series of twelve 23-h two-bottle preference tests between saccharin and water. The results indicated that the duration of the exposure-taste interval plays an increasingly more important role in determining the initial extent of the aversion as the dose decreases. The course of recovery from taste aversion seems more affected by dose than by the temporal parameters of the conditioning trial.