Plutonium production and particles incorporation into the human body.

Plutonium is one of the most toxic radioactive substances known. The isotope 239Pu gained attention when it had become known as a potential explosive material for atomic bombs. This paper describes the main problems encountered during the early years of operation of the first plutonium production plant in the former Soviet Union, the Mayak Production Association (Mayak PA). Mayak PA caused severe radioactive contamination of the environment and exposure personnel and population living in the vicinity areas to high radiation doses. The authors focus on key findings of large-scale studies on the internal dosimetry of workers for use in assessment of radiological risks from exposure to plutonium. This work presents an overview of the important issues for inhalation dose assessments such as generation of plutonium particles, plutonium intake, dissolution of plutonium particles, distribution of plutonium in humans, related exposures and health effects. Understanding the relationship between health effects, radiation dose and route of exposure helps quantify the health risks associated with occupational exposure in the nuclear industry and validate the radiation protection standards used in the Russian Federation and worldwide.

Comparison of dose estimation from occupational exposure to 239Pu using different modelling approaches.

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.

Mayak worker dosimetry study: an overview.

The Mayak Production Association (MPA) was the first plutonium production plant in the former Soviet Union. Workers at the MPA were exposed to relatively large internal radiation intakes and external radiation exposures, particularly in the early years of plant operations. This paper describes the updated dosimetry database, "Doses-2005." Doses-2005 represents a significant improvement in the determination of absorbed organ dose from external radiation and plutonium intake for the original cohort of 18,831 Mayak workers. The methods of dose reconstruction of absorbed organ doses from external radiation uses: 1) archive records of measured dose and worker exposure history, 2) measured energy and directional response characteristics of historical Mayak film dosimeters, and 3) calculated dose conversion factors for Mayak Study-defined exposure scenarios using Monte Carlo techniques. The methods of dose reconstruction for plutonium intake uses two revised models developed from empirical data derived from bioassay and autopsy cases and/or updates from prevailing or emerging International Commission on Radiological Protection models. Other sources of potential significant exposure to workers such as medical diagnostic x-rays, ambient onsite external radiation, neutron radiation, intake of airborne effluent, and intake of nuclides other than plutonium were evaluated to determine their impact on the dose estimates.

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.

Discussion of 241Am role as the factor of internal radiation exposure in Mayak PA workers.

Radiation monitoring with whole body counter (WBC) has a series of advantages, as this technique is efficient and is considerably cheaper than indirect urine bioassay method. Experience of WBC operation in the system of Mayak PA worker internal radiation monitoring as well as qualitative analysis of the obtained results is considered. The groups of workers under study are described, and a brief analysis of data obtained in comparison with individual exposure parameters is presented. The number of individuals with 241Am is higher among the workers employed in the early years of Mayak PA operation. Fraction of 241Am in total body burden relative to sum of actinides is higher for workers who started to work in conditions of exposure in the last decade (1990-2000) and sometimes is as high as 25%.