A Bayesian analysis of plutonium exposures in Sellafield workers.

The joint Russian (Mayak Production Association) and British (Sellafield) plutonium worker epidemiological analysis, undertaken as part of the European Union Framework Programme 7 (FP7) SOLO project, aims to investigate potential associations between cancer incidence and occupational exposures to plutonium using estimates of organ/tissue doses. The dose reconstruction protocol derived for the study makes best use of the most recent biokinetic models derived by the International Commission on Radiological Protection (ICRP) including a recent update to the human respiratory tract model (HRTM). This protocol was used to derive the final point estimates of absorbed doses for the study. Although uncertainties on the dose estimates were not included in the final epidemiological analysis, a separate Bayesian analysis has been performed for each of the 11 808 Sellafield plutonium workers included in the study in order to assess: A. The reliability of the point estimates provided to the epidemiologists and B. The magnitude of the uncertainty on dose estimates. This analysis, which accounts for uncertainties in biokinetic model parameters, intakes and measurement uncertainties, is described in the present paper. The results show that there is excellent agreement between the point estimates of dose and posterior mean values of dose. However, it is also evident that there are significant uncertainties associated with these dose estimates: the geometric range of the 97.5%:2.5% posterior values are a factor of 100 for lung dose, 30 for doses to liver and red bone marrow, and 40 for intakes: these uncertainties are not reflected in estimates of risk when point doses are used to assess them. It is also shown that better estimates of certain key HRTM absorption parameters could significantly reduce the uncertainties on lung dose in future studies.

Worldwide bioassay data resources for plutonium/americium internal dosimetry studies.

Biokinetic models are the scientific underpinning of internal dosimetry and depend, ultimately, for their scientific validation on comparisons with human bioassay data. Three significant plutonium/americium bioassay databases, known to the authors, are described: (1) Sellafield, (2) Los Alamos and (3) the United States Transuranium Registry. A case is made for a uniform standard for database format, and the XML standard is discussed.

Mortality and cancer morbidity experience of female workers at the British Nuclear Fuels Sellafield plant, 1946-1998.

BACKGROUND: Studies of nuclear workers have focused mainly on the experience of male workers. To date, little has been published specifically on the experience of female workers in the nuclear industry. METHODS: We report on the mortality, cancer morbidity, and tracing experience of the 6,376 females ever employed at the British Nuclear Fuels Ltd. plant at Sellafield to the end of 1998. These workers have accumulated 142,337 person-years of experience. RESULTS: Radiation workers were exposed to low doses of radiation. No statistically significant associations were noted between mortality or cancer morbidity and cumulative assessed organ-specific internal plutonium dose or cumulative external whole body radiation dose overall, or for any of the individual disease groupings examined. The power of the study was insufficient to detect the risks indicated in other radiation studies. CONCLUSION: This study offers reassurance that there is no detrimental effect on the health of the female workers from occupational exposures at Sellafield. Am. J. Ind. Med. 44:653-663, 2003.

The assessment of organ doses from plutonium for an epidemiological study of the Sellafield workforce.

An epidemiological study of mortality and cancer rates in plutonium workers at the Sellafield nuclear installation has been carried out by researchers at the London School of Hygiene and Tropical Medicine. The study required the assessment of organ-specific doses from plutonium for more than 5000 workers over a period of 40 years. This was a major undertaking as it involved the reconstruction of annual received doses from the results of some 223,000 urine samples that had been provided by the workers in the study. This paper outlines the techniques and strategies adopted in order to generate best estimates of dose from the available data, and presents summaries of these doses.

Chromosome aberrations in radiation workers with internal deposits of plutonium.

Chromosome analysis of G-banded peripheral blood lymphocytes was performed on two groups of plutonium workers with 20-50% and >50% maximum permissible body burdens (MPBB) of plutonium from the British Nuclear Fuels plc (BNFL) facility at Sellafield, UK, 10 years after an earlier study had reported increases in both symmetrical and asymmetrical aberrations. For each plutonium exposure group there was a significant difference in frequencies of symmetrical aberrations between plutonium workers, workers with similar histories of exposure to mainly external gamma radiation but with little or no intakes of plutonium, and controls with negligible exposure (<50 mSv). In contrast, no significant differences for asymmetrical aberrations were found, and since these are short-lived, this suggests that recent exposure of mature lymphocytes was minimal. Frequencies of symmetrical aberrations had increased significantly since the earlier sampling time. Additional external radiation exposure was negligible in the plutonium worker groups over this period. These results are consistent with the hypothesis that hemopoietic precursor cells are being irradiated by internally deposited plutonium with subsequent selection resulting in only cells with symmetrical aberrations reaching the peripheral lymphocyte pool. After removal of aberrations involving only chromosomes 7 and/or 14, which are thought to arise in vivo during immunological development, the breakpoints involved in the aberrations were distributed randomly among the chromosomes according to length in all three groups of workers. Within the chromosomes the distribution between terminal, interstitial and centromeric regions for the plutonium workers did not conform to that expected, there being an excess in the terminal regions and a deficit in the interstitial regions.