Caldwell and Co-Workers Explained:
Mortality among Military Participants at the 1957 Plumbbob Nuclear Weapons Test Series and from Leukaemia among Participants at the Smoky Test.
Reference: Caldwell, G.G., Zack, M.M., Mumma, M.T., Falk, H., Heath, C.W., Till, J.E., Chen, H. and Boice, J.D. (2016) Mortality Among Military Participants at the 1957 Plumbbob Nuclear Weapons Test Series and from Leukaemia Among Participants at the Smoky Test, Journal of Radiological Protection, 36, pp. 474-489.
What were the research questions?
The U.S. conducted a series of 30 nuclear tests at the Nevada test site in 1957 codenamed Plumbbob which included a test codenamed Smoky. Studies published in 1979 indicated that military veterans of the Smoky test had elevated levels of leukaemia. This raised concerns as to whether there had been similar health effects for those who participated in the other Plumbbob tests.
The research team who performed this study wanted to know if participation in these nuclear tests increased the risk of leukaemia and/or reduced life expectancy. They also investigated whether these health effects were related to the radiation dose. To achieve this aim, the authors reassessed the doses that had been assigned to these veterans in previous studies.
How was the scientific problem approached?
The authors estimated new doses for the veterans using a process called reconstruction, which combines film-badge data with knowledge of the circumstances in which exposure occurred. The research team was assisted by digital records that were released by the U.S. Department of Defence which give details of the duties and activities of each veteran.
The research team used state and federal records to obtain mortality and leukaemia data for the Plumbbob veterans. The researchers could then assess whether there were any relationships between the doses received and health outcomes.
What did the research involve?
The researchers sought to recruit all of the Plumbbob veterans using a database called NuTRIS (nuclear test review information system). The scientists found 95% of the participants using their personal details such as name, date of birth, U.S. social security number and service identification number.
Then the authors checked whether each veteran was alive or dead on the 31st December 2010 through the U.S. Social Security Administration Service and the Department of Veterans’ Affairs. They found the cause of death in 97% of cases using the U.S. National Death Index and other official records.
Bone marrow doses were estimated using reconstruction based on film badge and service record data. If this information was insufficient, then the researchers used the rank and unit for a given veteran to infer their probable exposure. For example, members of helicopter and other transport units were more likely than other veterans to be exposed.
Dose reconstructions were performed for 1% of the participants of the Plumbbob tests series and for all cases of leukaemia, except chronic lymphatic leukaemia which is not thought to be caused by ionising radiation.
What did they find?
Overall, the Plumbbob veterans were found to live longer than the American public. However, the veterans who took part in the Smoky test had a higher mortality compared to the general population and were found to have higher recorded level of leukaemia deaths.
With regards to the new reconstructed doses, these estimates were generally low, e.g. 71% of Smoky participants received doses below 5 mGy and only 5% of Plumbbob participants received doses greater than 50 mGy.
How did the researchers interpret their results?
The researchers suggested that the longer life expectancy of the Plumbbob veterans was a consequence of them receiving mostly low doses and the healthy soldier effect. This means that people who have served in the military are likely to have better health than the public. This is because military personnel are generally fitter than the general public at enlistment, are required to maintain a certain standard of fitness during service and have better access to medical care during and after service.
The researchers could not explain why the Smoky veterans had a lower life expectancy and a higher rate of leukaemia. They found no relationship between the estimated doses and the leukaemia deaths which led them to discount ionising radiation as the cause of this. The authors suggested that the excess leukaemia cases may be due to a high proportion of the Smoky veterans being smokers, however, further research is required to prove this.
Who did this research?
This research was performed by a team of researchers from the University of Kentucky, the U.S. National Centre for Chronic Disease Prevention and Health Promotion, the International Epidemiology Institute, the U.S. Centres for Disease Control, the Risk Assessment Corporation (a private company) and Vanderbilt University. The research was funded by the U.S. National Cancer Institute, the U.S. Department of Energy and the Vanderbilt-Ingram Cancer Centre.
Most U.S. veterans of the Plumbbob series of tests including the Smoky test have been found to have received low doses of radiation (< 20 mGy), though 5% of participants received doses > 50 mGy.
The Plumbbob veterans lived longer than members of the U.S. general public.
The Smoky veterans had higher mortality and higher levels of leukaemia than the U.S. general public.
The trends for the Smoky veterans were not related to the radiation dose received and the reason for this is not known.
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