Non-cancer mortality among workers at British Nuclear Fuels - A study by Westlakes Scientific Consulting

The study [1] is based on a cohort of nearly 65,000 people who had been employed by BNFL or related organisations at three sites in north-west England and one site in south-west Scotland during 1946-2002. Information on external radiation exposure, usually measured with film badges, was available for about 42,000 of these workers. Some of the BNFL radiation workers – mostly those who had not additionally been monitored for possible internal radiation exposure - had been included in a previous analysis of non-cancer mortality among radiation workers from 15 countries [2] . Since the BNFL workers excluded from the 15-country analysis tended to have higher external radiation doses than BNFL workers who were included in that analysis, and because of the longer period of follow-up, the new study has higher statistical power than the 15-country analysis to look for any trend in mortality with external dose. A forthcoming analysis of the HPA-operated National Registry for Radiation Workers - based on over 170,000 UK radiation workers, including virtually all of the BNFL radiation workers - will have even more statistical power.

BNFL workers had lower rates of mortality from various non-cancer diseases, compared to the general population of north-west England , irrespective of whether or not they had been radiation workers. This “healthy worker effect” has been seen in many studies of occupational groups – not solely in the nuclear industry – and is likely to reflect the recruitment and continued employment of relatively healthy people, as well as socio-economic differences in mortality [3] . Within the group of BNFL radiation workers, mortality from all circulatory diseases combined increased to a statistically significant extent with increasing external radiation dose. This statistical association was particularly strong for ischemic heart disease. The evidence for an association varied according to whether or not workers had additionally been monitored for internal radiation exposure, and also differed between workers classified as “industrial” and those who were “non-industrial”.

The mean cumulative external radiation dose for BNFL workers in this study was 53 mSv (millisieverts). The distribution of doses was wide and some workers had cumulative doses of several hundred mSv. By way of comparison, the annual average dose to the UK population is 2.7 mSv, most of which is due to natural and medical radiation [4] . At BNFL and elsewhere in the nuclear industry, average annual doses to radiation workers have declined markedly in recent decades [4].

If the findings for non-cancer diseases among the Japanese atomic bomb survivors exposed to high doses could be extrapolated in a linear fashion down to low doses, then this would imply that the risk of circulatory diseases might be increased by about 1 or 2 % following a dose of 100 mSv and by lower amounts at lower doses. The findings from the BNFL worker study – if extrapolated in a similar way - would suggest that the risk of circulatory diseases might be increased by around 4 to 10 % following a dose of 100 mSv. However, much of the evidence for a raised risk in this study relates to workers exposed at higher doses, of the order of several hundred mSv.

Interpretation of the findings is limited by the lack of information on known risk factors for circulatory diseases, such as smoking habits, alcohol consumption and diet. Attempts to examine these factors and the possible role of occupational factors such as shiftwork would be valuable. Attention should also be given to information that will arise from new and ongoing research initiatives, including the National Registry for Radiation Workers and:

• An analysis of circulatory disease risk among workers at the Mayak nuclear plant in Russia , for which information has been collected on factors such as smoking and alcohol. This is being conducted under the SOUL project [5] , with support from the European Commission's Radiation Protection research programme.
• Research supported by the European Commission into the pathogenesis of radiation-induced heart disease, conducted under a new project called Cardiorisk, and into understanding whether low radiation doses may cause non-cancer diseases, conducted under the NOTE project [6].
• A review of radiation exposure and circulatory disease risk, which will commence soon under the auspices of a sub-group of HPA's independent Advisory Group on Ionising Radiation.

HPA will continue to monitor findings from studies of circulatory disease risk and radiation exposure and advise on the possible implications for radiation protection.

1.  McGeoghegan D et al. The non-cancer mortality experience of male workers at British Nuclear Fuels plc, 1946-2005. International Journal of Epidemiology (2008). Available at http://ije.oxfordjournals.org/cgi/content/abstract/dyn018v1

2.   Vrijheid M et al. Mortality from diseases other than cancer following low doses of ionizing radiation: results from the 15-country study of nuclear industry workers. International Journal of Epidemiology;36:, 1126-35 (2007).

3.   Baillargeon J. Characteristics of the healthy worker effect. Occupational Medicine;16:, 359-366 (2001).

4.   Watson SJ et al. Ionising radiation exposure of the UK population: 2005 review. Chilton, HPA-RPD-001 (2005).

5. SOUL. Southern Urals Radiation Risk Research. http://www.gsf.de/soul

6. NOTE. Non-targeted effects of ionising radiation. http://www.note-ip.org/

Last reviewed: 23 July 2009