Chronic low level radiation and mortality: information from the UK national registry for radiation workers

Studies of radiation workers provide a direct means of assessing risks associated with chronic low dose radiation exposure. The National Registry for Radiation Workers (NRRW) is the largest epidemiological study of UK radiation workers. The first NRRW analysis was based on a cohort of about 95000 workers with a collective dose of about 3200 man Sv, followed up in most instances to the end of 1988. There was a clear healthy worker effect, mortality rates for major causes of death were lower than national values. Analyses of mortality in relation to external dose showed a statistically significant trend with dose in the risk of leukaemia (other than chronic lymphatic leukaemia). The confidence intervals for radiation risks estimated from this study are wide. However, the results from the NRRW and from other occupational studies are consistent with the risk estimates recommended by International Commission on Radiological Protection. Further analyses of the NRRW utilising a larger cohort with a longer follow-up, together with an on-going international collaborative study of radiation workers, will reduce uncertainties in estimates of cancer risks associated with low doses and low dose rates.