Further assessment of the effects of occupational radiation exposure in the United Kingdom Atomic Energy Authority mortality study

The United Kingdom Atomic Energy Authority mortality study was designed to investigate the relation between exposure to ionising radiation and mortality among the Authority's employees. The study covered the years 1946 to 1979 during which time the frequency with which personal film dosimeters were issued changed from weekly to monthly, and the threshold level below which measurements were not made decreased 20-fold. Exposure from 'below threshold' readings made an important contribution to total exposure in the early years. Estimates, based on the remeasurement of a sample of old films, indicated that the average whole body exposure before 1961 may have been about double that which was measured. Furthermore, although records were kept of when dosimeters were lost or damaged, the associated exposures were unknown and could only be estimated. Workers whose dosimeter readings were missing for more than 5% of the time during which they were monitored had higher all cause mortality and higher mortality from accidents and violence than other radiation workers. The results of analyses of mortality in relation to whole body exposure were compared when (a) the exposures included estimates of the below threshold and missing exposures and (b) when these exposures were assumed to be zero. (author)