ANS National
 Meetings/
 Sessions

November 1994

Roger J. Berry

Keith Binks

E. Janet Tawn

Paul Daniel

Andrej Slovak

(Westlakes Research Inst-UK)

7.Biological Markers, Morbidity, and Mortality in a Long-Serving Radiation Worker Population

               " The Sellafield plant, now operated by British Nuclear Fuels plc and comprising the Windscale and Calder Works, began operations early in the 1950s with two air-cooled nuclear reactors and a fuel reprocessing plant for the production of plutonium for defense purposes. The first electrical power generating gas-cooled nuclear reactors (Calder Hall) started operation in 1956; the civil nuclear program developed subsequently and continues, much enlarged, to the present. On October 10, 1957, one of the two air-cooled Windscale military piles caught fire, and this resulted in the permanent shutdown of both piles. Over the 40+ yr of operations on the Sellafield site, some 16000 persons have been employed on the nuclear reactors and processing plants, amassing a collective occupational radiation dose of ~1400 person-Sv. Large-scale studies of U.K. nuclear industry workers such as the Nuclear Industry Combined Epidemiological Analysis (NICEA) and the analysis by the U.K. National Radiological Protection Board (NRPB) of the data held on the National Registry for Radiation Workers are under way, but the vast majority of individuals in those studies will have accumulated occupational radiation doses no greater than the range of variation in natural background radiation exposure in the United Kingdom. We report here a study of stable chromosome aberrations inperipheral blood lymphocytes, flow cytometric studies of single-gene mutation, and a further 5- to 10-yr follow up since last publication of morbidity and mortality data in a cohort of 542 male workers, who had accumulated individual doses in excess of 500 mSv and up to ~2 Sv by the end of 1983, and an overlapping cohort of 470 workers who were involved in fighting the Windscale pile fire in 1957 or in subsequent cleanup operations, having a collective occupational radiation dose of ~180 person-Sv.

                "A clear correlation was seen between recorded cumulative external radiation dose and the incidence in peripheral blood lymphocyte chromosomes of translocations scored by banding, but as expected, no correlation was seen between total dose and the incidence of unstable aberrations such as dicentrics, rings, and acentric fragments. Preliminary data will be reported using fluorescence insitu hybridization (FISH) to visualize exchanges. A poor correlation was seen between the incidence of stable aberations in peripheral blood lymphocytes and body burden of plutonium, but this appears to be due to a perverse relationship between the plutonium body burden in individuals and their cumulative external radiation exposure. By contrast, preliminary studies using flow cytometric assay for glycophorin-A mutation on erythrocytes have shown poor correlation with recorded cumulative external radiation dose, although this mutation has been reported to correlate with acute radiation exposure received over 40 years ago in Hiroshima and Nagasaki A-bomb survivors.

                "In the >500-mSv cohort, overall mortality to date is not significantly different from the U.K. national average, corrected for age, sex, and social class, and the slight excess of observed over expected deaths is due not to cancer but to diseases of the circulatory system. There is actually a slight deficit overall against expectation to date of deaths from malignant disease, due in part to a large deficit against expectation of lung cancer deaths. However there is a non-significant increase against expectation in cancer deaths from haemopoietic and lymphatic tissues and a statistically significant excess of one death-the only death-from buccal cavity and pharynx cancer in a known lifelong pipe smoker. Comparable data for the Windscale fire cohort show asimilar deficit of cancer deaths against expectation.

                "Up-to-date cancer incidence data for these cohorts are reviewed and continue to show rates below those expected in the general population. Thus, in a population of workers exposed during their occupation over many years to radiation doses that would be considered unacceptable today and studied as a 'bellwether' for predicting risks to current workers, there is evidence at a cellular level of their having received that exposure, but as yet no evidence of unpredicted harm."