Mutant frequencies in workers at the Sellafield installation.

The frequency of hypoxanthine-guanine phosphoribosyltransferase (hprt) mutations has been determined in the peripheral T-lymphocytes of 18 workers at the Sellafield nuclear reprocessing installation with cumulative recorded radiation doses of about 500 mSv or more in comparison with a matched control group of 18 workers with doses less than 50 mSv. The mean dose of the exposed group was 663 mSv (range 449.3-880.8), and of the unexposed group 10.9 mSv (range 0-46.5). During the most recent 6 y the mean doses were 40.1 mSv (range 1.9-93.9) and 2.3 mSv (range 0-8.7), respectively. The logarithmic mean mutant frequency of the exposed group (9.3 x 10(-6)) was lower than that of the unexposed group (12.4 x 10(-6)). The apparent inverse association of mutant frequency and exposure varied in statistical significance tests from borderline to p < 0.01 depending on how the analysis was performed and whether recent or total exposure was considered.