The study cohort comprised 2,542 white males employed for at least 30 days from 1942 through plant shutdown in 1966. Excluded were 556 females, 43 nonwhite males, as well as those employed for less than 30 days or having "critical errors" in their data. Follow-up was through the end of 1988. The total person-years of follow-up was 79,600 with a median of 27.3 years. A typical worker was first employed in 1951 at 30 years of age and worked just over five and one-half years. The all causes SMR was 0.94 with 95% confidence interval 0.87 to 1.00. The elevation in the all cancers SMR of 1.13 (0.99 to 1.28) resulted from increases in a variety of cancers, particularly in those of the digestive and respiratory systems and prostate and brain cancer.
The single analytic file (ELL2542) contains a record, which includes vital status as of January 1, 1989, for each members of the cohort. The last Social Security Administration (SSA) submission for this population provided "alive" status as of January 1, 1985; the " alive" category is no longer obtainable from SSA. However, the National Death Index (NDI) provides a record of all deaths occurring since January 1, 1979, and Pension Benefit Information Incorporated (PBI) also identifies deceeased individuals. If not identified as deceased by SSA, NDI, or PBI, individuals last known to be alive before 1/1/79 were considered lost to follow- up on the last date known alive while those known to be alive after 1/1/79 were considered alive at the end of the study. There were 837 deaths from all causes with death certificates available for 98.2% of these individuals.
MCW was one of the oldest and largest uranium processing facilities in the U.S., operating in St. Louis from 1942 to 1958 and in Weldon Springs from 1958 through 1966. From 1946 through 1955 pitchblend ore was used in the processing of uranium dioxide and uranium metal. This ore was a dry solid which dusted easily and was up to 60% pure uranium, resulting in exposure levels that may have been nearly 200 times the contemporary maximum permissible concentration. Most of the uranium compounds present were relatively insoluble. Potential exposures included gamma (from radium), beta, and alpha radiation, thorium, and chemicals including nitric and hydrofluoric acids. Each employee had a pre-employment and annual physical exam, with abnormal findings leading to a transfer to another division of MCW. Transferred workers remain in this study cohort with follow-up through 1988.