Design, Analysis and Interpretation of Long-Term Mortality Studies of Coke Oven Workers

Abstract

Summary This paper describes the design, analysis and interpretation of the long term mortality studies of coke oven workers conducted by the Department of Biostatistics in the Graduate School of Public Health, University of Pittsburgh. Problems related to the uncertainties associated with occupational exposure histories, industrial exposure measurements and their impact on risk estimates are discussed. Methodologies to combat these difficulties using ancillary risk factor information are suggested. The coke oven workers major cohorts consist of 1060 men employed at the coke ovens in 1953 in two major coke plants in Allegheny County, Pennsylvania and 1860 men who worked between 1951 and 1955 at the coke ovens in ten coke plants from other areas of the United States and Canada. The major comparison groups consist of 2065 men for the Allegheny County cohort and 3579 men for the Non-Allegheny County cohort, who worked in the corresponding steel plants during the same periods but never in coke oven jobs. The cohorts have been followed for mortality from 1953 through 1982. Cause-specific mortality rates within different subgroups based primarily on length of employment and type of jobs are evaluated for various phases of follow-up using summary statistics such as standardized mortality ratios and relative odds ratios. Major findings indicate a strong relationship for increased respiratory cancer risks associated with longer duration and proximity to the coke ovens and an increased risk of prostate cancer among coke oven workers. Dose-response relationships between lung cancer risks and a measure of coke oven emissions, the benzene soluble fraction of the total particulate matter, commonly known as coal tar pitch volatile (CTPV), are investigated using both regression and biologically motivated models. Results from the regression models indicate that measures of exposure rates, duration of exposure and time since exposure terminated are important predictors of cancer risks. Results from the fitting of multistage and two-mutation models indicate both initiation and promotional effects of coke oven effluent on lung cancer.