The results of the study, available online, will be published in the June edition of the Journal of Occupational and Environmental Medicine.
In May 2000, the Connecticut Department of Public Health (CTDPH) began an investigation of a reported increase in brain cancer at the North Haven facility and identified several cases of glioblastoma (GB), the most common form of brain cancer. A preliminary comparative cancer incidence analysis was inconclusive, and the CTDPH recommended Pratt & Whitney hire an independent research group to conduct a comprehensive study.
In July 2002, Gary Marsh, Ph.D., director of the Center for Occupational Biostatistics and Epidemiology, Pitt Public Health, and Nurtan Esmen, Ph.D., Division of Environmental and Occupational Health Sciences, University of Illinois at Chicago (UIC), began work on a large, multi-part investigation to determine whether mortality from or the incidence of central nervous system (CNS) neoplasms, or tumors, including GB, were elevated among workers at the North Haven plant or seven other Pratt & Whitney facilities serving as comparison sites, and whether those rates were associated with specific workplace exposures.
“Pitt Public Health and UIC researchers analyzed the records of almost a quarter million subjects over a 53-year period, making it one of the largest and most comprehensive cohort studies in an occupational setting,” said Dr. Marsh. “It also is the first large-scale study of workers in the jet engine manufacturing industry.”
Pitt epidemiologists and biostaticians studied the employment records and death certificates of more than 223,000 Pratt & Whitney workers employed during a period stretching from 1952 to 2001. Researchers identified 723 workers diagnosed with CNS neoplasms during 1976 to 2004. Those tumors were malignant, benign or unspecified, and included 277 GB cases. Researchers interviewed workers or available family members to gain more detailed information on behavioral and personal lifestyle factors. Low participation rates precluded analysis of this data, but the Pittsburgh case-control study provided the basis for a more refined assessment of workplace exposures.
The UIC exposure assessment considered 11 chemical or physical agents on the basis of known or suspected carcinogenic potential that could affect the central nervous system or other organs. UIC generated quantitative exposure estimates for soluble and mineral oil metalworking fluids, nickel, cobalt, chromium, solvents and a combustion aerosol generated during high-speed and high-temperature grinding that was unique to the North Haven plant. Researchers assigned qualitative exposures for ionizing radiation, electromagnetic fields, polychlorinated biphenyls and lead-cadmium. Exposure to one or more of 20 jet engine part families and 16 process categories created for the study also was assigned.
The UIC quantitative estimates showed workers had decreasing exposures to these chemicals over the course of the study period; in addition, the quantitative exposure levels were similar to or lower than those in published data from other industries.
At the conclusion of the study, researchers found no statistically significant increase in overall CNS neoplasm rates among the Pratt & Whitney workforce as compared with the corresponding rates in the general populations of the U.S. and Connecticut. Comparisons among the five Pratt & Whitney plant groups revealed a slightly higher incidence of CNS neoplasms and GB among workers at the North Haven plant; however, further evaluation found no association with estimated workplace exposures.
“If not due to chance alone, the slightly elevated GB rates at the North Haven plant may reflect external occupational factors that we did not measure, or other factors unique to North Haven or the baseline plant used in the internal comparisons,” said Dr. Marsh.
During an overall evaluation of mortality rates from all causes of death, Pittsburgh and UIC researchers noted elevated chronic obstructive pulmonary disease (COPD)-related mortality rates in two of five plant groups studied, but found no association with the occupational factors examined in the study. Researchers could not rule out exposures workers received outside of the workplace, or other risk factors, such as smoking, as reasons for the observed COPD excesses.
Additional co-authors of this study include Ada O. Youk, Ph.D., Jeanine Buchanich, Ph.D., and Sarah Downing, B.S., Department of Biostatistics, Pitt Public Health; Kathleen J. Kennedy, M.S., and Roger P. Hancock, M.C.E., UIC Division of Environmental and Occupational Health Sciences; Steven E. Lacey, Ph.D., Department of Public Health, Indiana School of Medicine, Indianapolis; Jennifer S. Pierce, Ph.D., ChemRisk, LLC, Chicago; Mary Lou Fleissner, Dr.P.H., formerly with the CTDPH Division of Environmental Epidemiology and Occupational Health, Hartford.
The University of Pittsburgh and the University of Illinois at Chicago received funding from Pratt & Whitney for this research, but the design, conduct, analysis and conclusions are those of the authors.