Historical estimation of diesel exhaust exposure in a cohort study of railroad workers and lung cancer.
Laden-F; Eschenroeder-A; Smith-TJ; Gagnon-D; Jackson-SL; Dockery-DW; Speizer-FE; Garshick-E
Am J Respir Crit Care Med 2001 Apr; 163(5)(2)(Suppl):A717
Rationale: Although 95% of the locomotives in service in the US railroad industry were diesel by 1959, individual railroads transitioned from steam to diesel at different rates from 1945 to 1959. We hypothesize that accounting for these differences when modeling exposure will help characterize lung cancer risk attributable to diesel exhaust exposure in a cohort of 55,407 workers employed during this period and followed through 1996. Methods: We estimated the percent of diesel locomotives for each for the 95 largest railroads (93% of the cohort) using roster information and manufacturing data, and accounted for locomotive model using EPA emission factors and builder data. The railroad-specific diesel locomotive fraction for a given year was calculated, representing the probability of exposure in a specific year. Cumulative exposure (pre-1959) was defined for engineers/firemen and conductors/brakemen as the sum of the diesel fraction from 1945 to 1959. Results: The median diesel fraction was 8% in 1945 and 72% in 1952, the midpoint of the transition period. Rates of change from 25 to 75% diesel ranged from 1 to 12 years. The median adjusted cumulative exposure was 9.6 years (interquartile range 8.6-10.3). In analyses comparing each quartile of exposure with unexposed, the relative risks (RR) for the first three quartiles were all approximately 1.30, similar to the RR when exposure was modeled as a dichotomous variable (1.34). The RR for the fourth quartile was 1.43 (CI: 1.30-1.59). Conclusion: There was little variation in cumulative probability of pre-1959 exposure to diesel exhaust. Therefore, adjustment for railroad-specific rates of dieselization had little effect on lung cancer associations.
Respiratory-system-disorders; Lung-cancer; Lung-disorders; Diesel-emissions; Diesel-engines; Diesel-exhausts; Cancer; Carcinogens; Mortality-data; Mortality-rates; Railroad-industry; Exhaust-gases
Work Environment and Workforce: Mixed Exposures
American Journal of Respiratory and Critical Care Medicine. Abstracts of the American Thoracic Society 2001 International Conference, May 18-23, 2001, San Francisco, California
Harvard Medical School, Boston, Massachusetts