Abstract

Objectives: To estimate exposures to asbestos fibers of specific sizes among asbestos textile manufacturing workers exposed to chrysotile using data from transmission electron microscopy (TEM) and to evaluate the extent to which the risk of lung cancer varies with fiber length and diameter.

Methods: 3803 workers employed for at least 1 day between 1 January 1950 and 31 December 1973 in any of 3 plants in North Carolina, USA that produced asbestos textile products and followed for vital status through 31 December 2003 were included. Historical exposures to asbestos fibers were estimated from work histories and 3578 industrial hygiene measurements taken 1935-1986. Exposure-response relations for lung cancer were examined within the cohort using Poisson regression.

Results: Indicators of fiber length and diameter obtained by TEM were positively and significantly associated with increasing risk of lung cancer. Exposures to longer and thinner fibers tended to be most strongly associated with lung cancer, and models for these fibers fit the data best. Simultaneously modeling indicators of cumulative mean fiber length and diameter yielded a positive coefficient for fiber length and a negative one for fiber diameter.

Conclusions: The results support the hypothesis that the risk of lung cancer among workers exposed to chrysotile asbestos increases with exposure to longer fibers. More research is needed to improve the characterization of exposures by fiber size and number and to analyze the associated risks in a variety of industries and populations.