An epidemiologic study of the role of chrysotile asbestos fiber dimensions in determining respiratory disease risk in exposed workers

¹ University of Illinois at Chicago, School of Public Health, United States
² NIOSH, United States
³ Centers for Disease Control and Prevention, United States
⁴ Duke University Medical Center, United States

^* To whom correspondence should be addressed. E-mail: lstayner{at}uic.edu.

Accepted 14 December 2007

	Abstract

Background: Evidence from toxicologic studies indicates that the risk of respiratory diseases varies with asbestos fiber length and width. However, there is a total lack of epidemiologic evidence concerning this question.

Methods: Data were obtained from a cohort mortality study of 3072 workers from an asbestos textile plant which was recently updated for vital status through 2001. A previously developed job exposure matrix based on phase contrast microscopy (PCM) was modified to provide fiber size-specific exposure estimates using data from a reanalysis of samples by transmission electron microscopy (TEM). Cox proportional hazards models were fit using alternative exposure metrics for single and multiple combinations of fiber length and diameter.

Results: TEM-based cumulative exposure estimates were found to provide stronger predictions of asbestosis and lung cancer mortality than PCM-based estimates. Cumulative exposures based on individual fiber size-specific categories were all found to be highly statistically significant predictors of lung cancer and asbestosis. Both lung cancer and asbestosis were most strongly associated with exposure to thin fibers (< 0.25 ìm). Longer (> 10 ìm) fibers were found to be the strongest predictors of lung cancer, but an inconsistent pattern with fiber length was observed for asbestosis. Cumulative exposures were highly correlated across all fiber sizes categories in this cohort (0.28-0.99, p-values < 0.0001), which complicates the interpretation of the study findings.

Conclusions: Asbestos fiber dimension appears to be an important determinant of respiratory disease risk. Current PCM-based methods may underestimate asbestos exposures to the thinnest fibers, which were the strongest predictor of lung cancer or asbestosis mortality in this study. Additional studies are needed of other asbestos cohorts to further elucidate the role of fiber dimension and type.

Keywords: asbestos, asbestosis, chrysotile, dimension, lung cancer