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Vermiculite Worker Mortality: Estimated Effects of Occupational Exposure to Libby Amphibole

Larson, Theodore C. MS; Antao, Vinicius C. MD, MSc, PhD; Bove, Frank J. ScD

Journal of Occupational and Environmental Medicine: May 2010 - Volume 52 - Issue 5 - p 555-560
doi: 10.1097/JOM.0b013e3181dc6d45
Original Articles

Objective: To examine the relationship between cumulative fiber exposure (CFE) and mortality in a retrospective cohort study of vermiculite workers exposed to Libby amphibole (n = 1862).

Methods: Extended Cox regression was used to estimate the hazards associated with CFE as a time-dependent covariate of multiple-cause mortality.

Results: The Cox models for mesothelioma, asbestosis, lung cancer, and non-malignant respiratory disease were significant with rate ratios that increased monotonically with CFE. The model for deaths due to cardiovascular disease was also significant (rate ratio for CFE ≥44.0 f/cc-y vs <1.4 f/cc-y was 1.5; 95% confidence interval = 1.1 to 2.0).

Conclusions: By using a within-cohort comparison, the results demonstrate a clear exposure-response relationship between CFE and mortality from asbestos-related causes. The finding of an association between CFE and cardiovascular mortality suggests persons exposed to Libby amphibole should be monitored for this outcome.

From the Division of Health Studies, Agency for Toxic Substances and Disease Registry, Atlanta, Ga.

Address correspondence to: Theodore Larson, DHS/ATSDR, 4770 Buford Highway NE, MS F57, Atlanta, GA 30341; E-mail:

©2010The American College of Occupational and Environmental Medicine