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Exposure Estimates for Workers in a Facility Expanding Libby Vermiculite: Updated Values and Comparison With Original 1980 Values

Borton, Eric K. MS; LeMasters, Grace K. PhD; Hilbert, Timothy J. MS; Lockey, James E. MD, MS; Dunning, Kari K. PhD; Rice, Carol H. PhD


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Journal of Occupational and Environmental Medicine. 55(1):110, January 2013.

Journal of Occupational and Environmental Medicine: November 2012 - Volume 54 - Issue 11 - p 1350–1358
doi: 10.1097/JOM.0b013e31824fe174
Original Articles

Objective: Low cumulative fiber exposure (CFE) has been associated with health effects in a cohort exposed to Libby vermiculite. This study refines the original 1980 exposure estimates and compares the CFE results.

Methods: Cumulative fiber exposure estimates were developed using three times more industrial hygiene measurements and long-term workers' input. New adjustments included vermiculite ore source, seasonal overtime hours, time spent in various tasks, and recollection of historical dustiness.

Results: The overall mean (95% confidence interval) CFE (n = 513) in 1980 (0.80 [0.69 to 0.93]) was statistically similar to the overall mean (95% confidence interval) CFE in 2010 (0.74 [0.61 to 0.90]). The mean CFE in the lowest exposure category (<2 fiber-years/cm3) decreased from 0.36 to 0.22 fiber-years/cm3 (P < 0.05). The 2010 CFE estimate extended the upper bound of the range of previous estimates from 28.10 to 106.31 fiber-years/cm3.

Conclusions: The range of CFE values was expanded. These estimates may impact the understanding of Libby vermiculite health outcomes.

From the Departments of Environmental Health (Mr Borton, Drs LeMasters, Lockey, Dunning, and Rice, and Mr Hilbert) and Internal Medicine (Pulmonary Division) (Dr Lockey), University of Cincinnati College of Medicine, Cincinnati, Ohio.

This study was funded by the US Environmental Protection Agency (EPA) Region 8 as part of the management of the Libby Asbestos Superfund Site.

All authors have been partially funded by a grant from US EPA Region 8. Dr Lockey served as a fact and state-of-the-art witness for the US Department of Justice for the District of Montana, Missoula Division, in the case of United States of America vs WR Grace et al.

Address correspondence to: Carol H. Rice, PhD, Department of Environmental Health, University of Cincinnati College of Medicine, 3223 Eden Ave, ML 0056, Cincinnati, OH 45267 (

©2012The American College of Occupational and Environmental Medicine