Vermiculite Exposure - Longitudinal Study

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Abstract Online:

http://ajrccm.atsjournals.org/cgi/content/abstract/177/6/630?etoc

American Journal of Respiratory and Critical Care Medicine Vol 177.

pp. 630-637, (2008)

March 15, 2008

© 2008 American Thoracic Society

doi: 10.1164/rccm.200706-841OC

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Original Article

Low-Level Fiber-induced Radiographic Changes Caused by Libby

Vermiculite; A 25-Year Follow-up Study

Amy M. Rohs 1, E. Lockey 1, Kari K. Dunning 2, Rakesh Shukla

3, Huihao Fan 3, Tim Hilbert 3, Borton 3, Jerome Wiot 4,

Cristopher Meyer 4, Ralph T. Shipley 4, Grace K. LeMasters 3 and

Vikas Kapil 5

1 Departments of Environmental Health and Internal Medicine, 2

Department of Rehabilitation Sciences, and 3 Department of

Environmental Health, University of Cincinnati College of Medicine,

Cincinnati, Ohio;

4 Department of Radiology and Diagnostic Imaging, University of

Cincinnati Hospital, Cincinnati, Ohio; and 5 Agency for Toxic

Substances and Disease Registry, Centers for Disease Control and

Prevention, Atlanta, Georgia

Correspondence and requests for reprints should be addressed to

Lockey, M.D., M.S., Departments of Environmental Health and

Internal Medicine (Pulmonary Division), University of Cincinnati

College of Medicine, 3223 Eden Avenue, ML 0056, Cincinnati, OH

45267. E-mail: james.lockey@...

Rationale: From 1921 to 1990, vermiculite ore from Libby, Montana,

was shipped worldwide for commercial and residential use. A 1980

study of a manufacturing facility using Libby vermiculite was the

first to demonstrate a small but significant prevalence of pleural

chest radiographic changes associated with amphibole fibers

contained in the ore.

Objectives: This follow-up study of the original cohort evaluated

the extent of radiographic changes and cumulative fiber exposure

(CFE) 25 years after cessation of exposure.

Methods: From the original cohort of 513 workers, 431 (84%) were

living and available for participation and exposure reconstruction.

Of these, 280 (65%) completed both chest radiographs and interviews.

Primary outcomes were pleural and/or interstitial changes.

Measurements and Main Results: Pleural and interstitial changes were

demonstrated in 80 (28.7%) and 8 (2.9%) participants, respectively.

Of those participants with low lifetime CFE of less than 2.21

fiber/cc-years, 42 (20%) had pleural changes. A significant (P <

0.001) exposure–response relationship of pleural changes with CFE

was demonstrated, ranging from 7.1 to 54.3% from the lowest to

highest exposure quartile. Removal of individuals with commercial

asbestos exposure did not alter this trend.

Conclusions: This study indicates that exposure within an industrial

process to Libby vermiculite ore is associated with pleural

thickening at low lifetime CFE levels. The propensity of the Libby

amphibole fibers to dramatically increase the prevalence of pleural

changes 25 years after cessation of exposure at low CFE levels is a

concern in view of the wide national distribution of this ore for

commercial and residential use.

Key Words: vermiculite • pleural disease • amphiboles • fibrosis •

mineral fiber