Low-level fiber-induced radiographic changes caused by Libby vermiculite: a 25-year follow-up study.
BACKGROUND
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.


OBJECTIVE
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.


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.
Department of Environmental Health, University of Cincinnati College of Medicine, 3223 Eden Avenue, ML 0056, Cincinnati, OH 45267, USA.
Amy M
AM
Rohs
James E
JE
Lockey
Kari K
KK
Dunning
Rakesh
R
Shukla
Huihao
H
Fan
Tim
T
Hilbert
Eric
E
Borton
Jerome
J
Wiot
Cristopher
C
Meyer
Ralph T
RT
Shipley
Grace K
GK
Lemasters
Vikas
V
Kapil
D000368:Aged; D000538:Aluminum Silicates / Q000009:adverse effects*; D017636:Asbestos, Amphibole / Q000009:adverse effects*; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D006306:Health Surveys; D006801:Humans; D017563:Lung Diseases, Interstitial / Q000000981:diagnostic imaging* / Q000453:epidemiology / Q000209:etiology; D008297:Male; D008875:Middle Aged; D019016:Mineral Fibers / Q000009:adverse effects; D008906:Mining; D009009:Montana / Q000453:epidemiology; D009784:Occupational Diseases / Q000000981:diagnostic imaging* / Q000453:epidemiology; D016273:Occupational Exposure / Q000009:adverse effects*; D015995:Prevalence; D011859:Radiography
D000538:Aluminum Silicates; D017636:Asbestos, Amphibole; D019016:Mineral Fibers; C003760:vermiculite