Vermiculite, Respiratory Disease, and Asbestos Exposure in Libby, Montana: Update of a Cohort Mortality Study

Abstract

BackgroundVermiculite from the mine near Libby, Montana, is contaminated with tremolite asbestos and other amphibole fibers (winchite and richterite). Asbestos-contaminated Libby vermiculite was used in loose-fill attic insulation that remains in millions of homes in the United States, Canada, and other countries.ObjectiveThis report describes asbestos-related occupational respiratory disease mortality among workers who mined, milled, and processed the Libby vermiculite.MethodsThis historical cohort mortality study uses life table analysis methods to compare the age-adjusted mortality experience through 2001 of 1,672 Libby workers to that of white men in the U.S. population.ResultsLibby workers were significantly more likely to die from asbestosis [standardized mortality ratio (SMR) = 165.8; 95% confidence interval (CI), 103.9–251.1], lung cancer (SMR = 1.7; 95% CI, 1.4–2.1), cancer of the pleura (SMR = 23.3; 95% CI, 6.3–59.5), and mesothelioma. Mortality from asbestosis and lung cancer increased with increasing duration and cumulative exposure to airborne tremolite asbestos and other amphibole fibers.ConclusionsThe observed dose-related increases in asbestosis and lung cancer mortality highlight the need for better understanding and control of exposures that may occur when homeowners or construction workers (including plumbers, cable installers, electricians, telephone repair personnel, and insulators) disturb loose-fill attic insulation made with asbestos-contaminated vermiculite from Libby, Montana.

Update of Potency Factors for Asbestos-Related Lung Cancer and Mesothelioma

“…An application of the lung cancer model to their earlier follow-up (McDonald et al, 1986) resulted in an estimate of α = 1.91 with a ratio of K L 's estimated with α = 1 to α estimated of 2.8 (Berman and Crump, 2003). Also, an analysis of the recent follow-up of a different cohort from Libby (Sullivan, 2007) estimated α = 1.5 with a ratio of K L 's of 4.6 (Table B13) McDonald et al (2004) identified 12 deaths from mesothelioma, compared to only 2 identified in their earlier follow-up. These data were analyzed for exposure response using intensity of exposure, cumulative and a type of "residence weighted" exposure.…”

“…Individual cumulative fiber exposure estimates (f-yr/ml) were computed from job-specific exposure estimates and work histories . Sullivan (2007) categorized person-years of follow-up into four groups according to cumulative exposure and compared the observed number of deaths from lung cancer in each group with the number expected based on age-and calendar-year-specific rates for U.S. white males. These data are reproduced in Table B13.…”

“…With α = 1, the estimate is K L = 0.0088 (f−y/ml) −1 , 90% CI: (0.0048, 0.013). Sullivan (2007) reported 15 deaths from mesothelioma. Unfortunately these data were not summarized in a manner that allowed applying the mesothelioma model [Eq.…”

“…Because this study and the Sullivan (2007) study used virtually the same data and very similar approaches to analysis, the same values were assigned to uncertainty factors for this study that were assigned for the Sullivan (2007) study.…”

Reported Historic Asbestos Mines, Historic Asbestos Prospects, and Other Natural Occurrences of Asbestos in Oregon and Washington

“…The geology of asbestos and its application to identifying and managing the natural deposits is explained in Van Gosen (2007b). Several examples of occupational and environmental exposures to natural asbestos occurrences are described in Churchill and Hill (2000), Nolan and others (2001), Clinkenbeard and others (2002), Gianfagna and others (2003), Peipins and others (2003), Ross and Nolan (2003), Burragato and others (2005), Meeker and others (2006), Sullivan (2007), and Horton and others (2008). United States Federal asbestos regulations do not specifically address occupational exposures to natural occurrences of asbestos, nor do they mention every variety of asbestiform amphibole.…”