A review of scientific literature examining the mining history, geology, mineralogy, and amphibole asbestos health effects of the Rainy Creek igneous complex, Libby, Montana, USA

Our plain-English summary of A review of scientific literature examining the mining history, geology, mineralogy, and amphibole asbestos health effects of the Rainy Creek igneous complex, Libby, Montana, USA, by B.R. Bandli, M.E. Gunter (Inhalation Toxicology, 2006).

The study

• Authors: B.R. Bandli, M.E. Gunter
• Journal: Inhalation Toxicology
• Published: 2006;18(12):949-62
• Type of article: Historical article, Review
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This article reviews the past 90 yr of scientific research directed on multiple aspects of the unique geology and environmental health issues surrounding the vermiculite deposit found at Libby, MT. Hydrothermal alteration and extensive weathering of the ultramafic units resulted in the formation of a rich deposit of vermiculite that was mined for 67 yr and used in numerous consumer products in its expanded form. Later intrusions of alkaline units caused hydrothermal alteration of the pyroxenes, resulting in formation of amphiboles. Some of these amphiboles occur in the asbestiform habit and have been associated with pulmonary disease in former miners and mill workers. Identification of these amphibole asbestos minerals has received little attention in the past, but recent work shows that the majority of the amphibole mineral species present may not be any of the amphibole species currently regulated by government agencies. Epidemiological studies on former miners have, nevertheless, shown that the amphibole asbestos from the Rainy Creek igneous complex is harmful; also, a recent study by the Agency for Toxic Substances and Disease Registry shows that residents of Libby who had not been employed in the vermiculite mining or milling operations also appear to have developed asbestos-related pulmonary diseases at a higher rate than the general public elsewhere. Since November 1999, the U.S. Environmental Protection Agency has been involved in the cleanup of asbestos-contaminated sites in and around Libby associated with the mining and processing of vermiculite.

In plain English

This article was a review, not a new study. The authors reviewed about 90 years of published research on the Rainy Creek igneous complex near Libby, Montana, where vermiculite was mined from 1923 to 1990. The review covered the site's mining history, geology, mineralogy and health effects. The vermiculite ore was contaminated with amphibole asbestos. The authors reported that earlier health studies had called this mineral tremolite, but recent mineral work they reviewed found the most abundant amphiboles were winchite and richterite. Among the worker studies reviewed, McDonald and colleagues studied 406 men employed for at least 1 year before 1963. That study reported a standardized mortality ratio of 2.45 for lung cancer and 2.55 for nonmalignant respiratory disease compared with US White men. Amandus and colleagues studied 575 men hired before 1970 and reported ratios of 2.44 and 2.42. Preliminary results from a federal health agency (ATSDR) reported pleural abnormalities in 18% of the Libby residents studied. The authors noted that little is known about how much asbestos residents were actually exposed to. They concluded that correct classification of these amphiboles will require a change in regulations to protect human health.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Literature review of published research on mining history, geology, mineralogy and health effects of the Libby vermiculite deposit
• Who was studied: Published studies on the Rainy Creek igneous complex (Vermiculite Mountain) near Libby, Montana, its vermiculite mine (operated 1923 to 1990), former miners and mill workers, and Libby residents
• Exposure: Amphibole asbestos contaminating Libby vermiculite ore. Earlier studies called it tremolite. Recent work reviewed identified the most abundant amphiboles as winchite and richterite.
• Main results:
  • In the reviewed McDonald et al. cohort of 406 men employed at least 1 year before 1963, the SMR for lung cancer was 2.45 and for nonmalignant respiratory disease 2.55, compared with the US White male population.
  • McDonald et al. (1988), as reviewed, reported a 1% increase in the probability of a worker developing lung cancer for each fiber-year of exposure.
  • In the reviewed Amandus et al. studies of 575 men hired before 1970 and employed at least 1 year, the SMR for lung cancer was 2.44 and for nonmalignant respiratory diseases 2.42, compared with the US White male population.
  • Amandus and Wheeler (1987), as reviewed, estimated the increase in lung cancer risk at 0.6% per fiber-year of exposure.
  • According to the reviewed exposure estimates, dust levels in the dry mill were extremely high before W. R. Grace acquired the operation in 1963 and were reduced by approximately 75% by 1965.
  • Preliminary results of an ATSDR study of Libby residents, as reviewed, reported that 18% of the study population had pleural abnormalities.
  • Nolan et al. (1991), as reviewed, found that the chemistry of Libby amphibole asbestos samples previously identified as tremolite was not consistent with tremolite.
• The authors' conclusion: The authors concluded that the Libby amphiboles are not tremolite. In their view, correct classification of these asbestiform amphiboles will require a change in regulations to protect human health.
• Limitations the authors state:
  • The authors noted there is very little information about how much asbestos Libby residents were actually exposed to.
  • The authors noted that, in the reviewed exposure estimates, dust levels were not measured in all years and were assumed to stay constant until the next measurement.
  • The authors noted that the significance of the ATSDR/Peipens et al. data on environmental exposure is debated within the epidemiological community.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Talc and vermiculite.

Medical terms in this study, explained in our Lexicon: Mineralogy, Amphibole Asbestos, vermiculite, Hydrothermal Alteration, Pyroxene, Amphibole Group, Asbestiform.

Related studies

• Exposure to airborne amphibole structures and health risks: Libby, Montana — B. Price (2008)
• Mortality in a cohort of vermiculite miners exposed to fibrous amphibole in Libby, Montana — J.C. McDonald, J. Harris, et al. (2004)
• Exposure to asbestos-containing vermiculite ore and respiratory symptoms among individuals who were children while the mine was active in Libby, Montana — L.C. Vinikoor, T.C. Larson, et al. (2010)
• A review of the federal government's health activities in response to asbestos-contaminated ore found in Libby, Montana — K. Horton, V. Kapil, et al. (2006)
• Trees as reservoirs for amphibole fibers in Libby, Montana — T.J. Ward, T. Spear, et al. (2006)
• Separation and characterization of respirable amphibole fibers from Libby, Montana — J.S. Webber, D.J. Blake, et al. (2008)

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