Low levels of exposure to libby amphibole asbestos and localized pleural thickening

Our plain-English summary of Low levels of exposure to libby amphibole asbestos and localized pleural thickening, by K.Y. Christensen, T.F. Bateson, L. Kopylev (Journal of Occupational and Environmental Medicine, 2013).

The study

• Authors: K.Y. Christensen, T.F. Bateson, L. Kopylev
• Journal: Journal of Occupational and Environmental Medicine
• Published: 2013;55(11):1350-5
• Type of article: Review
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: To explore the relationship between low levels of exposure to Libby amphibole asbestos (LAA) and pleural abnormalities, specifically localized pleural thickening (LPT).

Methods: Three studies presenting the risks associated with quantitative LAA exposure estimates were reviewed, paying particular attention to lower exposure ranges.

Results: Studies reviewed were conducted among workers exposed to LAA at mining and milling operations in Libby, Montana, at a vermiculite processing facility in Marysville, Ohio, and community residents exposed to LAA from a vermiculite processing facility in Minneapolis, Minnesota. Pleural abnormalities were evaluated using radiographs. Despite differences in study populations and design, each study found that cumulative inhalation LAA exposure was associated with increased risk of LPT even at low levels of exposure.

Conclusions: Inhalation exposure to LAA is associated with increased risk of LPT even at the lowest levels of exposure in each study.

In plain English

This article was a review. The authors compared three earlier studies that estimated cumulative inhaled exposure to Libby amphibole asbestos, a mixture of amphibole fibers in vermiculite ore from Libby, Montana, and examined chest X-rays for localized pleural thickening. The studies covered 336 former mine and mill workers in Libby, 280 vermiculite plant workers in Marysville, Ohio, and 461 residents living near a vermiculite plant in Minneapolis, Minnesota. In the low-exposure groups compared, all below 1 fiber/cc-yr, prevalence was 20% among Libby workers, 6.7% among Marysville workers and 7.4% among Minneapolis residents. The Minneapolis figure counted pleural plaques, which the authors assumed represent localized thickening. Among Marysville workers without other asbestos exposure, prevalence rose across exposure quartiles from 6.7% to 40.7%. The authors concluded that inhaled Libby amphibole asbestos is associated with increased risk of localized pleural thickening even at each study's lowest exposure levels. They noted that exposure estimates were uncertain, particularly for earlier years and in Minneapolis, and that X-ray reading rules differed between the studies.

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: Review comparing three published studies that used quantitative exposure estimates for Libby amphibole asbestos and evaluated localized pleural thickening on chest radiographs
• Who was studied: Three study populations: 336 former vermiculite mining and milling workers in Libby, Montana (screened 2000–2001); 280 workers at the O.M. Scott vermiculite processing facility in Marysville, Ohio (assessed 2004–2005); and 461 community residents near the Western Minerals facility in Minneapolis, Minnesota, who had never worked there or lived with a worker (assessed 2001–2003)
• Exposure: Cumulative inhalation exposure to Libby amphibole asbestos (a mixture of amphibole fibers in Libby vermiculite ore), estimated in fibers/cc-yr. For the workers it came from industrial hygiene measurements and work histories. For the Minneapolis residents it came from emissions modeling and self-reported activities such as contact with waste piles.
• Main results:
  • Among the 336 Libby workers, 46% had some form of pleural abnormality and 35% had localized pleural thickening. Workers with localized pleural thickening had a median cumulative exposure of 5.8 fibers/cc-yr, compared with 2.1 fibers/cc-yr for those without it.
  • Among Marysville workers with no exposure to commercial asbestos (amosite, chrysotile, crocidolite), the prevalence of localized pleural thickening rose across exposure quartiles: 6.7%, 18.6%, 28.8%, 40.7%. The crude association was statistically significant in the third and fourth quartiles; odds ratios were not given.
  • Among the 461 Minneapolis community residents, 10.8% had any pleural abnormality and 9.8% (n = 45) had pleural plaques. There were 17 cases among those with cumulative exposure below the median of 0.063 fiber/cc-yr.
  • In the lower-exposure groups compared by the review authors, exposure was below 1 fiber/cc-yr in every group. Prevalence by group was: Libby workers, quartile 1 (0 to less than 0.4 fiber/cc-yr), 20% (17 cases, 68 noncases); Marysville workers, quartile 1 (0.01 to 0.28 fiber/cc-yr), 6.7% (4 cases, 55 noncases); Minneapolis residents, quartiles 1 and 2 (0 to less than 0.63 fiber/cc-yr), 7.4% (17 cases, about 213 noncases).
  • The authors stated that the prevalence of localized pleural thickening in the two worker cohorts was higher than background rates reported in previous studies.
• The authors' conclusion: The authors concluded that inhalation exposure to Libby amphibole asbestos is associated with increased risk of localized pleural thickening even at the lowest levels of exposure in each study.
• Limitations the authors state:
  • In both worker studies, exposure estimates for earlier years were quite uncertain.
  • For the Minneapolis community study, uncertainty in the exposure estimates could be an order of magnitude or more.
  • The Minneapolis study did not model localized pleural thickening separately. The review authors assumed that its pleural plaques represent localized pleural thickening for comparison.
  • The studies used different ILO guideline versions (1980 versus 2000), and the 2000 definition may include a wider range of pleural abnormality.
  • In the Libby worker study, exposure estimates covered only occupational exposure, although the workers also had take-home and background exposures.
  • The worker cohorts were mostly male while the community study was about half female, which could matter if sex affects susceptibility.

Topics

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

Medical terms in this study, explained in our Lexicon: Libby amphiboles, Pleural Thickening, vermiculite.

Related studies

• Exposure to airborne amphibole structures and health risks: Libby, Montana — B. Price (2008)
• Asbestos-related radiographic findings among household contacts of workers exposed to Libby vermiculite: impact of workers' personal hygiene practices — T.J. Hilbert, A. Franzblau, et al. (2013)
• Libby Amphibole Disease: Pulmonary Function and CT Abnormalities in Vermiculite Miners — A. Miller, J. Szeinuk, et al. (2018)
• Lung function, radiological changes and exposure: analysis of ATSDR data from Libby, MT, USA — D. Weill, G. Dhillon, et al. (2011)
• Localized pleural thickening: smoking and exposure to Libby vermiculite — K.Y. Christensen, L. Kopylev (2012)
• 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 — B.R. Bandli, M.E. Gunter (2006)

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