A review of the federal government's health activities in response to asbestos-contaminated ore found in Libby, Montana

Our plain-English summary of A review of the federal government's health activities in response to asbestos-contaminated ore found in Libby, Montana, by K. Horton, V. Kapil, T. Larson, et al (Inhalation Toxicology, 2006).

The study

• Authors: K. Horton, V. Kapil, T. Larson, O. Muravov, N. Melnikova, B. Anderson
• Journal: Inhalation Toxicology
• Published: 2006;18(12):925-40
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Vermiculite ore is a naturally occurring fibrous mineral widely used in various consumer products, such as attic insulation, lawn and garden products, and fireproofing material. While most vermiculite ore and products do not pose a health hazard, the vermiculite mined from Libby, MT was contaminated with naturally occurring asbestos. The federal Agency for Toxic Substances and Disease Registry (ATSDR) has documented a significant number of asbestos-related deaths among Libby residents. Additionally, as part of the ongoing investigation, ATSDR has learned that this contaminated ore was shipped to hundreds of locations around the United States for processing. While the Libby mine is now closed, studies from ATSDR and elsewhere show that people who worked in the Libby mine or vermiculite processing facilities may have been exposed to hazardous levels of asbestos while the facilities were in operation. People who lived or worked near these sites also may have been exposed to asbestos if they came into contact with contaminated vermiculite. Prolonged exposure to asbestos can cause serious and life-threatening health conditions, including asbestosis, lung cancer, and mesothelioma. In response, ATSDR has initiated 10 different activities to help evaluate the potential health effects among Libby residents and populations throughout the United States who might have been exposed to the asbestos-contaminated ore found in Montana. Some of these activities include conducting environmental exposure evaluations, health statistics reviews, community screenings, and disease-specific surveillance. This article presents the various follow-up activities that have been conducted to date by ATSDR and partnering state health departments.

In plain English

This article was a review by staff of the federal Agency for Toxic Substances and Disease Registry (ATSDR). It described 10 health activities that the agency and state health departments carried out after vermiculite ore from Libby, Montana, was found to contain amphibole fibers including tremolite, winchite and richterite. In a 1979–1998 Libby mortality review, asbestosis death rates in six local areas were 40 to 80 times higher than Montana and U.S. rates. In 2000–2001 screening, pleural abnormalities were seen in 17.8% of 6668 adults x-rayed, in 51% of 186 former W. R. Grace employees and in 26% of household contacts. Reviews of death and cancer records at 12 other U.S. sites that received Libby ore found no statistically significant excess of known asbestos-related diseases in their total populations. Among 236 Marysville, Ohio, workers, pleural changes rose from 5.1% to 44.1% across increasing quartiles of cumulative fiber exposure. The authors concluded that rates at the other sites did not reach those found in Libby. They listed limitations including population migration, smoking and small numbers.

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 of ATSDR's and partnering state health departments' activities (mortality review, community medical screening, health statistics reviews, a CT screening study, exposure evaluations, registries, surveillance and a worker follow-up study), with summarized results
• Who was studied: People who lived, worked or engaged in recreation in Libby, Montana, former vermiculite workers and their household contacts, and communities and workers near U.S. sites that received Libby ore. These included 12 sites with health statistics reviews, 28 sites with exposure evaluations, and the Minneapolis, Minnesota and Marysville, Ohio facilities.
• Exposure: Vermiculite ore from the Libby, Montana mine, contaminated with naturally occurring asbestiform fibers including the amphibole varieties tremolite, winchite and richterite. Exposure came through mining, milling, exfoliation processing, take-home contamination, and contact with vermiculite or waste rock.
• Main results:
  • Libby mortality review, 1979–1998: standardized mortality ratios for asbestosis in all six Libby geographic areas were 40 to 80 times higher than for Montana and the United States.
  • Libby mortality review: deaths from malignant neoplasm of respiratory and intrathoracic organs (which includes lung cancer) were significantly elevated compared with Montana rates in the Libby valley (SMR 139, 95% CI 116–166) and central Lincoln County (SMR 131, 95% CI 109–156).
  • Libby medical screening, 2000–2001: of 7307 people interviewed, 6668 aged 18 or older had chest x-rays. Pleural abnormalities were seen in 17.8% and interstitial abnormalities in less than 1%.
  • Libby medical screening: 51% of former W. R. Grace employees who received x-rays (n = 186) had pleural abnormalities, as did 26% of household contacts of workers.
  • Health statistics reviews at 12 U.S. sites that received Libby ore: none had statistically significant excesses of known asbestos-related diseases in their total populations.
  • Louisiana analyses split by sex and race: lung cancer incidence was elevated in ZIP code 70084 among Black females (SIR 2.1, 95% CI 1.3–3.1) and in ZIP code 70117 among White males (SIR 1.5, 95% CI 1.2–1.8). Mesothelioma was elevated in ZIP code 70121 among Black females (2 observed, 0.04 expected; SIR 47.4, 95% CI 8.4–118.2).
  • High-resolution CT study: CT detected pleural abnormalities in 98 (27.8%) of 353 people whose earlier chest x-rays were classified indeterminate. The highest prevalence (47.5%) was in household contacts of former vermiculite workers.
  • Marysville, Ohio preliminary analysis of 236 workers: pleural changes rose with cumulative fiber exposure, from 5.1% (3 of 59) in the lowest quartile (0.0007–0.361 fiber/cc-yr) to 44.1% (26 of 59) in the highest (2.565–28.112 fiber/cc-yr). This trend was significant at p less than .0001; overall prevalence was 26.3% (62).
  • Marysville: parenchymal changes were found in 2.5% (6/236). All six were over 60 years old and in the 90th percentile of exposure (more than 10 fiber/cc-yr).
  • Exposure evaluations: industrial hygiene data from exfoliation facilities in the 1970s and 1980s showed indoor airborne fiber levels up to two orders of magnitude above the current OSHA permissible exposure limit of 0.1 f/cc.
• The authors' conclusion: The authors concluded that findings so far from other U.S. sites did not show elevated rates of asbestos-related diseases to the extent found in Libby. They also concluded that, in the Marysville workers, exposure to vermiculite containing asbestos and asbestiform fibers was associated with increased pleural changes at both low and higher exposures. They identified former exfoliation workers, their household contacts, and community members (particularly children) with direct contact with vermiculite or waste rock as the most exposed groups.
• Limitations the authors state:
  • Libby mortality review: population migration, smoking prevalence, diagnostic bias, and problems with relying on death certificates.
  • Libby medical screening: selection and observer biases.
  • Health statistics reviews: exposure misclassification, large study areas, small numbers of events, underreporting of cancers, miscoding of deaths, population migration and other confounders. The authors advised caution in interpreting the results.
  • Louisiana: smoking histories were unknown, so the lung cancer excesses are hard to interpret. The mesothelioma excess was based on small numbers.
  • CT study: time lapses between x-rays and CT, participant refusals, a study population limited to people with indeterminate x-rays, and difficulties comparing across studies.
  • Exposure evaluations: exposure data were unavailable for much of the facilities' operating time. Most sampling data lacked exact fiber mineralogy and length distribution.

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: vermiculite, naturally occurring asbestos (NOA), ATSDR, Lung Cancer, Mesothelioma, Environmental Exposure.

Related studies

• 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)
• Libby: the long legacy of a public health disaster — A. van Dorn (2017)
• Select mortality and cancer incidence among residents in various U.S. communities that received asbestos-contaminated vermiculite ore from Libby, Montana — D.K. Horton, F. Bove, et al. (2008)
• 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)
• Exposure to airborne amphibole structures and health risks: Libby, Montana — B. Price (2008)
• Radiographic abnormalities and exposure to asbestos-contaminated vermiculite in the community of Libby, Montana, USA — L.A. Peipins, M. Lewin, et al. (2003)

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