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Asbestos in the United States: Occurrences, Use and Control
(Released April 2008)

  by Andreas Saldivar & Vicki Soto  


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Case Study: Libby, Montana


Libby Montana, a small town located in the Kootenai National Forest, has become known as one of the worst asbestos contamination sites in U.S. history. The contamination is a direct result of the nearby Vermiculite mine that operated from the 1920s to 1990 (, 2004).

The first mining operations, in the Libby area, started in the 1860s with the discovery of gold, silver, and lead. Vermiculite was discovered by gold miners in 1881. In 1919, E.N. Alley bought the Rainy Creek Claim and shortly after opened the Zonolite Company, which marketed vermiculite as an insulation, an additive to plaster, and an additive to soil. Vermiculite from this mine that was used in insulation was marketed under the name Zonolite. In 1963, W.R. Grace bought the mine and operated it until it closed in 1990 (, 2004).

Unfortunately one of the by products of the vermiculite in Libby is asbestiform amphiboles, primarily winchite, richterite, and tremolite. The U.S. Geological Survey characterized the "respirable fraction of the abestiform minerals as 84% winchite, 11% richterite, and 6% tremolite." Raw ore was estimated to be 21-26% asbestos by weight and the mill feed was 3.5-6.4% asbestos. The vermiculite shipped to processing plants was 0.3-7.0 %. It is estimated that the airborne dust in the Libby mill was 40% asbestos. The mine produced as much as 80% of the world's vermiculite supply (Sullivan, 2007). (Note, winchite and richerite are not currently on the list of regulated asbestiform minerals; however the new Ban Asbestos in America Act of 2007 does list them as such.)

The mine was a significant employer of Libby and surrounding area residents. During the life of the mine it is estimated that employees were exposed to asbestos levels ranging from <1 f/cc to as high as 182 f/cc. Occupational exposure was dependent on what job the employee did and when in the life of the mine they were employed (Sullivan, 2007).

In 1999 dozens of asbestos related illnesses and deaths were blamed on the mine. The U.S. EPA then began investigating. The Agency for Toxic Substances & Disease Registry (ASTDR), an agency of the Department of Health and Human Services, released a report on mortality in Libby (Agency for Toxic Substances and Disease Registry (ATSDR), 2007).

The updated report concluded that for the 20-year period examined, mortality in Libby resulting from malignant and nonmalignant respiratory diseases was significantly elevated.

The report showed that when compared to Montana and U.S. mortality, there was a 20 percent to 40 percent increase in malignant and nonmalignant respiratory deaths in Libby from 1979 to1998.

Specifically, asbestosis mortality in Libby was 40 to 80 times higher than expected and lung cancer mortality was 1.2 to 1.3 times higher than expected when compared to Montana and the United States. Mesothelioma mortality was elevated but because statistics on this extremely rare cancer are not routinely collected, it was difficult to quantify the increase. Other non-malignant, noninfectious respiratory deaths also were significantly elevated. Most of the increase in respiratory mortality noted in the revised report likely can be associated with occupational exposures.

Asbestosis and mesothelioma mortality were found almost exclusively in former workers. Some of the lung cancer mortality occurred in former employees of the vermiculite facility."(Agency for Toxic Substances and Disease Registry (ATSDR), 2007)

In February 2005 a Federal Grand Jury indicted seven executives from W.R. Grace for knowingly exposing residents of Libby, Montana to asbestos contamination (U.S. Department of Justice, 2005).

The vermiculite ore from the Libby mine was shipped to over 200 processing facilities around the country. Between 1964 and 1990 approximately 95% of the ore was shipped to exfoliation facilities.

Picture 11: This map shows the distribution of 195 facilities receiving vermiculite ore from the Libby, Montana Mine.
map of U.S.A.

Exfoliation is the process that expands the vermiculite into its commercially viable form. The process involves heating the ore to 2,000 F which causes the vermiculite to expand. The expanded vermiculite was marketed as an insulation product known as Zonolite (U.S. Government Accountability Office, 2007). Zonolite was an easily poured insulation ideal for walls and attics. In 1985 the U.S. EPA estimated that 940,000 homes contained or, had contained Zonolite attic fill (U.S. Environmental Protection Agency, Vermiculite Questions and Answers, 2008). If you suspect you have vermiculite insulation you should visit

Picture 12: Photo of Zonolite brand insulation
bag of zonolite

Picture 13: Amphibole Asbestos bundle in Libby Montana, AMA Analytical Services
rocky fragments

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