CDC logoSafer Healthier People  CDC HomeCDC SearchCDC Health Topics A-Z
NIOSH - National Institute for Occupational Safety and Health

Skip navigation links Search NIOSH  |  NIOSH Home  |  NIOSH Topics  |  Site Index  |  Databases and Information Resources  |  NIOSH Products  |  Contact Us

NIOSH Respiratory Diseases Research Program

Evidence Package for the National Academies' Review 2006-2007

NIOSH Programs > Respiratory Diseases > Evidence Package > 3. Interstitial Lung Diseases > 3.3 Fiber-Induced Diseases

3.3a) Reduce Occupational Hazard Associated with Asbestiform Fibers Contaminating Vermiculite from a Mine in Montana

previous 3.3 Fiber-Induced Diseases | 3.3b) Identification and Control of a Newly Recognized Occupational Lung Disease Affecting Flock Workers next


A now-closed mine near Libby, Montana, accounted for about three-fourths of worldwide vermiculite production for many decades during the last century. Vermiculite from that mine was mostly used as loose-fill thermal insulation for attics, but it also had uses in construction, horticultural, and other applications. While vermiculite is not itself notably toxic to the respiratory system when inhaled, this vermiculite ore was substantially contaminated with actinolite-tremolite asbestos and other closely related asbestiform amphibole fibers.

RDRP involvement with this amphibole-contaminated vermiculite goes back to 1979, when OSHA requested NIOSH to evaluate an unusual cluster of workers with bloody-pleural effusions of uncertain etiology at a fertilizer plant in Ohio. Airborne fibers had been identified in the plant, which used expanded vermiculite as a carrier for fertilizer chemicals in a popular line of lawn products marketed nationwide. It was soon established that the vermiculite used at this plant was highly contaminated with amphibole asbestos, and that the source of this vermiculite was the mine near Libby, Montana. The potential for widespread exposures of both workers and consumers was readily apparent, given the wide usage of this vermiculite.


In response to the initial OSHA request, RDRP investigators clinically reviewed the pleural disease cases at the fertilizer plant and concluded that occupational exposure to asbestos was the likely cause. This finding led the company to make a prompt change away from using vermiculite from the Libby mine and to contract for a study by University of Cincinnati, College of Medicine researchers of the affected fertilizer plant, for which RDRP scientists provided protocol review. The University of Cincinnati study found that pleural disease among workers at the fertilizer plant was associated in a dose-related manner with occupational exposure to amphibole fibers at the plant.84

After learning the source of the asbestos-contaminated vermiculite, RDRP alerted MSHA and immediately aimed our investigative efforts primarily at the source of the hazard in Libby. To assess the risk for workers exposed to the contaminating fibers at the Libby mining and milling operations (operated by W.R. Grace Company), RDRP investigators undertook retrospective exposure assessment and morbidity and cohort mortality epidemiological studies. The main findings were: asbestiform fiber exposures for the vermiculite workers in Libby exceeded federal occupational exposure limits for asbestos; vermiculite workers at the Libby operations experienced substantial excess lung cancer mortality, which was shown to be dose-related to occupational fiber exposures at the vermiculite mine and associated processing facilities in Libby;  and radiographically evident pneumoconiosis and mortality from non-malignant respiratory diseases among vermiculite workers in Libby were also associated with occupational exposure to these fibers. RDRP investigators informed MSHA and OSHA and communicated these findings at three separate meetings in Libby: with company management; with union and worker representatives; and in an open meeting for all current and former workers and other interested members of the general community in the mid-1980s.

In late 1999, a series of articles in the Seattle Post-Intelligencer newspaper brought renewed national attention to concerns over community exposures in Libby and elsewhere. EPA and Agency for Toxic Substances and Disease Registry (ATSDR) took leading roles at the federal level in assessing, communicating, and managing potential community health risks from asbestos exposures associated with vermiculite. RDRP experts provided EPA and ATSDR with both formal and informal consultation. An updated RDRP mortality study is intended to provide scientific information to enhance ongoing risk assessments about, among other things, low-level community exposures.

At OSHA’s request, RDRP investigators also recently undertook field studies to determine current levels of occupational exposure to asbestos fibers, if any, in vermiculite expansion plants and horticultural users of vermiculite currently produced by various mines in the U.S. and overseas. Little evidence was found to indicate that current exposures exceed the OSHA PEL. Jobs with the highest potential for asbestos exposure were expansion plant furnace operators and baggers, but none of the measured concentrations for workers in these jobs exceeded the current NIOSH REL or OSHA PEL for airborne asbestos fibers.

Recently, RDRP scientists also used findings from the contaminated vermiculite studies to support development of NIOSH support for MSHA’s proposal to bring the PEL for asbestos applicable in the mining industry into conformance with the long-standing and more protective OSHA PEL for asbestos in general industry.

Outputs and Transfer

To communicate findings from our major studies of the Libby vermiculite operations, RDRP scientists published a three-part set of peer-reviewed papers in the “American Journal of Industrial Medicine” in 1987 (1-3, A3-87, A3-88, A3-89). These have been cited a total of 80 times (ISI Web of Science as of 7/18/06) and were also recently cited by MSHA in its proposed revision of the asbestos standard for mining. In addition, the findings were included in a comprehensive textbook, “Occupational Respiratory Diseases,” produced by RDRP in 1986. RDRP also disseminated the Libby findings to the scientific and public health communities through presentations at the international Inhaled Particles conference (later published in a 1988 “Annals of Occupational Hygiene” supplement).

In response to the intense public attention on Libby vermiculite arising after 1999, we produced two NIOSH Fact Sheets (A3-90, A3-91) and related press releases to raise public awareness of our previous findings and outputs concerning health risks associated with amphibole-contaminated vermiculite. One of these Fact Sheets (“Recommendations for Limiting Potential Exposures of Workers to Asbestos Associated with Vermiculite from Libby, Montana, 2002”) targeted workers likely to face a risk from disturbing Libby vermiculite attic insulation (e.g. home re-modelers, cable installers, ventilation system installers, etc.) and included appropriate caution and recommendations for reducing exposures.

RDRP investigators recently produced a letter report to OSHA summarizing their findings concerning assessments of current fiber exposures at 10 different plants that process and/or use vermiculite from four different mines (HHE and Technical Assistance [HETA] 2000-0407, 2004, “Vermiculite Facilities Site Evaluations Close-Out Letter,” A3-92). RDRP had previously sent a detailed plant-specific report concerning findings at each of the 10 individual plants to the respective plant, OSHA, and EPA.

NIOSH provided formal testimony and comments, prepared and presented by RDRP staff, for several Congressional hearings relating to Libby vermiculite and in support of MSHA’s Libby-motivated effort to reduce its PEL for asbestos.

  • NIOSH Comments to MSHA Advance Notice of Proposed Rulemaking (2002, A3-93)
  • NIOSH Comments on MSHA Proposed Rule (2005, A3-94)
  • NIOSH testimony at MSHA hearing on rulemaking (2005, A3-95)

Intermediate Outcomes

Early work motivated many others to action. RDRP’s assessment of the pleural disease cluster among workers at a fertilizer plant in Ohio lead to investigations at the Libby mine that, in turn have lead to a chain of events that have included closure of the Libby mine, and actions by OSHA, MSHA, EPA, and others to address the problems associated with asbestiform amphibole contamination of Libby vermiculite.

ATSDR and EPA have sought and been provided with RDRP expertise relating to Libby vermiculite, asbestosis-related diseases, and asbestos-related toxicology. ATSDR and EPA are the federal agencies currently taking the lead in dealing with the legacy of Libby vermiculite, including historical community exposures and the potential for ongoing exposures in the Libby area, potential community exposures in neighborhoods occupied by plants that processed Libby vermiculite in the distant past, and the potential for ongoing exposures associated with residence in the estimated hundreds of thousands to millions of existing homes with Libby vermiculite installed as attic insulation.

For example, ATSDR and EPA requested RDRP assistance when designing the medical screening program for residents of the Libby area that eventually examined over 7,000 individuals in 2000 and 2001. A “Libby, Montana Asbestos Scientific Panel,” convened by EPA and ATSDR in February, 2000, to discuss ATSDR plans for screening included an RDRP expert as a member. In reporting on the excess of asbestos-related abnormities identified among the Libby-area residents screened in 2000 and 2001, ATSDR cited normative radiographic data  previously published by RDRP (4, A3-96). ATSDR sought and was provided our expert input on designing a study on the use of computed tomography scans of the chest to complement the traditional chest radiographic screening of members of the Libby community for asbestos-associated abnormalities.

An ATSDR report published in 2002 found that mortality from asbestosis was approximately 60 times higher than the rest of the U.S., complementing previous findings published by RDRP surveillance staff “WoRLD Surveillance Report 1996” (A3-97) indicating that Lincoln County (of which Libby is the county seat) was among the top three U.S. counties for asbestosis death rates. Also, ATSDR sought and was provided with our expertise in developing ATSDR’s National Asbestos Exposure Review (A3-98), which is evaluating more than 200 locations that received asbestos-contaminated vermiculite from Libby, Montana.

We provided expertise to ATSDR and EPA for a panel that considered the physiological fate of and health effects of asbestos and synthetic vitreous fibers structures less than 5 µm in length having aspect ratios greater than 3:1, and related research needs. The resulting “Report on the Expert Panel on Health Effects of Asbestos and Synthetic Vitreous Fibers: The Influence of Fiber Length” (Prepared for: ATSDR, 2003; A3-99 [Part1], [Part 2], [Part 3], [Part 4]) was specifically cited by EPA in a risk assessment for Libby.

Findings of the formal RDRP technical assistance to OSHA, which found essentially no current hazardous exposures to asbestos in the 10 vermiculite operations evaluated, have allowed OSHA, despite intense national concern about of the environmental and occupational health legacy of Libby vermiculite, to direct its limited resources primarily to other priorities.

Motivated by the concern over asbestos contamination of Libby vermiculite, which helped to highlight the fact that the MSHA PEL for the mining industry is 20 times higher than the OSHA PEL for general industry, MSHA recently published (Federal Register, 2005; A3-100) a proposed rule that will reduce its asbestos PEL and bring it into conformance with the more protective OSHA PEL that was itself established with substantial reliance on RDRP expertise (including NIOSH asbestos criteria documents from the 1970s). Recent formal NIOSH comments and testimony to MSHA, prepared and presented by our staff, have provided important support for the current MSHA effort to establish a more protective PEL. MSHA’s “Proposed Rule on Asbestos Exposure Limit” cites 18 publications by RDRP scientists  ( percent2D14510.asp [External link]).

Progress Towards End Outcomes

The Ohio fertilizer plant promptly stopped using the vermiculite from Libby in 1980 after learning of RDRP’s case cluster finding. Libby vermiculite was replaced in their formulation with vermiculite from another source that was virtually free of asbestiform fibers. While this substitution quickly and effectively minimized the ongoing occupational risk associated with amphibole-contaminated vermiculite at this fertilizer plant, elimination of additional risk to workers at this plant (as well as elimination of potential risk to consumers) was subsequently assured when this fertilizer company stopped using vermiculite altogether after modifying its lawn fertilizer formulation in 2001.

Similarly, soon after RDRP researchers completed and published the mid-1980s studies of the Libby mining and milling operations, the mine operator abandoned unsuccessful attempts to remove the contaminating fiber from its product and began to deactivate operations in Libby. The Libby mine and mill completely ceased operations in 1990, eliminating this commercial source of asbestos-contaminated vermiculite, which had historically supplied about three-fourths of the world’s total production of vermiculite. This eliminated ongoing occupational exposure for the Libby-based workers and for “downstream” vermiculite expansion-plant workers, vermiculite insulation installers, etc., throughout the U.S.

What’s Ahead

RDRP is currently engaged in updating and expanding the earlier (1980s) cohort mortality study of Libby vermiculite workers. Not only has the follow-up of the cohort been extended, but the cohort has been expanded to include short-term workers with brief work tenures, who were not included in the original cohort. The intent is to evaluate risk of respiratory disease mortality (lung cancer, mesothelioma, and asbestosis) associated with occupational exposure to Libby amphibole across the full range of exposure (including short term workers, some of whom had very low cumulative exposures). Potential fiber-related outcomes not evaluated in the original study (e.g. digestive cancer and autoimmune diseases) also will be assessed. Exposure-outcome relationships will be modeled. It is anticipated that findings will provide more precise risk estimates for low levels of fiber exposure. Such low-exposure risk estimates will be particularly relevant to current concerns relating to potential occupational and public health risks associated with ongoing exposure to asbestos-contaminated Libby vermiculite among construction renovation workers, cable installers, electrical workers, plumbers, insulators, and among homeowners currently residing in homes insulated with Libby vermiculite. We plan to publish scientific papers on this work and will disseminate study results to other federal agencies (e.g. ATSDR, EPA, OSHA, and MSHA), labor and industry associations, and occupational health professionals. Depending on the findings, we may develop and disseminate a NIOSH Alert or Fact Sheet and possibly a training manual for trade or vocational schools to inform future construction workers, plumbers, electricians, and painters on the hazards of asbestos exposure associated with in-place vermiculite insulation. Some of these goals have been realized while the current report was being written (A3-100s).

84. Lockey JE, Brooks SM, Khoury PR, McKay RT, Carson A, Morrison JA, Wiot JF, Spitz HB [1984].  Pulmonary changes after exposure to vermiculite contaminated with fibrous tremolite. Am Rev Respir Dis. 129(6):952-8.

NIOSH Program:

Respiratory Diseases

Evidence Package