Employees, their families and people living close to 28 exfoliation sites may have been exposed to amphibole asbestos from vermiculite mined in Libby, Montana between the 1920s and the early 1990s, a report from the Agency for Toxic Substances and Disease Registry (ATSDR) has concluded.

The report identifies groups of people most at-risk from exposure to this form of asbestos, makes public health recommendations for these sites and identifies 78 other sites that also received Libby vermiculite. All but one of the sites are former vermiculite exfoliation facilities located in 36 states.

Vermiculite is a group of minerals with a flaky, mica-like structure, used in insulation and gardening. No research has linked serious health effects with exposure to this mineral.

However, the specific vermiculite mined in Libby and distributed across the United States was contaminated with amphibole asbestos, which has been linked to pulmonary diseases including asbestosis, lung cancer, and mesothelioma. As many as 15 to 30 years can pass between a person’s exposure to asbestos and the time disease develops. Workers were exposed to asbestos through a process called exfoliation, in which vermiculite is heated until it expands. Since the Libby vermiculite contained asbestos, heating released asbestos fibers into the air where they could be inhaled.

People who believed they may have been exposed to amphibole asbestos are encouraged to discuss this with their health care professional. In addition ATSDR also recommends that exposed persons stop smoking, as smoking combined with asbestos exposure greatly increases the risk of developing lung cancer.

“While the number of people who were exposed to this asbestos is relatively low, ATSDR and our public health department partners are concerned about the health effects of this substance on the people who worked and lived around these facilities when they actively processed vermiculite from the Libby mine,” said William Cibulas, Ph.D., director of ATSDR’s Division of Health Assessment and Consultation. “The information we have developed and shared will help these people better understand the potential risks for exposure and what to do if they feel they have been exposed.”

The report identifies three groups at greatest risk for amphibole asbestos exposure:
  • Persons who worked in exfoliation facilities at some time from the 1920s to the early 1990s.
  • Persons who lived in the same households with these workers were exposed through asbestos-laden dust carried home on workers’ clothing.
  • Members of the community — particularly children — who had frequent, direct contact with vermiculite and waste rock (a by-product of exfoliation) from these facilities.
“Most people who live or work around these sites today are not being exposed to asbestos from the Libby mine,” Dr. Cibulas said. “Our goals are to inform the public and reach out to workers and families who may have been exposed and have not yet sought out necessary medical screening.”

ATSDR’s report calls for continued health education for persons who have been exposed to amphibole asbestos. The agency has prepared health education kits to assist public health and health care professionals and community members.

ATSDR’s investigations found that residual amphibole asbestos likely remains in settled indoor dust at former exfoliation sites as well as in exterior soil. With many of these sites still in use as commercial and industrial operations, ATSDR is recommending existing data for these sites be re-evaluated to learn more about the residual asbestos that may remain.

The ATSDR study also determined that non-exfoliation sites which handled vermiculite from Libby do not require follow-up studies at this time. However, the agency does recommend using the criteria of the U.S. Environmental Protection Agency’s (EPA) Technical Review Workgroup to review existing data for all sites that exfoliated Libby vermiculite using ATSDR’s improved methodologies.

ATSDR began evaluating Libby-related vermiculite sites at the request of EPA in response to documented health reports related to asbestos in Libby. In May 2008, ATSDR and EPA announced an $8 million initiative to advance the scientific understanding of asbestos-like fibers that occur naturally in the environment.

The document is Summary Report: Exposure to Asbestos-Containing Vermiculite from Libby, Montana at 28 sites in the United States.

ATSDR, a non-regulatory federal public health agency, will continue to provide technical assistance to state and local officials in communities where sites have been identified. For information about the report, please visit the ATSDR Web site:http://www.atsdr.cdc.gov/asbestos/sites/national_map