Mesothelioma and the Spread of Asbestos


Though it has been shut down for more than a decade, a mine in Libby, Montana is still raising health concerns for asbestos-contaminated ore it once shipped to hundreds of sites across the country. A report published in the June issue of Inhalation Toxicology finds that people living in several of the communities surrounding the ore processing sites may have a higher incidence of mesothelioma and other cancers.

From the time it opened in the early1920s, the Libby mine processed vermiculite ore. Though it was useful for insulation, fireproofing materials, and lawn and garden products, the mineral contained a type of asbestos, which has been linked to an increased risk of various lung disorders, including asbestosis (scarring of lung tissue), mesothelioma, and lung cancer. In 1999, researchers from the Agency for Toxic Substances and Disease Registry (ATSDR) looked into asbestos-related health concerns in Libby, and found that deaths from asbestos-related diseases there were 40 to 80 times higher than normal.

The mine was closed in 1990, but while it was still in operation, its asbestos-contaminated ore was shipped to, and processed at more than 200 different sites across the country. Because health officials have been concerned that people who worked with the ore or lived in areas surrounding these processing facilities might also be at increased risk for cancer and asbestosis, ATSDR launched another investigation in 2001 focusing on 70 sites in 23 states that had received ore from Libby.

Researchers reviewed death certificates and cancer registry records from these processing site communities. In 11 of the sites (including Portland, OR; Utica, NY; Hamilton Township, NJ; Jersey City, NJ; Newark, NJ; Tampa, FL; and Milwaukee, WI), they found a significantly increased incidence of mesothelioma and other asbestos-related cancers. In five of the locations the risk was greatest among men, suggesting that many of those exposed may have been workers in the processing facilities.

The sites that processed the most vermiculate from Libby, and presumably led to the greatest exposure, were called exfoliation facilities. “These facilities heated the vermiculite until it expanded and popped, like popcorn,” explains Barbara Anderson, PE, environmental health scientist in the Division of Health Assessment and Consultations at ATSDR. Although these were small operations, with only 15 to 20 workers each, it was likely that workers carried traces of the contaminated ore into their communities. “They probably inadvertently brought the asbestos fibers home on their clothing, shoes, and in their hair, and they may have exposed household contacts as well,” Anderson says.

The researchers say the cancer incidence they found at the 11 sites, though higher than normal, was still well below what they had seen in Montana. “Libby was a bit of a different situation compared to most of these other sites, because in Libby so much of the vermiculate ore went into the community,” explains Dr. Vikas Kapil, former chief of the Surveillance and Registry Branch in the Division of Health Studies, ATSDR, and currently associate director for Science in the Division of Injury Response at the National Center for Injury Prevention and Control. He notes that in Libby, the ore was used in ball fields and at other sites throughout the community, significantly increasing residents’ exposure.

Also, the authors caution that this study can’t conclusively prove that the contaminated ore was the source of the increased cancer incidence in the locations they analyzed. One of the study’s main limitations was that researchers did not have access to data on people’s smoking history (which is itself a risk factor for lung cancer), or occupation. “There’s certainly a potential that mesothelioma could be related to people’s other exposures in their occupational history,” says Dr. Kapil. “So this type of a review gives us clues to the potential for an increased mortality, but it doesn’t pinpoint what’s causing that.”

Still, the researchers found enough evidence of a link to warrant further investigation. “We feel that there are still some gaps in our knowledge of Libby and vermiculate-related illness,” says Frank Bove, ScD, senior epidemiologist in the Division of Health Studies at ATSDR. To bridge those gaps, and learn more about the long-term health effects of exposure to the Libby ore, ATSDR and the United States Environmental Protection Agency (EPA) have launched an $8 million health-risk initiative. The effort is expected to be completed in five years.

For now, those who were potentially exposed to the contaminated ore may have to deal with the long-term health implications. Many remain unaware that they are at risk. “The biggest challenge is identifying and finding folks,” says Dr. Bove. “A lot of these facilities are closed. Some of them had pretty transient worker populations.”

The authors say that during their research they tried to get the word out to the affected communities. “When we did these specific studies we would come into contact with these workers and provide information to those we knew had a high likelihood of being exposed,” Anderson says. They encouraged anyone who had been exposed to talk to their doctors about their exposure, and, if they were smokers, to stop smoking.

Though the Libby mine is long closed, its health effects may linger for many years, and not only in those who were exposed at or near the processing facilities. There is also concern about products made from the contaminated ore, which include a number of building materials still in use today. The EPA is currently investigating whether these materials might also pose a health risk.


Horton DK, Bove F, Kapil V. Select mortality and cancer incidence among residents in various U.S. communities that received asbestos-contaminated vermiculite ore from Libby, Montana. Inhalation Toxicology. 2008;20:767-775

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