Select mortality and cancer incidence among residents in various U.S. communities that received asbestos-contaminated vermiculite ore from Libby, Montana

Our plain-English summary of Select mortality and cancer incidence among residents in various U.S. communities that received asbestos-contaminated vermiculite ore from Libby, Montana, by D.K. Horton, F. Bove, V. Kapil (Inhalation Toxicology, 2008).

The study

• Authors: D.K. Horton, F. Bove, V. Kapil
• Journal: Inhalation Toxicology
• Published: 2008;20(8):767-75
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In response to the significantly elevated asbestosis mortality rates found in Libby, Montana, in 2000, this analysis evaluated whether other communities throughout the United States that received asbestos-contaminated vermiculite ore from Libby experienced similar excess rates of asbestos-related diseases. Standardized mortality ratios were calculated using state death certificates, and standardized incidence ratios were calculated using cancer registry records for populations living near facilities that processed or received Libby vermiculite. This analysis focused primarily on diseases that are directly associated with asbestos exposure (e.g., asbestosis; cancer of the peritoneum, retroperitoneum, and pleura, including mesothelioma; and mesothelioma). Lung cancer and cancers of the digestive system, also associated with asbestos exposure, were not included in the analysis because they have additional risk factors for which exposure information was not available. Data from 70 unique sites in 23 states were evaluated. No statistically significant excesses of asbestosis mortality similar to those in Libby were noted; however, 11 sites (plus a state with 6 pooled sites that were counted as 1 site) had excess rates of mesothelioma and cancer of the peritoneum, retroperitoneum, and pleura. Further investigation should be conducted at these sites with excess rates of mesothelioma and cancer of the peritoneum, retroperitoneum, and pleura by participating state health departments to determine whether exposure to Libby vermiculite might have been a contributing factor.

In plain English

This analysis, by the U.S. Agency for Toxic Substances and Disease Registry, used existing state death certificates and cancer registry records. It asked whether people living near 70 sites in 23 states that processed or received vermiculite ore from Libby, Montana, had more asbestos-related disease than U.S. rates would predict. Libby vermiculite contained asbestiform minerals including tremolite, winchite and richterite. Deaths were studied mainly for 1979 to 1998 and cancer diagnoses mainly for 1986 to 1995. None of the 62 sites with death records reviewed had a statistically significant excess of asbestosis deaths. Seven sites had a significant excess of deaths from cancer of the peritoneum, retroperitoneum and pleura (including mesothelioma). In Portland, Oregon, 16 such deaths were observed against 2.5 expected (SMR 6.5, 95% CI 3.7 to 10.6). Seven sites, with six Illinois sites pooled as one, had a significant excess of mesothelioma cases, three of them among women. In all, 11 sites plus the pooled Illinois sites showed excesses. Because the records lacked detailed job information, the analysis could not show whether the people affected had worked at these facilities. The authors concluded that state health departments should examine these excesses more closely.

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: Health statistics review (ecological analysis of existing records): standardized mortality ratios from death certificates and standardized incidence ratios from cancer registry records, with expected numbers based on U.S. rates
• Who was studied: Residents of defined areas (ZIP codes, census tracts, city limits or radius around the site) near 70 facilities in 23 U.S. states that processed (exfoliated) or received Libby vermiculite. Deaths were mostly from 1979 to 1998 and cancer diagnoses mostly from 1986 to 1995, with some states using different periods. The areas totaled 3,967,340 people for the death certificate review and 2,046,505 people for the cancer registry review.
• Exposure: Residence in the same analysis area as a facility that processed or received asbestos-contaminated vermiculite ore from Libby, Montana, which contained asbestiform minerals including tremolite, winchite and richterite. No individual exposure was measured.
• Main results:
  • No statistically significant excess of asbestosis deaths at any of the 62 sites where death certificates were reviewed
  • 7 of 62 sites had at least one statistically significant excess of deaths from cancer of the peritoneum, retroperitoneum and pleura (including mesothelioma), in the total, male or female population
  • Portland, OR, deaths from cancer of the peritoneum, retroperitoneum and pleura: total population 16 observed vs 2.5 expected, SMR 6.5 (95% CI 3.7 to 10.6); males 15 observed vs 1.4 expected, SMR 10.7 (95% CI 6.0 to 17.6)
  • Salt Lake City, UT, had death rates for these cancers that were statistically significantly lower than expected in all population groups
  • 7 of the 53 sites with cancer registry records had at least one statistically significant excess of mesothelioma cases
  • Pooled Illinois sites, mesothelioma cases in the total population: 35 observed vs 19.6 expected, SIR 1.8 (95% CI 1.3 to 2.5)
  • Excess mesothelioma cases among females were found at three sites. In Jefferson Parish, LA, there were 3 female cases observed vs 0.5 expected, SIR 6.7 (95% CI 1.3 to 19.4).
  • Across both analyses, significant excesses were found at 11 unique sites plus the 6 pooled Illinois sites
• The authors' conclusion: The authors concluded that the analysis did not show asbestosis death rates comparable to those in Libby. They did identify sites with significant excesses of mesothelioma cases and of deaths from cancer of the peritoneum, retroperitoneum and pleura, and said participating state health departments should consider examining these more closely, for example with existing ATSDR questionnaires, to see whether Libby ore may have contributed.
• Limitations the authors state:
  • Possible exposure misclassification
  • Overstated numerators or underestimated denominators, large study areas, small numbers of events, underreporting of cancer cases, miscoding of deaths, and population migration
  • Possible confounding from asbestos exposure at work or in the environment from sources other than these vermiculite sites; no information on smoking
  • The records lacked detailed job information, so the analysis could not determine how many of the people affected worked at facilities that received Libby ore
  • Because of the long latency of asbestos-related diseases, case numbers may continue to rise in these populations
  • Lung cancer and digestive system cancers were not analyzed because information on their other risk factors was not available

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Libby vermiculite mine, Montana

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Talc and vermiculite.

Medical terms in this study, explained in our Lexicon: vermiculite, standardized mortality ratio (SMR), Death Certificate, Standardized Incidence Ratio (SIR), Cancer Registry, Libby Vermiculite, Asbestos Exposure, Peritoneum.

Related studies

• Mortality in a cohort of vermiculite miners exposed to fibrous amphibole in Libby, Montana — J.C. McDonald, J. Harris, et al. (2004)
• Radiographic abnormalities and exposure to asbestos-contaminated vermiculite in the community of Libby, Montana, USA — L.A. Peipins, M. Lewin, et al. (2003)
• A review of the federal government's health activities in response to asbestos-contaminated ore found in Libby, Montana — K. Horton, V. Kapil, et al. (2006)
• 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)
• Vermiculite, respiratory disease, and asbestos exposure in Libby, Montana: update of a cohort mortality study — P.A. Sullivan (2007)
• Cancer incidence and mortality associated with non-occupational and low dose exposure to Libby vermiculite in Minnesota — T. Konen, J.E. Johnson, et al. (2019)

Browse more research in Inhalation Toxicology, or return to medical research.