Community exposure to asbestos from a vermiculite exfoliation plant in NE Minneapolis

Our plain-English summary of Community exposure to asbestos from a vermiculite exfoliation plant in NE Minneapolis, by J. Kelly, G.C. Pratt, J. Johnson, et al (Inhalation Toxicology, 2006).

The study

• Authors: J. Kelly, G.C. Pratt, J. Johnson, R.B. Messing
• Journal: Inhalation Toxicology
• Published: 2006;18(12):941-7
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Western Mineral Products/W. R. Grace operated a vermiculite plant in a mixed industrial/residential area of northeast Minneapolis from 1936 to 1989. The plant processed vermiculite ore contaminated with amphibole asbestos from a mine in Libby, MT. Air monitoring in the early 1970s found fiber concentrations in excess of 10 fibers per cubic centimeter of air (f/cc), indicating that worker exposure to asbestos was occasionally 100 times the current occupational standard. Residents of the surrounding community also had direct contact with vermiculite processing wastes (containing up to 10% amphibole asbestos) that were made freely available. Children played on waste piles and neighborhood residents hauled the wastes away for home use. In total, 259 contaminated residential properties have been found to date. Reported emission factors and plant process data were used as inputs to model airborne emissions from the plant over several operating scenarios using the U.S. Environmental Protection Agency (EPA) ISC-Prime model. Results estimate short-term air concentrations of asbestos fibers in residential areas nearest the plant may have at times exceeded current occupational standards. Exposure estimates for other pathways were derived primarily from assessments done in Libby by the U.S. EPA. The Northeast Minneapolis Community Vermiculite Investigation (NMCVI) was conducted by the Minnesota Department of Health to identify and characterize the exposures of a cohort of over 6000 people who live or lived in Northeast Minneapolis and may have been exposed to asbestos. This cohort is now being investigated in a respiratory health screening study conducted by the University of Minnesota and the Minnesota Department of Health.

In plain English

This report estimated past asbestos exposures around a Minneapolis vermiculite plant that operated from about 1936 to 1989. The plant processed ore from Libby, Montana, that was contaminated with amphibole asbestos of the actinolite–tremolite–winchite–richterite series, called Libby asbestos. The report estimated exposure only; it did not measure disease. Company air samples from the 1970s found fiber counts above 10 fibers per cubic centimeter (f/cc) for workers. The plant also used chrysotile in some products, so the authors noted that presumably not all of the fibers counted were Libby asbestos. Air modeling gave maximum estimates, generally at the site itself, of 0.026 f/cc over the long term and 0.89 f/cc for one hour during 1936–1972. Wastes containing 2% to 10% Libby asbestos were left in a free pile outside the plant. Using U.S. EPA measurements made in Libby, children playing in the piles were estimated at 1.66 f/cc per event. Investigators identified 259 contaminated residential properties. The authors concluded that occupational exposures were the most severe, but community exposures may also have been significant. They cautioned that the air model carries many uncertainties.

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: Exposure assessment report. It combined company industrial hygiene data, an air dispersion model (U.S. EPA ISC-Prime) and exposure estimates taken from U.S. EPA studies in Libby, MT. No health outcomes were measured.
• Who was studied: Workers and the surrounding mixed industrial/residential community near the Western Mineral Products/W. R. Grace plant at 1720 Madison Street NE, Minneapolis. The plant operated from about 1936 to 1989. The related NMCVI cohort numbers over 6000 people who live or lived in the neighborhood; their health was not studied in this report.
• Exposure: Libby asbestos: amphibole of the actinolite–tremolite–winchite–richterite mineral series in vermiculite ore from Libby, MT. Company records show over 138,000 tons of ore processed (138,910 tons shipped 1958–1988). Shipped ore was estimated at less than 1% to 7% asbestos, and processing wastes at 2% to 10% friable Libby asbestos. The plant also used commercial chrysotile asbestos in some products.
• Main results:
  • Workers: W. R. Grace industrial hygiene data showed fiber counts above 10 f/cc in the early 1970s, and short-term personal samples above 5 f/cc for furnace operators as late as 1978. The current OSHA limit is 0.1 f/cc. Samples were analyzed by phase-contrast light microscopy. Because chrysotile was also used, the authors noted that presumably not all fibers counted were Libby asbestos.
  • Modeled air concentrations, maximums generally at the plant site near emission points: 0.026 f/cc long-term and 0.89 f/cc one-hour (1936–1972); 0.0027 and 0.19 (1972–1989); 0.00038 and 0.029 (1989–1999); 0.00013 and 0.010 (1999–2001).
  • Plant wastes were dumped in a pile outside the plant with a sign saying they were free for the taking. According to W. R. Grace records, the wastes contained between 2% and 10% friable Libby asbestos. Residents reported that children played in the piles and adults took the wastes home.
  • Community exposure estimates were derived from U.S. EPA measurements in Libby, all per event: children playing in waste piles 1.66 f/cc; disturbing vermiculite insulation 0.57 f/cc; disturbing yards and gardens 0.23 f/cc; adults handling waste from piles 0.11 f/cc. Long-term exposure from disturbance of driveways and alleys was estimated at 0.001 f/cc.
  • 259 contaminated residential properties were identified, after visual inspection of over 1600 properties by U.S. EPA, MPCA and MDH personnel. Some were as far as 10 miles from the plant.
• The authors' conclusion: The authors concluded that occupational exposures were the most severe, but community exposures from ambient air and from handling or disturbing wastes may also have been significant. They added that residents closest to the plant may have had multiple exposure pathways.
• Limitations the authors state:
  • The air model has many sources of uncertainty: meteorological data, reliability of W. R. Grace historical information, variability in ore asbestos content, and fugitive dust and particle-to-fiber assumptions. Its numeric estimates are likely less reliable except near emission points, and are best used for relative comparison.
  • Exposures of workers' household contacts from dust carried home on clothing were likely but difficult to estimate.
  • The plant also used chrysotile asbestos, so presumably not all fibers in the workplace air samples were Libby asbestos.
  • Records of ore processed are incomplete, so the actual amount could have been higher.

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: Talc and vermiculite.

Medical terms in this study, explained in our Lexicon: vermiculite, Exfoliation Plant, Amphibole Asbestos, Air Sampling, Fibers per Cubic Centimeter (f/cc).

Related studies

• Radiographic evidence of nonoccupational asbestos exposure from processing Libby vermiculite in Minneapolis, Minnesota — B.H. Alexander, K.K. Raleigh, et al. (2012)
• Modeling community asbestos exposure near a vermiculite processing facility: Impact of human activities on cumulative exposure — J.L. Adgate, S.J. Cho, et al. (2011)
• Select mortality and cancer incidence among residents in various U.S. communities that received asbestos-contaminated vermiculite ore from Libby, Montana — D.K. Horton, F. Bove, et al. (2008)
• 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)
• Cohort study of mortality of vermiculite miners exposed to tremolite — J.C. McDonald, A.D. McDonald, et al. (1986)
• Exposure matrix development for the Libby cohort — C.W. Noonan (2006)

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