Radiographic Evidence of Nonoccupational Asbestos Exposure from Processing Libby Vermiculite in Minneapolis, Minnesota

By Alexander, Bruce H.; Raleigh, Katherine K. et al. | Environmental Health Perspectives, January 2012 | Go to article overview

Radiographic Evidence of Nonoccupational Asbestos Exposure from Processing Libby Vermiculite in Minneapolis, Minnesota


Alexander, Bruce H., Raleigh, Katherine K., Johnson, Jean, Mandel, Jeffrey H., Adgata, John L., Ramachandran, Gurumurthy, Messing, Rita B., Eshenaur, Tannie, Williams, Allan, Environmental Health Perspectives


BACKGROUND: Community exposure to asbestos from contaminated vermiculite ore from Libby, Montana, occurred in many processing sites in the United States, including a densely populated urban residential neighborhood of Minneapolis, Minnesota.

OBJECTIVE: We examined exposed community residents who never worked at the plant or never lived with a plant worker for radiographic evidence of lung changes consistent with asbestos exposure.

METHODS: We obtained posteroanterior chest radiographs to identify the prevalence of pleural abnormalities consistent with pneumoconiosis, as determined by consensus of two National Institute for Occupational Safety and Health--certified B-reader radiologists. We estimated cumulative asbestos exposure (fibers per cubic centimeters x months) with air dispersion model data and activity-based modeled exposure estimates for vermiculite processing waste contact. We modeled associations between pleural abnormalities and asbestos exposure using multiple logistic regression to adjust for year of birth, sex, and potential occupational asbestos exposure.

RESULTS: Radiographs were obtained for 461 participants. The prevalence of pleural abnormalities by B-reader consensus was 10.8%. A history of direct contact with the waste and ever playing in the waste piles was associated with pleural abnormalities (odds ratio [OR] 2.78 [95% confidence interval (CI): 1.26, 6.10] and 2.17 (95% CI: 0.99, 4.78), respectively, when adjusted for background exposure). The regression coefficients for log-transformed measures (fibers per cubic centimeters x months) of background exposure and activity-based exposure were 0.322 (95% CI: 0.078, 0.567) and 0.063 (95% CI: --0.013, 0.139), respectively, when adjusted for each other, and 0.283 (95% CI: 0.104, 0.463) for cumulative exposure from all sources.

CONCLUSION: These results support the hypothesis that community exposure to asbestos-contaminated vermiculite originating from Libby, Montana, is associated with measurable effects based on radiographic evidence.

KEY WORDS: amphibole, asbestos, community exposure, Libby vermiculite, lung diseases, pleural abnormalities. Environ Health Perspect 120:44-49 (2012). http://dx.doi.org/10.1289/ehp.1103529Online 12 October 2011]

Vermiculite ore from a mine near Libby, Montana, is known to be contaminated with amphibole asbestos (primarily winchite, rich-terite, and tremolite), which is liberated in the mining and processing of the ore [Agency for Toxic Substances and Disease Registry (ATSDR) 2008; Meeker et al. 2003]. The mining and processing of vermiculite in Libby have been associated with elevated mortality from lung cancer, nonmalignant respiratory disease, and mesothelioma (Amandus and Wheeler 1987; McDonald et al. 1986a; Sullivan 2007) in exposed workers, members of the community, and workers employed at distant vermiculite processing sites (Amandus et al. 1987; McDonald et al. 1986b; Peipins et al. 2003; Rohs et al. 2008). Environmental contamination from this source is not limited to Libby, as hundreds of thousands of tons of the ore were shipped throughout the country for processing. One of the destinations for the Libby vermiculite ore was the Western Minerals/W.R. Grace (WM/WRG) facility in Minneapolis, Minnesota.

The WM/WRG facility processed vermiculite ore mined in Libby, Montana, from 1938 to 1989. This facility was one of approximately 250 such processing facilities in the United States that received Libby ore. At the WM/WRG facility, the vermiculite ore was heated in two furnaces and expanded in a process known as exfoliation to make Zonolite [R] insulation, Monokote [R] fireproofing, and other building materials. In addition to the vermiculite product, the exfoliation produced a waste material that contained up to 10% amphibole asbestos [Minnesota Department of Health (MDH) 2005]. The waste rock was piled on the WM/WRG property and offered freely to the community. …

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Radiographic Evidence of Nonoccupational Asbestos Exposure from Processing Libby Vermiculite in Minneapolis, Minnesota
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