Radiographic evidence of nonoccupational asbestos exposure from processing Libby vermiculite in Minneapolis, Minnesota

Our plain-English summary of Radiographic evidence of nonoccupational asbestos exposure from processing Libby vermiculite in Minneapolis, Minnesota, by B.H. Alexander, K.K. Raleigh, J. Johnson, et al (Environmental Health Perspectives, 2012).

The study

• Authors: B.H. Alexander, K.K. Raleigh, J. Johnson, J.H. Mandel, J.L. Adgate, G. Ramachandran, R.B. Messing, T. Eshenaur, A. Williams
• Journal: Environmental Health Perspectives
• Published: 2012;120(1):44-9
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

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 × 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 × 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.

In plain English

This study looked for asbestos-related chest X-ray changes in residents near a Minneapolis plant that processed vermiculite ore from Libby, Montana, from 1938 to 1989. The ore was contaminated with amphibole asbestos, mainly winchite, richterite and tremolite. Participants had never worked at the plant or lived with a plant worker. Of 2,222 eligible people, 461 had a chest X-ray, read by certified B-readers. The authors estimated each person's exposure from plant air emissions and from activities such as playing on waste piles. Pleural abnormalities agreed on by two readers were found in 49 participants, 10.8% of those whose X-rays could be read (7 X-rays were of insufficient quality). After accounting for background air exposure, contact with the waste was associated with pleural abnormalities (odds ratio 2.78, 95% CI 1.26 to 6.10). For ever playing on the piles the odds ratio was 2.17 (95% CI 0.99 to 4.78). Associations were most consistent with long-term background exposure. The authors concluded that effects may occur at lower exposures than previously believed. They noted the study was small and relied on self-reported activities and a single X-ray view.

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: Cross-sectional radiographic study of community residents, using logistic regression to estimate prevalence odds ratios
• Who was studied: 461 residents of the community around the Western Minerals/W.R. Grace vermiculite plant in Minneapolis, Minnesota, who completed a clinic X-ray. They were drawn from 2,222 eligible members of the Northeast Minneapolis Community Vermiculite Investigation cohort. All eligible members had never worked at the plant, were not household contacts of plant workers, and were first at risk of exposure before 1980.
• Exposure: Libby vermiculite contaminated with amphibole asbestos (primarily winchite, richterite and tremolite). Exposure was estimated from two sources. Background exposure came from plant air emissions, based on residential history and an air dispersion model. Activity-based exposure came from moving waste rock, using waste rock at home, installing or removing vermiculite insulation, and playing on waste piles. All exposures were expressed in fibers per cubic centimeter times months.
• Main results:
  • Pleural abnormalities reported by any B-reader were found in 15.4% of the 461 participants.
  • Pleural abnormalities confirmed by two B-readers were found in 49 participants. That is 10.6% of all 461 participants. After excluding 7 X-rays of insufficient quality, the final prevalence was 10.8%. This comprised 45 participants with pleural plaques and 5 with diffuse pleural thickening.
  • Compared with no contact, any contact with the waste had an odds ratio of 3.60 (95% CI: 1.71, 7.58). Ever playing on the piles had an odds ratio of 3.23 (95% CI: 1.59, 6.52). After adjustment for background exposure, these fell to 2.78 (95% CI: 1.26, 6.10) and 2.17 (95% CI: 0.99, 4.78), respectively. All models were also adjusted for year of birth, sex and history of an asbestos-exposed job.
  • Log-transformed background, pile-playing, total activity and total exposure were each positively associated with pleural abnormalities when modeled separately. With background and activity exposure in the same model, the coefficient for background exposure was 0.322 (95% CI: 0.078, 0.567). The coefficient for activity exposure was 0.063 (95% CI: -0.013, 0.139; p = 0.102).
  • For a difference in total exposure equal to the interquartile range, the odds ratio for pleural abnormalities was 2.22 (95% CI: 1.34, 3.68).
  • Total exposure was compared by category against exposure below the median. The highest quarter had an odds ratio of 3.79 (95% CI: 1.76, 8.16). The third quarter had an odds ratio of 1.05 (95% CI: 0.44, 2.50).
  • When background exposure was analyzed by category, the association appeared limited to exposure at or above the 75th percentile. In that group the adjusted odds ratio was 2.52 (95% CI: 1.15, 5.50) compared with the lowest category.
  • Eight participants had parenchymal (lung tissue) abnormalities at ILO category 1/0 or above confirmed by consensus. This was too few to analyze statistically.
• The authors' conclusion: The authors concluded that community exposure from processing Libby vermiculite was associated with pleural abnormalities. They found associations most consistent with long-term, lower background exposure rather than intense intermittent activity exposure. They suggested effects of asbestos exposure may occur at lower levels than previously believed.
• Limitations the authors state:
  • The study was small, which limited the precision of its estimates.
  • Participation required a clinic visit, and participation may have been influenced by known health status.
  • Activity-based exposure relied on activities self-reported in 2001, with assumptions about duration that likely introduced exposure misclassification.
  • The air dispersion model assumed equal exposure for everyone at a residence, regardless of where they spent their day.
  • Only a single posteroanterior chest X-ray was used, so some pleural abnormalities may have been missed.
  • Associations were weaker if the 22 participants with disputed readings were counted as having pleural abnormalities. In that case the background exposure coefficient fell from 0.401 to 0.146 (95% CI: -0.091, 0.382).

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: Asbestos Exposure, Libby Vermiculite, vermiculite, Chest X-Ray, Pneumoconiosis, B-Reader, Fibers per Cubic Centimeter (f/cc), Odds Ratio.

Related studies

• The traveling Libby legacy: Minnesota community exhibits nonoccupational health impacts consistent with asbestos damage — T. Tillett (2012)
• Asbestos-related radiographic findings among household contacts of workers exposed to Libby vermiculite: impact of workers' personal hygiene practices — T.J. Hilbert, A. Franzblau, et al. (2013)
• 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)
• 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)
• Low-level fiber-induced radiographic changes caused by Libby vermiculite: a 25-year follow-up study — A.M. Rohs, J.E. Lockey, et al. (2008)
• The morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite: Part III. Radiographic findings — H.E. Amandus, R. Althouse, et al. (1987)

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