Lung function, radiological changes and exposure: analysis of ATSDR data from Libby, MT, USA

Our plain-English summary of Lung function, radiological changes and exposure: analysis of ATSDR data from Libby, MT, USA, by D. Weill, G. Dhillon, L. Freyder, et al (The European Respiratory Journal, 2011).

The study

• Authors: D. Weill, G. Dhillon, L. Freyder, J. Lefante, H. Glindmeyer
• Journal: The European Respiratory Journal
• Published: 2011;38(2):376-83
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In 2000, the Agency for Toxic Substances and Disease Registry (ATSDR; Atlanta, GA, USA) investigated lung disease in those exposed to the tremolite-contaminated vermiculite mine in Libby, MT, USA. Previously unreported spirometric results are presented here in relation to exposure and radiographic findings. 4,524 study participants were assigned to one of seven mutually exclusive exposure categories. Associations among radiographic findings, spirometric results and exposure were investigated, along with the effect of a reduction in exposure potential when production was moved to a wet process mill in the mid 1970s. Spirometry data for the total population by smoking status and age were within the normal range. Prevalence of pleural plaque increased with age, but was lowest in the environmentally exposed group (0.42-12.74%) and greatest in the W.R. Grace & Co. mineworkers (20-45.68%). For males, there was a significant (4.5%) effect of pleural plaques on forced vital capacity. For W.R. Grace & Co. workers and household contacts, a reduction in plaque (0.11 versus 1.64%) and in diffuse pleural thickening or costophrenic angle obliteration (1.94 and 0.13%) was noted for those exposed after 1976. These analyses do not support a clinically important reduction in spirometry of this cohort. The 1976 reductions in exposure have led to decrease in radiographic changes.

In plain English

This study reanalysed data from the US Agency for Toxic Substances and Disease Registry's (ATSDR) 2000 medical screening in Libby, Montana, where a vermiculite mine was contaminated with tremolite asbestos. The authors studied 4,524 people aged 25 to 90 who had lung function (spirometry) results. They first excluded people reporting traditional asbestos jobs, then sorted the rest into seven exposure groups. On average, lung function was within the normal range for both ever-smokers and never-smokers. Pleural plaque prevalence rose with age. It ranged from 0.42 to 12.74% in the environmentally exposed group and from 20 to 45.68% among mine workers. In men, plaques were linked to a small drop in forced vital capacity of 4.2 to 4.4% of predicted. Diffuse pleural thickening or costophrenic angle obliteration was linked to larger drops. Among residents who were neither Grace workers nor household contacts, plaque prevalence was 10.11% for those first exposed before 1976 and 1.64% for those exposed only after 1976. The authors concluded that the data do not support a clinically important reduction in lung function in the cohort as a whole.

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 reanalysis of existing ATSDR community screening data (questionnaires, spirometry and chest radiograph readings)
• Who was studied: Current and former Libby, Montana residents and former W.R. Grace & Co. workers screened by ATSDR in 2000. Of 7,307 participants, 4,524 aged 25 to 90 with spirometry results were studied, after excluding people with traditional asbestos occupations. They were placed in seven exposure groups, including 255 Grace workers and 1,894 with environmental exposure only.
• Exposure: Tremolite-contaminated vermiculite from the Libby mine, through work at W.R. Grace & Co., other vermiculite-related jobs, household contact with workers, or environmental exposure. Timing of exposure (before versus after 1976) was also compared.
• Main results:
  • Average lung function for both ever-smokers and never-smokers was within the normal range. Ever-smokers had lower values than never-smokers.
  • Pleural plaque prevalence across age groups was 0.42 to 12.74% in the environmental exposure group, 20 to 45.68% among those who worked at the mine, and 1.34 to 37.67% among those who lived with a mine worker.
  • People with pleural plaques and no other radiographic abnormality (n=482) had a mean forced vital capacity of 95.63% of predicted.
  • After adjustment for age, sex, smoking and body mass index, pleural plaques were associated with a small reduction in forced vital capacity in males only: 4.28% in never-smoking males and 4.43% in ever-smoking males.
  • Diffuse pleural thickening and/or costophrenic angle obliteration was associated with reduced forced vital capacity in all sex and smoking groups except never-smoking females. The reductions were 6.73% in ever-smoking females, 9.77% in ever-smoking males and 23.77% in never-smoking males.
  • People with more extensive diffuse pleural thickening (extent 2 or more and width a or more; n=30) had a mean forced vital capacity of 76.26% of predicted. Those with less extensive thickening (n=23) had 91.98% (p=0.0006).
  • This comparison excluded Grace workers, household contacts and people with non-tremolite asbestos exposure. Plaque prevalence was 10.11% for those first exposed before 1976 and 1.64% for those exposed only after 1976. Diffuse pleural thickening or costophrenic angle obliteration fell from 1.94% to 0.13%.
• The authors' conclusion: The authors concluded that the analyses do not support a clinically important reduction in lung function in the cohort as a whole, and that the 1976 reductions in exposure were followed by fewer radiographic changes. In the discussion they describe the mill closure as appearing to be associated with the reduction.
• Limitations the authors state:
  • In the before/after 1976 comparison, 33.44% of the pre-1976 group reported playing in vermiculite piles, compared with 12.39% of the post-1976 group, which the authors say introduces possible selection bias.
  • People in the 'other dusty occupation' group may have had occupational asbestos exposure, which could account for some pleural changes in that group.
  • The analyses relied on ATSDR's radiograph readings, lung function measurements and questionnaires rather than new data, and the exposure categories were qualitative.

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: Pleural plaques and thickening, Talc and vermiculite, Tremolite.

Medical terms in this study, explained in our Lexicon: ATSDR, Tremolite, vermiculite, Spirometry, Pleural Plaques, W.R. Grace, Diffuse Pleural Thickening, Costophrenic angle.

Related studies

• Asbestos-related pleural disease due to tremolite associated with progressive loss of lung function: serial observations in 123 miners, family members, and residents of Libby, Montana — A.C. Whitehouse (2004)
• 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)
• Libby Amphibole Disease: Pulmonary Function and CT Abnormalities in Vermiculite Miners — A. Miller, J. Szeinuk, et al. (2018)
• Low levels of exposure to libby amphibole asbestos and localized pleural thickening — K.Y. Christensen, T.F. Bateson, et al. (2013)
• Radiological survey of past and present vermiculite miners exposed to tremolite — J.C. McDonald, P. Sebastien, et al. (1986)
• Association between cumulative fiber exposure and respiratory outcomes among Libby vermiculite workers — T.C. Larson, V.C. Antao, et al. (2012)

Browse more research in The European Respiratory Journal, or return to medical research.