A clinical assessment and lung tissue burden from an individual who worked as a Libby vermiculite miner

Our plain-English summary of A clinical assessment and lung tissue burden from an individual who worked as a Libby vermiculite miner, by B. Black, R.F. Dodson, J.R. Bruce, et al (Inhalation Toxicology, 2017).

The study

• Authors: B. Black, R.F. Dodson, J.R. Bruce, L.W. Poye, C. Henschke, G. Loewen
• Journal: Inhalation Toxicology
• Published: 2017;29(9):404-413
• Type of article: Case report
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

During its days of operation (1920s-1990), the world's largest source of vermiculite was extracted from a mine located near Libby, Montana. The material mined at this site was shipped for various commercial applications to numerous sites in the United States. There was a "fibrous" component with toxic potential within the vermiculite deposit that has resulted in "asbestos-like" diseases/deaths being reported in numerous studies involving miners as well as residents of the town of Libby. The present case involves the clinical assessments of an individual who worked at the mine from 1969 to 1990. He had no other known occupational exposures to fibrous materials. He developed a clinical picture that included "asbestos-like" pathological features and eventually an adenocarcinoma. The clinical assessment including radiographic features will be presented. The evaluation will also include the analytical evaluation of the fibrous/ferruginous body composition of the lung tissue. This is to our knowledge the first time such an extensive evaluation has been conducted in a vermiculite miner from Libby, Montana.

In plain English

This case report described one man who moved to Libby, Montana in 1969 and worked as a millwright at the vermiculite mine until it closed in 1990. Company records estimated his exposure at 64 fiber-years, and he had a 34 pack-year smoking history. He developed shortness of breath on exertion, chest pain, and thin pleural thickening. In 2013 lung cancer screening found a lung nodule. It was confirmed as stage IA adenocarcinoma and removed by surgery, which also showed fibrosis of the parietal pleura. A section of his lung tissue showed changes the authors classified as Grade 1 asbestosis. Digested lung tissue contained 150,830 ferruginous bodies and 5,377,090 uncoated fibers per gram of de-paraffinized wet weight of tissue. All uncoated fibers analyzed, and the cores of the ferruginous bodies examined, were Libby amphiboles. He later died of complications of sepsis after peritonitis, a cause recorded as not asbestos related. The authors noted that the major fiber exposures in this case were not among the six fiber types federal rules define as asbestos. They questioned what the resulting fibrosis should be called, and took the position that it should be called asbestosis.

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: case report (single-patient clinical assessment with lung tissue fiber and ferruginous body analysis by light and transmission electron microscopy)
• Who was studied: One 74-year-old man who moved to Libby, Montana in 1969, worked as a millwright at the vermiculite mine until it closed in 1990, and left the area in 1991. He was identified with early lung cancer through low-dose CT screening at the Center for Asbestos Related Disease in Libby.
• Exposure: Libby vermiculite mine dust containing Libby amphiboles, with no other known occupational fiber exposure. Exposure was estimated at 64 fiber-years by WR Grace Company documentation. He also had a 34 pack-year smoking history and quit in 1984.
• Main results:
  • Surgical pathology confirmed stage IA adenocarcinoma of the lung (T1N0M0) in the left lower lobe.
  • At surgery, a thin, white layer of fibrotic tissue was seen on the parietal pleura. Biopsy histology confirmed pleural fibrosis.
  • Examination of a lung tissue section showed fibrosis around the bronchioles and ferruginous bodies with features of classical asbestos bodies. The authors classified this as Grade 1 asbestosis under the CAP-NIOSH grading scheme.
  • Digested lung tissue contained 150,830 ferruginous bodies per gram of de-paraffinized wet weight of tissue.
  • The 100 uncoated fibers counted were equivalent to 5,377,090 fibers per gram of de-paraffinized wet weight of tissue. All uncoated fibers analyzed were Libby amphiboles.
  • The uncoated Libby amphibole fibers averaged 13.03 micrometers in length. Eighteen of the 100 were shorter than five micrometers, and the longest was 63 micrometers.
  • The cores of the ferruginous bodies examined were Libby amphiboles: 3 bodies found at 15,000x magnification and 17 found at 2000x.
  • The authors compared these counts with an earlier series of twenty people with alleged occupational asbestos exposure and lung cancer. Both this man's ferruginous body count and his fiber count would have been the second highest in that series.
  • He remained free of lung cancer recurrence for two years after surgery. He later died of complications of sepsis after peritonitis, and his official cause of death was determined to be not asbestos related.
• The authors' conclusion: The authors concluded that the ferruginous bodies looked like asbestos bodies. They stated that the bodies were not formed on any of the mineral types defined as asbestos in federal regulations, and that the major fiber exposures in this case were not regulated asbestos types. This raised the question of what to call the resulting fibrosis. They took the position that it should be called asbestosis. They also suggested that a standardized CT reading method for pleural fibrosis would be useful.
• Limitations the authors state:
  • The fibers and ferruginous bodies measured reflect only what remained in the lung after years of clearance. Shorter fibers are more likely to have been cleared.
  • The cores of ferruginous bodies cannot be identified by light microscopy; identifying them requires electron microscopy.

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: Libby Vermiculite, vermiculite, Occupational Exposure, Adenocarcinoma, Ferruginous body.

Related studies

• A clinical evaluation and tissue fiber burden analysis of a lifetime resident of Libby, Montana with adenocarcinoma of the lung — R.F. Dodson, B. Black, et al. (2020)
• 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)
• Mortality in a cohort of vermiculite miners exposed to fibrous amphibole in Libby, Montana — J.C. McDonald, J. Harris, et al. (2004)
• 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)
• Libby Amphibole Disease: Pulmonary Function and CT Abnormalities in Vermiculite Miners — A. Miller, J. Szeinuk, et al. (2018)
• Vermiculite, respiratory disease, and asbestos exposure in Libby, Montana: update of a cohort mortality study — P.A. Sullivan (2007)

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