Lung content analysis of cases occupationally exposed to chrysotile asbestos

Our plain-English summary of Lung content analysis of cases occupationally exposed to chrysotile asbestos, by R.P. Nolan, A.M. Langer, J. Addison (Environmental Health Perspectives, 1994).

The study

• Authors: R.P. Nolan, A.M. Langer, J. Addison
• Journal: Environmental Health Perspectives
• Published: 1994;102 Suppl 5(Suppl 5):245-50
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The lung contents of six workers who had been occupationally exposed to chrysotile asbestos were examined. Five were lung cancer cases from Quebec, Canada. The sixth, an American worker who had developed pleural mesothelioma, was particularly interesting, with the lung content strikingly distinct from the Canadian cases; chrysotile, the predominant fiber in his lung, was present at a concentration 300 times that of the average total fiber content in the Canadian cases. The fiber length distribution of the chrysotile recovered from the U.S. mesothelioma case was indistinguishable from that of chrysotile specimens known to produce mesotheliomas in rats. It was also found that the characteristics of the calcium-magnesium-iron silicate fibers present in all six cases were not readily comparable to tremolite asbestos specimens known to induce mesotheliomas in animals.

In plain English

The authors used electron microscopy to examine lung fibers from six workers occupationally exposed to chrysotile asbestos. Five were male Quebec lung cancer cases exposed to chrysotile, though not exclusively. The sixth was a 59-year-old U.S. man with pleural mesothelioma. Counting fibers 0.5 micrometres or longer on-screen, concentrations ranged from 7 ± 4 million to 13,900 ± 2900 million per gram of dry lung. Chrysotile was present in all five Canadian cases but predominant in none. Amosite, crocidolite and calcium-magnesium-iron silicate fibers were also found in those cases. In the U.S. case, over 99% of identified fibers were chrysotile, and no amosite or crocidolite was found. Its average fiber concentration was about 300 times the Canadian average. On average across its two tissue specimens, only 1.5% of the 883 chrysotile fibers sized were 5 micrometres or longer. The authors found this similar to chrysotile samples that produced mesotheliomas in rats in earlier studies. The authors reported that the calcium-magnesium-iron silicate fibers were not readily comparable to tremolite asbestos known to cause mesotheliomas in animals. They noted that these fibers were not characterized well enough to be identified as tremolite.

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: Lung fiber content analysis of six individual cases by transmission electron microscopy, compared with reference mineral specimens whose effects in animals had been tested in earlier studies
• Who was studied: Six male workers. Five were lung cancer cases from Quebec, Canada, with lung tissue taken at autopsy. One was a 59-year-old U.S. worker with pleural mesothelioma, with tissue taken during surgery. A grid preparation from a Canadian chrysotile miner was also used for comparison.
• Exposure: Occupational exposure to chrysotile asbestos, although not exclusively, in Quebec, Canada. The U.S. case had an occupational history of asbestos exposure. The reference specimens were:
• UICC chrysotile A (Zimbabwe) and B (Canada)
• Calidria chrysotile from New Idria, California
• two short Canadian chrysotile specimens
• a residue of Canadian chrysotile sample 5
• tremolite asbestos from Jamestown, California
• Main results:
  • Across the six cases, using on-screen counting of fibers 0.5 micrometres or longer, fiber concentration ranged from 7 ± 4 x 10^6 to 13,900 ± 2900 x 10^6 fibers per gram of dry lung.
  • In the U.S. case, more detailed photomontage counting found approximately 27,600 x 10^6 fibers longer than 0.5 micrometres per gram of dry lung in each of the two tissue specimens.
  • Counting fibers of all lengths, the average concentration in the U.S. case was approximately 50,600 x 10^6 fibers per gram of dry lung.
  • In the five Canadian cases, chrysotile was present in all five but was the predominant fiber in none. Amosite, anthophyllite-talc, crocidolite and calcium-magnesium-iron silicate fibers were also identified.
  • In Canadian Cases 1 and 5, where no commercial amphibole asbestos was present, over 90% of the non-chrysotile fibers analyzed were calcium-magnesium-iron silicates.
  • In the U.S. pleural mesothelioma case (Case 6), more than 99% of the fibers identified were chrysotile.
  • The fiber concentration in the U.S. case was approximately 300 times greater than the average total fiber concentration in the Canadian cases.
  • No amosite or crocidolite fibers were found in the U.S. case. None were found among 350 fibers scanned in specimen 6a or among 180 fibers scanned in specimen 6b.
  • Calcium-magnesium-iron silicate fibers in the U.S. case corresponded to 223 ± 90 x 10^6 fibers per gram of dry lung.
  • In the U.S. case, on average across the two tissue specimens, 1.5% of the 883 chrysotile fibers sized were 5 micrometres or longer. The table gives 2.5% of 311 fibers in specimen 6a and 0.5% of 572 fibers in specimen 6b. The longest fiber found was 33 micrometres.
  • When fibers shorter than 0.5 micrometres were ignored, the fiber length distributions of reference chrysotile specimens i and iv and of the U.S. case were indistinguishable.
  • The rat mesothelioma results for the reference chrysotile specimens came from earlier studies by other researchers, not from this study.
  • In reference specimen v, which was mostly calcium-magnesium-iron silicates, 11% of the silicate fibers were 5 micrometres or longer. The mean for the three reference chrysotile specimens was 1.3%.
• The authors' conclusion: The authors concluded that the lung content of the U.S. pleural mesothelioma case was strikingly distinct from that of the Canadian cases. They found its chrysotile length distribution indistinguishable from chrysotile specimens known to produce mesotheliomas in rats. They also concluded that the calcium-magnesium-iron silicate fibers in all six cases were not readily comparable to tremolite asbestos specimens known to induce mesotheliomas in animals.
• Limitations the authors state:
  • The calcium-magnesium-iron silicate fibers, commonly referred to as tremolite, were not characterized in enough detail to justify identifying them as tremolite. The authors said this would be done in further studies.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Santa Rita mine, Joaquin Ridge near Coalinga, California

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile, Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Chrysotile, Lung Cancer, Pleural Mesothelioma, Fiber Length, Mesothelioma, Silicate, Tremolite.

Related studies

• Chrysotile biopersistence in the lungs of persons in the general population and exposed workers — A.M. Langer, R.P. Nolan (1994)
• Lung asbestos content in chrysotile workers with mesothelioma — A. Churg, B. Wiggs, et al. (1984)
• Quantification of the pathological response and fate in the lung and pleura of chrysotile in combination with fine particles compared to amosite-asbestos following short-term inhalation exposure — D.M. Bernstein, R.A. Rogers, et al. (2011)
• Persistence of long, thin chrysotile asbestos fibers in the lungs of rats — P.G. Coin, V.L. Roggli, et al. (1994)
• A biopersistence study following exposure to chrysotile asbestos alone or in combination with fine particles — D.M. Bernstein, K. Donaldson, et al. (2008)
• Sumas Mountain chrysotile induces greater lung fibrosis in Fischer344 rats than Libby amphibole, El Dorado tremolite, and Ontario ferroactinolite — J.M. Cyphert, A. Nyska, et al. (2012)

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