Dimensions of elongated mineral particles: a study of more than 570 fibers from more than 90 cases with implications for pathogenicity and classification as asbestiform vs. cleavage fragments

Our plain-English summary of Dimensions of elongated mineral particles: a study of more than 570 fibers from more than 90 cases with implications for pathogenicity and classification as asbestiform vs. cleavage fragments, by V.L. Roggli, C.L. Green (Ultrastructural Pathology, 2019).

The study

• Authors: V.L. Roggli, C.L. Green
• Journal: Ultrastructural Pathology
• Published: 2019;43(1):1-5
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos is well-recognized as the cause of a variety of disorders of the respiratory tract, including neoplastic as well as non-neoplastic conditions. Fiber dimensions and biopersistence are important determinants of the pathologic response, and analytical electron microscopy is a powerful technique for determining the fiber content of lung tissue samples. For decades our laboratory has examined lung tissue samples counting fibers measuring 5 µm or greater in length. More recent observations have indicated that fibers 10 µm or greater in length are pathogenic, and that a length of 10 µm and diameter less than 1.0 µm are useful features for distinguishing asbestiform fibers from cleavage fragments. We examined more than 570 fibers from more than 90 cases to determine the dimensions of fibers that might be classified as asbestos. The vast majority of fibers classified as amosite or crocidolite met the criteria for length greater than 10 µm and diameter less than 1.0 µm. However, a significant proportion of fibers classified as tremolite, actinolite, or anthophyllite did not meet these criteria. These findings have important implications for the identification and classification of elongated mineral particles, both in terms of pathogenicity as well as classification as asbestiform vs. cleavage fragments.

In plain English

Duke University authors reviewed their laboratory's electron microscope lung tissue analyses, which counted fibers 5 µm or longer and, since 2012, recorded their dimensions. They studied 573 fibers from 91 cases: 301 amosite, 84 crocidolite, 78 tremolite, 23 anthophyllite, 22 actinolite, 31 chrysotile, 32 Libby amphibole, and 2 for which amosite could not be told apart from crocidolite. They checked how many fibers fell short of recently published dimensions: at least 10 µm long and under 1.0 µm thick. Only 9% of amosite and 12% of crocidolite fibers were shorter than 10 µm. No amosite fibers, and 1% of crocidolite fibers, were both shorter than 10 µm and thicker than 1.0 µm. By contrast, 42% of tremolite and 41% of actinolite fibers were shorter than 10 µm. Also, 10% of tremolite and 14% of actinolite fibers met both conditions, which the authors considered likely cleavage fragments rather than true asbestos. The authors concluded that a significant proportion of tremolite, actinolite and anthophyllite fibers may be cleavage fragments with little or no pathogenic effect, while classification of amosite and crocidolite was minimally affected.

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: Retrospective review of one laboratory's records of lung tissue fiber analyses (scanning electron microscopy with energy dispersive x-ray analysis), measuring fiber length and diameter by fiber type
• Who was studied: 573 fibers from 91 cases (lung tissue samples) analyzed at the Duke University Medical Center laboratory, with dimensions documented since 2012. The fibers were 301 amosite, 84 crocidolite, 78 tremolite, 23 anthophyllite, 22 actinolite, 31 chrysotile and 32 Libby amphibole. There were also 2 fibers for which a distinction between amosite and crocidolite could not be made.
• Exposure: Fibers found in lung tissue: amosite, crocidolite, tremolite, actinolite, anthophyllite and chrysotile, plus Libby amphibole (which the article notes is not currently classified as asbestos). Fibers were counted if they were 5 µm or longer, with aspect ratios of at least 3:1 and roughly parallel sides.
• Main results:
  • Median length and diameter (µm) by fiber type: amosite 25 and 0.40; crocidolite 20 and 0.30; tremolite 10 and 1.00; actinolite 10.5 and 0.90; anthophyllite 23 and 0.90; chrysotile 12 and 0.50; Libby amphibole 18 and 0.85
  • Amosite fibers were 1.28 times longer than crocidolite fibers (p = 0.008). Crocidolite fibers were 25% thinner than amosite fibers (p less than 0.001).
  • Amosite fibers were 2.34 times longer and 54% thinner than tremolite fibers (p less than 0.001)
  • Libby amphibole fibers were 1.66 times longer than tremolite fibers (p = 0.003). They were only 12% thinner, a difference that was not statistically significant (p = 0.250).
  • Amosite fibers were 1.42 times longer and 31% thinner than the chrysotile fibers counted (p less than 0.001 for both)
  • Only 9% of amosite fibers and 12% of crocidolite fibers were less than 10 µm long. Only 1% of either type had a diameter greater than 1.0 µm.
  • No amosite fibers and 1% of crocidolite fibers were both shorter than 10 µm and thicker than 1.0 µm. The authors stated that their identification of amosite or crocidolite as asbestos was minimally affected by the newly published data.
  • Percent of fibers less than 10 µm long: tremolite 42, actinolite 41, anthophyllite 13, chrysotile 35, Libby amphibole 12.5. Percent with diameter greater than 1.0 µm: tremolite 36, actinolite 23, anthophyllite 39, chrysotile 23, Libby amphibole 31. Percent meeting both conditions: tremolite 10, actinolite 14, anthophyllite 0, chrysotile 3, Libby amphibole 3.
  • The authors considered the 10% of tremolite and 14% of actinolite fibers that were both shorter than 10 µm and thicker than 1.0 µm to be likely cleavage fragments
  • Of 108 asbestos bodies analyzed separately, more than 95% had a commercial amphibole core, mostly amosite with some crocidolite. No chrysotile or Libby amphibole asbestos bodies were found in this series.
  • Asbestos bodies were on average longer than uncoated fibers, with a grand median length of 32 µm (range 6 to 220 µm)
• The authors' conclusion: The authors concluded that excluding fibers under 10 µm, or treating short, thick fibers as likely cleavage fragments, has little or no effect on how their method classifies commercial amphiboles (amosite, crocidolite). They found the opposite for the non-commercial amphiboles (tremolite, actinolite, anthophyllite): lack of pathogenicity and likely cleavage-fragment status apply to a significant proportion of them, so the dimensions of these fibers need to be recorded when they are counted.
• Limitations the authors state:
  • The authors stated that chrysotile tends to break down into shorter fibers in the lung, and their method does not count these shorter fibers
  • The authors stated that many longer chrysotile fibers are too thin to be seen at their screening magnification, and that most chrysotile fibers they counted were fiber bundles

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestiform, Cleavage Fragment, Fiber Dimensions, biopersistence, Amosite, Crocidolite, Tremolite, Actinolite.

Related studies

• Comments on "Dimensions of elongated mineral particles with implications for pathogenicity and classification as asbestiform versus cleavage fragments" — M.M. Finkelstein (2019)
• Measuring EMPs in the lung what can be measured in the lung: Asbestiform minerals and cleavage fragments — V.L. Roggli (2018)
• Does qualitative examination of Elongated Mineral Particles (EMP) recovered from human and animal lungs provide reliable information on their carcinogenic and other effects? — B.W. Case (2018)
• Differential responses of murine alveolar macrophages to elongate mineral particles of asbestiform and non-asbestiform varieties: Cytotoxicity, cytokine secretion and transcriptional changes — T.O. Khaliullin, E.R. Kisin, et al. (2020)
• Pulmonary fibrosis in workers exposed to non-asbestiform tremolite asbestos minerals — H.Y. Yang, R.H. Shie, et al. (2013)
• Analysis and identification of elongated mineral particles in road coated aggregates — E. Leocat, C. Rielland, et al. (2018)

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