Critical values for dimensional parameters of mesotheliomagenic mineral fibers: evidence from the dimensions and rigidity of MWCNT

Our plain-English summary of Critical values for dimensional parameters of mesotheliomagenic mineral fibers: evidence from the dimensions and rigidity of MWCNT, by A.G. Wylie, A.A. Korchevskiy (Frontiers in Toxicology, 2025).

The study

• Authors: A.G. Wylie, A.A. Korchevskiy
• Journal: Frontiers in Toxicology
• Published: 2025;7:1568513
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

MWCNT (multi-walled carbon nanotubes) used in 72 animal instillation or inhalation studies were classified by average length, average width, Young's modulus, Rigidity Index (RI), and potency for mesothelioma in animals. The RI is based on the Euler buckling theory. MWCNT that induce mesothelioma have average lengths >2 µm and widths >37 nm, and average RI > 0.05 (µm2 x GPa x 104). Many noncarcinogenic MWCNT materials have RI < 0.05 and lack biological rigidity. In comparison, Elongate Mineral Particle (EMP) populations with one exception have RI > 0.05. Mineral particles likely to have RI < 0.05 include chrysotile fibrils with lengths >5 μm, amosite and crocidolite fibers with widths <60 nm, and sheet silicate fibers with widths <200 nm. The product of percent EMPA, average RI, and biosolubility among silicates correlates with known mesothelioma potency. The derived models reproduce published values of RM with high statistical significance (P < 0.05). Average RI, length, and width are critical parameters for mesotheliomagenicity for both MWCNT and EMPA mineral fiber.

Copyright © 2025 Wylie and Korchevskiy.

In plain English

The authors compiled published animal studies of multi-walled carbon nanotubes (MWCNT) and compared them with mineral fibers. From 72 animal inhalation and implantation experiments in 55 publications, they recorded each nanotube material's average length and width and calculated a "Rigidity Index" based on buckling theory. The shortest average length among nanotube materials causing mesothelioma was about 2 µm, and the narrowest average width was 37 nm. Index values between 0.1 and about 0.02 separated mesothelioma from other outcomes, and for modelling the authors selected 0.05 as an estimated central value, later giving a range of 0.02 to 0.1. Among 63 mineral occurrences, most elongate silicate particles were above 0.05, and low-rigidity fibers occurred only in the asbestiform habit. By calculation, single chrysotile fibrils lack rigidity above 5 µm. A model combining the share of long thin fibers, rigidity and biosolubility closely matched published mesothelioma potency values for chrysotile, amosite and crocidolite, but suggested erionite's may be lower than reported. The authors concluded that rigidity is a critical variable. They noted that nanotube stiffness and particle thickness were assumed.

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: Literature review and re-analysis of published animal studies of MWCNT, combined with calculations on an existing mineral particle dimensional database and regression modeling against published mesothelioma potency values (labelled by the journal as original research)
• Who was studied: 72 animal inhalation and implantation experiments with MWCNT reported in 55 publications. The authors also used dimensional data for 63 occurrences of elongate mineral particles from a database the authors say currently holds 567,000 records.
• Exposure: MWCNT materials classified by average length, average width, Young's modulus (stiffness) and Rigidity Index. These were compared with elongate mineral particles including chrysotile, amosite, crocidolite, tremolite, actinolite, anthophyllite, riebeckite, grunerite, erionite, balangeroite, fluoro-edenite, Libby amphiboles and fibrous talc, in asbestiform and non-asbestiform habits.
• Main results:
  • Among the MWCNT materials that caused mesothelioma, the smallest average length was about 2 µm.
  • The smallest average width among MWCNT materials causing mesothelioma was 37 nm.
  • Among MWCNT materials, a Rigidity Index between 0.1 and about 0.02 separated mesothelioma from other outcomes.
  • For modelling purposes, the authors selected 0.05 (in their units) as an estimate of the central value for the lower limit of rigidity of mesothelioma-causing populations.
  • Most elongate silicate (mineral) particles exceeded a Rigidity Index of 0.05.
  • Mineral populations containing low-rigidity fibers were restricted to the asbestiform habit. Long cleavage fragments were not narrow enough, and the narrowest fragments not long enough, to affect rigidity in a biologically significant way.
  • By the authors' calculation, nano-scrolls with the width of single chrysotile fibrils (20 to 40 nm) lack rigidity above 5 µm in length.
  • The model's predictor was the product of the fraction of long thin fibers (EMPA), the Rigidity Index and biosolubility. Across mineral types with non-zero published potency (RM, the increase in mesothelioma per fiber-year of exposure), this product correlated with RM with R = 0.91, R-squared 0.82, P less than 0.00071.
  • Using only the published potency values from Darnton (2023), for chrysotile, amosite, Libby amphiboles and crocidolite, the log-scale model gave R = 0.9996, R-squared 0.999, p less than 0.00041.
  • According to the authors, the model produced close estimates of potency for chrysotile, amosite, Libby amphiboles, asbestiform anthophyllite and crocidolite.
  • The model suggested erionite's potency may be lower than reported, though it still ranked erionite as the most potent mineral.
  • In the model, crocidolite was 48,000 times more potent than riebeckite fragments (the non-asbestiform form).
  • The model predicted a mesothelioma potency of 0.00002% for fibrous talc.
• The authors' conclusion: The authors concluded that, despite the uncertainties in their method, the data make a compelling case that rigidity is a critical variable in mineral fiber carcinogenicity.
• Limitations the authors state:
  • The exact Young's modulus (stiffness) of the MWCNT used in the animal studies was not known.
  • When all MWCNT were assumed to have a Young's modulus of 160 GPa, the rigidity threshold became 0.02 instead of 0.05. The authors said the threshold could be expressed as between 0.02 and 0.1.
  • The thickness of the particles in the database was not directly measured. It was modelled from a limited number of studies.
  • The authors assumed that average values are representative, although populations with the same averages may vary in range, especially in length.
  • Animal outcomes may differ because of dose, dosing method, time to autopsy and type of animal.
  • The width-to-thickness ratios used for erionite, balangeroite and talc were approximated from optical observations and have no published measurements.

Topics

Medical terms in this study, explained in our Lexicon: Mineral Fiber, Mesothelioma, elongate mineral particles (EMPs), Chrysotile, Fibril, Amosite, Crocidolite, Silicate.

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