Asbestos Fiber Preparation Methods Affect Fiber Toxicity

Our plain-English summary of Asbestos Fiber Preparation Methods Affect Fiber Toxicity, by A. Salamatipour, S.K. Mohanty, R.A. Pietrofesa, et al (Environmental Science & Technology Letters, 2016).

The study

• Authors: A. Salamatipour, S.K. Mohanty, R.A. Pietrofesa, D.R. Vann, M. Christofidou-Solomidou, J.K. Willenbring
• Journal: Environmental Science & Technology Letters
• Published: 2016;3(7):270-274
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

To measure the toxic potential of asbestos fibers-a known cause of asbestosis, lung cancer, and malignant mesothelioma-asbestos minerals are generally first ground down to small fibers, but it is unknown whether the grinding condition itself changes the fiber toxicity. To evaluate this, we ground chrysotile ore with or without water for 5-30 min and quantified asbestos-induced reactive oxygen species generation in elicited murine peritoneal macrophages as an indicator of fiber toxicity. The toxicity of dry-ground fibers was higher than the toxicity of wet-ground fibers. Grinding with or without water did not materially alter the mineralogical properties. However, dry-ground fibers contained at least 7 times more iron than wet-ground fibers. These results indicate that grinding methods significantly affect the surface concentration of iron, resulting in changes in fiber-induced reactive oxygen species generation or toxicity. Therefore, fiber preparation conditions should be accounted for when comparing the toxicity of asbestos fibers between reported studies.

In plain English

This laboratory experiment tested whether how chrysotile asbestos is ground before toxicity testing changes its measured toxicity. The authors ground hand-picked chrysotile fiber bundles from Arizona ore in a ball mill for 5, 15 or 30 minutes, dry or with water. They exposed macrophages (immune cells) taken from the abdominal cavity of mice to the fibers. They measured reactive oxygen species (ROS), reactive molecules used as an indicator of fiber toxicity. X-ray analysis showed no significant change in mineral type between dry and wet grinding. After 15 minutes, dry-ground fibers were shorter than 20 micrometres and wet-ground fibers exceeded 100 micrometres. These dry-ground fibers contained 2.3% iron by weight, against 0.3% for the wet-ground fibers. Fibers dry-ground for 15 minutes produced significantly more ROS than fibers wet-ground for 15 minutes; other dry-grinding times were not tested for ROS. Among wet-ground fibers, ROS fell significantly from 5 to 15 minutes of grinding, but not significantly with longer grinding. The authors concluded that preparation methods can affect fiber toxicity and should be considered when comparing studies. They stated that workplace fiber breakdown was outside the study's scope.

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: Laboratory experiment: chrysotile fibers were ground under different conditions, analyzed for mineral and chemical properties, and tested on mouse immune cells (macrophages) in culture
• Who was studied: Chrysotile ore from Arizona, and macrophages collected from the peritoneum (abdominal cavity) of mice. The number of mice is not given in the article text.
• Exposure: Chrysotile fiber bundles ground for 5, 15 or 30 minutes in a high-energy vibratory ball mill, with or without deionized water. Cells were treated with ground fibers at 20 µg/cm2 for 6 hours.
• Main results:
  • X-ray diffraction showed no significant change in the mineralogy of chrysotile fibers between dry and wet grinding
  • Dry grinding produced white fibers; wet grinding produced gray fibers
  • After 15 minutes of dry grinding, fiber length was less than 20 µm
  • After 15 minutes of wet grinding, fiber length exceeded 100 µm
  • Dry-ground fibers had an iron content of 2.3% by weight, nearly seven times that of wet-ground fibers
  • Wet-ground fibers had an iron content of 0.3%
  • Mouse macrophages exposed to asbestos fibers showed a significant increase in ROS compared with vehicle (PBS)-treated macrophages (p less than 0.0001)
  • Fibers dry-ground for 15 minutes generated significantly more ROS than fibers wet-ground for 15 minutes (p less than 0.0001 by one-way ANOVA; a later passage gives p less than 0.01)
  • For wet-ground fibers, increasing grinding time from 5 to 15 minutes significantly decreased ROS generation (p less than 0.0001)
  • For wet-ground fibers, grinding beyond 15 minutes did not significantly decrease ROS generation (p = 0.504)
• The authors' conclusion: The authors concluded that fiber preparation conditions can affect fiber toxicity. They linked the higher ROS from dry-ground fibers to their higher surface iron. They stated that the preparation method should be considered when studying asbestos toxicity or comparing results between studies.
• Limitations the authors state:
  • Suspending fibers in deionized water before electron microscopy and elemental analysis may have displaced some iron. The authors assumed this had minimal effect on the dry-versus-wet comparison.
  • The study did not examine asbestos fragmentation that may occur in the workplace
  • The effect of different dry-grinding times on ROS generation was not examined, because longer dry grinding damaged the fibers and would have confounded the results
  • An extra X-ray peak in wet-ground fibers could not be identified with certainty (possibly a weathering product such as talc)

Topics

Medical terms in this study, explained in our Lexicon: Lung Cancer, Mesothelioma, Asbestos, Chrysotile, Reactive Oxygen Species (ROS), Macrophage.

Related studies

• A total sample preparation method for the measurement of airborne asbestos and other fibers by optical and electron microscopy — N. Kohyama, S. Kurimori (1996)
• Standardized methods for preparation and bi-variate length & diameter counting/sizing of aerosol and tissue digestion fiber samples — D.M. Bernstein, P. Kunzendorf (2018)
• Siderophore-mediated iron removal from chrysotile: Implications for asbestos toxicity reduction and bioremediation — S.K. Mohanty, C. Gonneau, et al. (2018)
• Sample preparation method for visualization of nanoparticulate captured on mixed cellulose ester filter media by enhanced darkfield microscopy and hyperspectral imaging — N.M. Neu-Baker, A.C. Eastlake, et al. (2019)
• Preparation of asbestos fibers for experimental use — M.S. Badollet, W.A. Gantt (1965)
• "Rinse and trickle": a protocol for TEM preparation and investigation of inorganic fibers from biological material — R. Vigliaturo, S. Capella, et al. (2016)

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