Standardized methods for preparation and bi-variate length & diameter counting/sizing of aerosol and tissue digestion fiber samples

Our plain-English summary of Standardized methods for preparation and bi-variate length & diameter counting/sizing of aerosol and tissue digestion fiber samples, by D.M. Bernstein, P. Kunzendorf (Toxicology and Applied Pharmacology, 2018).

The study

• Authors: D.M. Bernstein, P. Kunzendorf
• Journal: Toxicology and Applied Pharmacology
• Published: 2018;361:174-184
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Most fiber length distributions fit a log-normal distribution with their being many more shorter fibers present as compared to the longer fibers. As the longer fibers have been suggested to be more important for possible pathogenesis giving equal weight to all fiber lengths when sizing fibers will under sample the longer fibers. The methods described here, are based upon the optimization of fiber counting/sizing rules over a number years of experience and have been developed to provide a stable estimate of the mean number of particles and fibers present in the size ranges: particles, fibers < 5 μm; 5-20 μm; and >20 μm. These methods were first applied using TEM, however, with the development of high resolution SEM, it was found that higher reproducibility could be obtained with SEM.

Copyright © 2018 Elsevier Inc. All rights reserved.

In plain English

This article was not a study of human health. It described standardized laboratory steps for preparing and examining fiber samples from aerosol filters and from rat lungs, diaphragms and lymph nodes after nose-only inhalation. The authors stated the method had been used with synthetic vitreous fibers, chrysotile, crocidolite and tremolite asbestos. Under scanning electron microscopy (SEM), normally at 10,000 times magnification, fibers were counted until minimums were reached in three length groups (100 up to 5 μm, 200 from 5 to 20 μm, 100 over 20 μm), or until 1 square millimetre of filter had been examined. For control-group samples only 0.5 square millimetre was evaluated. One chrysotile aerosol filter was split, and each half was analysed separately. The ratios between the two results ranged from 1.04 to 1.12, which the authors called a very good measure of reproducibility. On one crocidolite aerosol sample, transmission electron microscopy (TEM) gave lower fiber concentrations than SEM in all categories (1372 versus 2825 total fibers per cm3 air). TEM also shifted towards thinner fibers. The authors concluded the method allows reproducible assessment of fiber and particle distributions by length category.

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: Methods description paper (standardized sample preparation and fiber counting/sizing rules), with two comparative analyses of aerosol samples: a split-filter repeat analysis and a TEM versus SEM comparison
• Who was studied: Samples, not people. The samples were lungs, diaphragms and lymph nodes from rats exposed by flow-past nose-only inhalation, filters of aerosol samples from the exposure systems, and bulk test materials. The comparative analyses used aerosol samples from the authors' earlier chrysotile and crocidolite studies (Bernstein et al. 2014, 2015). Numbers of animals and dates were not given.
• Exposure: Fiber types to which the method had been applied: synthetic vitreous fibers (e.g. MMVF 21, HT fiber), chrysotile, crocidolite and tremolite asbestos. The comparisons used a chrysotile aerosol and a crocidolite asbestos aerosol.
• Main results:
  • Counting rules: fields of view were examined until a minimum number of fibers was recorded in each length category, or until a maximum of 1 square millimetre of filter had been examined. The minimums were 100 fibers up to 5 μm, 200 fibers between 5 and 20 μm, and 100 fibers over 20 μm.
  • For samples from the control group, only 0.5 square millimetre of filter was evaluated.
  • Split chrysotile aerosol filter, each half analysed independently by SEM: total fibers were 37364 and 40728 per cm3 air (ratio 1.09). Fibers longer than 20 μm were 161 and 180 per cm3 air (ratio 1.12). Fibers 5 to 20 μm were 1822 and 1897 per cm3 air (ratio 1.04). The authors described this as a very good measure of reproducibility.
  • Crocidolite asbestos aerosol sample, TEM versus SEM: TEM gave lower concentrations in all categories. Total fibers were 1372 (TEM) versus 2825 (SEM) per cm3 air (ratio 0.49). WHO fibers were 616 versus 1435 (ratio 0.43). Fibers longer than 20 μm were 62 versus 129 (ratio 0.48).
  • In the same crocidolite comparison, TEM shifted towards measuring thinner fibers than SEM. Mean diameter was 0.26 μm with TEM versus 0.35 μm with SEM.
  • The authors attributed the higher reproducibility of SEM largely to the larger filter area it allows and to its ability to follow longer fibers, which can be truncated with TEM.
• The authors' conclusion: The authors concluded that the method provides the ability to reproducibly assess particle and fiber distributions in the categories of particles, fibers under 5 μm, fibers 5 to 20 μm and fibers over 20 μm in length. They stated that it gives a standardized basis for comparing aerosol and respiratory tissue samples and different fiber types.

Topics

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

Medical terms in this study, explained in our Lexicon: Tissue Digestion, Fiber Length, Fiber Counting.

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