Efficacy of screens in removing long fibers from an aerosol stream--sample preparation technique for toxicology studies

Our plain-English summary of Efficacy of screens in removing long fibers from an aerosol stream--sample preparation technique for toxicology studies, by B.K. Ku, G.J. Deye, L.A. Turkevich (Inhalation Toxicology, 2014).

The study

• Authors: B.K. Ku, G.J. Deye, L.A. Turkevich
• Journal: Inhalation Toxicology
• Published: 2014;26(2):70-83
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Fiber dimension (especially length) and biopersistence are thought to be important variables in determining the pathogenicity of asbestos and other elongate mineral particles. In order to prepare samples of fibers for toxicology studies, it is necessary to develop and evaluate methods for separating fibers by length in the micrometer size range. In this study, we have filtered an aerosol of fibers through nylon screens to investigate whether such screens can efficiently remove the long fibers (L >20 µm, a typical macrophage size) from the aerosol stream. Such a sample, deficient in long fibers, could then be used as the control in a toxicology study to investigate the role of length. A well-dispersed aerosol of glass fibers (a surrogate for asbestos) was generated by vortex shaking a Japan Fibrous Material Research Association (JFMRA) glass fiber powder. Fibers were collected on a mixed cellulose ester (MCE) filter, imaged with phase contrast microscopy (PCM) and lengths were measured. Length distributions of the fibers that penetrated through various screens (10, 20 and 60 µm mesh sizes) were analyzed; additional study was made of fibers that penetrated through double screen and centrally blocked screen configurations. Single screens were not particularly efficient in removing the long fibers; however, the alternative configurations, especially the centrally blocked screen configuration, yielded samples substantially free of the long fibers.

In plain English

This laboratory methods study did not involve people or animals and did not test asbestos itself. To help prepare samples for toxicology studies of fiber length, the authors passed an aerosol of glass fibers (GW1, used as a stand-in for amphibole asbestos) through nylon screens with 10, 20 and 60 micrometer openings. They then measured under a microscope the lengths of the fibers that got through. Without a screen, about 40% of fibers were longer than 20 micrometers, a typical macrophage size. Single screens cut this to 26%, 15% and 6% for the 60, 20 and 10 micrometer screens. Two screens stacked together gave 25%, 2% and 3%. A screen with a disk blocking its center gave 18%, 6% and 6%. The authors concluded that single screens were not particularly efficient, while the alternative set-ups, especially the centrally blocked screen, gave samples substantially free of long fibers. They noted that glass may model chrysotile poorly, that fiber build-up on the screens was not studied, and that the method is still at the research stage.

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 testing a sample-preparation method: filtering an airborne fiber stream through screens to separate fibers by length
• Who was studied: No human or animal subjects. The material studied was a glass fiber powder (GW1) from the Japan Fibrous Material Research Association, used as a surrogate for amphibole asbestos. Typically 300 to 800 fibers were measured per sample.
• Exposure: Not a human exposure. The glass fiber aerosol, made by vortex shaking, was passed through nylon screens with 60, 20 and 10 micrometer mesh in single, double (back-to-back) and centrally blocked configurations. Fibers that got through were collected on a filter and measured by phase contrast microscopy.
• Main results:
  • Without a screen, about 40% of the aerosolized glass fibers were longer than 20 micrometers (Table 1: 40.0% and 40.9% in two runs).
  • With a single screen, the share of fibers longer than 20 micrometers was 26% for the 60 micrometer screen, 15% for the 20 micrometer screen and 6% for the 10 micrometer screen.
  • The authors considered a contamination level around 20% still too high for all but toxicity markers that respond at least ten times more strongly to long than to short fibers.
  • Single screens shifted the whole length distribution toward shorter fibers. For all screens the median length of fibers getting through was smaller than the screen opening, but a significant fraction of fibers longer than the opening still got through.
  • The share of fibers longer than 20 micrometers was 25%, 2% and 3% with double screens and 18%, 6% and 6% with centrally blocked screens, for the 60, 20 and 10 micrometer screens respectively.
  • Even the centrally blocked screens did not separate fibers by length better than an existing method, the Baron dielectrophoresis fiber length classifier.
• The authors' conclusion: The authors concluded that single screens were not particularly efficient at removing long fibers, but the alternative configurations, especially the centrally blocked screen, yielded samples substantially free of long fibers. They judged the 6% level suitable for a short-fiber control sample in a toxicology test of fiber length.
• Limitations the authors state:
  • Rigid glass fibers may be a poorer model for chrysotile asbestos, which is often longer, thinner, curved and more flexible, than for amphibole asbestos.
  • The effect of fibers building up on the screens over time was not investigated.
  • The technique is still at the research stage and is not yet an instrument that can produce the quantity needed for an inhalation toxicology experiment.
  • Only the short fibers that passed through the screens were studied, not the fibers captured on the screens.
  • In the 10 micrometer screen experiment, a suspected misalignment of the screen may have skewed fiber deposition on the filter.
  • Phase contrast microscopy systematically overcounted small fibers compared with electron microscopy, possibly by mistaking filter defects for fibers.

Topics

Medical terms in this study, explained in our Lexicon: Fiber Dimensions, biopersistence, elongate mineral particles (EMPs), Macrophage, phase contrast microscopy (PCM).

Related studies

• Standardized methods for preparation and bi-variate length & diameter counting/sizing of aerosol and tissue digestion fiber samples — D.M. Bernstein, P. Kunzendorf (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)
• An examination of MCE filter morphology and implications on preparation and analysis of air samples for asbestos — M. Getman, J. Webber, et al. (2017)
• Emission of airborne fibers from mechanically impacted asbestos-cement sheets and concentration of fibrous aerosol in the home environment in Upper Silesia, Poland — J.S. Pastuszka (2009)
• Thoracic fraction of inhaled fiber aerosol — Y.S. Cheng, W.C. Su (2013)
• Contemporary issues in fiber toxicology — D.B. Warheit, K.E. Driscoll, et al. (1995)

Browse more research in Inhalation Toxicology, or return to medical research.