Size Separation of Amosite by Filtration and Shaking Methods

Our plain-English summary of Size Separation of Amosite by Filtration and Shaking Methods, by T. Lee, R. Walker, J. Hummer, et al (Asbestos and Other Elongate Mineral Particles, 2021).

The study

• Authors: T. Lee, R. Walker, J. Hummer, E. Ashley, S. Mischler
• Journal: Asbestos and Other Elongate Mineral Particles
• Published: 2021;1632:265-280
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The objectives of this study are (1) to separate fibrous grunerite (amosite) by its length using filtration and shaking techniques utilized in a previous study and (2) to create two distinct length groups (short and long) of the amosite with higher output in a cost-effective way. The shaking system included an electrodynamic exciter, a linear power amplifier, and an audio-frequency signal generator and was attached to a cowl sampler as a funnel loaded with a polycarbonate filter. A suspension of amosite was passed through the 10-μm pore size polycarbonate filter in the shaking system and was transferred to a filtration system through five different pore sizes of polycarbonate membrane filters in series from the top: 10-, 5-, 2-, 1-, and 0.2-μm pore sizes. Each polycarbonate filter was tightly clamped with two conductive 25-mm spacers with a 25-mm stainless steel support screen to prevent leakage. The amosite length and diameter were manually measured with images from a field emission scanning electron microscope (FESEM). A sequence of fields was selected at random locations, and an image of each field was acquired. The length and width of approximately 500 fibers for each sample were measured with ImageJ software. Two significantly different length groups (short and long) of amosite were collected (p <0.05). Approximately 95% of separated amosite (n = 499) using the filtration system were shorter than 5 μm (short fiber group), and approximately 80% of separated amosite (n = 503) using the shaking system were longer than 5 μm (long fiber group).

In plain English

This was a laboratory study by researchers at the National Institute for Occupational Safety and Health (NIOSH). It tested low-cost ways to sort amosite asbestos fibers by length, so that separate short-fiber and long-fiber samples could later be used in toxicology testing. No people or animals were studied. The authors used a NIOSH amosite (fibrous grunerite) reference material from South Africa, prepared in 1979. A water suspension of the fibers was passed through polycarbonate filters with different pore sizes. One setup was a gravity filtration stack. The other shook each filter at 100 Hz. About 500 fibers per sample were measured on electron microscope images. With filtration, about 95% of the fibers on the smaller-pore filters (499 measured) were shorter than 5 micrometers. With shaking, about 80% of the fibers on the 2.0-micrometer filter were longer than 5 micrometers. The lengths of these two groups differed significantly (p less than 0.05). Air monitoring during the work found no fibers in the laboratory air. The authors concluded that the two methods can produce short and long fiber groups. They noted that both methods are labor intensive and that filtration did not fully separate short fibers from long ones.

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 methods study (separating fibers by length using filtration and shaking through polycarbonate filters); no human or animal subjects
• Who was studied: Not a human or animal population: a NIOSH reference sample of fibrous grunerite (amosite) from South Africa, prepared by NIOSH in 1979; about 500 fibers measured per separated sample, 6,567 fibers in total
• Exposure: Amosite (fibrous grunerite), processed by a centrifugal knife mill, suspended in pure water at 4 mg/mL (10 mL total for the shaking system), and passed through polycarbonate filters of pore sizes from 10 to 0.2 μm
• Main results:
  • Filtration system: about 95% of the amosite fibers measured on the smaller pore size filters (n = 499) were shorter than 5 μm, proposed as a short fiber group
  • Shaking system: about 80% of the fibers collected with the 2.0-μm pore size filter were longer than 5 μm; the 25th percentile length was 5.57 μm. This was proposed as a long fiber group
  • The lengths of the short group (filtration) and the long group (shaking) were significantly different (p less than 0.05, Mann-Whitney Rank Sum Test)
  • Filtration system: fibers from the 0.2-μm and 5-μm pore size filters were not statistically different in length
  • Shaking system: about 80% of fibers on the small pore size filters (0.6, 0.4 and under 0.4 μm) were shorter than 5 μm. The authors noted that the filtration system (about 95%) would be better for collecting fibers under 5 μm
  • Shaking system: the 95th percentile calculated aerodynamic diameters were 2.65 μm (under 0.4-μm filter) and 10.7 μm (10-μm filter). Not all fibers from the 10-μm filter might be in the respirable fraction
  • Personal and area air monitoring (NIOSH 7400 method) during separation identified no fibers in the laboratory air
• The authors' conclusion: The authors concluded that short (under 5 μm) and long (over 5 μm) amosite fibers can be collected with the filtration and shaking methods, respectively. They described the methods as relatively inexpensive, easy to decontaminate, and likely to minimize laboratory personnel exposure because they are wet procedures.
• Limitations the authors state:
  • Only 6,567 fibers were measured, by hand, which the authors called a limited and labor-intensive measurement
  • Short fibers were not completely separated from long fibers in the filtration system
  • Obtaining long fiber samples with the filtration system would be difficult because short fibers generally dominate
  • Shaking was repeated only three times; more repetitions might remove more short fibers from the long fiber group
  • Both methods are labor intensive

Topics

Medical terms in this study, explained in our Lexicon: Amosite, Grunerite.

Related studies

• A method of treating asbestos filter pads for virus filtration — N.S. Hyslop (1961)
• Effect of size fractionation on the toxicity of amosite and Libby amphibole asbestos — K.E. Duncan, A.J. Ghio, et al. (2010)
• A study of the size distributions of airborne amosite fibres in the manufacture of asbestos insulation boards — S.T. Beckett, J.L. Jarvis (1979)
• Regulated Asbestos Analysis: EPA Polarized Light Microscopy Method and the Implications for Reported Fiber Sizes — T.G. Laubenthal (2020)
• Correlation of in vitro and in vivo methods by means of mass dose and fiber distribution for amosite and fibrous ferroactinolite — D.L. Coffin, L.D. Palekar, et al. (1983)
• The separation of benign and malignant mesothelial proliferations — A. Churg, F. Galateau-Salle (2012)

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