A total sample preparation method for the measurement of airborne asbestos and other fibers by optical and electron microscopy

Our plain-English summary of A total sample preparation method for the measurement of airborne asbestos and other fibers by optical and electron microscopy, by N. Kohyama, S. Kurimori (Industrial Health, 1996).

The study

• Authors: N. Kohyama, S. Kurimori
• Journal: Industrial Health
• Published: 1996;34(3):185-203
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A total sample preparation method utilizing one membrane filter for all or some of the measurements by phase contrast optical microscopy (PCM), optical microscopy (OM), dispersion staining polarized microscopy (DS/PLM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), was developed in order to evaluate airborne asbestos and other mineral fibers comprehensively, including fiber number, sizes and types, in various environments. This method consists of two alternate procedures: parallel and serial preparation. The former uses different portions of a filter for each measurement of PCM, OM, DS/PLM, SEM and TEM. The latter uses a single filter portion for all OM, SEM and TEM measurements by which the same area and same fibers on the filter can be observed. This allows fiber numbers to be directly compared using these measurements on the same filter area, and the fibers observed by OM can be also examined by SEM and/or TEM equipped with an energy dispersive X-ray spectrometer (EDX) to determine the types and precise sizes. Using this method, it was found that OM measurements developed in this study can visualize thinner fibers than PCM measurements and make it easier to count fibers. We also found that currently used PCM measurement can detect fibers thicker than about 0.4-0.5 microns in diameter. This total sample preparation method can be used not only for air samples, but also for liquid and biological tissue samples.

In plain English

The authors described a method for preparing one membrane filter of air dust so the same filter could be examined by several microscopes. These included phase contrast optical microscopy (PCM, the usual workplace method), optical microscopy (OM) after low-temperature ashing, and scanning and transmission electron microscopy (TEM). They applied it to 1992 air samples from bag-opening and milling areas of a factory making asbestos cement boards with chrysotile and amosite. OM gave fiber concentrations about two times higher than PCM. TEM counted fibers longer than 0.5 µm and wider than 0.02 µm. Using only those longer than 5 µm and wider than 0.2 µm, TEM concentrations were about 2 to 4 times higher than PCM. In the example samples shown, TEM concentrations for all counted fibers were about 18 times the PCM concentration for chrysotile and about 11 times for amosite. The authors expressed this as only 6% and 9% of fibers counted by PCM. The authors estimated that PCM detects fibers wider than about 0.5 µm and OM fibers wider than 0.3 µm. TEM showed almost all fibers down to 0.02 µm. The authors concluded one filter could give comprehensive data on fiber number, size and type.

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-development study, with the method applied to air samples from one asbestos factory
• Who was studied: Air samples of about 300 liters collected in 1992 on 25 mm filters at work sites in an asbestos factory where asbestos bags were opened and milling took place. The authors' institute is in Japan. Samples 1-5 contained chrysotile and samples A-E mostly amosite.
• Exposure: Airborne chrysotile and amosite in a factory making asbestos cement boards. The factory stopped using amosite in 1994.
• Main results:
  • Fiber concentrations measured by OM were about two times higher than those measured by PCM
  • The TEM(1) method counted all fibers longer than 0.5 µm and wider than 0.02 µm
  • The TEM concentrations in Table 1 were calculated only for fibers longer than 5 µm and wider than 0.2 µm (described as PCM-equivalent fibers). They were about 2-4 times higher than PCM and a little higher than OM.
  • For chrysotile, these TEM concentrations were 3-4 times (3.87 on average) higher than PCM. For amosite they were 2-3 times (2.17 on average) higher.
  • In the size-distribution figures (chrysotile sample 1 and amosite sample A), chrysotile fibers were mostly thinner than amosite fibers. Amosite fibers had diameters on the order of 0.2-0.3 µm.
  • The fibers shown in the size-distribution figures were from chrysotile sample 1 and amosite sample A. Counting all of them by TEM gave 11.51 f/ml for chrysotile and 1.24 f/ml for amosite, about 18 and 11 times the PCM concentrations. The authors expressed this as only 6% of chrysotile fibers and 9% of amosite fibers being counted by PCM. This is a comparison of concentrations, not of the same individual fibers.
  • The authors estimated that current PCM detects fibers wider than about 0.5 µm in diameter. Their earlier data gave about 0.4 µm.
  • OM results corresponded to fibers wider than 0.3 µm in diameter
  • The TEM(1) method could show almost all fibers down to 0.02 µm in diameter
  • A low-vacuum SEM gave clear images of amosite fibers on samples without metal coating
• The authors' conclusion: The authors concluded that OM with low-temperature ashing is suitable for fiber counting. They also concluded that the total method can give comprehensive data on fiber number, sizes and types from one filter sample.
• Limitations the authors state:
  • Once the dispersion staining medium is applied to the slide, that sample cannot be used for further SEM or TEM examination
  • Chemical (EDX) analysis by SEM on the glass slide can pick up contaminating X-rays from the glass
  • The authors noted that standard NIOSH, EPA and ISO direct-transfer TEM procedures seem easier than their own procedure, which uses PVA solution

Topics

Medical terms in this study, explained in our Lexicon: dispersion staining, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Mineral Fiber.

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