Performance of membrane filters used for TEM analysis of asbestos

Our plain-English summary of Performance of membrane filters used for TEM analysis of asbestos, by J.S. Webber, A.G. Czuhanich, L.J. Carhart (Journal of Occupational and Environmental Hygiene, 2007).

The study

• Authors: J.S. Webber, A.G. Czuhanich, L.J. Carhart
• Journal: Journal of Occupational and Environmental Hygiene
• Published: 2007;4(10):780-9
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This article presents findings related to characteristics of membrane filters that can affect the recovery of asbestos and the quality of preparations for transmission electron microscopy (TEM) analysis. Certain applications and preparation steps can lead to unacceptable performance of membrane filters used in analysis of asbestos by TEM. Unless substantial care is used in the collapsing of mixed-cellulose ester (MCE) filters with an acetone hot block, grid preparations can suffer and fiber recoveries can be compromised. Calibration of the etching depth of MCE filters, especially at differing locations in an asher's chamber, is critical for reliable fiber recovery. Excessive etching of MCE filters with aerosol-deposited asbestos can lead to loss of short fibers, while insufficient etching of MCE filters with aqueous-deposited asbestos can, paradoxically, also lead to loss of short fibers. Interlaboratory precision on MCE filters is improved by aerosol-deposited asbestos, as opposed to aqueous deposition. In comparison, straightforward preparation, improved solvents, and reduced contamination make PC filters an increasingly acceptable alternative. Variations in the geometric configuration during application of carbon films can lead to fiber loss and unacceptable grid quality for either type of filter.

In plain English

This laboratory study examined how filter preparation affects electron microscope asbestos counts. The authors combined a survey of laboratories in New York State proficiency testing from 2000 to 2006, their own experiments with amosite, crocidolite and chrysotile, and observations from laboratory assessments. Among selected laboratories, chrysotile results averaged 155% of each sample's consensus mean for five laboratories collapsing filters with dimethylformamide (DMF), and 87% for nine using the hot block. Large variation between laboratories prevented statistical significance. Vigorous hot-block use washed fibers into ridges the authors called windrows. Short fibers were the most likely to stay tilted after collapsing. Etching was 50% greater in the chamber's front rows than its rear row. On a filter with aerosol-deposited asbestos, 50% etching left fewer fibers shorter than 1.8 micrometres than wedges given less etching (p less than 0.05). On a filter with water-deposited chrysotile, short fibers were not fully recovered until etching far exceeded 10%. Aerosol-generated test samples showed better agreement between laboratories than water-deposited ones. The authors concluded that several common preparation steps can bias results and called for well-designed investigations.

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 combining a survey of proficiency-testing laboratories, in-laboratory experiments on filter preparation, and observations from on-site laboratory assessments
• Who was studied: TEM laboratories that took part in New York State Department of Health Environmental Laboratory Approval Program (ELAP) proficiency testing rounds, 2000 to 2006, plus filters prepared in the authors' own laboratory
• Exposure: mixed-cellulose ester (MCE) and polycarbonate (PC) filters loaded with amosite, crocidolite or chrysotile, deposited from air (aerosol) or water (aqueous suspension); proficiency samples included amphibole and chrysotile
• Main results:
  • Among surveyed laboratories meeting participation and consistency criteria, chrysotile results averaged 155% of each proficiency sample's consensus mean for the 5 laboratories using DMF collapsing versus 87% for the 9 using the hot block (HB). Amphibole results differed little (97% to 120%). The difference was not statistically significant.
  • Recovery in the survey was defined as a laboratory's result divided by the proficiency sample's consensus mean, not as a share of a known true count
  • Vigorous hot-block collapse washed fibers into windrows on the filter surface
  • Hot block with a room-temperature slide gave the largest average fiber tilt (3.9 degrees) and the largest share of fibers tilted more than 10 degrees (19%). Shorter fibers were the most likely to be tilted.
  • Collapsed filters shrank by an average of 3% with the hot block and 6% with DMF
  • Without plasma etching, collapsed filters lost about 5% of their mass as water under the etcher's vacuum
  • Etching of wedges in the front two rows of the chamber was 50% greater than for wedges in the rear row
  • On a 0.45-micrometre MCE filter with aqueous-deposited chrysotile, short fibers (3.2 micrometres or less) were not fully recovered until etching far exceeded 10%
  • On a 0.45-micrometre MCE filter with aerosol-deposited asbestos, the wedge given 50% etching yielded fewer short fibers than wedges receiving less etching. The difference was significant for fibers shorter than 1.8 micrometres.
  • Interlaboratory relative standard deviation in proficiency testing was 0.28 for aerosol-generated samples versus 0.44 for aqueous-generated samples (all asbestos types)
  • The ethylenediamine solvent used to dissolve PC filters corroded copper alloy and molybdenum TEM grids
• The authors' conclusion: The authors concluded that several filter preparation steps in common use can bias results, and that well-designed investigations are needed to evaluate these practices with the goal of a standardized protocol
• Limitations the authors state:
  • Large variation between laboratories prevented detection of statistical significance in the collapsing-method comparison
  • The authors' carefully controlled hot-block use may not reflect current practice in other laboratories
  • The effect of aerosol versus aqueous deposition on PC filters was not investigated

Topics

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

Medical terms in this study, explained in our Lexicon: Transmission Electron Microscopy (TEM), Deposition.

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