A procedure for the estimation of asbestos collected on membrane filters using transmission electron microscopy (TEM)

Our plain-English summary of A procedure for the estimation of asbestos collected on membrane filters using transmission electron microscopy (TEM), by A.P. Middleton, E.A. Jackson (The Annals of Occupational Hygiene, 1982).

The study

• Authors: A.P. Middleton, E.A. Jackson
• Journal: The Annals of Occupational Hygiene
• Published: 1982;25(4):381-91
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

In plain English

This laboratory methods paper described a way to transfer airborne dust from Millipore MF-series membrane filters onto grids so that asbestos fibres could be counted and measured by transmission electron microscopy (TEM). The filter was collapsed with acetone vapour, etched in a low-temperature asher, coated with carbon and dissolved away with acetone. Fibre mass was then calculated from fibre lengths and diameters. Viewing the same filter areas at successive stages, the authors saw no fibre loss or breakage during etching or extraction. They tested the method on standard filters loaded with known weights of UICC chrysotile 'A'. Where 10 to the minus 9 grams was loaded, the method estimated 1.8 x 10 to the minus 9 grams. Where 10 to the minus 6 grams was loaded, it estimated 0.9 x 10 to the minus 6 grams. Nothing was detected on a blank. The authors concluded the method was accurate to better than an order of magnitude and needed about one man-day per sample. They noted three limits: fibres on photographs could be identified only by shape, uneven portions of the suspension could cause errors, and confidence limits were still to be tested on real air samples.

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 method development and testing: a sample-preparation technique for TEM, checked by direct observation and by analysis of standard filters with known chrysotile loadings
• Who was studied: No people were studied. The subjects were membrane filters (Millipore MF-series, pore sizes 0.8 and 1.2 micrometres), including standard filters loaded with known amounts of chrysotile and a blank filter
• Exposure: Standard filters prepared by filtering known volumes of a suspension containing a known weight of UICC chrysotile 'A'
• Main results:
  • Viewing the same filter areas by optical microscopy, SEM and TEM at successive stages showed no apparent fibre loss or fibre breakage at the etching stage or the solvent extraction stage
  • Standard filter with 10 to the minus 9 grams of chrysotile: estimated weight 1.8 x 10 to the minus 9 grams
  • Standard filter with 10 to the minus 7 grams of chrysotile: estimated weight 1.7 x 10 to the minus 7 grams
  • Standard filter with 10 to the minus 6 grams of chrysotile: estimated weight 0.9 x 10 to the minus 6 grams
  • Blank filter: no chrysotile detected
  • The authors judged that the procedure gave a result accurate to better than an order of magnitude, with no serious loss of fibre during preparation
  • The procedure required about 1 man-day per sample, with less than one week from receipt of a sample to a result
• The authors' conclusion: The authors concluded that the preparation technique caused neither significant fibre loss nor fibre breakage. They also concluded that the mass-estimation procedure gave acceptable accuracy on standard samples.
• Limitations the authors state:
  • Fibres measured from the photographic plates cannot be identified except by their shape; only a proportion of samples would be checked with EDXA and/or electron diffraction
  • Results on the standards may contain errors from non-uniform aliquots
  • The collapsed MF-series filters are rather beam sensitive in the SEM
  • The technique is not rapid
  • The statistics and confidence limits of the method had not yet been tested; this was to be done on real samples

Topics

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

Related studies

• A routine for the control of the performance of microscopists evaluating airborne asbestos fibre samples on membrane filters by phase contrast microscopy — J.R. Hoyes, R. Clayton (1980)
• In situ identification of asbestos fibres collected on membrane filters for counting — N.P. Vaughan, S.J. Rooker, et al. (1981)
• Airborne fiber size characterization in exposure estimation: Evaluation of a modified transmission electron microcopy protocol for asbestos and potential use for carbon nanotubes and nanofibers — J.M. Dement, E.D. Kuempel, et al. (2015)
• Determination of mineral fibre in human lung tissue by light microscopy and transmission electron microscopy — A.J. Rogers (1984)
• Size distributions of occupational airborne asbestos textile fibres as determined by transmission electron microscopy — A.P. Rood, R.R. Streeter (1984)
• A comparison of light microscopy and transmission electron microscopy results in the evaluation of the occupational exposure to airborne chrysotile fibres — A. Marconi, E. Menichini, et al. (1984)

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