Quantitative assessment of inorganic fibrous particulates in dust samples with an analytical transmission electron microscope

Our plain-English summary of Quantitative assessment of inorganic fibrous particulates in dust samples with an analytical transmission electron microscope, by F.D. Pooley, N.J. Clark (The Annals of Occupational Hygiene, 1979).

The study

• Authors: F.D. Pooley, N.J. Clark
• Journal: The Annals of Occupational Hygiene
• Published: 1979;22(3):253-71
• Cited by: 47 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

With the aid of an analytical transmission electron microscope it is possible to quantify by number and mass the various inorganic fibrous particulate phases that may occur in dust samples. Discrimination between fibres of various mineral types can be made by reference to their individual chemical compositions and number concentrations on filter preparations determined with a reasonable accuracy. Mass estimates can be obtained by sizing the length and diameter of the various individual fibrous particles, these dimensions then being used to calculate the mean fibre volume of individual fibrous phases which, in conjunction with a specific gravity value, a correction factor for fibre shape and number concentration data, can be used to calculate the weight of any particular mineral phase on a filter preparation. Careful standardization of the quantitative procedure should be performed before establishing a routine.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This laboratory methods paper from University College Cardiff described a procedure for counting, sizing and identifying fibres in filtered dust with an analytical transmission electron microscope and X-ray analysis, and for estimating fibre mass. The standard error of a grid mean was 22.8 (coefficient of variation 9.1%) for a concentrated preparation counted on 10 micrographs per grid; for a dilute one, the authors calculated it would be 1.6 (6.4%) for a grid mean based on 10 micrographs. The authors and the Public Health laboratories of Paris counted fibres in tissue from one post-mortem lung, with results described as very comparable. In a lung tissue dust extract examined by three observers, chrysotile was the main fibre by number, then tremolite and amosite. In prepared mixtures, mass calculated assuming round fibres was about 1.1 times the true value for crocidolite and 1.8 times for amosite, which the authors attributed to fibre cross-sectional shape. Chrysotile mass was underestimated when fibres were sized at 20 000 times magnification. The authors concluded that mass estimates need shape corrections differing by mineral and magnification.

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 describing and testing an electron microscope procedure for counting fibres and estimating their mass, using lung tissue dust extracts and prepared mineral samples
• Who was studied: Filter preparations of dust: extracts from human lung tissue (including samples from several positions in one post-mortem lung, also examined by the Public Health laboratories of Paris); artificial mixtures of amosite and crocidolite with kaolin, muscovite, quartz and talc (15 filter samples); UICC anthophyllite; and a super-fine chrysotile sample. Work was done at University College Cardiff. Dates are not given.
• Exposure: Fibre types measured: chrysotile, amosite (UICC sample), crocidolite (from the NW Cape, South Africa), tremolite and anthophyllite (UICC standard). Amounts of amosite plus crocidolite on filters ranged from 1 x 10^-7 to 45 x 10^-7 g.
• Main results:
  • Counting error, concentrated preparation (six grids, 10 micrographs each, average 252 fibres per micrograph): grid means ranged from 219 to 280, and the standard error of a grid mean was 22.8 (coefficient of variation 9.1%).
  • Counting error, more dilute preparation (78 micrographs recorded from 3 grids, mean 24.7 fibres per micrograph): the authors calculated that the standard error of a grid mean based on only 10 micrographs would be 1.6 (coefficient of variation 6.4%).
  • The authors' laboratory and the Public Health laboratories of Paris examined lung tissue samples from the same lung, and the authors described their fibre counts per gram of dried tissue as very comparable.
  • In a lung tissue dust extract examined by three observers, chrysotile was the major fibre by number, followed by tremolite and amosite. Crocidolite, anthophyllite, an unidentified aluminium silicate, a possible rutile fibre and a silicon dioxide fibre were also found.
  • Mass calculations were less erratic when the combined (aggregate) size data from all scans were used than when each scan's own sizes were used.
  • In the amosite and crocidolite mixtures, mass calculated by assuming circular fibre cross-sections was about 1.1 times the prepared mass for crocidolite and about 1.8 times for amosite. The authors attributed this to rectangular cross-sections of about 1.5:1 for crocidolite and 2.5:1 for amosite.
  • For UICC anthophyllite, calculated masses were much higher than the amounts prepared. After correcting for 20% impurity, the ratio of calculated to actual mass was 2:1.
  • For the chrysotile filter prepared with 250 x 10^-7 g, the calculated weight was 86.7 x 10^-7 g when fibres were sized at 20 000 times magnification. Sizing at 40 000 times gave about 192.2 x 10^-7 g, which the authors described as much closer. Allowing for about 20% impurity, the 20 000 times result was a factor of 2.1 too low.
• The authors' conclusion: The authors concluded that the procedure can quantify fibres of individual mineral types in filtered dust, and that a meaningful result can come from examining as few as a hundred fibres. They found fibre concentrations more accurate and reproducible than mass figures unless enough fibres are sized. They stated that mass estimates need corrections for fibre cross-sectional shape, and that these corrections vary by mineral and by sizing magnification.
• Limitations the authors state:
  • No estimate was obtained of the error in preparing the filter specimens.
  • The chrysotile correction factor of 2.1 would apply only if the chrysotile being measured had a diameter distribution similar to the standard sample used.
  • Mass estimates for minor fibre types found in the lung sample would need further examination to be accurate.
  • The chrysotile standard was not pure; the authors estimated it contained about 20% non-fibrous impurities by weight.

Topics

Medical terms in this study, explained in our Lexicon: Specific Gravity.

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