Development of a method for the determination of low contents of asbestos fibres in bulk material

Our plain-English summary of Development of a method for the determination of low contents of asbestos fibres in bulk material, by T. Schneider, L.S. Davies, G. Burdett, et al (The Analyst, 1998).

The study

• Authors: T. Schneider, L.S. Davies, G. Burdett, J. Tempelman, S. Puledda, O. Jørgensen, D. Buchanan, L. Paoletti
• Journal: The Analyst
• Published: 1998;123(6):1393-400
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos is a category 1 carcinogen under the EU classification, but in the absence of a method to quantify asbestos in a matrix at the 0.1% level, there has been a delay in implementing relevant directives to asbestos. An analytical scheme for identification and quantification of asbestos using polarised light microscopy (PLM) and phase contrast optical microscopy (PCM) has now been developed. When used on artificial mixtures by an experienced laboratory, it achieved the required target performance, at 0.1% asbestos concentration by mass in a bulk sample, to obtain a result, which with 90% probability, is correct within a factor of two. The method of identification by PLM and quantification by PCM has been assessed by interlaboratory comparisons. The method begins with an initial identification using PLM, and depending on asbestos type and matrix a combination of preparation procedures are used to produce the analytical filter. A gentle comminution method was used which reduces the risk of overmilling. The asbestos mass percentage on the filter is quantified using PCM in combination with a PLM attachment for identification of possible non-asbestos fibres. The final method is supported by efficient methods for fibre identification for size determination and calculation of total fibre volume. A statistical analysis of mass concentration estimates was made and the effect of preferred orientation of fibres on the analytical filter was quantified.

In plain English

European researchers developed a laboratory method for measuring asbestos at about 0.1% by mass in bulk materials such as talc, vermiculite, soil and demolition waste. The target was a result correct within a factor of two with 90% probability. Fibres were identified by polarised light microscopy. Samples were ashed or acid-digested where the material required, gently ground and dispersed in liquid, and asbestos mass was estimated by phase contrast microscopy. Development used 12 artificial test materials. Identification agreed very well with the known contents of 57 samples, differing only for some talc and dolomite samples containing tremolite or anthophyllite. At one laboratory, 88% of individual mass results fell within a factor of two, using a correction factor set to maximise that share. Per-sample figures covered five amphibole mixtures, not the chrysotile one. The method was generally unreliable for chrysotile-containing materials. In an interlaboratory comparison, one of the most experienced laboratories came very close to the target. The authors concluded that, with care and experience, results approaching the target are possible, but the target may have to be relaxed.

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 study using artificial test mixtures, with interlaboratory comparisons (round robins). Sample preparation steps were chosen according to asbestos type and matrix.
• Who was studied: Not people. The study used 12 artificial bulk test materials. Polarised light identification was tested on 57 samples drawn from these materials, with 22 re-analysed. Mass measurements were made by two counters at one laboratory. Two identification round robins of four samples each were sent to EU laboratories and UK laboratories accredited by UKAS. A two-round quantification intercomparison had 12 participating laboratories in round 1 and 11 in round 2.
• Exposure: The test materials included:
• New York talc containing anthophyllite (undiluted and diluted);
• acid-washed dolomite containing tremolite asbestos;
• amosite spiked into soil, into demolition waste (as asbestos cement fragments) and into talc;
• tremolite asbestos in vermiculite;
• chrysotile in olivine sand;
• crocidolite in sepiolite;
• non-asbestos fibrous wollastonite and plain dolomite.
  Spiked contents ranged from 0.01% to 1%.
• Main results:
  • Polarised light identification agreed very well with the known asbestos contents of all 57 samples tested. Differences occurred only for New York talc and digested dolomite samples containing tremolite or anthophyllite.
  • When identification was repeated on a sub-sample of 22 samples, all original results were reproduced.
  • The shape correction factor was set to 0.48 to maximise the number of results within the target range. The share of results within a factor of two of the known content was then reported for five samples, all containing amphibole asbestos (amosite, tremolite asbestos or crocidolite):
• sample 5: 87%
• sample 7: 100%
• sample 8: 80%
• sample 10: 92%
• sample 11: 83%
  These were measurements at one laboratory. No such figure was given for sample 9, the chrysotile mixture.
  • Overall, 88% of individual results were within the target performance range.
  • The method was generally unreliable for materials containing chrysotile.
  • Grinding time affected results in both directions:
• No milling underestimated fibre mass in samples where fibres were bound in a matrix.
• Long milling destroyed fibres: after 45 minutes of milling, no fibres were visible in the acid-washed dolomite.
  • In the identification round robins, none of the laboratories made errors that were analytically unacceptable and would have serious consequences in reality. Some less serious errors were made.
  • In the quantification intercomparison, one of the most experienced laboratories came very close to the target performance.
  • One intercomparison sample contained only chrysotile. Most laboratories wrongly reported some amphibole fibres in it, so their mass estimates for this sample were generally underestimated by an unknown amount.
• The authors' conclusion: The authors concluded that, with care, experience and perhaps considerable practice, results approaching the target performance range are possible. They also stated that the original target performance may have to be relaxed.
• Limitations the authors state:
  • The correction factor was derived with the standard graticule. It may need adjustment for the modified graticule and must be validated on a broader range of amphibole asbestos samples.
  • No suitable method was found for grinding chrysotile to the required fineness.
  • False negatives cannot be fully eliminated, for example in samples with large quantities of extremely thin fibres.
  • Very thin fibres must be counted as asbestos, which increases the risk of false positives.
  • Optical properties alone may not distinguish tremolite from actinolite from some sources, or tremolite from anthophyllite.
  • No rules were developed for the effective volume of fibre bundles and clusters.
  • Results depend on the training and experience of the microscopist and on quality assurance.

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