Amosite And Crocidolite Mining And Milling As Causes Of Asbestosis

Our plain-English summary of Amosite And Crocidolite Mining And Milling As Causes Of Asbestosis, by G.K. Sluis-Cremer, R.S.J. Du Toit (1973).

The study

• Authors: G.K. Sluis-Cremer, R.S.J. Du Toit
• Published: Biological Effects Of Asbestos (J.C. Wagner, Editor), Lyon: Iarc Scientific Publications, Volume 8, Pp. 160-164 (1973)
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library, J-M no. 002407. The article is still under copyright, so we describe it here rather than post it.

In plain English

This South African conference paper concerned amosite and crocidolite (amphibole) asbestos mines and mills. It made preliminary estimates of a dust concentration standard at which workers probably would not develop asbestosis. Only white and mixed-race workers' records were assessed; Bantu workers' records had not been investigated. For 37 Caucasian persons with asbestosis, the mean dust dosage was estimated at 1370 long fibre equivalents per cubic centimetre-years. For 42 mixed-race persons with asbestosis it was 3650, a difference reported as statistically significant. Forty-one persons with calcified pleural plaques only had a mean of 2400 long fibre equivalents per cubic centimetre-years. For the 37 Caucasian persons, allowing for progression, the authors estimated 2, 3 and 6 long fibres per cubic centimetre for dust residence-times of 50, 40 and 30 years. They believed the standard lay between 2 and 15 actual long fibres per ml, depending on the degree and mode of progression, working conditions and dust composition. They felt it premature to set any standard until full results of the Cumulative Dust Exposure Project were available. They noted that linear progression of asbestosis was unproven.

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: Descriptive conference paper with preliminary calculations from cumulative dust exposure records to estimate a maximum allowable dust concentration; it also reproduces earlier follow-up tables (Sluis-Cremer 1970)
• Who was studied: Workers in South African amphibole asbestos mines (North-West Cape and north-east Transvaal): 37 Caucasian miners with parenchymal asbestosis, 42 persons of mixed race with parenchymal asbestosis, and 41 persons (8 Caucasian, 33 mixed race) with calcified pleural plaques only. Only white and mixed-race workers' records could be assessed.
• Exposure: Dust in amosite and crocidolite mines and mills, measured by konimeters and thermal precipitators. It was expressed as long fibres, short fibres and 'long fibre equivalents', with weights for fibres shorter than 5 micrometres (0.2), quartz particles (0.5), other particles (0.1) and fibres longer than 5 micrometres (1.0).
• Main results:
  • The 37 Caucasian persons with asbestosis had an estimated mean dust dosage of 1370 long fibre equivalents per cubic centimetre-years.
  • The 42 mixed-race persons with asbestosis had an estimated mean cumulative dosage of 3650 long fibre equivalents per cubic centimetre-years. The difference from the Caucasian estimate was reported as statistically significant.
  • The 41 persons with calcified pleural plaques only had a mean of 2400 long fibre equivalents per cubic centimetre-years (described by the authors as mean exposure time).
  • For the 37 Caucasian persons, allowing for progression and using the group's mean residence-time of 13 years, the estimated level for a 50-year residence-time was 7 long fibre equivalents, or 2 long fibres, per cubic centimetre. The figures were 3 long fibres for 40 years and 6 long fibres for 30 years.
  • In the Caucasian dosage table, 2 of 124 workers in the lowest dosage band (250 long fibre equivalents per cubic centimetre-years and less) had asbestosis (proportion 0.016).
  • Of 79 persons certified as asbestosis patients, 41 had calcified pleural plaques as the only evidence of abnormality.
• The authors' conclusion: The authors believed a maximum allowable standard lay between 2 and 15 actual long fibres per ml, depending on the degree and mode of progression, particular working conditions and dust composition. They felt it was premature to lay down any standard until the full results of the Cumulative Dust Exposure Project were available.
• Limitations the authors state:
  • The records of service of Bantu miners had not yet been investigated.
  • Whether asbestosis progresses linearly had not been proven.
  • No allowance was made for differing severity of asbestosis between groups.
  • Dust counts came from konimeters and thermal precipitators. Preliminary observations suggested these must be multiplied by a factor of 1 to 6 to correlate with filter-paper fibre counts.
  • The estimates were preliminary.

Topics

Medical terms in this study, explained in our Lexicon: Amosite, Crocidolite, Amphibole Group, Bantu, Pleural Plaques.

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