Man-Made Mineral Fibers

Our plain-English summary of Man-Made Mineral Fibers, by J.W. Hill (1978).

The study

• Author: J.W. Hill
• Published: Journal of the Society of Occupational Medicine, Volume 28 (1978)
• Type of article: Journal article
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This article reviewed published research on man-made mineral fibres: glass, rock and slag wools and continuous glass filaments. It reported no new study. The review described chest X-ray and lung function surveys of US and UK glass fibre workers, and a German chest X-ray study, all reported as negative or showing no pathology attributable to occupation. It described a US study of 1448 glass wool plant employees. That study found no overall excess mortality, no mesothelioma and no excess cancer deaths, but a statistically significant excess of non-malignant respiratory deaths excluding pneumonia and influenza. The author criticised that finding, partly over the choice of comparison group. In rat experiments by others, glass and other fibres injected into the pleura produced tumours related to fibre diameter. Inhaled man-made mineral fibres did not produce tumours in animals, although similar inhalation experiments with asbestos produced lung carcinoma and mesothelioma. The author concluded that these fibres are not fibrogenic and lung carcinoma is not a hazard. No mesothelioma cases had been described in such workers, the author noted, though its latent period may be very long.

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: Narrative review of published literature (human case reports, prevalence and cohort studies, animal and cell culture experiments), with one anecdotal observation by the author
• Who was studied: Published studies on man-made mineral fibres made from glass, natural rock or slag, mainly studies of glass fibre production workers in the USA, UK and Germany, plus animal and cell experiments
• Exposure: Man-made mineral fibres: insulation wools (usually about 6 micrometres nominal diameter, some down to 2 micrometres in Europe), continuous filaments of 12 to 20 micrometres, and special US fibres of 1 micrometre or less. At points the article compares them with asbestos, including chrysotile
• Main results:
  • A typical plant producing 6 micrometre insulation wool had respirable airborne fibre counts of 0.003 to 0.051 fibres per cubic centimetre (mean 0.022). Gravimetric dust estimates in the same plant were 0.36 to 8.12 mg per cubic metre
  • When boards were sawn, the fibres from glass fibre reinforced board were 2000 times less numerous than those from chrysotile asbestos reinforced board (Hounham, 1973)
  • Chest X-ray and lung function studies of 1389 US insulation wool workers with 10 or more years of glass fibre exposure were negative (Wright, 1968; Utidjian and DeTreville, 1970)
  • A UK study of 70 production workers with an average of 20 years' exposure, compared with matched controls using chest X-rays, lung function and a bronchitis questionnaire, was also negative (Hill et al., 1973)
  • A German study of the chest X-rays of 36 glass fibre workers with more than 10 years, and 196 with more than 15 years, of exposure showed no pathology attributable to occupation
  • In a US cohort of 1448 glass wool plant employees followed to 1975 (Bayliss et al., 1976), there was no overall excess mortality compared with a control group, no mesothelioma and no excess cancer deaths
  • The only positive finding in that cohort was a statistically significant excess of non-malignant respiratory deaths excluding pneumonia and influenza. The author criticised this finding because smoking was not considered and because the control group was the total white male US population
  • A study of 416 retired glass fibre workers (Enterline, 1975) found a small excess of bronchitis (3 observed versus 0.5 expected). That study's author was disinclined to attach clinical significance to it
  • A post-mortem study of the lungs of 20 glass fibre workers with 16 to 23 years of exposure found no specific disease or tissue alteration attributable to fibrous dust
  • Three individual human cases with glass fibres in the lung (1947, 1957, 1961) were judged by the author to be associated primarily with infection, with the fibres possibly incidental
  • In rat experiments by others with fibres injected or implanted into the pleura and peritoneum, fibres including glass fibres produced tumours, and carcinogenic potency was related to fibre diameter
  • In those animal experiments, glass fibres of 0.5 micrometre diameter injected into the pleura produced mesothelioma (Wagner et al.), while fibres greater than 3 micrometres had little biological effect
  • In animal inhalation experiments, tumour induction by man-made mineral fibres was not found
  • Similar inhalation experiments with asbestos produced fibrosis, lung carcinoma and mesothelioma
  • In bacterial mutation tests (Chamberlain and Tarmy, 1976), neither asbestos nor glass fibres showed mutagenic activity
  • As an anecdotal observation, the author reported not having come across a case of mesothelioma in a glass fibre worker in over 20 years of enquiry at three local hospitals
  • In the author's summary, man-made mineral fibres are not fibrogenic but may exacerbate pre-existing lung disease like any nonspecific dust
  • The author noted that mesothelioma may have an extremely lengthy latent period
  • The author noted that no cases of mesothelioma had been described in workers exposed to man-made mineral fibres
• The authors' conclusion: The author concluded that lung carcinoma is not a hazard from man-made mineral fibres, citing the epidemiology and the animal experiments
• Limitations the authors state:
  • The author noted that the doses in the intrapleural animal experiments were unrealistic in terms of human exposure, which makes extrapolation difficult
  • For the German X-ray study, the author stated it was difficult to tell from the data how many workers had 20 or more years of exposure
  • The author stated that extrapolation from cell culture studies to living organisms is difficult and gives no clear indication
  • The author described the observation of no local mesothelioma cases as anecdotal
  • The author noted that the part of the Bayliss study on 1 micrometre fibres was criticised for small numbers, its statistical methods and incorrect attribution of exposure

Topics

Medical terms in this study, explained in our Lexicon: Mineral Fiber, Chest X-Ray, Pathology, Mesothelioma, Pleura, Carcinoma, Fibrogenic.

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