Health effects of refractory ceramic fibres: scientific issues and policy considerations

Our plain-English summary of Health effects of refractory ceramic fibres: scientific issues and policy considerations, by L.R. Glass, R.C. Brown, J.A. Hoskins (Occupational and Environmental Medicine, 1995).

The study

• Authors: L.R. Glass, R.C. Brown, J.A. Hoskins
• Journal: Occupational and Environmental Medicine
• Published: 1995;52(7):433-40
• Type of article: Review
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To review the scientific literature on the health effects of refractory ceramic fibres (RCFs). The adverse effects of exposure to asbestos has led to concern about the potential for other fibrous materials to cause diseases. For this reason the human populations most heavily exposed to synthetic mineral fibres have been examined for any adverse effects and many types of fibre have been studied in animal experiments. One type of man made vitreous fibres (MMVFs), refractory ceramic fibres (RCFs), are principally used in thermal insulation at high temperatures--up to 1400 degrees C. As manufactured RCFs exist in a glassy, non-crystalline (sometimes called amorphous) state, they have various compositions, physical properties, and sized fibres.

Methods: All reports on the health effects of RCFs available up to the end of 1994 have been examined and the scientific literature reviewed although all publications have not necessarily been referenced.

Conclusions: In recent inhalation experiments conducted with both rats and hamsters at the Research and Consulting Company, Geneva, at the highest dose tested (30 mg/m3) there was an increased incidence of tumours in both species. Lower doses were only examined in the rat and at these doses there was no significant excess of lung tumours. Epidemiological investigations of workers engaged in the manufacture of ceramic fibres have shown a small excess of pleural plaques. This phenomenon is being further investigated but could be due to confounding exposures. The populations available for study are small and their exposures fairly short, but it is considered prudent that they should remain under surveillance for some time to come. This is despite the fact that present exposures in the ceramic fibre industry are low (< 1 f/ml) and are being reduced.

In plain English

This article was a review, not a new study. The authors examined reports on the health effects of refractory ceramic fibres (RCFs), which are used in high-temperature insulation, available up to the end of 1994. In the Research and Consulting Company inhalation experiments, 42 of 112 hamsters at risk (those exposed for 12 months), or 38%, had mesothelial tumours after inhaling a kaolin-based RCF at 30 mg/m3. Rats at that dose had significantly more lung tumours than controls only with the unheated fibres. Rats at 3, 9 and 16 mg/m3 showed no excess of lung tumours. Among US manufacturing workers, small lung function decreases were not clinically significant. The studies found no excess risk of lung cancer and no mesotheliomas. Pleural plaques were seen in 12.5% (9/72) of workers with more than 20 years of exposure. The authors noted these figures were not age-corrected and that some plants may have used asbestos. They concluded there was so far no evidence that RCF exposure can cause respiratory disease. They added that animal studies probably overestimate hazard and that the worker groups were small, with short exposures.

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: Review of published and unpublished reports (animal experiments and studies of workers) on the health effects of refractory ceramic fibres
• Who was studied: Reviewed studies of rats (Fischer 344) and Syrian golden hamsters, and of workers manufacturing RCF in Europe (over 650 employees) and the United States (a cohort of 742 workers)
• Exposure: Refractory ceramic fibres (vitreous aluminosilicates). The Research and Consulting Company experiments used four types: kaolin based, high purity, zirconia (15% zirconia) and heated 'after service' kaolin. Animals were exposed at 30 mg/m3 (about 200 fibres/ml) for six hours a day, five days a week. A multidose rat study used 3, 9 and 16 mg/m3. Workers were exposed during RCF manufacture.
• Main results:
  • Among hamsters exposed to kaolin RCF at the maximum tolerated dose, 42 had mesothelial tumours. Table 3 gives 112 hamsters at risk and a mesothelial tumour incidence of 38%. Animals at risk were defined as those exposed for 12 months, not all exposed animals. The tumours were small and did not affect survival, and no hamsters developed lung tumours.
  • In rats at the maximum tolerated dose (30 mg/m3), lung tumour incidence was significantly different from controls only for the unheated fibres. The few mesotheliomas in each RCF group were not statistically significant.
  • In the multidose rat study (3, 9 and 16 mg/m3 kaolin RCF), there was no excess of lung tumours at any dose. One rat in the 9 mg/m3 group developed a mesothelioma.
  • The European study of over 650 RCF manufacturing employees found no evidence of lung disease in those who had never smoked
  • In the US cohort, forced vital capacity and forced expiratory volume in one second decreased by between 2% and 3%. The decreases were correlated with smoking and duration of exposure and were judged not clinically significant.
  • Pleural plaques were found in 0.9% of non-production workers (2/214) and of production workers with under 10 years of RCF exposure (1/117). The figure was 2.8% for those with 10 to 20 years (7/248) and 12.5% for those with over 20 years (9/72).
  • Deaths in the US cohort were consistent with the general population. There was no excess risk of lung cancer (4 observed, against an expected number printed in the scanned text as '3 5') and no mesotheliomas.
• The authors' conclusion: The authors concluded that, to date, there was no evidence that exposure to RCF can cause any respiratory disease in workers. They also stated that the surveys should be extended and that pleural plaques in a few workers were the main finding.
• Limitations the authors state:
  • The worker populations were smaller, and their exposures shorter, than other occupational cohorts
  • Many plants also made hard refractories and may have used asbestos, so effects cannot simply be attributed to RCFs
  • The pleural plaque figures were crude and needed correction for age
  • Historical worker exposures were extremely difficult to reconstruct
  • At the maximum tolerated dose, lung burdens in the animals may have overwhelmed lung clearance, and the authors judged animal studies likely to overestimate hazard
  • Only the kaolin RCF was tested in hamsters, and at only one dose

Topics

Medical terms in this study, explained in our Lexicon: Vitreous, Thermal System Insulation (TSI), Crystalline, Pleural Plaques, Confounding.

Related studies

• The in vivo biological activity of ceramic fibres — R.C. Brown, J.A. Hoskins, et al. (1995)
• Co-exposure to refractory ceramic fibres and asbestos and risk of pleural mesothelioma — A. Lacourt, M. Rinaldo, et al. (2014)
• Clinico-pathological features and somatic gene alterations in refractory ceramic fibre-induced murine mesothelioma reveal mineral fibre-induced mesothelioma identities — P. Andujar, C. Lecomte, et al. (2007)
• Exposure to refractory ceramic fibres in the metal industry — M. Linnainmaa, J. Kangas, et al. (2007)
• Refractory ceramic fibers: Fiber characteristics, potential health effects and clinical observations — M.J. Utell, L.D. Maxim (2018)
• Refractory ceramic fiber exposure and pleural plaques — J. Lockey, G. Lemasters, et al. (1996)

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