Inhalation studies on the effects of tremolite and brucite dust in rats

Our plain-English summary of Inhalation studies on the effects of tremolite and brucite dust in rats, by J.M. Davis, J. Addison, R.E. Bolton, et al (Carcinogenesis, 1985).

The study

• Authors: J.M. Davis, J. Addison, R.E. Bolton, K. Donaldson, A.D. Jones, B.G. Miller
• Journal: Carcinogenesis
• Published: 1985;6(5):667-74
• Cited by: 51 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Samples of commercially used asbestos, especially chrysotile, are frequently contaminated by small amounts of other fibrous minerals. Among these are tremolite and brucite although pure tremolite is also produced commercially in relatively small quantities. In order to determine how harmful commercially exploited tremolite might be in comparison with other asbestos types and to explore the possibility that small amounts of tremolite and brucite as contaminants could significantly affect the pathogenicity of industrially used chrysotile, long-term animal inhalation and injection studies using rats were undertaken with what were considered to be mineralogically pure samples of these minerals. Rats treated with tremolite developed very high levels of pulmonary fibrosis as well as 16 carcinomas and two mesotheliomas in a group of 39 animals. Tremolite thus proved to be the most dangerous mineral that we have studied. Animals treated with 'brucite' developed moderate levels of pulmonary fibrosis and two carcinomas. Both tremolite and brucite produced mesotheliomas in greater than 90% of animals following i.p. injection. However, it was found that the supposedly pure brucite in fact contained 10% chrysotile, a level of contamination that could well have been responsible for the pathological changes found in both inhalation and intraperitoneal injection studies. The greatest care should be exercised by industry in handling tremolite or materials contaminated with it.

In plain English

This was an animal experiment. Male Wistar rats breathed dust from a commercial Korean tremolite sample or from a 'brucite' sample for 7 hours a day, 5 days a week, for 224 days over 12 months. The planned respirable dust level was 10 mg/m3, and 36 rats with no dust exposure served as controls. Other rats received a 25 mg injection of either dust into the abdominal cavity. Among 39 tremolite-exposed rats, 16 developed lung carcinomas and 2 developed mesotheliomas. Among 38 brucite-exposed rats, 2 developed carcinomas. This difference was statistically significant, and no lung tumours were found in the controls. Tremolite also produced much more lung fibrosis than brucite. After injection, mesotheliomas developed in 27 of 29 tremolite rats (93%) and 27 of 28 brucite rats (96%). The 'brucite' sample turned out to contain about 10% chrysotile, and the authors stated that this contamination could well explain the brucite results. The authors concluded that pure tremolite and materials contaminated with it should be treated with appropriate care by industry.

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: Animal experiment: long-term inhalation study plus intraperitoneal (abdominal) injection study in rats
• Who was studied: Male Wistar rats of the AF/Han strain at the Institute of Occupational Medicine, Edinburgh, UK. Inhalation: groups of 48 rats per dust; 39 tremolite and 38 brucite rats were examined for lung tumours, along with 36 undusted controls. Injection: two groups of 32 rats. Study dates are not stated.
• Exposure: Inhalation of a commercial Korean tremolite sample (about 95% fibrous tremolite by mass) or a 'brucite' sample (85-90% brucite, with about 10% chrysotile and some pyraurite). The planned respirable dust concentration was 10 mg/m3, for 7 h a day, 5 days a week, for 224 days over 12 months. The injection study used 25 mg of the respirable dust fraction injected into the peritoneal cavity.
• Main results:
  • Inhalation, lung tumours: in the tremolite group (39 rats), 16 carcinomas (8 adenocarcinomas, 8 squamous carcinomas) and 2 mesotheliomas; in the brucite group (38 rats), 2 carcinomas
  • The difference in malignant tumours between the tremolite and brucite groups was statistically significant (p less than 0.001)
  • No lung tumours were found in the 36 control rats
  • Pulmonary adenomas (benign lung tumours): 2 in the tremolite group, 3 in the brucite group
  • Peribronchiolar fibrosis was greater with tremolite than with brucite at 12 months (23.0 vs 1.6) and at 18 months (13.4 vs 1.7) after the start of dusting. This was measured as the percentage of graticule squares containing lesions, in groups of 3 to 4 rats. The difference was statistically significant at both times.
  • Interstitial fibrosis at 27-29 months: 14.5% of lung tissue area in the tremolite group vs 2.9% in the brucite group, 12 rats each (p less than 0.01)
  • Fibre number concentration in the air (fibres longer than 5 microns, by light microscopy): 1600/ml for tremolite and 230/ml for brucite
  • In brucite-exposed rats killed 6 months after dusting ended, the mean lung dust content was 64 micrograms, and the authors concluded that almost all of it was chrysotile
  • Injection study: mesotheliomas developed in 27 of 29 tremolite-injected rats (93%) and 27 of 28 brucite-injected rats (96%)
  • Injection study: mean survival of rats with tumours was 352 days after tremolite and 418 days after brucite
  • Tumours outside the lung: the control group had the highest numbers, but these were not significantly higher than in the tremolite or brucite groups
• The authors' conclusion: The authors concluded that pure tremolite and any materials contaminated with it should be treated with appropriate care by industry. They wrote that tremolite proved to be the most dangerous mineral they had studied. They also wrote that the effects of the 'brucite' sample could be due to its chrysotile content, which shows how hard it is to attribute effects to single components of a mixed dust.
• Limitations the authors state:
  • The supposedly pure brucite contained about 10% chrysotile, which could well have caused the changes seen in both the inhalation and injection studies
  • The two electron-microscope observers gave different absolute fibre size estimates
  • Early lesions were assessed in small groups of rats, so the drop in tremolite lesions between 12 and 18 months was not statistically significant
  • Lung dust samples from the brucite rats killed at the end of dusting were destroyed during analysis
  • The tremolite sample also contained unidentified impurities seen on X-ray diffraction

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile, Tremolite.

Medical terms in this study, explained in our Lexicon: Tremolite, Brucite, Chrysotile, Pulmonary Fibrosis, Carcinoma, Mesothelioma.

Related studies

• Variations in the carcinogenicity of tremolite dust samples of differing morphology — J.M. Davis, J. Addison, et al. (1991)
• Chronic effects of dietary exposure to amosite asbestos and tremolite in F344 rats — E.E. McConnell, H.A. Rutter, et al. (1983)
• Biological effects of tremolite — J.C. Wagner, M. Chamberlain, et al. (1982)
• Tremolite/chrysotile ratios — G. Scansetti, G. Piolatto (1987)
• Mesothelioma in Cyprus: the role of tremolite — K. McConnochie, L. Simonato, et al. (1987)
• Inhalation and injection studies in rats using dust samples from chrysotile asbestos prepared by a wet dispersion process — J.M. Davis, J. Addison, et al. (1986)

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