Inhalation and injection studies in rats using dust samples from chrysotile asbestos prepared by a wet dispersion process

Our plain-English summary of Inhalation and injection studies in rats using dust samples from chrysotile asbestos prepared by a wet dispersion process, by J.M. Davis, J. Addison, R.E. Bolton, et al (British Journal of Experimental Pathology, 1986).

The study

• Authors: J.M. Davis, J. Addison, R.E. Bolton, K. Donaldson, A.D. Jones
• Journal: British Journal of Experimental Pathology
• Published: 1986;67(1):113-29
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000387).

Abstract

Long term inhalation studies and intraperitoneal injection studies in rats were undertaken with a series of chrysotile asbestos dusts. Three dust samples were generated from chrysotile modified by the wet dispersion process (WDC) and one was from unmodified chrysotile. Following a 1 year inhalation period, all the chrysotile samples proved extremely fibrogenic and carcinogenic and there were no significant differences between the WDC dusts and normal chrysotile. In all experimental groups approximately 25% of animals developed pulmonary carcinomas and in the oldest rats advanced interstitial fibrosis occupied on average 10% of all lung tissue. In the injection studies all the dust samples produced mesotheliomas in over 90% of animals. Very little chrysotile remained in the lungs of the animals that survived longest following dust inhalation and what there was was present as individual chrysotile fibrils. It is suggested that chrysotile is potentially the most harmful variety of asbestos as shown in these and other animal studies but that it is removed from lung tissue quite rapidly. In the long lived human species this may mean that except where exposure levels are very high and of long duration, chrysotile should be less hazardous than other asbestos types.

In plain English

In this animal experiment, groups of 48 rats breathed dust from one of four chrysotile asbestos preparations. Three came from chrysotile made by the 'wet dispersion' process (WDC), and one was ordinary chrysotile textile yarn. Dusting ran 7 hours a day, 5 days a week, for 224 days over 12 months, at about 4 mg/m3. Other rats had the dusts injected into the abdomen. All five dusted groups developed primary lung tumours in over 35% of animals, with no significant differences between groups. About 25% of animals developed lung carcinomas. Lung scarring (alveolar interstitial fibrosis) spread over time. In the oldest rats it averaged 8.8% to 12.8% of lung tissue across groups, and these differences were not statistically significant. Relatively few mesotheliomas developed after inhalation. After injection, every dust produced mesotheliomas in over 90% of rats. Very little chrysotile remained in the longest survivors' lungs. The authors suggested that chrysotile is removed from lung tissue quite rapidly. They suggested this may mean chrysotile should be less hazardous to humans than other asbestos types, except where exposure is very high and long-lasting.

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 studies and intraperitoneal (abdominal) injection studies in rats
• Who was studied: White SPF rats of the AF Han strain, in groups of 48 per inhalation dust preparation, plus control groups
• Exposure: Inhaled dust from four chrysotile preparations: WDC yarn, factory air dust from a WDC workshop, standard chrysotile textile yarn, and experimental WDC yarn. Dusting was 7 hours a day, 5 days a week, for 224 days over 12 months.
• Main results:
  • Dust was given at a mass level of 4 mg/m3
  • Fibre counts (fibres longer than 5 micrometres) were approximately 100 per ml for the experimental WDC cloud and 400 to 700 per ml for the other clouds
  • All five dusted groups developed primary pulmonary tumours in over 35% of animals, with no significant differences between treatment groups
  • In all experimental groups approximately 25% of animals developed pulmonary carcinomas
  • The factory WDC group, which had the highest overall figures, had 11 adenomas and 10 carcinomas
  • In control animals, one adenoma and one carcinoma were found
  • Alveolar interstitial fibrosis became more widespread in all treatment groups with increasing time after the end of dusting
  • Advanced lesions were assessed in the oldest animals: all those dying within 2 months of the final killing date, giving groups of 14 to 21 animals
  • Alveolar interstitial fibrosis ranged from a mean of 8.8% of lung tissue (chrysotile yarn group) to 12.8% (WDC yarn group); the differences were not statistically significant
  • Relatively few mesotheliomas developed in the inhalation groups
  • In the injection studies, all dust samples produced mesotheliomas in over 90% of animals
  • After injection, WDC yarn, factory WDC and experimental WDC produced mesotheliomas in an average of 310 to 340 days; standard chrysotile yarn required an average of 400 (days)
  • Mean lung dust at the end of dusting ranged from 250 to 500 micrograms across the five groups; 6 months later between 15% and 60% had been cleared
  • Very little chrysotile remained in the lungs of the longest-surviving inhalation animals, and what remained was present as individual fibrils
  • There were no significant differences in non-pulmonary tumours between the five dust exposure groups
  • All chrysotile samples were highly fibrogenic and carcinogenic, with no significant differences between WDC dusts and normal chrysotile
• The authors' conclusion: The authors suggested that chrysotile is removed from lung tissue quite rapidly. They suggested that in long-lived humans this may mean chrysotile should be less hazardous than other asbestos types, except where exposure levels are very high and of long duration.
• Limitations the authors state:
  • The low dust concentration used meant results were not directly comparable with the Institute's earlier inhalation studies at 10 mg/m3
  • Estimates of early pathological changes rested on small groups of animals from the first two kill dates
  • Most carcinomas were too widespread when found to be certain where they originated

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Fibrogenic, Carcinogenic, Carcinoma, Interstitial Fibrosis, Mesothelioma, Fibril.

Related studies

• Some observations on the in vitro cytotoxicity of chrysotile prepared by the wet dispersion process — I.P. Gormley, R.E. Bolton, et al. (1983)
• Inhalation studies on the effects of tremolite and brucite dust in rats — J.M. Davis, J. Addison, et al. (1985)
• Incidence of various types of thoracic malignancy induced in rats by intrapleural injection of 2 mg of various mineral dusts after inhalation of 222Ra — J. Bignon, G. Monchaux, et al. (1983)
• Kinetics of the bronchoalveolar leucocyte response in rats during exposure to equal airborne mass concentrations of quartz, chrysotile asbestos, or titanium dioxide — K. Donaldson, R.E. Bolton, et al. (1988)
• Accumulation of mixed mineral dusts in the lungs of rats during chronic inhalation exposure — C.H. McMillan, A.D. Jones, et al. (1989)
• The sizes, shapes, and mineralogy of asbestos structures that induce lung tumors or mesothelioma in AF/HAN rats following inhalation — D.W. Berman, K.S. Crump, et al. (1995)

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