Variations in the carcinogenicity of mineral fibres

Our plain-English summary of Variations in the carcinogenicity of mineral fibres, by R.E. Bolton, J.M. Davis, K. Donaldson, et al (The Annals of Occupational Hygiene, 1982).

The study

• Authors: R.E. Bolton, J.M. Davis, K. Donaldson, A. Wright
• Journal: The Annals of Occupational Hygiene
• Published: 1982;26(1-4):569-82
• Read it: PubMed

In plain English

This was a laboratory experiment in rats. The authors injected asbestos dust into the abdominal (peritoneal) cavity to compare how readily different dusts caused peritoneal mesothelioma. They used 232 male Wistar rats in seven groups of about 32. Each rat received 25 mg of one of seven 'elutriated' dusts, meaning dusts collected from airborne clouds. Two were of amosite origin (UICC and factory). Five were of chrysotile origin: UICC chrysotile 'A', factory, a sample heated to 850°C, an unheated Canadian 'parent' sample, and an experimental 'wet-dispersed' preparation. In six of the seven groups, over 90% of the rats available for long-term follow-up developed peritoneal mesothelioma. The heated chrysotile group had far fewer, 13 of 32. Because tumour counts were so similar, the authors also compared how quickly tumours appeared. The first tumour came at 178 days with wet-dispersed chrysotile and at 621 days with heated chrysotile. The authors concluded that the chrysotile samples tended to be more carcinogenic than the amosite samples. They also concluded that their fibre-length measurements did not explain the differences, partly because representative microscope samples were hard to prepare.

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 (intraperitoneal injection assay in rats)
• Who was studied: 232 male AF/HAN Wistar rats, 8-10 weeks old at injection, at the Institute of Occupational Medicine, Edinburgh. They were divided into seven treatment groups of about 32. After 11 early deaths from acute peritonitis, 221 rats were available for long-term follow-up.
• Exposure: A single 25 mg intraperitoneal injection of one of seven elutriated dusts: UICC amosite, factory amosite, UICC chrysotile 'A', factory chrysotile, chrysotile heated up to 850°C, unheated 'parent' commercial Canadian chrysotile, and experimental 'wet-dispersed' chrysotile. The factory chrysotile sample contained only 60% chrysotile and the factory amosite sample 90% amosite.
• Main results:
  • Table 2 gives tumour percentages among animals available for long-term follow-up, not among all animals injected. In six of seven groups, over 90% of these animals developed peritoneal mesothelioma. For example, the UICC chrysotile 'A' group had 30 mesotheliomas among 31 such animals (97%), although 36 animals had been injected.
  • Heated chrysotile was the exception to the similar tumour counts. The scanned Table 2 is scrambled, but its counts, which match the stated totals, show 13 mesotheliomas among 32 animals (41%) in this group.
  • The time to the first mesothelioma ranged from 178 days (wet-dispersed chrysotile) to 621 days (heated chrysotile).
  • Mean survival time of mesothelioma-bearing animals was shortest with wet-dispersed chrysotile (312 days in Table 4) and longest with heated chrysotile (840 days in Table 4).
  • Ranked by survival function, carcinogenicity ran in descending order: wet-dispersed chrysotile, factory chrysotile, UICC chrysotile, parent chrysotile, UICC amosite, factory amosite, heated chrysotile.
  • There was broad agreement with earlier in vitro cell-toxicity tests of the same dusts. The most carcinogenic dust, wet-dispersed chrysotile, was also the most toxic to cells.
  • The chrysotile and amosite samples had similar relative fibre length distributions in liquid suspension, yet the chrysotile was more carcinogenic. The authors therefore judged that the percentage of long fibres did not appear to be the most important factor.
  • Heating chrysotile to 850°C almost totally destroyed its fibrous component. The authors judged this the probable reason the heated sample was least carcinogenic.
• The authors' conclusion: The authors concluded that chrysotile samples tended to be more carcinogenic than amosite samples. They concluded that relative fibre length did not provide a useful measure of the carcinogenicity of the seven dusts. They also concluded that the relative carcinogenicity of similar dusts may be reasonably assessed from mean tumour latent period rather than from tumour counts, assuming the same mechanism for each dust.
• Limitations the authors state:
  • The near 100% tumour response in several groups meant treatments could not be distinguished by the number of tumours produced.
  • No dose-response information was available for intraperitoneal injection, so the 25 mg dose was chosen from previous experience.
  • Fibre numbers were not estimated for the samples.
  • Satisfactory fibre length distributions could not be produced for two of the dusts.
  • The fibre length figures did not account for the substantial non-fibrous component of the factory samples.
  • Variations in the size data were attributed mainly to problems preparing accurate, reproducible samples for electron microscopy.
  • The study could not separate an effect of fibre length from other particle-size factors such as surface area.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite, Chrysotile, Mesothelioma, Peritoneal mesothelioma.

Related studies

• Variations in the carcinogenicity of tremolite dust samples of differing morphology — J.M. Davis, J. Addison, et al. (1991)
• Fibrinolysis by rat mesothelial cells in vitro: the effect of mineral dusts at non-toxic doses — K. Donaldson, G.M. Brown, et al. (1988)
• Kinetics of deposition and clearance of inhaled mineral dusts during chronic exposure — J.H. Vincent, A.M. Johnston, et al. (1985)
• Enhanced generation of free radicals from phagocytes induced by mineral dusts — V. Vallyathan, J.F. Mega, et al. (1992)
• Mesothelioma dose response following intraperitoneal injection of mineral fibres — J.M. Davis, R.E. Bolton, et al. (1991)
• Results of current intraperitoneal carcinogenicity studies with mineral and vitreous fibres — M. Roller, F. Pott, et al. (1996)

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