Tumorigenic effect of fibrous dusts in experimental animals

Our plain-English summary of Tumorigenic effect of fibrous dusts in experimental animals, by F. Pott, F. Huth, K.H. Friedrichs (Environmental Health Perspectives, 1974).

The study

• Authors: F. Pott, F. Huth, K.H. Friedrichs
• Journal: Environmental Health Perspectives
• Published: 1974;9:313-5
• Cited by: 64 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Fibrous dusts (chrysotile, glass fibers, nemalite, palygorscite, and gypsum) and granular dusts (actinolite, biotite, hematite, pectolite, sanidine, and talcum) were injected intraperitoneally into rats. The fibrous dusts (other than gypsum) resulted in a high incidence of mesothelioma (30 - 67%). Gypsum produced only 5% and granular dusts none at all. It is suggested that the fibrous shape leads to a high multiplication rate of cells and predisposes to tumor formation. Fibrosis, in the other hand, does not so predispose. Milled chrysotile with 99.8% fibers than 5 mum in length are carcinogenic in our experience. The carcinogenicity of glass fibers in our experiments may have significance for occupational situations.

In plain English

This was an animal experiment. The authors injected dusts into the abdominal cavity of Wistar rats, in groups of 40 rats, with 80 control rats given salt water. They wanted to test whether the tumor-causing effect of asbestos depends on its chemistry or on its fibrous shape. The fibrous dusts were chrysotile asbestos (UICC standard and a milled form), glass fibers, nemalite, palygorscite and gypsum. The granular or platy dusts were actinolite, biotite, hematite, pectolite, sanidine and talcum. Chrysotile, glass fibers, nemalite and palygorscite produced abdominal tumors in 30% to 67.5% of rats, depending on the dust and dose. Gypsum, which dissolved in tissue, produced tumors in 5% of rats. Pectolite, sanidine and talcum each produced tumors in 2.5%. Actinolite, biotite, hematite and the controls produced none. Nearly all tumors were sarcomatous mesotheliomas. Milled chrysotile, with 99.8% of fibers shorter than 5 micrometres, produced tumors in 30% of rats. The authors concluded that tumor formation depends on fiber shape, not on fibrosis, and that their glass fiber results may matter for workplaces.

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 (abdominal cavity) injection of fibrous and granular dusts in rats, observed until spontaneous death or sacrifice, with all tumors examined histologically
• Who was studied: Wistar rats. Each test group had 40 rats, and 80 control rats were injected with pure saline. The study was done at the Medizinisches Institut für Lufthygiene und Silikoseforschung, Universität Düsseldorf, Germany. Study dates are not given.
• Exposure: Fibrous dusts: chrysotile A (UICC standard asbestos), milled chrysotile A, uncoated glass fibers (Na, Ca borosilicates), nemalite, palygorscite and gypsum. Granular or platy dusts: actinolite, biotite, hematite (precipitated and mineral), pectolite, sanidine and talcum. Dusts were suspended in saline at up to 25 mg per 2 ml, with weekly repeat injections for higher doses. Doses were 6 mg, 25 mg, 3 x 25 mg or 4 x 25 mg per rat.
• Main results:
  • In the text, the authors stated that UICC standard asbestos (chrysotile A), palygorscite, nemalite and glass fibers induced tumors in the abdominal cavity of 30-67% of the rats. In Table 3, the group tumor rates for these dusts ranged from 30% to 67.5%.
  • Tumor rates for chrysotile A were 67.5% at 6 mg (first tumor at 343 days), 65% at 25 mg and 37.5% at 4 x 25 mg. The rate for milled chrysotile A at 4 x 25 mg was 30%.
  • Glass fibers at 4 x 25 mg gave a tumor rate of 57.5%, with the first tumor at 197 days. Nemalite at 4 x 25 mg gave 62.5%, and palygorscite at 3 x 25 mg gave 65%.
  • Gypsum, which was fibrous but dissolved in animal tissue, induced tumors in only 5% of the animals.
  • Granular dusts: pectolite, sanidine and talcum (4 x 25 mg) each gave a tumor rate of 2.5%. Actinolite, biotite, both hematites and the saline controls showed no tumors.
  • Histologically, nearly all the tumors were sarcomatous mesotheliomas.
  • In ongoing experiments, the lowest effective dose of glass fibers was 2 mg per rat, with the first mesotheliomas at 17 months. At 100 mg, the first tumor appeared after 6.5 months.
  • Milled chrysotile A, in which 99.8% of fibers were shorter than 5 micrometres, still induced tumors. Rats in this group that died without a tumor showed only slight adhesions.
• The authors' conclusion: The authors concluded that carcinogenesis depends on the shape of the dusts, and that the fibrosis caused by fibrous dusts cannot be regarded as the starting point of malignancy. They believed that even short fibers under 10 micrometres can induce tumors. They suggested their glass fiber results may have significance for occupational situations, and recommended precaution in plants with high concentrations of fibers under 3 micrometres in diameter.
• Limitations the authors state:
  • Injection, not inhalation, was used. The authors said inhalation would be the best method but leads to enormous technical difficulties.
  • Dose was measured by weight rather than by number of fibers, because fibers of identical diameter and length could not be obtained.
  • The minimum and maximum fiber length and diameter needed for a carcinogenic effect could not yet be fully determined.
  • No tumors had yet been found in glass fiber industry workers. Because thinner glass fibers had been produced in Germany for only about 10 years, the authors said no epidemiological proof that the results apply to humans was possible before 1985.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma, Talc and vermiculite.

Medical terms in this study, explained in our Lexicon: Chrysotile, Actinolite, Hematite, Mesothelioma, Fibrosis, Carcinogenic.

Related studies

• The pulmonary response to fibrous dusts of diverse compositions — P. Gross, R.T. deTreville, et al. (1970)
• Dose-response relationship of fibrous dusts in intraperitoneal studies — M. Roller, F. Pott, et al. (1997)
• The long term fibrogenic effects of chrysotile and crocidolite asbestos dust injected into the pleural cavity of experimental animals — J.M. Davis (1970)
• Asbestosis in experimental animals — J.C. Wagner (1963)
• Epithelial outgrowths from lung tissue following intrapleural injection of asbestos dust in experimental animals — J.M. Davis (1971)
• Characteristics of tumors and tumor cells cultured from experimental asbestos-induced mesotheliomas in rats — J.E. Craighead, N.J. Akley, et al. (1987)

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