Induction of pulmonary carcinoma in rats by chronic inhalation of dust from pulverized asbestos pipe covering

Our plain-English summary of Induction of pulmonary carcinoma in rats by chronic inhalation of dust from pulverized asbestos pipe covering, by B.K. Leong, R.J. Kociba, H.C. Pernell, et al (Journal of Toxicology and Environmental Health, 1978).

The study

• Authors: B.K. Leong, R.J. Kociba, H.C. Pernell, R.W. Lisowe, L.W. Rampy
• Journal: Journal of Toxicology and Environmental Health
• Published: 1978;4(4):645-59
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy.

Abstract

Rats and hamsters were exposed to the dust of pulverized asbestos pipe covering at an average concentration of 85 mg/m(3) for 6 h/d, 5 d/wk, for 7 mo, followed by a lifetime observation period. In rats, the pulmonary responses were alveolar adenomatous proliferation, nonprogressive fibrosis, squamous metaplasia, and a substantial incidence of pulmonary carcinoma formation. A smaller group of hamsters exposed under these conditions experienced an earlier onset of mortality than control hamsters, which were not subjected to the exposure regimen. Although this prevented conclusive evaluation of the pulmonary response in this species, no pulmonary neoplasms were noted in the surviving hamsters.

In plain English

This was an animal experiment by researchers at Dow Chemical's toxicology laboratory in Midland, Michigan. An unused asbestos air-cell pipe covering, made in the fifties according to the article, was ground into a fine dust. About 50% of the dust was a material with the crystalline structure of chrysotile, and the airborne dust was mostly non-fibrous particles with some fibers. Fifty male rats and 15 male golden hamsters breathed the dust at an average of 85 mg/m3, 6 hours a day, 5 days a week, for 7 months, and were then observed for life. Equal numbers of unexposed animals served as controls. Among rats left after the interim kills at 7, 8 and 13 months, 6 of 34 exposed rats had lung carcinomas, compared with 0 of 35 controls, a statistically significant increase. Other tumors were similar in both groups. Exposed hamsters died earlier than controls, which the authors said prevented a conclusive evaluation. No tumors were seen in exposed hamsters. The authors concluded that the dust caused lung carcinomas in these rats. They noted that the dust concentrations were high and that lower concentrations needed study.

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 inhalation experiment in rats and hamsters, with unexposed control groups: 7 months of exposure followed by lifetime observation
• Who was studied: The exposed groups were 50 male Sprague-Dawley specific pathogen-free (SPF) derived rats of the Spartan substrain and 15 male golden hamsters. Comparable control groups of 50 rats and 15 hamsters were kept unexposed. The work was done at the Toxicology Research Laboratory, Dow Chemical U.S.A., Midland, Michigan. Five rats per group were killed for interim examinations at each of 7, 8 and 13 months (15 per group in total), and four per group at 25 months. Hamsters were not killed at interim examinations.
• Exposure: The dust came from a pulverized, unused prefabricated asbestos air-cell pipe covering, produced by a major manufacturer in the fifties. On a whole-dust basis, about 50% was a hydrated magnesium silicate having the crystalline structure of chrysotile. The dust contained mainly amorphous particles with some fibrous material. Animals were exposed at an average of 85 mg/m3 (with a variation of 52 mg/m3 either way), 6 hours a day, 5 days a week, for 150 exposures over 7 months.
• Main results:
  • Rats remaining after the interim kills at 7, 8 and 13 months (15 per group) and one cannibalized exposed rat were counted; these still included the four rats per group killed at 25 months. Among them, 6 of 34 dust-exposed rats had pulmonary carcinomas, compared with 0 of 35 control rats. Counted against all rats examined, the figures were 6/49 for exposed rats and 0/50 for controls.
  • By the Fisher exact probability test, the incidence of pulmonary carcinomas was significantly increased in the exposed rat group. Of the 49 exposed rats, 3 had papillary adenocarcinomas, 2 had epidermoid carcinomas and 1 had an adenomatous and mucinous carcinoma.
  • In rats, the incidences of nonpulmonary tumors were comparable in the dust-exposed and control groups.
  • From month 14 to the end of the study, other lung responses in exposed rats included focal alveolar hyperplasia, alveolar adenomatous proliferation, nonprogressive fibrosis and squamous metaplasia of alveoli. Before then, there were no marked fibrogenic responses.
  • Mortality did not differ significantly between exposed and control rats. Exposed rats' mean body weights were significantly lower than controls' until 21 experimental months.
  • In hamsters, 40% of exposed animals died during the 7-month exposure period, while no controls died before month 9. The authors stated that the exposed hamsters' life-span appeared to be significantly reduced by the exposure regimen.
  • No tumors were seen in the 15 exposed hamsters, while two tumors occurred in control hamsters. The authors found no conclusive evidence of a significant pulmonary response in hamsters.
• The authors' conclusion: The authors concluded that exposure to the pipe-covering dust under the conditions used caused pulmonary carcinomas in these male rats. They said this is the type of dust to which pipe insulation workers may be exposed, and that effects at lower concentrations needed to be examined.
• Limitations the authors state:
  • Early deaths of exposed hamsters severely limited evaluation of long-term lung effects in that species.
  • The animals were exposed to high dust concentrations, and lower concentrations would need to be studied to set a realistic guideline.
  • The dust also contained chemical adhesives or binders of unknown nature, which the authors said may have acted together with the asbestos.

Topics

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

Medical terms in this study, explained in our Lexicon: Carcinoma, Pipe Covering, Fibrosis, Neoplasm.

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• Studies on the inhalation toxicology of two fiberglasses and amosite asbestos in the syrian golden hamster. Part I. Results of a subchronic study and dose selection for a chronic study — T.W. Hesterberg, C. Axten, et al. (1999)

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