Considerations of Aetiological Mechanisms and Other Factors

Our plain-English summary of Considerations of Aetiological Mechanisms and Other Factors, by J.C. Wagner, G. Berry (1972).

The study

• Authors: J.C. Wagner, G. Berry
• Published: Biological Effects of Asbestos, Lyon. October 2-5, 1972. Paper 43
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This conference paper reviewed animal experiments with asbestos, mainly for cancer. The experiments put dust into the chest cavity (intra-pleural), the abdomen or the windpipe, or had animals breathe it. Most used rats. In an experiment reported by Wagner (1972), a 20mg intra-pleural dose produced mesotheliomas in 61% of rats for crocidolite, 36% for amosite, 34% for anthophyllite, 30% for Canadian chrysotile and 19% for Rhodesian chrysotile. Standard samples with their oils removed produced 58 mesotheliomas, compared with 56 for untreated samples. After inhalation, mesotheliomas occurred only occasionally, but lung adenomas and carcinomas were more frequent. In one study of rats breathing chrysotile (Gross et al., 1967), 24 of 72 surviving rats developed carcinomas. Mesotheliomas were also reported with non-asbestos materials such as fibre-glass. The authors concluded that the cancer-causing effect of asbestos was unlikely to be due to its oils and waxes or to trace elements, and suggested that fibre size and shape deserved further study. They noted that the intra-pleural method can be criticised as unrealistic.

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• Design: review of published and unpublished animal experiments (conference paper)
• Who was studied: Laboratory animals in experiments published or made available after the 1964 New York meeting, mostly rats, with some hamsters, mice and rabbits
• Exposure: Asbestos given by four routes: intra-pleural, intra-peritoneal, intra-tracheal and inhalation. Fibres included the UICC standard samples of crocidolite, amosite, anthophyllite, Canadian chrysotile and Rhodesian chrysotile, plus non-asbestos materials such as fibre-glass, glass-wool, silicon dioxide and brucite.
• Main results:
  • Wagner (1972), intra-pleural, 20mg dose of the five UICC samples in rats: mesotheliomas in 61% of animals for crocidolite, 36% for amosite, 34% for anthophyllite, 30% for Canadian chrysotile and 19% for Rhodesian chrysotile
  • Stanton and Wrench (1972), 40mg dose on fibre-glass pledgets: UICC crocidolite, amosite and Rhodesian chrysotile each produced mesotheliomas in about 60% of rats
  • Wagner (1972): the five UICC samples with oils removed produced 58 mesotheliomas, compared with 56 for the identical untreated samples
  • Across the inhalation experiments reviewed, mesotheliomas occurred only occasionally, while adenomas and adeno and squamous carcinomas were more frequent
  • Gross et al. (1967), inhalation of chrysotile in rats: of 72 rats that survived 16 months of exposure, 24 developed carcinomas and one developed a mesothelioma. Trace metals from a worn mill hammer were considered a possible factor.
  • Wagner (1972), inhalation of the five UICC samples at 12mg/m3 in rats: three mesotheliomas were observed, two of them with the shorter (1 day) exposure
  • In a follow-up inhalation experiment with exposures up to 2 years, all fibre types produced asbestosis, and the fibrosis progressed after removal from the dust
  • Stanton and Wrench (1972) reported mesotheliomas with silicon dioxide, glass-wool and fibre-glass, with the highest incidence (18%) for the finer fibre-glass samples
  • A brucite sample from a Canadian chrysotile mine produced as many mesotheliomas (56%) as the asbestos samples
  • In intra-tracheal experiments in hamsters and rats, chrysotile had a promoting action on the cancer-causing effect of benzo(a)pyrene
• The authors' conclusion: The authors concluded that the cancer-causing effect of asbestos was unlikely to be due to its oils and waxes or to trace elements, and suggested that further experiments on fibre size and shape would be profitable
• Limitations the authors state:
  • The authors acknowledged that intra-pleural application can rightly be criticised as unrealistic
  • In the grinding comparison (Wagner, 1972), a different mill was used, so factors other than particle size could not be ruled out
  • Tumours produced by silica and earlier reported as similar to mesotheliomas were later shown to be lymphomas

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Crocidolite, Amosite, Anthophyllite, Chrysotile, Carcinoma.

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