Wyers memorial lecture, 1965

Our plain-English summary of Wyers memorial lecture, 1965, by J.C. Gilson (1965).

The study

• Author: J.C. Gilson
• Published: Given at a meeting of the Society on 22 October 1965
• 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 was a lecture in which the author reviewed recent evidence on the biological effects and health hazards of asbestos. It was not a single new study. It described animal experiments by other researchers. In them, inhaled chrysotile caused less lung fibrosis than amosite or crocidolite and was cleared faster, and asbestos injected into the pleura produced mesothelial tumours in rats. UK figures showed asbestosis still being diagnosed, including in workers who entered the industry after 1933. New compensated cases rose from 37 in 1959 to 83 in 1964. A follow-up of asbestos textile workers by Knox, Doll and Hill found no excess lung cancer risk in men who entered scheduled jobs after 1933 and were followed 10 years or more. No diffuse mesothelial tumours had been found in South Africa's amosite or chrysotile mining areas. At the London Hospital, 21 of 51 cases linked to asbestos had contact only outside industry. The author concluded that asbestos had health hazards greater than were recognised in Wyers's time, while listing many unanswered questions.

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 (memorial lecture) of recent experimental and epidemiological evidence, not an original study
• Who was studied: No single study population. The lecture reviewed animal experiments (mainly rats); UK data on asbestosis deaths in one factory and on new cases diagnosed by Ministry of Pensions and National Insurance panels; a mortality follow-up of workers in an asbestos textile factory; and mesothelioma case series from South Africa, the United Kingdom, the USA and Canada
• Exposure: The four main commercial asbestos fibre types: chrysotile, crocidolite, amosite and anthophyllite. Also asbestos mining, textile, insulating and other industrial work, and contact outside industry (living near a factory, dusty work clothes brought home)
• Main results:
  • In inhalation experiments in rats reported by Wagner and colleagues (1963) and Morris et al. (1966), chrysotile produced less fibrosis than amosite or crocidolite for the same dose. This appeared to be due to its much more rapid elimination from the lung.
  • In rat experiments by Wagner, twenty mg of asbestos injected into the pleura produced mesothelial tumours in a high proportion of animals. This applied to chrysotile, amosite and crocidolite. Amosite had so far produced the fewest tumours, and the experiment was not yet complete.
  • In deaths with asbestosis in one factory, there was no striking change in years of exposure or duration of illness between the earlier (1931-46) and recent periods. Average age at death rose by nearly 10 years in men and 20 years in women.
  • Of 313 new cases of asbestosis diagnosed by Ministry of Pensions and National Insurance panels, 183 had entered the industry after 1933 and 32 after 1950.
  • New UK asbestosis cases diagnosed under the Industrial Injuries Act showed an upward trend over 1959 to 1964 (37, 25, 43, 52, 67, 83), while most other types of pneumoconiosis showed a downward trend.
  • In the textile factory follow-up by Knox, Doll and Hill, there was so far no excess lung cancer risk in men who entered the scheduled jobs after 1933 and were followed for 10 years or more. Among women followed for 10 years or more, there had been one lung cancer death.
  • Despite an intensive search over 5 years, no cases of diffuse mesothelial tumours had been discovered associated with the amosite or chrysotile mining areas of South Africa. The author judged that this evidence strongly suggests fibre type, or something closely associated with it, is an important factor in the high incidence in the crocidolite mining area.
  • In London Hospital cases analysed by Hourihane and investigated by Newhouse and colleagues, there was a highly significant association between diffuse mesothelial tumours of the pleura and asbestos bodies in the lungs. Of the cases with an association with asbestos dust, 21 out of 51 had contact with asbestos only outside industry. In nearly a third of the cases there was no history of asbestos exposure.
  • The better-authenticated mesotheliomas, with their probable type of exposure, were: South Africa 1956-1962, 120 cases, crocidolite; United Kingdom 1962-1964, 160 cases, mixed dust; USA 1963-1965, 16 cases, chrysotile; Canada 1952-1964, 6 cases, chrysotile.
  • In consecutive hospital autopsies of people over about age 50, asbestos bodies were found in about 5 to 50 per cent of lungs. Search methods varied, so valid comparisons were not yet possible.
• The authors' conclusion: The author concluded that asbestos has health hazards greater than were recognised when Wyers was writing, and that Wyers was wrong about the effectiveness of legislation in eliminating asbestosis. In the author's view, Wyers was right that fibre types differ in biological effect but probably put amosite and crocidolite in the wrong order.
• Limitations the authors state:
  • There were no reliable figures for the prevalence of asbestosis in the country or for the numbers of workers exposed.
  • The relative risk of different occupations could not be deduced because there were no figures for the numbers employed.
  • The follow-up period in the textile factory study was still not very long for many workers, and the latent period for asbestos-related tumours is very long.
  • UK research added little to comparing risk between fibre types because most cases had mixed exposures.
  • Long-term epidemiological studies in South African mining areas were technically difficult because of labour mobility and lack of records.
  • Once the association was known, later case series were more likely to be biased in how cases were collected.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Fibrosis, Amosite, Crocidolite, Pleura, Lung Cancer.

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