Further follow-up study of workers from an asbestos cement factory

Our plain-English summary of Further follow-up study of workers from an asbestos cement factory, by H.F. Thomas, I.T. Benjamin, P.C. Elwood, et al (British Journal of Industrial Medicine, 1982).

The study

• Authors: H.F. Thomas, I.T. Benjamin, P.C. Elwood, P.M. Sweetnam
• Journal: British Journal of Industrial Medicine
• Published: 1982;39(3):273-6
• Cited by: 74 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000711).

Abstract

A further follow-up traced 1970 workers employed at an asbestos cement factory for at least six months between 1936 and 1977. At the beginning of this period some crocidolite was used in the factory but by the end of 1936 chrysotile had become the only type of asbestos in use. Only 378 women were employed during the period concerned, and of the 30 who had died, none had a cause of death that is generally associated with exposure to asbestos. The mortality experience of the men was examined separately for all workers, all workers alive after 15 or more years after first exposure, and a smaller group of workers who were employed in 1935-6 and may have been exposed to crocidolite. In none of the three groups was there an appreciably raised standardised mortality ratio (SMR) for the causes of death investigated. These were: all causes, all neoplasms, cancers of the lung and pleura, and cancers of the gastrointestinal tract. An excess of lung cancers noted in the first follow-up study in 1964 was not found in this study. Two pleural mesotheliomas were identified but in both cases the men had worked at the factory before 1936 and therefore had been exposed to crocidolite. No cancers of the larynx were found.

In plain English

This further follow-up covered people who worked six months or more between 1936 and 1977 at an asbestos cement factory near Cardiff. Crocidolite was used there from 1932 to 1935, and only chrysotile from around 1935. The authors traced 1540 men (97%) and 358 women (95%) to the end of 1977 and compared deaths with England and Wales rates. None of the 30 women's deaths was from the cancers studied, so detailed analysis covered men only. Among men, the standardised mortality ratio (SMR) was 102 for all causes (excluding 18 war deaths), 92 for all neoplasms and 93 for lung and pleural cancers (30 deaths). The 1964 study's excess of lung cancer was not found. Two men died of pleural mesothelioma; both had worked there in 1932-5, when crocidolite was used. The authors concluded that the results suggested this population was not at excess risk of total mortality, all cancer mortality, lung and bronchus cancers or gastrointestinal cancers. They noted that smoking data were lacking and that high labour turnover prevented conclusions on sustained long-term chrysotile exposure.

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: Retrospective cohort mortality follow-up study, a further follow-up of a 1964 study of the same factory. It counted person-years at risk and compared deaths with England and Wales death rates as standardised mortality ratios.
• Who was studied: 1592 men and 378 women who worked for six months or more from 1936 to 1977 at an asbestos cement factory near Cardiff, UK. Vital status was followed to 31 December 1977, and 1540 men (97%) and 358 women (95%) were traced. Detailed analysis was of men in three groups: all men (1540), men alive 15 or more years after first exposure (1147), and men employed in 1935 (249).
• Exposure: Work at an asbestos cement factory. Crocidolite was used between 1932 and 1935. From around May 1935 until the factory closed in 1980, only chrysotile from South Africa and Canada was used, mainly to make building sheeting and fittings. Dust levels before 1968 were estimated at 0.1 fibre/ml at the cement machine to 20+ fibre/ml on the beater floor and at hard waste grinding. Regular counts from 1972 to 1980 were consistently below 2 fibres/ml.
• Main results:
  • Among all men, the SMR for all causes was 102 (351 deaths observed, 343.3 expected), excluding war deaths.
  • 18 war deaths were found among the men and were excluded from the SMR calculation.
  • All-cause mortality was not raised for men alive 15 or more years after first exposure (SMR 107) or for men employed in 1935-6 (SMR 94).
  • For all neoplasms, the SMR was 92 for all men, 95 for men alive 15 or more years after first exposure, and 103 for men employed in 1935-6.
  • For cancers of the lung and pleura, the SMR was 93 for all men (30 deaths observed; the table prints the expected number as '33 0'). It was also 93 for men alive 15 or more years after first exposure (24 observed, 25.8 expected). For men employed in 1935-6 it was 76 (7 observed, 9.2 expected).
  • In the 1964 study, men alive 15 or more years after first exposure had an SMR of 232 for lung, bronchus and pleural cancer (7 deaths observed). By the end of 1977 this SMR was 93 (24 observed, 25.8 expected).
  • Two men died of pleural mesothelioma. Both had been employed at the factory during 1932-5, when crocidolite was used.
  • For gastrointestinal cancers, the SMR was 92 for all men and 99 for men alive 15 or more years after first exposure. The SMR of 120 for men employed in 1935-6 reflected one extra death (6 observed, 5.0 expected).
  • No deaths from cancer of the larynx were recorded. Asbestosis was not mentioned on any male or female death certificate examined.
  • Among women, 30 deaths were identified, and none was from the specific cancers analysed.
• The authors' conclusion: The authors concluded that the results suggest this chrysotile asbestos cement factory population was not at excess risk of total mortality, all cancer mortality, lung and bronchus cancers, or gastrointestinal cancers. They stated that the two pleural mesothelioma deaths could not be attributed to chrysotile alone and were probably related to crocidolite exposure at the factory during 1932-5.
• Limitations the authors state:
  • No information was available on the men's smoking habits.
  • Labour turnover was high. The authors state this does not allow conclusions on the hazards of sustained long-term exposure to chrysotile.
  • Over half of the population studied was employed for under two years, and three-quarters for under four years.
  • Dust was not measured regularly until 1968; earlier levels are estimates.
  • There were too few women workers and deaths for detailed analysis of women.
  • The lung cancer SMR of 76 for men employed in 1935-6 rested on only seven deaths, and possibly only a small proportion of those first employed in 1936 used crocidolite.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos-Cement, Crocidolite, Chrysotile, Neoplasm, Pleura, Lung Cancer, Pleural Mesothelioma.

Related studies

• A follow-up study of workers from an asbestos factory — P.C. Elwood, A.L. Cochrane, et al. (1964)
• Absence of radiographic asbestosis and the risk of lung cancer among asbestos-cement workers: Extended follow-up of a cohort — M.M. Finkelstein (2010)
• Mortality of workers in a French asbestos cement factory 1940-82 — A.M. Alies-Patin, A.J. Valleron (1985)
• Mortality of factory workers in east London 1933-80 — M.L. Newhouse, G. Berry, et al. (1985)
• Fibre type and concentration in the lungs of workers in an asbestos cement factory — B. Gylseth, G. Mowé, et al. (1983)
• Lung function among asbestos cement factory workers: cross-sectional and longitudinal study — A. Siracusa, C. Cicioni, et al. (1984)

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