Asbestos disease at low exposures after long residence times

Our plain-English summary of Asbestos disease at low exposures after long residence times, by G.K. Sluis-Cremer (Annals of the New York Academy of Sciences, 1991).

The study

• Author: G.K. Sluis-Cremer
• Journal: Annals of the New York Academy of Sciences
• Published: 1991;643:182-93
• Cited by: 23 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 004494).

Summary of the article

The author reviewed his group's South African studies of crocidolite and amosite miners to examine disease at "low" exposure, defined as an average below 2 fibers/mL or a cumulative exposure below 5 fiber-years/mL, after long residence times (years since onset of exposure). In 807 miners autopsied between 1974 and 1988, no asbestosis was found below 2 fiber-years/mL, although few such men had residence times over 30 years. At 2-5 fiber-years/mL, asbestosis was found in 1 of 32 men with residence times under 15 years and 3 of 24 with 16-30 years. In 1,454 men X-rayed in 1970-1975 and again 2-16 years later, radiological progression from category 0/0 to 1/0 occurred in 12% of those with continued exposure and 10.5% of those whose exposure had stopped. Appreciable progression was seen with under 5 years or under 5 fiber-years/mL of exposure. In a mortality study of 7,317 white miners (1,225 deaths by 1980), the lung cancer SMR was 172.4, and 143.9 in the 1-5 fiber-years/mL group. In a case-referent analysis of autopsied men, asbestosis was the strongest predictor of bronchial cancer. There were 30 mesotheliomas, 20 in crocidolite miners, none with under 3 months' exposure. The author concluded that low industrial exposures with long residence times carry a considerable disease burden, though they remain far above environmental exposures.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This paper reviewed the author's own studies of South African miners exposed to the amphibole asbestos types crocidolite and amosite. 'Low' exposure meant under 2 fibers/mL average or under 5 fiber-years/mL cumulative. Among 807 autopsied miners, no asbestosis was found below 2 fiber-years/mL, though few had over 30 years since first exposure. At 2 to 5 fiber-years/mL, asbestosis appeared in 1 of 32 and 3 of 24 men in two residence-time groups. Among 1,454 miners X-rayed twice, those with normal first films (category 0/0) reached category 1/0 about as often after stopping exposure (58 of 549) as when continuing (80 of 648). In a mortality study of 7,317 white miners, lung cancer deaths were elevated (SMR 172.4), and asbestosis was the strongest predictor of lung cancer found at autopsy. Of 30 mesotheliomas among 1,225 deaths, 20 were in crocidolite miners, 4 in amosite miners, and 6 in men with mixed exposures, most also exposed to crocidolite. The author concluded that low industrial exposures with long residence times are associated with a considerable burden of disease, cautioning that findings may not apply to chrysotile.

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 the author's own previously published studies of South African amphibole asbestos miners: an autopsy study, a radiological follow-up cohort, and a mortality cohort with case-referent analyses
• Who was studied: South African amphibole asbestos miners in three groups: 807 white or mixed-race men autopsied 1974 to 1988; 1,454 men X-rayed between 1970 and 1975 and again 2 to 16 years later; and 7,317 white men on amphibole mine personnel records, with 1,225 deaths by the end of 1980
• Exposure: Mining of the amphiboles crocidolite and amosite (some men had mixed exposures). 'Low' exposure was defined as an average below 2 fibers/mL or a cumulative exposure below 5 fiber-years/mL. Residence time was defined as years since onset of exposure.
• Main results:
  • Among the 807 autopsied miners, no asbestosis was found in workers with cumulative exposures below 2 fiber-years/mL, regardless of residence time.
  • Among autopsied miners with 2 to 5 fiber-years/mL cumulative exposure, asbestosis was found in 1 of 32 with residence time under 15 years and in 3 of 24 with residence time of 16 to 30 years.
  • Among autopsied miners with cumulative exposure above 300 fiber-years/mL and 45 or more years of residence time, 82% (64/78) had asbestosis.
  • In the X-ray follow-up cohort, 80 of 648 workers (12%) who continued exposure and whose first X-ray was category 0/0 had progressed to 1/0 by the second X-ray. Among those who stopped exposure, 58 of 549 (10.5%) made the same change from 0/0 to 1/0.
  • Among workers whose first X-ray was category 0/1, 53 of 88 who continued exposure and 46 of 69 who stopped exposure showed progression. The author reported virtually no difference between the two groups in disease frequency or yearly rate of progression.
  • In the mortality cohort of 7,317 white amphibole miners, there were 63 bronchogenic carcinoma deaths, and the overall SMR for lung cancer was 172.4, significant at the 1% level.
  • In the mortality cohort, the SMR for bronchogenic carcinoma in the 1 to 5 fiber-years/mL group was 143.9. An increasing trend with residence time in that group just missed statistical significance at p less than 0.1.
  • In a case-referent analysis of 35 autopsy-proven bronchial cancer cases and 364 referents, the presence of asbestosis was the most significant predictor of bronchial cancer. Standardized proportional mortality rates (SPMRs) for autopsy-proven bronchial cancer were 88.7 with no asbestosis, 416.7 with slight asbestosis, and 562.5 with moderate or pronounced asbestosis.
  • There were 30 mesotheliomas among the 1,225 deaths in the mortality cohort: 20 in crocidolite miners (423 deaths), 4 in amosite miners (648 deaths), and 6 in men with mixed exposures, most of whom had also been exposed to crocidolite. No cases occurred with less than 3 months of exposure. The author concluded that crocidolite is far more dangerous than amosite.
• The authors' conclusion: The author concluded that low industrial exposures with long residence times are associated with a considerable burden of disease. The author also noted that these exposures are still two or three orders of magnitude higher than measured environmental exposures in nonindustrial settings.
• Limitations the authors state:
  • Fiber concentration data are the least reliable data in asbestos studies, and this includes the author's own low-level measurements.
  • Very few men in the lowest cumulative exposure categories had residence times over 30 years.
  • The small number of bronchogenic carcinoma cases created a statistical problem.
  • The findings concern only amphiboles and cannot necessarily be extrapolated to chrysotile.
  • Epidemiology cannot confidently say whether there is a zero-risk exposure level at such low exposures.

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Amosite, Cumulative Exposure, Fiber Year, Lung Cancer, Mesothelioma, Environmental Exposure.

Related studies

• Risk of asbestosis in crocidolite and amosite mines in South Africa — L.M. Irwig, R.S. du Toit, et al. (1979)
• Exploratory sampling of asbestos in residences near Thetford Mines: the public health threat in Quebec — M. Marier, W. Charney, et al. (2007)
• Asbestosis in South African asbestos miners — G.K. Sluis-Cremer (1970)
• Thickening of pulmonary interlobar fissures: exposure-response relationship in crocidolite and amosite miners — A. Solomon, L.M. Irwig, et al. (1979)
• Development of pleural hyalinosis in long term studies of persons exposed to asbestos dust — M. Navrátil, J. Dobiás (1973)
• Long-term mortality experience of chrysotile miners and millers in Thetford Mines, Quebec — W.J. Nicholson, I.J. Selikoff, et al. (1979)

Browse more research in Annals of the New York Academy of Sciences, or return to medical research.