Respiratory cancer in chrysotile textile and mining industries: exposure inferences from lung analysis

Our plain-English summary of Respiratory cancer in chrysotile textile and mining industries: exposure inferences from lung analysis, by P. Sebastien, J.C. McDonald, A.D. McDonald, et al (British Journal of Industrial Medicine, 1989).

The study

• Authors: P. Sebastien, J.C. McDonald, A.D. McDonald, B. Case, R. Harley
• Journal: British Journal of Industrial Medicine
• Published: 1989;46(3):180-7
• Cited by: 92 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. 000155).

Abstract

In an attempt to explain the much greater risk of respiratory cancer at the same cumulative exposure in asbestos textile workers in Charleston, South Carolina, than in Quebec miners and millers, both exposed to chrysotile from the same source, 161 lung tissue samples taken at necropsy from dead cohort members were analysed by transmission electron microscopy. Altogether 1828 chrysotile and 3270 tremolite fibres were identified; in both cohorts tremolite predominated and fibre dimensions were closely similar. Lung fibre concentrations were analysed statistically (a) in 32 paired subjects matched for duration of employment and time from last employment to death and (b) in 136 subjects stratified by the same time variables. Both analyses indicated that the Quebec/Charleston ratios for chrysotile fibre concentration in lung tissue were even higher than the corresponding ratios of estimated exposure intensity (mpcf). After allowance for the fact that regression analyses suggested that the proportion of tremolite in dust was probably 2.5 times higher in Thetford Mines, Quebec, than in Charleston, the results from both matched pair and stratification analyses of tremolite fibre concentrations in lung were almost the same as for chrysotile. It is concluded that neither fibre dimensional differences nor errors in estimation of exposure can explain the higher risks of lung cancer observed in asbestos textile workers. The possible co-carcinogenic role of mineral oil used in the past in asbestos textile plants to control dust provides an alternative hypothesis deserving consideration.

In plain English

Earlier studies of these two groups had found a much higher respiratory cancer risk, at the same estimated cumulative dust exposure, among chrysotile textile workers in Charleston, South Carolina, than among Quebec chrysotile miners and millers. The Charleston plant used chrysotile mostly from the Quebec mines. The authors examined lung tissue taken at necropsy from 161 deceased cohort members, 72 from Charleston and 89 from Thetford Mines, Quebec, using electron microscopy to count fibres longer than 5 micrometres. They identified 1828 chrysotile and 3270 tremolite fibres. Tremolite predominated in both groups, and fibre sizes were similar. They compared workers with similar years of employment and time since leaving work. Lung chrysotile concentrations were higher in Thetford by ratios close to the ratio of estimated dust intensity (4.3 versus 4.8 in 32 matched pairs) or above it (9.69 versus 6.70 in grouped cases). The authors concluded that neither fibre size differences nor errors in exposure estimates explained the higher lung cancer risk in textile workers. They suggested that mineral oil sprayed on asbestos at the textile plant might have acted as a co-carcinogen, a hypothesis they saw no way to test.

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: Comparative study of retained fibres in necropsy lung tissue from deceased members of two existing cohorts, analysed by transmission electron microscopy, with stratified and matched-pair statistical comparisons
• Who was studied: 161 deceased cohort members with necropsy lung tissue. All 72 usable specimens came from the Charleston, South Carolina chrysotile textile cohort (2543 men employed one month or more between 1938 and 1958). A sample of 89 came from Thetford Mines cases in the Quebec chrysotile mining and milling cohort (10 939 men born between 1891 and 1920).
• Exposure: Chrysotile in textile manufacture (Charleston) and in mining and milling (Thetford Mines, Quebec). The Charleston plant's chrysotile came mostly from the Quebec mines. Exposure was estimated from impinger dust data in million particles per cubic foot (mpcf). Mean dust intensity was 19 mpcf in the Charleston cases and 195 mpcf in the Thetford cases (medians 14 and 109).
• Main results:
  • A total of 1828 chrysotile fibres and 3270 tremolite fibres were analysed. Tremolite fibres were more numerous than chrysotile overall.
  • Tremolite represented 77% of all asbestos fibres analysed in the Thetford group. Tremolite fibres from Thetford and Charleston had similar elemental composition.
  • Size distributions of chrysotile and of tremolite fibres were almost the same in the two groups. The proportion of very long fibres was somewhat higher in Charleston, based on very small numbers. The authors stated the study does not support the longer-fibre explanation.
  • In the stratification analysis (14 duration and cessation cells with cases from both places), the geometric mean ratios of Thetford to Charleston were 6.70 for dust intensity (mpcf), 9.69 for lung chrysotile concentration and 23.00 for lung tremolite concentration.
  • In 32 pairs matched for duration of employment and time since last employment, the geometric mean Thetford to Charleston ratios were 4.8 for dust intensity (mpcf) and 4.3 for lung chrysotile concentration.
  • In the matched pairs, the geometric mean Thetford to Charleston ratio for lung tremolite was 12.3 in the results text (12.4 in table 7 and the discussion), 2.6 times the mpcf ratio.
  • From regression analyses, the authors estimated that the proportion of tremolite in dust was 2.5 times higher in Thetford than in Charleston. Applying this correction gave an exposure intensity ratio of 12.0 in the matched pairs, close to the 12.4 tremolite ratio. In the stratification analysis, the corrected ratio rose from 6.7 to 16.8, against 23.0 for tremolite.
  • Amosite and crocidolite concentrations above 0.1 fibres per microgram were measured in 32% of specimens from Charleston and 9% from Thetford. In Charleston, these commercial amphiboles were detected only in cases hired before 1940.
• The authors' conclusion: The authors concluded that neither differences in fibre dimensions nor errors in exposure estimation could explain the higher lung cancer risk in the asbestos textile workers. They rejected the hypothesis that Charleston exposures were systematically underestimated. They proposed as an alternative hypothesis a possible co-carcinogenic role of mineral oil, which was sprayed on the asbestos stock at the textile plant during 1925-54. They stated they saw no way at present to test this.
• Limitations the authors state:
  • The analysis assumed that lung retention was proportional to mean exposure intensity among cases with similar duration and cessation. The authors noted this assumption cannot be tested without good environmental data and may be questioned, especially for chrysotile.
  • The authors called the representativeness of the necropsy groups uncertain. Asbestos-related diseases were overrepresented in the Thetford series, although excluding such cases from the matched pair analysis gave similar results.
  • The authors had no direct evidence on the proportion of tremolite in dust at the two places. The 2.5 correction factor was inferred from regression equations.
  • Because of limited resources, only a sample of Quebec specimens (Thetford Mines cases) was analysed. High cumulative exposure values were overrepresented among the Thetford necropsied cases.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestos textiles, Chrysotile, Lung cancer, Tremolite.

Medical terms in this study, explained in our Lexicon: Chrysotile, Cumulative Exposure, Autopsy, Transmission Electron Microscopy (TEM), Tremolite, Thetford Mines, Lung Cancer, Carcinogenic.

Related studies

• Environmental pleural plaques in residents of a Quebec chrysotile mining town — A. Churg, L. DePaoli (1988)
• Exposure-specific lung cancer risks in Chinese chrysotile textile workers and mining workers — X. Wang, S. Lin, et al. (2014)
• Fiber burden and patterns of asbestos-related disease in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1993)
• Mineralogic correlates of fibrosis in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1989)
• Fiber size and number in workers exposed to processed chrysotile asbestos, chrysotile miners, and the general population — A. Churg, B. Wiggs (1986)
• Inferences on the kinetics of asbestos deposition and clearance among chrysotile miners and millers — M.M. Finkelstein, A. Dufresne (1999)

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