Respiratory health in chrysotile asbestos miners in British Columbia: a longitudinal study

Our plain-English summary of Respiratory health in chrysotile asbestos miners in British Columbia: a longitudinal study, by D.A. Enarson, V. Embree, L. MacLean, et al (British Journal of Industrial Medicine, 1988).

The study

• Authors: D.A. Enarson, V. Embree, L. MacLean, S. Grzybowski
• Journal: British Journal of Industrial Medicine
• Published: 1988;45(7):459-63
• Cited by: 8 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. 000214).

Abstract

A respiratory survey was undertaken in chrysotile asbestos miners in British Columbia consisting of a questionnaire, spirometry, chest radiography, and physical examination. The tests were performed in 1977 and again in 1983. The population groups studied included 63 "exposed" (working in the plant more than nine years), 52 "controls" (working in the plant less than five years), and 38 residents of the village at the minesite. A subset of 39 was identified with high exposure (worked in the mill more than five years). Measured levels of environmental particulates were similar over the entire period of operation of the plant (1.4 to 14.0 million particles per cubic foot and 0.7-88.0 fibres/cc in the mill; 0.2 to 2.7 mpcf and 0.6 to 9.3 f/cc in the mine). The exposed groups were more likely to report cough and breathlessness than the two other groups and were also more likely to have abnormal FVC and chest x ray films (the latter not significant, p greater than 0.05) and to be more likely to have a combination of these abnormalities. There was no trend to progression in the combination of abnormalities associated with exposure on follow up. The heavily exposed group showed a significantly worse trend in FVC. This adverse trend was confined to those with initial abnormalities. Tobacco smoking did not increase the trend to progression in this group.

In plain English

This longitudinal study examined chrysotile mine workers in northern British Columbia. The authors report that the mineral contained no amphibole. In 1977, 153 people had questionnaires, breathing tests, chest x rays and examinations. They were 63 "exposed" workers (nine or more years at the mine), 52 "controls" (under five years) and 38 village residents. At the 1983 follow-up, 77% of controls, 45% of residents and 46% of exposed workers were no longer in the area. In 1977, both exposed groups reported breathlessness significantly more often than controls. Compared with controls, and adjusting for age, height and smoking, mill workers were significantly more likely to have low forced vital capacity (FVC, a breathing measure), odds ratio 5.3. Between surveys, mill workers' FVC changed by minus 62 ± 41 ml yearly, versus plus 23 ± 14 ml in other groups. The authors reported this adverse trend was confined to people with asbestos-related abnormalities in 1977. Smoking habit made no significant difference to the FVC trend. Progression and regression rates of abnormalities did not differ significantly in any group. The authors said high worker turnover hampered the study.

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: Longitudinal respiratory health survey: examination in 1977 with re-examination of the same population in 1983
• Who was studied: 153 people examined in 1977 at a chrysotile mine and its village in northern British Columbia: 52 controls (under five years at the mine), 38 long-term village residents, and 63 exposed workers (nine or more years at the mine). The text puts 39 of the exposed workers in the mill subgroup and 24 in the 'other' subgroup, mostly the open pit.
• Exposure: Chrysotile asbestos described as pure, with no amphibole content. After 1975, company air measurements ranged from 0.7 to 88.0 fibres/cc in the mill and 0.6 to 9.3 fibres/cc at the mine (eight hour time weighted average), with no trend over time. Earlier measurements were 1.4 to 14.0 million particles per cubic foot in the mill and 0.2 to 2.7 at the minesite.
• Main results:
  • In 1977, compared with controls, cough was significantly more common in the exposed (other) group, and breathlessness was significantly more common in both exposed groups (adjusted for age and smoking).
  • Compared with controls, the exposed (mill) group was significantly more likely to have a low FEV1 (odds ratio 5.7) and a low FVC (odds ratio 5.3). For the exposed (other) group the odds ratios were 1.2 and 2.0, and for town residents 3.6 and 3.0; neither of these was significant. All were corrected for age, height and smoking.
  • In the exposed groups in 1977, the highest x ray profusion value was 1/1. Six films (11%) had parenchymal abnormalities considered definitely present, and one (2%) showed pleural abnormality.
  • In 1977, the exposed groups were significantly more likely than controls and residents to have two or more asbestos-associated abnormalities (breathlessness, crackles, abnormal x ray, abnormal FVC).
  • By the 1983 follow-up, 77% of controls, 45% of residents and 46% of the exposed groups were no longer in the area. People with abnormalities were more likely to have left, but the difference was not statistically significant.
  • From 1977 to 1983, the FVC trend in the exposed (mill) group (minus 62 ± 41 ml per year) differed significantly from all other groups (plus 23 ± 14 ml per year).
  • The authors stated that the adverse FVC trend in the heavily exposed group was confined to those with abnormalities at the first examination.
  • The FVC trend varied significantly with the number of asbestos-related abnormalities at the first examination. The mean annual trend was 68 ± 80 with none, minus 22 ± 102 with one, and minus 148 ± 102 with two or more (no units printed with these figures).
  • Smoking habit did not significantly change the FVC trend.
  • The two exposed groups were significantly more likely than residents or controls to show new x ray changes by 1983.
  • Abnormalities progressed in 30% and regressed in 26% of the exposed groups. In controls and residents, 7% progressed and 24% regressed. The differences between progression and regression were not statistically significant in any group.
• The authors' conclusion: The authors concluded that the exposed groups had more cough and breathlessness and that reduced FVC was restricted to mill workers. They found progression of asbestos-related abnormalities confined to people who already had signs at the first examination, and suggested these people may have had the greatest exposure or the greatest susceptibility.
• Limitations the authors state:
  • High mobility and turnover of workers at the site hampered the study.
  • By follow-up the control group could no longer be considered unexposed and had to be treated as an intermediate group.
  • The authors could not tell whether progression among those with initial abnormalities reflected greater exposure or individual susceptibility.
  • No measurements exist of the asbestos dust residents reported around the town in its first two decades.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Spirometry, Million Particles per Cubic Foot (mppcf).

Related studies

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• Exposure to asbestos-containing vermiculite ore and respiratory symptoms among individuals who were children while the mine was active in Libby, Montana — L.C. Vinikoor, T.C. Larson, et al. (2010)
• Chrysotile asbestos and health in Zimbabwe: I. Analysis of miners and millers compensated for asbestos-related diseases since independence (1980) — M.R. Cullen, R.S. Baloyi (1991)
• Chrysotile asbestos and health in Zimbabwe: II. Health status survey of active miners and millers — M.R. Cullen, L. Lopez-Carrillo, et al. (1991)

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