Chrysotile asbestos and health in Zimbabwe: II. Health status survey of active miners and millers

Our plain-English summary of Chrysotile asbestos and health in Zimbabwe: II. Health status survey of active miners and millers, by M.R. Cullen, L. Lopez-Carrillo, B. Alli, et al (American Journal of Industrial Medicine, 1991).

The study

• Authors: M.R. Cullen, L. Lopez-Carrillo, B. Alli, P.E. Pace, S.L. Shalat, R.S. Baloyi
• Journal: American Journal of Industrial Medicine
• Published: 1991;19(2):171-82
• Cited by: 8 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. 003784).

Abstract

As part of the effort to establish industrial practice and public policy regarding asbestos in Zimbabwe, we have conducted a cross-sectional study of the chrysotile mines and mills. A stratified random sample of workers with greater than 10 years of exposure has been evaluated by spirometry, chest radiographs, and employment history. The latter was converted to quantitative estimates of exposure dose, using a matrix based on measured and reconstructed fiber levels for each job and facility during the years of work. Based on these data, a clear dose-response between asbestos exposure and functional loss has been demonstrated, with mean losses from predicted of about 400-600 cc in vital capacity in the 10% of the population with heaviest exposures. Low-grade parenchymal radiographic abnormalities (ILO grade greater than or equal to 1/0) were evident in 8.7% of the total study group and were almost 10 times more common in those with more than 100 fibers/cc.years cumulative exposure than in those with 16 fibers/cc.years or less. Pleural disease was relatively rare, occurring in just under 10% of the study group, and was unrelated to exposure dose. Overall, these findings are compatible with results of similar studies in Quebec and Swaziland and suggest that similar control strategies are probably indicated.

In plain English

This cross-sectional study examined active workers at Zimbabwe's two chrysotile asbestos mine and mill sites, Shabanie and Gaths. Of a stratified random sample of 297 workers with at least 10 years of service, 272 black men took part. The authors tested lung function, reviewed chest X-rays, and estimated each man's cumulative exposure from work histories and job-based fiber levels. Higher cumulative dose was significantly associated with lower lung function. Mean vital capacity losses were about 400-600 cc below predicted in the most heavily exposed 10%. Smoking and mine site had no measurable effect. Of 264 men with X-rays, 19 had grade 1/0 and four had grade 1/1 lung-tissue changes. Men with over 100 fibers/cc-years had a 9.9-fold (CI 2.6-38.5) greater chance of grade 1/0 or higher than men with under 16. Pleural disease, seen in 27 men, was not related to dose. The authors concluded that the scarring effects of Zimbabwean chrysotile were comparable to those in miners elsewhere. They noted limitations including largely estimated exposures, a relatively primitive spirometer, one X-ray reader, and possibly under-represented diseased workers.

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: Cross-sectional study of a stratified random sample of active workers
• Who was studied: 272 of 297 invited active workers with at least 10 years of service at two chrysotile mine and mill sites in Zimbabwe (169 at Shabanie, 103 at Gaths). All were black men, aged 27 to 66, median age 46. The study dates are not stated.
• Exposure: Chrysotile asbestos in mining and milling. Cumulative exposure was reconstructed for each man from work histories and a matrix of fiber levels by job and facility: averages of measured values from 1980 on, and committee estimates for earlier years going back to 1945. The earlier estimates were 0.4 to 2.0 fibers/cc in the mines and 5 to 50 fibers/cc in the mills. Estimated cumulative exposure ranged from 1.1 to 654 fibers/cc-years, with a median of 8.5.
• Main results:
  • Among 111 men with at least 8 fibers/cc-years exposure and usable spirometry, only the logarithm of cumulative dose had a significant effect on the difference from predicted FVC and FEV1. Smoking status and mine had no measurable effect.
  • Mean losses from predicted vital capacity were about 400-600 cc in the 10% of the study population with the heaviest exposures.
  • Of the 264 men with available X-rays, 65 (24.6%) had parenchymal (lung-tissue) changes of grade 0/1, 19 (7.2%) grade 1/0 and four (1.5%) grade 1/1. No higher grade was seen.
  • The relationship held independent of age or latency. Men with more than 100 fibers/cc-years had a 9.9-fold (CI 2.6-38.5) increased chance of an X-ray grade 1/0 or higher, compared with men with less than 16 fibers/cc-years. Men with 16 to 100 had a 2.7-fold (CI 0.7-10.7) increased chance compared with the low-dose group.
  • Pleural disease was present in 27 men: bilateral in 17 and unilateral in ten.
  • Pleural disease showed no significant relationship to dose. It was significantly related to age and latency after adjusting for dose.
• The authors' conclusion: The authors concluded that the fibrogenic (scarring) properties of chrysotile asbestos in Zimbabwean miners and millers were comparable to those among miners elsewhere in the world. They judged that controls bringing air levels below 2 fibers/cc were justifiable and that strict preventive measures were warranted while cancer risk is studied.
• Limitations the authors state:
  • Exposure was reconstructed largely from estimates by senior personnel, because systematic measurements began only in 1980 and almost all exposure occurred before then.
  • Spirometry used a relatively primitive instrument and only one or two tracings. 27 of the 138 more heavily exposed men had to be excluded because they could not produce an acceptable tracing.
  • The X-rays were read by a single reader, with potential for reader bias.
  • The internal control group used to set predicted lung function values was small, and most of its members had some mineral dust exposure.
  • The study was cross-sectional with a limited sample size.
  • Diseased workers may have been underrepresented: no high-grade X-ray changes were seen, possibly because of company surveillance or the national Pneumoconiosis Bureau.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Shabani mine, Zimbabwe

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Spirometry, Chest X-Ray, Dose-response relationship, Asbestos Exposure, Cumulative Exposure.

Related studies

• 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)
• Present status of asbestos mining and related health problems in India--a survey — A.L. Ramanathan, V. Subramanian (2001)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: mortality 1976-88 — J.C. McDonald, F.D. Liddell, et al. (1993)
• Exposure to chrysotile mining dust and digestive cancer mortality in a Chinese miner/miller cohort — S. Lin, X. Wang, et al. (2014)
• Radiographic changes in a group of chrysotile miners and millers exposed to low asbestos dust concentrations — S. Cordier, G. Theriault, et al. (1984)
• Development of radiographic abnormality in chrysotile miners and millers — G.M. Eyssen (1980)

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