Prediction of Asbestos-Related Diseases (ARDs) and Chrysotile Asbestos Exposure Concentrations in Asbestos-Cement (AC) Manufacturing Factories in Zimbabwe

Our plain-English summary of Prediction of Asbestos-Related Diseases (ARDs) and Chrysotile Asbestos Exposure Concentrations in Asbestos-Cement (AC) Manufacturing Factories in Zimbabwe, by B. Mutetwa, D. Moyo, D. Brouwer (International Journal of Environmental Research and Public Health, 2022).

The study

• Authors: B. Mutetwa, D. Moyo, D. Brouwer
• Journal: International Journal of Environmental Research and Public Health
• Published: 2022;20(1)
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The use of historical asbestos measurement data in occupational exposure assessment is essential as it allows more quantitative analysis of possible exposure response relationships in asbestos-related disease (ARD) occurrence. The aim of this study was to predict possible ARDs, namely lung cancer, mesothelioma, gastrointestinal cancer, and asbestosis, in two chrysotile asbestos cement (AC) manufacturing factories. Prediction of ARDs was done using a specific designed job-exposure matrix for airborne chrysotile asbestos fibre concentrations obtained from the Harare and Bulawayo AC factories and through application of OSHA's linear dose effect model in which ARDs were estimated through extrapolation at 1, 10, 20, and 25 years of exposure. The results show that more cancer and asbestosis cases are likely to be experienced among those exposed before 2008 as exposure levels and subsequently cumulative exposure were generally much higher than those experienced after 2008. After a possible exposure period of 25 years, overall cancer cases predicted in the Harare factory were 325 cases per 100,000 workers, while for the Bulawayo factory, 347 cancer cases per 100,000 workers exposed may be experienced. Possible high numbers of ARDs are likely to be associated with specific tasks/job titles, e.g., saw cutting, kollergang, fettling table, ground hard waste, and possibly pipe-making operations, as cumulative exposures, though lower than reported in other studies, may present higher risk of health impairment. The study gives insights into possible ARDs, namely lung cancer, mesothelioma, gastrointestinal cancer, and asbestosis, that may be anticipated at various cumulative exposures over 1, 10, 20, and 25 years of exposure in AC manufacturing factories in Zimbabwe. Additionally, results from the study can also form a basis for more in-depth assessment of asbestos cancer morbidity studies in the AC manufacturing industries.

In plain English

This modelling study estimated, without counting actual cases, how many asbestos-related diseases to expect among workers at two chrysotile asbestos-cement factories in Harare and Bulawayo, Zimbabwe. The authors used 3066 personal air measurements of chrysotile fibres from company records, 1996 to 2020, summarised by job and time period. They applied a linear dose-response model from the US Occupational Safety and Health Administration (OSHA) to predict lung cancer, mesothelioma and gastrointestinal cancer deaths after 1, 10, 20 and 25 years of exposure, and asbestosis after 25 years. After 25 years at the factory-wide average exposure, predicted total cancer deaths were 324 per 100,000 workers in Harare (325 in the abstract) and 347 per 100,000 in Bulawayo. Predicted asbestosis after 25 years was 150 and 170 per 100,000, respectively. Predictions were highest for saw cutting and for exposure before 2008, when fibre levels were higher. The authors noted that the OSHA model was built partly on studies involving amphibole asbestos, so predictions may not reflect true cases. The authors concluded that mortality and morbidity studies are needed to establish the actual disease burden.

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: Risk-prediction (modelling) study: historical workplace air measurements were combined with OSHA's linear dose-response risk assessment model to estimate expected disease cases. No actual cases were counted.
• Who was studied: Workers at two asbestos-cement manufacturing factories in Harare and Bulawayo, Zimbabwe, between 1996 and 2020. The factories estimated about 390 to 420 workers in total (Harare 156 to 220; Bulawayo 190 to 204). Predictions are per 100,000 hypothetical exposed workers.
• Exposure: Airborne chrysotile asbestos in the manufacture of asbestos-cement sheets, facia boards, garden ware and (in Bulawayo) pipes. The products contained 10 to 20% asbestos. Exposure came from 3066 company personal air measurements counted by phase contrast microscopy, summarised as mean concentrations (about 0.04 to 0.19 f/mL) by job and time period, and turned into cumulative exposure in f/mL-years.
• Main results:
  • After a possible 25 years of exposure at the overall factory average, predicted total cancer deaths (lung cancer, mesothelioma and gastrointestinal cancer combined) were 324 per 100,000 workers in the Harare factory according to Table 3, or 325 per 100,000 according to the abstract. The Bulawayo factory figure was 347 per 100,000 in both places.
  • More cancer cases were predicted for workers exposed before 2008, because exposure levels and cumulative exposure were generally much higher then than after 2008.
  • Over 25 years, cumulative exposures ranged from 1.0 to 4.8 f/mL-years. The highest were for saw cutting operations in both factories, followed by ground hard waste operations, particularly before 2008.
  • Predicted asbestosis cases after 25 years of exposure ranged from 50 to 260 per 100,000 exposed workers, depending on job.
  • On average across both factories, predicted asbestosis after 25 years was 150 to 170 cases per 100,000 exposed workers: 150 in Harare (cumulative exposure 2.8 f/mL-years) and 170 in Bulawayo (3.0 f/mL-years).
  • After 1 year of exposure, predicted incidence of lung cancer, mesothelioma and gastrointestinal cancer was very low, from 0.0003 to 0.01% in almost all jobs.
  • Over 25 years, overall predicted cancer deaths ranged from 2.89 to 3.47 per 1000 workers across Harare operational areas and from 2.89 to 4.63 per 1000 in Bulawayo. The authors said this may present significant risk against OSHA's criterion of more than 1 per 1000, but not necessarily against the 4 per 1000 level used in the Netherlands and Germany.
• The authors' conclusion: The authors concluded that saw cutting operators, followed by kollergang and ground hard waste operators, in both factories may be at increased risk of asbestos-related diseases, especially if exposed before 2008. They said mortality and/or morbidity studies are needed to establish the actual disease burden from chrysotile in these factories.
• Limitations the authors state:
  • The OSHA model assumes excess risk is linear in dose, but excess cancer cases may not be linear, especially at high exposure levels.
  • The OSHA model was based on studies that included a significant amount of amphibole asbestos, generally considered more potent than chrysotile. The predicted numbers may therefore not reflect true cases in these mainly chrysotile factories.
  • There is uncertainty from extrapolating risk from high occupational exposures to much lower levels, from mass-to-fibre conversion factors, and from variability in the exposure estimates built into the model.
  • Dose-response data for gastrointestinal cancer are more limited than for lung cancer and mesothelioma.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Asbestos Exposure, Asbestos-Cement, Occupational Exposure, Lung Cancer, Mesothelioma, OSHA, Cumulative Exposure.

Related studies

• Trends in Airborne Chrysotile Asbestos Fibre Concentrations in Asbestos Cement Manufacturing Factories in Zimbabwe from 1996 to 2016 — B. Mutetwa, D. Moyo, et al. (2021)
• Job Exposure Matrix for Chrysotile Asbestos Fibre in the Asbestos Cement Manufacturing (ACM) Industry in Zimbabwe — B. Mutetwa, D. Moyo, et al. (2022)
• 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)
• Asbestos mining and occupational disease in Southern Rhodesia/Zimbabwe, 1915-98 — J. McCulloch (2003)
• An unjustified prognosis of the number of asbestos-related lung cancer cases caused by an increase in airborne asbestos concentrations as a result of removing of asbestos-cement products — N. Szeszenia-Dąbrowska, B. Świątkowska (2015)

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