Job Exposure Matrix for Chrysotile Asbestos Fibre in the Asbestos Cement Manufacturing (ACM) Industry in Zimbabwe

Our plain-English summary of Job Exposure Matrix for Chrysotile Asbestos Fibre in the Asbestos Cement Manufacturing (ACM) Industry 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;19(5)
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Occupational chrysotile asbestos exposure data in Zimbabwe is limited. The aim of this study was therefore to develop a job exposure matrix (JEM) specific to the chrysotile asbestos cement manufacturing industry using the available personal exposure concentration data. Quantitative personal exposure chrysotile fibre concentration data collected by the two factories from 1996 to 2020 were used to construct the JEM. Exposure groups from which data was extracted were classified based on the Zimbabwe Standard Classification of Occupations (ZSCO), 2009-2019. Analysis of amphiboles in raw chrysotile was done by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Descriptive statistics, namely mean, standard deviation and range were computed for the main variable, job/occupation. All jobs/occupations in both factories had annual mean personal exposure concentrations exceeding the OEL of 0.1 f/mL, except for the period from 2009 to 2016 in the Harare factory and the period from 2009 to 2020 in the Bulawayo factory. Despite the Harare factory having no AC manufacturing activity since 2017, personal exposure concentrations showed elevated levels for the period 2018-2020. Amphiboles were detected in almost all bulk samples of chrysotile asbestos analysed. The established JEM, which has been generated from actual local quantitative exposure measurements, can be used in evaluating historical exposure to chrysotile asbestos fibre, to better understand and predict occurrence of ARDs in future.

In plain English

The authors built a job exposure matrix, a table of typical exposure levels by job, factory and time period, for chrysotile asbestos in Zimbabwe's asbestos cement industry. They used 3066 personal air measurements from paper records of two factories, in Harare and Bulawayo, covering 1996 to 2020. Several jobs, including saw cutting, fettling and ground hard waste operators, had mean levels above the 0.1 fibres per mL exposure limit in 1996 to 2008 in both factories. At Bulawayo, levels in all key operational areas examined were below the limit in the latest period. At Harare, after asbestos cement manufacturing had stopped, 2018 to 2020 levels were above the limit except for saw cutting, which equalled it. The authors suggested fibres stirred up from uncleaned floors might explain this. Amphiboles were found in 4 of 6 local and 5 of 6 imported raw chrysotile samples, including crocidolite in two imported samples. The authors concluded the matrix gives quantitative exposure estimates by job and factory. They noted that the microscope method used could not tell chrysotile from amphibole fibres.

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: Development of a job exposure matrix from historical company personal air-monitoring records, with bulk sample analysis of raw chrysotile for amphiboles by scanning electron microscopy and energy dispersive spectroscopy
• Who was studied: Workers in job categories at two asbestos cement manufacturing factories in Harare and Bulawayo, Zimbabwe. The data were 3066 personal airborne chrysotile measurements covering about 25 years (1996 to 2020). The authors also analysed 12 bulk raw chrysotile samples (6 local, 6 imported) from the Bulawayo factory.
• Exposure: Airborne chrysotile asbestos fibre in jobs such as saw cutting, fettling, moulded goods, kollergang, ground hard waste, laundry, pipe joints, full-length pipe and multi-cutter operators. Fibres were counted by phase contrast microscopy. The authors also tested for amphiboles (tremolite, anthophyllite, crocidolite, actinolite) in raw chrysotile.
• Main results:
  • In 1996 to 2008, mean exposures were above the 0.1 f/mL limit for saw cutting, fettling and ground hard waste operators (both factories), laundry room and moulded goods operators (Harare), and pipe section operators (Bulawayo).
  • At the Harare factory after manufacturing stopped (2018 to 2020), exposures stayed above the 0.1 f/mL limit except for saw cutting operators, whose level equalled the limit. Levels were statistically significantly higher than in 2009 to 2016 (p less than 0.001).
  • At the Harare factory, concentrations ranged from 0.05 to 0.07 f/mL in 2009 to 2016, compared with 0.10 to 0.12 f/mL in 2018 to 2020.
  • At the Bulawayo factory, all key operational areas examined were below the limit in the latest measurement period. Some jobs in the matrix had no measurements for that period.
  • Exposure differed statistically significantly between time periods for job categories in both factories. The exception was the Harare fettling table operator (p = 0.561).
  • Amphiboles (tremolite and anthophyllite) were detected in 4 of 6 locally produced chrysotile samples.
  • Amphiboles (tremolite, crocidolite and actinolite) were detected in 5 of 6 imported chrysotile samples. Crocidolite appeared in two of the imported samples.
  • The authors suggested that fibre stirred up from floors that were never cleaned could be responsible for the elevated Harare levels in 2018 to 2020.
• The authors' conclusion: The authors concluded that the job exposure matrix provides quantitative estimates of personal chrysotile exposure based on job and factory location. They added that it may support future prediction of asbestos-related diseases and exposure-response analyses.
• Limitations the authors state:
  • There were fewer measurements for 2016 to 2020, which reduced the accuracy of mean exposure for that period.
  • Phase contrast microscopy cannot tell chrysotile fibres from amphibole fibres. Counted fibres were assumed to be chrysotile.
  • The factories did not take part in interlaboratory quality control programmes for fibre counting, especially in 2013 to 2020.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Asbestos-Cement, Asbestos Exposure, Amphibole Group, Scanning Electron Microscopy (SEM), energy dispersive X-ray spectroscopy (EDS).

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)
• Prediction of Asbestos-Related Diseases (ARDs) and Chrysotile Asbestos Exposure Concentrations in Asbestos-Cement (AC) Manufacturing Factories 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)
• Evaluation of exposure to the airborne asbestos in an asbestos cement sheet manufacturing industry in Iran — D. Panahi, H. Kakooei, et al. (2011)
• Asbestos lung burden and asbestosis after occupational and environmental exposure in an asbestos cement manufacturing area: a necropsy study — C. Magnani, F. Mollo, et al. (1998)

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