Non-malignant consequences of decreasing asbestos exposure in the Brazil chrysotile mines and mills

Our plain-English summary of Non-malignant consequences of decreasing asbestos exposure in the Brazil chrysotile mines and mills, by E. Bagatin, J.A. Neder, L.E. Nery, et al (Occupational and Environmental Medicine, 2005).

The study

• Authors: E. Bagatin, J.A. Neder, L.E. Nery, M. Terra-Filho, J. Kavakama, A. Castelo, V. Capelozzi, A. Sette, S. Kitamura, M. Favero, D.C. Moreira-Filho, R. Tavares, C. Peres, M.R. Becklake
• Journal: Occupational and Environmental Medicine
• Published: 2005;62(6):381-9
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Aims: To investigate the consequences of improvement in the workplace environment over six decades (1940-96) in asbestos miners and millers from a developing country (Brazil).

Methods: A total of 3634 Brazilian workers with at least one year of exposure completed a respiratory symptoms questionnaire, chest radiography, and a spirometric evaluation. The study population was separated into three groups whose working conditions improved over time: group I (1940-66, n = 180), group II (1967-76, n = 1317), and group III (1977-96, n = 2137).

Results: Respiratory symptoms were significantly related to spirometric abnormalities, smoking, and latency time. Breathlessness, in particular, was also associated with age, pleural abnormality and increased cumulative exposure to asbestos fibres. The odds ratios (OR) for parenchymal and/or non-malignant pleural disease were significantly lower in groups II and III compared to group I subjects (0.29 (0.12-0.69) and 0.19 (0.08-0.45), respectively), independent of age and smoking status. Similar results were found when groups were compared at equivalent latency times (groups I v II: 30-45 years; groups II v III: 20-25 years). Ageing, dyspnoea, past and current smoking, and radiographic abnormalities were associated with ventilatory impairment. Lower spirometric values were found in groups I and II compared to group III: lung function values were also lower in higher quartiles of latency and of cumulative exposure in these subjects.

Conclusions: Progressive improvement in occupational hygiene in a developing country is likely to reduce the risk of non-malignant consequences of dust inhalation in asbestos miners and millers.

In plain English

This retrospective study examined 3634 workers and ex-workers of Brazil's single chrysotile mining and milling company, 1940 to 1996. They were split into three groups. Group I (1940-66) worked at a Bahia mine with tremolite alongside chrysotile and no exposure control. Group II (1967-76) worked at the Canabrava mine in Goiás. Group III (1977-96) had routine fibre measurements and exposure control. Chest x-ray pleural and/or parenchymal abnormalities appeared in 22.2% of group I, 6.0% of group II and 2.5% of group III. Compared with group I, odds ratios were 0.29 (95% confidence interval 0.12 to 0.69) for group II and 0.19 (0.08 to 0.45) for group III, independent of age and smoking. Lung function was lower in groups I and II than group III. Breathlessness was associated with smoking, pleural abnormality and higher cumulative exposure, among other factors. The authors concluded that improved workplace conditions were associated with less non-malignant disease. They noted that early exposures were estimated subjectively, many group I workers could not be examined, and results should not be extrapolated to malignant disease.

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: Retrospective study of a single company's workforce, using questionnaires, chest x-rays and spirometry, comparing three historical exposure groups
• Who was studied: Workers and ex-workers with at least one year of employment at the single Brazilian asbestos mining and milling company (Sociedade Mineradora de Amianto SA), 1940 to 1996. Of 6098 eligible, 433 were dead and 3634 of the remaining 5665 (64.1%) were examined: group I (1940-66) n = 180, group II (1967-76) n = 1317, group III (1977-96) n = 2137.
• Exposure: Chrysotile asbestos mining and milling. Group I worked at the São Félix mine in Bahia (the methods give 1940 to 1967 for this mine), where tremolite was found with chrysotile and there was no exposure measurement or control. Group II worked at the Canabrava mine in Goiás (1967 to 1976), where no amphiboles were found. Group III (1977 to 1996) had routine fibre measurements and controlled chrysotile exposure. Exposure for groups I and II was estimated with a subjective colour-coded scale. Median cumulative exposure was 51.2, 20.2 and 2.4 fibre/y/cc for groups I to III.
• Main results:
  • Prevalence of pleural and/or parenchymal x-ray abnormalities was 22.2% in group I, 6.0% in group II and 2.5% in group III. Parenchymal abnormalities were 9.5%, 2.7% and 0.8%. Pleural abnormalities were 16.1%, 4.0% and 1.7%.
  • Compared with group I, odds ratios (95% CI) for parenchymal and/or non-malignant pleural disease were 0.29 (0.12 to 0.69) in group II and 0.19 (0.08 to 0.45) in group III, independent of age and smoking status.
  • Compared with group I, odds ratios (95% CI) for pleural abnormalities alone were 0.49 (0.28 to 0.86) in group II and 0.33 (0.16 to 0.67) in group III.
  • Workers with similar latency were also compared. At 30 to 45 years latency, abnormalities were more common in group I than group II (18.7% vs 9.2% pleural and/or parenchymal). At 20 to 25 years latency, they were more common in group II than group III (5.6% vs 3.1%).
  • Across all workers, breathlessness was independently associated with restrictive defect (OR 2.57), obstructive defect (OR 1.80), current or past smoking (OR 1.67), pleural abnormality (OR 1.50, 1.01 to 2.21), cumulative exposure of 10 fibres/y/cc or more (OR 1.47, 1.23 to 1.75) and age over 50 (OR 1.43).
  • Spirometric abnormalities were found in 776 subjects (24.7%), mostly mild obstructive impairment.
  • Mean spirometric values were close to normal in all groups. FVC was lower in group I, especially compared with group III. Within groups I and II, workers in the higher quartiles of cumulative exposure and latency had lower spirometric scores.
  • Combined parenchymal and pleural abnormalities were associated with an obstructive defect (OR 2.20, 1.55 to 3.11).
• The authors' conclusion: The authors concluded that improvements over time in workplace conditions were associated with a significant decrease in the risk of non-malignant abnormalities in Brazilian chrysotile asbestos miners and millers. They said this should be confirmed in prospective and controlled studies.
• Limitations the authors state:
  • Age and latency time, both confounding factors, differed among the three groups.
  • No non-exposed reference population was studied.
  • 35.9% of the target population could not be evaluated, particularly in group I. Healthy worker and survival effects may therefore have caused selection bias and led to underestimated abnormalities in older workers.
  • Exposure in the older groups was estimated by a subjective method and may have been overestimated.
  • More sensitive techniques (high resolution CT, lung diffusion capacity) were not used, so abnormalities may have been underestimated.
  • Pleural plaques were not distinguished from diffuse pleural thickening.
  • Asbestos-related mortality could not be assessed.
  • The results should not be extrapolated to asbestos-related malignant disease.

Mines named here

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

• Cana Brava mine, Uruaçu, Goiás

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Chrysotile, Latency, Cumulative Exposure, Odds Ratio.

Related studies

• Lung function profiles in the chrysotile asbestos mines and mills of Quebec — M.R. Becklake, G. Fournier-Massey, et al. (1976)
• The health of chrysotile asbestos mine and mill workers of Quebec — J.C. McDonald, M.R. Becklake, et al. (1974)
• Screening of miners and millers at decreasing levels of asbestos exposure: comparison of chest radiography and thin-section computed tomography — M. Terra-Filho, E. Bagatin, et al. (2015)
• Late progression of radiographic changes in Canari chrysotile mine and mill exworkers — J.R. Viallat, C. Boutin, et al. (1983)
• Mortality in the chrysotile asbestos mines and mills of Quebec — J.C. McDonald, A.D. McDonald, et al. (1971)
• Rheumatic complaints and pulmonary response to chrysotile dust inhalation in the mines and mills of Quebec — F.M. White, J. Swift, et al. (1974)

Browse more research in Occupational and Environmental Medicine, or return to medical research.