Does occupational exposure to brown coal dust cause a decline in lung function?

Our plain-English summary of Does occupational exposure to brown coal dust cause a decline in lung function?, by C. Finocchiaro, A. Lark, M. Keating, et al (Occupational and Environmental Medicine, 1997).

The study

• Authors: C. Finocchiaro, A. Lark, M. Keating, A. Ugoni, M. Abramson
• Journal: Occupational and Environmental Medicine
• Published: 1997;54(9):642-5
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To determine if the rate of change in forced expiratory volume in one second (FEV1) in subjects with high exposure to Latrobe Valley brown coal dust was significantly greater than the rate of change among subjects with low exposure.

Methods: A retrospective dynamic cohort design with variable time windows. This study was conducted over a period of 14 years from 1980 to 1994 and used data collected by the State Electricity Commission (SEC) Lung Function Unit for an asbestos surveillance programme. The subjects were exposed to low, medium, or high levels of coal dust. Basic spirometry with wedge bellows spirometers was used to assess lung function. A general linear model (GLM) was used to assess the effects of smoking and exposure to coal dust upon the change in forced expiratory volume in one second (FEV1) while adjusting for age and height.

Results: The mean (95% confidence interval (95% CI) rate of decline in FEV1 was 40 (36 to 44) ml/year. Age was a significant predictor of change. A significant effect was found for smoking (P = 0.02) and for exposure to coal dust (P = 0.008). The only significant difference with exposure to coal dust was between the high and mixed exposure categories.

Conclusion: There is no convincing evidence of excessive decline in FEV1 with exposure to coal dust > 0.75 mg/m3. The absence of a dose response relation provides some evidence against a causal relation. On the basis of this study, reduction of the exposure standards currently applied to brown coal dust in the Victorian electricity industry is not warranted to prevent respiratory disease.

In plain English

This study asked whether brown coal dust at work in Australia's Victorian electricity industry was linked to faster loss of lung function. It used lung tests collected from 1980 to 1994 by the State Electricity Commission for an asbestos surveillance programme. The authors studied 388 men tested at least twice over at least six years, grouped by low, mixed or high coal dust exposure. Their FEV1 (air blown out in one second) fell on average by 40 ml a year (95% CI 36 to 44). It was 39.9 ml (33.9 to 45.9) in the low, 30.7 ml (22.5 to 38.9) in the mixed and 47.5 ml (40.7 to 54.4) in the high exposure group. The only statistically significant exposure difference was high versus mixed; high versus low was not. Current smokers declined faster than non-smokers. The authors concluded there was no convincing evidence of excessive decline with exposure above 0.75 mg/m3 and that lowering exposure standards was not warranted. They noted possible selection bias: the 388 were about 10% of roughly 4000 employees with at least one lung test.

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 dynamic cohort study with variable time windows, using existing lung function records
• Who was studied: 388 men from the State Electricity Commission of Victoria workforce, mainly in the Latrobe Valley and some at the Newport power station in Melbourne. All had lung function tests on two or more occasions over at least six years, within the 1980 to 1994 study period. Of about 4000 employees with at least one lung function test, 448 met the inclusion criteria. 60 of these were then excluded, leaving 388; the exclusions included asthma or bronchodilator treatment (38) and asbestosis (5, plus 1 with asbestosis and asthma). Average follow-up was eight years.
• Exposure: Brown coal (lignite) dust. Workers were classed as high exposure (working in a power station or mine, other than office or laboratory staff), low exposure (office and laboratory workers, the gas-fired Newport power station, outdoor non-mining work) or mixed exposure. The cut-off between high and low was an estimated mean personal exposure to total dust of 0.75 mg/m3.
• Main results:
  • Across all 388 men, the mean rate of decline in FEV1 was 40 (95% CI 36 to 44) ml/year.
  • Mean decline in FEV1 by coal dust group: low exposure 39.9 ml/y (95% CI 33.9 to 45.9; n=172), mixed exposure 30.7 ml/y (95% CI 22.5 to 38.9; n=98), high exposure 47.5 ml/y (95% CI 40.7 to 54.4; n=118).
  • In the model adjusted for age and height, there was a significant effect for smoking (P=0.02) and for exposure to coal dust (P=0.008).
  • Among the coal dust groups, the only significant difference was high versus mixed: a difference of 16.8 ml/y (95% CI 4.5 to 29.2). High versus low was 7.7 ml/y (95% CI -3.1 to 18.4) and was not significant.
  • The lowest mean decline was in the mixed exposure group rather than the low exposure group, so there was no steadily increasing (dose-response) pattern.
  • Current smokers declined significantly faster than non-smokers: a difference of 12.9 ml/y (95% CI 1.8 to 24.0).
  • Age was a significant predictor of change in FEV1 (P<0.0001).
  • Only 16 of the 388 men had any exposure to welding fumes, and this exposure was not significantly related to decline in lung function.
• The authors' conclusion: The authors concluded that there was no convincing evidence of excessive decline in FEV1 with exposure to coal dust above 0.75 mg/m3. They said the absence of a dose-response relation provided some evidence against a causal relation. They considered that, on the basis of this study, reducing the exposure standards for brown coal dust in the Victorian electricity industry was not warranted, but that exposure should continue to be monitored.
• Limitations the authors state:
  • The main potential bias was selection bias. Subjects were chosen for repeated participation in the asbestos surveillance programme over at least six years: 388 out of about 4000 employees who had at least one lung function test, about 10%.
  • Smoking status was classified only at entry to the study, so the effect of smoking may have been underestimated.
  • Classifying coal dust exposure was harder than expected, and the boundaries between the groups were not distinct.
  • The exposure estimates covered only the follow-up period, not cumulative exposure over a working lifetime.
  • The study had only 18% power to detect the 5 ml/year difference expected from the literature, although its power exceeded 95% for a 20 ml/year difference.
  • The effects of welding fumes may have been underestimated.
  • Asbestos exposure was a potential confounder, though the authors judged it minimal because only six cases of diagnosed asbestosis occurred in over 4000 subjects.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, FEV1, Spirometry, confidence interval.

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