Respiratory effects of exposure to dust in taconite mining and processing

Our plain-English summary of Respiratory effects of exposure to dust in taconite mining and processing, by T.C. Clark, V.A. Harrington, J. Asta, et al (The American Review of Respiratory Disease, 1980).

The study

• Authors: T.C. Clark, V.A. Harrington, J. Asta, W.K. Morgan, E.N. Sargent
• Journal: The American Review of Respiratory Disease
• Published: 1980;121(6):959-66
• Cited by: 20 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. 000794).

Abstract

Taconite is a low-grade iron ore consisting of iron, quartz, and numerous silicates. Taconite from the eastern tip of the Mesabi Iron Range contains the amphibole silicate cummingtonite-grunerite, which is a mineral relative of amosite asbestos. In the present study, data were collected from 249 men with 20 or more years of exposure to taconite dust and 86 men without history of intimate exposure to taconite dust. Bronchitic symptoms and impairment of expiratory flow correlated significantly with history of cigarette smoking, but not with exposure to dust. Chest radiographs revealed three cases of possible silicosis. No case of definite interstitial fibrosis, ill-defined diaphragm, pleural calcification, or mesothelioma was found. We conclude that (1) cigarette smoking is significantly correlated with bronchitic symptoms and impairment of expiratory flow; (2) taconite workers are at risk of silicosis; (3) if dust containing cummingtonite-grunerite has biologic activity comparable to that of dust from asbestos, it is not evident after 20 years of low-level exposure.

In plain English

This was a survey of respiratory health in men at one taconite mining company in Minnesota. Taconite is a low-grade iron ore, and the ore from this area contains cummingtonite-grunerite, a mineral relative of amosite asbestos. The authors compared 249 men with 20 or more years of exposure to taconite dust with 86 men without a history of close exposure: company railroad and power-plant workers, and Duluth school employees. They used a symptom questionnaire, breathing tests and chest X-rays read by three readers. Cough, phlegm and reduced airflow were linked with cigarette smoking but not with dust exposure. Among exposed men, three had small rounded opacities, which the authors said might be lung disease from silica or silica and iron. Two had small irregular opacities, and one man had both. No unexposed man had either. Pleural thickening was found in 2.0% of exposed and 3.5% of unexposed men. No mesothelioma, pleural calcification or definite interstitial fibrosis was found. The authors concluded that any asbestos-like effect was not evident after 20 years of low-level exposure. They noted that 20 to 23 years is relatively short compared with the delay before asbestos-related disease appears.

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 survey comparing dust-exposed and unexposed men using a respiratory symptom questionnaire, spirometry, and chest radiographs read by three readers
• Who was studied: 249 taconite company workers with 20 or more years of exposure to taconite dust, compared with 86 men without intimate exposure. The unexposed men were the same company's railroad and power-plant workers plus 33 Duluth, Minnesota school system employees. All were men; eastern Mesabi Range, Minnesota.
• Exposure: Dust from mining and processing taconite ore. Mining and crushing dust was roughly equal thirds iron, quartz and silicates, including cummingtonite-grunerite, which the authors describe as essentially nonfibrous in this ore. Individual exposure was estimated retrospectively from work-zone dust surveys done 1955 to 1975.
• Main results:
  • Bronchitic symptoms and impaired expiratory flow were significantly associated with cigarette smoking, but not with dust exposure.
  • Mean FEV1/FVC percentage ranged from 74 to 82% across all smoking and dust categories.
  • No differences in maximal voluntary ventilation between the dust exposure groups were significant.
  • Among dust-exposed men, small rounded opacities were scored at profusion 1/0 in two cases and 1/1 in one case. No unexposed man had them.
  • The authors said the three exposed men with small rounded opacities may have had pneumoconiosis related to silica, or to silica and iron.
  • Small irregular opacities at profusion 1/0 were found in two dust-exposed men and in no unexposed men. One subject had both rounded and irregular opacities.
  • Pleural thickening was found in 5 dust-exposed men (2.0%) and 3 unexposed men (3.5%). The difference was not significant.
  • No case of definite interstitial fibrosis, ill-defined diaphragm, pleural calcification, or mesothelioma was found.
  • No large opacities suggesting progressive massive fibrosis were found. Shadows suggestive of cancer in 10 men had been seen on earlier films and were stable.
• The authors' conclusion: The authors concluded that smoking was associated with bronchitic symptoms and reduced airflow, and that taconite workers are at risk of silicosis. They also concluded that if this cummingtonite-grunerite dust has biologic activity comparable to asbestos dust, it was not evident after 20 years of low-level exposure.
• Limitations the authors state:
  • Exposure lasted only 20 to 23 years, which the authors call relatively short compared with the latent period of asbestos-related disease.
  • Individual dust exposure was estimated retrospectively from work-zone profiles. Individual breathing-zone sampling data were not available.
  • The intensity of dust exposure in the study population was not great.

Topics

Medical terms in this study, explained in our Lexicon: Taconite, Silicate, Iron Range, Amphibole Group, Cummingtonite-Grunerite, Amosite, Chest X-Ray, Silicosis.

Related studies

• The relationship between various exposure metrics for elongate mineral particles (EMP) in the taconite mining and processing industry — J. Hwang, G. Ramachandran, et al. (2014)
• Amphibole fibers in a taconite mine and in the lungs of the miners — B. Gylseth, T. Norseth, et al. (1981)
• Comprehensive assessment of exposures to elongate mineral particles in the taconite mining industry — J. Hwang, G. Ramachandran, et al. (2013)
• The origins of public concern with taconite and human health: Reserve Mining and the asbestos case — M.E. Berndt, W.C. Brice (2008)
• Mineralogical and microscopic evaluation of coarse taconite tailings from Minnesota taconite operations — L.M. Zanko, H.B. Niles, et al. (2008)
• Mortality experience among Minnesota taconite mining industry workers — E.M. Allen, B.H. Alexander, et al. (2014)

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