Exposure to tremolite asbestos and respiratory health in Swedish dolomite workers

Our plain-English summary of Exposure to tremolite asbestos and respiratory health in Swedish dolomite workers, by A.I. Seldén, N.P. Berg, E.A. Lundgren, et al (Occupational and Environmental Medicine, 2001).

The study

• Authors: A.I. Seldén, N.P. Berg, E.A. Lundgren, G. Hillerdal, N.G. Wik, C.G. Ohlson, L.S. Bodin
• Journal: Occupational and Environmental Medicine
• Published: 2001;58(10):670-7
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: Deposits of carbonate rock like limestone and dolomite may contain tremolite asbestos. This study assessed the exposure to tremolite asbestos and the respiratory health of Swedish dolomite workers.

Methods: 95% of 137 eligible workers at two dolomite producing companies completed a self administered questionnaire that included questions on respiratory symptoms and were examined with spirometry as well as chest radiography. Total exposure to dust was gravimetrically measured and the tremolite asbestos content of the dust was assessed with polarisation and phase contrast microscopy.

Results: Dolomite dust concentrations were moderate (median 2.8 mg/m3) and tremolite asbestos concentrations were generally below the limit of detection (<0.03 fibres/ml). Somewhat higher values, around 0.1 fibres/ml, were obtained in manual stone sorting and bagging. Respiratory symptoms suggestive of chronic bronchitis were more related to smoking than to estimates of individual exposure to dust. The mean vital capacity was 0.2 l lower than expected after adjustment for sex, age, height, and smoking but the decline in lung function was not associated with current or cumulative exposure to dust in a clear cut way. Two definite cases of pleural plaques and one possible case of simple pneumoconiosis were noted, but the plaques could not be attributed exclusively to exposure to tremolite asbestos.

Conclusions: Dolomite mining and milling may indeed entail low levels of exposure to tremolite asbestos, but this exposure was not a strong determinant of respiratory symptoms, lung function, or pneumoconiosis in exposed Swedish workers. This was true also for dolomite dust. The hazards of exposure to tremolite asbestos may vary across deposits, however, and additional studies at other sites of carbonate rock exploitation are warranted.

In plain English

This cross-sectional survey in late 1996 studied tremolite asbestos exposure and respiratory health at two dolomite mines in central Sweden. Of 137 blue collar workers and foremen, 130 took part. They answered a symptom questionnaire and had spirometry, and 126 of them had chest X-rays available for review. Current total dust levels had a median of 2.8 mg/m3. Most tremolite asbestos samples were below the detection limit of 0.03 fibres/ml. Manual stone sorting and bagging reached about 0.1 fibres/ml (maximum 0.14). Symptoms suggesting chronic bronchitis (three or more symptoms) were reported by 24 workers (18%) and were linked to smoking (odds ratio 4.0, 95% CI 1.3 to 12.0). The link with the highest overall dust category was not statistically significant. Vital capacity averaged about 0.2 litres below expected. The two X-ray readers agreed on two cases of pleural plaques, and the link to tremolite was unclear. The authors concluded that tremolite exposure was low and did not seem a major hazard for pneumoconiosis or impaired lung function, cautioning that results may not apply elsewhere.

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 respiratory health survey (questionnaire, spirometry, chest radiography) combined with current and historical workplace dust and tremolite asbestos measurements
• Who was studied: 130 of 137 blue collar workers and foremen at two dolomite mines with production facilities (companies A and B) in the Bergslagen area of central Sweden, surveyed in late 1996; aged 20 to 63 (median 43), 12% female. 126 chest radiographs were available for reassessment.
• Exposure: Dolomite dust (total dust measured by weight from full-shift personal samples) and airborne tremolite asbestos (stationary samples counted with polarising and phase contrast microscopy); historical total dust data from 1969 to 1996 were also reviewed. Asbestos (possibly anthophyllite, spelled 'antophyllite' in the article) had reportedly been added to some products in the 1960s and early 1970s.
• Main results:
  • Current total dust measurements had a median of 2.8 mg/m3, lower than the historical samples
  • Most current tremolite asbestos samples (70% at company A, 65% at company B) were below the detection limit of 0.03 fibres/ml
  • Manual stone sorting and bagging of pure dolomite gave about 0.1 fibres/ml, with a maximum of 0.14 fibres/ml at company B
  • 24 workers (18%) reported three or more respiratory symptoms, suggesting chronic bronchitis
  • In logistic regression with age and smoking, only smoking was significantly associated with three or more symptoms (odds ratio 4.0, 95% CI 1.3 to 12.0)
  • In the highest overall mean dust exposure category (above 10.0 mg/m3), the association with symptoms was not statistically significant (odds ratio 2.6, 95% CI 0.8 to 7.0)
  • Across all 130 workers, mean vital capacity was about 0.2 litres below expected (total deviation -0.22, 95% CI -0.33 to -0.12), somewhat more in men; mean FEV1 was close to expected for both sexes
  • The largest nominal vital capacity deficit, 0.52 litres, was in the current dust exposure category above 10 mg/m3, which contained only four workers
  • Three participants did not take part in the radiological examination, and one participant's films could not be retrieved, so 126 radiographs were reassessed
  • Of the 126 chest radiographs, 121 were classified as negative for pneumoconiosis. The two readers agreed on two cases of pleural plaques and disagreed on three films: two possible plaques, and one film read as ILO category 1/1 simple pneumoconiosis by one reader and normal by the other.
  • Of the two agreed plaque cases, one man had worked only 3 years in the industry. The other had worked 22 years, denied other asbestos exposure, and started work when asbestos was possibly still used as an additive. Even for him, the association with tremolite asbestos was unclear to the authors.
• The authors' conclusion: The authors concluded that tremolite asbestos exposure occurred at these companies but at low concentrations. In their view it did not seem to be a major health hazard for pneumoconiosis or impaired lung function. They cautioned against applying the results to other dolomite workers and called for further studies.
• Limitations the authors state:
  • There was no control group of unexposed workers
  • The analysis of respiratory symptoms lacked good reference data
  • The authors could not determine whether the reduced vital capacity was due to the work environment or to other factors such as body mass index
  • The vital capacity estimate for the highest current dust category was unstable because it rested on only four workers
  • No historical tremolite asbestos measurements existed, because no valid method had been available before this study
  • The acid treatment used before fibre counting may have broken up larger particles, which could have inflated tremolite fibre counts
  • Computed tomography (CT) might have found additional cases that standard chest X-rays missed
  • A possible selection effect, with workers who have sensitive airways leaving dusty jobs, could not be estimated
  • Statistical power was limited because two other relevant companies declined to take part
  • Because tremolite varies between deposits, the results may not apply to carbonate rock workers elsewhere

Topics

The National Library of Medicine indexes this study under subjects our site covers: Tremolite.

Medical terms in this study, explained in our Lexicon: Tremolite, Dolomite, Spirometry, phase contrast microscopy (PCM), Cumulative Exposure, Pleural Plaques, Pneumoconiosis.

Related studies

• Respiratory health of workers exposed to metal dusts and foundry fumes in a copper refinery — G. Ostiguy, C. Vaillancourt, et al. (1995)
• Inhalation studies on the effects of tremolite and brucite dust in rats — J.M. Davis, J. Addison, et al. (1985)
• The dust hazard in tremolite talc mining — L. Greenburg (1947)
• Health of vermiculite miners exposed to trace amounts of fibrous tremolite — J.C. McDonald, A.D. McDonald, et al. (1988)
• Health effects of tremolite. Now and in the future — B.W. Case (1991)
• The morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite: Part III. Radiographic findings — H.E. Amandus, R. Althouse, et al. (1987)

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