Health of vermiculite miners exposed to trace amounts of fibrous tremolite

Our plain-English summary of Health of vermiculite miners exposed to trace amounts of fibrous tremolite, by J.C. McDonald, A.D. McDonald, P. Sébastien, et al (British Journal of Industrial Medicine, 1988).

The study

• Authors: J.C. McDonald, A.D. McDonald, P. Sébastien, K. Moy
• Journal: British Journal of Industrial Medicine
• Published: 1988;45(9):630-4
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000253).

Abstract

A small cohort of 194 men with low exposure to fibrous tremolite (mean 0.75 f/ml y) in the mining and milling of vermiculite in South Carolina experienced 51 deaths 15 years or more from first employment. The SMR (all causes) was 1.17 reflecting excess deaths from circulatory disease. There were four deaths from lung cancer and 3.31 expected (SMR 1.21, 95% CI 0.33-3.09). Three of the four deaths were in the lowest exposure category (less than 1 f/ml y); no death was attributed to mesothelioma or pneumoconiosis. These findings contrast with those in Montana where the vermiculite ore was heavily contaminated with fibrous tremolite. A radiographic survey of 86 current and recent South Carolina employees found four with small parenchymal opacities (greater than or equal to 1/0) and seven with pleural thickening. These proportions were not higher than in a non-exposed group and much lower than had been observed in Montana. Examination of sputum from 76 current employees showed that only two specimens contained typical ferruginous bodies, confirming low cumulative fibre exposure. Any possible adverse effects of work with vermiculite, minimally contaminated with fibrous or non-fibrous tremolite, were thus beyond the limits of detection in this workforce.

In plain English

This study looked at vermiculite miners and millers in Enoree, South Carolina, where the ore was believed nearly free of fibrous tremolite. The cohort was 194 men employed six months or more and hired before 1 January 1971, with an estimated geometric mean cumulative fibre exposure of 0.75 f/ml y. There were 51 deaths. All-cause deaths exceeded those expected from US rates (SMR 1.17, 95% CI 0.87-1.51), mainly from circulatory disease. The excess was not statistically significant. There were four respiratory cancer deaths against 3.31 expected (SMR 1.21, 95% CI 0.33-3.09). Three of these were in the lowest exposure group, and no death was attributed to mesothelioma or pneumoconiosis. Chest x rays of 86 employees showed small parenchymal opacities scored 1/0 or more in four (5%) and pleural thickening in seven (8%). These proportions were not higher than in 25 non-exposed workers, whose age distribution was unknown. Only two of 69 analysed sputum samples had typical ferruginous bodies. The authors concluded that any adverse effects were beyond detection limits, noting the small number of subjects.

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: Cohort mortality study, with a chest x ray survey, a sputum study, and air and dust fibre measurements
• Who was studied: 194 men who worked six months or more for a vermiculite company in South Carolina and were hired before 1 January 1971, followed to 1 January 1986. The x ray survey covered 86 current and recent employees and the sputum study 76 current workers.
• Exposure: Fibres (mainly tremolite-actinolite) contaminating vermiculite in mining and milling, believed to be virtually free of fibrous tremolite. Estimated cumulative fibre exposure had a geometric mean of 0.75 f/ml y, and 53% of the cohort had less than 1 f/ml y.
• Main results:
  • In 1986 air samples, all but one of the mean phase contrast microscopy fibre concentrations were below 0.01 f/cc. Of the airborne fibres identified by electron microscopy, 47.6% were tremolite-actinolite.
  • 51 cohort members died. All-cause mortality compared with US white and black men gave an SMR of 1.17 (95% CI 0.87-1.51, from table 6), reflecting excess deaths from circulatory disease.
  • The all-cause excess was more pronounced in black men and mainly due to circulatory disease, but it did not reach statistical significance.
  • In the cohort there were four respiratory cancer deaths, against 3.31 expected (SMR 1.21, 95% CI 0.33-3.09).
  • Three of the four respiratory cancer deaths were in the lowest cumulative exposure category (less than 1 f/ml y). No death was attributed to mesothelioma or pneumoconiosis.
  • Of 86 Enoree employees x rayed, four (5%) had small parenchymal opacities scored 1/0 or more.
  • In a non-exposed group of 25 men from another division of the company, two (8%) had small opacities scored 1/0 or more, a higher proportion than in the Enoree group. The age distribution of this group was unknown.
  • Pleural thickening was found in seven (8%) of the Enoree films, two (8%) of the non-exposed group, and 10 (40%) of 25 Libby, Montana films. No pleural calcification was read at Enoree.
  • Of 76 sputum specimens, 7 could not be analysed. Of the remaining 69, nine had atypical ferruginous bodies and two had typical ferruginous bodies (one and five per pellet).
  • Mean cumulative exposure was 144.6 f/ml y in the earlier Montana mortality cohort, compared with 0.75 f/ml y in South Carolina.
• The authors' conclusion: The authors concluded that any possible adverse effects of work with vermiculite minimally contaminated with fibrous or non-fibrous tremolite were beyond the limits of detection in this workforce. They added that, bearing in mind the small number of subjects, this was what the Montana risk estimates would predict.
• Limitations the authors state:
  • The small number of people ever employed in the industry limited the study.
  • Cohort entry criteria were less demanding than in the Montana study in order to increase the size of the study group, with some loss in comparability.
  • Air samples could not describe peak exposures in the dry zone, so 90th percentile concentrations were used as stand-ins.
  • Personal air samples were too short to reflect complete shift exposure.
  • The age distribution of the non-exposed comparison group for x rays was unknown.

Topics

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

Medical terms in this study, explained in our Lexicon: vermiculite, Tremolite, Lung Cancer, Mesothelioma, Pneumoconiosis, Pleural Thickening, Sputum, Ferruginous body.

Related studies

• Cohort study of mortality of vermiculite miners exposed to tremolite — J.C. McDonald, A.D. McDonald, et al. (1986)
• Pulmonary changes after exposure to vermiculite contaminated with fibrous tremolite — J.E. Lockey, S.M. Brooks, et al. (1984)
• Radiological survey of past and present vermiculite miners exposed to tremolite — J.C. McDonald, P. Sebastien, et al. (1986)
• The morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite: Part II. Mortality — H.E. Amandus, R. Wheeler (1987)
• The morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite: Part I. Exposure estimates — H.E. Amandus, R. Wheeler, et al. (1987)
• 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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