Vermiculite: a review of the mineralogy and health effects of vermiculite exploitation

Our plain-English summary of Vermiculite: a review of the mineralogy and health effects of vermiculite exploitation, by J. Addison (Regulatory Toxicology and Pharmacology, 1995).

The study

• Author: J. Addison
• Journal: Regulatory Toxicology and Pharmacology
• Published: 1995;21(3):397-405
• Type of article: Review
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Vermiculite is a mica-type mineral that is being used in increasing quantities for insulation, in composite cements, and in horticulture. No serious health risks have been found resulting from the exposure to vermiculite alone nor are any anticipated in view of its long-term chemical durability, even with respect to fibers of vermiculite. Vermiculite ores may contain a variety of other minerals including asbestos, which, if present in significant quantities, could pose a health risk to producers and end users. A variety of regulations are in place that should prevent inadvertent exposure to asbestos in vermiculites, but great care is needed if true asbestos hazards are to be correctly identified. At the same time, vermiculites containing any of a variety amphibole minerals should not be excluded from use because of mistaken identification of these minerals as asbestos. A variety of test methods that have been developed are described and recommendations are made with respect to appropriate action levels for asbestos in vermiculites or other raw materials.

In plain English

This article was a review of vermiculite mineralogy, accessory minerals in vermiculite ores, published health evidence from vermiculite workforces, test methods and asbestos regulation. The author described vermiculite as a sheet silicate formed by alteration of micas, and stated that ore deposits always contain other minerals, which may include chrysotile, tremolite, actinolite or anthophyllite. The author reported that miners and processors in South Africa and South Carolina showed very few ill effects. South Carolina exposures ranged from 0.15 to 1.17 mg m-3 for respirable dust. In South Africa, small irregular opacities appeared in only 1.5% of the vermiculite-exposed group, and trends of increasing effect with exposure were not statistically significant. The only deposits showing serious health effects among workers were those where high concentrations of tremolite and actinolite asbestos existed in the ore and workers were exposed to high concentrations of airborne asbestos. For those deposits the review cited four deaths from malignant mesothelioma, excess respiratory cancer deaths and radiographic changes. The author wrote that the data would seem to indicate vermiculite itself has relatively low toxicity, while a carcinogenic potential could not yet be entirely excluded.

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: Narrative review of the mineralogy, health effects, test methods and regulation of vermiculite and its accessory minerals
• Who was studied: Not a primary study of people; the review discussed published studies of vermiculite miners and mineral processors in South Africa and South Carolina, and of workers at a mine whose ore contained tremolite and actinolite asbestos
• Exposure: Airborne vermiculite dust and vermiculite fibres, and asbestos minerals occurring as accessory minerals in vermiculite ores (chrysotile, tremolite, actinolite, anthophyllite), plus non-asbestos amphibole cleavage fragments
• Main results:
  • For the South Carolina operation, the review reported exposures ranging from 0.15 to 1.17 mg m-3 for respirable dust
  • In the South African vermiculite workforce, small irregular opacities were found in only 1.5% of the vermiculite-exposed group
  • In that same group, trends of increasing health effects with increasing exposure were not statistically significant
  • The deposits showing serious health effects were those where high concentrations of tremolite and actinolite asbestos were known to exist in the ore and the workers were exposed to high concentrations of airborne asbestos
  • At that deposit, the review cited four deaths from malignant mesothelioma and an increased risk of mortality from nonmalignant respiratory disease
  • Radiographic studies at that mine were reported with prevalences of 18.4, 57.9 and 11.9% (printed as referring to small opacities, pleural thickening and pleural calcification respectively)
  • Estimated risks of excess radiological change at that mine, for a cumulative exposure of 100 fiber years, were from 5.5 to 7.3%
  • At one mine with both tremolite and actinolite asbestos varieties at concentrations of up to about 5% of the total, the review cited substantial excess deaths from respiratory cancer (more than double expected) and a number of mesothelioma cases
  • The review reported that UK Health and Safety Executive method MDHS 77 (1994) accepts a distinction between asbestos and prismatic crystalline varieties of the same amphibole type and describes optical properties to distinguish them
• The authors' conclusion: The author wrote that the data would seem to indicate vermiculite itself has relatively low toxicity in comparison to minerals such as chrysotile or quartz. The author also wrote that the absence of epidemiological evidence of disease from normal non-asbestos amphiboles is probably enough now to suggest strongly that those minerals are not carcinogenic to humans.
• Limitations the authors state:
  • The author stated that the working populations in the vermiculite studies are small and most sites have not been operating for very long, so a carcinogenic potential for the mineral or its fibres could not yet be entirely excluded
  • The author stated that exposure data from South Africa were sparse, and the investigators there did not speculate on cumulative exposures

Topics

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

Medical terms in this study, explained in our Lexicon: vermiculite, Mineralogy, Mica, Amphibole Group.

Related studies

• Health of vermiculite miners exposed to trace amounts of fibrous tremolite — J.C. McDonald, A.D. McDonald, et al. (1988)
• Fiber contamination of vermiculites: a potential occupational and environmental health hazard — F. Moatamed, J.E. Lockey, et al. (1986)
• A review of scientific literature examining the mining history, geology, mineralogy, and amphibole asbestos health effects of the Rainy Creek igneous complex, Libby, Montana, USA — B.R. Bandli, M.E. Gunter (2006)
• Radiographic abnormalities and exposure to asbestos-contaminated vermiculite in the community of Libby, Montana, USA — L.A. Peipins, M. Lewin, et al. (2003)
• Cohort study of mortality of vermiculite miners exposed to tremolite — J.C. McDonald, A.D. McDonald, et al. (1986)
• Vermiculite, respiratory disease, and asbestos exposure in Libby, Montana: update of a cohort mortality study — P.A. Sullivan (2007)

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