Defining asbestos: differences between the built and natural environments

Our plain-English summary of Defining asbestos: differences between the built and natural environments, by M.E. Gunter (Chimia, 2010).

The study

• Author: M.E. Gunter
• Journal: Chimia
• Published: 2010;64(10):747-52
• Type of article: Review
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos - while most think they know what this material is, few understand the current issues surrounding it. Few would also realize that asbestos is the form of a mineral, and even fewer would know that there are different types of asbestos, that not only had different industrial applications, but pose differing health risks when inhaled. Asbestos was in wide-spread use mid-last century in many consumer products, and no doubt saved thousands of lives, but by the latter part of last century concerns over its health risk caused its use to wane, to the point it was removed from many buildings. So in many ways the asbestos story was coming to an end in the 1990s, but two events in the USA - the vermiculite ore produced from Libby, Montana which contained amphibole asbestos and was used in a million homes in the USA as attic insulation and the concern for exposure to asbestos occurring in its natural setting in El Dorado Hills, California led to an increased concern of the potential for low-level environmental exposure to asbestos to the general public. The current dilemma we find ourselves in, especially in the USA, deals with the relationships between our knowledge of handling asbestos and an understanding of its risk potential in the built environment versus the natural environment. And one perfect metaphor for this is the term used by many non-geologists to differentiate asbestos in the built vs natural environment - 'naturally occurring asbestos'. Clearly a misstatement, but only one of many we must deal with as we struggle to understand the risk to humans of natural occurrences of asbestos. This paper will try and address some of these issues centering around those occurring in the USA.

In plain English

This was an invited review article by a mineralogist about how asbestos is defined, focused on the USA. It did not study people or measure disease. The author explained that six minerals are regulated as asbestos: chrysotile, crocidolite, amosite, anthophyllite asbestos, tremolite asbestos and actinolite asbestos. Regulators count a particle as a fiber by its length-to-width ratio: greater than 3 to 1 under a polarized light microscope, or 5 to 1 under a transmission electron microscope. To a mineralogist, a fiber must be curved and flexible. Using photographs, the author showed that a non-asbestiform serpentine particle from Vermont gravel would be counted as asbestos under the regulatory rules. Three US soil samples contained between 2 and 7% amphibole. The author judged these amphiboles probably not asbestiform, but said the soils would be considered contaminated under current US regulations. Soils across the USA also contained other elongated minerals. The author concluded that asbestos can be very difficult to distinguish or define in the natural environment. The author also gave the opinion that common sense might suggest the risk from these natural materials is low.

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: Invited review and commentary article written from a mineralogist's perspective. It is illustrated with the author's microscope photographs and X-ray diffraction patterns of mineral and soil samples. There is no study of people.
• Who was studied: No human population. Illustrative mineral samples, including soils from Washington DC, southern Illinois and western Montana, and gravel from Vermont, USA
• Exposure: Not an exposure study. The article discusses the six regulated asbestos minerals (chrysotile, crocidolite, amosite, anthophyllite asbestos, tremolite asbestos, actinolite asbestos). It covers how they are distinguished from non-asbestiform minerals and from other elongated mineral particles in the natural environment.
• Main results:
  • Under regulatory rules, a particle seen in the polarized light microscope is counted as a fiber if its aspect ratio is greater than 3 to 1.
  • Under regulatory rules, a particle seen in a transmission electron microscope needs an aspect ratio of 5 to 1 to be counted as a fiber.
  • For air monitoring during asbestos removal from buildings, air samples were analyzed by phase contrast microscopy. Fibers were counted if their aspect ratio was greater than 3 to 1 and their length was greater than 5 microns.
  • To a mineralogist, a fiber must have certain physical properties: it must be curved and flexible.
  • A non-asbestiform serpentine group particle taken from gravel in Vermont would be counted as an asbestos particle under regulatory criteria.
  • Three US soil samples examined by X-ray diffraction contained between 2 and 7% amphibole.
  • The author judged the amphiboles in these soils probably not asbestiform. The author said the soils would still contain amphiboles meeting the fiber counting criteria and would be considered contaminated under current US regulations.
  • Elongated particles of other minerals, such as quartz and feldspars, were found in soils across the USA.
• The authors' conclusion: The author concluded that asbestos used in buildings and products could be distinguished from other materials. In the natural environment, however, the author said it can be very difficult to distinguish or define asbestos. The author offered the opinion that common sense might lead to the conclusion that the risk from these natural materials is low.

Topics

Medical terms in this study, explained in our Lexicon: vermiculite, Amphibole Asbestos, El Dorado Hills, Environmental Exposure, naturally occurring asbestos (NOA).

Related studies

• Elongate mineral particles in the natural environment — M.E. Gunter (2018)
• Differences in the sensitivity of hamster and rat lung cells exposed in vitro to natural and man-made fibres — M. Aufderheide, J.W. Knebel, et al. (1996)
• The Presence of Asbestos in the Natural Environment is Likely Related to Mesothelioma in Young Individuals and Women from Southern Nevada — F. Baumann, B.J. Buck, et al. (2015)
• Occupational differences in rates of lung cancer — H.R. Menck, B.E. Henderson (1976)
• Analysis of serpentine polymorphs in investigations of natural occurrences of asbestos — J. Wagner (2015)
• Where occupation and environment overlap: US Forest Service worker exposure to Libby Amphibole fibers — M. Harper, C. Butler, et al. (2015)

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