Reduction of the biological potential of chrysotile asbestos arising from conditions of service on brake pads

Our plain-English summary of Reduction of the biological potential of chrysotile asbestos arising from conditions of service on brake pads, by A.M. Langer (Regulatory Toxicology and Pharmacology, 2003).

The study

• Author: A.M. Langer
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2003;38(1):71-7
• Type of article: Review
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Data exist that show that chrysotile asbestos does not retain its mineral properties, or biological activity, at temperatures far below the olivine transformation point. Temperatures hundreds of degrees below this point cause the mineral to lose structural water with accompanying crystal structure degradation. The loss of structure is accompanied by modification of its surface and reduction or loss of biological activity. Using heating studies and milling as an approximation of thermal and mechanical shear stress that chrysotile is subjected to on a brake lining, biological blunting is shown to begin much earlier than the olivine transformation process. Minimal degradation of the chrysotile surface structure imparts a disproportionately great effect on its biological activity. Biological and epidemiological data for brake workers exposed to chrysotile asbestos should be viewed in context with the conditions of service to which the product was subjected over a lower range of temperatures than previously considered important.

In plain English

This single-author review brought together earlier published laboratory data on chrysotile asbestos and reported no new experiments. The author used heating data from a 1980 thesis and milling data from a 1978 study as stand-ins for the heat and grinding on a brake lining. In the heating data, chrysotile showed no structural change at 400 degrees Celsius, lost 30% of its structure at 500 degrees and 70% at 575 degrees, and lost all of it at 650 degrees. After 1 minute of milling, 3 of 191 measured fibers were still longer than 5 micrometers. By 5 minutes, all measured fibers and fibrils were shorter, and 3600 seconds of milling caused a 58% loss of structure. Between 1 and 5 minutes of milling, the fiber's ability to rupture red blood cell membranes fell by one-third. The author concluded that exposure to brake wear debris may be associated with little or no risk of asbestos disease. The author also noted that dust from beveling, arcing, cleaning and refurbishing brakes has not gone through the same service conditions.

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: Review and commentary by a single author that re-presents previously published laboratory data (heating data from Butler 1980; milling, structure and red-cell rupture data from Langer et al. 1978) as an approximation of brake pad conditions. No new experiments were reported.
• Who was studied: Laboratory samples of chrysotile asbestos, heated or milled in the earlier studies. For the milling data, 5169 fibers and fibrils were measured by transmission electron microscopy.
• Exposure: Chrysotile heated in the laboratory (400 to 810 degrees Celsius in the tabulated data) and milled (60 to 3600 seconds), used as approximations of the heat and mechanical shear stress on brake linings.
• Main results:
  • Heated chrysotile (Butler 1980 data): no structural change at 400 degrees Celsius, 30% of structure lost at 500 degrees, 70% lost at 575 degrees, and 100% lost at 650 and 810 degrees.
  • Milled chrysotile (Langer et al. 1978 data): fibers and fibrils 5 micrometers or longer were counted at each milling time.
• As received: 10 of 214 fibers (4.7%) and 10 of 800 fibrils (1.2%).
• After 60 seconds: 3 of 191 fibers (1.8%) and 0 of 779 fibrils.
• After 300 seconds: 0 of 251 fibers and 0 of 962 fibrils.
  • Milling for 3600 seconds reduced X-ray counts for chrysotile's strongest reflection from 8450 (as received) to 3541. This was a 58% loss of structure.
  • Red blood cell rupture (hemolysis) by milled chrysotile fell by one-third between 1 and 5 minutes of milling, which the author linked to a 12% loss of mineral structure. Hemolysis at 1 mg/ml was 100.0% as received, 65.0% at 300 seconds and 15.0% at 1200 seconds. The amount of chrysotile needed for 50% hemolysis rose from 0.4 mg to 7.5 mg at 3600 seconds.
  • Milling also reduced chrysotile's surface reactivity: its ability to reduce a stable free radical and to bind polar molecules.
• The authors' conclusion: The author concluded that brake service conditions heat and break down chrysotile, so that its biological activity is greatly reduced well below the olivine transformation temperature. In the author's view, exposure to brake wear debris may be associated with little or no risk of asbestos disease.
• Limitations the authors state:
  • The author stated that milling also involves heating, so some effects of milling and heating cannot be separated.
  • The author noted that dust from brake installation work (beveling and arcing pads, cleaning and refurbishing brake surfaces) has not gone through service conditions, so the conclusion about wear debris does not cover it.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Auto mechanics and brake work, Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, Brake Lining, Olivine, Crystal Structure.

Related studies

• Exposure to chrysotile asbestos associated with unpacking and repacking boxes of automobile brake pads and shoes — A.K. Madl, L.L. Scott, et al. (2008)
• Evaluation of the size and type of free particulates collected from unused asbestos-containing brake components as related to potential for respirability — M.A. Atkinson, M. O'sullivan, et al. (2004)
• Airborne asbestos concentration from brake changing does not exceed permissible exposure limit — C.L. Blake, D.R. Van Orden, et al. (2003)
• Re: Evaluation of the size and type of free particulates collected from unused asbestos-containing brake components as related to potential for respirability — D.J. Paustenbach, B.L. Finley, et al. (2006)
• Environmental and occupational health hazards associated with the presence of asbestos in brake linings and pads (1900 to present): a "state-of-the-art" review — D.J. Paustenbach, B.L. Finley, et al. (2004)
• A study of airborne chrysotile concentrations associated with handling, unpacking, and repacking boxes of automobile clutch discs — G.C. Jiang, A.K. Madl, et al. (2008)

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