Exposure to brake dust and malignant mesothelioma: a study of 10 cases with mineral fiber analyses

Our plain-English summary of Exposure to brake dust and malignant mesothelioma: a study of 10 cases with mineral fiber analyses, by K.J. Butnor, T.A. Sporn, V.L. Roggli (The Annals of Occupational Hygiene, 2003).

The study

• Authors: K.J. Butnor, T.A. Sporn, V.L. Roggli
• Journal: The Annals of Occupational Hygiene
• Published: 2003;47(4):325-30
• Cited by: 43 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: A large number of workers in the USA are exposed to chrysotile asbestos through brake repair, yet only a few cases of malignant mesothelioma (MM) have been described in this population. Epidemiologic and industrial hygiene studies have failed to demonstrate an increased risk of MM in brake workers. We present our experience of MM in individuals whose only known asbestos exposure was to brake dust and correlate these findings with lung asbestos fiber burdens.

Methods: Consultation files of one of the authors were reviewed for cases of MM in which brake dust was the only known asbestos exposure. Lung fiber analyses were performed using scanning electron microscopy (SEM) in all cases for which formalin-fixed or paraffin-embedded lung tissue was available.

Results: Ten cases of MM in brake dust-exposed individuals were males aged 51-73 yr. Nine cases arose in the pleura and one in the peritoneum. Although the median lung asbestos body count (19 AB/g) is at our upper limit of normal (range 0-20 AB/g), half of the cases had levels within our normal range. In every case with elevated asbestos fiber levels by SEM, excess commercial amphibole fibers were also detected. Elevated levels of chrysotile and non-commercial amphibole fibers were detected only in cases that also had increased commercial amphibole fibers.

Conclusions: Brake dust contains exceedingly low levels of respirable chrysotile, much of which consists of short fibers subject to rapid pulmonary clearance. Elevated lung levels of commercial amphiboles in some brake workers suggest that unrecognized exposure to these fibers plays a critical role in the development of MM.

In plain English

This was a case series of 10 people with malignant mesothelioma whose only known asbestos exposure was brake dust at work. The cases came from one author's consultation files and were all medico-legal consultations, five referred by plaintiffs and five by defendants of brake manufacturers. All were men, and the eight whose ages were recorded were 51 to 73. Nine had pleural mesothelioma and one had peritoneal mesothelioma. The authors measured asbestos in lung tissue and compared it with 20 reference cases. The median asbestos body count, 19 per gram of wet lung, was at the upper limit of their normal range, and half the cases were within that range. Excess commercial amphibole fibers, mostly amosite, were found in five of the six cases with elevated lung asbestos. Chrysotile was above the normal range in two cases, and both also had raised commercial amphiboles. Drawing also on earlier studies, the authors concluded that friction product exposure is unlikely to contribute to mesothelioma. They noted that the cases may not be representative and that interview histories are subject to recall bias.

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: Case series of 10 medico-legal consultation cases, with lung tissue mineral fiber analysis by light microscopy and scanning electron microscopy, compared with 20 reference cases
• Who was studied: 10 men with malignant mesothelioma (9 pleural, 1 peritoneal), taken from the consultation files of one author (V.L.R.), which hold more than 1900 mesothelioma cases. The text reports an age range of 51 to 73 (median 60), but Table 1 lists age as not determined for cases 7 and 10, so ages are known for eight men. The article gives no location or time period for the cases.
• Exposure: Occupational contact with brake dust as the only recognized source of asbestos exposure
• Main results:
  • Brake dust exposure lasted 7 to 40 years (median 24). All 10 men had direct exposure as automotive or brake mechanics.
  • In the 10 cases, the median lung asbestos body count was 19 per gram of wet lung, at the authors' upper limit of normal (0 to 20 per gram).
  • In 5 of the 10 cases (cases 4, 6 to 8 and 10), asbestos body content was within the normal range.
  • Excess commercial amphibole fibers were found in 5 of the 6 cases with elevated tissue asbestos content (cases 1 to 3, 9 and 10).
  • Amosite was the main commercial amphibole in four of these five cases. Crocidolite predominated in the fifth (case 9).
  • In one further case (case 5), asbestos body counts by light microscopy were marginally elevated.
  • Chrysotile was detected in 3 cases and exceeded the normal range in 2 of them (cases 1 and 9).
  • Non-commercial amphiboles (mainly tremolite) predominated over commercial amphiboles in half of the cases and were elevated in 2 cases (cases 3 and 9).
  • Every case with excess chrysotile or excess non-commercial amphibole fibers also had increased commercial amphibole fibers.
  • Pleural plaques were present in 4 of the 7 cases with information. Asbestosis was not seen histologically in any case.
  • Smoking information was available for 7 cases, and all 7 were smokers or ex-smokers.
• The authors' conclusion: Combining these findings with earlier lung fiber, industrial hygiene and epidemiological studies, the authors concluded that friction product exposure such as that of automotive mechanics is unlikely to contribute to the development of malignant mesothelioma.
• Limitations the authors state:
  • The cases were medico-legal consultations and may not be representative of all workers exposed to brake dust.
  • Exposure histories came from patient interviews about events decades earlier and are subject to recall bias.
  • The scanning electron microscopy method may have missed long chrysotile fibers thinner than 0.15 micrometers. The authors judged this unlikely.
  • The authors raised the possibility that chrysotile could cause the tumor and then be cleared from the lung without trace. They then argued that this idea lacks scientific support.

Topics

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

Medical terms in this study, explained in our Lexicon: Malignant Mesothelioma, Mineral Fiber, Chrysotile, Industrial Hygiene, Asbestos Exposure, Fiber Burden, Scanning Electron Microscopy (SEM), Pleura.

Related studies

• Asbestos dust exposure during brake repair — K. Rödelsperger, H. Jahn, et al. (1986)
• The analysis of asbestos count data with "nondetects": the example of asbestos fiber concentrations in the lungs of brake workers — M.M. Finkelstein (2013)
• Asbestos Fiber Concentrations in the Lungs of Brake Repair Workers: An Updated Analysis Using Several Regression Methods to Handle Nondetectable Measurements — Y. Liu, G.M. Marsh, et al. (2018)
• Environmental measurements of total dust and fiber concentration in manufacturer and user of man-made mineral fibers — J.H. Kim, H.S. Chang, et al. (1999)
• Assessing specific causation of mesothelioma following exposure to chrysotile asbestos-containing brake dust — M.D. Freeman, S.S. Kohles (2012)
• Evaluation of the fate and pathological response in the lung and pleura of brake dust alone and in combination with added chrysotile compared to crocidolite asbestos following short-term inhalation exposure — D.M. Bernstein, R.A. Rogers, et al. (2015)

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