Assessment of the physicochemical properties of chrysotile-containing brake debris pertaining to toxicity

Abstract

Grinding and drilling of chrysotile asbestos-containing brake pads during the 20^th century led to release of chrysotile, resulting in varying levels of workplace exposures of mechanics. Despite exposures, excess risk of mesothelioma remains in doubt.

Objectives: The toxicity of particulates is primarily derived through a combination of physicochemical properties and dose and as such this study aimed to determine properties of asbestos-containing brake debris (BD) which may influence pathogenicity and potential of mesothelioma.

Materials and Methods: Chrysotile-containing brake pads were ground – to reflect occupational activities, aerosolized, and size-fractionated to isolate respirable fractions. Analysis of morphology, biodurability, surface charge, and interactions with macrophages were undertaken.

Results: The respirable fraction of BD contained ∼15–17% free chrysotile fibers thereby constituting a small but relevant potential long fiber dose. Acellular biodurability studies showed rapid dissolution and fragmentation of chrysotile fibers that was consistent for pure chrysotile control and BD samples.

Conclusions: The long, free, respirable chrysotile fibers were present in BD, yet were of low bio-durability; incubation in artificial lysosomal fluid led to destruction of free fibers.

Keywords:

• Brake debris
• chrysotile asbestos
• fiber
• toxicity
• mesothelioma

Acknowledgments

The authors wish to thank Dr. Sofia Billett and Mr. Steve Clark for their expertise in SEM analysis and Ms. Gillian Carse and Ms. Carolyn McGonagle for their expertise in gravimetric and elemental analysis. The authors also wish to acknowledge funding from Honeywell International Inc. and Ford Motor Company.

Author contributions

Matthew S. P. Boyles and Craig A. Poland contributed equally to this work.

Disclosure statement

Concept Life Sciences and IOM Consulting undertake independent consulting activities for private companies, regulators and government agencies. The sponsors and their representatives’ roles were limited to providing study funding; they have had no input into the design/interpretation of the study or development of the paper. Neither the sponsors nor any of their in-house or outside legal counsel reviewed the paper prior to publication. The authors have not appeared in any regulatory or legal proceedings related to the content of this paper. The content and conclusions presented are the professional work of the authors and as such, may not represent the views of the sponsor or their employees. Honeywell and Ford are defendants in asbestos-product litigation involving automotive brakes.

Additional information

Funding

This work was funded by Honeywell International Inc. and Ford Motor Company.