Physico-Chemical Characterization and Oxidative Reactivity Evaluation of Aged Brake Wear Particles

Abstract

Brake wear dust is a significant component of traffic emissions and has been linked to adverse health effects. Previous research found a strong oxidative stress response in cells exposed to freshly generated brake wear dust. We characterized aged dust collected from passenger vehicles, using microscopy and elemental analyses. Reactive oxygen species (ROS) generation was measured with acellular and cellular assays using 2′7-dichlorodihydrofluorescein dye. Microscopy analyses revealed samples to be heterogeneous particle mixtures with few nanoparticles detected. Several metals, primarily iron and copper, were identified. High oxygen concentrations suggested that the elements were oxidized. ROS were detected in the cell-free fluorescent test, while exposed cells were not dramatically activated by the concentrations used. The fact that aged brake wear samples have lower oxidative stress potential than fresh ones may relate to the highly oxidized or aged state of these particles, as well as their larger size and smaller reactive surface area.

Copyright 2015 American Association for Aerosol Research

ACKNOWLEDGMENTS

The authors wish to thank Dr. Vincent Jamier from Institut Català de Nanotecnologia (ICN), Spain, for the microscopy analysis. They also thank the technicians from Institute for Work and Health (IST), Switzerland: Mr. Ferdinand Storti for the overall carbon test and Ms. Christine Kohler and Mr. Gregory Plateel for Fe, Cu, and Mn test. Further thanks go to Dr. Jean-Jacques Sauvain and Dr. Guillaume Suarez from IST for the helpful suggestions on cell-free ROS analysis. The authors would like to acknowledge Dr. Håkan Wallin from National Research Centre for the Working Environment, Denmark and Dr. Hanna Karlsson from Karolinska Institutet, Sweden for their helpful comments.

Funding

This study was supported by the EU 7th Framework Programme, Marie Curie Actions, Network for Initial Training NanoTOES (PITN-GA-2010-264506), and the Whitaker International Program.