Assessment of methods for collecting fallout brake pad wear debris for environmental analysis

Abstract

Three methods for collecting or generating fallout brake pad wear debris for environmental analysis were assessed: collection from wheels or hubs of automobiles (natural), generation from an inexpensive sanding process (sanded), and collection of fallout debris from dynamometer tests using the Los Angeles City Traffic protocol (LACT). Brake wear debris was collected from four automobiles with semimetalic brake pads and analyzed for physicochemical properties. For automobiles where all three types of debris were collected, bulk copper mass fractions ranged from 22–23% in sanded particles and 24–27% in LACTparticles, but were reduced to 1–6% in natural debris. The smaller copper mass fraction in natural debris was attributed to contamination with road dust, which was found to comprise 37–97% of the natural particles. The ratio of surface to bulk copper mass fraction was up to five times larger for natural than LACT debris, suggesting that copper may leach into stormwater faster and to a greater extent for natural particles. While the LACT method appears best for collecting only fallout particles, significant differences in copper distributions in the natural and LACT debris suggests that metal distribution in LACT debris may not be representative of fallout particles generated under actual driving conditions, where airborne road dust may play a role. Although dynamometer tests have been the preferred method for generating debris for assessment of metal dissolution from brake particles, data from this study indicate that such samples may result in biased estimates of metal leaching.

Keywords:

• Brake wear debris
• heavy metals
• copper content
• bulk and surface elemental distribution
• road dust contamination

Acknowledgments

The authors are grateful to Dr. Ray Arnold (Copper Development Association) for fruitful discussions, Dr. Chao Ni (University of Delaware) for his assistance with the electron microscopy analysis, and Dr. Michele Ostraat (Dupont Co.) for conducting the particle size analyses. Mr. John Stabley's (Stabley Auto Service, Stanton, DE) assistance with the collection of natural wear debris is also acknowledged. Funding for this research was provided by the Copper Development Association and the Center for the Study of Metals in the Environment at the University of Delaware.