Influence of the automotive brake wear debris on the environment - a review of recent research

Abstract

Automotive brake linings are complex composite materials. Some raw materials used by manufacturers or the compounds created during the friction process might be potentially hazardous and may cause various adverse effects. Different fractions of the brake wear debris can be released during braking: i) the airborne and ii) the nonairborne. Due to the small size and minimum gravitational action, the airborne particles could be spread for long distances from a source and typically remain suspended in the air for long periods of time. Our previous research demonstrated that the airborne fraction contains considerable amounts of different nanoparticulates. On the other hand, the emitted nonairborne fraction typically settles on vehicle/brake hardware surfaces and in the vicinity of roads. The nonairborne particles are considered to be relatively large, but it was shown that nano-sized particles readily attach to them and can be released later. This study is focused on the recent research in the field of brake wear debris detection in the environment (road dust, soil and sediments, water runoffs, air pollution) as well as on the possible impact on plants, animals and human health. The review of recently published papers allowed for the summary of the spectrum of relevant experimental techniques used currently for identification and analysis of brake wear debris, and for the most recent opinions on their impact on the environment and health. It is suggested that consideration of the environmental aspects becomes the necessary aspect of brake/friction materials design.