# Physicochemical and Toxicological Characterization of Airborne Brake Wear Particles Reveals Oxidative Stress–Mediated DNA Damage

## TL;DR

This study explores how brake wear particles in urban air pollution cause DNA damage through oxidative stress, focusing on their chemical composition and toxicity.

## Contribution

The study combines detailed physicochemical and toxicological analysis of brake wear particles to identify copper as a key contributor to oxidative stress and DNA damage.

## Key findings

- Brake wear particles are rich in iron oxide and show similar composition at nano- and microscales.
- Copper in non-asbestos organic brake pads significantly increases DNA damage and antioxidant depletion.
- Brake wear particles induce oxidative stress and DNA damage in human lung cells in a concentration-dependent manner.

## Abstract

Brake wear particles
(BWP) are a significant source of urban air
pollution, yet the toxicity linked to their chemical composition remains
poorly understood. While studies have examined either chemical composition
or toxicity, comprehensive investigations combining both remain limited.
Here, we conducted an in-depth physicochemical characterization of
airborne, size-separated BWP from two brake pad types and comprehensively
assessed their in vitro toxicity using human lung
epithelial cells (A549). Iron, primarily in the form of iron oxide,
was the most abundant element in the wear particles (33–50%
by mass), with evidence pointing to the brake disc as the main source.
A surprisingly high resemblance in elemental composition at the nano-
and microscale was observed. This, along with an absence of clear
differences in metal profiles or toxicological responses between size
fractions, suggests that brake wear microparticles may form through
compaction of vapor-condensed nanoparticles on the friction surfaces,
followed by their release through mechanical shearing. Acellular and
cellular assays showed the concentration-dependent ability of all
studied particles to induce reactive oxygen species production, antioxidant
depletion, and oxidative stress-mediated DNA damage. The nonasbestos
organic pad, with more than 50-fold higher copper levels than the
low-metallic pad, induced stronger DNA damage and acellular antioxidant
depletion, suggesting copper as a potential source for the enhanced
toxicity.