The particulate matter in brake dust can be more harmful to health than diesel emissions, a new study has found.
The research discovered that microscopic particles emitted from certain types of commonly-fitted brake pads can be more toxic than those found in diesel exhaust. The findings add further confirmation to studies that have previously highlighted the issues around particulate matter (PM) in brake dust.
According to the study, a higher concentration of copper in some pads is associated with increased harmful effects on sensitive cells from people’s lungs, as a result of particles being breathed in.
Exposure to pollution generated by cars, vans and lorries has long been linked to an increased risk of lung and heart disease. However, while past attention has mainly concentrated on exhaust emissions, particles are also released into the air from tyre, road and brake pad wear, emissions which are largely unregulated by legislation.
However, the problem of brake dust is likely to be worse with cheaper pads made by unrecognised brands, or counterfeit products that do not monitor the materials used in brake pad production.
These ‘non-exhaust’ pollution sources are now responsible for the majority of vehicle PM emissions in the UK and parts of Europe, with brake dust being the main contributor.
Brake dust still an issue in EVs
Lead author of the study, Dr James Parkin , explained that a move to electric cars is bringing the problem into sharper focus.
“People generally associate pollution from cars as being from exhaust pipes and think of electric vehicles as having zero emissions,” he commented. “However, EVs still produce particulate matter due to friction and wear of the road, tyres, and brakes.
“We wanted to understand how different types of chemical composition of pads affect the toxicity of the brake dust particles emitted and what this might mean for the health of individuals.”
The scientists undertook an in-depth study examining the effects on lung health of PM from four different types of brake pad with differing chemical compositions: low metallic, semi-metallic, non-asbestos organic and hybrid-ceramic. The researchers were particularly interested in the smallest particles of brake dust, PM2.5 and below, which is 30 times smaller than the diameter of a human hair.
These tiny particles can make their way beyond the upper airways and deeper into the delicate lung air sacs, which enable the exchange of oxygen and carbon dioxide to and from the blood stream.
Levels of toxicity
Brake pad particulate matter was collected using specialist equipment. In the laboratory, the Southampton team used samples of cells from the lining of the lung and exposed them to the fine particulate matter to measure its effects, such as oxidative stress, inflammation, or the death of cells.
Results showed that of the four types of brake pads, non-asbestos organic pads were the most potent in terms of inducing inflammation and other markers of toxicity, and more toxic to human lung cells than diesel exhaust particles. Ceramic pads were the second most toxic.
Importantly, both non-asbestos organic and ceramic pads contain high concentrations of copper, and later experiments to remove this copper found the PM became less toxic.
The findings, published in the journal Particle and Fibre Toxicology , suggest that a reduction of copper content in brake pads could help mitigate some of the harmful effects of vehicle particulate matter.
Project supervisor Professor Matthew Loxham commented: “This research has important implications for health and future policy because as we switch from diesel and petrol-powered cars to electric vehicles, non-exhaust particle emissions will remain. Non-exhaust emissions could increase over time due to electric vehicles being heavier than combustion engine vehicles and creating greater friction.”
The researchers highlight that while electric vehicles emit no exhaust emissions, they are not emission-free and that health effects from vehicle emissions will not necessarily be completely removed once the fleet is fully electrified.
They suggest that current legislation, which focuses on PM exhaust emissions, may be inadequate to fully mitigate the health effects of vehicles in the future.
