Researchers at Southampton have found that microscopic particles emitted from certain commonly fitted brake pads – those with a higher concentration of copper – can be more toxic than those found in diesel vehicle exhaust.
The research highlights that current legislation focusing on exhaust emissions, may be inadequate to fully mitigate the health effects of emissions from vehicles. This also has implications for the design of vehicles in the future.
Exposure to particulate matter generated by exhaust emissions from cars, vans and lorries has long been linked to an increased risk of lung and heart disease. However, particles are also released into the air from tyre, road and brake pad wear. These emissions are largely unregulated by legislation.
These ‘non-exhaust’ pollution sources are now responsible for the majority of vehicle particulate matter (PM) emissions in the UK and parts of Europe. Brake dust is the main contributor.
Implications for electric vehicles
Lead author of the study, Dr James Parkin, explains that moves to exhaust cleaning systems, and eventually electric cars, is bringing the problem into sharper focus.
James said, “People generally associate pollution from cars as being from exhaust pipes and think of particle emissions being much diminished with better exhaust technology, and essentially removed as we progress towards electric vehicles. However, these vehicles still produce particulate matter due to friction and wear of the road, tyres, and brakes (depending on the extent of regenerative braking).”
We wanted to understand how chemical composition of different types of brake pads affect the toxicity of the particles emitted and what this might mean for the health of individuals.
Dr James Parkin, Research Fellow in Air Pollution
The scientists undertook an in-depth study examining the effects on lung lining cells of PM from 4 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 particles known as PM2.5, often referred to as fine PM. These are 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. Fine PM from a variety of different sources is associated with over 4 million premature deaths per year worldwide.
Reducing copper content
Results showed that of the 4 types of brake pads, particles from non-asbestos organic pads were the most potent in terms of inducing inflammation and other markers of toxicity in human lung cells, compared to diesel exhaust particles.
Hybrid-ceramic pads were the second most toxic. Importantly, both non-asbestos organic and hybrid-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-emitted particulate matter.
Air pollution, including from cars, has been linked to a range of conditions, such as asthma, chronic obstructive pulmonary disease (COPD), cardiovascular diseases, dementia and idiopathic pulmonary fibrosis (scarring of the lung).
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.
Professor Matthew Loxham , Project supervisor
