Southampton researchers have discovered that some common brake pads can have a harmful effect on lung health.
The new study looked at microscopic particles emitted from certain brake pads. It found they can be more toxic than those in diesel vehicle exhaust.
The research shows that a higher concentration of copper in some pads is associated with increased harmful effects on sensitive cells from people’s lungs. This is as a result of particles being breathed in.
Dr James Parkin and Professor Matthew Loxham from the University of Southampton led the study.
Findings have been published in the journal Particle and Fibre Toxicology.
The research included contributions and equipment from the NIHR Southampton Biomedical Research Centre (BRC).
Hidden pollution sources
Exposure to pollution generated by cars, vans and lorries has long been linked to an increased risk of lung and heart disease.
Past attention has mainly concentrated on exhaust emissions. 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.
A move to electric cars is bringing the problem into sharper focus. Dr Parkin, who is a Research Fellow in Air Pollution, explained:
“People generally associate pollution from cars as being from exhaust pipes and think of electric vehicles as having zero emissions. However, electric vehicles 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 particles emitted and what this might mean for the health of individuals.”
Effect of small particles
The scientists undertook an in-depth study examining the effects on lung health of PM from four different types of brake pad. They had different chemical compositions: low metallic, semi-metallic, non-asbestos organic and hybrid-ceramic.
The researchers were particularly interested in the smallest particles, of PM2.5 and below (often referred to as fine PM). These are at least 30 times smaller than the diameter of a human hair.
These tiny particles can make their way beyond the upper airways. They can travel 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 four million premature deaths per year worldwide.
Brake pad PM was collected using specialist equipment. In the laboratory, the Southampton team used samples of cells from the lining of the lung. They exposed them to fine PM to measure its effects, such as oxidative stress, inflammation or the death of cells.
‘Important implications’
Researchers found that non-asbestos organic pads were the most potent in terms of inducing inflammation and other markers of toxicity. Results showed they are 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. Later experiments to remove this copper found the PM became less toxic.
The findings suggest that a reduction of copper content in brake pads could help mitigate some of the harmful effects of vehicle PM.
Air pollution, including from cars, has been linked to a range of respiratory conditions. These include asthma, chronic obstructive pulmonary disease (COPD), cardiovascular diseases, dementia and idiopathic pulmonary fibrosis (scarring of the lung).
Prof Loxham is part of the NIHR Southampton BRC's Respiratory and Allergy theme. He said:
“This research has important implications for health and future policy. 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. This is due to electric vehicles being heavier than combustion engine vehicles and creating greater friction.”
The researchers suggest that current legislation, which focuses on PM exhaust emissions, may be inadequate to fully mitigate the health effects of vehicles in the future.
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