The microscopic particles emitted from certain types of commonly fitted brake pads can be more toxic than those found in diesel vehicle exhaust, research has suggested.

A study by academics from the University of Southampton has found that a higher concentration of copper in some brake 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.

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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, the study argued.

These ‘non-exhaust’ pollution sources are now responsible for the majority of vehicle particulate matter (PM) emissions in the UK and parts of Europe, with brake dust being the main contributor.

Lead author of the study, research fellow in air pollution Dr James Parkin, said the transition to electric cars was bringing this problem into sharper focus. “People generally associate pollution from cars as being from exhaust pipes and think of electric vehicles as having zero emissions. 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 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 PM2.5 and below (often referred to as fine PM) – 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 four million premature deaths per year worldwide.

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.

The 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.

More generally, 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).

Separately, an air quality survey of UK working industrial areas has found pollution levels to be on average 63 times higher than in public spaces, such as bus and train stations.

The assessments, carried out by Zehnder Clean Air Solutions, suggest UK production workers are being left to breathe dangerously polluted air every day, putting them at risk of serious harm to their health.

The company measured the level of these PM2.5 particles at a range of industrial production areas, such as metal fabrication sites, bakeries, and packaging production lines. It then compared the readings to their respective offices, as well as public places such as transport hubs, supermarkets, and schools.

The average PM2.5 reading for industrial production areas was 78x higher than train stations, 87x higher than in supermarkets or shopping centres, and 92x higher than at bus stations, it found.

Ben Simons, head of Zehnder Clean Air Solutions Europe West, said: “Factory floors and production hubs – where workers spend all day, every day – continue to expose UK employees to serious harm. The levels of exposure are almost off the charts.

“We urgently need UK employers to understand how important it is to provide clean air at work. Doing so dramatically improves the quality of life for employees, reduces risks to health, and enhances the running of their businesses,” he added.

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