Researchers have discovered that dust released by worn brake pads can be more toxic and harmful to health than gases emitted by burning fuel

Study shows that particles released by brake pads can be more dangerous than gases from burning fuel, affecting air quality and health.

Air pollution is a global problem, associated with millions of premature deaths each year, according to the World Health Organization (WHO). When we think about pollution in cities, vehicle exhaust, especially diesel-powered vehicles, is often cited as the main culprit. However, a recent study has revealed that something even more toxic and neglected may be harming our health: dust released by worn brake pads.

This dust, part of the so-called “non-exhaust emissions“, includes particles generated by the friction of tires, brakes and the vehicle itself asphalt.

According to the researchers, this type of emissions has already surpassed exhaust emissions in many European countries. Most alarmingly, dust from brake pads has been shown to be more harmful to lung cells than particles from diesel.

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The laboratory experiment

To reach this conclusion, scientists grew lung cells in the laboratory, simulating the inner lining of human lungs.

These cells were exposed to brake dust and diesel exhaust particles. The results were surprising: the cells exposed to brake dust showed significant damage, with inflammatory responses linked to serious respiratory diseases such as cancer, asthma and pulmonary fibrosis.

Interestingly, tests showed that the copper present in these particles plays a crucial role in the observed toxicity.

When the dust was treated to neutralize the copper, the harmful impact on lung cells was significantly reduced.

Despite this, current regulations in the UK, for example, still focus only on exhaust emissions, completely ignoring this type of pollutant.

Particulate matter (PM) from brake wear of four different types of brake pads as well as PM from diesel exhaust were collected in a laboratory setting. Given that PM2,5–0,1 can reach the alveoli, we investigated the differential effects of vehicle-derived PM types on a submerged culture of type II alveolar epithelial cells. (Parkin et al.,
*Particle and Fibre Toxicology* , 2025)

The Toxic Past of Brake Pads

Brake pads were once made from asbestos, a material that is effective at dealing with the heat generated by friction, but is highly toxic.

Asbestos was banned in the UK in 1999 due to its links to serious respiratory diseases such as asbestosis and lung cancer. The ban has led to the emergence of alternatives such as non-asbestos organic (NAO) tablets.

However, the study revealed an ironic finding: The dust released by these NAO pads, designed to be safer, was found to be the most toxic of the options tested. It caused more damage to lung cells than diesel exhaust dust, challenging the common perception that brakes are a secondary problem.

Chemical analysis of these particles revealed high levels of metals, especially copper. Copper is an essential metal for many biological functions, but when inhaled in high concentrations, it can cause lung inflammation and other damage.

Previous studies have already associated excess copper in the air with impaired respiratory function and increased mortality.

The role of electric vehicles

With the growth of the electric vehicle (EV) fleet, many expected a significant reduction in urban pollution. While EVs eliminate tailpipe emissions, they do not solve the problem of non-tailpipe emissions.

On the contrary, the tendency is for this pollution to increase, since EVs, due to their heavy batteries, tend to have more mass, generating greater wear on tires, brakes and asphalt.

Although regenerative braking systems – which slow the vehicle down using the electric motor – reduce the use of traditional brakes, EVs still have friction brakes, which are responsible for the emission of these toxic particles. Therefore, the “zero-emission” label does not reflect the full environmental reality of these vehicles.

Regulations and innovations on the horizon

The introduction of Euro 7 emissions standards, scheduled for November 2026, promises to set limits on brake dust emissions.

This change could encourage the auto industry to develop less toxic materials and adopt mechanisms that capture these particles before they become airborne.

In the United States, states such as California and Washington have already taken the lead in restricting the use of copper in brake pads, mainly due to environmental concerns about contamination of waterways.

These regulations, although motivated by aquatic conservation, may also bring public health benefits by reducing human exposure to this metal.

An invisible danger in the air

Non-tailpipe emissions are estimated to account for around 60% of particulate matter released by vehicles in the UK.

This percentage tends to increase with the increase in the electric fleet. These particles, invisible to the naked eye, penetrate deep into the respiratory system and can reach the bloodstream, affecting several organs.

The challenge now is to convince authorities and manufacturers to expand regulations to address these hidden and dangerous emissions. Redesigning brake pads with less harmful materials is emerging as an urgent and viable measure.

The air we breathe in cities is full of these invisible particles, coming not only from exhaust pipes, but also from brakes, tires and road wear.

Science now makes it clear: ignoring these emissions is neglecting a silent threat to public health. The next step depends on joint action by governments, industries and society to address this still little-known but profoundly impactful risk.

Study available at particleandfibretoxicology and information from theconversation.

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Researchers have discovered that dust released by worn brake pads can be more toxic and harmful to health than gases emitted by burning fuel.