February 14, 2025

expert reaction to study of impact of emissions from brake pads on lung cells compared to diesel emissions

A study published in Particle Fibre and Toxicology compares the impact of emissions from break pads and diesel on lung cells. 

Dr Robert Hynds, Group Leader, Epithelial Cell Biology in ENT Research (EpiCENTR) Group, UCL GOS Institute of Child Health, said:

“This is a well-conducted research study that adds to growing evidence that the effects of fine particulate matter are variable depending on its composition. The study has potential implications for both vehicle design and emissions policy.

“The use of human alveolar cells is a real advantage of the study and, although it is difficult to recreate real-world human exposure to particulate matter in the laboratory, cell culture studies such as these provide an important window into the effects of particulates in the lung.”

Prof Anna Hansell, Professor of Environmental Epidemiology, University of Leicester, said:

“Air pollution has been reducing in recent decades and will reduce further as we continue to move away from fossil fuels to cleaner forms of energy. However, this paper reminds us that we will still have transport-related air pollution, even from emission-free vehicles. It shows that particulates from brake and tyre wear from both combustion-engine and electric vehicles have toxic impacts on human cells. Further studies, taking into account exposure levels, will help determine actual risks to human health and ecological systems.

“The study concentrated on impacts on health related to the metal content of particulates from brake wear. More studies are needed to look at health risks from other components of brake wear and also tyre wear.”

Dr Antonis Myridakis, Lecturer in Environmental Sciences, from Brunel University of London, said:

“This study provides a thorough and systematic investigation into the toxicological effects of brake-wear particulate matter (PM2.5), with a particular focus on copper-enriched brake dust. The research utilises an interdisciplinary approach to examine how different brake pad compositions impact alveolar epithelial cells. By comparing these effects to diesel exhaust PM, the study contributes to the growing body of evidence that non-exhaust emissions represent an increasingly significant yet underregulated source of airborne pollutants.

“The press release accurately reflects the main conclusions of the study, emphasising that copper-enriched brake-wear PM induces significant oxidative stress, inflammation, and metabolic reprogramming in lung cells, surpassing even the effects of diesel exhaust PM. This aligns with established evidence regarding the role of transition metals in PM toxicity, but also introduces new insights into the pseudohypoxic activation of hypoxia-inducible factor (HIF) signalling, which has been implicated in chronic lung diseases and cancer.

“The research is well-executed and effectively accounts for potential confounders. However, it is important to highlight that is an in vitro model study, which, while invaluable for mechanistic studies, may not fully capture the complexity of real life exposure scenarios. Future studies should consider animal models or real-world epidemiological correlations to confirm these findings.

“The study’s implications are significant, highlighting a major gap in air quality regulation. While diesel exhaust emissions are heavily legislated, non-exhaust PM remains largely unregulated despite its growing contribution to urban air pollution. Focusing solely on PM mass concentrations in regulations may be insufficient, as the composition of PM, particularly its metal content, is a critical determinant of toxicity.”

Dr Ian Mudway, Senior Lecturer at School of Public Health – Faculty of Medicine, Imperial College London, said:

“While the paper’s research appears sound, and the researchers have a strong track record, it’s premature to conclude that non-exhaust emissions from traffic, specifically brake pad wear, are worse than diesel exhaust. Too many variables remain uncontrolled: brake disc types (a highly varied category), diesel exhaust particle composition, and chosen endpoints, among others. The paper’s core message is that we shouldn’t assume all traffic-related pollution originates from exhaust and should not discount abrasion sources. It is important that brake wear and tire wear is part of the discussion about traffic related pollution. While this paper focuses on brakes, tire wear and road dust resuspension should also be considered. This has significant policy implications, as it suggests that policies solely targeting exhaust emissions will not fully mitigate the risks of traffic-related pollutants. Although regenerative braking may partially offset brake wear, it, along with tire wear, will remain a concern even with vehicle electrification. This is reflected in the upcoming Euro 7 regulation (2026), which, for the first time, introduces standards for tire and brake wear emissions, acknowledging their contribution to air pollution and potentially driving innovation in tire and brake technology.”

Prof Roy Harrison, Professor of Environmental Health, University of Birmingham, said:

“Non-exhaust particles, such as those from the wear of brakes and tyres now well exceed those from engine exhaust, and there is consequently a strong interest in the relative toxicity of the various particle types.  The authors of this paper apply a battery of toxicological tests to demonstrate the toxicity to lung cells of brake wear particles, and especially those containing copper.  In some tests, the brake wear appears to be more toxic than diesel exhaust particles.  While there must be some reservations over the way that the particles were presented to the cells in this study (collected on a filter and then suspended in water, rather depositing directly from the air), which may affect their toxicity, several studies have now demonstrated toxicity associated with brake wear particles.  As yet, studies in human populations have not shown exceptional toxicity, just that normally associated with exposure to fine particles.  The good news is that emissions of brake wear particles from an electric vehicle are much less than from conventional petrol and diesel vehicles due to regenerative braking.”

‘Copper-enriched automotive brake wear particles perturb human alveolar cellular homeostasis’ by James G H Parkin et al. was published in Particle and Fibre Toxicology at 06:00 UK time on Friday 14^th February.

DOI: 10.1186/s12989-024-00617-2

Declared interests

Dr Robert Hynds: I don’t have any interests to declare.

Prof Anna Hansell: I do not have conflicts of interest to report. I am Chair of the Committee on the Medical Effects of Air Pollution (COMEAP), but comments here are in a personal capacity as Professor in Environmental Epidemiology at the University of Leicester. 

Dr Antonis Myridakis: None

Dr Ian Mudway: No declarations of interest. I have worked on a USA Health Effects Institute study on non-exhaust emissions where one of the authours of this paper was on the Steering Committee as an independent advisor. I have also published a paper in 2020 comparing the toxic effects of diesel and brake abrasion dust, which demonstrated very similar responses (doi: 10.1039/c9mt00253g).

Prof Roy Harrison: He receives research funding from UKRI and EU Horizon programmes.  He is a member of the Defra Air Quality Expert Group and Deputy Chair of the DHSC committee on the Medical Effects of Air Pollutants, but writes in a personal capacity.  He has no conflict of interest with respect to this research study.