A new briefing paper from Imperial College London estimates that in 2021, 52% of all small particle pollution from road transport came from tires and brakes. The researchers, from Imperial College London’s Transition to Zero Pollution (TZP) initiative, warn that even though electric vehicles remove the problem of fuel emissions, we will continue to have a problem with particulate matter because of tire wear.

Six million tonnes of tire wear particles (TWP) are released globally each year, and in London alone, 2.6 million vehicles emit around nine thousand tonnes of tire wear particles annually. Despite this, research on the environmental and health impacts of tire wear has been neglected in comparison to the research and innovations dedicated to tackling fuel emissions.

Different shapes and sizes of tire wear particles imaged using scanning electron microscopy showing, relative to each other: (A) a PM₁₀ spherical tire wear particle; (B) a smooth, long and large tire wear particle; (C) a large uneven tire wear particle mass; and (D) a PM₁₀ tire wear sharp fragment resembling a crystal structure similar to silica. Scale bar of 10 μm = 0.01 mm (Mao, 2021) Tan et al.

The Imperial researchers say that the effect of new technologies on the generation and impact of tire wear should be a priority.

In the new briefing paper, a multidisciplinary group of Imperial experts including engineers, ecologists, medics, and air quality analysts have called for as much investment into tire wear research as there is for reducing fuel emissions—and for understanding their interactions.

Tire wear particles pollute the environment, the air we breathe, the water run-off from roads and has compounding effects on waterways and agriculture. Even if all our vehicles eventually become powered by electricity instead of fossil fuels, we will still have harmful pollution from vehicles because of tire wear.

We urge policymakers and scientists to embark on ambitious research into tire wear pollution to fully understand and reduce their impacts on biodiversity and health, as well as research to reduce the generation of these particles.

—Lead author Dr Zhengchu Tan

Where tire wear particles end up, illustrated with model values from Wagner et al., 2018.

As tires break down they release a range of particles, from visible pieces of tire rubber to nanoparticles. Large particles are carried from the road by rain into rivers, where they may leach toxic chemicals into the environment, whilst smaller particles become airborne and breathed in. They are small enough to reach into the deep lung.

These particles may contain a range of toxic chemicals including polyaromatic hydrocarbons, benzothiazoles, isoprene, and heavy metals such as zinc and lead.

Particulate matter from tire wear is a significant source of microplastics in rivers and oceans, and tire wear in cities could pose up to a four-fold greater risk to the environment than other microplastics.

While existing technological interventions, such as filters, and environmental policies could help to control our ecological footprint, there are huge gaps in our knowledge, understanding, and ability to forecast the impacts of tire wear pollution.

Our gaps in understanding make further research and development of new solutions vital so we can limit all types of vehicular pollution. Tire waste does not naturally degrade and instead builds up in the environment, and may interact with other pollutants as well as biological organisms.

—Co-author Dr Will Pearse

The impact of tire wear particles on human health is an increasing cause for concern, and the full long-term effects on our health urgently require more research, the ICL team says.

There is emerging evidence that tire wear particles and other particulate matter may contribute to a range of negative health impacts including heart, lung, developmental, reproductive, and cancer outcomes.

We are growing increasingly concerned by the impact of tire wear on human health. As some of these particles are so small they can be carried in the air, it’s possible that simply walking on the pavement could expose us to this type of pollution. It is essential that we better understand the effect of these particles on our health.

—Co-author Professor Terry Tetley

The researchers argue that reducing tire pollution should be seen as a critical part of making transport cleaner and more sustainable, alongside reductions in CO₂ and other exhaust emissions.

The report authors call for policymakers and scientists to investigate the complex problems related to tire-wear pollution, from the basics of wear-particle production, to understanding how these particles affect the health of people and the planet. Potential innovation solutions include particle capture technologies, new advanced materials, and disruptive business models that encourage different transport choices. These need to be coupled to clear policy and regulation and to a broader discussion around urban transport systems.

The research efforts, they say, should include the following:

• Establishing standardized ways of measuring environmental tire wear levels and their toxicity.

• Reducing harm to land and water species and in humans by tightening limits on the use of harmful components in tire materials.

• Launching new trials to better understand the short and long-term effects of different sized particles on the environment and human health.

• Efforts to better understand underlying wear mechanisms and to propose wear mitigation strategies such as reducing vehicle weight, using advanced driving techniques, and ensuring tire materials pass wear resistance regulations.

Resources

• Tan Z, Berry A, Charalambides M, Mijic A, Pearse W, Porter A, Ryan MP, Shorten RN, Stettler MEJ, Tetley TD, Wright S, Masen MA (2023) “Tyre wear particles are toxic for us and the environment.” Imperial College London (2023). doi: 10.25561/101707

• Mao, Y. (2021) “Tyre Thread Ageing Behaviour and Lung Toxicity of Tyre Wear Particles.” MSc. Imperial College London.

• Wagner, S., Hüffer, T., Klöckner, P., Wehrhahn, M., Hofmann, T. & Reemtsma, T. (2018) “Tire wear particles in the aquatic environment - A review on generation, analysis, occurrence, fate and effects.” Water Research 139, 83-100. doi: 10.1016/j.watres.2018.03.051