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A woman walks on an overpass in Beijing’s central business district on November 14. Tyres shed trillions of toxic microparticles, making up at least 10 per cent of the microplastics in the ocean, and small enough to interact with our cells, causing increasing concern to health scientists and environmentalists. Photo: AFP
Opinion
Outside In
by David Dodwell
Outside In
by David Dodwell

We’re choking on toxic tyre dust – we just didn’t realise it

  • Modern tyres are a chemical cocktail and scientists are realising that the microparticles they shed are actually quite harmful – to wildlife, the food chain and us
David Dodwell
David Dodwell
Why you can trust SCMP

Just when we thought we were getting on top of carbon dioxide and other exhaust emissions from our petrol-guzzling cars, along comes a newly noticed source of toxins from the world’s roughly 1.5 billion road vehicles.

And with exquisite perversity, it looks like battery-powered vehicles only make the problem worse. This time, the problem comes not from the fuel we burn but from our car tyres – and the way the rubber hits the road.

According to UK research group Emissions Analytics, an average car’s tyres emit over 1 trillion microparticles for every kilometre they travel. Over a car tyre’s average life, it sheds about 30 per cent of its tread – which amounts to about 1.5 million tonnes of tyre dust every year, according to a 2017 study.

We get more tyre dust with more cars, longer distances driven, more aggressive driving, underinflated tyres, faster acceleration power and heavier vehicles – and electric vehicle batteries add around half a tonne to the weight of the average EV.

As an Imperial College London report published in February this year put it, “by simply walking on the pavement we are exposed”.

This might not have been a problem back in 1888 when John Boyd Dunlop produced the first practical pneumatic tyre. His were made of natural rubber, and the tricycle he improved to protect his son from getting a sore bottom as he cycled to school along Belfast’s cobbled streets was hardly travelling at speeds likely to generate tyre dust.

Tyres at a Kuala Lumpur plant on February 8, 2002. Industrialised synthetic rubber was introduced in the 1930s but 20 years ago, tyre makers still consumed about 70 per cent of the world’s natural rubber, from the sap of trees grown mainly in Thailand, Indonesia, and Malaysia. Photo: Reuters
These days, natural rubber accounts for only 19 per cent of the average tyre. The rest is a complex and volatile cocktail of synthetic rubber, comprising butadiene, styrene and halobutyl rubber, as well as polymer fibre belting, reinforced high carbon steel wire and fillers such as carbon black or silica.

As Emissions Analytics CEO Nick Molden notes: “You’ve got a chemical cocktail in these tyres that no one really understands and is kept highly confidential by the tyre manufacturers.”

These ingredients provide a smoother ride, better road grip and longer lasting tyres – but also shed trillions of toxic microparticles that are of increasing concern to health scientists and environmentalists.
A research team at the Open University of the Netherlands estimated in 2017 that tyres account for 10 per cent of the microplastic waste found in the world’s oceans. The Imperial College report noted that an estimated 6 million tonnes of “tyre wear waste” are being shed every year, including nano-sized “ultrafine particles” “small enough to interact with our cells” being “abundantly released”.

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Cambodian artist transforms old tyres into giant King Kong

Cambodian artist transforms old tyres into giant King Kong

The exact amount of tyre dust, it said, depends on “contact interaction”: the weight of a vehicle, quality of its tyres, the driving style and road conditions. Rough roads generated larger particles, and smoother roads produced more micro-particles.

Around 45 per cent of the tyre dust stayed close to the road, but 55 per cent was dispersed into the wider environment – with 82 per cent of this carried off by water into drainage systems and our oceans.

Especially damaging, the report said, are toxic chemicals such as polyaromatic hydrocarbons, benzothiazoles and isoprene, as well as lead and zinc, which are having a “devastating impact” on wildlife and the food chain – and potentially on us. As Molden puts it, rather floridly: “Eat lettuce and you are eating tyres.”
Eating lettuce may not be as healthy as you think. Photo: Getty Images

While we pat ourselves on the back for our progress in reducing the toxic harm of exhaust emissions as we shift from fossil fuels to battery-powered vehicles, it has until recently not dawned on most of us that our tyres are inflicting as much harm, perhaps even more.

“When we think of products of strategic national significance, we rarely consider tyres,” Molden writes. Yet “the rate of release of these [tyre] particles is almost 2,000 times greater than the mass of particles from a modern exhaust pipe”.

With the world’s car population growing by more than 5 per cent last year to reach an estimated 1.5 billion, there is a pressing need for action.

China has the largest population of motor vehicles in use (about 415 million), but that amounts to less than one car for every three people, far short of the concentration of car ownership in North America, where there are 71 cars for every 100 people.

So most of the future growth in car use is likely to be in Asia, which means our region faces the most acute challenges in disposing of worn tyres, and mitigating the rise in the toxic impact of tyre dust.

Heavy traffic during the morning rush hour in Jakarta, Indonesia, on August 22. Photo: Bloomberg

Scientists are pointing firstly to an urgent need for more accurate and detailed monitoring of tyre dust emissions. Then, they are investigating the use of electrostatic plates fixed to car tyres (which might filter 60 per cent of emitted particles out of the air), and roadside “rain gardens” that can capture emitted particles as they are swept off in rainfall run-off.

They are calling for more transparency from tyre manufacturers, both to reveal the chemicals that go into each tyre and to reduce the chemicals they use. They are calling for more use of public transport and for lighter cars. And, of course, we don’t need scientists to tell us we need fewer potholed roads, fewer aggressive drivers and more fully inflated tyres.

David Dodwell is CEO of the trade policy and international relations consultancy Strategic Access, focused on developments and challenges facing the Asia-Pacific over the past four decades

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