As the world gradually transitions to electric vehicles it is hoped that air quality will improve, as cars and vans no longer pump out fumes filled with harmful gases and tiny particles.
However, one aspect of car pollution that will not end with a transition to battery-powered cars is an environmental hazard scientists uncovered about a decade ago; microplastics from tyres.
Previously undetected, it is now an increasing concern due to its potential harm to the environment.
“There are very substantial quantities leaving the motorway, particularly when it rains, and substantial quantities going up in the air,” Prof Richard Thompson, director of the Marine Institute at the University of Plymouth, said speaking of the chemical particles that are left on the road from wear and tear on vehicle tyres.
director of the Marine Institute, University of Plymouth, UK
Prof Thompson, a researcher of microplastics said that until recent years, techniques to measure them often tended to miss those produced from tyre wear.
Material can either run off from roads ending up on nearby land, potentially polluting waterways and the seas, or enter the air and be a potential health hazard when it is breathed in.
Recent research from the Emirates found high levels of microplastics in the soil of parks in Al Ain, something that one scientist said wear from tyres could be contributing to.
Depending on the location, about three to seven per cent of particles in the air come from tyres, according to Prof Ad Ragas, who researches tyre microplastics at Radboud University in the Netherlands.
“This relative share is expected to increase due to the emission reduction of other PM10 sources and the increase in the average weight of vehicles – that is, electric vehicles,” he said.
“How big this increase will be is difficult to say exactly, but I would expect it to double over the next 10 years.”
Electric vehicles tend to be heavier because of the battery, with such vehicles tending to produce more tyre microplastics.
Higher quantities of particles in the air have been associated with increased rates of conditions such as heart disease and lung cancer. However, directly attributing specific health consequences to tyre particulate matter is very difficult.
Clearer associations have been drawn between the release of chemicals from tyre particles and the effects on wildlife.
Last year, several Native American tribes from the US asked the country's Environmental Protection Agency to ban a rubber preservative used in tyres called 6PPD.
Run-off from roads into rivers was thought to be harming salmon eaten by members of the tribes.
Tyre manufacturers said at the time that they were looking for alternatives but warned that a rapid ban could compromise safety and would have an economic effect.
The Tyre Industry Project (TIP), a project covering 10 tyre companies, said that tyre and road wear particles (TRWP) were an approximately half-and-half mixture of tyre and road material that, because of their density, were “expected to sink in water”.
“The peer-reviewed studies we have sponsored to date have found TRWP are unlikely to pose a significant risk to human health and the environment,” the organisation said.
“However, we are mindful of an evolving scientific understanding of TRWP, including some research that has reached different conclusions, so we continue to support independent research to improve the knowledge base.”
TIP cited research in France that found that more than 60 per cent of TRWP that went into freshwater was transported to wastewater treatment complexes. The organisation said that only about two per cent went into the air.
While the tyre industry has indicated that it would be difficult to remove 6PPD from tyres, researchers say it should be possible to make some changes to tyre composition without significant changes.
“It might be possible to achieve the same effects, the same outcome, with potentially less harmful chemicals,” Prof Thompson said.
He added that there was also wide variation between tyres in their wear rate, so some could be manufactured to be more durable and produce fewer particles. However, this may not benefit manufacturers.
“When I talk to the product designers, they say these issues about wear, they’re not in the brief,” Prof Thompson said.
“Unfortunately they’re going to have to be. We cannot continue with this business model of designing for function without any consideration for environmental implications. We need much greater extended producer responsibility.”
Tyre companies are trying to juggle “a delicate balance” between safety, the resistance that the tyre generates and wear, Prof Ragas said.
While the problem of tyre wear could increase as vehicles become heavier, some measures can be taken to lessen the issues.
For example, authorities can construct porous road surfaces that are common in the Netherlands. According to TNO, the Dutch Organisation for Applied Scientific Research, more than 80 per cent of the country’s roads are made from porous asphalt.
“The tyre wear runs into the road. The road is a sponge for tyre-wear particles. Dutch highways release a lot less tyre wear than other roads because we have open asphalt concrete,” Prof Ragas said.
“You can make gutters on the side of the road to capture the run-off … There can be a basin where the particles sink to the bottom.”
Motorists too can try to reduce the wear on their tyres and the microplastics they produce.
“One very simple measure is less driving,” Prof Ragas said. “And more controlled driving: the amount of wear strongly depends on driving behaviour.
“If you pull [away] very quickly your tyre will wear more, if you drive fast through a corner it will wear more. Some people say if we go to self-driving cars it could control much better the optimum behaviour of the car, so the tyre wears less.”
Keeping tyres properly inflated is also important as wear increases when air pressure is not at optimum.
Prof Thompson said that it was important that a more collaborative way of working between researchers and the tyre industry developed to encourage less harmful tyres.
“We don’t have enough planet left to wait for bright environmental scientists to raise awareness of a problem that’s probably been there for decades,” he said.
“We cannot go on with this business model of contaminating the environment and hoping nobody notices.”
