Forget Dieselgate — a bigger emissions problem hides in plain sight
Tyres release many more polluting particles than an exhaust pipe but rarely come under scrutiny
Eat lettuce and you are eating tyres. Your diet may still be vegetarian, but not as green as you think.
We know this from a recent study that traced how a particular chemical was drawn up through the roots and into the leaves of a lettuce plant as it grew. This chemical is overwhelmingly found in vehicle tyres.
As we drive, our tyres wear down and release invisible particles that we inhale and ultimately ingest. Strikingly, the rate of release of these particles is almost 2,000 times greater than the mass of particles from a modern exhaust pipe. It looks likely, then, that these apparently mundane yet economically vital and technically sophisticated products are a source of pollution that will make Dieselgate — the exhaust emissions cheating scandal of 2015 — look minor. The difference? No rules are being broken, yet current US and EU polices promoting battery electric vehicles through subsidies are set to make the problem worse.
Tyres work hard. They are the only points of contact between a vehicle — which often weighs more than two tonnes — and the road. Those on battery vehicles, which often weigh an extra half tonne compared with conventional vehicles, are usually even bigger and wider to compensate. Add to that the sharper acceleration potential of battery vehicles, and you have a recipe for up to 20 per cent higher tyre emissions.
Very soon, if not already, the total tyre emissions from all vehicles in the US will exceed exhaust mass emissions. By the time sales of new internal combustion engine vehicles are banned in 2035, tyre emissions will be many times higher. We shouldn’t stop electrification, but we should recognise that battery vehicles are far from emission free. Car weight matters when it comes to the climate.
When we think of products of strategic national significance, we rarely consider tyres. Without them, though, economies would hardly function. Cement kilns are powered by burning tyres as cheap fuel. Asphalt roads contain pieces of them to reduce noise. Clever tyre formulations can deliver lower rolling resistance to vehicles, giving a carbon dioxide emissions benefit to the manufacturer. Even football pitches often rely on ground up old tyres. With their use, however, come adverse environmental impacts, such as deforestation in Asia, the deaths of salmon as a result of ingesting road run-off and lives lost to cancer from football pitch fumes.
Leading players in the tyre industry are already working to mitigate these effects, in advance of looming regulation. Modifying the ingredients and formulas for tyre-making can reduce the potential toxicity of particles released, although this puts the price up. When those tyres are worn out, drivers often replace them with the cheapest option. Therefore, the electrification of cars must come hand in hand with the regulation of replacement tyres.
European authorities are racing to develop the “Euro 7” regulation, part of which seeks to reduce tyre emissions on all vehicles by limiting the rate of rubber loss through abrasion, based on a standardised test. The flaw in the European approach, however, is that it only focuses on reducing the rubber mass shed by tyres, with little consideration for how to control the quality of replacement tyres, and of the chemical composition. The price of lower wear may be greater toxicity.
Tyres are all around and inside us — yet none carry an ingredients list. If there is any doubt about their potential damage, consider the Chinese subjects of a recent peer-reviewed scientific study, who had their urine tested. An average of 709 nanograms of the very same tyre preservative found in the lettuce were passed per person daily. That may seem a tiny amount, but zero nanograms would be preferable, given what we know about the toxic effects in fish. To avoid our decarbonisation mission backfiring, we must take the tyres problem seriously.