For decades, concerns about automobile pollution have focused on what comes out of the exhaust. Today, researchers and regulators say, we need to pay more attention to toxic emissions from tires as vehicles travel on the road.
At the top of the list of concerns is a chemical called 6PPD, which is added to rubber tires to help them last longer. As the tires wear down on the pavement, the 6PPD is released. It reacts with ozone to become a different chemical, 6PPD-q, which can be extremely toxic – so much so that it has been linked to repeated fish kills in Washington state.
The tire problems don’t stop there. Tires are primarily made from natural rubber and synthetic rubber, but they contain hundreds of other ingredients, often including steel and heavy metals such as copper, lead, cadmium and zinc.
As car tires wear, the rubber disappears in the form of particles, visible to the naked eye and microparticles. Tests by a British company, Emissions Analytics, found that a car’s tires emit 1 trillion ultrafine particles per mile driven, or between 5 and 9 pounds of rubber per internal combustion car per year.
And what’s in these particles is a mystery, because tire ingredients are owners.
“These tires contain a chemical cocktail that no one really understands and is kept highly confidential by tire manufacturers,” said Nick Molden, CEO of Emissions Analytics. “We find it hard to imagine another consumer product so widespread around the world and used by virtually everyone, where so little is known about what it contains.”
Regulators have only begun to tackle the problem of toxic tires, although action has been taken on 6PPD.
The chemical was identified by a team of researchers, led by scientists from Washington State University and the University of Washington, who were trying to determine why coho salmon returning to area streams Seattle to spawn were dying in large numbers.
Working for the Washington Stormwater Center, scientists tested some 2,000 substances to determine which was causing the deaths, and in 2020 they announced they had found the culprit: 6PPD.
The Yurok Tribe of Northern California, along with two other West Coast Native American tribes, have asked the Environmental Protection Agency to ban the chemical. The EPA said it is considering new rules governing the chemical. “We cannot stand idly by while 6PPD kills the fish that feed us,” Joseph L. James, chairman of the Yurok Tribe, said in a statement. “This deadly toxin has no place in any salmon watershed.”
California has begun taking steps to regulate the chemical, last year classifying tires containing it as a “priority product,” requiring manufacturers to research and test replacement products.
“6PPD plays a critical role in tire safety on California roadways and, at this time, there is no widely available safer alternative,” said Karl Palmer, deputy director of the Department of Control. state toxic substances. “For this reason, our framework is ideally suited to identify alternatives to 6PPD that ensure the continued safety of tires on California’s roadways while protecting California’s fish populations and the communities that depend on them.”
The American Tire Manufacturers Association says it has mobilized a consortium of 16 tire manufacturers to conduct an analysis of alternatives. Anne Forristall Luke, president and CEO of USTMA, said this “will provide the most effective and comprehensive review possible to determine whether a safer alternative to 6PPD in tires currently exists.” .
Molden, however, said there was a catch. “If they don’t do an investigation, they’re not allowed to sell in the state of California,” he said. “If they investigate and don’t find an alternative, they can continue selling. They don’t need to find a substitute. And today there is no alternative to 6PPD.”
California is also considering a request from the California Stormwater Quality Association to classify tires containing zinc, a heavy metal, as a priority product, forcing manufacturers to seek an alternative. Zinc is used in the vulcanization process to increase the strength of rubber.
On the other hand, with regard to tire particles, no measures have been taken, even if the problem is worsening with the proliferation of electric cars. Due to their faster acceleration and higher torque, electric vehicles wear tires faster and emit about 20% more tire particles than the average gasoline car.
A recent study in Southern California found that tire and brake emissions in Anaheim accounted for 30 percent of PM2.5, a small-particle air pollutant, while tailpipe emissions accounted for 19 percent. Tests by Emissions Analytics have found that tires produce up to 2,000 times more pollutant particles by mass than exhaust pipes.
These particles end up in water and air and are often ingested. Ultrafine particles, even smaller than PM2.5, are also emitted from tires and can be inhaled and travel directly to the brain. New research suggests that microparticles from tires should be classified as a pollutant of “high concern”.
In a report published last year, researchers from Imperial College London said the particles could affect the heart, lungs and reproductive organs and cause cancer.
People who live or work along roads, often with low incomes, are exposed to more toxic substances.
Tires are also a major source of microplastics. More than three-quarters of microplastics released into the ocean come from synthetic rubber in tires, according to a report from the Pew Charitable Trusts and British company Systemiq.
And there are still many unknowns about tire emissions, which can be particularly complex to analyze because heat and pressure can transform tire ingredients into other compounds.
An outstanding research question is whether 6PPD-q affects people and what health problems, if any, it might cause. A recent study published in Environmental Science & Technology Letters found high levels of the chemical in urine samples from a region in southern China, with the highest levels seen in pregnant women.
The discovery of 6PPD-q, Molden said, has sparked new interest in the health and environmental impacts of tires, and he expects an abundance of new research in the years to come. “The pieces of the puzzle are coming together,” he said. “But it’s a thousand-piece puzzle, not a 200-piece puzzle.”
This article was produced by KFF Health Newsa national newsroom that produces in-depth journalism on health issues and is one of the main operational programs of KFF — the independent source for health policy research, polling and journalism. KFF Health News is the publisher of California Health Linean editorial service independent of California Health Care Foundation.
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