Tyres: the microplastic source nobody talks about

Here is a microplastic source with no packaging, no straw and no guilt-trip marketing campaign attached: the four rubber rings under your car. Every kilometre, tyres grind off a little tread. That dust goes into the air, into gutters, into rivers and, it turns out, into the gills of salmon.

It gets less attention than plastic bags because there’s nothing to pick up off a beach. The tyre is simply a little lighter at the end of each trip, and the missing rubber is somewhere else.

How much tyre is ending up in the environment?

A lot, and the estimates are rough. The figures below are models built on tyre sales and distance driven, not direct counts.

• A widely cited 2017 review estimated tyre wear at 0.23 to 4.7 kg per person per year, with a global average of 0.81 kg. The same review estimated tyres account for 5–10% of the plastic reaching the oceans and 3–7% of fine particulate air pollution (PM2.5).
• A 2017 report for the International Union for Conservation of Nature (IUCN) modelled “primary” microplastics, the ones released already tiny rather than from bigger items breaking down. It estimated 1.5 million tonnes a year reaching the ocean, with synthetic textiles the largest share at 34.8% and tyres next at 28.3%. That counted only synthetic rubber. Counting the natural rubber in tyres too, tyres made up 46.2%. Road runoff was the main route to the sea, at 66%.
• A 2020 modelling study in Nature Communications put global tyre wear particle emissions at about 2,907 thousand tonnes a year, and estimated that around a third of the coarse airborne particles end up deposited in the ocean.
• Scientists at the European Commission’s research arm describe tyre microplastics as the major contributor of unintentionally released microplastics in all environmental compartments.

So “biggest” depends on what you count. For the ocean, the IUCN model put clothing slightly ahead. For everything that comes off products by accident, onto land, into air and water, tyres are at or near the top. We cover the clothing side in our piece on synthetic clothes.

Is tyre rubber even “plastic”?

This is where the argument starts. Tyres are mostly synthetic rubber (styrene-butadiene, made from oil, makes up about 60% of the polymer in tread), blended with natural rubber, carbon black, oils and dozens of additives. Rubber is an elastomer, not a thermoplastic like the polyethylene in a bag.

Researchers have not agreed on a definition. A 2019 paper trying to standardise the field noted that for microplastics, the materials to be included are under debate. The 2017 tyre review takes the broad view: rubber is also considered a class of plastic, and thermoplastics, thermosets and elastomers can all shed microplastics. The IUCN report hedged by counting only the synthetic rubber.

The tyre industry prefers its own term, “tyre and road wear particles”. There’s a physical reason for it: what comes off the road is rubber fused with road grit. One study by authors at a consultancy that has done much of the industry’s tyre-particle research found these particles are roughly half tread rubber and half road mineral by mass, and detected them in 97% of 149 river sediment samples across France, Japan and the US.

Our view: a fossil-fuel polymer, compounded with synthetic chemicals, ground into tiny persistent particles, belongs in the conversation whatever it’s called. The label matters less than the result.

The salmon mystery, and the tyre chemical that solved it

For years, something was killing coho salmon in Seattle’s creeks. After habitat restoration in the 1990s, biologists noticed returning adults swimming erratically, gaping and losing balance, then dying within hours, often before spawning. Daily surveys of one urban stream from 2002 to 2009 found 60–100% of each autumn’s run dying prematurely, compared with under 1% in a non-urban stream. The researchers ruled out low oxygen, disease and pesticides, and concluded the cause was an as-yet unidentified toxic chemical in urban runoff.

In 2021, a US research team named it in Science. The culprit was 6PPD-quinone, a transformation product of 6PPD, an antioxidant used in tyres worldwide. 6PPD is added to protect rubber from cracking by reacting with ozone in the air before the rubber does. It has been in tyres since the 1960s. The trouble is what it turns into.

The correction that made it worse

The 2021 paper reported 6PPD-quinone in roadway runoff and creeks at under 0.3 to 19 micrograms per litre, against a lethal concentration for half of exposed fish (LC50) of 0.8 micrograms per litre.

Then the same group corrected itself. Once a commercial reference standard became available, they found their in-house standard had skewed earlier measurements. Re-testing with the commercial standard, they put the LC50 at 95 nanograms per litre, about 8.3 times lower than first reported. They also said real-world concentrations were probably lower than first reported. The overall conclusion still held, and the chemical turned out to be more toxic than anyone had thought: the authors called it “very highly toxic” to aquatic life.

That’s how science is supposed to work, and the correction is worth knowing about if you see the older figures quoted.

Coho aren’t the only fish affected, but species differ hugely. A 2022 study found brook trout and rainbow trout also died at around 0.6 to 1 microgram per litre, while Arctic char and white sturgeon showed no deaths at up to 14.2. In 2024 the US EPA published a non-binding acute freshwater screening value for 6PPD-quinone of 11 nanograms per litre, which states and tribes may use in water quality programmes.

Is it in us?

Yes, at least in the people who’ve been tested. Whether it matters is unknown, and this is where we’ll be careful.

The first human study measured urine from 150 people in South China and detected 6PPD-quinone in 60–100% of samples, depending on the group. Pregnant women had the highest median levels (2.91 ng/mL), well above other adults (0.40) and children (0.076). A 2024 study found that in mice almost all 6PPD-quinone was broken down within 24 hours, and confirmed two of its metabolites in human urine. So urine tests for the parent chemical may miss some exposure.

A 2026 study of 368 people in South China linked higher urinary 6PPD-quinone with thyroid nodules, with odds more than doubled across exposure levels. That’s an association in a case-control study. It doesn’t show the chemical causes nodules.

EPA’s own review of the evidence, published in 2024, is a fair summary. It said the human biomonitoring studies are few, mostly from Asia and often small. It cited a study of 13 Parkinson’s patients and 11 controls that found 6PPD-quinone levels in spinal fluid about twice as high in patients, a small association that doesn’t show cause, and mouse studies showing liver and organ effects at high doses. It concluded that more research is needed to identify human health effects. It also noted that 6PPD itself is a known skin sensitiser and is classified by the European Chemicals Agency as a presumed reproductive toxicant (category 1B).

The honest bottom line: there’s clear evidence of exposure, early animal evidence of harm and no evidence yet of harm in people at real-world levels. For what’s known about breathing in road and household dust generally, see our piece on microplastics in dust and indoor air.

What regulators have done

United States: a petition granted, then a long wait

On 1 August 2023, Earthjustice, acting for the Yurok Tribe, the Port Gamble S’Klallam Tribe and the Puyallup Tribe of Indians, petitioned EPA to ban the manufacture, processing, use and distribution of 6PPD in tyres under the Toxic Substances Control Act. For these tribes, salmon are food, culture and treaty rights, not an abstraction.

EPA granted the petition on 2 November 2023. Granting it didn’t mean a ban. EPA committed to two things: publishing an “advance notice of proposed rulemaking” (a formal request for information) by autumn 2024, and issuing a rule by the end of 2024 requiring 6PPD makers and importers to hand over unpublished health and safety studies. It said it could not commit to a timeframe or outcome.

EPA did both on time. The advance notice was published on 19 November 2024, and the comment period was extended to 24 March 2025. Since then, things have slowed. The deadline for companies to submit those unpublished studies on 6PPD and 6PPD-quinone has been pushed back three times and now sits at 21 May 2027, during what EPA calls its “ongoing reconsideration” of the reporting rule. As of October 2026, the Federal Register shows no proposed rule on 6PPD itself.

Three years after the petition, the studies the industry holds are still not due, and no rule is on the table.

California: the industry asked to be regulated

Here the industry deserves some credit. The US Tire Manufacturers Association (USTMA) says it asked California’s Department of Toxic Substances Control in December 2020 to review 6PPD in tyres. In October 2023, California listed motor vehicle tyres containing 6PPD as a “Priority Product” under its Safer Consumer Products rules. That listing requires manufacturers selling into California to study alternatives.

A consortium of more than 30 tyre makers filed a first-stage alternatives analysis. It screened candidates including other chemicals in the same family, and California accepted it in August 2024. The second-stage report, which has to confirm whether any replacement actually works, is due on 1 October 2029, according to USTMA.

The industry’s position is that 6PPD does an essential safety job, stopping tyres from cracking and failing, and that no commercially available alternative matches it yet. EPA’s notice reached a similar conclusion: no effective alternative has been identified so far. That’s a real constraint; nobody wants tyres that blow out. But a 2029 deadline to finish studying a replacement, for a chemical identified as a salmon killer in 2021, is slow going.

Washington state tried to push harder. A 2026 bill to phase out 6PPD and “regrettable substitutes” in tyres passed two House committees but stalled in the House Rules Committee without a floor vote.

Europe: the first limits on tyre wear itself

The EU went after the wear rather than the chemical. Its Euro 7 vehicle emissions regulation, adopted on 24 April 2024, is the first law anywhere to set limits on how much tyres may abrade. It applies to new types of car tyres from 1 July 2028, van and light-truck tyres from 1 April 2030, and heavy-truck tyres from 1 April 2032. From 1 July 2030, non-compliant car tyres can’t be newly sold, although existing stock can be sold until 30 June 2032. The law ties this to the EU’s goal of cutting microplastic releases by 30% by 2030.

Euro 7 didn’t write the actual numbers itself; it left them to the UN body that harmonises vehicle rules. That body adopted UN Regulation No. 186 on car tyre abrasion in June 2026. Under its text, countries applying it can require first-stage approval for new car tyre types after 30 June 2028 and for all types after 30 June 2030. The UN’s tyre task force estimated the first limits would cut overall tyre abrasion by more than 10% and exclude around 30% of the high-abrasion tyres sold today in the European and Japanese markets.

Ten percent is a start, not a fix. It’s still more than any other jurisdiction has done.

Do electric cars make it worse?

This is the argument you’ll hear at barbecues, usually from someone who doesn’t want an EV. It’s partly right.

The case that EVs shed more: Tyre wear rises with weight, and batteries are heavy. The 2017 review estimated electric versions of common cars were about 20% heavier and, assuming wear rises in step with weight, would shed about 20% more tyre particles. A 2026 study comparing electric and petrol versions of the same car on the road measured 7.6 mg of tyre and road wear per vehicle-kilometre for the EV versus 5.8 for the conventional car. The error bars were wide, though, and it was a single car model.

The case that it’s roughly a wash: EVs have no tailpipe, and regenerative braking means they use friction brakes much less, so brake dust falls. In the same 2026 study, brake-wear particles made up 20.5% of the conventional car’s road particles but only 7.1% of the EV’s. A University of Birmingham analysis concluded that, overall, switching to EVs means only modest changes to total local particle emissions compared with a modern petrol or diesel car, and that the result depends heavily on how much the EV relies on regenerative braking.

So an EV doesn’t solve tyre pollution, and a very heavy one can make it a bit worse. But the big variable is weight, not the fuel. A two-tonne petrol SUV wears tyres too. The EU is aware of the issue: Euro 7 explicitly says the characteristics of battery and plug-in vehicles should be evaluated when tyre limits are set.

What you can actually do

Tyre wear is mostly a policy and engineering problem: tyre formulation, vehicle weight, road design and stormwater treatment. Here’s what’s in your control, ranked by how strong the evidence is.

1. Drive fewer kilometres. This is the strongest lever. Tyre wear is measured per kilometre driven (the 2026 comparison found 5.8 to 7.6 mg per vehicle-kilometre), so fewer kilometres means less rubber on the road. Walking, cycling, public transport and combining trips all cut it. A bus wears its tyres too, but that wear is shared across many passengers; that’s our reasoning, not a measured result.
2. Choose a lighter vehicle. Wear rises with weight. If you’re buying, the smallest car that does the job beats a heavy SUV, electric or not.
3. Keep tyres properly inflated. The US government’s fuel economy site says properly inflated tyres are safer and last longer, and improve mileage by 0.6% on average. A tyre that lasts longer has lost less rubber per kilometre. To be clear, we found no study measuring tyre particles against inflation directly, so this is a sensible inference, not a proven effect.
4. Drive smoothly. The 2017 review lists driving speed and style among the factors that shape tyre wear, and suggests gentle acceleration, slower cornering and fewer hard stops reduce it. The size of the effect hasn’t been well quantified, but it costs nothing.
5. When tyres are on sale with an abrasion rating, use it. From 2028 in the EU, the worst performers start leaving the market. Elsewhere, nobody is labelling tyre wear yet.
6. Push for the policy. The big wins are a safer replacement for 6PPD, stormwater filtering in salmon streams, and abrasion limits beyond Europe. EPA’s 6PPD docket is public, and state legislators in Washington and California have shown they’ll act when pushed.

What won’t help much: worrying about the particles on your own street. There’s nothing to filter at home, and the evidence on personal health risk is too thin to justify anxiety. Save that energy for the regulators. For how we judge evidence and claims, see our methodology, and for how scientists measure this stuff, see how microplastics are measured.