Big idea · a cause we're championing

What the Road Sheds

The biggest microplastic you've never heard of — and a tyre chemical that's killing salmon.

Every mile driven, tyres and brakes shed a fine dust of microplastics and metals. It blows into the air, washes off the road in the rain, and ends up in our rivers, the sea, the food chain — and us. It's one of the largest sources of plastic pollution on Earth, and almost nobody's talking about it.

The biggest microplastic you've never heard of

Tyres shed around 6 million tonnes of wear particles worldwide every year, and are estimated at roughly 45% of all the microplastics in our land and water — far more than straws or bags.
Hundreds of thousands of tonnes reach the ocean each year — through the air and washed off the land — making tyres one of the single largest inputs of plastic to the sea.
It's the invisible pollution: too small to see, so it never makes the headlines that a plastic bottle on a beach does.

~45%of microplastics in land & water estimated to come from tyre wear

6PPD‑qa tyre chemical that killed coho salmon within ~5 hours at road‑runoff levels

Non‑exhausttyres & brakes are now the dominant transport particle source as exhausts clean up

The chemical that's killing salmon

Tyres contain 6PPD, an additive that stops the rubber cracking. On the road it reacts with air to form 6PPD‑quinone — and when rain washes tyre dust off the tarmac into a river, that pulse of chemical is acutely lethal to salmon. In North America it's been pinned as the cause of mysterious mass die‑offs of coho salmon in urban streams. Researchers are now testing it on Atlantic salmon and brown trout — the very fish in Scotland's rivers.

Where roads meet salmon rivers

Moray and Speyside hold some of Scotland's greatest salmon rivers — the Spey, the Findhorn, the Lossie — and our trunk roads cross and hug them for miles. Every one of those crossings is a point where tyre and brake runoff can wash straight into salmon water in a downpour.

Red markers: major road × salmon‑river crossings in the Moray/Speyside area, where road runoff (tyre & brake particles, including 6PPD) can enter salmon waters — tap one for detail. Illustrative points on real crossings; rivers & roads © OpenStreetMap contributors.

Brake dust: the new tailpipe

As exhaust emissions fall, the pollution that remains is increasingly non‑exhaust — the dust from tyres and brakes, now the main source of traffic particles in many towns. Some brake pads shed particles carrying heavy metals that can be more toxic than diesel exhaust. And there's a twist: electric cars are heavier, so cleaning up the tailpipe can mean more tyre and brake wear unless we design for it.

It ends up in us

These particles don't vanish. They're eaten by the small creatures at the bottom of the food web and concentrate as they move up it — into the fish and shellfish we eat, and into us. The long‑term health picture is still being worked out, but the direction of travel is clear enough to act on.

What we're asking for

Regulate tyre wear — treat tyre‑particle and 6PPD pollution like the major emission it is, with standards and testing, and back the moves already starting in the UK and EU.
Design out the harm — safer tyre chemistry (6PPD alternatives), lower‑wear tyres, and brake and road‑runoff capture where roads meet rivers.
Count it honestly — measure and publish non‑exhaust pollution, not just what comes out of the exhaust pipe.

What we can do here

Citizen science — a road‑runoff layer for EnviroWatch so people can log outfalls and runoff points near our burns and rivers, feeding our River Health Monitor.
A local demonstrator — a rain garden / SuDS filter that catches road runoff before it reaches a watercourse, showing a fix that any community could copy.
Raise the alarm — because the first job is simply getting people to see the pollution that's hiding in plain sight.

We keep this evidence‑led and non‑partisan. We're not anti‑car — we're for tackling a large, overlooked pollution source honestly, so there are living rivers and safe food for the future.

See it on the map ↗ Sewage in our rivers ↗ Get involved ← All big ideas

Sources: tyre wear ~6 Mt/yr and ~45% of land‑and‑water microplastics, and among the largest ocean inputs (research syntheses, incl. Forbes/The Conversation 2024–25, and peer‑reviewed reviews); 6PPD → 6PPD‑quinone acute salmon mortality (Tian et al., Science 2020; acute‑toxicity testing on Atlantic salmon & brown trout, 2023; US EPA 6PPD‑q programme); non‑exhaust emissions now the main transport PM source, high‑copper brake pads and heavy‑metal content (University of Southampton; PMC reviews of brake/tyre wear health effects). Salmon‑river road crossings are indicative points on real Moray/Speyside crossings. Figures indicative, from public reporting, September 2026.