WASHINGTON, July 7 — The rubber that wears off your tires as you drive isn’t just disappearing. It’s undergoing a chemical transformation with a common air pollutant, creating a compound that scientists have linked to toxic effects in fish. The process is a concrete example of how different forms of pollution can interact in ways that compound environmental problems.
Here’s the chemistry in plain terms. Tire manufacturers add a chemical called 6PPD to rubber to keep it from cracking — it acts as an antioxidant and, specifically, an antiozonant.
But as tires wear down on pavement, tiny particles of rubber containing 6PPD are shed onto roads. Those particles then encounter ozone — O3 — which is itself a common air pollutant formed when sunlight reacts with pollutants like nitrogen oxides from vehicle exhaust. The reaction between 6PPD and ozone produces a new chemical: 6PPD-quinone, or 6PPD-Q.
This transformation product has been documented in scientific studies since at least 2020, when researchers first identified it as a toxicant to coho salmon. The practical upshot is that a chemical designed to protect tires is being converted into something far more concerning once it leaves the road.
How the reaction happens
The conversion of 6PPD into 6PPD-Q occurs on road surfaces and in the air itself. The reaction rate isn’t fixed — it depends on several factors including temperature, how much ozone is present, and the size of the tire particles. Once formed, 6PPD-Q is persistent in the environment.
It doesn’t break down quickly. The chemical can be transported via runoff into waterways — which is how it reaches fish like coho salmon.
There’s also potential for it to become airborne, meaning the compound could travel beyond the immediate roadside environment.
A direct link between emissions and tire pollution
What makes this process noteworthy is the direct link it establishes between two forms of vehicle-related pollution. The exhaust from your car produces nitrogen oxides, which help form ozone. That ozone then reacts with the rubber particles your tires shed.
The result is a chemical pollutant that wouldn’t exist in the same way if only one of those pollution sources were present. The so-what for ordinary drivers is this: your tires are not inert.
They are chemically active materials that interact with the environment around them. The same ozone that can aggravate human lungs is also transforming tire debris into something that can harm aquatic life.
What to watch next
Researchers continue to study how widespread 6PPD-Q contamination is and what concentrations pose risks to different species. The chemical’s persistence means it could accumulate in environments over time. For now, the science is clear on the basic mechanism: tires plus ozone equals a persistent toxicant.
What remains to be seen is how regulators and manufacturers respond to that fact.
