Tires do not just wear down on the road, they shed tiny particles and additives that end up in people. A recent human biomonitoring study measured 150 urine samples in South China and looked for two tire related chemicals.

Those chemicals are 6PPD and 6PPD-quinone, a transformation product that forms when 6PPD reacts during use. The researchers reported high detection across participants.

6PPD chemicals in humans

Henry Obanya of the University of Portsmouth has warned that tire pollution deserves its own category because it behaves differently from typical plastic fragments.

That concern lines up with what the lab data are showing in people. Both 6PPD and 6PPD-quinone were present in the urine dataset. 

Concentrations were not uniform across groups. Median 6PPD-quinone levels were higher in pregnant women than in adults and children, and the team estimated a daily excretion of about 273 nanograms per kilogram of body weight for pregnant women.

The results also pointed to coexposure. The authors saw a strong correlation between 6PPD and its quinone form, which fits what we know about how the parent compound transforms inside and outside the body.

How 6PPD enters human bodies

Tire wear releases particles and additives that move through air and water, then settle in soil and dust. These residues can be inhaled, swallowed with food, or brought indoors on shoes and clothing.

Multiple assessments place tire wear among the top sources of plastic particles in the environment.

Tires contribute roughly one quarter of primary microplastics in global estimates, which helps explain why tire related chemicals are now turning up widely.

Traffic exposes cities and suburbs to these particles every day. Roads funnel debris into storm drains and waterways, and braking and cornering keep generating fresh wear particles.

Households are not sealed off from this stream. Particles and the chemicals attached to them can accumulate in indoor dust, which is another route of exposure for families.

Fish deaths as a warning sign

Before scientists saw 6PPD-quinone in people, they saw what it did to fish. A 2021 paper identified 6PPD-quinone as the tire derived chemical in urban runoff that causes rapid deaths in returning coho salmon.

Those findings reshaped how researchers view tire additives in the environment. The compound is potent for several fish species, so even short pulses during rain events can be dangerous for sensitive salmonids (salmon, trout, and charr).

This is not just a West Coast story. Similar chemistry can play out in any watershed where busy roads meet streams, especially near culverts and outfalls during the first flush of rain.

Wildlife effects will not map cleanly onto human risk, but they do set off alarms. When a transformation product is this toxic to aquatic life, it makes sense to track where it goes and how people encounter it.

6PPD in human urine

Tire makers add 6PPD to protect rubber from cracking due to ozone and oxygen. That protection helps tires last, but it also creates a steady source of chemical residues as tread wears down.

6PPD-quinone forms from that same protective chemistry. The quinone is more mobile in water, it travels with stormwater runoff, and it shows up in roadway puddles and creek water after rain.

The human urine results fit with what we know about metabolism. In vitro tests with human liver material showed that 6PPD gets rapidly depleted, which helps explain why we see more of the quinone form in urine than the parent compound.

Exposure likely comes from several pathways at once. People living near busy roads, working around traffic, or handling contaminated dust may face higher combined exposure over time.

What regulators are starting to do

Environmental agencies are beginning to set benchmarks for aquatic life. In 2024, the U.S. Environmental Protection Agency (EPA) issued acute aquatic life screening values for 6PPD-quinone to guide short term protection for sensitive fish.

Those values are not full water quality criteria, but they matter. They give states and cities a reference point for roadway runoff controls and for testing stormwater treatment designs.

Scientists are also working on better detection methods. More sensitive monitoring of road runoff, sediments, and indoor dust can reveal where exposure is highest and how to reduce it.

Communities are trying tire particle capture ideas at the curb and on vehicles. It will take careful testing to prove what actually cuts concentrations in real settings.

Tires, 6PPD, and human health

The human biomonitoring signal is clear. People are picking up tire related chemicals, and one of them, 6PPD-quinone, is present in most samples from the study population.

Health effects in people remain uncertain. That is why researchers stress long term tracking and comparisons across ages, jobs, and neighborhoods.

“We urgently need to classify tyre particles as a unique pollution category,” said Obanya. The case for treating tire pollution as a distinct issue is growing. 

That step would focus research and standards on the chemicals most likely to cause harm. It would also help separate tire wear from other plastic sources that behave differently in the environment.

For now, the science points to a practical takeaway. Tracking these compounds in water, dust, and urine will show where exposure is highest and which fixes actually work.

Communities do not have to wait for a single silver bullet. Runoff treatment, smarter road design, and better tire formulations can each chip away at the problem if they are tested and verified.

The study is published in Environmental Science & Technology Letters.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–