Ace Business Desk – Roads carry a lot more than cars. Along their edges, in the soil of nearby fields, sits a fine grit that most of us never notice.

New research suggests these fragments are not just litter. They may be slow-release packets of chemicals that seep into soil and climb into the crops we eat.

That grit is worn rubber. Every mile of driving grinds tiny pieces off our tires, and those pieces drift into ditches, fields, and farmland.

Tires shed more than rubber

Roughly 1.5 billion tires are made worldwide each year. As they roll and brake and turn, they slough off particles that pile up wherever traffic runs heavy.

Scientists call these tire wear particles. They already rank among the largest sources of microplastic pollution on the planet.

But the rubber itself is only half the story. Manufacturers pack tires with additives during production, and those chemicals can leach out long after a particle lands.

A gap in what we knew

Earlier work had already found tire chemicals inside vegetables. Most of those experiments, though, dosed plants directly with the chemicals in water or spiked soil.

What nobody had shown clearly was whether the particles themselves could keep feeding contaminants into a field over time. That was the missing piece.

The new study was led by PhD student Chao Gao and Professor Benny Chefetz at the Hebrew University of Jerusalem, with partners at the University of Vienna.

Growing crops in tainted soil

The researchers mixed real tire particles into farm soil at levels found near actual roads, between 0.1 and 1 percent by weight. Then they grew two common crops in it, alfalfa and lettuce.

Over months, they tracked six chemicals known to come from tires. They measured how each one moved from the particles, into the soil, and finally into plant tissue.

Chemicals leak out in two stages

The release did not happen all at once. Some chemicals rushed off the particle surface early, while others crept out slowly from deep inside the rubber.

That second, slower trickle matters most. It means a tire fragment can keep dosing the soil for a long stretch after it settles.

“Our research shows that tire wear particles are not simply passive microplastics accumulating in the environment,” said Dr. Evyatar Ben Mordechay, the corresponding author of the study.

“They behave as short- and long-term reservoirs of chemicals, gradually releasing contaminants into soil where they become available for plant uptake.”

One compound stood out

Among the six chemicals, one called 1,3-diphenylguanidine, or DPG, drew the most attention. It kept leaking from the particles, lingered in the soil, and built up in both crops.

In lettuce, DPG reached far higher levels than any other tire chemical tested. That points to a source of dietary exposure researchers may have been underestimating.

There was a reason it behaved this way. At the soil’s pH, DPG carries a positive charge, which helps it cling to soil and stay within reach of roots.

A toxic byproduct shows up 

Another chemical raised separate alarms. Called 6PPD-quinone, it is highly toxic and already infamous for killing salmon in polluted runoff.

The team found it in both soil and plants. Its appearance in a food crop, even briefly, is the kind of result that invites closer study.

The plants did not leave these chemicals untouched. Inside their tissues, the team detected transformation products, the breakdown fragments of the original compounds.

That tells us plants can process some of what they take in. It also complicates the picture, since a chemical may change form on its way through the food system.

Why the source matters

Here the work offered a surprise. When tire particles were the source, most chemicals reached lower levels in lettuce than when the same chemicals arrived through irrigation water.

DPG proved the clear exception. Delivered by tire particles, it climbed higher than expected, which fits its stubborn habit of sticking around in soil.

“This study changes the way we think about tire wear pollution,” said Professor Chefetz, senior author of the study.

“Tire particles are often discussed primarily as a microplastic issue. Our findings show that they should also be viewed as long-term carriers of chemical contaminants capable of moving through soils and into crops.”

What we still need to learn

The work has clear limits, and the authors say so. They did not track breakdown products in the soil or roots, so they cannot always tell where a chemical transformed.

They also used rubber from a single kind of tire. Other tires carry other recipes, so the mix of chemicals could shift from one source to the next.

Still, the core message lands clearly. Tire particles are not inert crumbs sitting in the dirt, and the traffic outside a farm may leave a fainter mark on its harvest than anyone assumed.

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