Researchers fromThe Hebrew University Raised lettuce ואספסת In soil containing realistic concentrations of erosion particles TiresThey found that the particles do not remain in the soil as an inert material, but gradually release chemical additives, some of which are absorbed by the plant tissues.
Every car trip leaves behind more than just exhaust fumes. The constant friction between the tires and the road wears away tiny particles, which scatter along the sides of the road, are washed away by rainwater, and accumulate in the soil and in water sources. A new study led by researchers from the Hebrew University of Jerusalem shows that these particles could become a persistent source of chemical pollution in agricultural soils – and from there, reach food plants.
The study, published in the journal Environmental Research, was led by Zhao Gao, Prof. Benny Hefetz and Dr. Eviatar Ben Mordechai from the Hebrew University, in collaboration with an international team of researchers. The researchers sought to examine not only whether plants are able to absorb substances originating from tires – a phenomenon that has already been observed in previous studies – but also whether the tire particles themselves serve as a reservoir that releases the substances into the soil over time.
For the experiment, the researchers grew lettuce and alfalfa in agricultural soil to which tire wear particles were added at concentrations of 0.1% to 1%—a range they say is similar to concentrations measured in soils near roads and in agricultural areas exposed to traffic pollution. They then tracked the movement of six common tire-derived substances from the particles into the soil and from there into plant tissues.
Rapid release – followed by persistent infection
The results indicated a two-step process. Some of the substances were released quickly from the surface of the tire particles, while others slowly diffused from the rubber matrix. This means that a particle that reached the ground may continue to release chemicals long after it has sunk into the ground.
“Our research shows that tire wear particles are not just microplastic Passive that accumulates in the environment,” said Dr. Ben Mordechai, the researcher responsible for the article. “They function as short-term and long-term reservoirs of chemical substances, which are gradually released into the soil and become available for absorption by plants.”
One substance of particular concern was 1,3-diphenylguanidine, or DPG, an additive used in rubber manufacturing. The researchers found that it was continuously released from tire particles, remained in the soil, and accumulated in both alfalfa and lettuce. DPG concentrations in lettuce were significantly higher than those of other substances tested.
It was also discovered in the soil and plant tissues 6PPD-quinone, an oxidation product of the additive 6PPD. The original additive is used to protect rubber from ozone damage, but after reacting with ozone, 6PPD-quinone may be formed, a substance that has been found to be particularly toxic to several species of fish, including silver tang.
Not just plastic particles
In recent years, research has been expanding on non-tailpipe transportation emissions, including brake, road and tire abrasion. Tire abrasion particles contain a complex mixture of natural and synthetic rubber, fillers and additives designed to improve the tire's strength, flexibility and resistance to heat and oxidation.
The new study highlights that the risk stems not only from the particles themselves, but also from the chemicals they carry. Once the particles reach agricultural land, they may act as a persistent source of pollution, even after the original source of pollution – such as road runoff after rain – has passed.
However, the researchers do not claim that eating lettuce grown near a road is necessarily dangerous to health. The study demonstrated a possible pathway for contaminants to pass from the tire, through the soil, to the plant, but studies are still needed that examine actual exposure levels in commercial fields, the effect of cooking and digestion, and the health significance of the concentrations measured.
The researchers say the findings point to the need to address tire pollution as part of the overall environmental impacts of transportation. Beyond reducing vehicle traffic and improving public transportation, possible solutions may include developing safer tire additives, effectively collecting road runoff, and establishing buffer zones between busy roads and agricultural areas.
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Questions and Answers
How do pollutants from tires get to plants?
Rubber particles that wear away from tires are dispersed into the air or washed away with rainwater to the ground. The chemicals within them are gradually released, pass into the soil solution, and are absorbed through the plant's roots.
Which plants were tested in the study?
The researchers grew lettuce and alfalfa in agricultural soil that contained tire wear particles at concentrations that simulated environmental conditions.
What is DPG?
DPG, or 1,3-diphenylguanidine, is a substance used in rubber production. The study found that it was released from tire particles, remained in the soil, and accumulated in the tissues of lettuce and alfalfa.
What is 6PPD-quinone?
This is a product formed when the additive 6PPD in tires reacts with ozone. The substance is known for its high toxicity to several species of fish, and in the current study it was also detected in soil and plants.
Does the study prove that vegetables are dangerous to eat?
No. The study shows that tire-derived materials can migrate to soil and plants. It does not determine that exposure levels in commercial food pose a risk to humans, and further studies are needed to assess the health risk.
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