From Road to Table: Car Tire Chemicals make its way into our food

Every tire abrasion leaves traces in the environment: tiny particles produced while driving contain a variety of chemical additives. These residues end up in waterways, are deposited in the soil, and accumulate in ecosystems. A research team led by Thilo Hofmann (environmental scientist and co-director of the ECH), and researchers from the Hebrew University of Jerusalem has now been able to show for the first time that certain compounds from tires are also detectable in crops under realistic conditions.

As part of the study, the scientists grew lettuce on three different soils and watered the plants with water containing common tire chemicals. The result: Several substances, including 6PPD-quinone, which has already been linked to salmon deaths in North America, were detected in the lettuce leaves. Other substances, such as hexamethoxymethylmelamine (HMMM) and diphenylguanidine (DPG), remained in the soil to a greater extent and were absorbed by the plants to a lesser degree.

Absorption depended largely on soil type: while sandy soils allowed more pollutants to enter the plants, clay soils acted as a barrier. In addition, the outer leaves were more heavily contaminated than the inner ones.

The concentrations measured were low (nanograms per gram of plant tissue) and thus well below the levels that could cause acute health damage. Nevertheless, the study draws attention to a previously little-noticed route of pollutant exposure: via food, in addition to air and water. The concentrations are similar to those of pharmaceutical residues that enter food via the use of sewage sludge or treated wastewater.

“Our results show that we need to understand the role of soil as an interface between traffic, the environment, and agriculture in more detail,” emphasizes Thilo Hofmann, head of the study. “Even though the quantities detected are low, the study makes it clear that pollutants from road traffic can ultimately end up in the food chain.”

Especially in regions that rely on irrigation with treated wastewater, it is therefore important to identify potential entry paths at an early stage. “Of course, this is not about questioning the consumption of lettuce, but about gaining a better understanding of the complex interactions between infrastructure, the environment, and food systems,” say the authors of the study.