Plastic particles can enter the environment in many ways – for example through discarded plastic bottles floating in rivers and seas or shed fibers from synthetic clothing during a washing process. Car tires are also such a source. When you drive a car, your tires wear out all the time.

This resulting tire abrasion is blown into the environment with the wind and washed into rivers and sewage treatment plants by rain. Researchers at the University of Vienna have therefore investigated whether chemicals released from tires could get into lettuce plants and ultimately end up on our plates. Their analyses, which they published in the journal “Environmental Science

“Tire debris contains a range of organic chemicals, some of which are highly toxic,” explains Anya Sherman of the Center for Microbiology and Environmental Systems Science and co-first author of the study. Like other types of microplastic, the abrasion contains additives, which are intended to provide certain properties such as better durability.

For their investigations, the researchers added five chemicals to the nutrient solutions of lettuce plants. Four of these chemicals are used in tire manufacturing. The fifth chemical used in the study, 6PPD-Quinone, is a conversion product of one of these four chemicals that occurs when tires are in use. It has been shown to be toxic: the chemical has been linked to the mass die-off of salmon in the United States, for example.

“Our measurements showed that the lettuce plants took up all the compounds we examined via the roots, translocated them to the lettuce leaves and accumulated there,” says Anya Sherman. This was also evident when the lettuce plants were not directly exposed to the chemicals, but rather indirectly via the tire granules.

“The lettuce plants continuously absorb the potentially harmful chemicals that are released over the long term from the tire abrasion particles,” explains Thilo Hofmann, head of the research group. Half of the microplastics in the world come from the abrasion of car tires, Thilo Hofmann told the German Press Agency. According to the study, between 1,400 and 2,800 tons of tire abrasion is applied to agricultural land in Germany every year through sewage sludge alone.

Using high-resolution mass spectrometry methods, the researchers not only measured the extent to which the previously defined chemicals ended up in the lettuce plants. They also identified the substances to which these were metabolized in the lettuce plant: “The plants processed the substances and also created compounds that have not been described before. Since we do not know the toxicity of these metabolites, they pose an unpredictable health risk,” says Thorsten Hüffer, who was also involved in the study.

The identified metabolites are quite stable in the plant. It is therefore most likely that they were preserved except for the food plate. “In the human body, however, such compounds are broken down very easily. So if someone eats such a contaminated lettuce, the original chemicals could be released back into the body,” explains Anya Sherman.

In a recent article also in “Environmental Science

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