As if our food is not toxic enough, scientists recently investigated whether chemicals released from vehicle tires find their way into lettuce plants and could ultimately end up on our plates. The results from their analyses demonstrated that lettuce took up all the compounds studied – and some of them are highly toxic.
How can toxic debris from tires end up in our salad?
Driving a car produces tire wear particles, which are blown into the environment by the wind and washed into rivers and sewage by the rain. Through the atmosphere and with the waste water or the sewage sludge used as fertilizer in agriculture, the tire particles can reach agricultural soils.
Lettuce plants continuously take up toxic compounds from tire wear particles
Once the particles are in the agricultural soil where produce is grown, potentially harmful chemicals can be released from the tire particles into the environment. This can happen because tire wear particles and other types of microplastics contain additives (like phthalates) used to help plastics maintain their composition. Once in soils, the small plastic or tire particles usually release their pollutants in the upper soil layers. According to researcher Anya Sherman, “Tire wear particles contain a number of organic chemicals, some of which are highly toxic.” Thilo Hofmann, head of the research group, warns, “If these chemicals are released in the root zone of edible plants, provided the chemicals are taken up by the plants, they can be a health concern for consumers.” (source)
Lettuce Plants Metabolize the Toxic Chemical Compounds and Accumulate Their Transformation Products in the Leaves.
Although the compounds are metabolized in the plant, they are replenished by continuous tire leaching and their transformation products accumulate in the leaves.
Environmental geoscientists added five chemicals to the hydroponic solutions of lettuce plants. Four of these chemicals are used in tire production. Not all of them have already been confirmed to be harmful. Yet, the fifth chemical is a transformation product of one of these four, created once the tires are in use, and it is proven to be toxic: The chemical 6PPD-quinone (originating from 6PPD) has been linked to mass deaths of salmon in the U.S.
Using high resolution mass spectrometry methods, scientists not only measured the extent to which the previously defined chemicals ended up in the lettuce plants. They also identified the substances to which the lettuce plants metabolized the chemicals. The metabolites identified by the research team are quite stable in the plant. Most likely, they would therefore be preserved until reaching our plates.
“Our measurements showed that the lettuce plants took up all the compounds we investigated through their roots, translocated them into the lettuce leaves and accumulated them there.”
-Anya Sherman, researcher and PhD student at the Centre for Microbiology and Environmental Systems Science (CMESS)
This was also evident when the lettuce plants were not exposed to the chemicals directly, but indirectly via tire crumb.
“The lettuce plants continuously take up the potentially harmful chemicals that are released from the tire abrasion particles over the long term.”
-Dr. Thilo Hofmann, researcher
Journal reference: Stephanie Castan, Anya Sherman, Ruoting Peng, Michael T. Zumstein, Wolfgang Wanek, Thorsten Hüffer and Thilo Hofmann. Uptake, Metabolism, and Accumulation of Tire Wear Particle-Derived Compounds in Lettuce, Environmental Science & Technology Journal, American Chemical Society, December 28, 2022. https://doi.org/10.1021/acs.est.2c05660