Determining Presence of Tire Additives in Leafy Vegetables with Mass Spectrometry

Research published in Frontiers in Environmental Science, utilizing high-resolution mass spectrometry, reports that chemical substances from tire wear have found their way into the food chain (1,2).

Car tires consist of a complex mixture of materials that was formulated to improve durability and performance. These materials include 5–15% chemical additives, comprised of hundreds of substances, including (but not limited to) antioxidants, antiozonants, vulcanizing agents, and anti-aging agents, and assist in the high-tech performance of a modern tire. Some of these substances, as well as their transformation products, can possibly create ecological and toxicological hazards.

An international research team led by Thilo Hofmann at the Center for Microbiology and Environmental Systems Science at the University of Vienna (CeMESS), in collaboration with a team the Hebrew University of Jerusalem led by Benny Chefetz, examined vegetables from Switzerland and Israel for the presence of these materials, and analyzed whether lettuce plants absorb the chemicals released by car tires under natural growing conditions.

As early as 2023, the team was able to show that additives from car tires can in principle be absorbed by plants. "However,” explained Anya Sherman, first author of the paper in an interview with Phys Org News, “the question was whether this only happens in our mechanistic laboratory study or also in the field.” (2)

The team of researchers used high-resolution mass spectrometry to analyze the samples for a total of 16 tire-associated compounds. The countries of origin of the leafy vegetables in the Swiss samples from the supermarket were Italy, Spain, and Switzerland. In the Israeli samples, field vegetables from Israel directly after harvest were used.

"The toxicity of tire and road wear particles is related to their organic additives and associated transformation products," Sherman said.

The compounds extracted from car tires find their way into agriculture through atmospheric deposition, irrigation with treated wastewater, and the use of sewage sludge as fertilizer. "There they can be taken-up by plants, and thus also reach humans," Hofmann added.

The researchers extrapolated the measured values from the vegetables to the intake of these substances in the diet. "We calculated the intake per day based on what people in Switzerland and Israel eat," Sherman said.

The concentrations of the tire additives in leafy vegetables are low overall and are, for example, 238 nanograms ng/kg for benzothiazole (BTZ), or 0.4 ng/kg for 6PPD, a substance whose transformation product 6PPD quinone is known to be highly toxic for aquatic species like coho salmon. Depending on the diet, this leads to a daily intake per person of 12 to 1,296 ng for BTZ, or 0.06 to 2.6 ng for 6PPD. This is comparable in magnitude to drug residues, which also enter the food chain (2).

According to Hofmann, the study shows clear results: "While the concentrations and daily intake are fortunately relatively low, additives from car tires are still found in food. That's not where they belong." The next steps should involve investigating the environmental and human health aspects, Hofmann added.

Close up view of car wheel. AI generated illustration. © 3D - stock.adobe.com

References
1. Sherman, A.; Hämmerle, L. E.; Mordechay, E. B.; Chefetz, B.; Hüffer1, T.; Hoffman, T. Uptake of Tire-Derived Compounds in Leafy Vegetables and Implications for Human Dietary Exposure. Front. Environ. Sci.2024,12. DOI: 10.3389/fenvs.2024.1384506 (accessed 2024-06-19)

2. Irrigation with Treated Wastewater and Sewage Sludge Introduces Tire Additives into Leafy Vegetables, Study Finds.” Phys Org website. https://phys.org/news/2024-06-irrigation-wastewater-sewage-sludge-additives.html (accessed 2024-06-19)