A new study by scientists from the University of Vienna and the Hebrew University of Jerusalem has shown that, as well as drug residues, other chemicals such as chemical additives released through tyre wear, can be found in commercially available fruit and vegetables.

Car tyres contain a complex mixture of materials to improve their performance and durability, including chemical additives, which comprise hundreds of substances including antioxidants, antiozonants, vulcanizing agents, anti-aging agents and many others. These compounds can find their way into agriculture through atmospheric deposition, irrigation with treated wastewater and the use of sewage sludge as fertiliser, and they can then be taken-up by plants, making their way into the human diet.

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,” said study co-author Anya Sherman.

The concentrations of the tire additives in leafy vegetables are low overall (for example, 238 nanograms ng/kg for benzothiazole, 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, a level that is comparable in magnitude to drug residues, which also enter the food chain in the same way.

According to team leader Thilo Hofmann, “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.” He added that the next step should now be to investigate the environmental and human health aspects.

Having shown in the laboratory that additives from car tires could be absorbed by plants in principle, the team then set out to see if the issue occurred in commercially grown crops. “We examined real samples from supermarkets in Switzerland and field vegetables from Israel,” explained Thilo.” The international team used high-resolution mass spectrometry to analyse the samples for a total of sixteen 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 were tested directly after harvest.