Scientists have found in leafy vegetables traces of several chemicals used to prevent the aging and corrosion of car tires.

Through normal wear and tear, tires cast off countless tiny bits of rubber, which linger in the atmosphere or are washed down sewage drains and into waterways. In the air, these particles can affect the formation of clouds. In the water, they leach compounds that have been shown to be toxic to wildlife.

New research adds to the growing evidence that car tires are a considerable source of pollution. For the study, scientists tested leafy vegetables that had been grown in Switzerland, Spain, and Italy and sold in Swiss supermarkets. They also tested vegetables harvested directly from farmland in Israel.

Tire ingredients were found in 11 of 15 samples gathered from Swiss supermarkets and nine of 13 samples collected from Israeli fields. Among the chemicals discovered was 6PPD, an additive used to prevent cracking, which can transform into a compound that has proved deadly to coho salmon. The findings were published in Frontiers in Environmental Science.

Scientists say that farmers may be introducing tire additives by irrigating crops with treated wastewater or by using sewage sludge as fertilizer. It is also likely that airborne particles are settling on the soil. Tire chemicals are taken up by crops and, eventually, consumed by people.

“While the concentrations and daily intake are fortunately relatively low, additives from car tires are still found in food,” said coauthor Thilo Hofmann, a researcher at the University of Vienna. “That’s not where they belong.”

ALSO ON YALE E360

Road Hazard: Evidence Mounts on Toxic Pollution from Tires