Lab research from the University of Vienna has shown that lettuce uptakes chemical compounds of tire wear particle from its roots. Lettuce has metabolized and transformed them but toxicity of these derived compounds is unknown.
A team of microbiologists from the University of Vienna found that lettuce uptakes and metabolizes compounds from tire wear particle. These transformed compounds have been found in the leaves.
Published in Environmental Science & Technology, a scientific journal managed by the American Chemical Society, the results of the study bring new aspects to the potential environmental impact of tire wear particle. The toxicity of these transformed compounds found in a plant that humans usually eat raw is unknown.
Tires are made up of natural or synthetic rubber but also of chemical additives to ensure their durability or certain driving characteristics. Emissions of tire wear particle, additives also derive into other compounds during use, in the environment remain poorly quantified but it is estimated 5.9 million tons of microplastics per year released in nature worldwide come from tires, mostly come from cars.
And these tiny chemical compounds floating in the air or deposited on roads can eventually end up in water and farmland soils. With lettuce plants, the center for Microbiology and Environmental Systems Science has studied the uptake of a broad range of derived compounds from tire wear particle by an edible plant.
They grew lettuce seedlings into plants in vials with a hydroponic nutrient solution in a lab and exposed them directly or indirectly to five of these compounds. Not all are classified as toxic but the quinone transformation of the 6PPD, an antiozonant and antioxidant used to protect tires, has been identified as a responsible factor for the mortality of trout and coho salmon for instance.
And the experiment has shown all five derived compounds from tire wear particle were taken up by lettuce plants. They metabolize them and then accumulate their transformation products in the leaves.
For the scientists, the results “may be of concern to consumers, particularly because lettuce plants are eaten raw.” They suggest further research should be made to evaluate their toxicity to humans and the quantity of these compounds in field agricultural products.
Lab conditions differ since the availability and levels of exposure of these chemical compounds for plant uptake in farmlands would likely decrease. It is also unknown whether they may be degraded by soil microbial communities before they are taken up by the plants.