Tyre-related additives in the terrestrial environment: Contamination of soils and plants

Tyre wear particles play a major role in plastic pollution of the environment and their potential impact on soil, plants and indirectly on human health raise concern, as once emitted, they represent a source of pollutants, particularly for ecosystems and crops bordering transport routes. Sampling of soils and plants at 1, 2, 5 and 10 m from Swiss cantonal roads, as well as the acquisition of laboratory samples artificially contaminated with tyre particles, enabled to characterize the concentrations of 17 tyre-related additives, using ASE (accelerated solvent extraction) and UPLC-MS/MS analyses. For certain key additives, such as DPG and 6PPD, concentrations of more than 300 ng/g dry and 50 ng/g dry were recorded respectively in plants and surface soils bordering roads. A clear decrease in concentrations, up to a factor of 20, by increasing distance from the road was also identified for several additives. For laboratory samples exposed during 6 months to 1% dry mass of tyre particles, a greater transfer from soil to plants was observed for mobile additives such as 2-H-BTH, while hydrophobic compounds appear to remain more strongly bound to the soil. As tackled in the literature, several additives appear to be absorbed by plants before being metabolised into transformation products, which are sometimes more toxic, such as 6PPDQ or HDPA.