Environmental aging of tire and road wear particles and tire additives: a long-term field study

The long-term fate of tire and road wear particles (TRWP) significantly governs the distribution of tire-related chemicals. In addition to previous lab experiments a field study is performed, exposing TRWP and cryo-milled tire tread (CMTT) to sunlight for 20 months and to microorganisms in water in a sedimentation pond for 17 months. No indications of physical disintegration were obtained over all experimental times and conditions. The extractable concentration of 27 polar and moderately polar compounds was analyzed by liquid-chromatography-mass spectrometry (LC-MS), among them tire additives such as <i>para</i>-phenylenediamines, phenylguanidines, benzothiazoles and known transformation products. Total quantified extractables (TQE) decreased for about 62-92% within the first sampling period of 8-10 months. However, even after 17-20 months concentrations of 100-200 μg g^-1 of TQE remained in TRWP, mainly benzothiazolesulfonic acid (BTSA) and hydroxy-benzothiazole after sunlight exposure and <i>N</i>-(1,3-dimethylbutyl)-<i>N</i>'-phenyl-1,4-phenylenediamine (6-PPD) after exposure in the sedimentation pond. For the sunlight exposure the results of this long-term field study are well comparable to the results of a previous lab study. A laboratory study on (bio) degradation in water with optimized conditions appears to overestimate both leaching and (bio) degradation occurring in the sedimentation pond. Despite these differences, this field study confirms the previous conclusion that, while a substantial part of the polar and moderately polar chemicals is rapidly released, tire particles can be a long-term source of tire-related chemicals. Preventing TRWP from entering aqueous environments would substantially reduce the load of polar and moderately polar compounds transported with them.