Organic Markers of Tire and Road Wear Particles in Sediments and Soils: Transformation Products of Major Antiozonants as Promising Candidates

Tire and road wear particles (TRWPs) are one of the main sources of particulate traffic emissions, but measured data on TRWP contents in the environment are scarce. This study aims at identifying organic compounds suitable as quantitative markers for TRWPs by a tiered multistep selection process involving nontarget screening and subsequent identification by liquid-chromatography high-resolution mass spectrometry. Starting from several thousands of signals recorded in the extract of tire particles, the rigorous selection process considered source specificity, tendency of leaching, analytical sensitivity and precision, and stability during aging. It led to three transformation products of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6-PPD) as the most suitable marker candidates: N-formyl-6-PPD, hydroxylated N-1,3-dimethylbutyl-N-phenyl quinone diimine, and 6-PPD-quinone. A linear response in standard addition experiments with tire particles and the correlation with TRWP contents in a diverse set of environmental samples imply that these compounds are promising candidates as markers for the quantification of TRWPs. Organic markers for TRWP contents in the environment would allow TRWP quantification with the traditional tandem MS (LC-MS/MS) equipment of an organic trace analytical laboratory and, thus, allow easy generation of data on TRWP occurrence in sediments and soils and other environmental matrices.