Transformation products (TPs) are a class of widespread emerging contaminants whose environmental fate and risks are poorly understood. TPs originating from tire tread wear particles (TWP) can be generated throughout the tire rubber lifetime and may be transported to surface waters following storm events, in turn presenting a source of chemical exposure to aquatic life and humans. Our study investigated TP formation occurring during heterogeneous reaction of gas-phase ozone with the common tire rubber antioxidant 6PPD (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine), both as a pure compound and as a constituent of TWP. Oxidative transformation of pure 6PPD was observed during exposure to ozone, with 81% of total 6PPD mass reacting during 6-hours of exposure on the 6PPD coated slide. Conversion molar yield of 6PPD to 6PPDQ – a recently reported highly toxic TP – was confirmed from the investigation. The TWP ozonation was conducted as the similar manner as pure compound. By aligning the potential TP features from ozonation, we thus prioritized 20 unique 6PPD-associated TPs that were found in both ozonated 6PPD and TWP samples, underscoring the importance of 6PPD as a primary antioxidant in tire rubber products and major TP source when tire rubber is subjected to ozone exposure. Additionally, by screening environmental samples, we prioritized 9 TPs that formed from 6PPD ozonation as also being prevalent in receiving waters impacted by roadway runoff. The data imply that tire rubber antioxidants react with ozone to form various TPs that are released throughout the tire rubber service life and have potential impacts on aquatic environments.

Transformation product formation upon heterogeneous ozonation of the tire rubber anti-oxidant N-1,3-dimethylbutyl-N-phenyl-P-phenylenediamine

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.