Tire-wear particles and tire-related emerging contaminants: Characteristics, occurrence, and toxicity in the environment

The discovery of 6PPD-quinone as a toxic transformation product and aqueous contaminant from a common tire antioxidant has catalyzed extensive research into its environmental occurrence and other tire-related emerging contaminants (TRECs). However, many other tire-derived chemicals remain understudied, yet may pose significant environmental risks. This review provides a critical overview of the characteristics, occurrence, and fate of TRECs, as well as their toxicological impacts. While advancements in analytical techniques have enhanced the detection of these contaminants, knowledge gaps exist regarding their persistence, transformation, and long-term effects in various environmental compartments. Recent findings suggest that several TRECs, including diphenylguanidine (DPG) and hexamethoxymethylmelamine (HMMM), are frequently detected in road runoff, wastewater, sediments, and even biota. Given their widespread occurrence and potential toxicity, further investigations into their environmental behavior, regulatory implications, and mitigation strategies are urgently needed. This review highlights the pressing need for expanded research beyond 6PPD-quinone to address the broader risks associated with TRECs.