The emergence of rubber-derived quinones in environment: From Evidence-based toxicological views to policy...

Since 2020, there has been a swell of interest in a globally ubiquitous rubber additive, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its ozonation product, 6PPD-quinone. The trend soon expands to the antioxidant family of N,N'-substituted p-phenylenediamines (PPDs) and their quinone derivatives (PPD-quinones). The widespread occurrence of these contaminants has been demonstrated in various environments with deleterious biological impacts on living organisms, which in parallel promotes reinforcing policy actions to designate PPDs-containing tires, especially 6PPD as a priority product. Nevertheless, debates and uncertainties persist regarding the evaluation of evidence-based toxicological data for these quinone contaminants. The current review seeks to elaborate on the multifaceted hazards and intra- and interspecific biotoxicity of PPD-quinone contaminants across aquatic species, invertebrates, rodents and humans, interrogate exposure burdens of these xenobiotics on populations, and advocate policy interventions and alternative strategies to promote the circular economy of rubber-derived products. We also consolidate both qualitative mechanistic evidence and quantitative findings including LC₅₀/EC₅₀ values, biomarker fold changes, and tissue burden data to advance refined environmental risk assessment for PPD-quinone family contaminants.