A Nationwide Investigation of Substituted <i>p</i>-Phenylenediamines (PPDs) and PPD-Quinones in the Riverine Waters of China

<i>N</i>-(1,3-Dimethylbutyl)-<i>N</i>'-phenyl-<i>p</i>-phenylenediamine-quinone (6PPD-Q) has been identified as the cause of the "urban runoff mortality syndrome." Thus, the ecological risks of substituted <i>p</i>-phenylenediamines (PPDs) and their quinone derivatives (PPD-Qs) in water have gained global attention. However, large-scale observation of their pollution characteristics in surface water is still lacking. Herein, a nationwide investigation revealed the pervasive occurrence of PPDs and PPD-Qs in riverine waters across China, with the mean concentration of ∑₅PPD-Qs being 4.9 times higher than their parent ∑₅PPDs. Notably, the 6PPD-Q concentrations at eight sampling sites exceeded the median lethal concentration for <i>coho</i> salmon. National annual riverine fluxes were estimated at 113.1 and 276.2 tonnes/year for PPDs and PPD-Qs, respectively, with the Yangtze River contributing more than one-third of the total fluxes. The transformation of PPDs to PPD-Qs was dependent on atmospheric hydroxylation rates and the half-lives of PPDs. A combined multimedia exposure assessment revealed that water exposure accounted for 82.5% of human exposure to PPDs and PPD-Qs, surpassing the contributions from dust and air exposure. This study provides a comprehensive spatial picture of PPDs and PPD-Qs in China. The national atlas highlights their potential ecological risks and implies that targeted actions should be taken to mitigate potential exposure to PPDs and PPD-Qs.