P-Phenylenediamines and Their Quinones in Estuarine-Coastal Sediments of Zhejiang Province: Occurrence, Prioritization, and Risk Assessment

As emerging contaminants of concern, p -phenylenediamines (PPDs) and their quinone transformation products (PPD-Qs) serve as critical indicators of pollutant inputs from urban runoff and tire wear to coastal ecosystems. However, their occurrence, distribution, and pollution sources in Zhejiang’s estuarine-coastal sediments remain uncharacterized. This study investigated the pollution levels and ecological risks of PPDs and PPD-Qs in estuarine and coastal sediments in Zhejiang Province. The results revealed the widespread occurrence of eight PPDs and seven PPD-Qs. The concentrations of Σ 8 PPDs in estuarine and coastal sediments were 3.13–9.03 ng/g dry weight (dw) and 2.30–23 ng/g dw, with N -Isopropyl- N' -phenyl- p -phenylenediamine (IPPD) being the predominant congener. Concentrations of Σ 7 PPD-Qs ranged from 1.64 to 4.35 ng/g dw in estuarine sediments and from 0.80 to 6.87 ng/g dw in coastal sediments, and were dominated by N , N' -Bis(methylphenyl)-1,4-benzenediamine quinone (DTPD-Q) and 6PPD-Q. Notably, a significant ( P < 0.05) positive correlation was observed between the concentrations of PPDs and PPD-Qs in estuarine sediments. Priority assessment identified that N, N' -Bis(2-naphthyl)- p -phenylenediamine (DNPD), N, N′ -Bis(methylphenyl)-1,4-benzenediamine (DTPD), DTPD-Q, and 6PPD-Q were of highest priority. Moreover, 6PPD-Q was identified as a medium or high ecological risk at all sites. This study provides critical baseline data and risk insights for emerging rubber-derived contaminants (PPDs/PPD-Qs), enabling targeted conservation strategies for ecologically vulnerable estuarine-coastal systems.