Patterns, variability, and predictors of p-phenylenediamine quinones and parent p-phenylenediamines in pregnant women across three trimesters

p-Phenylenediamine quinones (PPD-Qs), oxidative derivatives of rubber antioxidant p-phenylenediamines (PPDs), have garnered increasing concern due to their environmental ubiquity and toxicity. However, evidence regarding the exposure assessment of these emerging contaminants in humans, especially pregnant women, remains limited. Herein, we measured the levels of six PPD-Qs and their parent six PPDs in 1,278 urine samples collected from 426 pregnant women over three trimesters with the aim of evaluating the exposure profiles, variability, and predictors of PPD-Qs and PPDs during pregnancy. Most PPD-Qs exhibited high detection frequencies (>50 %) in the urine of pregnant women, except for DTPD-Q (9.3 %). The median specific gravity-adjusted concentration of ∑PPD-Qs (10.38 ng/mL) was significantly higher (p < 0.0001) than that of ∑PPDs (1.20 ng/mL). The urinary concentrations of PPD-Qs and PPDs were associated with maternal age, parity, education level, pre-pregnancy body mass index, occupational status, and sampling season. In addition, this longitudinal study found that the PPD-Qs and PPDs concentrations varied across trimesters, with the highest concentrations of most PPD-Qs observed in the first trimester, highlighting a relatively higher exposure risk during early pregnancy. High variability for most PPD-Qs and PPDs highlights the need for multiple measurements to ensure accurate exposure assessment during pregnancy. The median daily excretion of PPD-Qs and PPDs was estimated at 192.54 ng/kg bw/day and 25.18 ng/kg bw/day, respectively, highlighting the urgency of addressing the potential health impacts of these pervasive yet largely ignored contaminants during pregnancy. While this study provides the first longitudinal biomonitoring of PPD-Qs and PPDs during pregnancy, further research integrating longitudinal monitoring with toxicokinetic and epidemiological investigations is essential to better understand the potential health risks associated with these emerging contaminants.