Enantioselective transplacental transfer of p-phenylenediamine quinones

As emerging environmental pollutants, p-phenylenediamine quinones (PPD-Qs) have widespread human exposure and documented human health toxicity, including the pregnant women. However, the enantiomer-specific transport behaviors of these chemicals across the human placental barrier have not been well elucidated. To address this gap, this study analyzed 228 paired maternal and cord serum samples for nine PPD-Qs using an enantioselective method. In maternal serum, the major PPD-Qs were N, N'-di(o-tolyl)-p-phenylenediamine quinone (PTPD-Q; mean 1.89 ng/mL, range < LOD-6.69 ng/mL) and N-phenyl-N'-cyclohexyl-p-phenylenediamine quinone (CPPD-Q; 1.72 ng/mL, < LOD-9.38 ng/mL). For cord serum, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q; mean 1.70 ng/mL, range < LOD-5.69 ng/mL) and PTPD-Q (1.32 ng/mL, < LOD-6.19 ng/mL) were found at relatively higher concentrations. In maternal serum and cord serum, mean enantiomer fraction values of 6PPD-Q were 0.41 and 0.38, respectively. The highest transplacental transfer efficiency (TTE) was observed for 6PPD-Q (mean 0.98, range 0.03-4.24), followed by N, N'-di-sec-butyl-p-phenylenediamine quinone (0.91, 0.03-3.91), CPPD-Q (0.81, 0.02-4.42), and PTPD-Q (0.66, 0.02-3.46). S-6PPD-Q (mean 1.34) exhibited a higher mean TTE value than R-6PPD-Q (1.11). The physicochemical properties of PPD-Qs did not significantly correlate with their calculated TTE values. For the first time, we provide evidence of enantioselective transplacental transfer of PPD-Qs, highlighting the need for enantioselective risk assessment of these emerging contaminants during pregnancy.