Distribution of Phthalate Metabolites between Paired Maternal-Fetal Samples

Phthalic acid esters (PAEs) are readily metabolized to phthalate metabolites (mPAEs) in the human body. The occurrence of mPAEs in adult human samples is well documented; however, the maternal-fetal transmission of mPAEs has seldom been studied. In this study, 78 paired maternal-fetal samples, including maternal urine (MU), maternal serum (MS), cord serum (CS), and amniotic fluid (AF), were collected from pregnant women in Tianjin, China. Seven mPAEs were detected in MS, CS, and AF, whereas all 11 investigated 2 mPAEs were found in MU. The median concentration of Sigma mPAEs was the highest in MU (128 ng/mL, with a range of 20.2-973 ng/mL), and proceeded in the order of CS (44.9, 13.9-315 ng/mL), MS (24.6, 3.75-156 ng/mL), and AF (10.4, 7.69-79.8 ng/mL). The values of Sigma mPAEs and several individual mPAEs were significantly correlated between MU and MS, with generally higher concentrations in MU, which indicated that urinary mPAEs is a good indicator of PAEs' exposure in adults. Notably, the median CS:MS ratios of Sigma mPAEs (1.58) were higher than 1, indicating that fetuses were exposed to mPAEs before birth. Significant correlations were also observed between MS and CS, which suggested that mPAEs in MS provide an indication of the fetal exposure. This study presents the first systematic analysis of the distribution and transmission of various mPAEs between mothers and fetuses.