Structure-Dependent Maternal-Fetal Transfer and Fetal Hepatic Accumulation of PFOA and Hexafluoropropylene Oxide (HFPO)-Based Alternatives: Implications for Fetal Liver Metabolic Disruption

Hexafluoropropylene oxide (HFPO)-based compounds have been increasingly adopted as replacements for legacy per- and polyfluoroalkyl substances (PFAS) such as perfluorooctanoic acid (PFOA), yet evidence on developmental toxicity remains limited. This study investigated structure-dependent maternal-fetal transfer, fetal tissue distribution, and hepatic effects of PFOA and four HFPO-based alternatives, including hexafluoropropylene oxide dimer acid (HFPO-DA) and hexafluoropropylene oxide trimer acid (HFPO-TA) homologues, in gestational mice. All compounds were detected in maternal serum, fetal tissues, and amniotic fluid in a dose-dependent manner, but transplacental transfer efficiencies varied markedly. C9 HFPO-TA showed the greatest fetal accumulation, indicating enhanced fetal retention. Desorption electrospray ionization mass spectrometry imaging revealed preferential hepatic localization of PFOA and HFPO trimers, with fetal hepatic burden increasing with van der Waals volume, suggesting structure-dependent enrichment. Metabolomics showed broad alterations of fetal hepatic metabolism, dominated by altered lipids and lipid-like molecules. 5-Aminolevulinic acid, a key heme precursor, was consistently reduced, whereas ALAS1 and ALAD protein levels increased, indicating perturbation of heme biosynthesis. The provisional, study-specific developmental reference doses derived from fetal or placental endpoints were comparable to or lower than those based on maternal hepatomegaly, suggesting greater developmental sensitivity. These findings reveal structure-dependent fetal liver accumulation and support incorporating fetal-specific endpoints into PFAS risk assessment.