Transplacental transfer efficiency of perfluoroalkyl substances (PFAS) after long-term exposure to highly contaminated drinking water: a study in the Ronneby Mother-Child Cohort.

Background: Perfluoroalkyl substances (PFAS) are stable chemicals used in various applications. PFAS exposure has been associated with lower birth weight and immunological effects in children, and limited evidence further suggests adverse neurodevelopmental effects. Previous studies show that PFAS cross the placental barrier during pregnancy leading to prenatal exposure of the fetus. Research on the transplacental transfer efficiency (TTE) of PFAS in highly exposed populations is lacking.

Objective: This study aimed to estimate the TTE of eight PFAS and three perfluorooctane sulfonic acid (PFOS) isomers in a birth cohort with a wide range of PFAS exposures and to investigate if maternal exposure level impacted the estimated TTE.

Methods: The participants, most of whom had been exposed to PFAS-contaminated municipal drinking water, were recruited between 2015 and 2020 after the end of exposure. We collected maternal serum samples during pregnancy and at delivery, as well as umbilical cord serum. Serum samples were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). TTE was estimated as the ratio of the PFAS concentration in cord serum to maternal serum. We used generalized additive mixed models accounting for maternal characteristics to assess if maternal exposure level (i.e., high, intermediate, or background) modified the estimated TTE.

Results: The study included 200 dyads with matched cord and maternal serum samples. The exposure profile was dominated by perfluorohexane sulfonic acid (PFHxS) and PFOS. We observed the highest overall transfer efficiency for PFHxS (median TTE: 0.68) and the lowest for the n-PFOS isomer (median TTE: 0.33). Higher TTEs were observed for PFHxS and PFOS (total and isomers) in background-exposed dyads.

Impact statement: In a birth cohort with a wide range of exposures to primarily PFOS and PFHxS from contaminated drinking water, we found that the transplacental transfer efficiencies (TTE) of eight PFAS and three PFOS isomers were of considerable magnitude. The highest TTE were observed for PFOA and PFHxS, and for branched PFOS isomers compared with linear. Although we observed slightly lower TTE in mother-child dyads with high and intermediate exposures compared with dyads with background levels of exposure, the considerable TTE in highly exposed mothers implies high absolute prenatal exposure in children in contaminated areas.