Penetration of Perfluorooctanesulfonate Isomers and Their Alternatives from Maternal Blood to Milk and Its Associations with Chemical Properties and Milk Primary Components.

Perfluorooctanesulfonate (PFOS) and its alternatives, including chlorinated polyfluorinated ether sulfonates (Cl-PFESAs), are mainly detected per- and polyfluoroalkyl substances (PFAS) in human samples such as milk. However, the mechanism of their blood to milk transfer was not well studied. Here, 145 paired maternal serum and human milk samples were analyzed for six PFOS isomers and Cl-PFESAs to evaluate the transfer efficiency from maternal serum to human milk (TE HM/MS ). Besides physicochemical properties, this study for the first time evaluated the influencing effects of the primary components in human milk (carbohydrate, lipid, and protein) on TE HM/MS of PFAS. No significant association was observed between TE HM/MS and the albumin binding affinity of the compounds ( p = 0.601), but TE HM/MS was significantly negatively correlated with the logarithmic octanol-water partition coefficients ( r 2 = 0.853, p = 0.001), the logarithmic membrane-water partition coefficients ( r 2 = 0.679, p = 0.012), and the carbohydrate contents in human milk. The effect of carbohydrate was further confirmed using in vitro tests. The negative associations between TE HM/MS and hydrophobicity, membrane passive permeability, and the carbohydrate content in human milk consistently indicated that passive diffusion through the paracellular route might be the main transfer pathway for PFOS and Cl-PFESAs from blood to milk in humans.