Distribution of per- and poly-fluoroalkyl substances and their precursors in human blood.

Many studies have examined per- and poly-fluoroalkyl substances (PFASs) in human blood. However, the distribution of PFASs in human blood remains not well known, especially for perfluorooctane sulfonate (PFOS) precursors. In this study, human blood samples (n = 162) were collected from general Chinese population, and then the isomer-specific partitioning of PFASs between human plasma and red blood cells (RBCs) were investigated. Perfluorooctanoate (PFOA) and PFOS were consistently the predominant PFASs in both human plasma and RBCs. In human blood, among C4-C7 perfluoroalkyl carboxylates (PFCAs), the calculated mean mass fraction in plasma (Fp) values increased from 0.76 to 0.82 with the increasing chain length. C7-C13 PFCAs exhibited a trend of gradually decreasing mean Fp with chain length. Among PFAS precursors, 6:2 fluorotelomer phosphate diester had the highest mean Fp value (0.87 ± 0.11). Calculated Fp values of N-methyl perfluorooctanesulfonamide (N-MeFOSA) and N-ethyl perfluorooctanesulfonamide (N-EtFOSA) were 0.66 ± 0.13 and 0.70 ± 0.12, respectively. Individual branched isomers consistently had greater Fp values than their corresponding linear isomers for PFOA, PFHxS, and perfluoroctane sulfonamide. To our knowledge, this study first reports the distribution of N-MeFOSA and N-EtFOSA in human blood, contributing to the better understanding of the occurrence and fate of PFASs in humans.