Isomer-specific binding affinity of perfluoroalkyl substances with red blood cells

Wide presence of perfluoroalkyl substances (PFASs) in human blood has attracted great attention. Interactions of PFASs with serum proteins have been well investigated, but with red blood cells (RBCs), a nonnegligible cellular constituent of blood, remains not well known. In this study, rat and human RBCs were incubated with PFASs (10 or 100 ng/mL) to investigate their isomer-specific binding affinity (F_r; mass fraction in RBCs). Immobilized artificial membrane (IAM) chromatography was used to assess the isomer-specific sorption of PFASs to RBC membranes (K_IAM; retention capacity factor). F_r calculation suggested that binding affinity of linear perfluoroalkyl carboxylates (PFCAs) with rat and human RBCs consistently increased with chain length. Perfluorohexane sulfonate (PFHxS) exhibited lower mean F_r than perfluorooctane sulfonate (PFOS) and perfluorobutane sulfonate (PFBS), suggesting weak RBC affinity. Log K_IAM of PFCAs linearly increased as perfluoroalkyl chain length increased from C₄- (mean 0.61) to C₁₄-PFCAs (0.68), and a similar trend was observed between PFBS (2.1) and PFOS (4.8). Branched perfluorooctanoate, PFOS, and perfluorooctane sulfonamide (PFOSA) isomers showed weaker binding than linear isomers. PFOSA showed higher affinity with rat and human RBCs and IAM, than PFOS. Overall, this study provides important data for understanding the behaviors and fate of PFASs in human blood.