Nontarget Screening of Per- and Polyfluoroalkyl Substances Binding to Human Liver Fatty Acid Binding Protein

Abstract

More than 1000 per- and polyfluoroalkyl substances (PFASs) have been discovered by nontarget analysis (NTA), but their prioritization for health concerns is challenging. We developed a method by incorporating size-exclusion column co-elution (SECC) and NTA, to screen PFASs binding to human liver fatty acid binding protein (<i>h</i>L-FABP). Of 74 PFASs assessed, 20 were identified as <i>h</i>L-FABP ligands in which eight of them have high binding affinities. Increased PFAS binding affinities correlate with stronger responses in electrospray ionization (ESI^-) and longer retention times on a C18 column. This is well explained by a mechanistic model, which revealed that both polar and hydrophobic interactions are crucial for binding affinities. Encouraged by this, we then developed an SECC method to identify <i>h</i>L-FABP ligands, and all eight high-affinity ligands were selectively captured from 74 PFASs. The method was further applied to an aqueous film-forming foam (AFFF) product in which 31 new <i>h</i>L-FABP ligands were identified. Suspect and nontargeted screening revealed these ligands as analogues of perfluorosulfonic acids and homologues of alkyl ether sulfates (C₈- and C₁₀/EO<i>_n</i>, C₈H₁₇(C₂H₄O)<i>_n</i>SO₄^-, and C₁₀H₂₁(C₂H₄O)<i>_n</i>SO₄^-). The SECC method was then applied to AFFF-contaminated surface waters. In addition to perfluorooctanesulfonic acid and perfluorohexanesulfonic acid, eight other AFFF chemicals were discovered as novel ligands, including four C₁₄- and C₁₅/EO<i>_n</i>. This study implemented a high-throughput method to prioritize PFASs and revealed the existence of many previously unknown <i>h</i>L-FABP ligands.