Effect‐Directed Analysis Based on Transthyretin Binding Activity of Per‐ and Polyfluoroalkyl Substances (PFAS) in a Contaminated Sediment Extract

Only a fraction of the total number of per and polyfluoroalkyl substances (PFAS) are monitored on a routine basis using targeted chemical analyses. Here, an approach for identifying bioactive substances in environmental samples using effect-directed analysis (EDA) by combining toxicity testing, targeted chemical analyses, and suspect screening is reported. PFAS compete with the thyroid hormone thyroxin (T4 ) for binding to its distributor protein transthyretin (TTR). Therefore, a TTR-binding bioassay was used to prioritize unknown features for chemical identification in a PFAS-contaminated sediment sample collected downstream of a factory producing PFAS-coated paper. First, the TTR-binding potencies of 31 analytical PFAS standards were determined. Potencies varied between PFAS depending on carbon chain length, functional group, and, for precursors to perfluoroalkyl sulfonic acids (PFSA), the size or number of atoms in the group(s) attached to the nitrogen. The most potent PFAS were the seven and eight carbon PFSA, perfluoroheptane sulfonic acid (PFHpS) and perfluorooctane sulfonic acid (PFOS), and the eight carbon perfluoroalkyl carboxylic acid (PFCA), perfluorooctanoic acid (PFOA), which showed approximately 4- and 5-times weaker potencies, respectively, compared to the native ligand T4 . For some of the other PFAS tested, TTR-binding potencies were weak or not observed at all. For the environmental sediment sample, not all of the bioactivity observed in the TTR-binding assay could be assigned to the PFAS quantified using targeted chemical analyses. Therefore, suspect screening was applied to the retention times corresponding to observed TTR-binding - identifying five candidates. Targeted analyses showed that the sediment was dominated by the di-substituted phosphate ester of N-ethyl perfluorooctane sulfonamido ethanol (SAmPAP diester), while it was not bioactive in the assay. SAmPAP diester has the potential for (bio)transformation into smaller PFAS, including PFOS. Therefore, when it comes to TTR-binding, the hazard associated with this substance is likely through (bio)transformation into more potent transformation products.