LTPE extraction and LC-MS/MS analysis of perfluorinated substances in sewage and sludge from sewage treatment plants

Perfluorinated alkyl substances (PFAS) are used in the manufacture of various items, such as food packaging, non-stick utensils and waterproof textiles, and solvents. The two main substances of this class, which are the most studied and reported, are PFOA-perfluorooctanoic acid and PFOS-perfluorooctanesulfonic acid. The most used method to extract these substances from aqueous matrices employs solid phase extraction (SPE), and in this work we tested the use of low temperature partition extraction (LTPE)-a simpler and cheaper method-to extract PFOA and PFOS from sewage and sludge matrices. Validation of the analytical method, which employed acetonitrile as solvent and LC-MS/MS equipment with Phenyl-Hexyl column, was satisfactory for the analysis of these perfluorinated compounds in both matrices, with the lowest correlation coefficient (r²) equal to 0.9884 for PFOS in sewage samples. In such matrix, the detection and quantification limits of the method were 1.50 µg/L and 4.54 µg/L for PFOA, and 2.11 µg/L and 6.40 µg/L for PFOS, respectively. As for the sludge matrix, the limits of detection and quantification for PFOA were 1.34 µg/kg dw (dry weight) and 4.05 µg/kg dw, whereas for PFOS, they were 0.32 µg/kg dw and 0.96 µg/kg dw. Samples collected at two Brazilian sewage treatment plants (STP) which employ different treatment technologies were analyzed, and PFOA was detected in four sludge samples in the range of 9.09-10.26 µg/kg. On the other hand, PFOS was quantified in all sewage samples (with concentrations ranging from 17.05 to 53.58 µg/L) and all sludge sample in concentrations that varied from 8.14 to 12.50 µg/kg dw. The obtained LQs confirm the applicability of the method for µg-level screening and monitoring of sewage treatment plants, especially in the context of limited analytical resources. Importantly, this represents the first reported application of low-temperature partition extraction (LTPE) for PFAS analysis in sewage and sludge, demonstrating the feasibility and potential of this simplified approach for future environmental investigations.