For PFBS, PFTrDA, and PFTeDA, for which the labeled standards are not marketed,13C4-PFOS, for the first, and 13C2-PFDoA for the other two compounds, were used. A mixture of the isotopically labeled standards was prepared at 100 g L−1 and used to spike samples and standards at the concentration of 1 g L−1 in the final extract.Full names, abbreviations, chemical formula and precursor ions of the selected compounds are reported in Table 1S, supplementary material.