Residues of antibiotics and sulfonamides in honeys from Basque Country (NE Spain)

BACKGROUND: The aim of this work was to ensure that Label Basque market honey is free of veterinary residues. RESULTS: A total of 567 Basque honey samples were previously analyzed with the respective Charm II system—68 samples were presumptive positive for sulfonamides (SA‐s), 24 samples for tetracyclines (TC‐s), and no positive samples for chloramphenicol (CAP) (<0.3 µg kg −1 ) residues. The residues were mostly confirmed by liquid chromatography fluorescence detection (LC‐FD) and tandem mass spectrometry (LC‐MS/MS), according to the latest European Union criteria for the analyses of veterinary drug residues (2002/657/EC). These techniques confirmed that 19 of the 68 samples, presumptive contaminated with SA‐s, contained sulfathiazole (STZ) residues at levels from 20 to 210 µg kg −1 , and the 24 samples presumptive contaminated with TC‐s, were also confirmed, showing tetracycline (TC) levels from 15 to 920 µg kg −1 . Linearity range, decision limit (CCα), detection capability (CCβ), precision and reproducibility were also determined. CONCLUSION: Residues of veterinary drugs were confirmed in a very limited number of honey samples: sulfathiazole (3.40%) and tetracycline (4.22%). This work reports the advantages of the Charm II assay, but also its limitations, detecting SA‐s in most (87.7%) of the heather ( Erica vagans ) honey samples. The false positives detected in this honey were assumed to be of an unknown compound that has not been confirmed as a drug residue. Until now, no studies have been performed to find out if other heather honeys of different geographical origins give similar false positives for SA‐s.