SinS - Abstract

Abstract Information :

The presence of antimicrobial (AM) residues in soil has frequently been reported due to the intense use of these pharmaceuticals in animal husbandry. As a result, AM multi-resistant bacterias have emerged, raising global health concerns. Within this context, the present work aimed to develop an accurate analytical method for the simultaneous analysis of twenty-four AMs in soil:compost samples by means of Ultra-High Performance Liquid Chromatography coupled to a triple-quadrupole mass spectrometer (UHPLC-QqQ). To that aim, two extraction techniques, focused ultrasound solid-liquid extraction (FUSLE) and QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) were evaluated and compared. According to the results, a wider group of AMs was extracted from the matrix using QuEChERS (at pH 2.5), retrieving higher recoveries and more adequate repeatability compared to FUSLE. The clean-up step using solid phase extraction (SPE) was also thoroughly studied and loading 3.5 mL of the sample adjusted at pH 4 to 200 mg cartridges resulted to be the optimal conditions in terms of accuracy. The method was successfully validated at 10 µg·kg-1, 25 µg·kg-1 and 50 µg·kg-1 showing adequate trueness (70-130 %) and repeatability (RSD<30 %) in all the concentration levels, with few exceptions. Procedural limits of quantification (LOQPRO) were also determined and values ranged from 0.45 to 7.50 μg·kg-1. Pefloxacin was the only AM that could not be validated at the lowest level since the LOQPRO value was 10 μg·kg-1. Nevertheless, the calculated LOQPRO were sufficiently low to detect the target compounds in soil samples collected from four small cheese producers from the Basque Country. Among the twenty-four compiled samples eight showed positive presence of AM, being the higher concentrations detected for sulfamethazine, trimethoprim and danofloxacin at 7.9 ± 0.8 µg·kg-1, 4.9 ± 0.5 µg·kg-1, and 27.1 ± 1.4 µg·kg-1, respectively. All the samples were also analysed through UHPLC coupled to a high-resolution mass-spectrometer (UHPLC-qOrbitrap) in order to extent the multitarget method to suspect screening of more than 22,281 suspects (for by-products simulation BioTransformer 3.0 software and NORMAN database were used). Propiconazole and 5-azulenemethanol, both with AM properties, were identified at 2a and 2b Schymanski levels, respectively. In order to determine potential transformation products of AMs, an experiment using soils fortified with oxytetracycline (one of the most occurring compounds in agricultural soils) at 1 mg·kg-1 and 150 mg·kg-1 was designed under controlled conditions of light, temperature and humidity during 30 days, and the data processing is currently underway.