Analysis of transformations of oxytetracycline in water/sediment systems by HPLC-MSn

IVANIC, FEDERICO M.; CANDAL, ROBERTO J.; BUTLER, MATIAS

Rio de Janeiro

Conferencia; III Iberoamerican Conference on Mass Spectrometry; 2022

Brazilian Society of Mass Spectrometry

Introduction: Oxytetracycline (OTC) is a broad-spectrum antibiotic that, due to its intensive use in livestock, may be regarded as emerging contaminant (EC). As other ECs, OTC may degrade in the environment, generating transformation products (TPs), which could potentially be more harmful than their parent compound. Laboratory experiments allow to simulate diverse environmental conditions and characterize multiple TPs of low abundance through HPLC-MSn.Methods: Aerobic and anaerobic OTC degradation experiments (AX and ANX, respectively) were carried out in water/sediment reactors at pH 5.5, under biotic and abiotic conditions, during 45 days, based on existing guidelines [1]. High OTC concentrations were employed to facilitate TPs characterization. Aqueous and sediment samples were taken periodically and, after conditioning [2], were analyzed using HPLC-MSn. Multiple tandem mass spectra were acquired using a linear ion trap mass spectrometer (Thermo LTQ XL) equipped with an electrospray source in positive-ion mode. Search of transformation products was accomplished by an untargeted screening approach, using MatLab software to filter potential candidates.Results: Biotic degradation of OTC in solution proved to be faster in both AX and ANX than under abiotic conditions, rendering also a higher diversity of TPs, specially at short times. When comparing decrease in OTC concentration between AX and ANX conditions, the latter was faster. Moreover, TPs displaying higher m/z values than OTC were more numerous in AX than in ANX, mainly as a result of oxidative reactions. Considering all tested conditions, from a total amount of 50 TPs detected, half of them could be structurally characterized through their ion fragments. Interestingly, even though several TPs were detected in all conditions, differences in their time evolution and persistence were found.Roughly 45% of all detected TPs in water seem to be more persistent in water than OTC, particularly in AX. Furthermore, analysis of sediments not only showed that OTC was still detectable at the end in all conditions, but also around 30% of all detected TPs were also present in them. No correlation could be detected between structural modifications in TPs and their persistence.Conclusions: Batch simulated degradation experiments have proven to be useful to examine the fate of OTC in water/sediment systems under different conditions. HPLC-MSn and extensive ion fragment analysis allowed to characterize several TPs and to assess their persistence in solution and sediments.