An optimized sample treatment method for the determination of antibiotics in seawater, marine sediments and...

Antibiotics used in marine aquaculture have been reported to accumulate in sediments and non-target aquatic organisms, modifying the biodiversity and the environmental conditions in areas close to the fish farms. Improved analytical methods are required to assess the spread and the impacts of aquaculture antibiotics in the marine environment, as well as to estimate resistance development risks. In this study, we have optimized a method for simultaneous quantitative determination of oxytetracycline, florfenicol and flumequine in marine samples using liquid chromatography coupled to time-of-flight high resolution mass spectrometry (LC-TOF/MS). The method optimization was carried out for seawater, sediment and biological samples (biofilm and two benthic invertebrate species: Gammarus aequicauda and Monodonta articulata). Special attention was paid to the optimization of the extraction and purification steps, testing: liquid-liquid and solid-liquid extractions, the use of silica and other commercial sorbents' clean-up, and single and tandem solid phase extraction procedures. The limits of quantification (MQLs) achieved with the developed method are 0.1-0.5 μg L-¹ in seawater; 1-5 μg kg^-1 in marine sediments; 5-25 μg kg^-1 in biofilm; and 100-500 μg kg^-1 in invertebrates, with good accuracy and precision. Method recoveries in spiked samples are 65-120% in seawater and sediment samples, and 63-110% in the biological samples. The method has been successfully implemented for the determination of antibiotic concentrations in sediment and invertebrate samples collected from a Mediterranean bay in south-east Spain. These represent significant advances in the analysis of antibiotics in environmental samples, especially for wild marine taxa, and attend for a proper assessment of the environmental fate and side effects of aquaculture antibiotics in the marine environment.