Development of LC-MS/MS methods to study diclofenac and some transformation products in bivalve, fish, sediment and watercress. Application to a contaminated model ecosystem
Résumé
Pharmaceuticals are ubiquitously found in the aquatic environment, mainly at trace levels, however long-term exposure can have negative impacts on biotic communities due to the intrinsic biological activity of these drugs. Diclofenac (DCF) is one of the most frequently detected human pharmaceuticals in water and it has recently been included on the “watch” list of the European Union. Nevertheless little data deals with the the detection of this substance and its transformation products in aquatic organisms. In this context, analytical methodologies based on LC-MS/MS analysis, after a QuEChERS or an ASE extraction, were developed to quantify traces of DCF along with nine of its biotic and abiotic transformation products in bivalve, fish, sediment and watercress collected from lotic mesocosm experiments. The analytical protocol was optimized and validated for each matrix of interest separately: sticklebacks, zebra mussels, sediment and watercress. Uncontaminated matrices were used for the optimization steps, they corresponded to the matrices introduced into the mesocosms before the contamination with DCF. Considering the great diversity of transformation products and metabolites, a focus was made in this study on chemically stable and commercially available substances. The developed methods were next applied to samples collected after a 6-months exposure in mesocosms where DCF was continuously introduced at three concentrations (5; 0.5 and 0.05 μg/L). The QuEChERS extraction was implemented for all matrices, except for sediment where best results were obtained with ASE extraction. DCF was quantified in zebra mussels and sediment for both highest exposure conditions and in watercress solely for the highest concentration. In sticklebacks DCF resulting concentration was inferior to our quantification limits probably due to rapid depuration as fishes were collected one week after the end of experiments. Among the selected metabolites, 4’OH-DCF was the most often quantified : it was observed in sticklebacks, sediment and watercress for the highest exposure concentration. The metabolites DCF-lactam and 5-OH-DCF were also measured as well as the 2-indolone either in sediment, watercress or bivalves. In this presentation, the optimization of the extraction and clean-up steps will be described. The results of the quantification of DCF, along with nine of its degradation products and metabolites, in organisms and watercress collected from mesocosms will be presented.