Antimicrobiais sulfametoxazol e trimetoprima em efluente hospitalar: determinação, degradação através de eletrocoagulação e identificação de subprodutos e metabólitos

Abstract

In this study, it was developed a methodology using liquid chromatography coupled to tandem mass spectrometry for the determination of antimicrobials sulphamethoxazole and trimethoprim in hospital effluent and for monitoring the electrocoagulation process applied to synthetic solutions, as well as, to the hospital effluent fortified with the antimicrobials, both at the same concentration of 1 mg L-1. The achieved limits of detection and quantification were 0.25 and 0.5 μg L-1, respectively. The linear range of the method was 0.5 to 100 μg L-1, with a correlation coefficient always greater than <0.9995 for both antimicrobials. The average concentration of sulphamethoxazole and trimethoprim found for the hospital effluent was 27.8 and 6.6 μg L-1, respectively. In order to study the best conditions for conducting the electrocoagulation, factorial design with surface response methodology was used. It was set as variables the distance of the electrodes, the concentration of electrolyte (NaCl) and the applied current (mA). As evaluation parameter it was used the chemical oxygen demand (COD) reduction of the hospital effluent. The best result for the COD reduction (57.9%) was achieved using 500 mg of NaCl, electrode distance of 30 mm and current of 800 mA. By means of the application of the electrocoagulation process to synthetic solutions of the antimicrobials and Soxhlet extraction, it was confirmed the true degradation or the reduction of the antimicrobial concentration by possible adsorption on the generated process sludge. From the average reduction of 84.7% of the initial sulphamethoxazole concentration, 6.0% of which were adsorbed by the sludge, resulting an average reduction 79.3%, at pH 5 and 7. The antimicrobial trimethoprim, at pH 5 and 7, showed an average reduction of 28.7% of the initial concentration by sludge adsorption, and no degradation occurred. The identification of the metabolites in hospital effluent and the degradation products generated by the electrocoagulation of the synthetic solution was performed using liquid chromatography quadrupole linear ion trap mass spectrometry. The metabolites identified were N4-acetylsulphamethoxazole and dihydroxitrimethoprim, and their paths of fragmentation were proposed. The degradation products of sulfamethoxazole identified were dihydroxyl sulphamethoxazole (identified only after 60 minutes treatment) and dehydrogenate sulphamethoxazole. For the electrocoagulation of the hospital effluent fortified with standard solutions of both antimicrobials, it was observed no degradation. Therefore, the degradation products in real effluent samples could not be studied. The electrocoagulation process applied to the hospital effluent was efficient by reducing COD under the conditions evaluated; but, it was not efficient by the degradation of the fortified antimicrobials in the effluent. The developed methodology used as analytical tool, LC-MS/MS_QTrap operating in lineal way, for the determination of the investigated antimicrobials in hospital wastewater, as well as for the efficiency evaluation of the electrocoagulation process by the concentration reduction or the degradation in synthetic solution and hospital wastewater, proved to be fast, sensitive, selective, sparing laborious manipulation of the sample.