Biodegradação/bioacumulação de fármacos pela cianobactéria Microcystis novacekii coletada no Parque Estadual do Rio Doce-MG

Abstract

The potential for bioaccumulation/ biodegradation of drugs in aqueousmedium by the cyanobacterium Microcystis novacekii was investigated. The experiments were performed in a WC (water culture) medium and in a real pharmaceutical effluent. The drugs studied were: ethinylestradiol (sexual hormone), diclofenac and ibuprofen (anti-inflammatory), tetracycline (antibiotic), atenolol (beta blocker), clofibric acid and bezafibrate (antilipemics) In the first part of the present study, each drug was tested separately and incubated together with the cyanobacteria in a WC medium. To estimate the efficiency of drugs removal, the analyte concentrations in the extracellular medium were monitored for a period of 7 days. It was found that this cyanobacterium showed no ability to bioaccumulate / biodegrade the following drugs: ibuprofen,atenolol, clofibric acid and bezafibrate. On the other hand, the removal rate of ethinylestradiol reached 65-68% at the concentrations tested. For tetracycline removal rates varying from 60 to 100 % were observed, whereas for diclofenac a reduction rate ranging from 70 to 96 % was determined. Control experiments indicated that these three drugs underwent spontaneous degradation in an insignificant rate whereas their presence did not affect the cyanobacterium growth. Careful analysis by chromatography coupled to mass spectrometry indicated noformation of degradation products. To evaluate the removal mechanism and to determine the bioaccumulation rate of these drugs into the cyanobacterium intracellular medium, an unprecedentedprocedure for cell lysis was developed. For ethinylestradiol and tetracycline approximately 35 % and 0.5 % of the initial drugs were bioaccumulated, respectively. The removal mechanism was proposed to be bioaccumulation combined with mineralization. For diclofenac, which was not detected in the intracellular medium and whose biodegradation did not lead to the formation of metabolites, a mineralization mechanism was proposed. In the second part of the present study, the drugs that were biodegraded by the cyanobacterium (ethinylestradiol, tetracycline and diclofenac) were added to a pharmaceutical effluent that contained several other organic contaminants (including pharmaceutical compounds). After 7 days of treatment, the cyanobacterium was able to reduce approximately 50% of the total organic content, measured by analysis of chemical (COD) and biological (BOD) demand of oxygen.Consistent with the results previously described, only ethinylestradiol andtetracycline were detected inside the cells of the cyanobacteria. These results therefore confirm that the cyanobacterium Microcystis novacekii has potential to be used in the treatment of wastewater contaminated with large amounts of organic matter.