The toxicological evaluation of Sewage Effluents and Pharmaceuticals with the use of Zebrafish as a model organism

Sammanfattning: The presence of pharmaceuticals in the environment has been an issue of increasing concern and sewage treatment plants have been identified as the principal sources ofpharmaceuticals and endocrine disrupting chemicals in the aquatic environment.In this study, zebrafish juveniles and adults were exposed to sewage effluents that had undergone treatment processes (A1-A7) at Hammarby Sjostad’s sewage treatment plant in order to evaluate the effectiveness of the treatment processes. This was conducted with the aid of the fish embryotoxicity test (FET), reproduction test and the fish sexual development test (FSDT). A reduction in the spawning ability and fecundity (number of eggs produced by the females) was observed in the reproduction test in sewage effluent A4 (Biofilter). The zebrafish exposed to sewage effluent A2 (after sedimentation treatment) had a highernumber of successful spawnings than the controls, while the fish exposed to effluents A3(Outlet L1) and A5 (ozone) exhibited a decrease in spawning ability. The induction ofvitellogenin was detected in male zebrafish exposed to A2 (after sedimentation treatment), A3 (Outlet L1) and A4 (Biofilter) treatment processes in the fish sexual development test(FSDT). In the FET conducted on the offsprings of the adult zebrafish exposed to the various sewage effluents, no effect was observed. In addition, eight pharmaceuticals from different therapeutic classes viz Clozapine (anti psychotic), Atenolol (β-blocker), Cimetidine (anti histamine), Fluoxetine (anti depressant), Loperamide (anti diarrhoeal), Verapamil (Calcium channel blocker), Bezafibrate (lipid lowering agent) and Cyclophosphamide (anti neoplastic) were evaluated for their potential toxicity to zebrafish embryos with the aid of the fish embryotoxicity test. The zebrafish embryos were exposed to five different concentrations of the pharmaceuticals in 96 well plates. The exposure concentrations were 1μg/L, 10μg/L, 100μg/L, 1mg/L and 10mg/L. Dimethyl sulphoxide(DMSO) and standardized fish water were used as controls. A concentration of 0.1% DMSO was maintained in the test solutions. A mixture of musk ketone and phenylthiourea was used as positive control. The endpoints monitored included hatching time, heart rate, tail extension, circulation, coagulation, spinal deformation, death and oedema. A decrease in the heart rate was observed in the zebrafish embryos exposed to the highest concentration of clozapine (10 mg/L) and abnormalities were observed in the embryos exposed to all the concentrations of clozapine.The results of this investigation indicate that the FET could be improved upon in order to render it more sensitive for the toxicity testing of substances. Also, ozonation appears to be an effective treatment technique in sewage treatment plants for the reduction of sewage effluents and pharmaceuticals.