Toxicological evaluation of some sewage effluents with the aid of the Zebra fish sexual development test.

Aquatic organisms such as fish are usually exposed to complex mixtures of environmental pollutants such as sewage effluents in the aquatic milieu. Several adverse effects such as endocrine disruption, impaired reproductive abilities of aquatic organisms, genotoxicity and immunotoxicity have been attributed to the presence of estrogenic chemicals in sewage effluents from sewage treatment plants (STPs). The major aim of the investigation was to evaluate the toxicity of the sewage effluents obtained from different treatment processes (A1- A7) at a STP situated in Stockholm, Sweden. The sewage effluents were evaluated with a fish sexual development test and zebra fish (Danio rerio) was used as a model test species. Sewage effluents A2 (After sedimentation treatment), A3 (Outlet L1) and A4 (Biofilter) evoked significant increments in vitellogenin concentration in the exposed fish compared to the controls. In addition, there were more females in the groups exposed to sewage effluents A2 (45%), A3 (46%), A4 (47%) and in the internal control A8 (46%) compared with control group A1 [clean reference water, 35%]. The results indicated that the treatment techniques at the STP were incapable of completely reducing the levels of estrogens and perhaps other aquatic pollutants in the sewage effluents. The treatment techniques should be improved upon in order to ensure successful proliferation of aquatic organisms.