AVALIA??O DA TOXICIDADE DO LODO DE ESGOTO DE DUAS ESTA??ES DE TRATAMENTO PARA O INVERTEBRADO AQUáTICO Daphnia similis

摘要

The use of sewage sludge as a fertilizer is an important alternative for the disposal of that residue which is a source of essential nutrients for plants. Nevertheless, depending on the origin, the sewage sludge can be a reservoir of organic toxic compounds and heavy metals that can impact the life of the aquatic communities. In the present work, it was evaluated the adverse effect of the sludge from the sewage treatment stations of Franca (SP) and Baruerí (SP) cities on the freshwater invertebrate Daphnia similis. The immobility in the treated organisms (14 days exposure) with 2 or 10 g.L-1 of sludge (wet weight) was more than 90.0% comparing with the controls, where this value was between 3.1 and 21.8%. This toxic effect was observed for the material from both stations and do not seem to be related with changes in the water pH, conductitity and dissolved oxigen. However, higher toxicity was observed for Barueri sludge, where the effects appeared earlier. Results of short term exposure with this sludge indicated that the presence of organic compounds in the acetonic extract may have extreme importance in the toxicity of the test material. The remaining residue of the acetonic extraction also promoted highly diminution of the D.similis mobility. The use of sludge from both sources for agriculture purposes may constitute risk to the adjacent aquatic systems when the material is applied at the agronomic rate or more.