The discharge of effluents and toxic compounds into aquatic systems represents a growing environmental problem involving an impact on water ecology and potential effect on human health. Most municipal wastewaters are complex mixtures; their complexity led as to carry out a hazard assessment using chemical analyses and biological tests. This study investigates biochemical alteratiobns in two sentinel organisms, the Anodonta cygnea mussel and the Xenopus laevis frog exposed for different lengths of time to various concentration of wastewater of the S. Antonino Ticino treatment plant. The results point out the long-life of toxic compounds.