The monitoring of water bodies means the attempt of protecting vulnerable groups of organisms inhabiting streams and rivers. Industrial and domestic discharges may worsen the water quality and affect biological balance, structure and the functioning of the ecosystem. Cubatão City, is one of the largest industrial centers in Brazil and in Latin America, where the constant discharge of effluents into Cubatão River and its tributaries caused a degradation scenario in the hydrographic basin of the

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... egion. The objective of this study was to evaluate the acute and chronic effects of surface water from Cubatão River and two of its tributaries (Perequê and Pilões) by ecotoxicological assays. In addition, physical chemical parameters were analyzed. Ceriodaphnia dubia and Vibrio fischeri were exposed-organisms during the studied period. The study was conducted between 2010 and 2011 in four campaigns and nine sites along the basin of Cubatão River. The ecotoxicity was measured by Vibrio fischeri bioluminescence, EC50 values ranging from 31.25% to 71.61%. In contrast, based on a bioequivalence t-test statistical analysis, the results obtained with Ceriodaphnia dubia revealed no toxicity in the sampling sites. A critical analysis of raw data of luminescence was carried out showing higher values during the 2 nd campaign. From the numbers obtained for physical-chemical parameters P5 was far the worst due to chlorides, hardness and conductivity. From the Pearson correlation analysis carried out with toxicity to V. fischeri and the physical chemical parameters, the dissolved oxygen in water resulted in a moderate positive correlation. Sediment contamination was also demonstrated in the region.