Induction of micronucleus of Oreochromis niloticus exposed to waters from the Cubatão do Sul River, southern Brazil

•Evaluation of genotoxic effects of a complex environmental mixture on fish.•River course urbanization contributes to the genotoxic effects on aquatic ecosystems.•Runoff of toxic substances to a river can affect MN frequency in fish.

In an effort to characterize the pollution of surface waters by potentially genotoxic agents, this study aimed at assessing the frequency of micronucleated (MN) erythrocytes of the fish species, Oreochromis niloticus, from the Cubatão do Sul River. This river is the source of drinking water for the region of Florianópolis, capital of Santa Catarina State, Brazil. Negative control fish showed low frequency of MN, ranging between 0.49‰ and 0.90‰. Positive control (potassium dichromate 2.5 mg/L) organisms showed high MN frequency (16.82–17.25‰). The MN frequency increased along the river (Site 1 – 1.24‰ winter 2011; Site 4 – 9.76‰ summer 2011).Based on the observation of elevated MN erythrocytes frequency in O. niloticus exposed to water samples from along the river course, we conclude that the complex environmental mixtures of water from the Cubatão do Sul River have genotoxic potential. This genotoxicity most likely originated from agricultural runoff and domestic effluents released without treatment, based on the evidence from literature data and a survey in the region. This study provides a scientific basis for future studies regarding the genotoxicity of complex environmental mixtures in natural environments.