Oxidative stress and hypermethylation induced by exposure of Oreochromis niloticus to complex environmental mixtures of river water from Cubatão do Sul, Brazil

• Evaluation of DNA methylation in fish exposed to complex environmental mixtures.
• Runoff of toxic substances to a river can cause oxidative stress in fish.
• River course urbanization contributes to the genotoxic effects in aquatic ecosystems.

In this study, we investigated the effects of oxidative stress and hypermethylation through lipid peroxidation and DNA methylation, respectively, in erythrocytes of Oreochromis niloticus exposed to environmental complex mixture of water from Cubatão do Sul River throughout the year. This river is the source of drinking water for the region of Florianópolis, the capital of Santa Catarina State, Brazil. Lipid peroxidation was quantified by the rate of malondialdehyde (MDA) formation, and DNA methylation was quantified by the rate of 5-methyldeoxycytosine (m5dC) formation. In all studied sites, the river water samples caused metabolic changes in O. niloticus. MDA formation rates were significantly different when compared to the negative control (except for samples from Site 1 during spring 2010, summer 2011 and fall 2011). All samples (except Site 1, spring 2010) induced increases in the m5dC formation rates, and at the end of the study, the values were near the values found in the positive control (potassium dichromate 2.5 mg/L). The results showed that samples of environmental complex mixtures of water from Cubatão do Sul River are capable of inducing high levels of oxidative damage and hypermethylation in O. niloticus.