DNA damage of erythrocytes of fish Oreochromis niloticus (Perciformes, Cichlidae), after acute exposure to river water receiving effluent from an oil refinery

The comet assay was applied to erythrocytes of fish Oreochromis niloticus (Perciformes, Cichlidae), exposed in the laboratory to water samples taken from the Paraiba do Sul (Brazil), a river that receives effluents from an oil refinery. Water samples were collected at three points: point 1 – upstream from the discharge of effluent from the oil refinery; point 2 – the dump location of the effluent from the oil refinery, and point 3 - downstream from the oil refinery dump. Artesian well water was used as the control. Samples were collected in May and August of 2004 (dry season) and in November of 2004 and January of 2005 (rainy season). The data obtained indicated the presence of genotoxic substances in points 2 and 3 in all the sampling months. We conclude that the final effluent from the oil refinery, even after treatment, can affect the quality of the Paraiba do Sul River. Keywords: aquatic biomonitoring, comet assay, genotoxicity, Nile tilapia.