Integrated biomarker response index to assess toxic effects of environmentally relevant concentrations of paracetamol in a neotropical catfish (Rhamdia quelen).

The nonsteroidal anti-inflammatory drugs (NSAIDs) are amongst the most commonly detected classes of pharmaceuticals in freshwater environments, with paracetamol being the most abundant. The aim of this study was to evaluate the possible toxic effects of environmentally relevant concentrations (0.25, 2.5 and 25 μg.L) of paracetamol in Rhamdia quelen fish exposed for 14 days using different biomarkers. The total count of leukocytes and thrombocytes was reduced at the highest concentration. In the gills, all concentrations of paracetamol reduced the glutathione S-transferase (GST) activity and the reduced glutathione (GSH) levels compared to the control group. The activity of catalase (CAT) was not altered and glutathione peroxidase (GPx) activity increased at the highest concentrations. The superoxide dismutase (SOD) activity decreased at 25 μg.L and the LPO levels increased at 2.5 μg.L when compared to the control group. The concentration of ROS was not different among the groups. In the posterior kidney the activities of GST (2.5 μg.L), CAT (2.5 μg.L and at 25 μg. L) and GPx and GSH levels increased at all concentrations when compared to the control group. The SOD activity and LPO levels did not change. Paracetamol caused genotoxicity in the blood and gills at concentrations of 2.5 μg.L and in the posterior kidney at 2.5 and 25 μg.L. An osmoregulatory imbalance in plasma ions and a reduction in the carbonic anhydrase activity in the gills at 0.25 μg.L were observed. Histopathological alterations occurred in the gills of fish exposed to 25 μg.L and in the posterior kidney at 0.25 and 25 μg.L of paracetamol. The integrated biomarker index showed that the stress caused by the concentration of 25 μg.L was the highest one. These results demonstrated toxic effects of paracetamol on the gills and posterior kidneys of fish, compromising their physiological functions and evidencing the need for monitoring the residues of pharmaceuticals released into aquatic environment.