Behaviour and biomarkers of oxidative stress in Gambusia holbrooki after acute exposure to widely used pharmaceuticals and a detergent

Pharmaceuticals are continuously dispersed into the environment, as a result of human and veterinary use, and have become a relevant environmental concern. In the present study, the acute toxicity of three therapeutic agents (diazepam, clofibrate, and clofibric acid) and a detergent, sodium dodecylsulphate (SDS), to the euryhaline fish Gambusia holbrooki was evaluated. Special attention was devoted to oxidative stress parameters. G. holbrooki males, captured in the estuary of the Minho River (NW Portugal), were exposed for 96 h to the selected compounds. The following oxidative stress biomarkers were evaluated in gills and liver tissues: reduced and oxidised glutathione, lipid peroxidation, and several antioxidant enzymes, namely (1) total and selenium-dependent glutathione peroxidase (GPx), (2) glutathione reductase (GRed), (3) copper–zinc superoxide dismutase (Cu–ZnSOD) and manganese superoxide dismutase (MnSOD), and (4) glutathione-S-transferases (GSTs). In the particular case of diazepam, swimming behaviour was also evaluated. The obtained results indicate an overall diminished oxidative stress response caused by SDS and diazepam. Oxidative-based alterations were observed after exposure to clofibrate and clofibric acid, with modifications of several enzymatic activities. Diazepam caused evident behavioural changes: animals showed dark pigmentation and also abnormal postures, namely lethargy and anomalous movement.