Hepatic oxidative stress and catalyst metals accumulation in goldfish exposed to carbon nanotubes under different pH levels

Experiments were conducted to investigate the effect of three different carbon nanotubes [single-walled carbon nanotubes (SWCNTs), hydroxylated multi-walled carbon nanotubes (OH-MWCNTs), and carboxylated multi-walled carbon nanotubes (COOH-MWCNTs)] on antioxidant parameters and metals accumulation in the liver of Carassius auratus. A semi-static test system was used to expose C. auratus to either a freshwater control, 0.1, or 0.5 mg/L CNTs at three pH levels (5.0, 7.25, and 9.0) for 3 and 12 days. The activities of three antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), together with the level of glutathione (GSH) and malondialdehyde (MDA) were determined in liver on the 3rd and 12th day. The results showed that there was a significant increase in MDA concentration and SOD activity in fish exposed to CNTs, indicating that CNTs exposure induces an oxidative stress response in fish. According to integrated biomarker response (IBR) index, the effect of these three CNTs on liver can be ordered as SWCNTs > OH-MWCNTs > COOH-MWCNTs and they are more toxic to fish in an alkaline environment. Moreover, the concentrations of catalyst metals (Co, Ni, and Mo) and bioelements (Cu, Fe, Zn, and Se) in liver were changed, depending on the CNTs concentration, the pH level, and the exposure duration. Generally, all CNTs groups showed that catalyst metals could be concentrated significantly into the liver of fish, and changes in hepatic Cu, Zn, Fe, and Se contents are consistent with the activity of antioxidant enzymes.