Ammonia in the presence of nano titanium dioxide (nano-TiO) induces greater oxidative damage in the gill and liver of female zebrafish.

Water pollution caused by a highly hazardous chemical ammonia and a widespread application nanomaterials-nano titanium dioxide (n-TiO) in nature water has attracted extensive concern of the world. However, the potential joint effects of the two factors are unknown. Aim to investigate the potential interactive effects of ammonia and n-TiO and the behind mechanisms, adult female zebrafish (Danio rerio) were co-exposed for 8 weeks by total ammonia nitrogen (TAN; 0, 3, 30 mg/L) and n-TiO (0, 0.1, 1 mg/L) in different combination conditions based on a full-factorial design. The analysis of absorption kinetics confirmed that n-TiO could absorb free ammonia (NH) in aqueous solution and the loss rate of free NH increased with the rise of n-TiO concentration. Consistent with this, free NH concentrations in the gill and liver were higher in the presence of n-TiO compared to TAN exposure alone. The increases of MDA and PC concentrations in the gill and liver of fish indicated that TAN and n-TiO alone or in combination caused oxidative stress. Simultaneously, the activity and transcription of antioxidant enzymes (T-SOD, CuZn-SOD, Mn-SOD, CAT, GPx and GST) as well as antioxidant GSH contents were extensively inhibited by TAN and n-TiO via Nrf2-Keap1 signaling. The significant interactive effects of TAN and n-TiO were detected on levels of GSH, GST and gstr1 mRNA in the gill, and on levels of GSH, T-SOD, Mn-SOD, CAT levels as well as gpx1a and keap1 mRNAs in the liver, implying synergistic toxic risk of TAN and n-TiO. The more severe histopathological alterations and higher IBR analysis in co-treatment groups further proved that the existence of n-TiO excavated ammonia-induced toxicity in the gill and liver, especially in liver. In conclusion, ammonia and n-TiO have a synergistic toxic risk of fish health because ammonia and n-TiO cause oxidative-antioxidative imbalance by inducing ROS overproduction.