Ammonia in the presence of nano titanium dioxide (nano-TiO2) induces greater oxidative damage in the gill and liver of female zebrafish
Honghui Guo, Yu Kuang, Kang Ouyang, Ce Zhang, Hui Yang, Siqi Chen, Rong Tang, Xi Zhang, Dapeng Li, Li Li
Abstract
Water pollution caused by a highly hazardous chemical ammonia and a widespread application nanomaterials-nano titanium dioxide (n-TiO2) 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-TiO2 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-TiO2 (0, 0.1, 1 mg/L) in different combination conditions based on a full-factorial design. The analysis of absorption kinetics confirmed that n-TiO2 could absorb free ammonia (NH3) in aqueous solution and the loss rate of free NH3 increased with the rise of n-TiO2 concentration. Consistent with this, free NH3 concentrations in the gill and liver were higher in the presence of n-TiO2 compared to TAN exposure alone. The increases of MDA and PC concentrations in the gill and liver of fish indicated that TAN and n-TiO2 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-TiO2 via Nrf2-Keap1 signaling. The significant interactive effects of TAN and n-TiO2 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-TiO2. The more severe histopathological alterations and higher IBR analysis in co-treatment groups further proved that the existence of n-TiO2 excavated ammonia-induced toxicity in the gill and liver, especially in liver. In conclusion, ammonia and n-TiO2 have a synergistic toxic risk of fish health because ammonia and n-TiO2 cause oxidative-antioxidative imbalance by inducing ROS overproduction.