Sub-lethal effects of titanium dioxide nanoparticles on the physiology and reproduction of zebrafish

There are limited data on the sub-lethal physiological effects of titanium dioxide nanoparticles (TiO(2) NPs) in adult fishes, and the consequences of TiO(2) NP exposure on reproductive success are also unclear. This study aimed to examine the sub-lethal effects of a 14-d aqueous TiO(2) (TiO(2) NP, 0.1 or 1.0 mg l(-1); TiO(2) bulk, 1.0 mg l(-1)) exposure on the physiology and reproductive health of zebrafish. After the 14-d exposure, fish were examined for haematology, whole body electrolyte and trace metal profiles, biochemistry, and histopathology. Then, during a 21-d post exposure recovery period, effects of the TiO(2) exposure on reproductive success were evaluated. Whole body Ti concentrations increased significantly in fish exposed to both the 1.0 mg l(-1) TiO(2) NP and bulk TiO(2) compared to controls, but concentrations returned to control levels by the end of the recovery period. No change in erythrocyte counts were observed, but there was a two-fold decline in leukocyte counts in all TiO(2) treatment groups relative to time-matched controls. Whole body electrolyte and trace metal profiles were not affected by exposure to TiO(2), and there were no changes in Na(+)K(+)-ATPase activity in brain, gill or liver tissues. Total glutathione (GSH) levels in brain, gill and liver tissues were higher in fish exposed to TiO(2) NP (both 0.1 and 1.0 mg l(-1)) compared to bulk TiO(2) and control fish. Histological examination of gill, liver, brain and gonad tissues showed little evidence of treatment-related morphological change. At the end of the 14-d exposure adult zebrafish were able to reproduce; however, the cumulative number of viable embryos produced was lower in fish exposed to 1.0 mg l(-1) TiO(2) (both NP and bulk) by the end of the 21-d recovery period. Overall, this study showed limited toxicity of bulk or nano scale TiO(2) during the exposure; however reproduction was affected in both bulk and NP 1.0 mg l(-1) groups.