Efficacy of the hatching event in assessing the embryo toxicity of the nano-sized TiO2 particles in zebrafish: A comparison between two different classes of hatching-derived variables

• Exposure to nTiO2 led to a significant: premature hatching and general decrease in time required for normal hatching; and change in HR and hpe interrelations in a dose-dependent manner.
• The major change in hatchability between the treatment and control occurred at 58 hpe (62 hpf), when the treatment with nTiO2 induced significant premature hatching compared to only 6% of the hatched embryos in the control at the same time point.
• EC10 and EC50 values that cause premature hatching at 58 hpe for nTiO2 are 0.073 µg ml-1 and 107.2 µg ml-1 respectively.

The aim of the present study was to evaluate the nano-TiO2 toxicity to zebrafish embryos through evaluating the success in hatching in relationship with hours post-exposure instead of considering just the total hatching rate. Zebrafish embryos 4 h post-fertilization were exposed to nTiO2 (0, 0.01, 10, and 1000 µg mL−1) for 130 h. The hatching rate (HR) was calculated for each concentration (treatment). The HR magnitude was significantly (p<0.001) correlated (using simple regression) to hours post-exposure time interval (hpe; 34, 58, 82, 106, and 130), noted as HR.hpe. The HR descriptive statistics (HRds) and the parameters of the regression models (i.e., constant, x, F, and r2) were recruited to define 15 HRds- and 4 h.hpe-derived variables, respectively. The efficacy of the variables was evaluated. Exposure to nTiO2 led to a significant: premature hatching and general decrease in time required for normal hatching; and change in HR and hpe interrelations in a dose-dependent manner. The major change in hatchability between the treatment and control occurred at 58 hpe (62 hpf), when the treatment with nTiO2 induced significant premature hatching compared to only 6% of the hatched embryos in the control at the same time point. EC10 and EC50 values that cause premature hatching at 58 hpe for nTiO2 are 0.073 µg mL−1 and 107.2 µg mL−1 respectively. In general, this study shows multivariate differences among exposure concentrations of nTiO2 recruiting hatching-derived endpoints.