| Summary: | Among nanoparticles (NPs), titanium dioxide is one of the most highly manufactured worldwide and widely used in multiple products for both industrial use and personal care products. This increases the probability of release into aquatic environments, potentially affecting these ecosystems. The present study aimed to evaluate TiO<sub>2</sub> P25 NP toxicity in zebrafish embryos and eleutheroembryos by evaluating LC<sub>50</sub>, hatching rate, embryo development, and chemical analysis of the TiO<sub>2</sub> concentration accumulated in eleutheroembryo tissues. Zebrafish embryos ~2 h post-fertilization (hpf) were exposed to 75, 100, 150, 200, and 250 mg/L TiO<sub>2</sub> P25 NPs for 48 and 96 h. A total of 40–60 embryos were placed in each Petri dish for the respective treatments. Three replicates were used for each treatment group. Ti<sup>4+</sup> concentrations were determined by inductively coupled plasma optical emission spectrometry (ICP-OES), and a conversion factor was used to calculate the TiO<sub>2</sub> concentrations in the tissues. The highest calculated concentrations of TiO<sub>2</sub> in zebrafish larvae were 1.0199 mg/L after 48 h and 1.2679 mg/L after 96 h of exposure. The toxicological results indicated that these NPs did not have a significant effect on the mortality and hatching of zebrafish embryos but did have an effect on their development. LC<sub>20</sub> and LC<sub>30</sub> were determined experimentally, and LC<sub>50</sub> and LC<sub>80</sub> were estimated using four different methods. Up to 11% of embryos also presented physical malformations. These effects can be detrimental to a species and affect ecosystems. Physical malformations were observed in all treatments, indicating teratogenic effects.
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