This study investigates the synthesis, characterization, and ecotoxicology of zinc oxide nanoparticles (ZnO NPs) using in vivo models, specifically Artemia salina and adult zebrafish. ZnO NPs were synthesized via the polyol process and characterized using X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, and ultraviolet-visible (UV-Vis) spectroscopy. The NPs exhibited a wurtzite structure with an average particle size of 32.2 ± 5.2 nm. The hydrodynamic size and zeta potential were determined using a Zetasizer, confirming the stability of the NPs in both deionized and system water. Acute toxicity tests on Artemia salina revealed a lethal concentration (LC50) of 86.95 ± 0.21 μg/mL, with significant physical malformations observed at 50 μg/mL after 96 hours. The study also assessed the bioaccumulation of ZnO NPs in adult zebrafish, finding higher concentrations in the gastrointestinal tract compared to other tissues. ICP-OES analysis confirmed the presence of ZnO NPs in zebrafish tissues, with the highest concentrations in the gastrointestinal tract at 100 μg/mL exposure. The study highlights the importance of using Artemia salina and zebrafish as models for assessing the toxicity and bioaccumulation of ZnO NPs. The findings suggest that ZnO NPs pose ecotoxicological risks, particularly through their potential to disrupt aquatic ecosystems. The results emphasize the need for further research to understand the long-term effects of ZnO NPs on organisms and their potential impact on human health. The study underscores the significance of considering the environmental and health implications of ZnO NPs, advocating for continued research to fully comprehend their effects.This study investigates the synthesis, characterization, and ecotoxicology of zinc oxide nanoparticles (ZnO NPs) using in vivo models, specifically Artemia salina and adult zebrafish. ZnO NPs were synthesized via the polyol process and characterized using X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, and ultraviolet-visible (UV-Vis) spectroscopy. The NPs exhibited a wurtzite structure with an average particle size of 32.2 ± 5.2 nm. The hydrodynamic size and zeta potential were determined using a Zetasizer, confirming the stability of the NPs in both deionized and system water. Acute toxicity tests on Artemia salina revealed a lethal concentration (LC50) of 86.95 ± 0.21 μg/mL, with significant physical malformations observed at 50 μg/mL after 96 hours. The study also assessed the bioaccumulation of ZnO NPs in adult zebrafish, finding higher concentrations in the gastrointestinal tract compared to other tissues. ICP-OES analysis confirmed the presence of ZnO NPs in zebrafish tissues, with the highest concentrations in the gastrointestinal tract at 100 μg/mL exposure. The study highlights the importance of using Artemia salina and zebrafish as models for assessing the toxicity and bioaccumulation of ZnO NPs. The findings suggest that ZnO NPs pose ecotoxicological risks, particularly through their potential to disrupt aquatic ecosystems. The results emphasize the need for further research to understand the long-term effects of ZnO NPs on organisms and their potential impact on human health. The study underscores the significance of considering the environmental and health implications of ZnO NPs, advocating for continued research to fully comprehend their effects.