Rapid advances in nanotechnology have increased the volume of nano wastes, and their potential release into aquatic environments pose potential threats to aquatic organisms. Therefore, the corresponding health and safety of engineered nanoparticles (NP) requires further assessment. Previous studies have documented the negative adverse effects of metal NPs to fish1,2, however, most studies have been conducted under pristine laboratory conditions where the influence of abiotic factors that could alter the behaviour and toxicity of the NPs were not considered1. This study investigated the developmental and cardiovascular toxicity of two PVP coated AgNPs of different sizes (50nm and 5nm) and uncoated CuONPs on zebrafish embryos. Experiments were conducted by exposing zebrafish embryos to different NP concentrations in the presence and absence of abiotic factors including humic acid (HA) and artificial sunlight (UV). A dose-dependent decrease in hatch rate, survival, heart rate and increased developmental deformities were observed in zebrafish embryos exposed to both AgNPs, with the smaller 5nm AgNP being more toxic. In contrast, CuONPs completely inhibited embryos from hatching. The two abiotic factors were found to induce different effects on the toxicity of NPs to the the zebrafish embryos. The presence of HA mitigated the toxicity of all three NPs to the zebrafish, however, UV irradiation was found to enhance the toxicity of both AgNPs, and slightly decreased that of CuO NPs. These results suggest the effect of the abiotic factors (HA and UV) were NP-specific. Overall, the results of this study clearly demonstrated the dynamic influences of abiotic factors, which may be a result of dynamic and complex transformation behavior of the NPs that could not be explained by size and surface charge alone. Therefore, this study highlighted the importance of abiotic factors for environmental realistic toxicity assessment of emerging contaminants, such as metal NPs, in the future.