Impact of co-exposure to titanium dioxide nanoparticles and Pb on zebrafish embryos

Complex interactions have been established between nanoparticles (NPs) and heavy metals in real environments. Herein we used zebrafish embryos to investigate the influence of titanium dioxide NPs (n-TiO₂) on the uptake, bioconcentration, and depuration, and toxicity of Pb. The formation of n-TiO₂-Pb complexes was confirmed in an exposure suspension. An increase in Pb bioconcentration was observed in zebrafish embryos upon co-exposure to n-TiO₂ and Pb; moreover, n-TiO₂-Pb complexes could be found in the embryos, indicating the bioavailability of NPs. However, there was no difference in the depuration rates of Pb in the presence of n-TiO₂. Metallothionein (MT) content was significantly increased upon exposure to Pb alone, and the content significantly increased even further upon co-exposure. A downregulation in the expression levels of the neurodevelopment-related genes gfap, syn2α, and elavl3 was observed in the embryos, and we also noted a reduction in the swimming speed of and the total distance traveled by the larvae. To summarize, our results indicate that n-TiO₂ can act as an effective carrier of Pb to enhance its uptake, bioavailability, and toxicity in zebrafish embryos.