The nanotechnology industry offers many benefits to society, however its potential depends upon the knowledge of its impact on public health and the environment. NPs can enter the body bypassing epithelia, accumulating in spleen, gut, liver and brain as shown in fish as environmental species. While the mechanism of uptake and metabolism of NPs is unknown, their size and physical characteristics suggest that they may enter the epithelia through an endocytotic mechanism. The aim of this study is to investigate the toxic mechanism of metal- (Ag and TiO2) NPs. These NPs were selected for their impact on health and environment due to their commercially widespread use. Specific goals will be investigating NPs kinetics (uptake/trafficking/excretion) by the monitoring of NPs intracellular localization through time using polarized intestinal cells thus enabling the evaluation of apical and basolateral uptake and possible bioaccumulation effects. Toxicity of Ag- and TiO2-NPs will be evaluated by monitoring the incorporation and trafficking of vesicles containing NPs through time using state of the art electron microscopy. In parallel, biochemical and molecular cellular responses will be measured including specific effect on Cu homeostasis. Thus, Cu-ATPase function will be tested by monitoring its trafficking behaviour. In addition, Cu intracellular availability will be measured using molecular markers of Cu availability. The mechanistic knowledge generated in this project is envisioned to support human and environmental risk assessment with regard to metal ion and metal NP exposure. Moreover, the proposed development of the polarized cell line models based on the Caco2 (human) and RTgutGC (fish) cell lines for evaluating mechanism of NP interactions will not only be of great importance from a biological point of view (apical/basolateral uptake) but will also contribute to the efforts to establish animal-free, in vitro alternatives in environmental risk assessment.