Decrease of particle size in the nanoscale has been identified as a main parameter for the increased toxicity of different materials. Polystyrene, for instance, is a very biocompatible polymer used in cell culture. Nanoparticles, however, made from this material are cytotoxic (Mayer et al., 2009). Accumulation of metal and metal

oxide NMs is seen also in lower animals such as fruit flies, mussels, planktonic crustaceans, rainbow trouts and in plants (Harris and Bali, 2008, Pan and Wang, 2004, Panacek et al., 2011, Scown et al., 2009 and Zhu et al., 2009). In laboratory animals accumulation of XL184 these particles especially in liver, spleen and kidney is seen (Bu et al., 2010, Chen et al., 2006, Kim et al., 2009, Kim et al., 2010, Meng et al., 2007, Park et al., 2011, Wang et al., 2007a and Zhang et al., 2010a). For physiologically relevant testing it would be important to have an approximate idea learn more on the levels of NMs to which humans are exposed. This estimation is quite difficult to make. Models based on per capita daily intake of various foods combined with expected distributions of chemicals or biological hazards in food work

less well with NMs. The content of ingredients in form of nanoparticles is generally not indicated in food, interaction with food compounds is expected and physical changes of particles in the gastrointestinal tract are likely. Concentrations of metal and metal oxide in water and soil have been reported to reach 15.2 ng/l and 1.28 μg/kg for TiO2, 0.76 ng/l and 22.7 ng/kg for silver and 0.01 μg/l

and 0.093 μg/kg for ZnO, respectively (Gottschalk et al., 2009). Compared to other metal and metal oxide nanoparticles intake of TiO2 by food is relatively high: Powell et al. (2010) estimate ingestion of 5 mg TiO2/person/d with an unknown part of it in nanoform. Total dietary intake only of nano-TiO2 is estimated to be 2.5 mg/individual/d (0.036 mg/kg for a person of 70 kg; (Lomer et al., 2000)). The intake of nano- and microparticles, however, shows great variations: 0–112 mg/individual/d has been reported (Lomer Phosphatidylinositol diacylglycerol-lyase et al., 2004). Metal and metal oxide nanoparticles can accumulate in plants (Harris and Bali, 2008) and in animals of the food chain (Lankveld et al., 2010) and may reach considerably higher levels in humans. Consequently, chronic effects rather than acute toxic effects on the human organism are expected. NMs are subjected to wide variations in the orogastrointestinal tract. pH variations from slightly acid to neutral in the oral cavity and in the small intestine to a very acid pH in the stomach have a strong effect on surface charge of the particles and, as a consequence, on agglomeration and cellular uptake. Differences in the pH between fasted and fed state are prominent in the stomach (Horter and Dressman, 2001).