Effects of the food additive titanium dioxide on plant systems

Titanium dioxide (TiO2) E171 is a widely used food additive considered harmless for humans as it is defined not digestible or absorbable in tissues. E171 consists in a white powder with aggregates greater than 100 nm. Recently, structural analyzes have highlighted the co-presence of a variable percentage (15-40%) of nanoparticles (NPs) with at least one dimension less than 100 nm. In general NPs can modify their physicochemical properties with respect to the bulk material resulting much more reactive. The presence of NPs in E171 deserves particular attention given its wide use and dispersion in the environment, with consequent entry of TiO2 NPs into the food chain. It is therefore very important to assess the environmental impact risks of E171 through ecotoxicological tests, simulating a real contamination. In this study, a commercial E171 food additive was characterized for its possible phytotoxic and genotoxic effects on two plant systems, Allium cepa L. (model plants in ecotoxicological studies) and Lens culinaris L.. Initially, analysis by Transmission Electron Microscope and Environmental Scanning Electron Microscope determined a 15% of NPs and no other element besides titanium and oxygen in E171. Hence, five different concentrations of E171 (0.05 gL-1, 0.1 gL-1, 0.5 gL-1 , 1 gL-1 and 2 gL-1) were texted for their possible toxic effect after 3 days from seed germination on the two plants. Phytotoxicity results (seed germination and root length endpoints) clearly indicated no acute effects both in A. cepa and in L. culinaris while cytogenetic results (mitotic index, cytogenetic anomalies and micronuclei endpoints) indicated a dose-dependent genotoxic effect. Ultrastructural analysis of root cells are in progress to evaluate the possible NPs internalization and their effects in the two plants after E171 exposure. These data are in agreement with the recent warning from the scientific community on the urgent regulation on the use of E171 in food also to limit its release into the environment, as a further cause of damage to animal and plant organisms.