Phytotoxicity of halloysite-supported ionic liquid-like phase (HNT-SILLP) catalyst on Raphanus sativus L.

Nanotechnologies and nanomaterials are increasingly involved in the production of fillers, opacifiers, catalysts, semiconductors, cosmetics, microelectronic components and drug carriers with improved properties. Nevertheless, the production, use and disposal of nanomaterials, will inevitably lead to their release into the soil, with potential phytotoxicity on plants and negative impacts on economy, society and environment (1). In the last years halloysite nanotubes (HNT) emerged as promising materials with appealing perspective for technological applications. We have recently reported the generation of HNT derivatives carrying octylimidazolium moieties on the external surface (HNT supported ionic liquid-like phase, HNT-SILLP) and employed them as supports for palladium catalyst (HNT-SILLP/Pd) (2, 3). These studies have shown that these materials are good catalysts and encourage their potential application in large-scale industrial processes. The present research aimed to investigate the potential phytotoxicity of HNT, HNT-SILLP and HNT-SILLP/Pd, by considering different endpoints as seed germination physiology and cytogenetic analyses (4). Raphanus sativus L. seeds were imbibed in distilled water (control) or in HNT, HNT-SILLP and HNT-SILLP/Pd, incubated at 25°C in the dark, under continuous agitation up to 72 h. Germination percentage and mean germination time, together with fresh and dry weights were evaluated in control and HNTs-treated seeds. To further rule out possible impacts of these nanomaterials on genetic stability, the accumulation of nanotubes during seedling development by means of thermogravimetric analysis, IR spectroscopy and cytogenetical analysis on radical meristems were performed. The preliminary results here presented show that these nanomaterials do not affect the germinative process and the development of the seedling. Thermogravimetric analysis and IR spectroscopy studies additionally showed that exposure to the investigated nanomaterials does not lead to an accumulation into the seedling organs since the plant cell wall might act as a barrier, efficiently preventing entry of these nanoparticles into the cell.