Uptake, Toxicity and Translocation of Engineered Nanoparticles in Plants

Recent developments on environmental fate models indicate that as nano waste, engineered nanomaterials/nanoparticles (ENM/Ps) could reach terrestrial ecosystems thus potentially affecting environmental and human health. Plants can be therefore exposed to ENM/Ps but controversial data in terms of fate and toxicity are currently available. Furthermore, there is a current lack of information on complex interactions/transformations to which ENM/Ps undergo in the natural environment as for instance with existing toxic compounds. The main aim of current study is to evaluate potential toxicological risks due to the exposure of plants to ENM/Ps in their natural environment, and investigating different routes of exposure (i.e. water and soil). The aim of the first study reported in chapter 1 was to asses behavior and biological effects of titanium dioxide nanoparticles (n- TiO2) (Aeroxide P25, Degussa Evonik) and its interaction with cadmium (CdCl2) in plants using radish seeds (Raphanus sativus parvus) as model species. Radish seeds were exposed to different concentrations of n-TiO2 (range 1-1000 mg/L) and CdCl2 ( range 1-250 mg/L) alone and in combination using a seed germination and seedling growth toxicity test OECD 208. Percentages of seed germination, germination index (GI) and root elongation were calculated. Cell morphology and oxidative stress parameters as glutathione-S-transferase (GST) and catalase activities (CAT) were measured in radish seeds after 5 days of exposure. Z-Average, PdI and Z-potential of n-TiO2 in Milli-Q water as exposure medium were also determined. DLS analysis showed small aggregates of n-TiO2, negative Z-potential and stable PdI in seed’s exposure media. Germination percentage, GI and root length resulted affected by n-TiO2 exposure compared to controls. Exposure of CdCl2 significantly abolished germination % and GI compared to control seeds and a concentration dependent decrease on root elongation was observed against controls (p<0.05). As well, significant decrease of germination %, GI and root elongation was observed in seeds co-exposed to n-TiO2 and CdCl2 at the highest concentrations (1000mg/L n-TiO2 and 250 mg/L CdCl2) compared to co-exposed seeds at low concentration (1mg/L n-TiO2 and 1 mg/L CdCl2) and controls (p<0.05). Root elongation significantly increase compared to controls at the lowest co-exposure concentration (p<0.05). Similarly at intermediate concentrations of 10 and 100 mg/L in co-exposure conditions, n-TiO2 did not affect CdCl2 toxicity. Concerning antioxidant enzymes, a significant increase of CAT activity in seeds exposed to single high n-TiO2 concentration (1000 mg/L) was observed while n-TiO2 (1 mg/ L), CdCl2 (1 and 250 mg/L) and co-exposure resulted significantly decreased compared to controls (p<0.05). Regarding GST activity, a slight increase in seeds exposed to 1000 mg/L n-TiO2 but no significantly was observed, however both n-TiO2 and CdCl2 alone (1 and 250 mg/L, respectively) or in combinations caused a significant decrease in GST activity (p