Phytotoxicity Of Several Typical Engineered Nanoparticles

Effects of nano-rutile TiO2 on seed germination of three higher plant species (rape, maize and cucumber) was investigated firstly. Maize(Zea mays L.) showed a significant inhibitory effect. The results indicated that the EC50 value was about 100mg/L for maize. Therefore, maize was used as plant for further study of phytotoxicity.The effects of nano-rutile TiO2 and multiwalled carbon nanotubes on the growth and antioxidant enzymes of maize seedlings were investigated under hydroponic conditions. Nano-rutile TiO2 (≥50 mg/L) significantly decreased root and shoot growth (p<0.05) after 9 days, while MWCNTs did not influence the biomass obviously. Treatment with 10,50,100 mg/L nano-rutile and nano-anatase TiO2 inhibit the root growth on day 10 (by 49%,57%,57% and 36%,38%,59%), which also inhibit the shoot growth on day 10 (by 36%,37%,46% and 23%,37%,44%)compared with control. There were no significant differences in biomass between three bulk TiO2 treatment and the control. In contrast to control plants, the young leaves showed slight chlorotic symptoms in the group of plants treated with nano-TiO2 for 10 days.The mechanism of nanoparticles on maize was also investigated in this study. Under two stress conditions, the antioxidant system was activated respectively. Compared to the control, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were up-regulated (p<0.05). Lipid peroxidation in terms of malondialdehyde (MDA) content was enhanced by TiO2 exposure, whereas, MWCNTs and bulk TiO2 did not cause oxidative damages in maize seedlings. The results indicated that the phytotoxicity of nano-TiO2 was much higher than that of MWCNTs and bulk TiO2, and oxidative stress induced by nanoparticles(NPs) exposure might play a role in the phytotoxicity of NPs. The remarkable effect of nano-TiO2 is probably attributed to particle composition and shape. The results indicated that nano-TiO2 could induce the increase of reactive oxygen species (ROS) in maize cells, excessive ROS inhibited the activities of SOD and CAT, caused lipid oxidation, and destroyed the maize cells and resulted in the death of maize cells. This may be one of mechanisms of nanoparticles inhibiting the growth of plant. However, more detailed mechanism should be further confirmation.Analytical methods indicated that the nano-Ag are able to penetrate the cell wall and cell membrane of maize cells, while nano-CuO adhere to the cell wall and cell membrane.