Abstract

ZARATE-CRUZ, Griselda S.; ZAVALETA-MANCERA, Hilda A.; ALARCON, Alejandro  and  JIMENEZ-GARCIA, Luis F.. Phytotoxicity of ZnO nanoparticles on the aquatic fern Azolla filiculoides Lam. Agrociencia [online]. 2016, vol.50, n.6, pp.677-691. ISSN 2521-9766.

Nanoparticles of ZnO are disposed of in the environment and abound in wastewater, but their toxicity to plants is little known. The objective of this study was to evaluate the physiological response of Azolla filiculoides to the presence of two ZnO particle sizes: analytical grade nanoparticles (NPs, 26.7±1 nm) and pharmaceutical grade submicrometric particles (SMPs, 238±30.7 nm), in three concentrations (100, 200, and 400 mg L-1), and a control. The experimental design was completely randomized, data were analyzed with an ANOVA and means were compared with Tukey (p≤0.05). Transmission Electron Microscopy (TEM) showed that the NPs were isodiametric, while the SMPs were elongated. Plants were incubated in Yoshida solution containing the NPs and SMPs in a greenhouse for 6 d. The small particles (NPs) and the concentration of 400 mg NPs ZnO L-1 reduced growth and concentration of chlorophylls (Chla, Chlb, Chl total) and of carotenes and xanthophylls (c+x). Chlorophyll fluorescence (Fv/Fm) was decreased in all tested concentrations compared with the control, especially with NPs, which were more toxic than SMPs. NPs reduced total antioxidant activity and total phenolic compounds, relative to SMPs. Nitrogenase activity decreased in all the ZnO particle concentrations regardless of size. The Zn element microanalysis with energydispersive X-ray spectroscopy on scanning microscopy (EDS-SEM) showed that Zn was more abundant on the abaxial side of the frond, in function of NPs concentration, in contrast with that of SMPs. In conclusion, ZnO particle size is more determinant in degree of toxicity than concentration. Chlorophyll fluorescence and nitrogenase activity were good indicators of toxicity in this species.

Keywords : Phytotoxicity; water fern; nanoparticles; ZnO NPs.

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