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Oxidative potential of UV‐A irradiated or non‐irradiated suspensions of TiO2 or SiO2 nanoparticles on Allium cepa roots

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The effect of UV‐A irradiated or non‐irradiated suspensions of agglomerates of TiO2 or SiO2 nanoparticles on roots of the onion (Allium cepa) has been studied. The reactive potential of TiO2 nanoparticles which have photocatalytic potential and the non‐photocatalytic SiO2 nanoparticles with the same size of agglomerates was compared. We measured the activity of antioxidant enzyme glutathione reductase (GR), ascorbate peroxidase (A‐POD), guaiacol peroxidase (G‐POD), catalase (CAT) and lipid peroxidation to assess the oxidative stress in exposed A. cepa roots. A wide range of concentrations of nanoparticles was tested (0.1 to 1000 µg/mL). The sizes of agglomerates range in both cases from 300 to 600 nm and the exposure time was 24 h. Adsorption of SiO2 nanoparticles on the root surface was minimal, but became significant when roots were exposed to TiO2 agglomerates. No significant biological effects were observed even at high exposure concentrations of SiO2 and TiO2 nanoparticles individually. Plants appear to be protected against nanoparticles by the cell wall, which shields the cell membrane from direct contact with the nanoparticles. We discuss the need to supplement conventional phytotoxicity and stress endpoints with measures of plant physiological state when evaluating the safety of nanoparticles. Environ Toxicol Chem © 2013 SETAC

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