Article

Effects of zinc oxide and titanium dioxide nanoparticles on green algae under visible, UVA, and UVB irradiations: No evidence of enhanced algal toxicity under UV pre-irradiation

Department of Environmental Science, Konkuk University, 1 Hwayang-dong, Gwangjin-gu, Seoul 143-701, Republic of Korea.
Chemosphere (Impact Factor: 3.34). 01/2013; 91(4). DOI: 10.1016/j.chemosphere.2012.12.033
Source: PubMed

ABSTRACT

Some metal oxide nanoparticles are photoreactive, thus raising concerns regarding phototoxicity. This study evaluated ecotoxic effects of zinc oxide nanoparticles and titanium dioxide nanoparticles to the green algae Pseudokirchneriella subcapitata under visible, UVA, and UVB irradiation conditions. The nanoparticles were prepared in algal test medium, and the test units were pre-irradiated by UV light in a photoreactor. Algal assays were also conducted with visible, UVA or UVB lights only without nanoparticles. Algal growth was found to be inhibited as the nanoparticle concentration increased, and ZnO NPs caused destabilization of the cell membranes. We also noted that the inhibitory effects on the growth of algae were not enhanced under UV pre-irradiation conditions. This phenomenon was attributed to the photocatalytic activities of ZnO NPs and TiO(2) NPs in both the visible and UV regions. The toxicity of ZnO NPs was almost entirely the consequence of the dissolved free zinc ions. This study provides us with an improved understanding of toxicity of photoreactive nanoparticles as related to the effects of visible and UV lights.

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    • "growth by TiO 2 -NPs was shown to be larger under ultraviolet and fluorescent light irradiations (Hong and Otaki, 2006). On the other hand, no enhancement of the effects of TiO 2 or ZnO-NPs on growth inhibition of green alga Pseudokirchneriella subcapitata was observed under UV radiation with respect to visible light (Lee and An, 2013). However, in these studies the NP concentrations were in the mg L −1 ranges, several orders of magnitude higher than those expected in the aquatic environment. "
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    • "A very recent study of Xia et al. (2015) reported for Nitzschia closterium population (96 h) EC50 values of 88 and 118 mg L −1 for 21-and 60-nm TiO 2 NPs, respectively. Actually lower EC50 values were observed for P. subcapitata (Aruoja et al. 2008, Lee et al. 2013) and for different marine algae; Li et al. 2015 reported TiO 2 EC50 values of 10 mg L −1 for Karenia brevis and 7 mg L −1 for the diatom Skeletonema costatum while 1– 3 mg L −1 TiO 2 was reported to exert a significant adverse effect upon some marine phytoplankton population (Thalassiosira pseudonana, S. costatum, Dunaliella tertiolecta, and Isochrysis galbana) only under natural levels of ultraviolet radiation (Miller et al. 2012). In the main, studies about SiO 2 and TiO 2 NP toxicity toward microalgae are hardly comparable because of several differences in testing matrices, test organisms, and standardized experimental conditions (Minetto et al. 2014). "
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