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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Available from: Woo-Mi Lee, Sep 28, 2015
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    • "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 "
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    ABSTRACT: Nanoparticles (NPs) are widely used in many industrial applications. NP fate and behavior in seawater are a very important issue for the assessment of their environmental impact and potential toxicity. In this study, the toxic effects of two nanomaterials, silicon dioxide (SiO2) and titanium dioxide (TiO2) NPs with similar primary size (~20 nm), on marine microalgae Dunaliella tertiolecta were investigated and compared. The dispersion behavior of SiO2 and TiO2 NPs in seawater matrix was investigated together with the relative trend of the exposed algal population growth. SiO2 aggregates rapidly reached a constant size (600 nm) irrespective of the concentration while TiO2 NP aggregates grew up to 4 ± 5 μm. The dose-response curve and population growth rate alteration of marine alga D. tertiolecta were evaluated showing that the algal population was clearly affected by the presence of TiO2 NPs. These particles showed effects on 50 % of the population at 24.10 [19.38-25.43] mg L(-1) (EC50) and a no observed effect concentration (NOEC) at 7.5 mg L(-1). The 1 % effect concentration (EC1) value was nearly above the actual estimated environmental concentration in the aquatic environment. SiO2 NPs were less toxic than TiO2 for D. tertiolecta, with EC50 and NOEC values one order of magnitude higher. The overall toxic action seemed due to the contact between aggregates and cell surfaces, but while for SiO2 a direct action upon membrane integrity could be observed after the third day of exposure, TiO2 seemed to exert its toxic action in the first hours of exposure, mostly via cell entrapment and agglomeration.
    Environmental Science and Pollution Research 06/2015; DOI:10.1007/s11356-015-4790-2 · 2.83 Impact Factor
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    • "The dissolution of Zn 2+ from ZnO NPs can also account for its toxic potentiality (Aruoja et al., 2009; Lee and An, 2013; Chen et al., 2012). A few researchers (Lee and An, 2013; Chen et al., 2012) have noted that the ZnO NPs caused destabilization of the cell membrane, which in turn inhibited the growth of algae in a linear proportion to the NPs concentration. Ji et al. (2011) observed that the toxicity of ZnO NPs towards green algae Chlorella sp. "
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    ABSTRACT: Continuous increase in the usage of ZnO nanoparticles in commercial products has exacerbated the risk of release of these particles into the aquatic environment with possible harmful effects on the biota. In the current study, cytotoxic effects of two types of ZnO nanoparticles, having different initial effective diameters in filtered and sterilized lake water medium [487.5±2.55nm for ZnO-1 NPs and 616.2±38.5nm for ZnO-2 NPs] were evaluated towards a dominant freshwater algal isolate Scenedesmus obliquus in UV-C, visible and dark conditions at three exposure concentrations: 0.25, 0.5 and 1mg/L. The toxic effects were found to be strongly dependent on the initial hydrodynamic particle size in the medium, the exposure concentrations and the irradiation conditions. The loss in viability, LDH release and ROS generation were significantly enhanced in the case of the smaller sized ZnO-1 NPs than in the case of ZnO-2 NPs under comparable test conditions. The toxicity of both types of ZnO NPs was considerably elevated under UV-C irradiation in comparison to that in dark and visible light conditions, the effects being more enhanced in case of ZnO-1 NPs. The size dependent dissolution of the ZnO NPs in the test medium and possible toxicity due to the released Zn(2+) ions was also noted. The surface adsorption of the nanoparticles was substantiated by scanning electron microscopy. The internalization/uptake of the NPs by the algal cells was confirmed by fluorescence microscopy, transmission electron microscopy, and elemental analyses. Copyright © 2015 Elsevier B.V. All rights reserved.
    Aquatic Toxicology 03/2015; 162. DOI:10.1016/j.aquatox.2015.03.004 · 3.45 Impact Factor
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    • "They noticed that UV-C/TiO 2 exerted a higher mortality compared to UV irradiation alone. Most of the algal toxicity studies on TiO 2 NPs till date were carried out under different irradiation conditions such as visible light and UV light especially, UV A and UV B (Lee and An, 2013; Ji et al., 2011). To the best of our knowledge, there are limited reports highlighting the photocatalytic effects of UV-C on the toxicity of TiO 2 NPs. "
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    ABSTRACT: In view of the increasing usage of anatase and rutile crystalline phases of titania NPs in the consumer products, their entry into the aquatic environment may pose a serious risk to the ecosystem. In the present study, the possible toxic impact of anatase and rutile nanoparticles (individually and in binary mixture) was investigated using freshwater microalgae, Chlorella sp. at low exposure concentrations (0.25, 0.5 and 1mg/L) in freshwater medium under UV irradiation. Reduction of cell viability as well as a reduction in chlorophyll content were observed due to the presence of NPs. An antagonistic effect was noted at certain concentrations of binary mixture such as (0.25, 0.25), (0.25, 0.5), and (0.5, 0.5) mg/L, and an additive effect for the other combinations, (0.25, 1), (0.5, 0.25), (0.5, 1), (1, 0.25), (1, 0.5), and (1, 1) mg/L. The hydrodynamic size analyses in the test medium revealed that rutile NPs were more stable in lake water than the anatase and binary mixtures [at 6h, the sizes of anatase (1mg/L), rutile NPs (1mg/L), and binary mixture (1, 1mg/L) were 948.83±35.01nm, 555.74±19.93nm, and 1620.24±237.87nm, respectively]. The generation of oxidative stress was found to be strongly dependent on the crystallinity of the nanoparticles. The transmission electron microscopic images revealed damages in the nucleus and cell membrane of algal cells due to the interaction of anatase NPs, whereas rutile NPs were found to cause chloroplast and internal organelle damages. Mis-shaped chloroplasts, lack of nucleus, and starch-pyrenoid complex were noted in binary-treated cells. The findings from the current study may facilitate the environmental risk assessment of titania NPs in an aquatic ecosystem. Copyright © 2015 Elsevier B.V. All rights reserved.
    Aquatic Toxicology 02/2015; 161C. DOI:10.1016/j.aquatox.2015.02.006 · 3.45 Impact Factor
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