The reactivity and toxicity of the soluble toxicants in the presence of the engineered nanomaterials is not well explored. In this study, the probable effects of TiO2 and Al2O3 nanoparticles (n-TiO2, n-Al2O3) on the toxicity of Cr(VI) were assessed with the dominant freshwater algae, Scenedesmus obliquus, in a low range of exposure concentrations (0.05, 0.5 and 1μg/mL). In the presence of 0.05μg/mL n-TiO2, the toxicity of Cr(VI) decreased considerably, which was presumably due to the Cr(VI) adsorption on the nanoparticle surface leading to its aggregation and precipitation. The elevated n-TiO2 concentrations (0.5 and 1μg/mL) did not significantly influence Cr(VI) bio-availability, and a dose dependent toxicity of Cr(VI) was observed. On the other hand, n-Al2O3 did not have any significant effect on the Cr(VI) toxicity. The microscopic observations presented additional information on the morphological changes of the algal cells in the presence of the binary toxicants. The generation of reactive oxygen species (ROS) suggested contribution of oxidative stress on toxicity and LDH release confirmed membrane permeability of algal cells upon stress.

Amitava Mukherjee

Centre for Nanobiotechnology

Vellore Campus

Chandra Sekaran N

Dalai S

Pakrashi S

Bhuvaneshwari M

Iswarya V

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Aquatic Toxicology

Gold nanoparticles (GNPs) are widely used for medical purposes, both in diagnostics as well as drug delivery, and hence are prone to release and distribution in the environment. Thus, we have explored the effects of GNPs with two distinct surface capping (citrate and PVP), and three different sizes (16, 27, and 37&nbsp;nm) at 0.01-, 0.1-, and 1-mg&nbsp;L−1 concentrations on a predominant freshwater alga Scenedesmus obliquus in the sterile freshwater matrix. We have also investigated how an abundant metal ion from freshwater, i.e., Zn2+ ions may modulate the effects of the selected GNPs (40&nbsp;nm, citrate, and PVP capped). Preliminary toxicity results revealed that gold nanoparticles were highly toxic in comparison to zinc ions alone. A significant modulation in the toxicity of Zn ions was not noticed in the presence of GNPs. In contrast, zinc ions minimized the toxicity produced by GNPs (both CIT-37 and PVP-37), despite its individual toxicity. Approximately, about 42, 33, and 25% toxicity reduction was noted at 0.05-, 0.5-, and 5-mg&nbsp;L−1 Zn ions, respectively, for CIT-37 GNPs, while 31% (0.05&nbsp;mg&nbsp;L−1), 24% (0.5&nbsp;mg&nbsp;L−1), and 9% (5&nbsp;mg&nbsp;L−1) of toxicity reduction were noted for PVP-37 GNPs. Maximum toxicity reduction was seen at 0.05&nbsp;mg&nbsp;L−1 of Zn ions. Abbott modeling substantiated antagonistic effects offered by Zn2+ ions on GNPs. Stability and sedimentation data revealed that the addition of zinc ions gradually induced the aggregation of NPs and in turn significantly reduced the toxicity of GNPs. Thus, the naturally existing ions like Zn2+ have an ability to modulate the toxicity of GNPs in a real-world environment scenario

Environmental Science and Pollution Research

Modulatory effects of Zn2+ ions on the toxicity of citrate- and PVP-capped gold nanoparticles towards freshwater algae, Scenedesmus obliquus

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 1. mg/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 6. h, the sizes of anatase (1. mg/L), rutile NPs (1. mg/L), and binary mixture (1, 1. mg/L) were 948.83. ±. 35.01. nm, 555.74. ±. 19.93. nm, and 1620.24. ±. 237.87. nm, 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. © 2015 Elsevier B.V.

Combined toxicity of two crystalline phases (anatase and rutile) of Titania nanoparticles towards freshwater microalgae: Chlorella sp

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 Zn2+ 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. © 2015 Elsevier B.V.

Cytotoxicity of ZnO NPs towards fresh water algae Scenedesmus obliquus at low exposure concentrations in UV-C, visible and dark conditions

The mechanism of disinfection by pulsed plasma technology was investigated in detail, with Escherichia coli as the model bacteria. Studies were carried out to investigate the behavior of bacterial surface potential as a function of applied energy, based on molecular level analysis of DNA and proteins. The cell survival and morphological changes during plasma treatment were correlated with membrane damage using SEM analysis, along with DNA degradation and protein leakage. In addition, cell size (Z-average) and poly-dispersive index (PI) of E. coli cells were measured to understand the colloidal behavior of disinfected bacterial cells in plasma reactors. Significant membrane deformities and morphological changes were observed under SEM analysis, and lactate dehydrogenase (LDH) assay confirmed a drastic increase in membrane permeability upon plasma treatment. An energy dependent DNA fragmentation and protein leakage confirmed the killing of bacterial cells. The E. coli cell membrane zeta potential (-14.81 ± 2.08 mV) was neutralized to -1.08 ± 0.83 mV in 6 min of treatment time due to the propensity of H+ ions on bacterial membranes. The FTIR confirmed the changes occurring in the functional groups of bacterial cell membranes, which further emphasized the possible interaction with ROS/RNS and membrane damage. © The Royal Society of Chemistry 2016.

RSC Advances

Disinfection of water by pulsed power technique: a mechanistic perspective

This work demonstrates the application of plasma generated by pulsed corona discharge for the rapid degradation of carbofuran from aqueous solution. Carbofuran with a concentration of 0.5 mg/L to 30 mg/L was effectively removed within 4 to 10 min of treatment time, at 101.5 W input power. Degradation yield (2.95 g/kWh) was much higher for 10 mg/L carbofuran concentration compared to degradation yield (0.37 g/kWh) for 0.5 mg/L carbofuran. The effect of pulsed voltage, pulsed frequency, initial pesticide concentration, pH, and effect of radical scavengers (HCO3-, CO32-, and humic acid) was also investigated in detail. Appearance of some key intermediates confirmed the possibility of formation of some demethylated products due to direct electron impaction during degradation process. Seven intermediates were identified, and possible oxidation and reduction mechanism of carbofuran degradation pathway was proposed. Microalgae ecotoxicity study confirmed the complete detoxification of carbofuran after 14 min corona discharge. © 2016 American Chemical Society.

Industrial and Engineering Chemistry Research

Rapid Removal of Carbofuran from Aqueous Solution by Pulsed Corona Discharge Treatment: Kinetic Study, Oxidative, Reductive Degradation Pathway, and Toxicity Assay

In the current study, two aspects concerning (i) the cytotoxicity potential of TiO2 nanoparticles (NPs) toward freshwater algal isolate Scenedesmus obliquus and (ii) the potential detoxification of NPs by the microalgae were assessed under light (UV-illumination) and dark conditions at low exposure levels (≤1μg/mL), using sterile freshwater as the test medium. The statistically significant reduction in cell viability, increase in reactive oxygen species production and membrane permeability (light vs. dark) suggested photo-induced toxicity of TiO2 NPs. The electron micrographs demonstrated adsorption of the NPs onto the cell surface and substantiated their internalization/uptake. The fluorescence micrographs and the confocal laser scanning (CLSM) images suggested the absence of a definite/intact nucleus in the light treated cells pointing toward the probable genotoxic effects of NPs. In a separate three cycle experiment, a continuous decrease in the cytotoxicity was observed, whereas, at the end of each cycle only fresh algae were added to the supernatant containing NPs from the previous cycle. The decreasing concentrations of the NPs in the subsequent cycles owing to agglomeration-sedimentation processes exacerbated by the algal interactions played a crucial role in the detoxification. In addition, the exo-polymeric substances produced by the cells could have rendered the available NPs less reactive, thereby, enhancing the detoxification effects. © 2013 Elsevier B.V.

Cytotoxicity of TiO2 nanoparticles and their detoxification in a freshwater system

The growing commercial applications had brought aluminium oxide nanoparticles under toxicologists' purview. In the present study, the cytotoxicity of two different sized aluminium oxide nanoparticles (ANP1, mean hydrodynamic diameter 82.6±22nm and ANP2, mean hydrodynamic diameter 246.9±39nm) towards freshwater algal isolate Chlorella ellipsoids at low exposure levels (≤1μg/mL) using sterile lake water as the test medium was assessed. The dissolution of alumina nanoparticles and consequent contribution towards toxicity remained largely unexplored owing to its presumed insoluble nature. Herein, the leached Al3+ ion mediated toxicity has been studied along with direct particulate toxicity to bring out the dynamics of toxicity through colloidal stability, biochemical, spectroscopic and microscopic analyses. The mean hydrodynamic diameter increased with time both for ANP1 [82.6±22nm (0h) to 246.3±59nm (24h), to 1204±140nm (72h)] and ANP2 [246.9±39nm (0h) to 368.28±48nm (24h), to 1225.96±186nm (72h)] signifying decreased relative abundance of submicron sized particles (&lt;1000nm). The detailed cytotoxicity assays showed a significant reduction in the viability dependent on dose and exposure. A significant increase in ROS and LDH levels were noted for both ANPs at 1μg/mL concentration. The zeta potential and FT-IR analyses suggested surface chemical interaction between nanoparticles and algal cells. The substantial morphological changes and cell wall damage were confirmed through microscopic analyses (SEM, TEM, and CLSM). At 72h, significant Al3+ ion release in the test medium [0.092μg/mL for ANP1, and 0.19μg/mL for ANP2] was noted, and the resulting suspension containing leached ions caused significant cytotoxicity, revealing a substantial ionic contribution. This study indicates that both the nano-size and ionic dissolution play a significant role in the cytotoxicity of ANPs towards freshwater algae, and the exposure period largely determines the prevalent mode of nano-toxicity. © 2013 Elsevier B.V.

Cytotoxicity of aluminium oxide nanoparticles towards fresh water algal isolate at low exposure concentrations

The ever increasing industrial and consumer applications of titanium dioxide nanoparticles (TiO2 NPs) raise concern over the possible risk associated with their environmental exposure. Still, the knowledge regarding nanoparticle behavior in a freshwater ecosystem is lacking. The current study focuses on the toxicity of TiO2 NPs towards Ceriodaphnia dubia (a dominant daphnid isolated from the freshwater) under two different conditions; (1) light and dark photoperiod (16:8 h) and (2) continuous dark conditions, for a period of 48 h. An increase in toxicity was observed with an increase in the concentration, until a certain threshold level (under both photoperiod and dark conditions), and beyond which, reduction was noted. The decrease in toxicity would have resulted from the aggregation and settling of NPs, making them less bioavailable. The oxidative stress was one of the major contributors towards cytotoxicity under both photoperiod and dark conditions. The slow depuration of TiO2 NPs under the photoperiod conditions confirmed a higher NP bioaccumulation and thus a higher bioconcentration factor (BCF) compared to dark conditions. The transmission electron micrographs confirmed the bioaccumulation of NPs and damage of tissues in the gut lining. © 2013 Dalai et al.

Fulltext

PLoS ONE

Acute Toxicity of TiO2 Nanoparticles to Ceriodaphnia dubia under Visible Light and Dark Conditions in a Freshwater System

The aim of the present study was to explore the difference in toxicity mechanism of TiO2 nanoparticles (NPs) at low concentrations (≤1 μg mL-1), in a freshwater bacterial isolate, Bacillus licheniformis, under light (UV-illuminated) and dark (non-illuminated) conditions. Standard plate count and MTT assays showed the dose dependent decrease in the bacterial cell viability. The difference in reduction of cell viability under light (20.7%) and dark conditions (21.3%) was statistically non-significant at 1 μg mL-1 concentration and 2 h interaction period. The fluorescence microscopy of the NP interacted cells (1.0 μg mL-1, 2 h) under light and dark conditions showed the mixture of live and dead cells. A significant dose dependent increase in intracellular ROS generation compared to control was noted. The ROS level after 2 h of interaction was significantly higher under light conditions (7.4 ± 0.13%) as compared to dark conditions (4.35 ± 0.12%). The LDH analyses confirmed a statistically significant increase in membrane permeability under dark conditions compared to the light conditions. The NPs were stable against aggregation in sterilized lake water matrix for a period of 24 h, under both light and dark conditions. However, in the presence of bacterial cells an elevated rate of sedimentation was noted under dark conditions. The electron microscopic (SEM, TEM) observations suggested the concentration buildup of NPs near the plasma membrane leading to internalization. The zeta-potential analysis proved that NP attachment was not charge based. The FTIR studies demonstrated the possible involvement of surface functional groups in the attachment. The concentration of dissolved Ti4+ ions was found to be negligible during the test period. The dominant cytotoxicity mechanism under light conditions was found to be ROS generation, whereas, NP attachment to the cell membrane leading to membrane damage significantly contributed in dark conditions. © 2012 The Royal Society of Chemistry.

Toxicology Research

A comparative cytotoxicity study of TiO2 nanoparticles under light and dark conditions at low exposure concentrations

The cytotoxicity of Al 2O 3 nanoparticles (NP) at very low exposure levels (1 μg/mL and less) to a dominant bacterial isolate from freshwater (lake water), Bacillus licheniformis, was examined. Sterile lake water was directly used as a test medium or matrix to simulate the freshwater environment. Exposure to 1 μg/mL Al 2O 3 NP for 2 h caused a 17% decrease in cell viability (as determined by plate count and MTT assay). During the test period, the particles were found to be stable against aggregation in the matrix and exerted a nano-size effect on the exposed test organisms. The decrease in cell viability was proven not to be due to the release of Al 3+ ions from the nanoparticles in the dispersion. The zeta potential and FT-IR analyses suggested that the surface charge based attachment of nanoparticles on to the bacterial cell wall was responsible for flocculation leading to toxicity. The cell wall damage confirmed through SEM and the lipid peroxidation assay also contributed toward toxicity. This study warns of possible ecotoxicity of nanoparticles even at environmentally relevant concentrations. However, detailed studies need to be carried out to establish probable mechanistic aspects of this low concentration toxicity phenomenon. © 2011 American Chemical Society.

Journal	Data powered by TypesetAquatic Toxicology
Publisher	Data powered by TypesetElsevier BV
ISSN	0166-445X
Open Access	0