Adhesion of microalgae or biofouling on submerged artificial surfaces is a universal problem in freshwater environments.

Mrudula P

Centre for Nanobiotechnology

Vellore Campus

Amitava Mukherjee

Chandra Sekaran N

Natarajan S

Shanthana Lakshmi D

Bhuvaneshwari M

Iswarya V

Fulltext

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

RSC Advances

Titanium dioxide nanoparticles (TiO2 NPs) find applications in our day-to-day life because of unique physicochemical properties. Their release into the aquatic environment poses a possible risk to the organisms. However, the continuing exposure of NPs might reduce their bioavailability to marine organisms owing to aggregation and sedimentation in the aqueous systems thus significantly reducing their toxic impact. In this regard, the present study investigates the effect of continuous exposure of TiO2 NPs to marine microalgae Chlorella sp. under UV-A irradiation through "tanks in series" mode of experiments. In a three-cycle experiment, concentration of TiO2 NPs in the first cycle was fixed at 62.6 μM, and the interacted nanoparticles was subsequently exposed to fresh batches of algae in the next two cycles. After the interaction, the NPs underwent severe aggregation (mean hydrodynamic diameter 3000 ± 18.2 nm after cycle I) leading to gravitational settling in the medium and thus decreased bioavailability. The aggregation can be attributed to interactions between the particles themselves (homo-aggregation) further aggravated by the presence of the algal cells (hetero-aggregation). Cellular viability after cycle I was found to be only 24.2 ± 2.5%, and it was enhanced to 96.5 ± 2.8% after the cycle III in the course of continuous exposure. The results were validated with estimation of oxidative stress markers such as intracellular ROS (total ROS, superoxide and hydroxyl radicals) and LPO after each cycle of exposure. The continuing decrease in the EPS across the cycles further confirmed the diminishing toxicity of the NPs.

Chemosphere

Diminishing bioavailability and toxicity of P25 TiO2 NPs during continuous exposure to marine algae Chlorella sp.

This study investigated the formation of NiFe nanoparticles (nano zero valent iron/Nickel) by the green synthesis approach using ethanolic extract of Punica granatum (pomegranate) peels. Detailed antioxidant analyses and gas chromatography–mass spectrometry (GC-MS) results established that 2-furancarboxaldehyde 5-(hydroxymethyl), 1,2-Di(2-furyl)-1,2-ethanedione and 2,5-furandicarboxaldehyde present in the extract could serve as reducing agents during synthesis. The synthesized particles were characterized through various techniques like X-Ray Diffraction (XRD), FE-SEM (Field Emission-Scanning Electron Microscopy), FT-IR (Fourier Transform-Infra Red) spectroscopy, Brunauer Emmett-Teller (BET) surface analyses. The biosynthesized NiFe nanoparticles were further used for the tetracycline (TC) removal from aqueous solutions. Tetracycline removal was optimized with respect to nanoparticle concentration using Response Surface Methodology (RSM) approach. Under the optimized conditions (initial TC concentration: 20 mg/L; NiFe nanoparticles concentration: 300 mg/L; interaction time: 90 min) 93 ± 1.55% TC removal could be obtained. The mechanism(s) of TC removal by NiFe nanoparticles was studied with help of LC-MS, TOC (Total Organic Carbon), FTIR, XRD, and ORP (Oxidation-reduction potential) analyses. It was observed that both the sorption and degradation phenomena were involved in TC removal. The application potential of the NiFe nanoparticles was investigated in ground water and lake water samples spiked with TC and the removal was found to be 77 ± 1.12 and 70 ± 2.02% respectively. Residual toxicity assays with TC by-products after interaction with NiFe nanoparticles were conducted on algal and bacterial species with the results indicating that the TC by-products were less toxic as compared to TC alone. © 2018 Elsevier Ltd

Journal of Cleaner Production

Green synthesis of NiFe nano particles using Punica granatum peel extract for tetracycline removal

Biofouling is the main problem for marine water systems such as the immersed leisure vessels, oceanographic sensors, heat exchangers, and ship hulls. The obstacle of biofouling created by barnacles, mussels, bacteria, and micro and/or macro algal species. To overcome this problem, some metal nanoparticles incorporated films and membranes were employed to control the biofouling. In this study, metal nanoparticles (Ag NPs and TiO2) of different concentrations (0.25, 0.5, 0.75 wt %) were incorporated with chitosan polymer to fabricate nanocomposite and pristine films. The biofouling inhibition was examined using the marine microalgal species Dunaliella salina. The higher performance in algal viability (45.42 ± 0.36%) was observed by TiO2 and concentration maintained Ag NPs incorporated chitosan nanocomposite (0.5 wt% Ag/ 0.75 wt% TiO2) films under UV-C condition, in comparison with other nanocomposite and pristine concentrations. The same concentration showed higher activity in the slime formation (Glycocalyx test), mass assessment, exo-polymeric substances (EPS), and membrane damages (LPO) under UV-C condition. The release of silver ions (Ag+) and uptake of Ag showed good performance of Ag NPs incorporated nanocomposite film at higher concentration (0.5 wt% TiO2/ 0.75 wt% Ag). The surface morphology of nanocomposite were characterized using SEM, and AFM, and the surface modifications of chitosan nanocomposites were examined by XRD, and FTIR. TiO2 and Ag NPs being photoactive induce more ROS that damage the cell membrane leading to algal cell death and control of biofouling formation. © 2018 Elsevier Ltd. All rights reserved.

Journal of Environmental Chemical Engineering

Antifouling and anti-algal effects of chitosan nanocomposite (TiO2/Ag) and pristine (TiO2 and Ag) films on marine microalgae Dunaliella salina

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

TiO2 and Ag NPs are widely used as antibacterial agents against many bacterial pathogens. Chitosan (polymer) itself acts as a strong antibacterial agent. Hence, chitosan/TiO2/Ag NPs incorporated nanocomposite film was prepared against packed drinking water bacterial strains. A concentration-dependent increase in the reduction of cell viability was observed in all the isolates under UV-C and dark exposure conditions. The bacteria consortium showed greater resistance against antibacterial effects of chitosan/TiO2/Ag nanocomposite as compared to single isolates. Glycocalyx test and mass assessment conclude the effective antibacterial activity by inhibiting bacterial adhesion on the film surface. The release of LDH and generation of ROS act as the predominant antibacterial mechanism induced by TiO2/Ag NPs. Surface characterization of chitosan/TiO2/Ag nanocomposite was studied by FTIR and XRD analyses and SEM analysis after interaction with the bacteria. © 2016, Springer-Verlag Berlin Heidelberg.

Antibacterial and antifouling activities of chitosan/TiO2/Ag NPs nanocomposite films against packaged drinking water bacterial isolates

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.

Aquatic Toxicology

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

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.

Journal	Data powered by TypesetRSC Advances
Publisher	Data powered by TypesetRoyal Society of Chemistry (RSC)
ISSN	20462069
Open Access	Yes