Nanomaterials in Plants, Algae and Microorganisms: Concepts and Controversies [2] 0128114886, 9780128114889

Table of contents :
Cover
Nanomaterials in Plants, Algae, and Microorganisms: Concepts and Controversies: Volume 2
Copyright
Dedication
List of Contributors
1 . Phytotoxic Properties of Zinc and Cobalt Oxide Nanoparticles in Algaes
1.1 Introduction
1.2 Production and Applications of ZnO and CoO Nanoparticles
1.3 Methods to Assess Toxicity of Metal Oxide Nanoparticles in Algae
1.3.1 Damage to Cell Wall Integrity
1.3.2 Oxidative Damage
1.4 Factors Influencing Phytotoxicity of ZnO and CoO Nanoparticles
1.4.1 Physicochemical Characteristics of Nanomaterials
1.4.2 Processes Affecting Stability of Nanoparticles and Toxicity
1.4.3 Environmental Factors
1.5 Toxicity of Zinc and Cobalt Oxide Nanoparticles: Possible Mechanisms
1.5.1 Dissolution
1.5.2 Aggregation
1.5.3 Adsorption
1.5.4 Interaction, Entry, and Toxic Impact
1.5.5 Photo-Induced Toxicity
1.6 Toxicity of CoO Nanoparticles
1.7 Future Research Directions
1.8 Conclusion
References
2 . Carbon Nanotubes as Plant Growth Regulators: Impacts on Growth, Reproductive System, and Soil Microbial Community
2.1 Introduction
2.2 Carbon Nanotubes: Uptake and Translocation
2.3 Release and Uptake of Carbon Nanotubes
2.4 Role of Carbon Nanotubes
2.4.1 Impact of Carbon Nanotubes on Soil and Pesticide Accumulation
2.4.2 Impact of Carbon Nanotubes on Wastewater Treatment
2.4.3 Role of Carbon Nanotubes in the Production of Synthetic Plant Hormone
2.4.4 Role of Carbon Nanotubes in Seed Germination
2.4.5 Carbon Nanotubes as Plant Growth Regulators
2.4.6 Role of Carbon Nanotubes in the Microbial Community
2.5 Industrial Application of Carbon Nanotubes
2.6 Conclusion
References
3 . Zinc Oxide Nanoparticle-Induced Responses on Plants: A Physiological Perspective
3.1 Introduction
3.2 Properties of ZnO NPs
3.3 Synthesis of ZnO NPs
3.3.1 Physical Methods
3.3.2 Chemical Methods
3.3.3 Biological Method or Green Synthesis
3.3.3.1 Plant Extract
3.4 Positive Impacts of ZnO NPs on Plants
3.5 Negative Impacts of ZnO NPs on Plants
3.6 Conclusion
References
Further Reading
4 . Effects of Nanoparticles in Plants: Phytotoxicity and Genotoxicity Assessment
4.1 Introduction
4.2 Plant Uptake of NPs
4.3 Phytotoxicity and Genotoxicity Induction and Assessment
4.3.1 Plant Bioassays
4.4 Phytotoxicity and Genotoxicity of the Most Widespread Nanoparticles
4.4.1 Phytotoxic and Genotoxic Effects of Silica NPs
4.4.2 Phytotoxicity and Genotoxicity of TiO2 NPs
4.4.3 Genotoxicity of ZnO NPs
4.4.4 Genotoxicity of Aluminum Oxide NPs
4.4.5 Genotoxicity of Carbon-Based NPs
4.4.6 Genotoxicity of CeO2 NPs
4.4.7 Genotoxicity of CuO NPs
4.4.8 Genotoxicity of Ag NPs
4.5 Conclusion
References
5 . Industrial Nanoparticles and Their Influence on Gene Expression in Plants
5.1 Introduction
5.2 Basic Principle Behind the Study
5.2.1 An Overview
5.2.2 Mechanism and Hypothesis
5.3 Conclusion and Future Perspective
References
6 . Role of Nanoparticles on Photosynthesis: Avenues and Applications
6.1 Introduction
6.2 Nanoparticles and Growth of Plants
6.3 Nanoparticles and Photosynthesis
6.3.1 Light-Dependent Reactions
6.3.2 Carbon Dioxide Fixation Reactions
6.4 Nanomaterials and Photosynthesis Under Abiotic Stresses
6.5 Nanoparticles and Yield of Plants
6.6 Conclusion and Future Prospects
References
Further Reading
7 . Nanoparticle-Induced Ecotoxicological Risks in Aquatic Environments: Concepts and Controversies
7.1 Introduction
7.2 Nanoparticle Toxicity Determination
7.2.1 Nanoparticle Engineering
7.2.2 Comparative Approaches Among Engineered Nanoparticles
7.2.3 Structural and Functional Aspects of Engineered Nanoparticles
7.3 Understanding the Mechanisms of Engineered Nanoparticle Toxicity
7.3.1 Oxidative Stress Mediated By Engineered Nanoparticles
7.3.2 Light-Induced Activity of Engineered Nanoparticles
7.3.3 Adsorption Properties in Engineered Nanoparticles
7.3.4 Interaction of Engineered Nanoparticles With Environmental Materials
7.4 Engineered Nanoparticle Toxicity Across the Aquatic Food Web
7.4.1 Engineered Nanoparticle Toxicity in Fish
7.4.2 Engineered Nanoparticle Toxicity in Aquatic Invertebrates
7.4.3 Engineered Nanoparticle Toxicity in Phytoplanktons
7.4.4 Engineered Nanoparticles Toxicity in Aquatic Plants
7.5 Engineered Nanoparticles in the Ecological Cycle
7.6 Conclusion and Future Perspectives
References
8 . Phytotoxicity of Silver Nanoparticles to Aquatic Plants, Algae, and Microorganisms
8.1 Introduction
8.2 Environmental Concentration of Silver Nanoparticles
8.3 Silver Nanoparticles' Fate in Water
8.4 Importance of Shape and Size for Silver Nanoparticles' Toxicity in Photosynthetic Organisms
8.5 Aquatic Photosynthetic System
8.6 Effects of Silver Ions on the Aquatic Photosynthetic System
8.7 Mechanisms of Uptake into Aquatic Photosynthetic Organisms
8.8 Silver Nanoparticles' Effects on Aquatic Plants
8.9 Silver Nanoparticles' Effects on Algae
8.10 Silver Nanoparticles' Effects on Cyanobacteria
8.11 Silver Nanoparticles' Effects on Phytoplankton
8.12 Silver Nanoparticles' Bioaccumulation and Biomagnification
8.13 Biosynthesis of Silver Nanoparticles in Cyanobacteria and Microalgae
8.14 Discussion
8.15 Conclusion and Future Prospects
References
Further Reading
9 . Therapeutic Potential of Plant-Based Metal Nanoparticles: Present Status and Future Perspectives
9.1 Introduction
9.2 Synthesis of Nanomaterials
9.2.1 Traditional or Chemical Methods for Synthesis of Metal-Based Nanoparticles
9.2.2 Bottom-Up Approach
9.2.3 Top-Down Approach
9.3 Biological Synthesis of Metal-Based Nanoparticles
9.3.1 Plant-Based Green Synthesis of Nanoparticles
9.3.2 Mode of Biosynthesis of Plant-Based Nanoparticles
9.3.3 Applications of Plant-Based Metal-Based Nanoparticles
9.4 Antifungal Activity of Nanoparticles
9.5 Mechanism Underlying the Antifungal Activity of Nanoparticles
9.6 Limitations in Practical Use of Nanoparticles for Antifungal Activity
9.7 Conclusion
References
Further Reading
10 . Antifungal Impact of Nanoparticles Against Different Plant Pathogenic Fungi
10.1 Introduction to Disease-Causing Plant Microbes
10.2 Various Technologies Used for Control of Plant Pathogens
10.2.1 Physical Methods
10.2.2 Chemical Methods
10.2.3 Biological Methods
10.3 Antimicrobial Activity of Nanoparticles
10.3.1 Antimicrobial Activity of Silver Nanoparticles
10.3.2 Antifungal Activity of Silver Nanoparticles
10.3.2.1 Mechanism of Antifungal Activity
10.4 Nanoparticles Against Plant Pathogens
10.5 Oxide Nanoparticles
10.6 Other Nanoparticles Used for Plant Pathogens Control
10.7 Conclusion and Future Prospects
References
Further Reading
11 . Synthesis of Nanoparticles Utilizing Sources From the Mangrove Environment and Their Potential Applications: an Overview
11.1 Introduction
11.2 Synthesis of Nanoparticles from Various Sources in the Mangrove Environment
11.2.1 Synthesis of Nanoparticles Using Bacteria
11.2.2 Synthesis of Nanoparticles Using Fungi
11.2.3 Synthesis of Nanoparticles Using Plants
11.2.4 Synthesis of Nanoparticles Using Other Sources
11.3 Applications of Nanoparticles Synthesized Using Mangrove Environment Sources
11.3.1 Biomedical Applications
11.3.2 Agricultural Applications
11.3.3 Industrial Applications
11.3.4 Other Applications
11.4 Future Prospects
11.5 Conclusion
References
Further Reading
12 . Recent Developments in Green Synthesis of Metal Nanoparticles Utilizing Cyanobacterial Cell Factories
12.1 Introduction
12.2 Bionanotechnology
12.2.1 Types of Nanoparticles
12.2.2 Techniques Used for the Characterization of Nanoparticles
12.3 Cyanobacterial “Cell Factories” and Bionanotechnology
12.4 Mechanism of Green Synthesis of Metal Nanoparticles
12.5 Recent Developments in Green Synthesis of Metallic Nanoparticles Utilizing Cyanobacteria
12.6 Applications of Nanotechnology
12.7 Conclusion and Future Prospects
References
Further Reading
13 . Chitosan and Its Nanocarriers: Applications and Opportunities
13.1 Introduction
13.2 Chitosan-Based Nanomaterials and Their Biological Activities
13.2.1 Use of Chitosan-Based Nanomaterials in Plants
13.2.1.1 Promotion of Seedling Growth and Development
13.2.1.2 Physiological Response
13.2.1.3 Plant Nutrient Uptake
13.2.1.4 Present Status and Future Prospects of Chitosan-Based Nanomaterials in Plants
13.2.2 Antimicrobial Activity of Chitosan-Based Nanomaterials
13.2.3 Antibacterial and Antifungal Activity of Chitosan-Based Nanomaterials
13.2.4 Antiviral Activity of Chitosan-Based Nanomaterials
13.3 Carboxymethyl Chitosan: One of the Prominent Chitosan Derivatives
13.3.1 Physicochemical Properties of Carboxymethyl Chitosan
13.3.1.1 Moisture Retention
13.3.1.2 Chelating and Associated Properties
13.3.2 Biological Properties of Carboxymethyl Chitosan
13.3.2.1 Antimicrobial Effects
13.3.2.2 Antioxidant Activity
13.3.2.3 Antiapoptotic Effect
13.3.2.4 Modulation of Cell Functioning
13.3.3 Applications of Carboxymethyl Chitosan
13.3.3.1 Cancer Treatment
13.3.3.2 Bioimaging
13.3.3.3 Sustainable Chemistry
13.3.3.4 Cosmetics
13.3.3.5 Biosensors
13.3.3.6 DNA Delivery
13.3.3.7 Permeation Enhancer
13.3.3.8 Wound-Healing Agents
13.3.3.9 Other Uses
13.4 Nanovehicles for Delivery of Specific Drugs
13.4.1 Anticancerous and Antiinflammatory Drugs
13.4.2 Antifungal and Antimicrobial Drugs
13.4.3 Peptides and Vaccines
13.8 Conclusion
References
Further Reading
14 . Biosensor Technology—Advanced Scientific Tools, With Special Reference to Nanobiosensors and Plant- and Food-Based Biosensors
14.1 Introduction
14.2 Types of Biosensor
14.2.1 Nanobiosensors
14.2.2 Plants Engineered With a Specific Biosensor
14.2.3 Biosensors Based on Mode/Transducers
14.2.4 Biosensors Based on Receptors
14.3 Application of Biosensors
14.3.1 Biosensors Used for Quantification of Nitrates in Plants
14.3.2 Biosensors in Plant Disease Detection
14.3.3 Food Safety and Contaminations (Toxin and Xenobiotic Compounds)
14.3.4 Maintaining Food Quality
14.3.5 Process Control: Fermentation and Pasteurization
14.3.6 Biotechnology and Genetically Modified Organisms
14.4 Conclusion and Future Perspectives
References
15 . Impact of Nanoparticles on Abiotic Stress Responses in Plants: an Overview
15.1 Introduction
15.2 Physiological Impacts of Nanoparticles on Plants
15.3 Impact of Nanoparticles on ROS and Antioxidant System
15.4 Nanoparticles and Metal Stress in Plants
15.5 Nanoparticles and Drought Stress in Plants
15.6 Nanoparticles and Salinity Stress
15.7 Nanoparticles and Other Abiotic Stresses
15.8 Conclusion and Perspectives
References
Further Reading
16 . Physicochemical Perturbation of Plants on Exposure to Metal Oxide Nanoparticle
16.1 Introduction
16.2 Sources of Metal Nanoparticles
16.2.1 Natural Sources
16.2.2 Dust Storms
16.2.3 Extraterrestrial Dust
16.2.4 Forest Fires
16.2.5 Volcanic Eruptions
16.2.6 Ocean and Water Evaporation
16.3 Anthropological Interventions
16.3.1 Fossil Fuel Combustion
16.3.2 Indoor Pollution
16.3.3 Cigarette Smoke
16.3.4 Construction and Demolition
16.3.5 Cosmetics and Other Consumer Products
16.3.6 Engineered Nanomaterials
16.4 Global Financial Status of Engineered Metal Nanoparticles
16.5 Fate of Engineered Nanoparticles
16.6 Physicochemical Stress in Plants: the Whys and the Wherefores
16.7 Major Metal Nanoparticles Affecting Plants
16.7.1 Silver Nanoparticles
16.7.2 Gold Nanoparticles
16.7.3 Titanium Nanoparticles
16.7.4 Copper Nanoparticles
16.7.5 Zinc Nanoparticle
16.7.6 Iron Nanoparticles
16.7.7 Magnesium Nanoparticle
16.7.8 Cerium Nanoparticles
16.7.9 Nickel Nanoparticles
16.7.10 Aluminium Nanoparticles
16.7.11 Cadmium Nanoparticles
16.7.12 Ytterbium, Lanthanum, and Gadolinium
16.8 Amelioration of Nanoparticle-Induced Damage to Plants
16.9 Conclusion
References
Index
A
B
C
D
E
F
G
H
I
K
L
M
N
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P
Q
R
S
T
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V
W
X
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Z
Back Cover

Citation preview

Nanomaterials in Plants, Algae, and Microorganisms Concepts and Controversies: Volume 2 Edited by

Durgesh Kumar Tripathi Motilal Nehru National Institute of Technology Allahabad Allahabad, Uttar Pradesh, India

Parvaiz Ahmad King Saud University, Riyadh, Saudi Arabia University of Kashmir, Srinagar

Shivesh Sharma Motilal Nehru National Institute of Technology Allahabad Allahabad, Uttar Pradesh, India

Devendra Kumar Chauhan University of Allahabad, Allahabad, Uttar Pradesh, India

Nawal Kishore Dubey Banaras Hindu University, Varanasi, India

Academic Press is an imprint of Elsevier 125 London Wall, London EC2Y 5AS, United Kingdom 525 B Street, Suite 1650, San Diego, CA 92101, United States 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom Copyright © 2019 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-811488-9 For information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Candice Janco Acquisition Editor: Candice Janco Editorial Project Manager: Emily Thomson Production Project Manager: Nilesh Kumar Shah Cover Designer: Mark Rogers Typeset by TNQ Technologies

Dedicated to One of the eminent Botanist of India and our beloved teacher Prof. P K Khare

Professor and Former Head Department of Botany, University of Allahabad, Allahabad, India

Dr. Durgesh Kumar Tripathi Prof. Devendra Kumar Chauhan

List of Contributors Vishnu Agarwal Department of Biotechnology, Motilal Nehru National Institute of Technology, Allahabad, India Haseen Ahmed Laboratory of Photobiology and Molecular Microbiology, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, India Simran Asawa Department of Biotechnology, National Institute of Technology Warangal, Warangal, India Maumita Bandyopadhyay Plant Molecular Cytogenetics Laboratory, Centre of Advanced Study, Department of Botany, Ballygunge Science College, University of Calcutta, Kolkata, India Aditya Banerjee Department of Biotechnology, St. Xavier’s College (Autonomous), Kolkata, India Marcella Bracale Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy Marian Brestic Department of Plant Physiology, Slovak University of Agriculture, Nitra, Slovak Republic Gitishree Das Research Institute of Biotechnology and Medical Converged Science, Dongguk UniversitySeoul, Gyeonggi-do, Republic of Korea Guido Domingo Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy Nawal Kishore Dubey Lab of Herbal Pesticides, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, India Abhishek Kumar Dwivedy Lab of Herbal Pesticides, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, India Rout George Kerry P. G. Department of Biotechnology, Utkal Univesity, Vani Vihar, Odisha, India Lucia Giorgetti National Research Council (CNR) - Institute of Agricultural Biology and Biotechnology (IBBA), Pisa, Italy

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LIST OF CONTRIBUTORS

Sushanto Gouda Amity Institute of Forestry and Wildlife, Amity University, Noida, Uttar Pradesh, India Meeta Jain School of Biochemistry, Devi Ahilya University, Khandwa Road, Indore, India Sunita Kataria School of Biochemistry, Devi Ahilya University, Khandwa Road, Indore, India Zesmin Khan Department of Botany, Cotton University, Guwahati, India Pradeep Kumar Department of Forestry, North Eastern Regional Institute of Science and Technology (Deemed University-MHRD), Nirjuli-, Arunachal Pradesh, India Manoj Kumar Lab of Herbal Pesticides, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, India Jayanta Kumar Patra Research Institute of Biotechnology and Medical Converged Science, Dongguk UniversitySeoul, Gyeonggi-do, Republic of Korea Shiliang Liu College of Landscape Architecture, Sichuan Agricultural University, Chengdu, China; School of Renewable Natural Resource, Louisiana State University Ag Center, Baton Rouge, LA, United States Dipendra Kumar Mahato Department of Agriculture and Food Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, India Indrani Manna Plant Molecular Cytogenetics Laboratory, Centre of Advanced Study, Department of Botany, Ballygunge Science College, University of Calcutta, Kolkata, India Seema Nara Department of Biotechnology, Motilal Nehru National Institute of Technology, Allahabad, India Abha Pandey Laboratory of Photobiology and Molecular Microbiology, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, India Himanshu Pandey Faculty of Pharmaceutical Sciences, Sam Higginbottom Institute of Agriculture Technology and Sciences, Allahabad, India Parul Parihar Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad, India

LIST OF CONTRIBUTORS

Anuradha Patel Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad, India Jainendra Pathak Laboratory of Photobiology and Molecular Microbiology, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, India Jayanta Kumar Patra Research Institute of Biotechnology & Medical Converged Science, Dongguk University-Seoul, Gyeonggi-do, Republic of Korea Bhanu Prakash Lab of Herbal Pesticides, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, India Sheo Mohan Prasad Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad, India S. Rajeshkumar Department of Pharmacology, Saveetha Dental College and Hospitals, SIMATS, Chennai, TN, India Rajneesh Laboratory of Photobiology and Molecular Microbiology, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, India Radha Rani Department of Biotechnology, Motilal Nehru National Institute of Technology, Allahabad, India Anshu Rastogi Department of Meteorology, Poznan University of Life Sciences, Poznan, Poland Aryadeep Roychoudhury Department of Biotechnology, St. Xavier’s College (Autonomous), Kolkata, India Abhishek Sharan Department of Biotechnology, Motilal Nehru National Institute of Technology, Allahabad, India Nandita Sharma Department of Biotechnology, Motilal Nehru National Institute of Technology, Allahabad, India Deepmala Sharma Department of Mathematics, National Institute of Technology, Raipur, India Devendra Singh Department of Biotechnology, Motilal Nehru National Institute of Technology, Allahabad, India Deepak K. Singh Laboratory of Photobiology and Molecular Microbiology, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, India

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LIST OF CONTRIBUTORS

Rachana Singh Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad, India Shailendra P. Singh Laboratory of Photobiology and Molecular Microbiology, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, India Rajeshwar P. Sinha Laboratory of Photobiology and Molecular Microbiology, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, India Thounaojam Thorny Chanu Department of Botany, Cotton University, Guwahati, India Sanjesh Tiwari Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad, India Durgesh Kumar Tripathi Department of Biotechnology, Motilal Nehru National Institute of Technology, Allahabad, India Neha Upadhyay Lab of Herbal Pesticides, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, India Hrishikesh Upadhyaya Department of Botany, Cotton University, Guwahati, India Candida Vannini Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy   Marek Ziv ca´k Department of Plant Physiology, Slovak University of Agriculture, Nitra, Slovak Republic

CHAPTER

PHYTOTOXIC PROPERTIES OF ZINC AND COBALT OXIDE NANOPARTICLES IN ALGAES

1

Abhishek Sharan, Seema Nara Department of Biotechnology, Motilal Nehru National Institute of Technology, Allahabad, India

1.1 INTRODUCTION The application and utilization of nanomaterials has emerged as a rapidly growing multibillion-dollar commercial industry. Increased industrial production efficiency and recent advances in the research and development of nanomaterials have enormously increased the number of nanomaterial-based industrial, medical, and consumer products (Nanomaterials state of the market Q3 2008). By 2020 an increase from 1000 to 58,000 tons is expected in the total amount of nanomaterials produced globally (Nanoscience and nanotechnologies: Opportunities and uncertainties, 2004). With the growing interest in and good future prospects for nanomaterials, metal-based and metal oxide nanoparticles in particular are likely to find applications in the areas of paint, fillers, medicine, food and food packaging, cosmetics, electronics, textiles, energy, and agriculture. Metal oxide nanoparticles are mostly used as components in numerous commercial products, and their industrial applications have led to serious concerns about their potential toxic impact on human health, plants, and the environment (Aschberger et al., 2011; Tripathi et al., 2017aed; Singh et al., 2016; Singh et al., 2017). Most sewage and industrial wastewater is discharged into water bodies, including rivers, lakes, coastal waters, etc., inevitably causing the deposition of these nanoparticles in the aquatic environment (Daughton, 2004). Increasing use of metal oxide nanoparticles may eventually result in increased release of these nanoparticles into the aquatic system, adversely affecting the aquatic life. Thus the unexplored area of toxicity in the aquatic environment induced by metal oxide nanoparticles has been the subject of special interest recently (Blaise et al., 2008; Farre´ et al., 2009). In the past decade, metal oxide nanoparticles such as zinc oxide (ZnO) and cobalt oxide (CoO) have been utilized in wide range of products. ZnO and CoO nanoparticles emerged as a prominent class of commercially important metal oxide nanoparticles because of their unique physicochemical properties. They are extensively used in industrial processes and consumer goods, including in pigments, catalytic processes, magnetism, sensor development, energy storage, and electrochemistry (Liu et al., 2005; Papis et al., 2009). As metal oxide nanoparticles are used in many products related to daily life activities, they are easily flushed out into the aquatic environment and affect the sustainability of the aquatic ecosystem. It is estimated that the annual production of skincare and cosmetic products containing ZnO nanoparticles is approximately 1000 tons worldwide, and around 25% of these Nanomaterials in Plants, Algae, and Microorganisms. https://doi.org/10.1016/B978-0-12-811488-9.00001-9 Copyright © 2019 Elsevier Inc. All rights reserved.

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CHAPTER 1 PHYTOTOXIC PROPERTIES OF ZINC AND COBALT OXIDE

products are washed off during bathing and swimming and discharged into the aquatic environment (Pikethly, 2004; Danovaro et al., 2008). ZnO nanoparticles are also deposited in high concentrations in surface waters and become toxic to the aquatic ecosystem (Gottschalk et al., 2009). Zn2þ is a wellestablished toxicant for aquatic life, and it is essential to study the toxic effects of nanosized ZnO particles to establish the risk to aquatic life. CoO nanoparticles have found applications in sensors, pigments, photocatalysts, energy storage, and biomedical applications (Asif et al., 2014). Toxicity of CoO nanoparticles has been studied with mammalian cells, but their toxic effects on aquatic life are underexplored. Because the environmental impact of these nanoparticles is not clearly understood, their phytotoxic effects of in aquatic ecosystem have attracted much greater concern. As less information related to phytotoxic effects of nanoparticles in the aquatic environment is available, the present scientific interest is to investigate the effects of nanoparticles on aquatic ecosystems, particularly on algae. Phytoplankton and algae are major constituents of the aquatic food chain and play the key role of being primary producers in aquatic ecosystems. They are also responsible for the transfer of energy and nutrients to higher trophic levels. Many researchers have made efforts to understand the toxic impact of ZnO nanoparticles in marine and freshwater algal species. The toxic effects of ZnO nanoparticles are briefly summarized in Table 1.1. Microalgae show high levels of sensitivity toward water pollutants and present themselves as an excellent aquatic model to study the phytotoxic effects of nanoparticles in aquatic ecosystems (Chen et al., 2012c). In this chapter industrially important and widely used metal oxide nanoparticles, namely ZnO and CoO, are explored as prominent contaminants of aquatic life with severe phytotoxic effects on algae. The factors responsible for influencing the fate and phytotoxic effect of these nanomaterials in aquatic systems and the plausible mechanism involved in toxicity generation are discussed later in this chapter.

1.2 PRODUCTION AND APPLICATIONS OF ZNO AND COO NANOPARTICLES The production and utilization of metal-oxide-based nanomaterials have increased remarkably and they are used in various industrial processes and products, such as catalysts, cosmetics, pigments, sunscreens, and food additives (Aitken et al., 2006; Shi et al., 2013). The worldwide annual production of ZnO nanoparticles lies in third position, with a volume of 550 tons, after SiO2 (5500 tons) and TiO2 nanoparticles (3000 tons) (Piccinno et al., 2012). CoO nanoparticles are considered as a low-volume product, and the minimum global production was estimated to be approximately 5 tons in 2014 (Nanomaterial: Future markets, 2015). ZnO nanoparticles market share is distributed across two important industries: cosmetics and paint. Cosmetics (including sunscreens) have in the largest market share at 70%, while the market share of the paint industry is about 30% (Piccinno et al., 2012). Apart from industrial applications, nanoparticles can also be utilized as nanofertilizers to provide macronutrients and micronutrients to the crops as ZnO nanoparticles (Zhao et al., 2013; Shweta et al., 2016; Tripathi et al., 2017b; Singh et al., 2017). The unique physicochemical properties of ZnO nanoparticles have favored their utilization in widespread applications, such as the component protecting against ultraviolet (UV) radiation in cosmetics like beauty products, sunscreens, and toothpastes (Serpone et al., 2007). The photoactive nature of ZnO nanoparticles means they find applications in production of liquid crystal displays and solar cells. They are also widely used in paint and pigments, chemical fibers, textiles, and electronics

Table 1.1 Toxicity of Zinc Oxide Nanoparticles to Microalgae Duration

Toxicity Assessed

Effect Concentration

References

Thalassiosira pseudonana C. gracilis P. tricornutum T. pseudonana S. marinoi D. tertiolecta I. galbana T. pseudonana

100 h

Growth rate inhibition (log linear cell division rate)

EC100 ¼ 10 mg/L

Peng et al. (2011)

96 h 96 h

Growth rate inhibition Growth rate inhibition

LOEC ¼ 0.5 mg/L LOEC ¼ 1.0 mg/L

Miller et al. (2010)

48 h

Growth rate, Fv/Fm, chlorophyll a (Chl a)

Miao et al. (2010)

S. costatum T. pseudonana D. tertiolecta T. weissf logii

96 h 96 h 96 h 7d

Growth inhibition Growth inhibition Growth inhibition Growth reduction

IC50 ¼ 0.39 mM (growth); 3.83 mM (Fv/ Fm); 6.94 mM (Chl a) IC50 ¼ 2.36 mg/L IC50 ¼ 4.56 mg/L EC50 ¼ 2.42 mg/L LOEC ¼ 0.094 mg/L

D. tertiolecta

Freshwater Species

72 h

D. tertiolecta

96 h

Growth inhibition Genotoxic effect Growth inhibition

T. suesica

96 h

Growth inhibition

P. subcapitata P. subcapitata Chlorella sp. C. reinhardtii C. vulgaris S. dimorphus Chlorococcum sp.

72 h 72 h 6d 12 d 72 h 72 h 96 h

Growth inhibition Growth inhibition Growth inhibition Growth inhibition Growth inhibition Growth inhibition Growth inhibition

S. rubescens

96 h

Growth inhibition

EC50 ¼ 2.0 mg/L EC50 ¼ 5.0 mg/L IC50 ¼ 1.50 mg/L (f2 medium) IC50 ¼ 2.10 mg/L (f2 medium) IC50 ¼ about 0.04 mg/L IC50 ¼ 0.06 mg/L EC30 ¼ 20 mg/L LOEC ¼ 1 mg/L EC50 ¼ 0.01 mg/L EC50 ¼ 0.09 mg/L IC50 ¼ 0.75 mg/L (1/2N BG-11 medium) IC50 ¼ 14.27 mg/L (bold basal medium)

Wong et al. (2010) Manzo et al. (2013) Bielmyer-Fraser et al. (2014) Schiavo et al. (2016) Aravantinou et al. (2015)

Aruoja et al. (2009) Franklin et al. (2007) Ji et al. (2011) Luo (2007) Pendashte et al. (2013) Aravantinou et al. (2015)

1.2 PRODUCTION AND APPLICATIONS OF ZNO AND COO NANOPARTICLES

Marine Species

Test Species

Chl a, chlorophyll a; EC, effective concentration; IC, inhibitory concentration; LOEC, lowest observed effect concentration.

3

4

CHAPTER 1 PHYTOTOXIC PROPERTIES OF ZINC AND COBALT OXIDE

(Heng et al., 2010; Song et al., 2010). And despite the very small global production, recent research has shown promising characteristics of CoO nanoparticles and they are therefore attracting huge interest in potential industrial applications such as pigments, catalytic processes, energy storage, sensor development, electrochemistry, magnetism (Liu et al., 2005; Papis et al., 2009; Li et al., 2011), development of nonenzymatic glucose sensors (Madhu et al., 2015), magnetic resonance imaging (Bouchard et al., 2009), etc. Thus daily increasing use of metals containing nanoparticles in consumer products has raised serious concerns about their proliferation in aquatic ecosystems and subsequent toxicity in aquatic life forms. Many studies have suggested the induction of toxicity in aquatic plants such as microalgae when exposed to nanoparticles (Table 1.1).

1.3 METHODS TO ASSESS TOXICITY OF METAL OXIDE NANOPARTICLES IN ALGAE There is wide variation in the toxic effects generated by metal oxide nanoparticles interacting with aquatic plants, especially microalgae. These variations can be the result of physicochemical properties of a particular nanoparticle, the surrounding environmental conditions, or behavior of nanoparticles in aquatic systems. Thus proper assessment of the toxicity produced in algal species in aquatic systems is of utmost importance. ZnO and CoO nanoparticles have been shown to differ from each other in their behavior in aquatic systems. For example, ZnO nanoparticles are highly soluble in water, so most of the toxicity produced is because of Zn2þ ions, while CoO nanoparticles are poorly soluble in water (Papis et al., 2009) and most of the toxicity observed is because of nanoparticle interaction with algal cell walls and subsequent internalization. There are various methods and techniques applied to assess these toxic effects, and some are discussed below.

1.3.1 DAMAGE TO CELL WALL INTEGRITY Nanoparticles in a particulate form can be adsorbed on to the cell wall of algae and compromise cell wall integrity by producing reactive oxygen species (ROS) in close proximity to the surface, increasing the pore size of rigid cell walls, and causing an increase in membrane permeability. Because of these effects, reduction in growth and cell lyses takes place, and even cell death. Many methods have been used to determine cell wall damage caused by nanoparticles and the resulting effects in algae. When the algal cell wall is exposed to ZnO or other metal oxide nanoparticles, the cell wall/membrane permeability is modified and cytoplasmic enzyme such as lactate dehydrogenase (LDH) is released outside the cell in the aqueous media. The intactness of the cell membrane is estimated by determining the amount of LDH in the media. LDH assay and acid phosphatase assay are the two important methods applied in evaluation of the toxicity of CoO and ZnO nanoparticles for microalgae (Rebello et al., 2010; Suman et al., 2015; Bhuvaneshwari et al., 2015). The cell wall integrity of microalgae can also be examined by a fluorescent dye staining technique. Propidium iodide (PI) is a fluorescent dye mostly used in assessment of cell membrane integrity. PI can only pass through the cell wall/membrane when the membrane is damaged and permeability is increased; it binds with nucleic acid to produce red fluorescence, indicating compromised cell wall integrity. Flow cytometric analysis also uses PI-based fluorescent dye assay (Suman et al., 2015).

1.3 METHODS TO ASSESS TOXICITY OF METAL OXIDE NANOPARTICLES

5

Lipid peroxidation (malondialdehyde assay) can be used to evaluate indirectly the degree of cell membrane damage in microalgae. When nanoparticle-induced extracellular ROS attack membrane lipids, fatty acid radicals are generated, known as lipid hydroperoxides. Lipid hydroperoxides are further decomposed into water-soluble toxic by-products such as aldehydes, ketones, alkanes, glycols, lipid epoxides, alcohols, etc., which are highly toxic to cells and organelles (Gill and Tuteja, 2010). Malondialdehyde (MDA) is one of the by-products of lipid peroxidation, and is synthesized as a result of nanoparticle-induced peroxidation of membrane lipids. An elevated level of MDA is observed when algae are exposed to metal oxide nanoparticles (Wang et al., 2008; Chen et al., 2012a; Tang et al., 2015). In general, morphological changes and cell growth can be determined by microscopic analysis and other cell-counting techniques. Surface modifications on algal cell walls can also be analyzed by scanning electron microscope or field emission scanning electron microscope (Ji et al., 2011; Chen et al., 2012b; Suman et al., 2015).

1.3.2 OXIDATIVE DAMAGE Once internalized, metal oxide nanoparticles in either dissolved ionic form or particulate form can induce oxidative stress by generating ROS. Oxidative damage to the algal cells can be assessed by fluorescent/nonfluorescent probes, enzymatic and nonenzymatic antioxidant assay, inductively coupled plasma mass spectrometry (ICPeMS), etc. The overall intracellular ROS produced can be estimated by applying widely used highly sensitive probes. One commonly used probe is H2DCF-DA (20 ,70 -dichlorodihydrofluorescein diacetate), which is highly permeable through cell membranes and rapidly enters cells by passive diffusion. When inside the cell, it reacts with intracellular ROS and is converted to the DCF (20 ,70 -dichlorofluorescein) fluorescent form. The extent of ROS generation is measured by measuring the fluorescent intensity of DCF (Foucaud et al., 2007; Tang et al., 2015). Oxidative stress disturbs the antioxidant system in the cell. The measurement of enzymatic and nonenzymatic antioxidants in algal cells can be used to assess the oxidative damage caused by metal oxide nanoparticles. An increase in the activity of antioxidant enzymes such as superoxide dismutase (SOD) indicates nanoparticle exposure and subsequent ROS generation in algae. But overaccumulation of ROS will further reduce the activity of the SOD enzyme (Zhou et al., 2014; Suman et al., 2015). An assay using a nonenzymatic antioxidant such as glutathione (GSH) is performed to assess the oxidative stress when ROS level is below critical concentration (von Moos and Slaveykova, 2014). GSH assay is a good method to determine minute amounts of ROS generated in the cell. The reduction in GSH level in algae exposed to ZnO nanoparticles is indicative of the amount of ROS (Suman et al., 2015). To determine the amount of the intracellular ionic form of nanoparticles, such as ZnO nanoparticles, the ICPeMS technique is used. The detection of Zn2þ released from ZnO nanoparticles by ICPeMS, including intracellular zinc and zinc bound to the cell wall of C. vulgais, has also been reported (Zhou et al., 2014). Apart from conventional methods of toxicity assessment, a high-content imaging technique has been used to detect toxicity to aquatic life. The toxic effects of metal oxide nanoparticles such as ZnO, CuO, NiO, and Co3O4 have been assessed in embryo and larvae of zebrafish by using bright-field and fluorescent-based high-content imaging. Bright-field imaging is used to visualize the phenotypic and developmental abnormalities (hatching in embryo), while high-content fluorescent-based imaging can

6

CHAPTER 1 PHYTOTOXIC PROPERTIES OF ZINC AND COBALT OXIDE

be used to assess heat shock protein (Hsp70), which is overexpressed in interaction with a high dose of nanoparticles. Thus high-content imaging is a promising tool for in vivo hazard ranking and dose response relationship assessment for nanoparticles in aquatic ecosystems (Lin et al., 2011).

1.4 FACTORS INFLUENCING PHYTOTOXICITY OF ZNO AND COO NANOPARTICLES Before assessing the commercial implications of nanomaterials, nanotoxicity and the action of metal oxide nanoparticles in aquatic environments must be studied as a priority. Many factors influence the toxicity of metal and metal-oxide-based nanoparticles for aquatic life, including physicochemical characteristics of nanomaterials (shape, size, charge, etc.), behavior of nanoparticles (aggregation, dissolution, etc.) in aquatic systems, concentration, and environmental parameters (temperature, pH, salinity, etc.). A general overview of ZnO nanoparticle interactions in marine ecosystems is illustrated in Fig. 1.1.

Transfer via food chain

Fish

Physiology of biota Indirect uptake Microzooplankton Microplankton UV radiation

Direct uptake

ROS Surface modifications

Interaction between NPs and biota Dissolution

ZnO-NPs

Zn2+

Influences of temperature salinity pH of water

Aggregation DOM adsorption

Behavior of NPs

Sedimentation

Endobenthic species

Bioaccumulation and biotransformation

FIGURE 1.1 Overview of interaction of ZnO nanoparticles with marine biota, behavioral modifications, and transformation. Reprint with permission from Yung, M.M.N., Mouneyrac, C., Leung, K.M.Y., 2014. Ecotoxicity of zinc oxide nanoparticles in the marine environment. In: Bhushan B. (Ed.) Encyclopedia of Nanotechnology. Springer Netherlands, Dordrecht, pp. 1e17. https://doi.org/10.1007/978-94-007-6178-0_100970-1.

1.4 FACTORS INFLUENCING PHYTOTOXICITY OF ZNO AND COO

7

1.4.1 PHYSICOCHEMICAL CHARACTERISTICS OF NANOMATERIALS The unique physicochemical characteristics of each nanoparticle govern its industrial applications in commercial products; they include size, shape, surface charge, reactivity, dispersivity, etc. Since metal oxide nanoparticles are widely used engineered nanomaterials, changes or variations in their physicochemical characters drastically influence their toxicity. A brief description of toxic effects due to physicochemical properties of ZnO nanoparticles is summarized in Table 1.2. With decreasing size of nanoparticles, their surface area increases, thereby enhancing their surface characteristics in terms of charge. It is observed in many studies based on size-dependent toxicity of nanoparticles that those with a smaller size range are more toxic compared to their larger size counterparts. With decrease in size their ability to penetrate into plant tissue increases. It is suggested that the primary particle size of the dispersed nanoparticles affects the overall toxicity (Manzo et al., 2013). When green algae D. subspicatus is exposed to TiO2 nanoparticles of particle size range 25e100 nm, it was observed that the smaller ones inhibited growth to a larger extent (Hund-Rinke and Simon, 2006). Beyond the size of metal oxide nanomaterials, morphology also influences the toxicity of the nanoparticles toward aquatic life forms, including microalgae. In a study it was observed that the toxicity of rod-shaped ZnO nanoparticles to marine algae P. tricornutum was greater than that of sphere-shaped nanoparticles (Peng et al., 2011). Thus it is necessary to characterize the shape of metal oxide nanoparticles exactly to evaluate their shape-dependent toxicity. Surface charges are also found to be important in establishing contact between the nanomaterials and cell walls of microalgae. Algal cell walls have a negative charge and therefore may attract positively charged nanoparticles or their ionic forms, such as Zn2þ ions, and enable strong chemical interactions between nanoparticles and algal cell walls (Wong et al., 2010). As the size decreases, nanoparticles become more reactive. This unusual reactivity makes them more toxic, and the corresponding charge of nanoparticles makes them more reactive toward cells and proteins compared to their natural bulk counterparts (Stark, 2011; Deng et al., 2013).

1.4.2 PROCESSES AFFECTING STABILITY OF NANOPARTICLES AND TOXICITY Mobility and dispersal of nanoparticles in water bodies play a significant role in toxicity generation. Different processes like adsorption, aggregation, dissolution, and concentration have significant effects on the fate of nanoparticles in aquatic environments. The processes of adsorption and aggregation during ZnO nanoparticle interaction with Chlorella sp. have resulted in deformed algal cell morphology, reduced viability, and compromised membrane integrity. These effects are due to dissolution of ZnO nanoparticles into zinc ions, causing mechanical damage to cell walls (Chen et al., 2012b). The increased rate of dissolution of Zn2þ ions can reduce cell growth and chlorophyll concentration in marine phytoplankton T. pseudonana when exposed to ZnO nanoparticles. Freshwater algae may suffer similar effects when exposed to ZnO nanoparticles (Ma et al., 2013; Miao et al., 2010; Franklin et al., 2007). On the other hand, aggregations of nanoparticles lead to formation of larger particles and removal from the water column in the form of sediments. In marine environments it has been found that aggregates of nanoparticles are formed and settle in the form of sediments (Bian et al., 2011). Although the aggregates of nanoparticles are sedimented in aquatic systems, they can be taken up by benthic organisms and filter feeders; this results in bioaccumulation or biomagnification in food chains, generating possible toxicity. Concentration of metal oxide nanoparticles in both dissolved ionic form and as nanoparticles in an aqueous system may affect algal growth severely, even at low levels.

Table 1.2 Effect of Physicochemical Properties of ZnO Nanoparticles in Microalgae

Size

D. tertiolecta

ZnO nanoparticles were found more toxic than their bulk counterpart.

S. obliquus

Increased reduction in cell viability and photosynthetic pigment content were observed with small-sized nanoparticles compared to larger particles in a lake water study under visible light, UV-C, and dark conditions. One-dimensional rod-shaped nanoparticles caused significant growth inhibition compared to spherical particles.

Shape

P. tricornutum

Surface Charge

S. costatum and T. pseudonana

Surface Area

T. pseudonana

Concentration

C. vulgaris (marine)

S. costatum

Photoactivity

P. subcapitata

S. obliquus

Effect/Observation

Surface charges were found to be important in establishing contact between nanomaterials and surfaces of microalgae. Higher Zn2þions were released from nanoZnO and adsorbed on to positively charged microalgae surfaces, generating ROS. Solubility of nanoparticles is influenced by surface area. A change in Zn2þ release was found to be dependent on a particle’s surface area. Reduction in cell viability was observed with increased concentration of nanoparticles from 50 to 300 mg/L. Significant reduction in LDH level at 300 mg/L concentration confirmed cell wall damage. Decrease in cell density was observed with increasing concentration of ZnO nanoparticles. Inhibition of algal growth reported under visible, UV-A, and UV-B light conditions. Reduced cell viability was observed under UV-C irradiation compared with visible light and dark condition.

Size of Nanoparticles (nm) 900 nm (nanoZnO) 1300 nm (bulk ZnO) 487.5 and 616.2 nm (diameter in lake water)

References Manzo et al. (2013) Bhuvaneshwari et al. (2015)

6.3e15.7 nm (spheres) 242e862 nm (rod shaped) 20 nm

Peng et al. (2011)

20 nm

Miao et al. (2010)

40e48 nm

Suman et al. (2015)

50 nm

Zhang et al. (2016)

264 nm

Lee and An (2013)

40e44 nm

Bhuvaneshwari et al. (2015)

Wong et al. (2010)

CHAPTER 1 PHYTOTOXIC PROPERTIES OF ZINC AND COBALT OXIDE

Studied Algal Species

8

Physicochemical Properties

1.5 TOXICITY OF ZINC AND COBALT OXIDE NANOPARTICLES

9

A cytotoxic effect on C. vulgaris at low concentrations of 50 mg/L ZnO nanoparticles is observed. The viability of C. vulgaris decreased by 90.49  0.3% at 24 h at 50 mg/L ZnO nanoparticles, whereas at 300 mg/L the viability of C. vulgaris significantly reduced to 23.69  1.8%. A complete suppression of growth of three marine diatoms is observed at 10 mg/L of nanoZnO (Suman et al., 2015; Peng et al., 2011). In another study, different concentrations of CoO nanoparticles are applied to Navicula and Chetoceros spp. and it is observed that exposure to 0.2 mg/mL CoO nanoparticles for 5 days resulted in decreased cell densities in both microalgae (Rebello et al., 2010). It is also reported that ZnO nanoparticles at low concentration (0.081 mg/L) are toxic to freshwater algal species, but in marine species they are not toxic (Aravantinou et al., 2015).

1.4.3 ENVIRONMENTAL FACTORS Metal oxide nanoparticles can exhibit different toxicities to aquatic organisms under different environmental conditions. Ionic strength, pH, and temperature play very important roles in the degree of dissolution and aggregation and the related toxicity in the aquatic environment. Due to its high ionic strength, rapid aggregation of nanoparticles tends to take place in seawater compared to freshwater. Experimental evidence suggests that aggregate size of ZnO nanoparticles significantly increases with increasing salinity, and therefore toxic effects of ZnO nanoparticles toward the marine diatom T. pseudonana are reduced in terms of growth inhibition and photosynthetic performance with increased salinities (Yung et al., 2015). The pH of water bodies keeps changing, which can also bring changes in aggregation and ionic dissolution of nanoparticles. An elevated toxicity of ZnO nanoparticles in marine diatom T. pseudonana is observed at low pH and at the same time an increase in ionic dissolution from ZnO nanoparticles is observed in the exposure medium (Miao et al., 2010). Temperature is another important environmental factor governing the algal physiology and growth in aquatic systems. The effect of temperature was evaluated on the marine diatom S. costatum when exposed to ZnO nanoparticles. Growth inhibition is observed beyond the thermal tolerance limits of microalgae based on IC10 (inhibitory concentration at which growth is reduced to 10%) value for 96 h of exposure (Wong and Leung, 2014). The reactivity of metal oxide nanoparticles can also be increased at higher temperature. Elevated temperature can increase the rate of dissolution of metal oxide nanoparticles and thereby increase their toxicity. Apart from high temperature, low pH and minimum particle size also enhance the rate of dissolution of nanoparticles (Bian et al., 2011; Zhang et al., 2010; Liu and Hurt, 2010).

1.5 TOXICITY OF ZINC AND COBALT OXIDE NANOPARTICLES: POSSIBLE MECHANISMS As discussed above, the toxic impacts of metal oxide nanoparticles in aqueous environments may be influenced by many physicochemical and environmental factors, but their mechanism of toxic action is not clearly understood. Views proposed by different groups on toxicity mechanisms of a particular nanoparticle are dissimilar. ZnO and CoO nanoparticles show different solubility behavior in aqueous media. ZnO nanoparticles have a very good rate of solubility and therefore most ZnO nanoparticles are dissociated into ionic form in aqueous media. In contrast, CoO nanoparticles are partially soluble in water and most of their nanoforms are retained in aqueous media. Both of these nanoparticles show

10

CHAPTER 1 PHYTOTOXIC PROPERTIES OF ZINC AND COBALT OXIDE

different reactivity with the surrounding environment; thus their mechanisms of toxicity in aqueous media can be explained by dissolution, aggregation, and adsorption. Most of the literature available to date focuses on the first mechanism of toxicity, but aggregation and adsorption also affect the toxicological impact of these nanoparticles in aquatic food chains.

1.5.1 DISSOLUTION Many metal oxide nanoparticles tend to dissociate into ions in aqueous media. The extent of dissolution depends upon the solubility characteristics of nanoparticles. As mentioned, ZnO nanoparticles are more easily soluble in water than CoO nanoparticles; most of the information available to date concerns the dissolution-based toxicity of ZnO and much less work has been done on CoO nanoparticles. In most of the research it has been observed that ionic zinc dissociated from ZnO nanoparticles is significantly responsible for the toxicity in aquatic environments. Toxicity in marine algae has been found to be closely related to the concentration of released Zn2þ. The rate of dissolution is affected by various physicochemical factors, such as particle size, surface area, roughness, morphology, etc. (Farre´ et al., 2009). Miao et al. (2010) systemically examined the kinetics of Zn2þ release under different conditions and found that it is mainly influenced by pH and specific surface area of the ZnO nanoparticles. Moreover, the extent of nanoparticle solubility depends upon their size. Yang and Xie (2006) find faster release of ionic zinc from ZnO nanoparticles than from its microsize particles. In addition to size and surface area, other physicochemical factors like roughness and curvature may influence the dissolution of metal oxide nanoparticles in aquatic environments (Borm et al., 2006). Solubility behavior of nanoparticles is different in different water systems. ZnO nanoparticles show higher solubility than their bulk counterpart in saltwater than freshwater (Wong et al., 2010). Dissolved Zn2þ ions reduce cell growth and chlorophyll concentration in marine phytoplankton T. pseudonana when exposed to ZnO nanoparticles. Freshwater algae may suffer similar effects when exposed to ZnO nanoparticles (Ma et al., 2013; Miao et al., 2010; Franklin et al., 2007). In another study, Ates et al. (2016) found that cobalt oxide nanoparticles are more soluble in seawater than nickel oxide nanoparticles, resulting in a higher level of ionic dissolution. Though there is a wide acceptance of the idea that toxicity is induced by dissolved Zn2þ in aquatic environments, it is still not clearly understood to what extent ionic zinc contributes to the toxicity of ZnO nanoparticles. Some researchers have proposed that ZnO nanoparticles also produce toxicity in algae and other aquatic organisms in particulate form (Nair et al., 2009; Wong et al., 2010). According to a recent study, ZnO nanoparticle toxicity through dissolved Zn2þ and nanoparticle-dependant effects are observed to express distinct genes in D. manga. Three distinct biomarker genes, multicystatin, ferritin, and C1q, are identified to express differentially under ZnO nanoparticle exposure. Thus environmental exposure to ZnO nanoparticles in aquatic organisms can be identified by using different biomarker genes (Poynton et al., 2010). The ion-induced and particle-dependent toxicity of ZnO nanoparticles can be determined by applying this biomarker gene expression method in a precise way. In the case of partially soluble nanoparticles, such as CoO nanoparticles, it seems more acceptable.

1.5.2 AGGREGATION It has been demonstrated that the stability of nanoparticles in aqueous media is inversely proportional to their tendency to aggregate (Mackay et al., 2006). Once nanoparticles enter a water system, the

1.5 TOXICITY OF ZINC AND COBALT OXIDE NANOPARTICLES

11

strength of repulsive forces acting between charged surfaces of nanoparticles determines the formation of aggregates of nanoparticles. For example, a ZnO nanoparticle is surrounded by adjacent particles in a liquid medium and carries an equal positive charge, causing development of electrostatic repulsion between two adjacent particles. The ZnO nanoparticles remain separate and stabilized in the liquid suspension only if the electrostatic repulsion is higher than force of attraction (van der Waals attraction force). However, in marine environments high ionic strength reduces the interparticle electrostatic repulsion forces, resulting in the formation of nanoparticle aggregates which settle as sediments (Bian et al., 2011). Aggregation limits the rate of dissolution and the resulting ionic toxicity. The size and shape of nanoparticles influence the character of toxicity in aquatic systems. Small-size nanoparticles possess larger surface area and reactivity. When aggregation occurs between spherical particles, only a very small contact point is occupied, resulting in increased aggregate size, and the overall surface area of all the particles in the aggregate remains the same as that of separate particles. But tightly packed and densely aggregated nanoparticles may have few available reactive surfaces, and this may hinder the particle solubility and dissolution (Borm et al., 2006). CoO nanoparticles show slow ionic dissolution and directly interact with algal cells in particulate form. The process of aggregation to such partially soluble nanoparticles may influence their ecotoxicity. Although the aggregates of nanoparticles are sedimented in aquatic systems, they can be taken up by benthic organisms or filter feeders and result in bioaccumulation or biomagnification in food chains, generating possible toxicity in the long run.

1.5.3 ADSORPTION Nanomaterials can come into direct contact with microalgae and generate toxicity by the process of adsorption. Adsorption is governed by physicochemical properties of nanoparticles, water chemistry, and the type of target species. The forces which regulate the process of adsorption are hydrophobic forces, electrostatic attraction, van der Waals forces, receptoreligand interactions, and hydrogen bonding (Ma and Lin, 2013). As high surface area and enhanced surface reactivity are two very important physicochemical characteristics of nanoparticles, they can easily adsorb on to pollutants and dissolved organic compounds in the aquatic environment. Dissolved organic compounds such as humic acid and fulvic acid are abundantly available in aquatic systems, mainly derived from algae or plants. At neutral pH, dissolved organic compounds are mostly negatively charged and contain different functional groups (phenolic, carboxylic, etc.), which make them highly functionalized organic compounds. The adsorption of nanoparticles on these compounds can bring modifications in their surface charge and reactivity, thereby increasing their stability in suspension form by enhancing electrostatic repulsion. For example, ZnO nanoparticles adsorbed on humic acid are observed to be more dispersed and stabilized in suspension than free ZnO nanoparticles, owing to increased electrostatic repulsive forces (Yang et al., 2009b). Tang et al. (2015) investigated the effects of humic acid adsorption on the toxicity of ZnO nanoparticles to Anabaena sp. Observation by scanning electron microscopy confirmed that adsorption on humic acid prevented the attachment of ZnO nanoparticles to algal cells due to the increased electrostatic repulsion, and minimized the toxicity. Apart from the direct toxic effects of nanoparticles through adsorption, indirect toxicity to aquatic microalgae and other organisms may result from adsorption of essential nutrients and biomolecules by nanoparticles, thereby limiting their bioavailability for the growth and survival of other organisms (Horie et al., 2009).

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CHAPTER 1 PHYTOTOXIC PROPERTIES OF ZINC AND COBALT OXIDE

1.5.4 INTERACTION, ENTRY, AND TOXIC IMPACT Behavioral aspects of nanoparticles in aquatic systems can be explained by the above-mentioned processes, but to understand the complete mechanism of toxicity it is important to know that how these metal oxide nanoparticles interact with microalgae and other aquatic organisms (Fig. 1.2). Both ZnO and CoO nanoparticles have been found to generate toxicity either through dissolution into ionic form or by particulate form. Basically, metal ions are internalized into cells by ion channels or transporters present on the cell surface, while the metal oxide nanoparticles gain entry via the process of endocytosis. Nanoparticles which are not completely soluble in water and are present in particle form may be taken up by cells through a combination of both ion channels and endocytosis (Misra et al., 2012). The cell walls of algae provide an extra barrier to nanoparticles beyond cell membranes. Algal cell walls contain small pores of 5e20 nm size, which is sufficient to facilitate the entry of smaller nanoparticles (von Moos et al., 2014). Various pathways involved in the entry of nanoparticles into algae have been explained in recent research. Dissolution, passive transport, facilitated transport, and endocytic pathways are the major pathways involved in internalization of nanoparticles into cells. Ion channels such as the Naþ channel can be used to facilitate entry of metal ions dissociated from nanoparticles. Damage to cell membranes caused by nanoparticles results in increased permeability, which also facilitates the transfer of nanoparticles across the cell membrane. Algal cell walls contain carrier proteins which help algae to assimilate nutrients from media. These carrier proteins are highly selective and can allow selective entry of specific nanoparticles into the cell. It has been observed that

Membrane lipid bilayer

A B

ROS

M+

M+

C

Unicellular Microalgae

NP D ROS

ROS

Light

FIGURE 1.2 Overview of entry of nanoparticles into microalgae. (A) Facilitated transport. (B) Ion channel transport. (C) Endocytic entry. (D) Direct internalization and photoinduced ROS generation. Mþ, metal ion; NP, nanoparticle.

1.5 TOXICITY OF ZINC AND COBALT OXIDE NANOPARTICLES

13

the endocytic mechanism is highly developed in microalgae, and can permit the entry of larger-sized nanoparticles (von Moos et al., 2014; Schultz et al., 2015). When nanoparticles enter water they tend to form aggregates. These aggregates may release toxic ions in close proximity to cell walls after coming into contact with algae (Li et al., 2015; Suman et al., 2015), which can produce toxic effects on the cells (Golbamaki et al., 2015). After entering an algal cell, nanoparticles or their ionic form exert toxic effects on cellular functions, resulting in inhibition of growth and cell death. Formation of ROS is a widely studied nanotoxicity mechanism. ROS can induce oxidative stress, causing cytotoxicity and genotoxicity. ROS can further trigger antioxidant enzymes like SOD, catalase, and glutathione peroxidases, and the activity of these antioxidant enzymes can be used as a biomarker to assess exposure to nanoparticles (Vale et al., 2016). Upon entering the cell, nanoparticles may disturb the balance between oxidanteantioxidant processes and induce intracellular oxidative stress. Increased levels of oxidative stress and cellular inflammation may also modify proteins, lipids, and nucleic acid and further depress antioxidant defense systems, cause DNA damage and even cell death (Yang et al., 2009a; Golbamaki et al., 2015). Metal oxide nanoparticles tend to dissociate in aqueous media owing to their small size and increased surface area, and interact with algal cells in ionic form, causing toxicity. Toxic ions interfere with cell organelles and disturb their functioning by inducing oxidative stress. In contrast, nanoparticles may directly interfere with cell division, DNA replication, and transcription, resulting in suppressed growth and cell death (Singh et al., 2009; Xia et al., 2015). Because of their small size, nanoparticles may enter cells by passing across cellular membranes or cell walls, where they can impair cellular functions. Even an inert nanoparticle can be harmful if it gets inside the cell (Bystrzejewska-Piotrowska et al., 2009). Nanoparticles may enter during cell division (Magdolenova et al., 2013) or through holes in cell walls (Navarro et al., 2008b; Li et al., 2015), where they get access to the nucleus and cause damage to nucleic acid (Singh et al., 2009). The size of the nanomaterial also influences the generation of ROS and resulting oxidative stress. Khare et al. (2011) demonstrated that ZnO nanoparticles of 25 nm are more toxic to C. elegans than 100 nm particles. Also, overproduction and accumulation of ROS can damage cell membranes, leading to cell lyses and cell death, or can facilitate accumulation of nanoparticles inside the cell and exert severe toxicity (Wahab et al., 2010; Xie et al., 2011). Zhou et al. (2014) conclude that ZnO nanoparticles are the cause of ROS, which induced cell damage in C. vulgaris, and the toxicity is dose dependent. Moreover, direct interaction of nanoparticles with algal cell walls may damage membrane permeability and release the LDH enzyme in solution, an impact of toxicity caused by nanoparticles. Further, lipid peroxidation is another impact of nanoparticles on increased permeability of cell membranes.

1.5.5 PHOTO-INDUCED TOXICITY Many metal oxide nanomaterials behave as semiconductors, and their reactivity can be dramatically altered by exposure to UV and visible light. Photo-induced changes in reactivity may affect the toxicity of these nanomaterials (Fu et al., 2014). Apart from toxicity generated by ZnO and CoO nanoparticles in their ionic and particulate forms based on their physicochemical properties, they also show photocatalytic properties. CoO nanoparticles are known as an oxidative catalyst, while ZnO nanoparticles are a potent photocatalyst (Asif et al., 2014). The popularity of ZnO nanoparticles for photocatalytic use is second only to that of TiO2 nanoparticles. Toxicity of ZnO nanoparticles toward aquatic organisms, particularly algae, is also attributed to their photoactive nature. With UV radiation, ZnO

14

CHAPTER 1 PHYTOTOXIC PROPERTIES OF ZINC AND COBALT OXIDE

nanoparticles are activated and generate ROS in aqueous media (Ma et al., 2013). The photocatalytic nature of ZnO nanoparticles is based on bandgap energy (3.37 eV, equivalent to 368 nm). When ZnO nanoparticles absorb UV radiation with energy at or above its bandgap energy, subsequent excitation of electrons occurs; these react with surface bound molecules (such as oxygen) in aqueous media and generate ROS such as superoxide and hydroxyl free radicals, causing phototoxicity (Hoffmann et al., 2007). Most photo-induced toxicity to algal species has been observed under laboratory conditions, where a fluorescent light source is used which emits negligible or no UV radiation. It is noteworthy that 6% of the sunlight energy reaching the Earth’s surface is equivalent to the energy of UV irradiation of a 368 nm or lesser wavelength (Ma et al., 2013). Some studies suggest that natural sunlight can induce phototoxicity while laboratory fluorescent lights are not sufficient to cause phototoxicity. It has been demonstrated in several reports that the toxicity of ZnO nanoparticles significantly increases under natural sunlight compared to fluorescent laboratory lighting (Adams et al., 2006; Lipovsky et al., 2009). The first demonstration of photoinduced toxicity of ZnO nanoparticles in higher organisms was shown by Ma et al. (2011). It is observed that under natural sunlight ZnO nanoparticles of 60e100 nm size cause severe toxicity in the nematode C. elegans within 2 h of exposure (2 h, lethal concentration (LC50) of 25 mg/L), whereas no adverse effects are observed with the same concentrations of ZnO nanoparticle exposure under laboratory conditions (lighting or dark). Similarly, photoinduced inhibition is reported in green algae when UV preirradiated ZnO nanoparticles (