Environmental Toxicity of Nanomaterials

Environmental Toxicity of Nanomaterials

http://taylorandfrancis.com


Edited by

Vineet Kumar Nandita Dasgupta Shivendu Ranjan

CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2018 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed on acid-free paper International Standard Book Number-13: 978-0-8153-6652-2 (Hardback) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www .copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

Contents Preface........................................................................................................................vii Editors..........................................................................................................................ix Contributors.................................................................................................................xi 1. Toxic Effects of Nanomaterials on Environment............................................. 1 Rajeev Kumar, Moondeep Chauhan, Neha Sharma, and Ganga Ram Chaudhary 2. Nanotoxicity: Impact on Health and Environment....................................... 21 Ponnala Vimal Mosahari, Deepika Singh, Jon Jyoti Kalita, Pragya Sharma, Hasnahana Chetia, Debajyoti Kabiraj, Chandan Mahanta, and Utpal Bora 3. Nanotoxicological Evaluation in Marine Water Ecosystem: A Detailed Review............................................................................................. 47 Anna Giulia Cattaneo 4. Interaction of Carbon Nanomaterials with Biological Matrices.................. 77 S. Gajalakshmi, A. Mukherjee, and N. Chandrasekaran 5. Interaction of Inorganic Nanoparticles with Biological Matrices.............. 109 Priya Sharma, Vineet Kumar, and Praveen Guleria 6. Effects of Engineered Nanoparticles on Bacteria........................................ 125 Changjian Xie, Xiao He, and Zhiyong Zhang 7. Comparative Risk Assessment of Copper Nanoparticles with Their Bulk Counterpart in the Indian Major Carp Labeo rohita........................ 159 Kaliappan Krishnapriya and Mathan Ramesh 8. Toxic Effects of Nanomaterials to Plants and Beneficial Soil Bacteria..... 179 Shiwani Guleria, Praveen Guleria, and Vineet Kumar 9. Nanotoxicity of Silver Nanoparticles: From Environmental Spill to Effects on Organisms................................................................................. 191 Kevin Osterheld, Mathieu Millour, Émilien Pelletier, Adriano Magesky, Kim Doiron, Karine Lemarchand, and Jean-Pierre Gagné

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10. Nanotoxicity on Human and Plant Pathogenic Microbes and Aquatic Organisms.................................................................................. 241 Akhilesh Dubey, Vishal Mishra, Sanjeev Kumar, Shahaj Uddin Ahmed, and Mukunda Goswami 11. Methods of In Vitro and In Vivo Nanotoxicity Evaluation in Plants.......... 281 Ilika Ghosh, Manosij Ghosh, and Anita Mukherjee 12. In Vitro and In Vivo Nanotoxicity Evaluation in Plants.............................. 305 Homa Mahmoodzadeh 13. Phytochemicals and Their Functionalized Nanoparticles as Quorum Sensing Inhibitor and Chemotherapeutic Agent......................................... 349 Brajesh Kumar and Kumari Smita 14. Nanotoxicological Evaluation in Freshwater Organisms............................ 377 Lindsey C. Felix and Greg G. Goss 15. Guidelines and Protocols for Nanotoxicity Evaluation............................... 413 Bindu Sadanandan, Vijayalakshmi V, and Mamta Kumari 16. Regulations for Safety Assessment of Nanomaterials................................. 447 Preetika Biswas and Ashutosh Yadav Index......................................................................................................................... 497

Preface This book is a comprehensive reference book containing in-depth information on nanoecotoxicity and its implication in various disciplines of sciences. The chapters focus on the causes and prevention of toxicity induced by various nanomaterials. This book foresights the safe utilization of nanotechnology, so that the tremendous prospective of nanotechnology does not harm living beings and environment. Nanomaterials leach from nanomaterial-containing products and contaminate the basic components of environment, air, water, and soil. Every living organism, including terrestrial, aquatic, and amphibians, is in continuous contact with the physical components of environment. Further, advances in the synthesis of nanomaterials leading to desired size, shape, and surface properties will increase their burden on the environment. At present there is complete uncertainty regarding toxicity behavior of nanomaterials. There is no clarity how nanomaterials will behave once in complex environment. The future of nanomaterials in various industries depends upon their impact on environment and ecosystem. This book critically describes all these aspects of nanotoxicity in detail. The book includes an introduction to nanoecotoxicity, various factors affecting toxicity of nanomaterials, various factors that can impart nanoecotoxicity, various studies in the area of nanoecotoxicity evaluation, and the future risk assessment strategies. The book contains contribution from international experts and will be a valuable resource for undergraduate and graduate students, doctoral and postdoctoral scholars, industrial personnel, academicians, scientists, researchers, and policy makers from different nanotechnology-associated industries. The book will be beneficial for graduate students to understand the detailed concept of nanoecotoxicology. The book will be beneficial to doctoral and postdoctoral scholars as they can learn the basics of techniques, recent advancements, challenges, and opportunities in this field. This book will provide critical and comparative data to nanoecotoxicologists, and thus it will be beneficial for scientists and researchers working in this field. This book will also be beneficial for academicians to give the basics of nanoecotoxicology as many universities throughout the world have nanobiotechnology as a subject that cannot be completed without discussing nanoecotoxicology. Once in environment, nanomaterials will affect you.

—Vineet Kumar Dedicated to those who are suffering because of hazardous materials.

—Dr. Nandita Dasgupta and Dr. Shivendu Ranjan

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Editors Vineet Kumar is currently an assistant professor (bio technology) in the School of Biotechnology and Bio sciences at Lovely Professional University, Phagwara, Jalandhar, Punjab, India. Previously he was an assistant professor in the Department of Biotechnology, Dayanand Anglo-Vedic (DAV) University, Jalandhar, Punjab, India and a University Grant Commission–Dr Daulat Singh Kothari postdoctoral fellow (2013–2016) at the Department of Chemistry, Panjab University, Chandigarh, UT, India. He has worked in different areas of biotechnology and nanotechnology at various institutes and universities, including Council of Scientific and Industrial Research (CSIR)–Institute of Microbial Technology, Chandigarh, UT, India, CSIR–Institute of Himalayan Bioresource Technology, Palampur, HP India, and Himachal Pradesh University, Shimla, HP India. His interests include green synthesis of nanoparticles, nanotoxicity testing of nanoparticles and application of nanoparticles in drug delivery, food technology, sensing, dye degradation, and cataly sis. He has published many articles in these areas in peer-reviewed journals. He also serves as an editorial board member and reviewer for international peer-reviewed journals. He has received numerous awards, including a senior research fellowship, best poster award, postdoctoral fellowship, etc. Nandita Dasgupta has a vast working experience in micro/nanoscience and currently serves at VIT University, Vellore, Tamil Nadu, India. She has been exposed to vari ous research institutes and industries, including CSIR– Central Food Technological Research Institute, Mysore, India and Uttar Pradesh Drugs and Pharmaceutical Co. Ltd., Lucknow, India. Her areas of interest include micro/ nanomaterials fabrication and their application in differ ent fields, such as medicine, food, environment, agricul ture, biomedical, etc. She has published many books with Springer and is contracted with Springer, Elsevier, and CRC Press. She has also pub lished many scientific articles in international peer-reviewed journals and also served as an editorial board member and referee for international peer-reviewed journals. She has received a Elsevier Certificate for Outstanding Contribution in Reviewing from Elsevier, The Netherlands. She has also been nominated for the Elsevier advisory panel. She is an associated editor in Environmental Chemistry Letters, a Springer jour nal of 2.9 impact factor. She has received several awards from different organizations, including best poster award, young researcher award, special achiever award, research award, etc.

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Shivendu Ranjan has expertise in micro/nanotechnology and currently works at Vellore Institute of Technology (VIT) University, Vellore, Tamil Nadu, India. His research is multidisciplinary, including micro/nanobiotechnology, nano-toxicology, environmental nanotechnology, nano medicine, and nanoemulsions. He has published many scientific articles in international peer-reviewed journals. He has recently published five edited books with Springer and has contracted three books with Elsevier, and four at CRC Press, all of which cover vast areas of applied micro/ nanotechnology. He has vast editorial experience: associ ate editor of Environmental Chemistry Letters (a Springer journal with a 3.59 impact factor), the editorial panel of Biotechnology and Biotechnological Equipment (Taylor & Francis, 1.05 impact factor), and executive editor and expert board panel of several other journals. He has recently been nominated to the Elsevier Advisory Panel. He has received several awards, such as best poster award, special achiever award, achiever award, research award, young researcher award, etc.

Contributors Shahaj Uddin Ahmed Department of Biotechnology India Preetika Biswas Material Science University of Augsburg Bavaria, Germany Utpal Bora Bioengineering Research Laboratory Department of Biosciences and Bioengineering Indian Institute of Technology Guwahati Guwahati, India Anna Giulia Cattaneo Department of Biotechnology and Molecular Sciences University of Insubria Varese, Italy N. Chandrasekaran Centre for Nanobiotechnology Vellore Institute of Technology Vellore, India Ganga Ram Chaudhary Department of Chemistry and Center of Advanced Studies in Chemistry Panjab University Chandigarh, India Moondeep Chauhan Department of Environmental Studies Panjab University Chandigarh, India

Hasnahana Chetia Bioengineering Research Laboratory Department of Biosciences and Bioengineering Indian Institute of Technology Guwahati Guwahati, India Kim Doiron Institut des Sciences de la Mer de Rimouski Université du Québec à Rimouski Rimouski, Québec Akhilesh Dubey Netaji Subhas Institute of Technology New Delhi, India Lindsey C. Felix Department of Biological Sciences University of Alberta Edmonton, Alberta, Canada Jean-Pierre Gagné Institut des Sciences de la Mer de Rimouski Université du Québec à Rimouski Rimouski, Québec, Canada S. Gajalakshmi Centre for Nanobiotechnology Vellore Institute of Technology Vellore, India Ilika Ghosh Cell Biology and Genetic Toxicology Laboratory Department of Botany University of Calcutta Kolkata, India

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Contributors

Manosij Ghosh Cell Biology and Genetic Toxicology Laboratory Department of Botany University of Calcutta Kolkata, India

Debajyoti Kabiraj Bioengineering Research Laboratory Department of Biosciences and Bioengineering Indian Institute of Technology Guwahati Guwahati, India

and

Jon Jyoti Kalita Bioengineering Research Laboratory Department of Biosciences and Bioengineering Indian Institute of Technology Guwahati Guwahati, India

Environment and Health Katholieke Universiteit Leuven Leuven, Belgium Greg G. Goss Department of Biological Sciences University of Alberta Edmonton, Alberta, Canada Mukunda Goswami Genetics and Biotechnology Division ICAR-Central Institute of Fisheries Education (Deemed University) Ministry of Agriculture Government of India Andheri West, India Praveen Guleria Department of Biotechnology DAV University Jalandhar, India Shiwani Guleria Department of Microbiology Lovely Professional University Jalandhar, India Xiao He Key Laboratory for Biological Effects of Nanomaterials and Nanosafety Institute of High Energy Physics Chinese Academy of Sciences Beijing, China

Kaliappan Krishnapriya Unit of Toxicology Department of Zoology School of Life Sciences Bharathiar University Coimbatore, India Brajesh Kumar Department of Chemistry Tata College Kolhan University Chaibasa, India and Centro de Nanociencia y Nanotecnologia Universidad de las Fuerzas Armadas-ESPE Sangolqui, Ecuador Rajeev Kumar Department of Environment Studies Panjab University Chandigarh, India Sanjeev Kumar Netaji Subhas Institute of Technology New Delhi, India

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Contributors Vineet Kumar Department of Biotechnology Lovely Professional University Phagwara, Punjab

Ponnala Vimal Mosahari Centre for the Environment Indian Institute of Technology Guwahati, India

Mamta Kumari Opps Corp. Learning and Development Pvt. Chennai, India

A. Mukherjee Centre for Nanotechnology Vellore Institute of Technology Vellore, India

Karine Lemarchand Institut des Sciences de la mer de Rimouski Université du Québec à Rimouski Rimouski, Québec, Canada

Anita Mukherjee Cell Biology and Genetic Toxicology Laboratory Centre of Advance Study Department of Botany University of Calcutta Kolkata, India

Adriano Magesky Institut des Sciences de la mer de Rimouski Université du Québec à Rimouski Rimouski, Québec, Canada Chandan Mahanta Centre for the Environment Indian Institute of Technology Guwahati and Department of Civil Engineering Indian Institute of Technology Guwahati Guwahati, India Homa Mahmoodzadeh Department of Biology Mashhad Branch Islamic Azad University Mashhad, Iran Mathieu Millour Institut des Sciences de la mer de Rimouski Université du Québec à Rimouski Rimouski, Québec, Canada Vishal Mishra Netaji Subhas Institute of Technology New Delhi, India

Kevin Osterheld Institut des Sciences de la mer de Rimouski Université du Québec à Rimouski Rimouski, Québec, Canada Émilien Pelletier Institut des Sciences de la mer de Rimouski Université du Québec à Rimouski Rimouski, Québec, Canada Mathan Ramesh Unit of Toxicology Department of Zoology School of Life Sciences Bharathiar University Coimbatore, India Bindu Sadanandan Department of Biotechnology M S Ramaiah Institute of Technology Bengaluru, India Neha Sharma Department of Environment Studies Panjab University Chandigarh Chandigarh, India

xiv Pragya Sharma Department of Bioengineering and Technology Gauhati University Institute of Science and Technology Guwahati, India Priya Sharma Plant Biotechnology and Genetic Engineering Lab Department of Biotechnology DAV University Jalandhar, India Deepika Singh Bioengineering Research Laboratory Department of Biosciences and Bioengineering Indian Institute of Technology Guwahati Guwahati, India Kumari Smita Centro de Nanociencia y Nanotecnologia Universidad de las Fuerzas Armadas-ESPE Sangolqui, Ecuador

Contributors Vijayalakshmi V Department of Biotechnology M S Ramaiah Institute of Technology Bengaluru, India Changjian Xie CAS Key Lab for Biomedical Effects of Nanomaterials and Nanosafety Institute of High Energy Physics Chinese Academy of Science Beijing, China Ashutosh Yadav Material Science University of Augsburg Bavaria, Germany Zhiyong Zhang Biological Effects of Nanomaterials and Nanosafety Institute of High Energy Physics Chinese Academy of Sciences Beijing, China

1 Toxic Effects of Nanomaterials on Environment Rajeev Kumar, Moondeep Chauhan, Neha Sharma, and Ganga Ram Chaudhary CONTENTS 1.1 Introduction......................................................................................................... 1 1.2 Risk and Hazard of Exposure to Nanomaterials................................................ 4 1.3 Fate and Behavior of Nanomaterials in the Environment.................................. 5 1.3.1 Fate and Behavior of Nanomaterials in Air........................................... 5 1.3.2 Fate and Behavior of Nanomaterials in Water....................................... 7 1.3.3 Environmental Fate of Nanomaterials in Soil........................................ 9 1.4 Human Exposure................................................................................................. 9 1.4.1 Exposure through Inhalation................................................................ 10 1.4.2 Exposure through Dermal Deposition................................................. 11 1.4.3 Exposure through Ingestion................................................................. 12 1.5 Bioaccumulation of Nanomaterials................................................................... 13 1.6 Effect of Nanomaterials on Agriculture and Food........................................... 14 1.7 Conclusion......................................................................................................... 14 References................................................................................................................... 15

1.1 Introduction According to the definition given by the US National Nanotechnology Initiative, nanotechnology may be defined as understanding and control of matter at dimensions of roughly 1–100 nm, where unique phenomena enable novel applications. At this level, the physical, chemical, and biological properties of materials differ in fundamental and valuable ways from the properties of individual atoms and molecules or bulk matter. This means that at least one dimension in the approximate range of 1–100 nm and difference in the properties of matter from that of its bulk form are the two fundamental criteria which must be satisfied in order to consider a material as nanomaterial. This definition is extensively broad under which different materials are covered, and undoubtedly nanotechnology has origins, significance, and application in different fields such as agriculture, aerogels, aerospace, automotive, catalysts, coatings, paints and pigments, composites, construction, cosmetics, electronics, optics, energy, environmental remediation, filtration and purification, food products, medical, packaging, paper and board, plastics, security, sensors, and textiles, and research is underway on 1

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many new applications. Hence, nanotechnology is generally defined as a cross disciplinary technology (Foss Hansen et al. 2007). Similar to conventional substances, it is now known that some nanomaterials may be hazardous, and thus demand for standardization of the term nanomaterial and various other terms related to nanotechnology has increased. Many countries and standardization organizations have developed working definitions to identify nanomaterials based on the size of the material, its novel properties, or a combination of both, depending on their scope and the type of applications. For example, according to the International Organization for Standardization (ISO 2010), nanomaterial may be defined as “material with any external dimension in the nanoscale or having internal structure or surface structure in the nanoscale,” where nanoscale is “length ranging from approximately 1 nm to 100 nm” (Saner and Stoklosa 2013). The European Union defines nanomaterial as a “natural, incidental or manufactured material containing particles, in an unbound state or as aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1nm–100 nm. In specific cases where concerns exist for environment, health, safety or competitiveness they provide exception that number size distribution threshold of 50% may be replaced by a threshold between 1% and 50%.” The emphasis in the definition on external dimensions may exclude materials with an internal structure (e.g., porous materials with relatively large internal surface area) or materials with a surface structure at the nanoscale. Thus, it is becoming clear that many parameters other than size modulate risk, including particle shape, porosity, surface area, and chemistry. Some of these parameters become more relevant at smaller scales—but not always. The transition from “conventional” to “unconventional” behavior, when it does occur, depends critically on the particular material and the context. A “one size fits all” definition of nanomaterials will fail to capture what is important for addressing risk (Maynard 2011). Nanomaterials can be classified into different types on the basis of their source, dimensions, and chemical composition and their potential toxicity level (Dolez 2015). Erupting volcanoes, breaking sea waves, forest fires, sand storms, and soils are some of the major natural sources of inorganic nanomaterials. Some nanomaterials such as ferritin, calcium hydroxyapatite, biogenic magnetite, and ferromagnetic crystalline are naturally found in living organisms and thus are an organic source of nanomaterials. Some nanomaterials are unintentionally produced as by-products of human activity such as internal combustion engines, power plants, incinerators, jet engines, metal fumes (smelting, welding, etc.), polymer fumes, heated surfaces, food transformation processes (baking, frying, broiling, grilling, etc.), and electric motors. Finally, nanomaterials are now manufactured using a large diversity of chemical constituents, for example, metals, semiconductors, metal oxides, carbon, and polymers. There are some nanomaterials designed for specific functionalities and can be surface treated or coated. They come in a large variety of forms, such as spheres, wires, fibers, needles, rods, shells, rings, plates, and coatings, as well as in more exotic flower-like designs. Compared to natural and incidental nanomaterials, manufactured nanomaterials are characterized by their controlled dimension, shape, and composition. On the basis of dimensionality, nanomaterials can be categorized as zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and three-dimensional nanomaterials (3D). Zero-dimensional nanomaterials have all the three external dimensions at the nanoscale (i.e., between 1 and 100 nm), for example quantum dots and metal

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oxide nanoparticles (NPs). 1D nanomaterials have two external dimensions at the nanoscale, the third one being usually at the microscale such as nanofibers, nanotubes, nanowires, and nanorods. With only one external dimension at the nanoscale, 2D nanomaterials comprise thin films, nanocoatings, and nanoplates. The last dimensional category of nanomaterials, 3D nanomaterials, also termed as bulk nanomaterials, display internal nanoscale features but no external dimensions at the nanoscale. This includes nanocomposites and nanostructured materials. On the basis of potential toxicity, nanomaterials can be categorized as fiber-like NPs; biopersistent granular NPs; CMAR NPs (carcinogenic, mutagenic, asthmagenic, reproductive toxin); and liquid and soluble NPs. On the basis of chemical composition, nanomaterials can be classified as carbon-based nanomaterials, metal-based nanomaterials, dendrimers, and composite nanomaterials. Carbon-based nanomaterials are composed mostly of carbon. This classification includes fullerenes, carbon nanotubes, graphene, and the like. Metal-based nanomaterials are materials made of metallic NPs such as gold, silver, and metal oxides; for example, titanium dioxide (TiO2) NPs are extensively used in applications such as paint, sunscreen, and toothpaste. Dendrimers are nanosized polymers built from branched units. They can be functionalized at the surface and can hide molecules in their cavities. A direct application of dendrimers is for drug delivery. Composite nanomaterials contain a mixture of simple NPs or compounds such as nanosized clays within a bulk material. The NPs give better physical, mechanical, and/or chemical properties to the initial bulk material. Nanotechnology is one of fastest developing business sectors, as 380 billion dollars of worldwide market was reported for year 2013, which is expected to reach 950 billion dollars by 2020 (Dolez 2014). Approximately 2.6 × 105 – 3.09 × 105 metric tons of global nanomaterials was estimated to be produced in 2010 (Keller 2013). The nanotechnology Consumer Products Inventory (CPI), which documents the marketing and distribution of nanotechnology-related products into the commercial market place, currently lists 1814 user products (30 times increase in number of nano-enabled products in relation to 54 products which were listed originally in 2005) from 622 firms located in 32 different countries. Although, according to CPI, an increase in number may not completely represent market growth as methodology evolved over time, a stable progress of the registered nanotechnology-related products indicated that the popularity of nanotechnology has increased constantly. The Health and Fitness category was reported to have the largest listed products (762), followed by automotive (152), cross cutting (95), food and beverages (72), electronics (70), appliances (39), and goods for children (23). Within the health and fitness category, personal care products (e.g., toothbrushes, lotions, and hairstyling tools and products) were reported to include the biggest subcategory (39% of products). In the nanomaterial composition group, metals and metal oxides were maximum advertised and were reported to be registered in 37% of products. On a mass basis, TiO2, silicon dioxide, and zinc oxide were the most produced nanomaterials. However, silver NPs which were only 2% of TiO2 (on a mass basis) were present in 438 products (24%), thus the most popular advertised nanomaterials in the CPI. About 29% of the CPI (528 products) contained nanomaterials were suspended in a variety of liquid media (e.g., water, skin lotion, oil, car lubricant), and solid products with surfacebound NPs (e.g., hair curling and flat irons, textiles) was the second largest group with 307 products (Vance et al. 2015). The Nanodatabase, which is another inventory of nano-enabled products in the European market, presently enlists 2231 products.

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According to the Nanodatabase, majority of the products belong to the health and fitness category (55%), followed by home and garden (21%) and automotive (12%). One thousand two hundred twelve nano-enabled products were originally reported in 2012 which increased to more than 2200 in 2015. As per the Nanodatabase report, 10–25 products are added per week, the reason being increased marketing and uses and applications of nanomaterials (Hansen et al. 2016). Thus, as the applications of nanomaterials are continuously increasing, their quantity in the environment keeps on increasing. In spite of the innumerable number of evident benefits of nanomaterials, there are some serious concerns about how the nanomaterials used in various applications may interact with the environment. There are significant arguments regarding the adverse effects of nanomaterials on the environment with the potential to cause toxicity to humans and other living organisms. Thus, it is important for nanotoxicology to investigate the effect of nanomaterials to the environment, so the potential damage could be avoided.

1.2 Risk and Hazard of Exposure to Nanomaterials According to the US Environmental Protection Agency (USEPA), hazard may be defined as the “inherent toxicity of a compound.” According to this definition, if a chemical substance has the property of being toxic, it is therefore hazardous. Any exposure to a hazardous substance will consequently lead to an adverse health effect or even death for the individual. Hence, hazard may be thought of as the consequence of an event occurring, such as the consequence for an individual being exposed to a toxic or hazardous substance. USEPA defines risk as “a measure of the probability that damage to life, health, property, and/or the environment will occur as a result of a given hazard.” If the probability of an event occurring is high and the consequences are significant, the risk is considered to be high. However, human health risks are considered to be high, if the hazard or consequence is adverse health effects, even though the probability of occurrence is low. It is therefore important to consider both the frequency of the event and the degree of severity of the consequences, if the event were to take place. Risks, unlike hazards, can be managed and minimized. Risk may be classified into two categories, known/identified risks and hypothetical/potential risks, depending upon a cause-and-effect relationship. When the relation between a cause and an effect is established, we talk of known or identified risks. The responsibility of such risk can generally be attributed. When the causal relation is established, prevention can be applied. When the relation between a cause and a damage is not well established, we talk of hypothetical or potential risks (Helland 2004; Hristozov and Malsch 2009). Exposure is a combination of the concentration of a substance in a medium multiplied by the duration of contact. Dose is the amount of a substance that enters a biological system and can be measured as systemic dose, the total amount taken up by the biological system, or the amount in a specific organ (skin, lung, liver, etc.). The likelihood that a hazardous substance will cause harm (the risk) is the determinant of how cautious one should be and what preventative or precautionary measures should be taken. Assessing the risks imposed by the use of nanomaterials in commercial products and environmental applications requires a better understanding of their mobility, bioavailability, and toxicity. For nanomaterials to comprise a risk,

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there must be both a potential for exposure and a hazard that results after exposure (Nowack and Bucheli 2007). As more products containing nanomaterials are developed, there is greater potential risk for exposure of human and the environment to nanomaterials. The environment and humans may be exposed to nanomaterials throughout all stages of their life cycle, starting from production, storage, and transport to use and disposal. Releases of nanomaterials to the environment can be purposeful or deliberate such as remediation of contaminated lands or use of iron NPs to remediate groundwater as well as unintentional release due to wear and tear of materials containing nanomaterials. Emissions of nanomaterials to the environment may also occur by accidental spills during production or transportation and when products are disposed of at the end of their use phase. Release of NPs may come from point sources such as production facilities, landfills, or wastewater treatment plants or from nonpoint sources such as wear from materials containing nanomaterials. Regardless of whether nanomaterials are released intentionally or unintentionally, deliberately or accidentally, directly or indirectly, they all will end up in air, water, or soil and may result in direct exposure to humans via skin contact, inhalation, and direct ingestion of contaminated drinking water or plants or animals which have accumulated nanomaterials (Brook 2002). Upon emission into the environment, the behavior and distribution of nanomaterials will be determined by the intrinsic properties of the nanomaterial as well as the specific environmental conditions. Assessing the risks imposed by the use of nanomaterials in commercial products and environmental applications requires a better understanding of their mobility, bioavailability, and toxicity. Therefore, in order to determine the extent of environmental exposure to nanomaterials, it is necessary to understand their behavior in the environment.

1.3 Fate and Behavior of Nanomaterials in the Environment The fundamental properties concerning the environmental fate of nanomaterials are not well understood, as there are few available studies on the environmental fate of nanomaterials. The following sections discuss about the fate of nanomaterials in air, soil, and water (USEPA 2007).

1.3.1 Fate and Behavior of Nanomaterials in Air The natural sources of nanomaterials in the atmosphere include volcanic eruptions, forest fires, hydrothermal vent systems, physical and chemical weathering of rocks, precipitation reactions, and biological processes. However, the natural background of nanomaterials in the atmosphere is low compared to the levels caused by releases of nanomaterials in the ambient air resulting from the manufacture of nanomaterials, the handling of NPs as aerosols (such as nanotubes), cleaning and conditioning of production chambers (compression, coating, and composition), road traffic, and stationary combustion sources (Biswas and Wu 2005). It has been assessed that the amount of incidental nanomaterials in the atmosphere due to human activity is more than 36% of the total particulate concentrations, and the forecast for the years ahead is that there will be a strong increase in atmospheric nanomaterials due to the activity in industries related to the use of nanomaterials (Farré et al. 2011). Atmospheric

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nanomaterials have three major sources: (1) primary emission, which refers to those that are openly released from road traffic exhaust and industrial combustion; (2) secondary emission, which refers to those that are produced in the atmosphere from the compression of low volatility vapors produced from the oxidation of atmospheric gases; and (3) formation at the time of diesel exhaust dilution. A large number of nanomaterials present in the urban environment can be attributed to urban vehicular traffic and emissions from stationary sources. These are essentially primary pollutants with distinct source-related properties. However, once released, nanomaterials, because of their very large surface areas, chemically interact with other pollutants already present in the ambient air or with solar radiation, thereby creating secondary nanomaterials with properties significantly different from those of the primary pollutants (Shi et al. 2001). It is this ever-changing nature of nanomaterials that makes them difficult to identify and quantify. Daughton (2004) eloquently referred to both the parent NPs and their transformation products as “structurally undefinable ubiquitous xenobiotics.” The higher mobility of nanomaterials in the environment indicates greater potential for exposure because these particles are dispersed over longer distances from their origin (Wiesner et al. 2008). As a result, they may pose respiratory hazards on inhalation exposure. The fate of nanomaterials in the air is determined by the duration of time particles remain airborne, their interaction with other particles or molecules in the atmosphere, and the distance they are able to travel in the air before deposition. The processes important to understanding the dynamics of nanomaterials in the atmosphere are diffusion, agglomeration, wet and dry deposition, and gravitational settling. These processes are relatively well understood for ultrafine particles (aerosols); knowledge can be applied to nanomaterials as well (Wiesner et al. 2006). In some cases, however, intentionally produced nanomaterials may behave quite differently from incidental ultrafine particles, especially when the latter cannot agglomerate because they are coated. In addition, there may be differences between freshly generated and aged nanomaterials. Particles in the lower end of the size range of 1–100 nm will be governed by other transport processes than those in the higher end (Mädler and Friedlander 2007). For particles in the micrometer scale, inertial and gravitational forces dominate. With decreasing particle size, diffusional forces dominate and particle behavior is more like a gas or vapor. The particle diffusion in air is governed by Brownian motion, and the rate of diffusion is inversely proportional to particle diameter, while the rate of gravitational settling is proportional to particle diameter. Particles with high diffusion coefficients (such as those in the nanoscale) therefore have high mobility and will mix rapidly in aerosol systems. This increased particle mobility in air at the nanoscale is important for the transformation processes since the rate of agglomeration is governed primarily by particle mobility and number concentration, both of which increase as particle size decreases. Thus, “aerosolized” NPs may agglomerate rapidly, even at a low mass concentration (Aitken 2004). With respect to the period that particles remain airborne, particles can generally be classified into three groups: Small particles (diameters 2000 nm, beyond the discussed 80 and