ReviewInteraction of engineered nanoparticles with various components of the environment and possible strategies for their risk assessment
Introduction
A remarkable progress has been noted in the area of nanotechnology in recent years as evident from its widespread use in textile, electronics, pharmaceuticals, cosmetics, foods and environmental remediation (Dunphy Guzman et al., 2006, Royal Society, 2004). Despite tremendous benefits, the inevitable release of engineered nanoparticles (ENPs) in the environment with the development of nanotechnology is a serious case of concern of environmental biologists worldwide. However, a few studies have already demonstrated the toxic effects of nanoparticles on various organisms, including mammals (Handy et al., 2008a). But scanty and fragmentary information are available on probable inputs, fate and interactions of these nanoparticles with various components of the environment. Thus the present review is aimed to address the current understanding of the structure, fate, behaviour, ecotoxicity test methods and environmental risks assessment of ENPs.
Section snippets
Natural vs engineered nanoparticles
The existence of naturally occurring nanoparticles in water, air and soil is known from the beginning of earth’s history as they have been recorded from 10 000 years old glacial ice cores. These nanoparticles are assumed to be derived from natural combustion processes and deposited into the ice core via atmospheric deposition (Murr et al., 2004). Likewise, the presence of natural nanoparticles has also been recorded from the sediments of Cretaceous–Tertiary (K–T) boundary at Gubbio, Italy (Verma
Production of engineered nanoparticles
Theoretically ENPs can be produced from any chemical but usually most of the ENPs are synthesized from transition metals, silicon, carbon/single-walled carbon annotates, fullerenes and metal oxides (Drobne, 2007). Top-down and bottom-up fabrication are two distinct methods for the production of ENPs. In top-down method, lithographic techniques are used to cut larger pieces of a material into NPs. Particles with sizes lesser than 100 nm and 30 nm can be produced using extreme UV photolithography
Classes of engineered nanoparticles
ENPs can be divided into several classes, such as, carbonaceous nanomaterials; metal oxides; semi-conductor materials; zero-valent metals and nanopolymers (Fig. 1). Carbonaceous nanomaterials include fullerene compounds, nanotubes, nanowires, etc. The discovery of first fullerene (C60-atom hollow sphere, also known as the buckyball) in 1985 marked the origin of this class (Kroto et al., 1985). C60 fullerenes possess a regular truncated icosahedron, the vertices of which bear the carbon atoms (
Physico-chemical properties of engineered nanoparticles
Physico-chemical properties of ENPs are one of the most important factors that regulate the behaviour of ENPs in the environment. Engineered nanoparticles are synthesized for a particular application therefore, the physico-chemical properties of each nanoparticles vary considerably. However, universally agreed and essentially required properties for ENPs are chemical composition, mass, particle number and concentration, surface area concentration, size distribution, specific surface area,
Release of engineered nanoparticles in the environment
Increased production and widespread use ENPs in various industries cause their frequent release into the environment. ENPs enter the environment through intentional as well as unintentional releases such as atmospheric emissions and solid or liquid waste streams from production sites. Intentional release of ENPs in the environment includes the uses of nanoparticles for remediation of contaminated soil and water (Klaine et al., 2008). A proportion of nanoparticles used as one of the components
Biological uptake of engineered nanoparticles
The probable mechanisms of uptake of ENPs by living organisms are not well known so far. But, it has been believed that animals incorporate NPs in their bodies mainly via gut (Baun et al., 2008). NPs can enter in the gut cells by diffusing through cell membranes (Lin et al., 2007), through endocytosis (Kim et al., 2006) and adhesion (Geiser et al., 2005) as shown in Fig. 2. The uptake of NPs via ion transporters seems unlikely considering the larger size of NPs than ions (Handy et al., 2008a).
Ecotoxicity of engineered nanoparticles
Though a detailed mechanism of toxicity caused by ENPs is not yet elucidated, a few mechanisms like damage to membrane integrity, protein destabilization and oxidation, damage to nucleic acids, production of reactive oxygen species (ROS), interruption of energy transduction, release of harmful and toxic components are likely involved in the damage caused by ENPs (Klaine et al., 2008).
Cell membrane is a potential target of damage from ENPs. Carboxyfullerene and gold NPs have been reported to
Ecotoxicity test strategies and biological hazard assessment
Frequent release and interaction of ENPs with various components of environment as well as probable risks necessitate the development of certain strategies to test the potential hazards of ENPs. The toxicity of ENPs vary with their size and shape and other basic properties, therefore, it is essential to study these basic properties while assessing its biological hazards. But studying the basic properties of ENPs becomes difficult because of two reasons. First, their relevant concentration (in ng
Legislations on the management of risk related to engineered nanoparticles
Due to serious environmental risk posed by the release of ENPs in the environment, it becomes essential to set specific standards for the manufacture, use, and disposal of ENPs (Handy and Shaw, 2007). The Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR, 2005) reports that the existing legislations do not mention or define ENPs. However, a number of organizations have evolved development-, description- and usage-associated standards for ENPs (Bard et al., 2009). The
Future research
Considering the wide application of ENPs and their entry into the environment, the study of their impact on the ecosystem, at biotic as well as abiotic level, has become mandatory. Only a limited number of areas have been covered as far as ecotoxicity tests and assessment of the hazardous effects of ENPs are concerned. Therefore, it is required to study their release, uptake, and mode of toxicity in the organisms. Furthermore, to understand the long-term effect of ENPs on the ecosystem,
Acknowledgements
We are thankful to Professor Aditya Shastri, Vice Chancellor of Banasthali University for kindly extending the facilities of “Banasthali Centre for Education and Research in Basic Sciences” sanctioned under CURIE programme of the Department of Science and Technology, New Delhi.
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