Nanotechnology is the term given to those areas of science and engineering where phenomena that take place at dimensions in the nanometre scale are utilised in the design, characterisation, production and application of materials, structures, devices and systems. Although in the natural world there are many examples of structures that exist with nanometre dimensions (hereafter referred to as the nanoscale), including essential molecules within the human body and components of foods, and although many technologies have incidentally involved nanoscale structures for many years, it has only been in the last quarter of a century that it has been possible to actively and intentionally modify molecules and structures within this size range. It is this control at the nanometre scale that distinguishes nanotechnology from other areas of technology.
Clearly the various forms of nanotechnology have the potential to make a very significant impact on society. In general it may be assumed that the application of nanotechnology will be very beneficial to individuals and organisations. Many of these applications involve new materials which provide radically different properties through functioning at the nanoscale, where new phenomena are associated with the very large surface area to volume ratios experienced at these dimensions and with quantum effects that are not seen with larger sizes. These include materials in the form of very thin films used in catalysis and electronics, two-dimensional nanotubes and nanowires for optical and magnetic systems, and as nanoparticles used in cosmetics, pharmaceuticals and coatings. The industrial sectors most readily embracing nanotechnology are the information and communications sector, including electronic and optoelectronic fields, food technology, energy technology and the medical products sector, including many different facets of pharmaceuticals and drug delivery systems, diagnostics and medical technology, where the terms nanomedicine and bionanotechnology are already commonplace. Nanotechnology products may also offer novel challengies for the reduction of environmental pollution.
However, just as phenomena taking place at the nanoscale may be quite different to those occurring at larger dimensions and may be exploitable for the benefit of mankind, so these newly identified processes and their products may expose the same humans, and the environment in general, to new health risks, possibly involving quite different mechanisms of interference with the physiology of human and environmental species. These possibilities may well be focussed on the fate of free nanoparticles generated in nanotechnology processes and either intentionally or unintentionally released into the environment, or actually delivered directly to individuals through the functioning of a nanotechnology based product. Of special concern would be those individuals whose work places them in regular and sustained contact with free nanoparticles. Central to these health risk concerns is the fact that evolution has determined that the human species has developed mechanisms of protection against environmental agents, either living or dead, this process being determined by the nature of the agents commonly encountered, within which size is an important factor. The exposure to nanoparticles having characteristics not previously encountered may well challenge the normal defence mechanisms associated with, for example, immune and inflammatory systems. It is also possible for there to be an environmental impact of the products of nanotechnology, related to the processes of dispersion and persistence of nanoparticles in the environment.
Wherever the potential for an entirely new risk is identified, it is necessary to carry out an extensive analysis of the nature of the risk, which can then, if necessary, be used in the processes of risk management. It is widely accepted that the risks associated with nanotechnology need to be analysed in this way. Many international organisations ( e.g. Asia Pacific Nanotechnology Forum 2005), governmental bodies within the European Union (European Commission 2004,), National Institutions (e.g. De Jong et al 2005, Roszek et al 2005, US National Science and Technology Council 2004, IEEE 2004, US National Institute of Environmental Health Sciences 2004), non-governmental organisations (e.g.UN-NGLS 2005), learned institutions and societies (e.g. Institute of Nanotechnology 2005, Australian Academy of Sciences 2005, METI 2005, UK Royal Society and Royal Academy of Engineering 2004) and individuals (e.g. Oberdörster et al 2005, Donaldson and Stone 2003) have published reports on the current state of nanotechnology, and most draw attention to this need for a thorough risk analysis.
The European Council has highlighted the need to pay special attention to the potential risks throughout the life cycle of nanotechnology based products and the European Commission has signalled its intention to work on an international basis towards establishing a framework of shared principles for the safe, sustainable, responsible and socially acceptable use of nanotechnologies.
3.2 Definitions and Scope
There are several definitions of nanotechnology and of the products of nanotechnology, often these been generated for specific purposes.
In this Opinion, the underlying scientific concepts of nanotechnology have been considered more important than the semantics of a definition, so these are considered first. The Committee considers that the scope of nanoscience and nanotechnology used by the UK Royal Society and Royal Academy of Engineering in their 2004 report (Royal Society and Royal Academy of Engineering 2004) adequately expresses these concepts. This suggests that the range of the nanoscale is from the atomic level, at around 0.2 nm up to around 100nm. It is within this range that materials can have substantially different properties compared to the same substances at larger sizes, both because of the substantially increased ratio of surface area to mass, and also because quantum effects begin to play a role at these dimensions, leading to significant changes in several types of physical property.
The present Opinion uses the various terms of nanotechnology in a manner consistent with the recently published Publicly Available Specification on the Vocabulary for Nanoparticles of the British Standards Institution (BSI 2005), in which the following definitions for the major general terms are proposed:
Nanoscale: having one or more dimensions of the order of 100 nm or less.
Nanoscience: the study of phenomena and manipulation of materials at atomic, molecular and macromolecular scales, where properties differ significantly from those at a larger scale.
Nanotechnology: the design, characterization, production and application of structures, devices and systems by controlling shape and size at the nanoscale.
Nanomaterial: material with one or more external dimensions, or an internal structure, which could exhibit novel characteristics compared to the same material without nanoscale features.
Nanoparticle: particle with one or more dimensions at the nanoscale. (Note: In the present report, nanoparticles are considered to have two or more dimensions at the nanoscale).
Nanocomposite: composite in which at least one of the phases has at least one dimension on the nanoscale.
Nanostructured: having a structure at the nanoscale,
It should be noted that nanoscience and nanotechnology have been emerging rapidly during recent years, and that the vocabulary used within the contributing disciplines has not been consistent during this time. Also, as this report notes, there have been, and continue to be, serious difficulties with the precise measurement of the parameters of the nanoscale, such that it is not always possible to have complete confidence in the data and conclusions drawn about specific phenomena relating to specific features of nanostructures and nanomaterials. This Opinion recognises the inevitability of this situation and has drawn some general conclusions in the knowledge that the literature may contain inconsistencies and inaccuracies. Whilst, therefore, this Opinion uses the definition that nanoscale should now be considered to involve dimensions up to 100 nm, it recognises that some of the literature will have represented nanoscale as having larger dimensions than 100 nm. Much of the literature related to particles, especially that concerned with aerosols, air pollution and inhalation toxicology, has referred to particles as either ultrafine, fine or conventional. This report has assumed that, unless otherwise stated, ‘ultrafine particles’ are essentially equivalent to nanoparticles.
Also, in relation to nanoparticles, it must be borne in mind that a sample of a substance that contains nanoparticles will not be monodisperse, but will normally contain a range of particle sizes. This makes it even more difficult to assess accurately the parameters of the nanoscale, especially when considering the doses for toxicological studies. In this Opinion reference is frequently made to studies of exposure and toxicology data concerned with particles and will quote the particle size given in the papers as either single figures (e.g. 40 nm) or ranges (e.g. 40 – 80 nm) recognising that these will be approximations.
Moreover, there will be a tendency in some situations for nanoparticles to aggregate. It might be assumed that an aggregate of nanoparticles, which may have dimensions measured in microns rather than nanometres, would behave differently to the individual nanoparticles, but at the same time there is no reason to expect the aggregate to behave like one large particle. Equally, it might be expected that the behaviour of nanoparticles will be dependent on their solubility and susceptibility to degradation and that neither the chemical composition nor particle size are guaranteed to remain constant over time.
With the above definitions and caveats in mind, it is clear that, as far as both intrinsic properties and health risks are concerned, there are two types of nanostructure to consider, those where the structure itself is a free particle and those where the nanostructure is an integral feature of a larger object.
In the latter group are nanocomposites, which are solid materials in which one or more dispersed phases are present as nanoscale particles, and nanocrystalline solids, in which individual crystals are of nanoscale dimensions. This group also includes objects which have been provided with a surface topography with features of nanoscale size, and functional components that have critical features of nanometre dimension, primarily including electronic components. . For medical purposes surface modifications can be obtained by using specific coatings composed of nanosized materials (Roszek et al 2005). This Opinion recognises the existence of such materials and products, and recognises that material features of nanoscale dimensions can influence interactions with living systems. However, although the science of interactions between biological systems and nanotopographical features is developing rapidly, very little is known of the potential of such interactions to induce adverse effects . The risk would be dependent on the strength of the adherence to the carrier material, and associated with the release during use or at the end of the life time of the product. As long as the nanomaterials are fixed on the surface of the carrier there is at the moment no reason to suppose that immobilized nanoparticles pose a greater risk for health or environment than the larger scale materials.
It is the former group, involving free nanoparticles, that provides the greater concern with respect to health risks, and which is the subject of the major part of this Opinion. The term ‘free’ should be qualified, since it implies that at some stage in production or use the substance in question consists of individual particles, of nanoscale dimensions. In the application of the substance, these individual particles may be incorporated into a quantity of another substance, which could be a gas, a liquid or a solid, typically to produce a paste, a gel or a coating. These particles may still be considered to be free, although their bioavailability will vary with the nature of the phase in which they are dispersed. Ultrafine aerosols and colloids, and cream-based cosmetics and pharmaceutical preparations would be included in this category, and it is with these examples that much of the recent work on nanotechnology health risks has been concerned.
This opinion essentially discusses the potential risks associated with the manufacture and use of products incorporating engineered nanomaterials. Nanostructures of biological origin such as proteins, phospholipids, lipids etc. are not considered in this context.