How to make nanotechnology safe

There are conflicting predications about the consequences of introducing new materials into our lives. This article looks at whether nano will help or harm.

Few scientists or members of the general public can fail to notice the high profile of nanotechnology at the moment. The prefix nano- for any new product, seems to guarantee press attention and newspapers andmagazines often contain references to how nanotechnology will change our world for the better. Typical actual headlines are "Nanotechnology can produce self-cleaning clothes", "Nanotechnology can cure smelly feet", "Nanotubes can be woven into super strong rope for tethered satellites". There is little doubt that the development of new nanotechnologies will have a positive impact on our lives via a wide range of applications.

Nanotechnology may be able to cure smelly feet –
but is the nanoscience industry safe?

However, as is the case for the introduction of most types of new technology, there are also conflicting predictions about the harmful consequences of introducing these new nanomaterials into our lives. Again, as is usually the case, the truth probably lies between the two and this article sets out to describe some of the background towards achieving a safe nanotechnology industry.

What is it?
Nanoscience studies themanipulation ofmaterials at the molecular and nanometer scales, where properties differ significantly from those of the larger scale.

Nanotechnology is the design, characterisation, production and application of structures, devices and systems produced by controlling shape and size at the nanometer scale. A feature of the science of advanced materials has been the ability to control structure at smaller and smaller scales, eg the silicon chip. As understanding of these processes increases we have finally reached components with at least one-dimension under 100 nanometres.

These materials differ from their larger counterparts because of the large surface area and quantum effects that produces materials with a more reactive surface, hence their unusual chemico-physical properties. Many of the actual and predicted uses of nanomaterials are likely to be beneficial. In the field of medicine we can expect faster and more accurate diagnosis, imaging and drug delivery and so the benefits of "nanomedicine" will be considerable.

There are, however, situations where the use of nanomaterials may pose a tangible risk to human health and to the general environment. In the case of human health these are situations where nanoparticles and nanotubes (described below) are either inhaled, swallowed or possibly make contact with the skin. In the case of the environment, accumulation of nanoparticles in various levels of the ecosystem may have undesirable consequences.

Environmental nanoparticles
In the latter half of the 20th Century it became obvious that nanoparticles produced by combustion of fossil fuels and in the internal combustion engine, produced ill-health. This knowledge has been the main driver for concern that "engineered" nanoparticles produced in the nanotechnology industry might also have harmful effects. At present we only have studies on the effects of combustion-derived nanoparticles to go on, since the new nanoparticles are not yet well-studied. Fortunately the harmful effects of combustion-derived nanoparticles are quite well understood.

Exposure to nanoparticles in cities derives mostly from traffic, eg diesel soot, and is well-known to produce a range of adverse human health effects.

These tend to occur in well-defined, already-ill populations, that include asthmatics and those with smokers lung disease – COPD (Chronic Obstructive Pulmonary Diseae). Surprisingly, however, the biggest adverse health impact is in people with cardiovascular (heart and circulatory) disease who suffer from increased hospitalisations and deaths.

All of these findings are new and so although we do understand in part the action of these types of environmental nanoparticles, we are far from having a complete picture.

Engineered nanoparticles
Because of the findings described above regarding the harmful effects of environmental, combustion-derived nanoparticles, the purposeful production of engineered nanoparticles in the nanotechnology industry has raised concern. Engineered nanoparticles are amajor part of the nanotechnology business andmany new types of nanoparticles are being produced for various industrial applications.

In the search for novel nanoparticles a whole new range of different nanoparticle types are being produced in small quantities for experimental purposes or in bulk.

The major concern is firstly for those involved in manufacture. High occupational exposure to some types of particles is already well-known to produce lung disease such as silicosis, lung cancer and asbestosis.

Additionally, the release of nanoparticles in industrial effluent could lead to contamination of ecosystems. Eventually, as nanoparticles are mass-produced and introduced into more products, there will be a risk of release of nanoparticles into the environment as these products weather and undergo normal attrition.

There is then potential for general environmental exposure of humans and other species, although at generally lower levels than those encountered in the occupational setting.

Interactions between nanoparticles and the skin is a special case since nanoparticles are already present in a number of preparations that are applied directly to the skin, eg sunblock cream where the tiny particles reflect sunlight. There is, surprisingly, little known about the transfer of nanoparticles across the skin or their ability to harm skin and so much more research is needed in this area.

Nanoparticles are also present in processed food, but it isn' known whether they produce adverse effects on the gut. However, there is a clear link between modern Western life styles and inflammatory bowel disease, with dietary components, including nano- and microparticles, being implicated in the disease process.

Nanotubes
Carbon nanotubes are a special type of nanoparticle which have a long, thin tubal structure of either single or multiple graphite sheets. Nanotubes can be a few nanometres in diameter and up to several microns or even centimetres long.

Nanotubes are very strong and possess unusual electrical properties so they have numerous applications; consequently the production of nanotubes is growing.

The fibre-like shape of nanotubes brings to mind the structure of amphibole asbestos (the harmful form of asbestos) which is characterised by a long thin needle-like structure and insolubility in the lungs. Carbon nanotubes would appear to have the same kinds of physical properties as amphibole asbestos and so may be able to produce the same kinds of pathology, given a high enough exposure.

Nanoparticles and the environment
Nanoparticles have been suggested as useful tools for remediation, ie the removal of pollutants from contaminated land environments. The large surface area and reactivity of the particles provides a site
for chemical reactions that allow toxic substances to be transformed into less toxic materials. The incorporation of nanoparticles for this purpose into a matrix will also help to minimise the release of such nanoparticles into the environment.

A SiO₂ helical nanospring: spring has sprung

On the other hand, very little is known about the accidental release of engineered nanoparticles into the environment, their prevalence in various ecosystems or their effects on the organisms in these environments. One of the major routes of entry for nanoparticles into the environment probably includes release into waste water during disposal and cleansing.

For example, nanoparticulate TiO₂ particles are included in products such as white paint, cosmetics, foods and suntan lotions, products that are frequently washed into the waste water systems. At present nothing is known of the effectiveness of wastewater treatment processes in removing nanoparticles, or indeed the effects of nanoparticles on such processes.

Many wastewater treatment processes rely on degradation of organic wastematter by bacteria. There are some suggestions that nanoparticles inhibit bacterial growth, hence their inclusion in wound dressings.

If wastewater treatments are not effective at removing nanoparticles then this will lead to their release into the environment with unknown consequences.

Recent studies suggest that Buckyballs, a "nano- football" of 60 carbon atoms (C60 or fullerenes), are taken up by some species of fish leading to oxidation of lipids in the brain.

Such processes are associated with diseases such as Parkinsons and Alzheimers in humans, and in fish could lead to changes in behaviour or even death. The brain of Buckyball-exposed fish was observed to be more susceptible to lipid oxidation than the gills or liver, and this was suggested to be due to the tendency of Buckyballs to concentrate in lipid-rich environments like the brain.

Such studies, as well as providing an insight into environmental impacts may shed light on human effects.

Nothing is known regarding the effects of nanoparticles on other, simpler species such as molluscs and other filter feeders.

These species are likely to accumulate large amounts of non-digestible nanoparticles that could further concentrate in the next animal up the food chain.

The potential for nanoparticles to bio-accumulate has not been investigated, but due to their stability and general indestructibility, it is feasible that bioaccumulation will be an issue.

Working with nanomaterials
We have enormous knowledge and experience in the principles and practices of safe handling of potentially hazardous materials. In this respect, nanomaterials are no different from other more commonly used materials and chemicals.

For all potentially hazardous materials, risks to health only arise where exposure occurs by inhalation, ingestion or through the skin. The key to reducing these risks is to reduce exposures by some form of control.

A risk assessment should be the first step in ensuring that all work–related exposure are appropriately and effectively controlled. In the UK, the Health and Safety Executive (HSE) has produced a number of documents to guide this process and has recently published an information note on nanotechnologies – http://www.hse.gov.uk/pubns/hsin1.pdf.

The HSE does, however, recognise that, inmany cases, there are significant gaps and uncertainties in the knowledge available for nanoparticles. In these cases, the risk assessment should be suitably cautions and provide higher levels of protection than would normally be required.

Risk assessments should be reviewed on a regular basis and whenever new information becomes available. Steps should also be taken to address the gaps in information. Any risk assessment should also address the risks of fire or explosion, whichmay be greater for nanomaterials than for larger particles of the same material.

It is quite likely that methods we have now for controlling exposure by inhalation will be effective for many forms on nanoparticles, provided that these methods are used andmaintained properly. The same is not necessarily true for dermal exposure although whether there are any adverse health effects associated with dermal exposure to nanoparticles remains to be seen.

In any case, it is necessary to take account of the greater uncertainties about the hazardous nature of these materials and their different physical and behavioural properties before designing and implementing effective control strategies, and minimising the risk to health of those working with them.

Nanotechnology is a budding industry that promises much that will improve our future world; safe working practices, based on sound risk assessment, will mean that this can be achieved at no extra cost to human health.

By Kenneth Donaldson Medical School, University of Edinburgh, Edinburgh, Rob Aitken and Lang Tran, Institute of Occupational Medicine, Edinburgh and Vicki Stone, School of Life Sciences, Napier University, Edinburgh Corresponding author: Professor Ken Donaldson, ELEGI Colt Laboratory, University of Edinburgh, Edinburgh

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