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The nanoworld might be small but it has the potential to make big changes—both positive and negative—in the way we live our lives.

A nanometre (nm) is 10^-9, which is one-thousandth of a micrometre, or one-billionth of a metre. This is the scale at which we measure atoms and the molecules they make.

As investment in nanoscience and nanotechnology grows, some people are voicing ethical, environmental and economic concerns. While science-fiction theories of ‘grey goo’ (millions of self-replicating nanomachines with the potential to destroy the world) are far fetched, there are valid concerns about other areas of nanoscience.

For example, how do manufactured nanoparticles interact with biological systems of the human body and what health effects might this have? In laboratory tests, certain nanomaterials have been shown to affect the formation of fibrous protein tangles, which are similar to those seen in some brain diseases. There is some evidence that nanoparticles could . Nanoparticles have also been examined for their impact on the .

Long-term exposure to nanoparticles, particularly as they become more common in everyday items, is something that needs to be monitored. Dr Sam Bruschi, toxicologist and member of Australia's Nanotech Advisory Group of the National Industrial Chemicals Notification and Assessment Scheme (NICNAS), noted that carbon nanotubes, about 5000 tonnes of which are produced each year for commercial use, have been shown to produce cancer in animal testing, and many resemble the shape and size of asbestos fibres.

The way that nanomaterials  also needs further study. How a particle behaves in the lab may be very different to how it behaves in water, air or soil, and how it interacts with organic matter. Indeed, the way nanoparticles behave in the environment depends not only on their individual physical and chemical characters, but also on the character of the receiving environment—whether it is hot, wet, acidic and so on. When exposed to an environment, nanoparticles may remain intact, or undergo one of the following processes:

• dissolution (dissolving into parts or elements)
• speciation (association with other ionic or molecular dissolved chemical substances)
• settling
• agglomeration (assembling together)
• deagglomeration (breaking up or dispersing)
• biological or chemical transformation to other chemicals.

Further research is needed in these areas and appropriate controls set up to manage risks.

There is also the possibility that nanomaterials may move from organism to organism, or through food chains. The fact that there are many different types of nanomaterials means there is the potential for a wide range of effects. Some experiments have shown that they could have harmful effects on invertebrates and fish, including changes to their behaviour, development and reproduction.

Risk assessment and testing needs to keep pace with the technology, especially as the use of nanomaterials expands into the production of ever more consumer goods. Testing needs to include methods for estimating exposure and identifying hazards. At present, the nanoparticles that present the highest potential risk are free, insoluble nanoparticles, such as those dispersed in a dust or liquid.

The unique physical and chemical properties of nanomaterials often differ from those of bulk materials and require special assessment. Despite these concerns, most scientists think that nanoscience will lead to huge advances in medicine, biotechnology, manufacturing, information technology and other equally diverse areas.