Nanotechnology has become a worry. Pressure groups are calling for a moratorium on research; in the UK, the Royal Society and the Royal Academy of Engineering have been charged by the government to investigate; and the US government is earmarking funds for societal and environmental issues. Last month, a conference in the UK ( brought together researchers to discuss the implications for health of nanoparticles and nanomaterials.

It is important to put these risks into context. As toxico-pathologist Vyvyan Howard of the University of Liverpool pointed out, the human race has been exposed to environmental nanoparticles, such as salt crystals from the action of waves, viruses, and from combustion processes, for thousands of years. But in the last century, we have added to this burden of natural nanoparticles with those from motor vehicle exhausts. Despite the well-known health risks that the inhalation of particles pose, our understanding of exposure and the cellular damage mechanisms need to be improved, said Steffen Loft of the University of Copenhagen, Denmark.

Now we are about to embark on the mass manufacture of nanoparticles and nanomaterials and add to that potential burden still further. A critical factor here is an awareness of how risk depends not only on the hazard, but also on the exposure. Even if a particular type of nanoparticle is hazardous, if there is no exposure, there will be little risk. But we also need to be aware of who is exposed, particularly during the manufacturing process. The dangers for pregnant women and children, for example, will require particularly careful assessment, according to Howard and Jonathan Grigg from the University of Leicester, respectively.

Paul Borm of Hogeschool Zuyd, the Netherlands and the Heinrich-Heine-Universität Düsseldorf, Germany raised an interesting paradox. The diseases that may benefit the most from advances in nanotechnology, such as lung inflammation and cancer, are also those typically associated with the adverse effects of nanoparticles. Not only does this make an important case for not halting or curtailing nano-related research, it also serves to indicate the complexity of this issue. As David B. Warheit of DuPont also points out in a review in this issue of Materials Today (page 32), new data are, initially at least, unlikely to lead to any quick and easy conclusions.

The jury seems to be still well and truly out on whether nanoparticles and nanomaterials are a potential hazard or mostly harmless. Only a concerted effort by scientists across the disciplines can provide an answer. Borm made a plea at the conference for the development of medical applications and toxicological testing to be pursued hand-in-hand at multidisciplinary centers.

But if the scientific community does not engage at this early stage, it could run the risk of being crippled by overcautious regulations or found negligent in the future if problems arise.

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DOI: 10.1016/S1369-7021(04)00057-4