The field's potential could be compromised unless the scientific community can implement a programme of systematic risk research, they warn.

Writing in Nature journal, the team says that fears about nanotechnology's possible dangers may be exaggerated, but not necessarily unfounded.

The five challenges are designed to be completed over the next 15 years.

"The threat of possible harm - whether real or imagined - is threatening to slow the development of nanotechnology unless sound, independent and authoritative information is developed on what the risks are and how to avoid them," author Andrew Maynard and his colleagues write in Nature.

The five grand challenges include developing instruments to evaluate exposure to engineered nanomaterials in air and water and developing methods for assessing their toxicity. The group of experts says that if the global research community can take advantage of the safety infrastructure already in place for biotechnology and computing, then nanotechnology has a rosy future. But Dr Maynard, from the Woodrow Wilson International Center for Scholars in Washington DC, and colleagues say that the way science is carried out means it is ill-equipped to address novel risks from emerging technologies. Research into understanding and preventing risk often has a low priority in the world of technology development, research funding and intellectual property, they say.

NANOTECH'S FIVE CHALLENGES Develop instruments to assess exposure to engineered nanomaterials in air and water within next 3-10 years Create and test ways of evaluating the toxicity of nanomaterials in 5-15 years Generate models to predict their possible impact on the environment and human health over the next 10 years Develop ways to assess the health and environmental impact of nanomaterials over their entire lifetime, within the next five years Organise programmes to enable risk-focused research into nanomaterials, within the next 12 months

"Without strategic and targeted risk research, people producing and using nanomaterials could develop unanticipated illness arising from their exposure," the authors warn in Nature.

"Public confidence in nanotechnologies could be reduced through real or perceived dangers and fears of litigation may make nanotechnologies less attractive to investors and the insurance industry."

Safety studies

Recent studies on nanoparticles in cell cultures and animals show that a variety of factors influence their potential to cause harm. These include their size, surface area, surface chemistry and ability to dissolve in water.

This should come as no surprise. Inhaled dust has been known to cause disease for many years. Small particles of inhaled quartz can lead to lung damage, with the potential for progressive lung disease. But the same particles with a thin coating of clay are less harmful.

Long, thin fibres of asbestos can also lead to lung disease if inhaled, but grinding the fibres down to shorter particles reduces their harmfulness.

In May, the UK's Royal Society called on industry to disclose how it tests products containing nanoparticles.

A joint report by the Royal Society and Royal Academy of Engineering two years ago said there was no need to ban nanoparticle production.

But it said tighter UK and European regulation over some aspects of nanotechnology - manipulation of molecules - was needed to ensure its long-term safety.