Nanotechnology doubtless has much potential.

For instance: tiny nano landscape "moulds" 100,000 times smaller than the tip of a pencil, could convert stem cells rapidly into a cell of choice. The topology structuring the stem cell as it is placed into the three dimensional mould modifies its behaviour and ultimate fate. Work on this is being done at Northwestern University in the US.

Another example. Half the world's population lacks clean drinking water. In one project, "biodegradable teabags" are being made of a mesh of water soluble polymer nano fibres that have been impregnated with antimicrobial agents that kill 99% of all bacteria. The "teabag" occupies the neck of a water bottle and could change water consumption in the developing world, researchers say.

Nano technology is also being touted for space-based applications. Because of the expense of bringing things into orbit, nano-sized sensors providing analyses and diagnoses in space could become vital. More efficient solar cells based on nano technology could make large panels on spacecraft redundant.

There are numerous other examples. But what are the drawbacks of nanotechnology? Back on Earth, the prosaic matter of using silver nano particles to remove sweat odour from sports clothes has come under criticism

Researchers in Sweden are finding that the amount of silver in sewage works sludge is rising.

And this is a problem, claim researchers at the Royal Institute of Technology in Stockholm. Silver ions kill bacteria yet they are toxins, at least as poisonous as mercury. And silver nano particles are quickly washed out of the clothes they originally impregnated. According to the Swedish chemicals inspection authority, after ten washes the stuff is gone. The toxic silver makes bacteria in the sludge antibiotic resistant, because the toxic stuff thickens cell walls in an attempt to resist penetration from the heavy metal.

Unfortunately these are the same cell membranes that antibiotics pass through to kill the cells. When the sludge is spread on fields as fertiliser there is risk of spreading the resistant bacteria as well as the silver itself enters the wider environment. Worse, the odour-killing nano particles do not make clothes smell less even while they are still in the garments, according to tests by the Textile University at Borås. The Swedish Water Association now wants the Swedish government to raise the issue at EU level, where the new biocide convention is currently being negotiated.

The executive of a company manufacturing antibacterial silver for clothes says that there is not enough cotton for the world's population in the future, set to grow by two billion by 2050. The problem of artificial fibres, that they absorb sweat smells, has to be dealt with in some way.

The amount of silver in the sludge is much less than it was two decades ago and that a lot silver is used for water purification. Less than one percent of silver is used for odour-free clothing. The problem of antibiotic resistant bacteria caused by silver is so marginal the EU, which recently published its strategies on antibiotic resistance, does not even mention silver.

So does that mean the Swedish water inspection authority is being unduly alarmist? Well maybe not. The problem with current chemicals conventions is that they do not cover nanomaterials. The chemical convention REACH, the EU's biggest piece of legislation when negotiated through in the early 2000s, was aimed at identifying "substances of very high concern" and then replacing them with safer alternatives.

REACH is run from a big bureaucratic machine based in Helsinki and all chemicals used in industry have to undergo an authorisation process. But science often moves faster than legislation. And there is no doubt that some chemicals - the organic compounds that have been termed Persistent Organic Pollutants, for instance - do affect health.

Prof John Turnidge at the Australian Society for Microbiology argues that a lot of these materials are being wheeled out without much public discussion. The problem is resistance takes a long time to develop and the picture is hard to determine by which time it could be too late. On the other hand there is the danger of being overly alarmist and silver undoubtedly has many uses in hospitals as bacterial killer. Some surveys show that no resistance has yet been developed.

Scientists have to get in early on the public debate on this, else there is a danger of the issue being seized by activists, as has happened with GM and nuclear. It would be terrible if yet another useful bit of science were removed out of irrational fears.

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Pelle Neroth -- EU correspondent