http://www.abc.net.au/science/articles/2010/11/19/3070940.htm?topic=

Concerns over nanosilver run-off

Carl Holm

The risks that nanosilver poses to the environment need to be more stringently examined, according to a new report published today.

The use of nanosilver in consumer goods is currently under intense scrutiny from occupational scientists and regulators, as they try to determine exactly how toxic the substance is.

Dr Bernd Nowack, of Empa, the Swiss Federal Laboratory for Materials Science and Technology, argues in a literature review published in the journal Science, that silver is the most commonly used nanoparticle in consumer goods, yet very little is known about what happens to it once it enters the wastewater system.

Silver is regarded as harmless to humans unless it is present in high concentrations, but it is toxic to microorganisms like bacteria and viruses.

Professor Thomas Faunce, research council future fellow studying nanotechnology and public health at theAustralian National University in Canberra, says that is why nanosilver is so extensively used in consumer goods.

Unique toxicity

"Nanosilver is the nanotech substance most widely spread in consumer products. There's a large amount of it being used in clothing, washing machines and all sorts of applications that could end up in our water ways", he says.

"The problem is that while we've known for a long time that silver is a very potent biocide, nanosilver appears to have a quite unique toxicity purely because of its size."

Nowack says the physical and chemical properties of particles in the nano-range can be different from larger particles or dissolved compounds. He says because of these different properties there should be "a new and more rigourous human and environmental risk assessment."

According to previous European studies, about 15% of the total silver flow into wastewater is biocidal silver, from consumer goods and medical uses.

In his review, Nowack reports that some silver nanoparticles have been identified bonding with sulphur to form harmless silver sulphide nanoparticles in sewage sludge.

That has led to the conclusion that sulphur plays an important role in removing silver from wastewater, but how efficiently it does this, and how toxic the remaining silver is, isn't known.

Nowack's review also raises concern that the sludge and wastewater from treatment plants is often sold to farms as fertiliser. From there nanosilver could potentially enter the food chain.

Faunce says that's not the only potential problem with nanosilver entering the sewage system.

"There are major concerns because our sewerage systems work using nitrifying bacteria. If the silver gets into those systems it may inhibit them working properly."

Clear guidelines needed

Professsor Graeme Hodge, director of the Monash University Centre for Regulatory Studies, says in order to have an effective discussion on the use and regulation of nanoparticles, definitions first need to be nailed down.

Hodge has been working with a team of nanotechnology and public health co-authors of the International Handbook on the Regulation of Nanotechnologies. He says the first barrier that needs to be overcome is the "language game".

"There's always been a language game with nanotechnology in that it means everything to everybody and asking whether nanotechnology is safe is in some ways a ridiculous question.

"It's like asking if micro-technology or macrotechnology or steam technology or aeronautical technology is safe.

"The question is at the end of the day is it something we can benefit from, and can we look after ourselves in terms of risk?"

"I think (Nowack's) article is in some ways quite positive. The message is that this potentially toxic silver particle seems to be treated into something that's less harmful."

But Faunce says Nowack's review is a clear wake-up call.

"I think our regulators have to look at the question of nanosilver as a priority pollutant and actually control the consumer implications of it", he says.

"We really don't want nano-silver to be lining our socks and our underpants and all sorts of other places where bacteria gather, simply because it's convenient.

"There are untold consequences in terms of bacterial resistance, in terms of damaging the food chain and our sewerage works if we continue letting nanosilver interfere with bacteria, many of which are valuable to us."

"I don't think we should just cross our fingers and hope that everything's all right. There's too much at stake."