Anti-microbial silver nanoparticles labelled 'pesticides'

Wrangles over a washing machine have pressured the US’ Environmental Protection Agency to regulate commercial products containing silver nanoparticles. But it is not yet clear how the surprising policy, which has been called a ’kneejerk reaction’, will be enforced. 

Under the EPA’s regulation, any company marketing a product as using silver nanoparticles to kill bacteria must provide scientific evidence that the particles don’t pose an environmental health risk. 

As nanotoxicology studies are in their infancy, it is unclear how manufacturers are to make their case. ’We don’t really have the science to prove anything one way or the other,’ pointed out Tim Harper, CEO of nanotechnology consultants Cientifica. ’It seems a kneejerk reaction in response to a few scare stories,’ he said. 

The decision follows complicated wrangles over Samsung’s ’Silver Wash’ washing machine, marketed as containing silver nanoparticles which kill bacteria in clothes. Some US water authorities worried that discharged nanosilver might concentrate in wastewater treatment plants, killing bacteria which were meant to detoxify the wastewater. 

In this sense, the nanosilver could be considered an environmental pesticide, which would have to be registered and tested under the Federal insecticide, fungicide and rodenticide act (Fifra). 

Last year EPA officials classified the washing machine as a ’device’ which killed the bacteria dumped into it. That classification exempted it from Fifra. The EPA have now reconsidered their decision. ’The release of silver ions in the washing machines is a pesticide, because it is a substance released into the laundry for the purpose of killing pests,’ said EPA spokesperson Jennifer Wood. 

Although this particular washing machine uses silver ions, which may not constitute nanoparticles, silver nanoparticles are used to kill germs in such products as air-fresheners, shoe liners, socks and food-storage containers. These products would likely all have to be tested under the regulations. Silver nanoparticles are also added to bandages to speed healing; but these and other medical applications are regulated by the US’ Food and Drug Administration, not the EPA. 

’Regulating nanosilver as a pesticide seems a bit of a stretch of the imagination,’ said Harper. But David Berube, communications director of the International Council on Nanotechnology, told Chemistry World: ’Reclassification as a pesticide will require registration which will provide new information for the consumer - and that is always desirable.’ Berube considered it a ’landmark decision’, though he was surprised at the EPA’s precautionary attitude. ’They normally wait for some mild disaster and then respond to it,’ he said. 

Only products marketed as anti-microbial will have to be regulated, providing a legal loophole for companies who drop anti-microbial claims from their nanosilver products. 

Kneejerk responses and uncertain practicalities aside, the regulation should trigger more research into the toxic effects of nanoparticles, Mark Morrison, scientific manager of the UK’s Institute of Nanotechnology, told Chemistry World. ’But will it be government-funded research, or will the government put the onus on manufacturers?’ he wondered.