14 June 2010, by Sara Coelho
Scientists have found that tiny silver nanoparticles floating in rivers may not be as damaging to fish as previously thought.
After deodorants and washing machines, tiny silver nanoparticles are the new secret weapon against unwanted bodily odours.
Nanosilver kills the microbes that produce nasty smells and it is now widely used in t-shirts, socks and many types of sports clothes. But when these high-tech outfits go in the washing machine, the nanosilver is washed out and ends up in our rivers.
'Although silver can cause harmful effects at high exposure levels, it is not especially toxic to humans or other mammals,' says Professor Charles Tyler, from the University of Exeter. But for fish, it's a different story. Silver has a strong toxic effect on fish – it interferes with the way fish regulate the balance of ions in their cells.
Tyler and colleagues wanted to find out if tiny silver nanoparticles are more toxic to fish than regular silver: does the small size confer an extra toxicity to metals?
There have also been reports that, when tested on laboratory mammals, silver nanoparticles can cause damage to cells which is not seen for regular-sized particles. 'This is a pretty important thing to nail down,' he says, given the increasing importance of nanoparticles in modern technology.
'Despite much recent concern around nanoparticle pollution, we found that the fish took up nanosilver in only very small amounts' Professor Charles Tyler, University of Exeter
Working with rainbow trout, the team exposed the fish to water enriched with different sizes of nanosilver. The idea was to see if the silver would find its way into the trout and where the tiny particles were more likely to accumulate.
After ten days of exposure Tyler and the team analysed the fish, looking for damage to the cells or to the genes that control essential cell processes.
What they discovered is good news: 'Despite much recent concern around nanoparticle pollution, we found that the fish took up nanosilver in only very small amounts,' says Tyler.
The team identified nanosilver in the trout's gills, the first point of entry into the body, and in the liver, the organ that handles toxic compounds. 'But no significant uptake was seen in other body tissues, and nothing in the brain,' Tyler adds.
'The smallest nanosilver particles induced a bit of stress in the gills, although nothing massive,' he says.
But before we assume that silver nanoparticles are completely safe, Tyler warns that there is more to nanosilver than meets the eye. Commercial nanosilver, like many other nanoparticles, comes in all shapes and sizes and with all sorts of coatings to enable it to perform a specific task. The different types may have very different effects in our bodies. Manufacturers rarely provide the detailed information that is essential to help unravel which nanoparticle properties might adversely affect health.
Tyler and his team had the particles they used carefully characterised: 'we knew exactly what we were exposing our fish to,' he says. Other studies exposing fish to slightly different nanosilver particles might yield different results.
'There is still a lot to be done to characterise nanoparticles and to come up with standardised tests to assess their toxic effects,' says Tyler.