Valued for it's antibacterial and odor-fighting properties,
nanoparticle silver is becoming the star attraction in a range of
products from socks to bandages to washing machines. But as silver's
benefits propel it to the forefront of consumer nanomaterials,
scientists are recommending a closer examination of the unforeseen
environmental and health consequences of nanosilver.
 | | A biosensor made from an array of silver nanoparticles deposited on glass |
“The general public needs to be aware that there are
unknown risks associated with the products they buy containing
nanomaterials,” researchers Paul Westerhoff and Troy M. Benn
said in a report scheduled for the 235th national meeting of the American
Chemical Society (ACS).
Westerhoff and Benn report that ordinary laundering can wash
off substantial amounts of the nanosilver particles from socks
impregnated with the material. The Arizona State researchers suggest
that the particles, intended to prevent foot odor, could travel through
a wastewater treatment system and enter natural waterways where they
might have unwanted effects on aquatic organisms living in the water
and possibly humans, too.
“This is the first report of anyone looking at the
release of silver from this type of manufactured clothing
product,” said the authors.
Behind those concerns lies a very simple experiment. Benn and
Westerhoff bought six pairs of name brand anti-odor socks impregnated
with nanosilver. They soaked them in a jar of room temperature
distilled water, shook the contents for an hour and tested the water
for two types of silver — the harmful
“ionic” form and the less-studied nanoparticle
variety.
“From what we saw, different socks released silver
at different rates, suggesting that there may be a manufacturing
process that will keep the silver in the socks better,” said
Benn. “Some of the sock materials released all of the silver
in the first few washings, others gradually released it. Some didn't
release any silver.” The researchers will present the
specific brands they studied at their ACS presentation.
If sufficient nanosilver leeches out of these socks and
escapes waste water treatment systems into nearby lakes, rivers and
streams, it could damage aquatic ecosystems, said Benn. Ionic silver,
the dissolved form of the element, does not just attack odor-causing
bacteria. It can also hijack chemical processes essential for life in
other microbes and aquatic animals.
“If you start releasing ionic silver, it is
detrimental to all aquatic biota. Once the silver ions get into the
gills of fish, it's a pretty efficient killer,” said Benn.
Ionic silver is only toxic to humans at very high levels. The toxicity
of nanoparticle silver, said Westerhoff, has yet to be determined.
Westerhoff and Benn did not intend to establish the toxicity
of silver. “The history of silver and silver regulation has
been set for decades by the U. S. Environmental Protection Agency
— we're not trying to reexamine or reinvent that,”
said Westerhoff.
They do hope to spark a broader examination of the
environmental and health consequences of nanomaterials, as well as
increasing awareness of nanotechnology's role in everyday consumer
goods.
Silver has been used historically since ancient roman times,
though its nanoparticle form has only recently appeared in consumer
products. Beyond socks, nanosilver appears in certain bandages,
athletic wear and cleaning products. Benn suggested that most consumers
are unaware of these nano-additions.
“I've spoken with a lot of people who don't
necessarily know what nanotechnology is but they are out there buying
products with nanoparticles in them. If the public doesn't know the
possible environmental disadvantages of using these nanomaterials, they
cannot make an informed decision on why or why not to buy a product
containing nanomaterials,” said Benn.
To that end, the researchers suggest that improved product
labeling could help. Westerhoff proposes that clothing labels could
become like the back of a food packaging, complete with a list of
“ingredients” like nanosilver.
Westerhoff and Benn expect to expand their leeching
experiments to other consumer products imbued with nanomaterials. They
hope to find the moment in each product's lifecycle when nanomaterials
could be released into the environment, as well as developing better
detection methods to characterize nanoparticles in water and air
samples.
“Our work suggests that consumer groups need to
start thinking about these things,” said Benn.
“Should there be other standards for these
products"”
Posted 7th April 2008
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