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UH: Is nanosilver toxic?

Author: minna.merilainen 28.02.2013 13:10


University of Helsinki
Communications / Kumpula Science Campus
28 February 2013

Is nanosilver toxic?

According to Finnish-Estonian joint research with data obtained on two
crustacean species, there is apparently no reason to consider silver
nanoparticles more dangerous for aquatic ecosystems than silver ions. The
results were reported in the journal "Environmental Science and Pollution
Research" late last year. Jukka Niskanen has utilised the same
polymerisation and coupling reactions in his doctoral dissertation studying
several hybrid nanomaterials, i.e. combinations of synthetic polymers and
inorganic (gold, silver and montmorillonite) nanoparticles. Niskanen will
defend his doctoral thesis at the University of Helsinki in April.


Part of the magic of nano-science is that on the scale of a billionth of a
metre, matter and materials behave in ways that are not yet known. Neither
is it always known what types of effects the nano version of the parent
matter will have on its environment.

- Due to the fact that silver in nanoparticle form is bactericidal and also
fungicidal and also prevents the reproduction of those organisms, it is now
used in various consumer goods ranging from wound dressing products to
sportswear, says Jukka Niskanen from the Laboratory of Polymer Chemistry at
the University of Helsinki, Finland.

While the usefulness of silver has been established, the debate over the
toxicity mechanisms of its various forms to microorganisms but also to
non-target species continues. Anne Kahru, Head of the Laboratory of
Environmental Toxicology at the National Institute of Chemical Physics and
Biophysics, Estonia, talks about a whole new field of ecotoxicology:
nanoecotoxicology.

So far, little is known about the environmental effects of silver
nanoparticles and their toxicity to aquatic organisms. A joint study from
the University of Helsinki and the National Institute of Chemical Physics
and Biophysics (Tallinn, Estonia),  Toxicity of two types of silver
nanoparticles to aquatic crustaceans Daphnia magna and Thamnocephalus
platyurus, shows that silver nanoparticles are apparently no more hazardous
to aquatic ecosystems than a water-soluble silver salt. The study compared
the ecotoxicity of silver nanoparticles and a water-soluble silver salt.

- Our conclusion was that the environmental risks caused by silver
nanoparticles are seemingly not higher than those caused by a silver salt.
However, more research is required to reach a clear understanding of the
safety of silver-containing particles, Niskanen says.

Indeed, silver nanoparticles were found to be ten times less toxic than the
soluble silver nitrate - a soluble silver salt used for the comparison.


The bioavailability of silver varies in different test media

To explain this phenomenon, the researchers refer to the variance in the
bioavailability of silver to crustaceans in different tested media.

University lecturer Olli-Pekka Penttinen from the Department of
Environmental Sciences of the University of Helsinki goes on to note that
the inorganic and organic compounds dissolved in natural waters (such as
humus), water hardness and sulfides have a definite impact on the
bioavailability of silver. Due to this, the toxicity of both types of
tested nanoparticles and the silver nitrate measured in the course of the
study was lower in natural water than in artificial fresh water.

The toxicity of silver nanoparticles and silver ions was studied using two
aquatic crustaceans, a water flea (Daphnia magna) and a fairy shrimp (
Thamnocephalus platyurus). Commercially available protein-stabilised
particles and particles coated with a water-soluble, non-toxic polymer,
specifically synthesised for the purpose, were used in the study. First,
the polymers were produced utilising a controlled radical polymerisation
method. Synthetic polymer-grafted silver particles were then produced by
attaching the water-soluble polymer to the surface of the silver with a
sulfur bond.

Jukka Niskanen has utilised such polymerisation and coupling reactions in
his doctoral dissertation,  Polymeric and hybrid materials: polymers on
particle surfaces and air-water interfaces, studying several hybrid
nanomaterials , i.e., combinations of synthetic polymers and inorganic
(gold, silver and montmorillonite) nanoparticles. Niskanen will defend his
doctoral thesis in the field of polymer chemistry at the University of
Helsinki in April 2013.

It was previously known from other studies and research results that silver
changes the functioning of proteins and enzymes. It has also been shown
that silver ions can prevent the replication of DNA. Concerning silver
nanoparticles, tests conducted on various species of bacteria and fungi
have indicated that their toxicity varies. For example, gram-negative
bacteria such as Escherichia coli are more sensitive to silver
nanoparticles than gram-positive ones (such as Staphylococcus aureus). The
difference in sensitivity is caused by the structural differences of the
cell membranes of the bacteria. The cellular toxicity of silver
nanoparticles in mammals has been studied as well. It has been suggested
that silver nanoparticles enter cells via endocytosis and then function in
the same manner as in bacterial cells, damaging DNA and hindering cell
respiration. Electron microscope studies have shown that human skin is
permeable to silver nanoparticles and that the permeability of damaged skin
is up to four times higher than that of healthy skin.



Read more: Environmental Science and Pollution Research,
http://link.springer.com/article/10.1007/s11356-012-1290-5

Additional information:

Doctoral student Jukka Niskanen, Laboratory of Polymer Chemistry at the
University of Helsinki, jukka.niskanen@helsinki.fi, +358 9 191 50329

University lecturer Olli-Pekka Penttinen, environmental ecology, Department
of Environmental Sciences, University of Helsinki,
olli-pekka.penttinen@helsinki.fi, +358 50 316 0559

Anne Kahru, Head of the Laboratory of Environmental Toxicology at the
Estonian National Institute of Chemical Physics and Biophysics,
anne.kahru@kbfi.ee, +372 6 398 373


Best regards,
Minna Merilšinen-Tenhu, Press Officer, +358 9 191 51042





Minna Merilšinen-Tenhu
Science, media & society
(09) 191 51042, +358 50 415 0316

Member of the Finnish  Association of Science Editors and Journalists
8th World Conference of Science Journalists, Helsinki, June 24-28, 2013,
http://wcsj2013.org/

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