Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Barely any nanosilver from consumer products in the water

18.04.2013
Environmental toxicology

Nanosilver in wastewater can cause severe environmental damage if it occurs as a metal. A study conducted within the scope of the National Research Programme "Opportunities and Risks of Nanomaterials" (NRP 64) now shows that nanosilver is quickly transformed into less problematic substances on its way to the wastewater treatment plant. In addition, it is efficiently retained in the sewage sludge so that only a small portion of it reaches the water systems.

Nanosilver is the show horse in the nanotechnology stable – not only does it hold great promise for the future, it is already contained in hundreds of consumer products today. Cosmetics, food packaging, disinfectants and cleaning agents are but some examples. Nanosilver is also commonly used in antibacterial socks and functional clothing. An estimated 300 tonnes or more of nanosilver are used each year the world over – and a substantial part of it enters the water cycle via wastewater. Within the scope of the National Research Programme "Opportunities and Risks of Nanomaterials" (NRP 64), a team led by Ralf Kägi from Eawag in Dübendorf has for the first time examined more closely (*) just what happens to nanosilver on its journey from the drainpipe to the wastewater treatment plant, and in what form it is eventually released into the environment.

Wastewater samples and laboratory experiments
The researchers took samples from the Swiss wastewater system in order to study how nanosilver is transported. In addition, they established through laboratory experiments what happens to nanosilver in wastewater or in the wastewater treatment plant. They discovered that nanosilver does not remain in its metallic form for very long: it is efficiently transformed into a silver sulfide salt. "We presume that sulfidation already largely takes place in the sewer channel," Kägi says. That's good news, because "these salt crystals cause much fewer problems, the silver is much less soluble in this form". Dissolved ions are the main reason why silver can be harmful to the environment and can stop bacteria from getting to work in the sewage sludge.

The Eawag researchers have for the first time clearly shown that nanosilver, too, is quickly transformed into silver sulfide – regardless of how the particles are coated. Until now this effect was only known from wastewater produced by the photo industry. Whether as metallic nanoparticles, as dissolved silver ions or as an insoluble silver saline deposit, the original form of the silver apparently does not play a crucial role in sulfidation. However, the salination speed depends heavily on the size of the particles: small nanosilver (10 nanometres) is very rapidly transformed, while larger particles may never fully sulfidise and may continue to release silver ions into the environment.

Efficiently removing silver from wastewater
The researchers were also able to show that approximately 95% of the nanoparticles are bound in the sewage sludge. Only 5% of the silver remains in the treated water. This percentage could be further reduced by using better particle filters. Venturing into the nano dimension would not be necessary, though: the sulfidised nanosilver aggregates almost entirely on large particles in the wastewater. With a reasonable effort, they could be removed more efficiently from the wastewater than is presently the case.

The study did not examine what happens to nanosilver in the sewage sludge thereafter. In Switzerland, it is not permissible to use sewage sludge on farmland, and most of the sludge is therefore burned. The heavy metals separated in this process should not be released into the environment in large quantities.

(*) Kägi Ralf, Voegelin Andreas, Ort Christoph, Sinnet Brian, Thalmann Basilius, Krismer Jasmin, Hagendorfer Harald, Elumelu Maline and Mueller Elisabeth. Fate and transformation of silver nanoparticles in urban wastewater systems (2013). Water Research: doi 10.1016/j.watres.2012.11.060
(available as a PDF from the SNSF; e-mail: com@snf.ch)

About NRP 64
The aim of the National Research Programme "Opportunities and Risks of Nanomaterials" (NRP 64) is to close research gaps so that the opportunities and risks of using nanomaterials can be more accurately assessed. The results of the 23 research projects will serve as a basis for the preparation of guidelines for the production, use and disposal of nanomaterials. This will support the development and application of safe technologies, optimise the benefits of using nanomaterials and minimise risk for humans and the environment. NRP 64 has a budget of CHF 12 million and will run until October 2016.


Contact
Dr. Ralf Kägi
Eawag
Überlandstrasse 133
Postfach 611
8600 Dübendorf
Switzerland
Tel.: +41 58 765 52 73
E-mail: ralf.kaegi@eawag.ch

Communication division | idw
Further information:
http://www.nfp64.ch
http://www.snsf.ch

More articles from Life Sciences:

nachricht Cells communicate in a dynamic code
19.02.2018 | California Institute of Technology

nachricht Studying mitosis' structure to understand the inside of cancer cells
19.02.2018 | Biophysical Society

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

Im Focus: Hybrid optics bring color imaging using ultrathin metalenses into focus

For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.

But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...

Im Focus: Stem cell divisions in the adult brain seen for the first time

Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.

The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...

Im Focus: Interference as a new method for cooling quantum devices

Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters

Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Contacting the molecular world through graphene nanoribbons

19.02.2018 | Materials Sciences

When Proteins Shake Hands

19.02.2018 | Materials Sciences

Cells communicate in a dynamic code

19.02.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>