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Silver Nanoparticles Coming Out in Wash

(Beyond Pesticides, April 30, 2008) New research shows that socks impregnated with silver nanoparticles to keep them microbe and odor free, release these particles when washed. Once washed down the drain, the silver particles enter the environment where they may pose numerable unknown adverse effects. Researchers from Arizona State University report their findings in a study entitled; “Fate and transport of ionic and nanoparticle silver released from commercially available socks,” published in Environmental Science and Technology. Six commercial brands of nanosilver-treated socks were tested and their nanosilver content measured before and after wash. The socks were soaked in 1- or 24-hour-long wash cycles in distilled water without detergent to limit variables in the tests. One batch was soaked in tap water to simulate a more realistic washing.Using scanning and transmission electron microscopy, the remaining silver was analysed. Under the microscope, nanoparticles were found clumped together in the fabric, while some socks had tiny corkscrew-shaped nanosilver particles that stuck like burrs to the fabric, clinging more tightly than some simpler nanosilver forms. They found that socks had variable leaching rates, which suggests that the sock manufacturing process and how they are impregnated with silver may influence the release of silver. In spite of how they were attached to the fabric, some socks lost the bulk of their nanosilver after two to four washings.

“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,” says Troy Benn, graduate student and co-author of the study. “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.”

Nanosilver that leashes out of fabrics are released into wastewater treatment systems and into nearby aquatic systems. To determine the fate of these particles, the researchers also tested activated sludge from a local wastewater treatment plant. They found that the sludge did indeed contain nanosilver washed out from the socks. This may pose a concern for agriculture, since sludge is often used as agricultural fertilizer. Contaminated sludge would be unable to sustain the necessary microbes needed for healthy soil and crop cultivation. Silver particles may also leach from sludge into surface runoff, where they may enter rivers and streams.

Another important issue is that most nanosilver becomes ionic silver in water. Ionic silver does not just attack odor-causing bacteria, but can also hijack chemical processes essential for life in other microbes and aquatic animals.

“If you start releasing ionic silver, it is detrimental to a variety of aquatic organisms. Once the silver ions get into the gills of fish, it’s a pretty efficient killer,” said Mr Benn.

Although the exact amount is unknown, they estimate that more than half of the nanoparticles dissolve into ionic silver. Ionic silver could also react with sulfur to eventually form silver sulfides in the environment, which is less toxic than silver alone, but more persistent and may be more biologically available. This report is the first to detail the release of nanosilver from textiles in a domestic setting. The researchers concede that more work needs to be done to examine the environmental and health consequences of nanomaterials, as well as to increase awareness of nanotechnology’s role in everyday consumer goods.

Nanosilver has been touted for its antibacterial properties and is used in many products such as sporting goods, band-aids, clothing, baby and infant products, and food and food packaging. However, very little is known about where these particles end up when such products are put to use. In July 2007, a broad international coalition of 40 consumer, public health, environmental, and labor organizations released Principles for the Oversight of Nanotechnologies and Nanomaterials (see Daily News). This report calls for strong, comprehensive oversight of the new technology and its products, which is built on a precautionary foundation to prevent risks to the public, workers and the environment.

Source: ES&T Science News


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