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Conditions Affect Release of Nanosilver from Treated Products

(Beyond Pesticides, October 14, 2009) New research by scientists at the Swiss Federal Laboratories for Materials Testing and Research provides a first look at the behavior of nanosilver textiles under real-world washing conditions. This work builds on earlier studies conducted in water which show that nanosilver leaches from fabrics and textiles during washing to enter the environment.

The study, “The Behavior of Silver Nanotextiles during Washing” published in Environmental Science and Technology, found that the total amount and form of silver (dissolved or particulate) that leaches during washing varies significantly depending on the product and the conditions. The goal was to determine the amount and the form of silver released during washing from nine fabrics with different ways of silver incorporation into or onto the fibers. The effect of pH, surfactants, and oxidizing agents was also evaluated. In the washing machine the majority of the nanosilver (at least 50% but mostly >75%) was released in the size fraction more than 450 nm, indicating the dominant role of mechanical stress. The researchers found that under typical washing conditions (pH 10–11, with high levels of surfactants), dissolved concentrations of silver were 10 times lower than at pH 7. However, when bleaching agents such as hydrogen peroxide or peracetic acid (a mixture of acetic acid and hydrogen peroxide) were added, the dissolution of nanosilver particles was greatly accelerated.

The results do not contradict the previous Arizona State study, which found that socks impregnated with nanosilver release these particles when washed. This new study goes one step further to show that washing conditions matter in the leaching of silver nanomaterials from fabric. The study “gives us a much better idea of how silver might be released into the environment from the new wave of silver-nanoparticle-containing fabrics,” says Andrew D. Maynard, chief science adviser at the nonprofit Project on Emerging Nanotechnologies.

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. Nanosilver that leaches out of fabrics is released into wastewater treatment systems and into nearby aquatic environments. The environmental risks are not clear however. Many particles may aggregate or associate with other ions or materials in the environment and deposit into sediments and soils. Some however, can remain in surface waters, where they can be absorbed and/or ingested by aquatic organisms. Microbial populations especially those in wastewater treatment plants (WWTPs) are vulnerable to silver nanoparticles contamination.

Many consider silver to be more toxic than other metals when in nanoscale form and that these particles have a different toxicity mechanism compared to dissolved silver. Scientists have concluded that nanoparticles can pass easily into cells and affect cellular function, depending on their shape and size. Preliminary research with laboratory rats has found that silver nanoparticles can traverse into the brain, and can induce neuronal degeneration and necrosis (death of cells or tissue) by accumulating in the brain over a long period of time.

For more information on nanosilver, visit the Nanosilver section at our Antibacterial Program Page.

Source: Chemical & Engineering News


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