By Editor
Humans have known since ancient times that silver kills or stops the growth of many microorganisms. Hippocrates, the father of medicine, is said to have used silver preparations for treating ulcers and healing wounds. Until the introduction of antibiotics in the 1940s, colloidal silver (tiny particles suspended in a liquid) was a mainstay for treating burns, infected wounds and ulcers. Silver is still used today in wound dressings, in creams and as a coating on medical devices.
Since the 1990s, manufacturers have added silver nanoparticles to numerous consumer products to enhance their antibacterial and anti-odor properties. Examples include clothes, towels, undergarments, socks, toothpaste and soft toys. Nanoparticles are ultra-small particles, ranging from 1 to 100 nanometers in diameter – too small to see even with a microscope. According to a widely cited database, about one-fourth of nanomaterial-based consumer products currently marketed in the United States contain nanosilver.
Multiple studies have reported that nanosilver leaches out of textiles when they are laundered. Research also reveals that nanosilver may be toxic to humansand aquatic and marine organisms. Although it is widely used, little is understood about its fate or long-term toxic effects in the environment.
We are developing ways to convert this potential ecological crisis into an opportunity by recovering pure silver nanoparticles, which have many industrial applications, from laundry wastewater. In a recently published study, we describe a technique for silver recovery and discuss the key technical challenges. Our approach tackles this problem at the source – in this case, individual washing machines. We believe that this strategy has great promise for getting newly identified contaminants out of wastewater.
A textile silver lode
Use of nanosilver in consumer products has steadily risen in the past decade. The market share of silver-based textiles rose from 9 percent in 2004 to 25 percent in 2011.
Several investigators have measured the silver content of textiles and found values ranging from 0.009 to 21,600 milligrams of silver per kilogram of textile. Studies show that the amount of silver leached in the wash solution depends on many factors, including interactions between detergent and other chemicals and how silver is attached to the textiles.
In humans, exposure to silver can harm liver cells, skin and lungs. Prolonged exposure or exposure to a large dose can cause a condition called Argyria, in which the victim’s skin turns permanently bluish-gray.
Silver is toxic to many microbes and aquatic organisms, including zebra fish, rainbow trout and zooplankton.
Once silver goes down the drain and ends up at wastewater treatment plants, it can potentially harm bacterial treatment processes, making them less efficient, and foul treatment equipment. More than 90 percent of silver nanoparticles released in wastewater end up in nutrient-rich biosolids left over at the end of sewage treatment, which often are used on land as agricultural fertilizers.
This poses multiple risks. If plants take up silver from soil, they could concentrate it and introduce it into the food chain. It also can leach into groundwater or wash into rivers via rainstorms or erosion.
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