Treated fabrics exposed to faux sweat release silver nanoparticles.
Kulthong, K, S Srisung, K Boonpavanitchakul, W Kangwansupamonkon and R Maniratanachote. 2010. Determination of silver nanoparticle release from antibacterial fabrics into artificial sweat. Particle Fibre Toxicology 7(1):8.
Researchers find that fabrics laced with silver nanoparticles designed to limit bacterial growth release those particles when the fabric is exposed to artificial human sweat. The findings raise questions about human exposure to the small particles through skin absorption.
Nanotechnology has opened the door for development of various new materials and instruments that are used in a wide range of industrial and consumer applications. As a result, more products incorporate the tiny manufactured materials, and consumers are increasingly exposed to them with largely unknown health effects.
Generally, nanomaterials are very small, measuring from 1 to 100 nanometers, as defined by the U.S. Environmental Protection Agency. To give perspective, a human hair is about 80,000 nanometers wide.
Their size gives them unique properties not found in their larger-scaled versions. These properties help boost product performance in applications as diverse as electronics, medicine, personal care products and textiles. Many products from stain resistant clothing to drugs to ultrasensitive chemical detectors contain nanomaterials.
The potential health effects of exposure continues to be investigated, and for many newer materials, remains largely uncharacterized. A major concern – when compared to their larger counterparts – is an increased ability to be absorbed into and distributed throughout the bodies of people and wildlife. For example, graphite pencils and chemical sensing nanotubes are both made of carbon. After an equal amount of exposure, much more of the nano-sized particles would be absorbed than the larger particles from the pencil. Studies show that some nanoparticles can cross protective barriers and cell membranes in the nose, lungs and nervous system that larger particles would not be able to enter (Folkmann et al. 2008; Wang et al. 2008).
Although a primary focus of nanomaterial development is carbon nanotube technology, other materials such as silica, plastics and various metals – including silver – are also used.
Silver is an antiseptic, long-used to reduce bacterial growth on skin. Lacing fabrics and bandages with silver compounds is not new. But now, silver nanoparticles do the job in both medical and consumer applications, such as socks and shirts.
Exposure to silver at levels higher than is needed to kill microbes can lead to poisoning (argyria), an irreversible skin discoloring (argyrosis) and extremely large exposures can lead to neurological damage. Silver's absorption, distribution, and toxicity may be altered at the nano-scale level.
The researchers tested and compared five fabrics treated in the laboratory with a silver nanoparticle solution and six commercially-made shirts sold as containing nanosilver to determine how much of the silver nanoparticles the fabrics would release when exposed to artificial human sweat.
Silver is added to clothes to reduce bacterial growth and odor. Laboratory-prepared fabrics were treated with either 0, 0.5, 1, 5 and 10 grams per liter of the silver solution, which is made from nanoparticles of silver chloride and titanium dioxide. The four formulations of artificial sweat contained the same components as human sweat (i.e. lactic acid, salt compounds, water) and varied in acidity.
Fabric samples were incubated in the different artificial sweat formulations for 24 hours, at which point the fabric was removed and the artificial sweat was analyzed for silver nanoparticles.
Investigators determined which fabrics effectively reduced bacterial growth for two common species, Staphylococcus aureus (responsible for staph infections) and E. coli (an intenstitinal bacteria). They incubated the bacteria with fabric samples and counted the resulting colony formations.
The silver content in the laboratory-prepared fabrics ranged from 36 to 425 milligrams of silver per kilogram (mg/kg). The laboratory-prepared fabrics treated with silver nanoparticles released up to 322 mg/kg of fabric weight. The silver particles ranged in size from approximately 200 - 500 nm. Nanometers are one billionth of a meter.
The consumer fabrics contained far less silver to begin with – between 1 and 15 mg/kg – and therefore released much less silver into the artificial sweat than the laboratory-prepared fabrics. As well, half of the store-bought shirts labeled as “nanosilver” did not contain any silver or have any antibacterial properties.
Generally, the laboratory-prepared fabrics released more silver nanoparticles into the artificial sweat and had a greater capacity for reducing bacterial growth. However, one consumer fabric that released far less silver nanoparticles into artificial sweat solutions (0.5 mg/kg) demonstrated excellent bacterial growth reduction at levels similar to laboratory prepared fabric.
Laboratory-prepared and commercial fabrics treated with silver nanoparticles release the tiny metal materials into artificial human sweat. The amount of silver released depended on the type of fabric, the initial amount of silver and the type of artificial sweat.
This is the first study to use faux sweat to mimic conditions of human skin; it determined that silver nanoparticles can migrate out of fabric after exposure to the simulated perspiration. It is not known if the silver materials in sweat would be absorbed through human skin.
Other studies have reported that silver can migrate from treated fabrics during washing in a washing machine (Geranio et al. 2009). The silver from these particles is presumed to be carried into the environment by wastewater.
As nanotechnology becomes increasingly prevalent in consumer products, the potential for exposure to nanoparticles increases. Yet, little is known about how these silver materials may interact with people's bodies. There is concern that the tiny particles may be more toxic than other, larger-sized and more traditional types of silver compounds, as the smaller particles could be more easily absorbed and distributed throughout the body.
The silver nanoparticles described here are larger than the ultrafine carbon nanoparticles, generally 1 – 10 nm in diameter. The ultrafine carbon materials have garnered more research attention in terms of potential health effects because of their extremely small size.
This research provides a poignant example of the expanding use of nanotechnology and nanomaterials in an increasing number of consumer products. The extremely small size of these particles may alter their toxicological properties, creating new challenges for health science researchers and regulatory agencies in ensuring this new technology develops safely for consumers and the environment.
While this study does not provide direct evidence of toxicity, it describes a novel exposure source of nanoparticles that we know very little about in terms of the potential health effects. The authors suggest more research is needed to better understand the risks associated with nanotechnologies as more consumer products, such as socks and other clothing fabrics, incorporate silver nanoparticles in an attempt to reduce bacterial growth and the odors associated with it.
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Geranio, L, M Heuberger, and B Nowack. 2009. The behavior of silver nanotextiles during washing. Environmental Science and Technology 43(21):8113–8118.
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