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For some lines of clothing, nanoparticles are the new fashion accessory. Manufacturers add the materials to clothing to prevent stinky molds from growing on sweaty socks or to protect people from the sun’s ultraviolet light. However, some toxicologists worry that the intimate contact between the clothing and skin may expose people to nanoparticles. In a new study, researchers measured how much of the materials leach off clothing into simulated sweat. (Environ. Sci. Tech. 2013, DOI: 10.1021/es304329w). They found that some pieces of clothing released significant levels of silver nanoparticles.

Two common types of nanoparticles found in clothing are titanium dioxide and silver: They’re used to make UV-resistant and antimicrobial apparel, respectively. Little is known about what effects these materials have on human health. In fact, researchers in Germany are currently conducting a large toxicological study on these particles and other nanomaterials, says Natalie von Götz of the Swiss Federal Institute of Technology (ETH), Zurich.

Besides learning about the materials’ toxicology, researchers also need to determine exposure levels under real-world conditions, von Götz says. She and her colleagues noted that people often wear nanoparticle-treated clothing during sporting or outdoor activities. So to estimate exposure levels, the team simulated the wear-and-tear a piece of clothing would undergo if worn by an active person and measured how many nanoparticles sloughed off.

The researchers studied fabric samples from garments they determined had titanium dioxide nanoparticles, silver nanoparticles, or both. This apparel included socks, shirts, and trousers. They put the samples into plastic bottles containing acrylic balls and up to 180 mL of artificial sweat, a water solution containing salts and organic molecules similar to that of human perspiration. Then, they placed the bottles into a washing machine and allowed the bottle to bounce around for at least 30 minutes. After agitating the samples, the researchers measured the concentration of nanoparticles in the artificial sweat with inductively coupled plasma optical emission spectroscopy. They also measured the sizes of the particles using scanning transmission electron microscopy.

Using that data, the team next estimated how much of the particles would end up on a person’s skin after strenuous exercise, such as playing tennis. They considered only levels of titanium dioxide and silver particles smaller than 450 nm, because larger particles are less likely to be absorbed through the skin, von Götz says. In making their exposure estimates, the reseachers also took into account a person’s gender and body weight, along with the size of the garment.

Based on these estimates and comparisons to other exposure sources of the metals, the team concluded that exposure levels for silver nanoparticles could be significant. For example, a 77-kg man wearing trousers and a T-shirt containing silver nanoparticles would receive about 1.3 mg of silver per day. Meanwhile, the exposure level from dietary supplements that contain silver is at most 0.5 mg per day. The scientists also concluded that exposure levels for titanium dioxide nanoparticles weren’t a great concern. The calculated maximum exposure level was significantly less than that of a single application of sunscreen.