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Illumination magazine.
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Aeration in action at the Regional Wastewater Treatment Plant in Columbia. Aeration basins add air to a mixture of wastewater, sludge and bacteria, a process that enhances the ability of helpful microorganisms to consume harmful organic matter.

Other nanoscale materials differ from their bulk counterparts in how they conduct electricity, in their strength, in their magnetic properties and in their color. Nanoscale materials also have far more surface area than do bulk species. Depending on the nanoparticle size, one ounce of a nanomaterial could have the same surface area as one ton of the bulk material. This is an important distinction. Because interactions between materials take place at the surface, a larger surface area will create a greater opportunity for reactions.

Potential applications for nanomaterials stretch the imagination, ranging from stronger, lighter metals to revolutionary drug delivery systems. The Project on Emerging Nanotechnologies, established in April 2005 as a partnership between the Woodrow Wilson International Center for Scholars and the Pew Charitable Trusts, reports an estimated global research and development investment of nearly $9 billion per year in nanotechnology. The organization reports that between March 2006 and February 2008, the number of nanomaterial products on the market nearly tripled, from 212 to more than 600. These products are produced by some 300 companies located in 20 countries.

Nanosilver is by far the most commonly used nanomaterial. One estimate, published recently by the emerging nanotechnologies project, reports that nanosilvers can be found in about half of today's nanotech products. A sampling of these nanosilver goods would include household appliances, cleaners, bedding, clothing, food storage containers, soap, toothpaste, cosmetics, personal care products, drink supplements, pacifiers, stuffed animals and coated electronics.

For Hu, with his focus on wastewater, one of the most worrisome products are so-called "silver care" washing machines that produce either silver ions or nanosilver during each wash cycle. The idea is to use silver's antimicrobial power to disinfect clothes, thereby reducing the need for hot water and detergent -- perhaps even allowing the garments to be worn multiple times between washings.

These are all eco-friendly goals. But Hu points out that the nanosilver wash water might not be so eco-friendly when it goes down the drain.

Whether this is the case depends on a lot of factors, from the concentration of nanosilver in the water to how nanosilver, a highly reactive material, changes once it hits sewage, detergents and other materials. Another question is more basic: whether nanosilver, in fact, actually has the antibacterial property manufacturers claim. And if it does, which bacteria are most likely to be affected?

To address these questions, Hu and his graduate student, Okkyoung Choi, exposed various kinds of bacteria to nanosilver they synthesized. This is a necessary step because commercial nanosilver tends to aggregate in water until the particles are no longer even on the nanoscale. Hu and Choi then monitored the respiration rates of the bacteria exposed to the nanosilver and compared them to those of control bacteria. Bacteria exposed to nanosilvers showed a lower respiration rate, indicating a toxic effect. They then did the same test using silver ions and silver chloride colloids, two forms of bulk silver, in place of the nanosilver.

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