Nanomaterials in the Aquatic Environment

By Bill Clayton

The potential for a massive emission of carbon nanotubes (above) and other designer nanomaterials is significant, given the breadth of their potential applications.

Substances with dimensions less than 100 nm often act surprisingly different from larger materials with the same elemental composition. (A nanometer is a billionth of a meter. A human hair is about 80,000 nanometers wide.) Furthermore, the very properties of nanostructured materials that make them so attractive could potentially lead to unforeseen health or environmental hazards - for example, silver, gold and other metals that kill bacteria and odor-causing microbes are finding their way as nanomaterials into shoes, athletic equipment and other plastic or nylon products. And from those products, nanomaterials are bleeding into the environment. Most of them will quickly disappear or simply add a small fraction to existing natural nanocolloids. But some may persist. More knowledge about such nanomaterials is necessary. (Nanocolloids are finely divided nano-scale particles that are dispersed within a continuous medium in a manner that prevents them from being filtered easily or settled rapidly.)

To date, manufacturers have used nanoparticles in underwear, shirts, paint, deodorant, mineral supplements, toothpaste, refrigerators, vacuum cleaners, ink, makeup, soap, rubber gloves, dishwashing liquid, baby milk bottles - the list goes on. More than 350 nanoproducts are already on the market, and conservative estimates say that the market value for nanotechnology-related products in the world economy will exceed one trillion dollars by the year 2010.

With this proliferation of nanomaterials, it's inevitable that they'll get into the air we breathe, the food we eat and one of our most precious resources: water.

Whereas researchers have conducted extensive studies of airborne nanoparticles - finding that conventional aerosol emission controls can mitigate their effects - investigators know comparatively little about the way nanoparticles behave in the aquatic environment. Nor do they know much about the hazards people face if they eat food, breathe air, touch objects or drink water with nanoparticles.

Walt Weber, Gordon M. Fair and Earnest Boyce Distinguished University Professor of Environmental Science and Engineering in the Department of Chemical Engineering, and a world authority on water science and technology, is leading an interdisciplinary team that will address these and other problems as part of the University of Michigan's Environmental Initiative.

Team member Nick Kotov said that stable nanocolloids or carbon and titanium dioxide "do exist currently in nature, however we don't know what their circulation path is and how it is affected by the influx of new materials. A key question for us is, 'Can they become concentrated in humans or animals?'"

Researchers will add the nanoparticles to soil and sediment samples in which there are aquatic worms (Lumbriculus variegates) and earthworms (Eisenia foetida), organisms strategically critical in the natural food chain. They'll study the absorption and toxic effects, if any, of the nanomaterials, then compare them to the absorption and toxic qualities of macro-scale materials or dissolved salts comprising the same elements.

"The potential for massive emission of carbon nanotubes and other designer nanomaterials is significant, given the breadth of their potential applications," Weber said, "so it's better to be safe than sorry - we need to learn about any potential problems ahead of time. This is an excellent example of cross-university, multidisciplinary work because it's bringing together people at the College of Engineering as well as from the schools of Medicine and Public Health. The results of the study may also be very helpful for the biomedical applications of nanotubes and other nanocolloids," he said.

The information that the U-M team gleans from this work on nanomaterials in the aquatic environment will enrich other programs within the Graham Environmental Sustainability Institute - particu­larly "Freshwater and Marine System Sustainability" and "Human Health and the Linkage to a Changing Environment." The team's work will also help develop a new nanotechnology research focus for the University's Nanoscale Science and Engineering Initiative. There's even a possibility that, by working with other nanotechnology leaders within the University, the interdisciplinary group could function as a nucleus for the formation of a center in environmental nanotechnology. - E