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Tuesday, September 25, 2007

Quick and dirty advice for keeping nanotech clean

IEEE Spectrum discusses how to keep nanoparticles safe

There is a growing body of evidence that ­nanotechnological chemicals and related substances could pollute the air, soil, and water and damage human health. Preliminary studies from Arizona State University suggest that nanoparticles accumulate in the food chain and could cause problems later on. There is an opportunity to deploy nanoparticles properly.

We need to look at nano­technology broadly, anticipate its adverse effects, and prevent problems. Prudently avoiding a crisis is always better than trying to repair damage later on.


The IEEE Spectrum article is discussing nanotechnology to mean:
When we talk about nanotechnology, we mean that the materials involved exist as microscopic particles with at least one dimension that is between 1 and 100 nanometers. To put this in perspective, consider that the typi­cal nanosize particle of titanium dioxide in sunscreen is 20 nm in diameter. The particle is a clump of about a ­million molecules. A grain of pollen is about 1000 times the size of this titanium dioxide nano­particle; bacterial cells are around 100 times as large, and the width of a human hair is about 4000 times as great.

Nanotechnology refers to manufactured materials in the nanosize range, or to manufactured products containing these materials.


The health risks and concerns of nanoparticles:
In 2003, Chiu-wing Lam of NASA’s Johnson Space Center, in Houston, instilled carbon
nanotubes into the lungs of mice and reported that they triggered granulomas, or areas of ­inflammation. In a similar experiment, David Warheit at Dupont’s Haskell Laboratory for Toxicity and Industrial Medicine, in Newark, Del., found such inflammation in rats’ lungs in the same year. Perhaps most troubling of all, nanoparticles can make their way into the brain by passing from the nose through the blood-brain barrier, a membrane that protects the brain from chemicals in the blood while allowing oxygen, carbon dioxide, sugars, and certain amino acids to pass through unaltered.

In 2004, experiments by Eva Oberdörster, a lecturer in bio­logical sciences at Southern Methodist University, in Dallas, found that the buckyball, a nanostructure made of carbon atoms, can penetrate the brains of bass via the gills. There, the nanoparticles trigger a reaction in brain enzymes called oxidative stress, a change in brain chemistry that indicates harm. Eva Oberdörster (a daughter of Günter) also discovered that buckyballs are toxic to daphnia, tiny freshwater fleas used to test toxicity in aquatic systems [see photo, “Aquatic Mine Canaries”]. The buckyballs did not clump together and sink harmlessly to the bottom of the test sites as researchers had expected.

Researchers are also concerned about persistence. Because of their small size and light weight, nanoparticles can stay aloft in the upper atmosphere much longer than coarse particulate air pollutants, and current filter technologies for controlling particles have holes that are a thousand times too big to trap nanoparticles. Nanoparticles may also bioaccumulate. For example, bacteria can ingest them, so the particles could become part of our food chain. And we know that chemical pollutants, like some pesticides, can also accumulate in the chain. At the moment, though, we don’t know what effect nanomaterials will have on the food supply.


Good things that are happening and green nanotechnology trends to continue:
One bright sign is that industry groups and government agencies are beginning to include concerns about nanotechnology in their long-term research planning. An encouraging new initiative is Green Nanotechnology, pioneered by the EPA and the Woodrow Wilson Inter­national Center for Scholars, in Washington, D.C. The two organizations are developing a framework and recommended practices that would help prevent manufacturers from releasing substances currently recognized as pollutants into the atmosphere, as well as prevent the manufacture of products containing nanomaterials that would knowingly harm the environment. The development of guidelines for Green Nanotechnology would let consumers or governments reward companies that are performing well, on the model of Energy Star, a joint program of the EPA and the Department of Energy. It sets guidelines for energy efficiency of consumer products and allows products that meet those guidelines to display Energy Star labels.

Recently, there was a small but significant victory: manufacturers of gold nanoparticles used for paint and, potentially, environmental cleanup and cancer treatment, developed a manufacturing method that eliminated the use of a toxic organic chemical and replaced it with water, reducing energy use at the same time.

Green Nano also means using nanotechnology itself to clean up production processes. The semiconductor industry can replace dangerous chemicals such as the perfluorooctane sulfonate polymers used in photo resists, antireflective coatings, and reagents with less toxic nano alternatives. Nanomembranes can filter out waste and pollutants in chemical processes. Nano-enabled sensors can improve process control and monitor emissions. Nanoproducts that improve energy efficiency, such as solar cells or better conducting materials, indirectly improve the environment through lower power-plant emissions.