Machine Design

Nanowaste: The Next Big Threat?

Could nanomaterials damage the environment or human health?

Senior Editor

If you believe the hype, nanotechnology will grow into a $3 trillion industry over the next 10 to 15 years and spur revolutionary new devices. For now, however, commercial nanotech is confined to nanomaterials, particles and compounds that range from 1 to 100 nm (10- 9 meters) in size. Nanoscale titanium-dioxide particles, for example, are used in cosmetics and sun blocks, and nanosized silica acts as filler in several consumer products, including dental fillings.And next year, Frontier Carbon Corp., a Japanese company, plans to begin annual production of 40 tons of bucky balls, the C-60 molecule formally called Buckministerfullerene. The firm hopes other companies will find ways to modify the molecule and make it commercially useful.

A recent discovery by researchers at Rice University, however, is making some people think twice about charging ahead in nanotechnology. Scientists had long thought bucky balls were strongly hydrophobic and strictly insoluble in water. They believed bucky balls dropped into the open environment could not be transported by water, but would simply stick to the soil and other organic materials. But with a little effort, Rice researchers got the C60 molecules to clump together in what they call nano-C60. It measures up to 500 nm across and easily travels in water if conditions are right. What's more worrisome is that the researchers also found that small concentrations of nano-C60 (20 parts/billion) killed half of the human liver and skin cells in lab samples. Other studies have shown that nano-C60 damages brain cells in fish and halts the growth of bacteria.

All this gives plenty of ammunition to those interested in shocking headlines and pulling in the reins on technology. And combine it with what scientists know — or don't know — about nanomaterials, and even reasonable people can have doubts.

Nanocubes from BASF made of metalorganic compounds use their numerous pores and channels to store hydrogen. Two grams of nanocubes have an internal area equal to a soccer field. The cubes measure a few micrometers on a side but have been dubbed nanocubes based on their nanometersized internal spaces.

In fact, scientists have no way to track nanomaterials like bucky balls or nanotubes in the environment. If one were to drop a cubic meter of them (about a ton) from a flying airplane, there would be no way to find them. And even if they could be found, there is no way to remove them from the soil or water. There's also no acceptable way to find or remove them from the human body. (Of course, it's possible to find some, such as gadolinium-based image-enhancing agents for MRI scans. They are engineered to show up in MRIs.)

To make matters worse, no one has studied the effects nanotubes, bucky balls, and other newly created nanomaterials have on the environment or human physiology. The fear is that because nanomaterials are smaller than cells, they might enter and create havoc or bioaccumulate in smaller creatures, then work their way up the food chain in ever-increasing concentrations until they do cause problems for humans.

Pedro Alvarez, chairman of the civil engineering program at Rice and president of the Association of Environmental and Science Professor, worries that nanomaterials could harm bacteria, the engine behind practically every ecosystem and food chain. He refers to a quote from Louis Pasteur: "The role of the infinitely small in nature is infinitely great."

With these questions unanswered, and possibly unanswerable, some groups want to halt nanotechnology in its tracks until its safety can be proven. The Etc. Group, for example, has insisted since 2002 that the world needs a moratorium on nanotech until an international body sets lab and manufacturing protocols for handling, using, and disposing of nanomaterials. (The Etc. Group examines the effect new technologies might have on health, the environment, society, and economies.) The group also wants countries to be informed about and prepared for any changes new technologies such as nanotech or genetically modified foods might bring.

Bucky balls, or C60, behave differently in different mixtures of water and solvents. In vial 1, for example, C60 dissolved in toluene does not partition into water. In the second vial, C60 dissolves in tetrahydrofuran (THF), a solvent. In the third vial, water added to the C60/THF solution creates a yellow suspension of nano-C60 or clumped together C60. In vial number four, THF has been evaporated off, leaving a suspension of nano-C60 in only water. Vial 5 has nano-C60 slowly dissolving into an upper layer of toluene. And in vial 6, the addition of a mild oxidant drives the bucky balls from the water and back into its organic phase.

Although the prefix nano (Greek for dwarf) has only recently gained popularity, people have been creating and using nanomaterials for thousands of years. Medieval glaziers, for example used nanometer-sized particles of gold and silver in their red and yellow stained glass. Diesel engines also emit nanomaterials in the soot they generate. There are also natural sources of nanomaterials, including forest fires which create bucky balls and volcanoes which put a variety of chemicals into the atmosphere in aerosol form. There's even a bacteria that digests iron and leaves nanosized particles of magnetite behind.

But before nanotech took the limelight and earned top billing in every marketing guru's lexicon, scientists and engineers were studying nanomaterials under the term "ultrafine particles." They learned of the health problems associated with small particles, and that such problems almost exclusively involve breathing them in. So scientists and engineers are not totally ignorant of the threat nanomaterials pose. And they also know how to filter them out of indoor air and workspaces. Or at least they think they do.

The current theory on filters for small particles relies on a concept called diffusional capture. It says that particles larger than 0.3 m get stuck to fibers in the filter medium while smaller particles, including those in the nanometer range, get stuck to those particles clinging to the fibers. The National Institute for Occupational Safety and Health (NIOSH) is currently funding a study to see if current filters follow this theory and actually screen out nanomaterials.

Researchers also know that some nanomaterials break down naturally over time, much like plastics, says Alvarez. "Others are rapidly absorbed by the soil, which presumably reduces bioavailability and the threat of exposure to humans and other living creatures. And some nanomaterials we know are very safe based on their approval and use in medical applications. But that doesn't mean all nanomaterials are safe," says Alvarez.

Alvarez and his associates at Rice University are studying bucky balls, as are a host of other research teams. But instead of trying to ferret out some killer nano-app, they are seeing how the materials react to various environmental factors such as sunlight, water, and time. For example, they've discovered that adding simple chemicals to bucky balls, such as hydroxls or carboxl groups, makes them less toxic to cells. In fact, bucky balls with the most chemical groups added were the least toxic. It took 10 million times as many "decorated" balls as plain bucky balls to have the same effect (i.e., kill half the cells in a sample). This could give future engineers a way to make bucky balls and other nanomaterials safer, if not totally harmless.

An electron microscopy image shows bucky balls clumping together in water and forming nano-C60, a watersoluble form of carbon made up of thousands of bucky balls. The size of the nano-C60 particles depends on water pH and how fast bucky balls are mixed with the water. The particles rely on a negatively charged surface to stay afloat. Adding ions, such as table salt, can render the surface neutral so that the particles will sink and form a solid glob, according to researchers.

Of course, UV radiation from sunlight or other chemicals in the environment might strip off the hydroxls and other chemical additions. But if bucky balls and other nanomaterials are used in the human body or encapsulated in a consumer product, they might remain intact and safe. The Rice team is investigating along those lines, trying to collect more data on the life cycle and reactions we can expect from nanomaterials. For example, they discovered that neither C60 nor nano-C60 (clumped together C60) damaged DNA in any of their cell cultures. This strongly indicates the substances are not carcinogenic. The team is now cataloging the effect the size and shape of titanium dioxide nanoparticles have on toxicity.

Another set of factors that would minimize any possible risks of nanomaterials is that they are still very expensive, costing thousands off dollars a pound for engineered versions of bucky balls and nanotubes. So companies are unlikely to view them as waste products and simply send them down the drain into a nearby river. They are also being made in relatively small quantities. While perhaps 50 to 60 tons of bucky balls will be made next year, that's still small potatoes compared to the 1.4 million tons of titanium dioxide made annually or the 40 million tons of sulfuric acid.

Water droplets bead up on wood treated with BASF's nanomaterials-based Mincor coating. The coating makes the wood extremely water repellent and decreases the contact area between the water and wood. The coating also makes surfaces self-cleaning.

Researchers at BASF are adding nanosized particles of polyisocyanates as crosslinking agents in a polyurethane coating. The particles could make the coating tough and chemical resistant, but also flexible and therefore scratch resistant.

While some groups want to halt nanotech in its tracks until it is proven totally safe or acceptable standards are established, others want to move ahead and bring the benefits of the technology to society as soon as possible and turn a profit while doing so. In the middle, a growing number of people want to investigate the possible dangers of nanomaterials without halting progress or banning anything without solid evidence of risk. There's also a growing consensus that nanomaterials shouldn't be released into the environment until more is known about their life cycle outside the lab.

"The issue of nanomaterials and their consequences is getting a growing amount of attention," notes Peterson. The EPA and OSHA, for example, are funding studies on the health and environmental risks posed by nanomaterials. The U.K.'s Royal Society of Engineering and the European Union are calling for rules to protect humans and the environment from nanomaterials. And in a case of nanotech making strange bedfellows, the chairman and CEO of DuPont got together with the president of the Environmental Defense to pen an editorial in the Wall Street Journal saying its time for "identifying and addressing the risks" posed by nanotechnology. Environmental Defense is a group dedicated to protecting the environmental rights of all people, including future generations.

Christine Peterson, vice president of public policy at the Foresite Nanotechnology Institute, a nonprofit think tank that focuses on nanotechnology, points out that many of the thousands of substances created every year for decades could be categorized as nanomaterials or made as particles smaller than 100 nm. "What kind of safety and toxicity testing are done on them?' she asks. "How do we currently regulate new chemicals and substances?"

"My understanding is that the EPA does not require health testing on these new chemicals," she says. "For years, we have not required testing on any new chemical as a general rule. So instead of focusing on nanomaterials, holding them to a higher standard and ignoring the rest, we should take a couple steps back and answer some basic questions. Shouldn't we treat all new substances similarly? Either we need to test all new materials or none at all. Why exempt one group and not another?"

Currently, the U.S. Occupational Safety and Health Administration (OSHA), instructs companies to handle bucky balls as if it were carbon black, a material similar to graphite. And although OSHA officials know that bucky balls don't behave exactly like carbon black, the restrictions provide some safeguards, especially to those making, handling, and working with these new materials.

Researchers at Rice University are studying the life cycle of bucky balls (C60) and how it interacts in the environment.

Most nanotech researchers urge a reexamination and restructuring of how safety organizations like OSHA and EPA define and treat nanomaterials. One common recommendation is that the federal government spend more money studying the health and environmental effects of nanomaterials. Today, about 4% of the federal nanotech budget goes into these efforts. Industry leaders and social activists agree it should be more on the order of 10%. Some also believe companies looking to cash in on nanotech should shoulder some of the R&D that will prove their products safe to manufacture, use, and dispose of.

"It's important to consider the ecological implications of nanomaterials and take a proactive approach to reducing unnecessary risks and unwanted consequences," says Alvarez. "We don't know the full story yet and we have to move carefully, but that doesn't justify paralysis by analysis. We need to be careful but not afraid. And we cannot ignore the huge potential benefits of nanotechnology. It might solve our energy problems, help alleviate hunger, and open a new door to cures for all kinds of illnesses."


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