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Some say a nanorevolution is at hand, perhaps not an overly zealous assessment considering the emerging pervasiveness of nanotechnology and its rapid pace of development. The water resource field is among those areas expected to benefit from nanotechnology, its application holding special promise for treatment and remediation; sensing and detection; and pollution prevention. That cuts a rather wide swath in the water resources field.
The nanorevolution or movement is being met with both optimism and caution as scientists ponder how best to take advantage of its benefits and at the same time understand and reckon with its possible risks.
What is Nanotechnology?
A promising prospect with something of a sci-fi appeal, nanotechnology or nanotech is about size rather than a particular scientific discipline. Nanomaterial, a billionth of a meter, is to matter what a nanosecond is to time, a billionth of a second. A nanometer is roughly 10,000 times smaller than the diameter of a human hair and 1 million times smaller than a single grain of sand. Without hyperbole, Nano Magazine, devoted to covering nanotech issues, bills itself as the “Magazine for Small Science.”
Understanding the small science of nanotechnology requires thinking at an ultrasmall scale, downscaling one’s perceptions to the atomic and molecular level. Researchers at the nanoscale work to control matter about 100 nanometers or smaller, the smallest particles of matter that can be manipulated.
Nanotech involves assembling atoms and molecules to meet exact specifications to create new materials or modify existing ones. Nano-scaled materials and devices can be developed with a vast range of applications. Stuart Lindsay, Arizona State University Regents’ professor and director of the Biodesign Institute’s Center for Single Molecule Biophysics, says, “What is so striking is that events occurring at the nanoscale have implications for chemistry, biology, physics, materials science, engineering, you name it.” Lindsay is the author of the just released “Introduction to Nanoscience,” a comprehensive guide to the nanotech world.
Even prior to the recent burgeoning interest, nanotechnology had been used in water treatment. Troy Benn, an ASU researcher in environmental engineering, explains: “Water treatment has always worked at the nanoscale but it was not recognized as nanotechnology. Nanotech is about size, and for years filtration has worked at the nanoscale. Dissolved ions or particles are removed at the nanoscale.... What is new today is a greater control of the process.”
Key to understanding the workings of nanotechnology and its possible real world applications is knowing the changes that occur to materials at the nanoscale. Nanomaterials are not merely a greatly downsized version of the same material at the micro or macroscale; the physical and chemical properties of nano-scaled materials often change from what characterizes them at the bulk scale.
For example, nanotitanium dioxide is a more effective catalyst than microscale titanium dioxide and can be used to treat water by chemically degrading organic pollutants that are harmful to the environment. Nanosilver also is used to disinfect drinking water. Both are successful adaptions to the nanoscale to serve a beneficial use. Other materials at the nanoscale might act differently, possibly posing environmental or health hazards. Researchers seek to optimize nano-benefits and avoid nano-risks.
Regulatory problems have arisen because of possible changes occurring at the nanoscale. Of an earlier vintage, current regulations do not adequately address the development and use of nanomaterials. Complicating the regulatory task is the need to determine if a nanomaterial is actually a new substance or not. This can be a controversial issue. EPA would have the authority to regulate a nanoform if its different properties warrant it being considered a new substance.
Nanotechnology and Water
Some nano-scaled particles have properties that make them very suitable for treating water. They often have enhanced catalytic properties, with the potential to improve such processes as adsorption, catalysis and disinfection. Nanoparticles are especially valued as a type of building block to custom make other particles for specific applications.
A prime water resource application of nanotechnology is to further improve membrane technology. Nanofiltration membranes are already in use removing dissolved salts and micro pollutants as well softening water and treating wastewater. Meanwhile new classes of nanoporous materials are in the works with pores sufficiently small to filter out the tiniest micro-organism.
Further, the pores can be developed that are straighter than conventional filters allowing water to flow through faster. Acting as a physical barrier, the membrane filters out particles and microorganisms larger than its pores and selectively rejects substances. Nanotechnology may significantly reduce the cost of desalination.
Work is underway to apply nanocatalysts and magnetic nanoparticles to treat heavily polluted water for use in drinking, sanitation and irrigation. Nanocatalysts have stronger catalytic properties due to their nanosize or their modification at the nanoscale. They can chemically degrade pollutants including those that current technologies treat inefficiently and at great cost.
Also, research is looking at the use of magnetic nanoparticles to bind with contaminants that are then removed by a magnet. Having large surface areas relative to their volume, magnetic nanoparticles readily bind with water-borne contaminants such as arsenic or oil. Along with treating water-borne contaminants nanotechnology also can be applied to detect them. New sensor technologies combining micro and nanofabrication are being developed to create small, portable and highly accurate sensors capable of detecting single cells of chemical and biochemical substances in water.
Another promising application of nanotechnolgy is its use to address water problems in developing countries by helping to resolve technical challenges to removing water contaminants. Nanotechnology holds promises for more varied, affordable, effective water treatment methods that are more adaptable to the needs of developing countries.
Nanotechnolgy research is underway at Arizona universities. See page 6 for a description of a University of Arizona research project using nano scale zero valent iron to bioremediate water containing uranium. James A. Field and Reyes Sierra of the UA department of chemical and environmental engineering are conducting the research. The two researchers along with Farhang Shadman, also from ChEE, Scott Boitano, UA college of medicine, and Buddy Ratner, University of Washington, also are involved in a project studying the toxicity of nano-sized materials for the semi-conductor industry. In another project Sierra, Shadman and Field are looking at the fate of nanoparticles in municipal wastewater treatment plants.
At ASU, Paul Westerhoff, civil, environmental and sustainable engineering, has researched the fate of commercial nanomaterials in drinking water and wastewater treatment plants, and their potential human toxicity.
Caution is Urged
Amidst the promising news, the potential risks of nanotechnology are not to be overlooked, with some advocating more research to determine the potential health and environmental risks of using nanotechnology for water treatment. A prime concern is that the enhanced reactivity of nanoparticles increases their toxicity. Further, nanoparticles are extremely small and very difficult to contain raising the concern that they could escape into the environment and pose a threat to aquatic life. Whether handled at the treatment plant or consumed in treated water nanomaterials pose an unknown risk. Benn says, “Nanotechnology provides a strategy to improve water quality through treatment and remediation. Also, however, the use of nanotechnology has raised concerns that nanoparticles might end up in water supplies ... Our research is looking at the release of engineered nanomaterials that could potentially enter water systems. We are considering nanomaterials as an emerging contaminant.”
Benn mentions nano iron as an example. Used for the remediation of groundwater contaminated with organic solvents, nano iron injected into an aquifer breaks down the more toxic forms of the organic solvents. Meanwhile questions have been raised about whether iron in its nanoform is harmful to the environment and human health. Benn asks: “As we inject a nanomaterial into groundwater to remediate a problem are we simultaneously creating a new problem by injecting a material that may have adverse environmental effects?”
Nanosilver provides another example. Nanosilver’s use to disinfect drinking water was noted earlier. It is effective as an absorbant media in membrane technology. It also has been used in other water quality applications including cleaning or treating water in swimming pools. Also, nanosilver serves as a tool in environmental remediation.
Nanosilver’s ability to cleanse and purify is useful in other applications besides water. For example, nanosilver is used as an anti-microbial agent in clothing. When clothing with nanosilver is washed particles are released that then flow to a water treatment plant. In sufficient quantities the nanosilver could be a problem, killing bacteria necessary in the treatment process. Particles in treated water might be released directly into the environment, including streambeds, or be in the solid waste spread on agricultural lands. What, if any, environmental effects this would have are essentially unknown. Nanomaterials are already in hundreds of commercial products.
Like nanosilver, other nanoparticles used in consumer and other products could end up in the environment including lakes and streams. Many of their environmental effects are unknown. It is becoming increasingly clear that the manufacture and use of nanomaterials have broad implications, far beyond the science lab.
The Broader View
With the science of nanotechnology moving rapidly forward, some researchers argue that studies of the ethical, legal and social implications of nanotechnology lag behind. They call for catch-up in these areas to consider the effect the small world of nanotechnology will have on our larger world.
ASU’s Center for Nanotechnology in Society and ASU’s Consortium for Science, Policy and Outcomes has taken up this challenge. CNS works with scientists and engineers such as Jonathan Posner, an assistant professor of mechanical and chemical engineering in ASU’s Ira A. Fulton Schools of Engineering, encouraging them to consider the significance the emerging technology will have on society.
In a March 2 ASU press release, Posner stated that because of nanotechnology’s privileged position at the leading edge of science and engineering today “it will increasingly have health, environmental, social, political and economic implications, and raise ethical issues.
“There is a pressing need to understand the impact of nanotechnology on human health, the environment and society, to give us an informed background from which we can craft government policy and regulation, as well as legal and ethical guidelines.”