|Nanosilver attacks microorganism cell wall.|
image: Zhiqiang Hu, University of Missouri
Hu says introduction of large amounts of silver could interfere with the bacteria's ability to break down sewage. Also, solid biomass from treatment facilities is sometimes distributed to farms as fertilizer, and that could carry silver to the soil. "If the level of the metal made of those silver [particles] is high enough," says Hu, "that probably can cause environmental impact in the soil systems." Plants depend on nitrogen-fixing bacteria in soil. Kill that bacteria and crops and other plants won't grow.
There are several potential holes in the theory, though. Transport of nanosilver and silver ions through all these stages has yet to be documented. (Hu and his colleagues are doing research to determine that now.) Silver may combine with other elements along the way and become less harmful or precipitate out and get trapped by wastewater filters. Another consideration is that using silver in washing machines may significantly reduce the amount of detergent and water needed to wash clothes, which would reduce pollution and conserve precious water.
But with nanosilver now in hundreds of products that are not required to be registered with the EPA, is this more useful — but possibly more harmful — form of silver becoming ubiquitous and unregulated?
The EPA tends to exclude two categories of microbicides from their regulations (except in cases where there is clear evidence of some toxic or environmental impact.) 1) Personal care products and cosmetics like hand-sanitizing gels and antibacterial toothpastes usually fall under FDA regulation. 2) Antimicrobials designed to protect the product itself, like those in mildew-resistant paint, tend to get a pass on EPA regulation. Only when the product disperses a pesticide or toxic chemical is the EPA really interested.
Many other products that contain nanosilver have since removed all mention of any antimicrobial properties. This is a gray area, according to Dale Kemery of the EPA. If the product still contains silver but makes no claim, it can fall through the regulatory cracks.
This has left citizens with less information about the products they choose.
One ounce = one ton
Another problem with regulating nanosilver is figuring out how to quantify its risks. Typically, pollution is regulated by the amount of contaminant in the environment by weight or volume. But these may not be useful measures of the effects — either positive or negative — of nano-sized particles. The reactive part of silver is on its surface, and nano-sized particles have thousands or even millions of times the surface area of bulk material. That means one ounce of nanosilver dust could have the same surface area as one ton of bulk silver, depending on the particle size. Eventually, regulations might have to be based on number of particles per volume or even a calculated surface area.
In 2008, the EPA launched the Nanoscale Materials Stewardship Program, which invites companies to send in any data they have of the characterization of nanomaterials and any safety and environmental research results that they have produced. The EPA also funds research of the impact of new materials.
But some people feel it's not enough. For one thing, the program is voluntary. Companies can exclude materials or results that they don't care to share with the public. And environmental groups are wary to let industry be responsible for its own safety testing. The U.S. has a long history of failing to respond to the danger of hazardous materials in a timely manner.
Sean Murdock of the Nanobusiness Alliance says many people don't realize how far we've come in predicting and responding to potential hazards. "In all of these things, manufacturers are doing testing to ensure that they're safe. And frankly, we've much more robust science to help understand both the short term safety as well as the long-term safety of the materials that we're working with."
Price of innovation
This year, the National Nanotechnology Initiative, the major government funding for nanotechnology research, is up for reauthorization. Andrew Maynard, chief science advisor to the policy group Project on Emerging Nanotechnologies, would like to see a larger portion of those funds put toward environmental, health, and safety research. "Nanotechnology industries are desperate for clarity and a reduction in uncertainty here. So they want the research that is going to show us which nanomaterials are harmful and how to use them safely, because without that clarity, they just cannot do business."
Lux Research predicts that globally, $2.6 trillion worth of goods will incorporate nanotechnology by 2014. Maynard says now is the time to get the safety issues right: as nanotechnology moves from the laboratory to the factory. "Governments clearly want to see a new technology like nanotechnology come along which is going to stimulate the economy, lead to new jobs. But again, they don't want to create a legacy of harm that somebody else is going to have to clear up."
Publications: Environmental Science & Technology, April 2008; Water Research, March 2008.
Research funded by: National Science Foundation, U.S. Environmental Protection Agency, Water Environment Research Foundation, and the University of Missouri Research Board.