Issue Date: April 13, 2009
LITTLE IS KNOWN about what happens to nanoparticles when they end up in landfills or in wastewater treatment plants, or when they are incinerated. But as more and more consumer products made with nanotechnology hit the market, researchers are beginning to ask questions related to safe design and disposal of nanoscale materials.
These questions were at the heart of a two-day workshop in March sponsored by the International Council on Nanotechnology (ICON) at Rice University. At the gathering, participants from around the world brainstormed to identify critical knowledge gaps and opportunities in "eco-responsible" design and disposal of engineered nanomaterials. The more than 50 attendees were mostly academics and policymakers.
Current waste disposal regulations were created long before nanomaterials entered the commercial landscape, and they may need to be updated to deal with the growing inventory of nanotech products, observers say. While state and federal regulators and industry struggle to manage nanotech waste under existing laws, researchers are beginning to investigate whether it is even possible to design nanomaterials that are safe for the environment and living organisms.
Organizers of the workshop, however, were careful not to use the words "safe by design" or "safe disposal," because, as Vicki L. Colvin, executive director of ICON and professor of chemistry and chemical engineering at Rice University, pointed out rhetorically: "Can anything be truly safe?"
The workshop was the third in a series held to identify information needs for predicting nanomaterial impacts on living systems. The first two workshops, held in 2007, were designed to explore the biological interface, Kristen Kulinowski, director of ICON, said. This third one, she added, was focused more on the environmental issues, addressing questions such as whether nanomaterials can be designed to be harmless to the environment and how to dispose of them safely.
But before anyone can talk about designing nanomaterials that are safe for the environment, they have to know how nanomaterials behave and interact in the environment, a fact that quickly became obvious at the workshop. The participants noted that analytical methods for detecting nanomaterials in complex environmental matrixes are lacking. As a result, there are many unanswered questions about the fate and transport of nanomaterials in soil, water, and air, as well as the flow of nanomaterials through the food chain. For this reason, "the analytical techniques are a critical need for being able to design safer materials," Kulinowski said.
To design safe nanomaterials, it also is necessary to identify what it is about a nanomaterial that gives it a certain industrially interesting property or that causes it to interact in the environment in a particular way, Kulinowski said. Several participants at the workshop pointed out that investigating the physicochemical properties that drive the behavior of nanomaterials in the environment will provide the basis for such revelations.
Sharon Walker, a chemical and environmental engineering professor at the University of California, Riverside, suggested that human exposure to nanomaterials could be minimized by manipulating physical properties, particularly the morphology of particles. "The issue of aggregation is critical," Walker said. "Perhaps when aggregated, nanomaterials are no longer mobile, and no longer have the same reactivity."
THE AQUISITION or loss of coatings on nanoparticles in the environment came up numerous times at the workshop. Coatings could influence aggregation and "affect mobility, behavior, and impact," said Pedro J. Alvarez, a professor of environmental engineering at Rice.
But getting a handle on what properties of nanomaterials are important for toxicity and environmental interactions is difficult because of the vast number of different nanomaterials out there. "It's a combinatorial problem," Colvin said. "We have many types of nanotubes and many ways of making them," she noted, pointing out that there are more than 50,000 distinct types of single-walled carbon nanotubes.
One group of participants recommended selecting a small number of nanomaterials that are expected to have the biggest environmental impact. They suggested developing standard reference materials for those high-priority materials, among them carbon nanotubes, that could be used to determine what properties play a critical role in toxicity and environmental interactions.
Throughout the workshop, however, participants kept coming back to the question of whether it is possible to minimize the biological effects and still hang on to the performance characteristics of a nanoparticle. Opinions were mixed.
"I'm actually not of the belief that we can design out all of the potentially adverse effects from these materials," said Gregory V. Lowry, a professor of civil and environmental engineering at Carnegie Mellon University. "The reason we are interested in these materials and will use and benefit from them is because they generate reactive oxygen species or electron holes or pairs. If we design that out, they won't serve their function anymore. I am leaning toward the side of trying to limit exposure more," he said.
Bearing the flag for the green chemistry community, Julie B. Zimmerman, a professor of environmental engineering at Yale University, replied: "If we rely on exposure controls, they will, as a probability function, fail at some point. I do believe we can get performance without toxicity. There shouldn't be a trade-off. If we get to a trade-off, we haven't innovated far enough."
It is challenging to talk about designing safer nanomaterials and managing nanotech waste, however, because relatively little is known about the biological effects of nanomaterials, something this workshop series and other meetings have focused on. Progress in this area has been hampered by a lack of standardized toxicity testing protocols and methods for characterizing nanomaterials (C&EN, Dec. 15, 2008, page 25).
"People are measuring acute effects and chronic effects to some degree, but without standardized testing it is difficult to compare results. Further, it's not even possible at this point to take a data set from the literature and try to extrapolate it to make some kind of global conclusion from it," said Stephen J. Klaine, professor and director of the Clemson University Institute of Environmental Toxicology.
Another problem is the lack of information provided by manufacturers about products that contain nanomaterials. "How can you have an informed discussion about disposal if you don't know what is being produced and where it is going and how it is being managed?" Kulinowski pointed out.
MANY PARTICIPANTS voiced concern about the lack of mandatory reporting requirements for nanomaterial manufacturers. "We have hardly any systematic data to be able to calculate what concentrations will be in the environment. We can have rough guesses, but we really need that data from the manufacturers," noted Samuel Luoma of the John Muir Institute of the Environment at UC Davis.
Currently U.S. manufacturers provide the Environmental Protection Agency information about nanomaterials in their products through a voluntary program. Participation in the program has been relatively low, leaving the agency with little information about what nanomaterials are actually out there (C&EN, Jan. 19, page 42).
The State of California, Canada, and the European Union recently beefed up their efforts to get manufacturers to provide information about nanotech products. In March, the EU updated legislation that will require manufacturers to release information about nanomaterials in cosmetics (C&EN, March 30, page 23). Environment Canada, a national regulatory agency, announced in February that it would send out a one-time request for information to companies that manufactured or imported more than 1 kg of a nanoscale substance during 2008 (C&EN, Feb. 9, page 24). And in January, California regulators sent out a similar request to private and public facilities, giving them one year to provide information about their nanoscale materials.
When thinking about how to manage nanomaterial waste, it is important to examine the entire life cycle of nanomaterials, from synthesis to disposal, several workshop participants emphasized.
For example, Zimmerman pointed to one analysis published by her group that showed that for every 1 kg of nanomaterial produced, 102 to 105 kg of waste was generated. And that study only considered the synthesis stage, not the entire life cycle. "The biggest environmental impact in terms of synthesis is the purification step. That would be a good place to do research to reduce waste generation during nanomaterial manufacturing," she said.
OTHER WORKSHOP participants focused more on minimizing waste through reclamation, regeneration, and reuse of nanomaterials. "There's a lot of brainpower, materials, and energy that goes into making our engineered nanocomposites," said Barbara Karn of EPA's Office of Research & Development (ORD). "We need to design for the recovery of these valuable and highly engineered materials."
But for those products that can't be recycled, safe disposal could be an issue. The existing regulatory frameworks for the disposal of waste do not specifically address disposal of nanomaterials, several participants pointed out.
For example, little is known about the ignitability, corrosivity, reactivity, and toxicity of nanomaterials. Those four characteristics are used under the Resource Conservation & Recovery Act to determine whether solid waste must be handled as hazardous waste or whether it can go to a regular landfill.
And few studies have been conducted to determine how nanomaterials will behave in landfills. "There is a need to establish the possibility of leaching from landfills," said Edward M. Heithmar, a research chemist with EPA's ORD. "A lot of those tests may not be applicable to nanomaterials at this time. They may need to be modified."
Luoma and others at the workshop voiced concern about nanomaterials that are mobile and end up in wastewater. Nanoscale silver particles, in particular, were mentioned because of their known antimicrobial properties. Such particles could affect aquatic ecosystems and interfere with the wastewater treatment process. New technologies for pretreatment or removal of nanomaterials from wastewater may be necessary, several participants suggested.
Other researchers at the meeting brought up the need to examine whether nanomaterials will end up in sewage sludge from wastewater treatment plants that could be spread on agricultural fields.
In some countries, incineration is likely to be a major route of disposal, said one group of participants. But it now is unclear whether nanomaterials are destroyed, activated, or mobilized during incineration, some noted.
Without any guidance from the regulatory agencies, industry is stuck trying to figure out how to manage its nanomaterial waste stream. "One of the biggest problems we see as far as managing our nanomaterial waste is that there is no policy or regulations out there," said Christy Yorek, who manages hazardous waste for fighter-jet maker Lockheed Martin. She suggested that EPA develop best management practices that the agency could share with industry.
Although other industry participants were invited, Yorek was the only person representing industry at the workshop. Kulinowski told C&EN that the weak economy and reduced travel budgets were responsible for the lack of industry participation.
For those who were unable to attend, more details about the workshop will be available in an upcoming ICON report (icon.rice.edu) due out in a few months.
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