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Posted: Jun 08, 2009
Not so 'green' nanotechnology manufacturing
(Nanowerk Spotlight) After a slow start, research on the environmental and health impact of nanoparticles is gaining a great deal of momentum. Studies are becoming increasingly sophisticated but most of the attention is given to the final nanomaterial product; the environmental impacts of impurities and byproducts associated with low-efficiency nanomanufacturing processes has not received as much focus.
In a previous Nanowerk Spotlight ("Nanotechnology - not that green?") we wrote about the fact that the environmental footprint created by today's nanomanufacturing technologies are conflicting with the general perception that nanotechnology is 'green' and clean. Adding to these concerns, a new study looks at the waste solids generated by the production of metallofullerenes and fullerenes and addresses the question whether feedstock-associated metals pose potential risks to aquatic receptors.
The intent of this new study was to communicate that the purity of nanomaterials should be heavily characterized to ensure that the toxicological ramifications of the actual finished nanoproduct is accurately represented. Additionally, the authors suggest that carbon nanomanufacturing byproducts should be characterized so as to facilitate more informed decision-making on management of their associated waste streams.
"Our study was intended to screen whether mobilized impurities from nanomaterials and nanomaterial byproducts may be of potential concern for environmental regulators and for researchers attempting to address toxicity due to nanoparticles alone," Alan J. Kennedy tells Nanowerk. " While specific modeling of impurity concentrations that may partition into the environment was beyond the scope of this study, we investigated the metals composition of two different nanomanufacturing outputs: a commercially available, as-produced fullerene product, and two distinct samples of metal-containing fullerene (i.e., metallofullerene) waste byproduct."
Specifically, Kennedy, a research biologist at the US Army Corps of Engineers Environmental Laboratory, and his collaborators from the ERDC nanomaterials research cluster, NanoSafe, Inc., and the Department of Civil and Environmental Engineering at Virginia Polytechnic Institute, determined whether feedstock metals associated with the production of these materials can become mobilized and reach toxic concentrations in simulated aquatic systems.
"This particular research focus was first brought to our attention in 2004 by Matt Hull, who was working to develop management strategies for carbon nanomaterial waste streams," Kennedy explains. "We elected to conduct this study since there have been a number of review papers that have communicated that characterization of nanoparticle purity is important. The presence of impurities is not commonly quantified in environmental health and safety studies and we were not aware of any published ecotoxicological investigations that specifically looked into this issue."
Furthermore, there also is a paucity of information on the environmental implications of waste streams or discharges that may leach from low purity nanomanufactured byproduct material from sources such as landfills.
Hull, Kennedy and their team therefore set the goal of testing a specific byproduct material of metallofullerenes and fullerenes to communicate the importance of considering the overall effects of impurities in toxicological studies and in the regulation of waste materials – not just for the two subject materials but for other carbon-based materials such as carbon nanotubes.
"It is important to recognize that our test materials do not represent nanomaterials as a whole," says Kennedy. "Rather, our findings should be considered a case study to communicate the presence and possibility of a more general problem."
This work alerts researchers and regulators alike to two different issues when conducting environmental, health and safety investigations of nanomaterials: Firstly, manufacturing of carbon nanomaterials such as fullerenes and nanotubes is not always an efficient process.
"In our experience, this can lead to the generation of large amounts of mixed solid waste streams that either need to be stored on-site or disposed of in an appropriate manner," says Hull. "Since these materials may contain impurities such as metals, organic solvents, or residual nanomaterials, it should not be considered for regulation equivalent to that of carbon black."
Secondly, researchers need to be aware that even finished nanomaterial products may have impurities that can confound toxicology studies.
According to Kennedy, their study provides strong support that metals – particularly copper, an agent used to enhance yields of certain fullerene species – leach from metallofullerene soot at concentrations sufficient to induce complete mortality in two U.S. EPA-recommended aquatic test organisms: Pimephales promelas and Ceriodaphnia dubia.
"Today, there is much interest in determining whether new mechanisms of toxicity exist for nanoscale materials" says Hull. "But as our results demonstrate, it's important that researchers characterize test materials adequately and fully consider the toxicological effects of residual impurities, particularly metals."
These findings have immediate applications to toxicological studies with nanoscale materials and to waste management strategies for nanomanufacturing waste streams. Researchers evaluating the toxicity of manufactured nanotechnology products should work with manufacturers to understand the potential impacts of all input materials on the final products. Further, nanomanufacturing waste streams should be characterized to determine whether or not they contain potentially hazardous materials, and then disposed of accordingly.
Kennedy points out that, while their results were based on only two specific types of carbon nanomaterials and their byproducts, additional studies should be performed to assess the impurity and environmental implications of other types of nanoparticles, dependent on the efficiency of their manufacturing processes and the nature of their associated waste streams. The researchers also suggest that that the state of nanomanufacturing practices in general should be assessed to determine the dominant forms of manufacturing and raw materials used.