Closing the Nanotechnology Knowledge Gap
EPA's stewardship program is taking shape--a promising development as researchers see progress on analytical obstacles in this field.
- By Marc Barrera
- Sep 01, 2007
NANOTECHNOLOGY safety regulations may be years away. Many have suggested OSHA can use existing standards and the General Duty Clause to regulate safe nanotechnology practices, but the latter requires having some guidance on exposure limits and best practices from EPA or non-regulatory organizations.
EPA recently announced in the Federal Register a concept paper outlining the design and development of its stewardship program for nanoscale materials under the Toxic Substances Control Act (TSCA) (15 USC 2601). At press time, a public meeting was planned in August to discuss comments received. The draft document's title is "TSCA Inventory Status of Nanoscale Substances -- General Approach, and a proposed Information Collection Request"; it can be found at www.epa.gov/oppt/nano/nmspfr.htm. The document states that the purpose of this stewardship program is to help EPA "assemble existing data and information from manufacturers and processors of existing chemical nanoscale materials; Identify and encourage use of risk management practices in developing and commercializing nanoscale materials; Encourage the development of test data needed to provide a firmer scientific foundation for future work and regulatory/policy decisions; Encourage responsible development."
In this way and, more importantly, in scientific research, nanotechnology knowledge continues to advance. The toxicity of nanomaterials remains a major concern, but equally so is finding the proper method to measure exposures. John Volckens, Ph.D., assistant professor at Colorado State University, said there is not yet a definite answer regarding the best measuring method to employ, whether it involves measuring particle mass, particle surface area, or particle concentration. Of the three, measuring mass seems currently the least likely candidate. "It's really, really hard to measure the mass of nanoparticles," he said. "They just don't weigh enough to try to detect the mass, so we try to detect other properties that relate that measurement to their mass."
Measuring surface area distribution doesn't yield much more help because nanoparticles have been found to contribute only about 10 percent of the total surface area. Volckens said one possible technique is to use a diffusion charger (they can cost up to $20,000) to get a good idea of surface area, although measurements are still susceptible to bias from large particles.
Number concentration seems to be the most viable option because of the ease of using condensation particle counters (CPCs) or optical particle counter/sizers (OPCs) to take measurements in real time, but there is some question as to their effectiveness to measure all nanoparticles accurately--some devices can measure down to only about 20 to 30 nanometers.
New Instruments, New Uses for Older Ones Sought
Dr. Charles L. Geraci, CIH, branch chief at NIOSH's Nanotechnology Research Center (NTRC), said the Nanoparticle Occupational Safety and Health consortium is funding research in many specific areas, one of which includes the development of a hand-held, direct-reading instrument for nanoparticles. (NIOSH was invited to serve on the consortium by DuPont as a technical advisor and contributor.) During an open meeting at the 2006 American Industrial Hygiene Conference & Expo in Chicago, vendors were invited to make proposals on developing such an instrument.
"The new instruments that are being proposed will be more specific in the nanoparticle range, but they won't be specific about the elemental makeup of those materials or whether they are engineered or incidental. But you'll have a higher degree of confidence that you're measuring nanoparticles versus other particles," Geraci said.
Development of such an instrument would address the need for more accurate measurements but lacks one critical element: the ability to identify nanoparticles in real time. Particle identification is extremely important to ensure good exposure data because engineered nanoparticles can easily be mistaken for naturally occurring, or incidental, nanoparticles. Many possible sources of incidental nanoparticles can skew test results, including sources such as propane burners, forklift trucks, gas-fired heaters, and automobile exhaust. No existing instrumentation at this time can identify nanoparticles in real time, but there are other ways around the problem.
Volckens and Geraci agreed a possible solution is to use the very same instruments and techniques that nanoparticle manufacturers employ to verify the quality of their products, such as surface spectroscopy. "When folks make nanoparticles, they usually put them on an electron microscope grid to look at them and judge their quality," Volckens said. "So if we could capture airborne nanoparticles on, say, a transmission electron microscope grid, we can use some of the similar technologies that engineered nanoparticle manufacturers and nanotechnology researchers use to gauge the quality . . . we can use these spectroscopic techniques to look at nanoparticles, look at their chemical composition, then we can begin to identify them."
Even these methods have limitations, Geraci pointed out. "It's a combination of costs and having access to people with experience to do that," he said. "Getting a sample analyzed by electron microscopy today isn't the cheapest thing you can have done, but it's not the most expensive thing done, either. You don't want to do it every day, but you can use that approach." Also, if a manufacturer is able to get past the expense hurdle with this approach, another question remains: how best to capture that exposure for testing?
One possible solution Volckens is considering is developing a commercial thermal precipitator to address this. "Most nanotechnology researchers will use thermal precipitators to collect their particles so they can look at them, but there are no commercially available precipitators," he said. "If a thermal precipitator or even an electrostatic precipitator can be used to capture airborne nanoparticles, and then use the nanotechnology's spectroscopy methods to look at their chemical composition, then you're starting to answer the questions 'What are they made of? Where do they come from? What are they?' "
For now, obtaining funding is the chief hurdle in the way of developing such an instrument.
Whether or not a hand-held, direct-reading instrument for nanoparticles or a commercial thermal precipitator eventually arrives, Volckens and Geraci agreed industrial hygienists must continue to do good detective work now and in the future to test and control exposures in their workplaces as a way to negate their inability to identify nanoparticles in real time.
"You can do background measurements and then, when the process is running, you could look at new levels of nanoparticles," Volckens said. "Now, you're still not answering the question of whether or not you're looking at the engineered nanoparticles' signature readings, but you're going to get a relative sense. If there's no change at all with the concentration, you might be able to make the conclusion that it appears our controls are working."
A Glossary of Nano Terms
ASTM International--in partnership with the American Institute of Chemical Engineers, American Society of Mechanical Engineers, Institute of Electrical and Electronics Engineers, Japanese National Institute of Advanced Industrial Science and Technology, NSF International, and Semiconductor Equipment and Materials International--published a standard last year, ASTM E 2456-06 Terminology for Nanotechnology, to promote clear communication across all fields of nanotechnology development. It contains a list of uniform definitive terms that include:
fine particle, n—in nanotechnology, a particle smaller than about 2.5 micrometers and larger than about 0.1 micrometers in size.
nanoparticle, n—in nanotechnology, a sub-classification of ultrafine particle with lengths in two or three dimensions greater than 0.001 micrometer (1 nanometer) and smaller than about 0.1 micrometer (100 nanometers) and which may or may not exhibit a size-related intensive property.
nanostructured, adj—containing physically or chemically distinguishable components, at least one of which is nanoscale in one or more dimensions.
nanotechnology, n—A term referring to a wide range of technologies that measure, manipulate, or incorporate materials and/or features with at least one dimension between approximately 1 and 100 nanometers (nm). Such applications exploit the properties, distinct from bulk/macroscopic systems, of nanoscale components.
ultrafine particle, n—in nanotechnology, a particle ranging in size from approximately 0.1 micrometer (100 nanometers) to .001 micrometers (1 nanometer).
To access the standard in its entirety, including all 13 definitions, visit www.astm.org or contact ASTM Customer Service at email@example.com.
Control Banding Useful
Because of the endless possibilities for the creation of new nanomaterials, toxicity research on these materials may never end. As more and more data pile up in the near future, however, a growing concern will be how best to use these transitional data in a quick, helpful, and easy-to-understand way for workers. Geraci said a possibility that seems to be a natural fit is control banding--the same concept created by the pharmaceutical industry in 1980 to manage materials whose toxicity wasn't yet completely characterized.
"A lot of that has good reapplication in dealing with nanomaterials," he said. "I think over the next couple of years, we're going to have more information on some of the major classes of nanomaterials and their biologic activity, so we'll be able to start breaking out and segmenting these into broader classes that will require different levels or degrees of control."
Using the control banding concept, a chart could be created with different categories that classify groups of nanomaterials by certain criteria, such as low, medium, and high dustiness, opposite particle size classifications of ultrafine, fine, and small. Determining where a certain material fits in both criteria and intersecting the two categories on the chart would determine in which hazard category the process falls. Manufacturers and workers would then follow the proper guidance set for that hazard level. For example, Hazard 1 classification could require the use of general ventilation, while a Hazard 4 classification could require complete containment and a specialist's consultation.
Progress Made on Guidance Documents
Data useful for this method may still be a few years away, but manufacturers are not being left in the dark. One tool they can use is "Nano Risk Framework," a document released in June 2007 with guidance for handling nanomaterials during their entire life cycle, including manufacture, use, disposal or recycling, and ultimate fate.
Resulting from a partnership formed in 2005 between DuPont and Environmental Defense, the guidance is organized in six steps: Describe Material and Application; Profile Lifestyle(s); Evaluate Risks; Assess Risk Management; Decide, Document, and Act; Review and Adapt. Available at www.NanoRiskFramework.com, it has an editable Output Worksheet template that is meant to facilitate evaluation, management, and communication by organizing all of the information captured when following the framework. The document states that the ultimate purpose of this framework document is to "promote responsible development of nanotechnology products, facilitate public acceptance, and support the development of a practical model for reasonable government policy on nanotechnology safety."
Geraci said two similar but as-yet-untitled documents are in various levels of development at NIOSH. The first is a risk management guidance document for manufacturers of nanomaterials that is aimed primarily at smaller businesses using the pharmaceutical industry's control banding framework. It is intended to identify key steps that should be followed and provides helpful checklists and tools, Geraci said. The second document will be a more detailed, expert-level treatment.
"It's going to be good to have both of those out because the company that doesn't have a lot of experience with risk management, industrial hygiene, or EH&S management will benefit from the first document as this basic guide," he said. "The more expert-level document pretty much assumes that the reader has some good experience in industrial hygiene and exposure measurement and control technologies, and understands some of the basics that are being presented in there and how to apply those basics."
In final review and clearance stage at press time was a cross-federal framework document for health surveillance of workers exposed to nanomaterials, Geraci said. "There are questions about what kind of medical evaluations, if any, should be done on people who are working with, handling, or producing nanomaterials. And the second, follow-up question is, should we be thinking about or should we consider some type of surveillance for people who are brand-new into this?" he said. "They're the first group of workers ever exposed to these kinds of materials. Should exposure registries be created? How would we track prospectively this group? So it's kind of a treatment to two different topics: the medical evaluation issue and then the surveillance issue."
Geraci noted this issue was deliberately left out of the "Approaches to Safe Nanotechnology: An Information Exchange with NIOSH" document that NIOSH originally posted online in 2005 and updated in August 2006, because the agency didn't know where it was going to go at the time. An update to that document is also in progress. "We're certainly going to have updated information on the toxicology studies, the health effects. We've done a respectable number of field studies between the last update and this one, so we'll incorporate that into what we have seen on controls that are in place that appear to be effective, or the effectiveness of controls," he said.
Researchers' Confidence Growing
Nano research continues to move forward at a breakneck pace. The best thing manufacturers can do at this stage is actively seek and then implement good practices and guidance. The documents mentioned above will provide an abundance of resources for manufacturers, and ultimately they could progress to the formation of an industry standard. Geraci said he is confident that good progress is being made.
"Two years ago, we said, 'Well, we think this sounds like a good approach,' and then a year ago, we said, 'We're very confident that this is a good approach,' " he said. "Now, what we want to say is, 'Based on our direct experience in doing this in the field at nanoparticle production facilities, here's what we are doing.' "
This article originally appeared in the September 2007 issue of Occupational Health & Safety.