Perils and Promise of the Infinitesimal
^What do a pair of Dockers brand "Go" khaki pants, a Wilson tennis racket, Burt's Bees "Chemical Free" sunscreen, a Samsung washing machine, Land's End earmuffs, a face cream from fashion house Chanel, and my Apple laptop computer have in common with a billion-dollar U.S. government program, a Berkeley, California, city ordinance, and a novel about invisible robots run amok?1 All involve what are called nanomateri-als, synthetic materials engineered at the microscopic scale of one to 100 nanometers—a nanometer being one-billionth of a meter. To get a sense of the scale it helps to know that a human hair is about 80,000 nanometers wide. This is so small it can mean manipulating materials at the atomic level.2
What makes nanomaterials so unlike the materials with which we are more familiar—and is the source of both their promise and their potential perils—is that at this infinitesimal scale materials change in fundamental ways. Not only are nanomaterials so small that they may be able to penetrate skin and cell membranes and so get to places that their conventionally sized counterparts cannot, but as Vicki Colvin, professor of chemistry and director of the Center for Biological and Environmental Nanotechnology at Rice University, explains, "Size changes chemistry."3
At the nano-scale, materials have surface areas and geometries that give them chemical, physical, and biological properties that may be completely different than those they possess at the macro or even micro scale. They can take on new optical properties that allow them to absorb special wavelengths of light, lending themselves to applications like dyes and medical tracers. Elements like gold, aluminum, or carbon, for example, which are without inherent biological activity at conventional sizes, can interact in ways that would not otherwise be expected when engineered into nanomaterials. These reactions can—again, for example—be directed toward creating polymers, developing materials that detoxify pollutants, and constructing those that will knit wounded cell membranes. It is precisely these novel characteristics and possibilities that make nano-materials such intriguing chemical tools. These properties are also what enable them to behave in ways that we do not yet fully understand and that are prompting widespread concern about their environmental and health impacts.
These concerns have given rise to science fiction scenarios of runaway molecules replicating and invading—Michael Crichton's "nanobots" and Eric Drexler's "gray goo"—but also to a serious public discourse that has the potential to bring about a sea change in how we consider new materials and technologies. And while there is nothing intrinsically "green" about nanotechnology per se (it can use toxic elements and produce hazardous materials just as conventionally sized synthetic chemistry can), it is this new universe of chemical behaviors—particularly the potential to create more resource-efficient materials—along with the opportunity to establish a more proactive approach to the safety of new materials than currently exists, that presents important opportunities for green chemistry.
On the performance side, at the nano-scale, novel reactions made possible at this size can in some instances eliminate the need for reagents (process chemicals used to induce other chemical reactions) that can be hazardous and expensive, and thus both environmentally and economically costly. This reactivity can also be used to make molecules bind effectively and efficiently in ways that can create layered surfaces and polymers and repair damaged materials. It can also be put to work detoxifying or otherwise destroying unwanted molecules without the use of additional chemicals, giving nanomaterials great potential in the realm of stain removal and chemical remediation. All these are applications that, if accomplished without hazard, meet green chemistry goals.
But unusual properties also require new ways of assessing these new materials' potential toxicity, environmental disruption, and health hazards. Existing test methods simply do not encompass all the possible ways in which nanomaterials can interact. Nanomaterials behave so differently from other materials that even cleaning a spill means stopping to think whether or not one can safely reach for a vacuum cleaner or a mop. And standard personal protection equipment may not be what's required to ensure safety for those working with nanomaterials in a lab or manufacturing plant.
These many unknowns are also prompting leading nanotechnology practitioners to call for ways of investigating nanomaterials' environmental and health impacts—and disseminating this information—that are substantially different than those that have been used historically. Yet despite these cautions, nanomaterials have been proliferating so quickly that in early 2009 researchers estimated that it could cost U.S. industries over a billion dollars and take more than fifty years to conduct toxicity testing for the various nanomaterials already in existence.4
While nanomaterials are turning up in items as mundane as hats and underwear, the scientists who work with them are exploring a terrain that is in its way as exotic as the deep ocean or outer space. Some nanoma-terial names even sound exotic: quantum dots, carbon nanotubes, ful-lerenes. Nanomaterials can only be viewed under high-powered microscopes, but even a quick glimpse through such a lens offers a clear picture of how materials change at this scale. For instead of seeing the seamless flat surface of a solid snip of metal, for example, what you see is something resembling a honeycomb or grate or a series of slices of a sphere— or in the case of nanoparticles of carbon, something that resembles multiple strands of hair or thread. It is this expanded, multidimensional molecular territory with which scientists are working—both physically and chemically—as they manipulate nanoparticles.
It is by exploiting the scale-dependent properties—which, depending on the material, enable nanomaterials to reflect or absorb certain wavelengths of light, bind with, and destroy undesirable bacteria or tumor cells—that nanomaterials are being put to work in products that range from improved cancer treatment, more efficient solar cells, faster computers, and cleaner water to stain-resistant neckties, smell-resistant socks, and toothpaste that promises whiter teeth. Nanomaterials are being used as antibacterial agents, catalysts that remediate pollution, and as drug-delivery vehicles. They can also create incredibly strong and light building materials (this is why nanomaterials are attractive for aircraft and sports gear) and can be used to create semiconductor circuitry. An inventory compiled by the Woodrow Wilson Center's Project on Emerging Nano-technologies—the only such comprehensive compilation to date of nanomaterial-infused products—lists more than 800 consumer products containing nanomaterials, a list that does not include specialized medical or industrial applications.5
Among the behaviors that distinguish nanomaterials—and why they are attracting green chemists—is how they lend themselves to applications that can be used to reduce waste within the manufacturing process. Take the fact that these tiny particles can be engineered and combined in ways that eliminate the need for additional process chemicals and other potentially costly resources to spur a chemical reaction. This is often described by those in the field as a "bottom-up" approach to chemical synthesis or, to use a phrase that has helped spur fears of "nanobots," "self-assembly." What this means is working with the molecules' existing nature, putting them in a position of natural attractions and reactions rather than pushing them into reactions that require applied force, whether chemical or physical. (Hence the self-assembly and possibility for replication.) Reducing or doing away with the need for solvents and additional steps in a chemical synthesis or manufacture of chemical-intensive products like semiconductors and pharmaceuticals has great potential in terms of reducing overall resource use and the potential for harmful byproducts, environmental impacts, and health hazards. But to ensure that substituting one set of materials for another doesn't sim ply create new hazards, big and hard questions need to be asked about nanomaterials.
These materials and their properties are so new that Barbara Karn of the EPA's Office of Research and Development calls the advent of nanotechnology a paradigm shift. "In science we assume that no matter how much we slice a material, its properties are retained. At nano-scale, this is not the case and it's counterintuitive to the way we've been working," she told me.6
"Size-dependent properties are what make nanomaterials powerful," explains James Hutchinson, professor of organic and materials chemistry and director of the Materials Science Institute at the University of Oregon.7 Size is also the primary cause for concern about nanomaterials' implications for human health and the environment, as Vicki Colvin explains: It's nanoparticles' large surface areas that open the possibility for biological interactions. This means that a material that is environmentally benign when used at a larger scale—such as the conventionally sized titanium dioxide used as a masking agent in sunscreen—has the potential to behave completely differently when used as nanoparticles.
While the skin may be an effective barrier against a substance at the micro scale, for example, nanoparticles of the same material may be able to permeate skin and other cellular membranes. These minute particles may be able to enter the bloodstream, to permeate lung tissue, or to target specific organs, including the brain. With specially designed medical or pharmaceutical products, this may be desirable and even highly beneficial. But nanomaterials that reach organs unintentionally present the possibility for adverse impacts. "We don't yet have a good grasp of how nanoparticles change in the human body," says Kristen Kulinowski, director of the International Council of Nanotechnology (ICON).8 She and her colleagues at Rice University in Texas are working to develop models that will assess the behavior of nanomaterials in biological settings, something about which relatively little is known.
So what does happen when we are exposed to products containing nanomaterials? How does the exposure to nanoparticles one may get by applying a nano-sunscreen, wearing socks with an antimicrobial nanomaterial, or using a golf club made with a nano-carbon affect health? Or do they affect health at all? What about exposure to nanomaterials for people working in factories or laboratories where these products are made? What happens when these products are disposed of? Right now, these questions about the potential hazards of nanomaterials are just beginning to be answered, and one of the challenges is that assessing these materials adds considerable complexity to considerations of biological activity and toxicity.
Risk changes significantly when you make a transition to the use of materials at the nano-scale, Colvin points out. "Any new technology brings new risks," she says, citing the examples of DDT that helped curb malaria, pesticides that improved crop yields yet turned out to be human carcinogens, and efficient refrigerants that led to the ozone hole. Clearly one of the looming questions is: Can we do better job of dealing with these hazards and risks than we have in the past?
But, cautions Colvin's colleague Kristen Kulinowski, "we don't want to throw the baby out with the bathwater. The medical applications have enormous promise. There could indeed be a cure for cancer. There's enormous promise for bioremediation products. The goal is not to condemn or exonerate nanotechnology because we don't yet have answers about product behavior, but to head off or anticipate problems before they occur—not just in post-market scrutiny"—that is, after they are already in the marketplace.
What makes this even more complicated is that in addition to their novel size-dependent properties, nanomaterials are also structurally complex. James Hutchinson of OSU explains that nanomaterials are typically engineered to have what's called a core and a coating—a shell made out of one material surrounding a core of another. Both core and shell can vary in size (or thickness) and chemical composition. These variations will determine how a nanomaterial interacts with other substances, and thereby influence a nanomaterial's biological activity and, hence, potential toxicity. Those working in nanotechnology call this set of variations on a set of chemical combinations a "library" of materials.
As this is being explained to me, I remember exercises from my elementary school "new math" workbooks where we were asked to list permutations based on a list of ingredients: how many different combinations could you make, we were asked, given a hot dog, ketchup, mustard, sauerkraut, cheese, lettuce, mayonnaise, and two slices of bread. Add a hamburger to this list, and see how the variations expand. Now imagine that the behavior of that hamburger or hot dog—the taste, the smell, how it could be digested, and even its nutrients—might completely change depending on the addition of condiments and you begin to get an idea of what's involved in assessing libraries of nanomaterials. "Nanoma-terials have dynamically changing surfaces, kind of like the corona of the sun," explains Kulinowski. So to understand a nanomaterial's environmental impacts, one must assess the behavior of a whole suite of these variations.
Part of the research going on at Colvin's lab at Rice and Hutchinson's at the University of Oregon is a systematic attempt to characterize "libraries" of nanomaterials in order to understand their environmental impacts. This will help develop what Hutchinson calls "design rules"—or guidelines—intended to prevent creation of hazardous and toxic products. "Will there be any really nasty surprises coming from nano?" asks Terry Collins, director of the Institute for Green Oxidation Chemistry at Carnegie Mellon University. "People in chemistry get excited by technical performance. But we can't assume there will be no interactions with humans and we need to be aware that at the molecular scale of nanomateri-als, barriers present for larger materials will not be present. At the molecular scale, these substances can permeate our bodies relatively easily. There are an unbelievable number of interactions that are possible," he says, "so we need to be very careful."
These unknowns have prompted calls for caution from government agencies, academics, and citizen groups—in May and June of 2007 alone more than half a dozen such reports were released—and have since been followed by many more.9 A number of scientists working in the field, however, including Colvin, Collins, Hutchinson, and Karn see this concern as an opportunity to ask questions vital to protecting human health and the environment from what have often been called the "unintended consequences" of new materials and technologies. Their interest led in 2008 to the creation of the International Alliance for NanoEHS (Environmental Health and Safety) Harmonization, organized by a group of materials scientists and toxicologists from the United States, Europe, and Japan who will work on developing environmental, health, and safety standards for nanomaterials, standards that do not currently exist.10 This information will be available to scientists worldwide, and funding for this work will come from the participants' research institutions rather than from sponsors of a particular material or product. Both the extent of information-sharing planned and the noncommercial funding represent a departure from the traditional approach to both commercial chemistry and evaluation of its products.
"We need to learn from the past and think about issues of safety and sustainability as early as possible," says Colvin. "We need to engineer materials as safe materials from the beginning to understand the mechanisms of toxicity," she says, so they can be incorporated into the design and application of new materials. Given the chemistry and geometry of nanomaterials, understanding the full behavior of these molecules, whether they're destined for consumer products, pharmaceuticals, or industrial applications, requires even more scrutiny than it does with conventionally sized materials.
In advocating for this design-stage approach to new material safety, what Colvin, Collins, Hutchinson, and their colleagues are aiming to foster is a merging of green chemistry with nano-science. Hutchinson has called this a "proactive approach" to nanotechnology, with a goal of creating new materials with "high performance that pose minimal harm to human health and the environment."11
"Some of the same questions to ask about nano are the same questions we should be asking about any chemical materials," says Paul Anas-tas, director of the Center for Green Chemistry and Green Engineering at Yale University. "Can the substance get into the body? Can it be inhaled or absorbed into the skin? What does the substance do to the body and what does the body do to the substance? Is it persistent or bioaccumulative? Does it contain known toxics?" Anastas also cites the need for life-cycle analyses of nanomaterial to ensure that those that are deemed safe will be produced sustainably—to make sure the environmental footprint of the entire production process does not undermine the apparent efficiencies of using nanotechnology. But thus far, says Anastas, "these questions are only being asked by a fraction of practitioners."12
"Just like the rest of chemistry, nanotechnology is not exempt from biology," Collins points out. For example, "we need to understand that it's not a good idea to make a distributive technology [a product that's going to be produced at high volume and widely distributed] with a known hazardous substance such as cadmium. If you don't stay away from toxic elements, nanotechnology is just another way of distributing toxics."13
The complexity and many variations on the use of particular elements in nanomaterials makes assessing their toxicity a challenge that's been compounded thus far by a lack of clarity and agreement about what results of such testing actually mean. Right now, particularly where consumer products are concerned (where nanomaterials are inconsistently labeled at best), the kind of nanomaterials being used and any safety information that might exist for them are generally unknown. Given our experience thus far with unexplained new substances, erring on the side of caution is an easy impulse to understand. Nanomaterials also raise the issue of appropriate technology. If, for example, conventional materials work perfectly well in a lip balm, why introduce elements of the unknown by using a nanomaterials-infused product instead?
Colvin, only partially jesting, calls discussion of dangerous nanopar-ticles the "Darth Vader" side of nanotechnology. This dark side includes accidentally or incidentally produced nanomaterials that may unintentionally be inhaled or absorbed through the skin—and speculation about the impacts. Recently published papers indicate that inhaled nanopar-ticles of titanium dioxide and iron oxide may cause adverse impacts to lung tissue cells and that single-walled carbon nanotubes may cause damage to cardiovascular tissue and cause damage to lung tissue like that caused by asbestos fibers, for example.14 There is also some evidence that nanoparticles of titanium dioxide, such as those that are already in many sunscreens, as well as nanoparticles of other metals—zinc, copper, and silver—can damage beneficial bacteria, an impact that has the potential to harm soil and aquatic ecosystems.15
Part of the difficulty in assessing nanomaterials' safety and behavior is that we don't yet have templates in place to guide us to the appropriate questions. The current standard Material Safety Data Sheet poses questions about a material's behavior, which many environmental safety experts and advocates consider far from adequately rigorous for any materials, treats nanomaterials simply like macro or bulk materials. Yet already, workers are shaping materials based on nano-scale carbon, for example, into elements of aircraft, specialized technical machinery, and more ordinary things like bicycle frames. So it is crucial to know what sort of respirator, protective mask, or other gear will effectively block these infini-tesimally small particles from reaching nose, eyes, mouth, and skin. Understanding nanomaterials' behavior is key to understanding what sort of personal protective equipment might be needed. Again, nanomaterials' size-dependent properties adds to the challenge.
As an example of nanomaterials' complexity, Colvin explains that evidence thus far indicates that some nanomaterials constructed from carbon are environmentally benign, while others, in aggregated form, can be very toxic. Scientists working with nanomaterials however, are also quick to point out that nanoparticles do occur naturally and their properties have been used throughout history. But isolating these particles, creating engineered nanomaterials, and putting them into high-volume commercial production and into widely distributed consumer products is very different from knowing that it's the optical properties of nanoparticles of metal that impart color to stained glass.
To illustrate how many variations of a single substance used at nano-scale can complicate issues of toxicity, Colvin gives the example of a carbon nanostructure known as Carbon-sixty or C60. In some configurations, C60 is extremely hydrophobic and tends to gravitate toward oils and fats or lipids, and under certain circumstance will destroy fats in cell membranes and thus be very cytotoxic—poisonous to cells in general. But in other configurations, C60—the discovery of which won a Nobel Prize—is now being used to create specifically targeted drugs and to build artificial membranes.
Even more difficult to assess than how nanomaterials will behave in a controlled or constricted environment—including within a cell—is how they will behave when released to the global environment. While some studies have shown certain nanomaterials to have little impact on soil microbes (to offer one example of environmental behavior) some nanoma-terials have been engineered specifically to destroy microbes, while others not intended to damage bacteria apparently do.16 Andrew Maynard, science adviser to the Woodrow Wilson Center Project on Emerging Nanotechnologies, poses a question about antimicrobial nanomaterials similar to one that has been running through my head. What we're talking about are the nanoparticles of silver that are now being used to keep socks and underwear odor-free. "They're reasonably safe under certain circumstances," says Maynard. "But in the environment, what would happen over time?" he asks. What would happen after disposal of the finished product that contains these nanomaterials or the disposal of the antimicrobial agent itself? "Could they carry on killing microbes for years and years, knocking out a bottom layer of the ecosystem?" asks Maynard. At this point we simply don't know.
Dr. Peter Lichty, occupational medical director at the Lawrence Berkeley Laboratory points out that from a laboratory perspective nanomateri-als are not dramatically different from other new materials created in the lab. "We create very small quantities of material and follow OSHA lab safety standards and have chemical hygiene plans that protect individuals from materials of unknown properties," he tells me. When the lab disposes of nanomaterials that it has used or created, they're treated as hazardous waste. Lichty also points out that laboratory and commercial production procedures tend to vary significantly. Commercially, speed is often a priority and materials are used in large quantities compared to laboratory use, which is typically more controlled and entails only small quantities that are more easily contained. (This, I think, as he describes commercial production, is where we begin to get into trouble.)
But overall, says, Lichty, despite careful work and precautions, "Toxicity information is not sufficient at this point."17
This information gap is what led the Berkeley City Council to initiate conversations with the Lawrence Lab and the University of California that resulted in guidelines for the local production and disposal of nano-materials—the first such ordinance in the United States. Cambridge, Massachusetts—another research hot spot—is now considering community oversight procedures for nanotechnology, and other such regulations are likely to follow elsewhere. "Why did the city do this?" Berkeley city councilor Gordon Wozniak asks rhetorically. "We have a very active citizenry and we're concerned about a lot of things, including health risks in general. There was a general concern that [nanotechnology] was all unknown and we should be careful," he says.18
So, Colvin asks, "How do you create a safe system for these materials? How do you make decisions with a science in progress?" Part of what makes developing safety protocols, let alone standards for nanomaterials so complex, Colvin reminds me, is that "there are so many permutations of a nanoparticle that it upends the traditional strategy of single-item toxicology."19 This means that new safety procedures are needed for handling, working with, and producing nanomaterials—something being called for by industry and scientists, and also now by governments. In 2005, however, less than 4 percent of the U.S. federal spending budget dedicated to nanotechnology was designated for environmental, health, and safety research.20 In 2007, I was told off-the-record by an EPA official that much of the oversight of nanotechnology that had been done was being carried out not by the federal government but by the Wilson Center and other institutions, although much of this research did receive EPA funding. The implication was that the federal government had fallen behind on the job and that the Bush administration let that happen.
Since then, there has been a litany of reports—including from the National Research Council—pointing out lack of oversight in nanotechnol-ogy, the lack of resources currently available for such work within the U.S. Food and Drug Administration and Consumer Product Safety Commission, and the lack of adequate safety testing for nanomaterials cur rently in consumer products, now processed foods among them. According to the Wilson Center, as of December 2008, the worldwide nanotechnology food market was estimated to grow to more than $20 billion by 2010. By the center's count there were already some 84 consumer products in the food-and-beverage sector that manufacturers claim are nanotechnology products.21
There has now also been a flurry of efforts to regulate nanotechnol-ogy. In January 2009, a nanotechnology research bill that would increase funding for environmental health and safety work was introduced by Representative Barton Gordon of Tennessee along with twenty-one cosponsors and support from the House Science and Technology Committee. At about the same time, Canada proposed legislation that would require companies using nanotechnology products to detail their use. And under a law passed by the European Union in March 2009 that will become effective in 2012, all cosmetics made with nanomaterials will have to undergo safety testing and have all such ingredients listed if they're to be sold in the EU.22 But as of April 1, 2009, the United States has no specific provisions for testing the safety of products containing nano-materials or any labeling requirements for such products.
Currently, for practical purposes—as far as consumer products are concerned—nanomaterials are generally being treated like any other new synthetics that come onto the market. They have been launched into commercial production with little real knowledge of what their long-term environmental or health impacts may be. And while green chemistry advocates like Anastas, Colvin, Collins, and Hutchinson have articulated quite clearly—both in terms of policy and their own work—how important it is to consider the full range of nanomaterials' impacts at the design stage, the products of such thinking have yet to become the norm.
At a "Safer Nano" conference I attended in 2007, I listened to a presentation that described a series of nanomaterials that were layered compounds with reactive properties that can be used in insulation and cooling materials. (One possible application is in vehicle upholstery.) One of the compounds described contained antimony, lead, silver, and tellurium. "Lead. What is lead doing in a 'safer' material?" I wondered. Aren't we now keeping children off playing fields coated with artificial turf because it contains lead dust and taking toys off shelves because of lead contamination? And these now-barred products have big—not nano-scale— particles of lead. After decades of being misled that the lead content in paint was not a health hazard, why should the public accept the assurance that lead in a nanomaterial that heats car seats is not a problem? The amounts of lead in such a product might be so small as to be insignificant even by the most sensitive measures of health effects. On the other hand, the particles might be so small as to create new problems. Again, at this point we just don't know. And the challenge is to figure out how to develop transparent and effective testing that will protect public and environmental health but not impede innovative technology.
Thousands of synthetic chemicals have gone into high production volume and into innumerable consumer products over the past 100 years. Many have later been found to be toxic to human health and the environment. In most cases—with the possible exception of genetically modified and irradiated food—there has been little, if any, public outcry about these substances or technologies prior to the discovery of serious problems. Nanotechnology, with its futuristic-sounding nanotubes and fuller-enes, its promise of materials that can self-assemble, and its alluring applications, has captured public attention in an entirely different way. Still, a poll released in December 2008 found that nearly half of the thousand Americans surveyed said they had heard nothing about nanotechnol-ogy—an indication that relying on public pressure to result in public health protection may not be adequate.23
Precisely because nanomaterials are distinctly different from others, they create a special imperative, says Paul Anastas, "to get things right at the design stage." With nanomaterials, says Anastas, we need to have "innovation by design and not by accident." And because the products are already on store shelves, in our kitchen and bathroom cabinets, it is especially imperative that we begin to catch up with this avalanche of new materials. Anastas adds: "We're on the verge of having a very scared public—irrationally in some cases—if we don't ask the questions that could cut the risks."
If the unknowns of nanotechnology prompt such questions about the environmental and health impacts of these new materials' molecular design—and time is taken to answer them thoroughly as these materials are being designed, not after they're in commercial use—then, as Terry Collins suggests, "Nano may be bringing green chemistry to the forefront." Clearly, there is a lot of catch-up to do and it will not be easy, but if, as has been proposed, nanotechnology practitioners and innovators collaborate and share information, it might indeed be possible to begin to get this right.
Continue reading here: Toward a Greening of Chemistry
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