Nanomaterials' Fate: A Conversation with Mark Wiesner
Mark Wiesner, professor of civil and environmental engineering
Mark Wiesner, professor of civil and environmental engineering at Duke’s Pratt School of Engineering and an expert on the transport and fate of nanomaterials in the environment, was an invited speaker at BioVision 2007: The World Life Sciences Forum taking place in Lyon, France, from March 11-14.
According to the BioVision web site, the forum addresses global issues in the life sciences in an effort to “mobilize foremost specialists along with policy makers, members of government, ethicists, decision-makers, researchers, consumer representatives, patients associations, NGOs & media, with the aim of fostering open debate and exchange between Science, Society at Large and Industry.” Speakers at this year’s event included several Nobel Prize winners, the former head of the World Health Organization and many others.
Pratt science writer Kendall Morgan talked with Wiesner prior to the meeting about some of the issues he planned to raise during his presentation in France.
Pratt News: Can you tell me a little bit about what you plan to discuss at the Biovision meeting next week?
Wiesner: The meeting, as you might gather, is not specific to nanotechnology. It looks at a broad range of issues having to do with technology and issues associated with health very much on a global level. The thing they had asked me to speak about addresses the issue of nanotechnology as it might have impacts on human health and the environment, and the impacts can be positive or negative. There’s the whole aspect of various technologies that we can create for taking pollutants out of air and water, remediating hazardous waste sites, generating energy in a more environmentally benign fashion and so on, but then there’s also the issue of the impacts of these technologies and underlying materials on the environment from a negative perspective. Some have suggested that these might be a whole new class of emerging contaminants. Perhaps the best way it has been summarized is with a question: “Is this the next best thing since sliced bread, or is this the next asbestos?” And it’s a question, we don’t know.
Pratt News: While nanomaterials are relatively new, are there historical examples that demonstrate some of the issues now raised by them?
Wiesner: The Nobel Prize for creating [the pesticide] DDT went to a chemist, MÃ¼ller, in the ‘40s with the notion that this is going to eradicate malaria, this is a wonderful thing. As we learned more and more about that particular chemical product and as the product was used and abused to a great degree -- people started applying it, lathering it on pretty thick in some places of the world, the United States in particular, and not always just for mosquito control, right, all sorts of various pesticide applications -- the result was we saw all these very negative environmental impacts and the question looking back retrospectively is: Could we have foreseen the impacts if we had thought about the chemical a bit more initially? It should be noted perhaps that the World Health Organization has rehabilitated DDT. Now, they are saying there really are places where we need to think about its use to control malaria.
A microscope image of tiny calcium particles precipitated on a membrane. Credit: Wiesner
Pratt News: There still aren’t safer alternatives to DDT?
Wiesner: There’s really nothing as good. And, I haven’t looked in detail at the studies, but my sense is that when you look at the benefits that accrue to human health in reducing malaria versus the risk that the benefits, in those limited applications, come out on top.
Pratt News: And bringing this back to nanomaterials?
Wiesner: These are the same sorts of balances that we’re confronted with as we look at nanomaterials, except it’s much less certain. We have new materials that are going to find uses that we can’t even imagine. We even have a hard time trying to predict the quantity of these materials that might be produced and the whole life cycle of the materials, again what products they’ll be incorporated into, how those products will be used, the exposure of the workers making the material, when the products are thrown away, where they will be thrown away, the conditions that might lead to the release of nanomaterials in the environment and how they might make it into air, water, soil and so on.
Pratt News: Given so many unknowns, how do you even begin trying to determine what the impacts of nanomaterials might be?
Wiesner: It’s a very dynamic process and one that is riddled with challenges, some of them ethical. We’re not allowed not to ask the question anymore, you know after our experience with products like DDT and asbestos and freon and a whole list that you could go down. We need to ask the question. And the kind of research required to answer those questions and the way that you deal with the information that comes out of that research involves some important decisions just in their own right. For example, it’s a relatively complex system, what are the best choices for research initially? Risk has two components: exposure and then effect. Well, with the limited sums that we have, how much do we research in the area of exposure -- where these things will go, how persistent they’ll be in the environment, whether they’ll break down and transform -- and how much of this research do you do on the effects -- if they arrive at a given human or ecological target, will they have a mutagenic or toxic effect, just to give an example. Making choices about broad areas of research, exposure versus effects, is one issue.
Then you have all these various nanomaterials. Right now we don’t have general principles. We don’t even know how to necessarily name these things or differentiate them let alone in many cases measure them, so there are a lot of research issues that really are targeting that aspect of it -- trying to come up with categorizations of nanomaterials that might have some relevancy for predicting, ultimately, risk. Nonetheless, right now we more or less do these things on a case by case basis. You need to look at each nanomaterial as being a different substance that needs to be evaluated, and one nanomaterial can exist in many forms. One thing that makes it different from chemical compounds is you can think of these things as objects and these objects can group and interact. When they do so, their properties may change, so their mobility in the environment and their impacts on organisms can change and trying to categorize and describe those is a challenge. It’s, as I said, a dynamic process, a dynamic system, where you’re trying to fill in all the blanks on this field of unknowns and what we really need is a risk assessment framework that can be updated and respond dynamically to the information that we do have as it becomes available.
Another topic that we’ve worked on is just looking at how nanomaterials themselves are made. It’s what I call the Silicon Valley effect. Computer chips haven’t really caused to my knowledge a great environmental problem, but the production of computer chips has caused a problem. Groundwaters have become contaminated with organic solvents and metals and it could be that, as this new nanomaterials industry rolls out that if we don’t design the system as a system and reflect on it carefully at the outset, we might end up with environmental impacts just simply from the nanomaterials’ production independent of the impact of the nanomaterials themselves.
Pratt News: In light of your focus on the potential for environmental risk, do you still see a lot of promise in nanomaterials?
Wiesner: Oh, there’s tremendous promise. Just like we are not allowed to not ask the question about the risks that these materials cause, I don’t believe we’re allowed to turn our back on the various benefits that this approach can yield. The potential for saving energy through reduced losses in transmission and improved storage devices, the potential for generating electricity and other sources of energy through nanomaterials is huge. The molecular manipulations that are characteristic of the nanochemistry approach are going to be important in everything from drug delivery and medicines to molecular electronics to common consumer goods, and so I think the potential there is great.
Pratt News: Is this nanostuff regulated in any kind of way?
Wiesner: There are not really any regulations specific to nanomaterials to my knowledge right now. There are many issues before you could put a regulation in place that one would have to address. First of all, what are you regulating? What would you call it? I’ll give you one example: there is a material, a nanomateiral, that looks like a soccer ball, C60. It’s 60 atoms of carbon that make a ball about 1 nanometer, a little over 1 nanometer, in diameter. Those atoms can form aggregates and it looks like the aggregates have different properties with respect to both mobility and therefore exposure and then ultimately toxicity. What do you regulate? Do regulate C60, do you regulate the aggregates of C60? If you regulate the aggregates, what size aggregate becomes an issue? Is it when you have two C60s, 10, 1,000, 10,000? So just simply naming it is one issue.
The way we make regulations in this country typically is on a risk-based paradigm and that means that you understand the potential for exposure and impact, so that you can weigh the calculated risk that results against other sources of risk and then decide on the appropriate level of regulation. What level would we pick when we don’t yet know about exposure and hazards and effects that result from the materials?
Finally if we knew all of the above, how would you measure it? We don’t have nanoprobes that can go out there and specifically measure many of these materials. So there are just so many steps, in very practical terms, that we need to address before we can reasonably come up with regulations.
Now, one could take a different approach, a precautionary approach or principle, and say we don’t have all the data and therefore we’re not going to allow or use this material at this time, and some people have advocated for that. The problem with that again is what will you then ban? Many things that we commonly use involve the production of nanomaterials. Do you ban the use of the titanium dioxide nanoparticles that go into most of the paints we put on houses? Are those nanomaterials? They weren’t called nanomaterials a few years ago and now, if you began to put those labels on it, they might be considered nanomaterials.
Pratt News: That brings up an interesting point. What really is the difference between a nanomaterial and a traditional chemical or material?
Wiesner: It’s not at all clear yet. What’s fascinating about many of these materials is they exist right in the grey area between what we traditionally think of as molecules that might be individual species in a continuum like water or airÂ…and then the idea of a particle, which is a higher order assembly of many molecules. They have properties that in some case are useful to look at from a molecular standpoint, for instance their spectroscopy, some of their electrical properties and so on. Those behave very much like we expect molecules to behave and we measure them in a fashion similar to that. On the other hand, some of their behavior looks more like a separate phase composed of a number of these molecules, where you have an interface between one phase, the nanoparticle, and then the surrounding fluid. It’s a fascinating area and we’re still trying to struggle with what all the appropriate tools are for looking at their properties.
Pratt News: Given the rate at which nanotechnology is progressing, how quickly do the issues you’re talking about need to be addressed to avoid ending up with another DDT?
Wiesner: We’re working as fast as we can. You know, working too quickly and too hurriedly has its own ethical dimensions. There was, most likely with the best of intentions, some early research that pointed to toxicity of certain particles, of certain kinds of nanomaterials, early on that is widely cited in the press. I mean it’s become urban mythology that, for example, if you modify the surface chemistry of certain nanoparticles that we know what the mechanism is by which it will change their toxicity. In fact, we don’t really know that their toxicity will change and we certainly don’t know the mechanism, and yet laws could potentially get based on the notion that we do know that information. So there’s this balance between turning out information quickly as we know things and also being responsible in the way that we release these data and communicate these data so that we act responsibly in the social side of the equation.
Pratt News: You mentioned that there are lots of kinds of nanomaterials, and you’ve mentioned C60 specifically, what are some other nanomaterials that are attracting your attention right now?
Wiesner: We’re very interested in all the carbon-based, or fullerene-based, nanomaterials, so C60 is one, but there’s an absolutely world class guy here at Duke, Jie Liu over in chemistry, who makes carbon nanotubes. We’re very excited about the potential for collaboration with him in looking at the uses and abuses of those materials. We continue to do work with other nanomaterials. We actually in my group have developed one kind of nanoparticle, an iron nanoparticle, called a ferroxane nanoparticle. The uses of that have some very interesting potential in fuel cells, for making improved fuel cell membranes. We’re looking at quantum dots, at titanium dioxide and other mineral nanoparticles. The whole gamut is of interest to us.
And there are just so many exciting people to work with here at Duke, like Anne Lazarides in materials, Adrienne Stiff-Roberts and Rob Clark, and certainly Kam Leong over in biomedical engineering, and we’re working with people in the medical school, I mean it’s just a really exciting environment here.