Earth & Sky

More with Dr. Pinkerton:

I should explain that we are just beginning our studies, so we are also in the process of learning exactly, just what are nanoparticles and nanomaterials. My research in the past has been looking at airborne particles and potential health effects of breathing in particles. Primarily, these are particles though that we find in the environment, either through just natural consequences of burning or combustion or emissions that might come from power plants, or from automobiles or from diesels, that sort of thing. And so, we’ve had quite a bit of experience looking at these types of environmental particles that seem to be fairly ambient, because they seem to be everywhere. And the work to do with nanoparticles somewhat overlaps with that, because my understanding of nanoparticles is just simply that these are very tiny particles that are less than 1/10 of a micron in diameter. And so, when we look at ambient particles in our environment, many of those particles are on that scale. So, this is new in the sense that we’ll be looking at particles that are manufactured, and are not simply a byproduct of something, but simply are of the same scale. So it really is a new and exciting field for us to investigate.

I think that nanotechnology is a new and growing area. It really is not defined as just a single field because it’s going to have tremendous applications across many different products and many different applications. But, one item that it shares in common is that these are solid pieces of matter that are almost impossible to comprehend because they tend to be so small. Therefore, they are going to have different, unique properties that we may not be aware of because we’re only accustomed to things being on a larger scale than nanoparticles.

Well, if we’re just talking about nanoparticles in general, that is the majority of the particles that are found in the environment. About 95–98% of all particles that are present in the environment are less than a micron in diameter. In fact, these particles are so small, that not even rain will remove them from the environment. They actually act more like gasses than particles. When a droplet of water comes through the air, these nanoparticles will actually be moved out of the way. So, in a sense, that’s a really unique feature about this type of potential particle in our environment. That, they’re not going to be removed by the natural ways that other particles are removed, such as when it rains, we always see that the air looks so clear and clean, and yet particles that are at the scale that we designate as nano, they cannot be removed by those natural processes. And at the moment, nanomaterials, and especially manufactured nanomaterials, they’re probably very few of those materials in the environment, as far as we know. This is something that is simply a new area, and since we do know about nanomaterials that are produced by combustion, and the difficulty of removing them from the air, I think our concerns would be if manufactured nanomaterials also become airborne, how easily would they be removed from the air, and what eventually will be their fate in the environment. Will they be broken down, or will they remain as the original material that when they were manufactured. So it’s really something where I don’t think we want to give the impression that nanomaterials are already bad, or they are hazardous. I think that we still need to understand better what characteristics they have. In the little work that we’ve done so far, we’re finding that some of the processed nanomaterials, such as carbon nanotubes, are very difficult to see them become aerosolized because they have such unusual properties based on the size and the surface of the particle relative to it’s mass. It’s so unusual, that they actually generate charges that look as though they prevent them from actually becoming airborne. But we really have questions about what happens over time, will those surface charges change? Will they be of such a change that it actually allows the particles to separate from one another and then become airborne? What happens if we combine them with other materials? Does that further change their properties in terms of how they are present in the environment, or whether, again, they can be aerosolized. And so the critical feature there is that if they are airborne, then they have the potential to be inhaled. But if they can’t be inhaled, if they don’t have the potential to become airborne, then they perhaps will not really represent any kind of health risk, at least by inhalation.

Well, nanoparticles in the environment can come from a wide variety of sources. For example, sea salt can be present in our environment at the nanoscale. Also, combustion of materials can result in solid particles that are of a nanoscale. And again, if these particles are less than 1/10 of a micron, they are very difficult to remove from the atmosphere because they have behaviors that do not necessarily cause them to settle out. Their mass is so negligible they don’t necessarily settle by gravity, and therefore they can remain suspended in the atmosphere for weeks, if not months, or longer. There are natural sources for nano–scaled particles as well. Volcanic eruptions, although much of the mass will fall out of the atmosphere, there are billions, and billions of particles that will remain suspended that will literally circle the globe and although they’re so small that individually, they do not come out of the atmosphere – they remain suspended – but they can also result in changes in the climate, in global temperature changes. So, it’s kind of along those directions that we wonder about manufactured nanomaterials. Could they be similar in properties for becoming aerosolized and remain in our environment for an indefinite amount of time. And again, as I say, right now, some of the nanomaterials that we’re working with have such unusual properties that they tend to cling together. You don’t see them as individual particles. But yet they are literally billions of particles massed together. And again, if there are things that may change those properties to allow them to disaggregate and become single particles, then there’s the possibility that they may become aerosolized and remain in the atmosphere for long periods of time.

It may be due to different forces that are placed on them, a charge, maybe the manner in which they are manufactured may also influence whether they are created as single particles and if so, then they can become aerosolized in that way. What is interesting is that these particles, because of their surface to mass ratio, they have very unusual properties. And that’s what makes them so exciting. They can take on different properties from what we’ve ever seen before. But associated with some of the materials, at least with carbon nanotubes, they tend to have a surface charge that’s associated with them that causes them to be attracted to one another. But if you remove that surface charge, then they will disaggregate. And we know that in the airways, that we actually have a charge that’s in our airways that actually may interact with the charge of a nanoparticle to cause it to disaggregate. So, even when particles are clumps, I mean we may actually have a billion particles that are as a single clump, but still, because of the individual size of each of the particles, they’re so small, it’s still a billion particles that might be easily inhaled into the lungs without any problems at all. And then if they land on a surface, there’s a possibility that there may be interactions that take place with these particles and the biological systems of the cells that are there that may cause them to disaggregate and disperse. And again, these are the types of questions that we’d like to address in our future research to see what exactly might happen. Our problem is that we just don’t know. We have ideas, but we don’t have any data to tell us what the potential effects may be.

I anticipate that our studies will primarily be done in small laboratory animals. So we’ll be working with mice and rats, doing inhalation studies. We have designed a special system that allow us to take very, very small amounts of material and aerosolize them in a system so that we can actually work with very minute amounts of materials over a long period of time, to aerosolize them and have the animals be able to breath them in a natural setting so that we can look at the potential effects that are there. These systems are not something that we can go down to the local store and buy. We have to design them and test them out. At the moment, we are testing a number of nanomaterials to see how the system is working. We’ve been using some carbon nanotubes for our work; we’ve also been using carbon black, something that’s been used for tremendous amounts of time for toner materials, things like that. We’re beginning to see some successes. We actually have now (this week) been able to generate small volumes of this material that are in concentrations well below the air quality standards, form the sense that we are not even close to what would be considered a harmful concentration of particles in the air. But we figure that from these initial steps we’ll begin to do studies with laboratory rodents to look at short–term effects of exposure. These studies will just allow us to look to see if there are changes that occur in terms of the inflammatory cells that are present in the lungs that help to maintain the sterility. We’ll see if there are any changes or recruitment of new cell into the lungs to remove these particles from the airspaces. We’ll look for changes in cell permeability. We’ll look to see if cell begin to show injury and die. We’ll look for protein levels within the lung lining layer, the ling lining fluids. And these will be our initial steps to look at it. One of the things that we’re most interested in is the fact that when you manufacture many of these nanomaterials, there are small trace amounts of contaminants that are associated with it. And we’re particularly interested in the potential effects of metals that may be a trace contaminant in these materials that are incredibly hard to remove. So when a nanomaterial, such as carbon nanotubes are produced, they will have small amounts of metals that are present. And we want to look at whether those contaminants may produce health effects as well as the nanoparticles themselves. And these metal contaminants are on this nanoscale as well.

Yes, the Environmental Protection Agency has given us a grant that will be for three years, and we are working with a chemist here at UC Davis who is an expert in nanotechnology and the manufacture of carbon nanotubes. And, we anticipate being able to do studies beginning this summer that will go on for a couple of years. And hopefully, we’ll start getting some information on all of this. It’s interesting too with carbon nanotubes, one of the reasons why I’m quite interested in both is that those are fibers, and my initial research was in asbestos, which is a fiber. I’ve always been curious – we know that asbestos fibers are quite toxic. And, some of that toxicity is due to that shape. A carbon nanotube is also a fiber. And, it will be of interest if there is any toxicity associated with its shape as well, although granted it is an incredibly small particle.

I think that the concentrations of nanomaterials that we’ll be using are more representative to what one might experience in an occupational setting. So, these initial studies are really designed to look at concentrations of nanomaterials that may be present during the process of their manufacture. And, we don’t anticipate these initial studies to necessarily reflect nanomaterials that are introduced into the environment because our concentrations would be more of an occupational level than an environmental level.

And I wouldn’t want to give the impression that we’re anticipating similar properties between asbestos and carbon nanotubes, or nanowires. It’s just simply that they are of the same shape, and we know that part of the toxicity is due to the shape for asbestos. Carbon nanotubes, in contrast, are so small that their shape should not create a problem in terms the materials and removing them from the lungs. But again, we really don’t know. Again, it seems like this is life. We start out with very large things, and now everything is miniaturized, and this is just another example for me. When we first started doing asbestos research, we certainly knew of its toxicity, we just didn’t understand the mechanisms by which it produced its harmful effects. And, I think that with carbon nanotubes, it’s the same thing. I guess there are studies that show if you instill carbon nanotubes into the lungs of small animals, they actually will produce injury to the lungs. But again, that’s not the way in which we would be exposed to those particles in an occupational setting or an environmental setting. It’d be more by simply inhalation rather than our instilling that material into our lungs. But again, it’s just interesting to see that toxicity has been found with the materials, but at unnatural levels of exposure. So, what happens if we now bring it down to what one might experience if they’re in the process of manufacturing these materials, and eventually, what would happen if they are introduced into the environment at even lower levels. Would we see effects? And that’s really the bass for the research that we wish to pursue through funding with the Environmental Protection Agency.

Well, I guess that I would have to say that I really just don’t know. We know that there are many particles that are present in the environment, such as smoke, such as combustion materials that have potential toxic effects to the respiratory system, and that’s simply because they can gain access to the respiratory tract and interact with the fluids and the cells that make up the lungs. So we can only assume that if a nanomaterial can gain access to the respiratory system, that there is the potential for similar interactions to occur. But we just are not knowledgeable about what those interactions may be. Certainly, we know that surface and size of the particle are very important for gaining access to the lungs, and even for them being able to penetrate into the cells and into areas where they may be retained for prolonged periods of time. One of the features of a very small particle is the fact that it can get to places where large particles can’t, from just simply to being inhaled, to then depositing on a surface, then being taken up into cells, that other particles, that would not happen. And, what the potential interactions may be once a particle is inside a cell is very different from when it’s outside the cell. So again, we need to do new research, additional research, to find out what those potential interactions might be. We think that anything that damages membranes, anything that generates free radicals, which are basically changing molecular oxygen so that it has an additional electron, it can create all sorts of problems with cell membranes, with proteins, and with the DNA as well, to create changes that possibly may have adverse consequences in the long term.

I would just simply say that I’m very excited with nanotechnology. I think it’s a wonderful, exciting, new area that will potentially have tremendous benefit to many individuals, to many different applications. And I think that all we want to do is to make sure that we’re safe in the process of improving our lives with new materials like nanomaterials.

I think it really may depend on the properties and the features of each of the nanomaterials that we’re talking about. Right now, with our perspective of working with carbon nanotubes, we have the materials in an open beaker, and we’re not doing anything that would be unusual in terms of the way that we’re trying to protect ourselves from this, and it’s simply because of the fact that it has such unusual properties that, I guess at the same time I guess we’re being a little bit naive from the fact that we just really don’t understand these materials. And so I guess the best thing for us to do is to look at these with trying to take every precaution that we can before we really make a judgment about whether they are safe or not. But again, the carbon nanotubes are made at such incredibly high temperature, several thousand degrees of temperature, in the process of manufacture those have to be contained in a furnace away from oxygen. Otherwise, they just simply burn up. And so, much of the manufacture of these materials is done in a way that they’re kept away from the worker. And because they’re so expensive, there are many steps that are present that avoid the loss of these materials, even in the workplace. But again, as they’re manufactured on a larger scale, then the potential for their release into the environment, into the workplace will become greater. And again, I think we just simply have to learn more about them to use the best safety practices when we’re working with this type of material.

Thanks to:

Kent Pinkerton
Professor–In–Residence in the Institute of Toxicology and Environmental Health at the University of California, Davis