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Living with nanoparticles
OPINION
Living with nanoparticles Read some accounts of nanotechnology risks, and you might be forgiven for concluding that a single engineered nanoparticle can kill you. Andrew D. Maynard | Woodrow Wilson International Center for Scholars | [email protected]
A little critical thinking soon dispels this notion – we are constantly bombarded with incidental nanoparticles (NPs) from sources that include cars, incinerators, and fires; we have been since birth. And as critics of ‘risk extremists’ often point out, we seem to be doing just fine in this nano-rich environment. But does this mean that the potential risks associated with engineered NPs are little more than a myth? As I write this, sitting in my favorite coffee shop, I am breathing in four billion NPs per minute. I know this because I have a portable condensation particle counter sitting on the table next to me – courtesy of aerosol instrument manufacturer TSI Incorporated. This sounds like an awful lot of particles to be inhaling, and I must admit that my barista is looking a little peaky (although I’m not sure the NPs are to blame on this occasion). Yet, it underlines the reality that exposure to NPs is a fact of life, and our bodies do a pretty good job of handling them. It’s something we as a species have evolved to deal with through millennia of being exposed to naturally occurring nanosized clumps of matter in the air. But before we get complacent about allowing any foreign matter into our lungs, think about this: occupational illness has been associated with inhaling airborne particles for thousands of years, and remains a major cause of ill health within workplaces today1. Between 1990 and 1999, there were over 30 000 deaths in the US associated with occupational exposure to airborne materials2. Predictions of worldwide deaths from asbestos exposure lie between 250 000 and 400 000; and, in the UK, deaths as a result of asbestos-related mesothelioma are not expected to peak for another ten years – despite imports and use of asbestos peaking in the 1960s3. In the general environment, estimates of the number of people who died from
64
inhaling particles in the London smog of 1952 are as high as 12 0004. At a more subtle level, exposure to fine airborne particles has been associated with an elevated likelihood of dying, and there is increasing evidence linking nanoscale particle exposure with impacts on the cardiovascular system5. Some – but not all – of these figures are associated with particles that are not nanoscale. But they are all associated with respirable particles – capable of reaching and depositing in the deepest parts of the lungs, as NPs do. The message is clear – we ignore the dangers of inhaling airborne particles at our peril. The trouble is, all NPs are not created equal and to generalize will be to make mistakes – perhaps costly ones. Our knowledge of airborne particles in general and incidental NPs in particular illuminates our approaches to engineered NPs. But just as the health risks from asbestos, vehicle emissions, and welding fume differ, we will not be able to derive everything we need to know about engineered NPs just by looking at the incidental varieties. While we have evolved to deal with naturally occurring NPs, do we know how our bodies will cope with engineered NPs that are not found in the natural world? We know that we have a hard time dealing with chemicals that do not occur naturally – will the same hold true for nanomaterials? And could precisely engineered NPs interfere with our biology in new and unusual ways? I don’t know the answers to these questions, but I suggest that as our confidence grows in engineering increasingly sophisticated nanostructured materials, we make sure our knowledge of their likely impact keeps pace. And there is still the issue of dose – how much material is needed to cause damage? “The dose makes the poison” is the toxicologists’ mantra – acknowledging that the most toxic substances
FEB-APR 2008 | VOLUME 3 | NUMBER 1-2
can be harmless (or even beneficial) at low enough doses, while nothing is good for you in excess. Four billion particles per minute might sound like a lot, but it is a minuscule amount of material when you consider the mass – I am probably inhaling no more than 50 ng (nanograms) of NPs per minute in the coffee shop, and only for a few minutes. (In contrast, a highly toxic dust like crystalline silica has an occupational exposure limit that equates to inhaling around 1000 ng per minute over eight hours. The equivalent limit for something like TiO2 is a whopping 300 000 ng per minute.) Yet recent toxicology studies suggest we might have to rethink how we evaluate NP dose – it might be the number of particles that is important in some cases after all, and not the mass. The critical step is to be clear about what is important, and not to overgeneralize. I can drink my coffee and inhale the local NPs with no obvious ill effects because I’m not exposed for that long and my body knows how to deal with them. There are probably plenty of engineered nanomaterials I could do the same with. I know that a single NP won’t kill me – probably a few billion wouldn’t be enough to do much damage. But I’m under no illusion that all engineered NPs will be safe, just because I’m breathing in incidental NPs all the time. We need to get the science right and avoid speculation if possible. Now, where’s my coffee... REFERENCES 1. Maynard, A. D., and Kuempel, E. D., J. Nanoparticle Res. (2005) 7, 587 2. Work-related lung disease surveillance report 2002, 2003-111, DHHS (NIOSH), 2003 3. Late lessons from early warnings: The precautionary principle 1896-2000, European Environment Agency, Denmark, (2001) 4. Dooley, E. E., Environ. Health Perspect. (2002) 110, A748 5. Mills, N. L., et al., N. Engl. J. Med. (2007) 357, 1075
Living with nanoparticles Read some accounts of nanotechnology risks, and you might be forgiven for concluding that a single engineered nanoparticle can kill you. Andrew D. Maynard | Woodrow Wilson International Center for Scholars | [email protected]
A little critical thinking soon dispels this notion – we are constantly bombarded with incidental nanoparticles (NPs) from sources that include cars, incinerators, and fires; we have been since birth. And as critics of ‘risk extremists’ often point out, we seem to be doing just fine in this nano-rich environment. But does this mean that the potential risks associated with engineered NPs are little more than a myth? As I write this, sitting in my favorite coffee shop, I am breathing in four billion NPs per minute. I know this because I have a portable condensation particle counter sitting on the table next to me – courtesy of aerosol instrument manufacturer TSI Incorporated. This sounds like an awful lot of particles to be inhaling, and I must admit that my barista is looking a little peaky (although I’m not sure the NPs are to blame on this occasion). Yet, it underlines the reality that exposure to NPs is a fact of life, and our bodies do a pretty good job of handling them. It’s something we as a species have evolved to deal with through millennia of being exposed to naturally occurring nanosized clumps of matter in the air. But before we get complacent about allowing any foreign matter into our lungs, think about this: occupational illness has been associated with inhaling airborne particles for thousands of years, and remains a major cause of ill health within workplaces today1. Between 1990 and 1999, there were over 30 000 deaths in the US associated with occupational exposure to airborne materials2. Predictions of worldwide deaths from asbestos exposure lie between 250 000 and 400 000; and, in the UK, deaths as a result of asbestos-related mesothelioma are not expected to peak for another ten years – despite imports and use of asbestos peaking in the 1960s3. In the general environment, estimates of the number of people who died from
64
inhaling particles in the London smog of 1952 are as high as 12 0004. At a more subtle level, exposure to fine airborne particles has been associated with an elevated likelihood of dying, and there is increasing evidence linking nanoscale particle exposure with impacts on the cardiovascular system5. Some – but not all – of these figures are associated with particles that are not nanoscale. But they are all associated with respirable particles – capable of reaching and depositing in the deepest parts of the lungs, as NPs do. The message is clear – we ignore the dangers of inhaling airborne particles at our peril. The trouble is, all NPs are not created equal and to generalize will be to make mistakes – perhaps costly ones. Our knowledge of airborne particles in general and incidental NPs in particular illuminates our approaches to engineered NPs. But just as the health risks from asbestos, vehicle emissions, and welding fume differ, we will not be able to derive everything we need to know about engineered NPs just by looking at the incidental varieties. While we have evolved to deal with naturally occurring NPs, do we know how our bodies will cope with engineered NPs that are not found in the natural world? We know that we have a hard time dealing with chemicals that do not occur naturally – will the same hold true for nanomaterials? And could precisely engineered NPs interfere with our biology in new and unusual ways? I don’t know the answers to these questions, but I suggest that as our confidence grows in engineering increasingly sophisticated nanostructured materials, we make sure our knowledge of their likely impact keeps pace. And there is still the issue of dose – how much material is needed to cause damage? “The dose makes the poison” is the toxicologists’ mantra – acknowledging that the most toxic substances
FEB-APR 2008 | VOLUME 3 | NUMBER 1-2
can be harmless (or even beneficial) at low enough doses, while nothing is good for you in excess. Four billion particles per minute might sound like a lot, but it is a minuscule amount of material when you consider the mass – I am probably inhaling no more than 50 ng (nanograms) of NPs per minute in the coffee shop, and only for a few minutes. (In contrast, a highly toxic dust like crystalline silica has an occupational exposure limit that equates to inhaling around 1000 ng per minute over eight hours. The equivalent limit for something like TiO2 is a whopping 300 000 ng per minute.) Yet recent toxicology studies suggest we might have to rethink how we evaluate NP dose – it might be the number of particles that is important in some cases after all, and not the mass. The critical step is to be clear about what is important, and not to overgeneralize. I can drink my coffee and inhale the local NPs with no obvious ill effects because I’m not exposed for that long and my body knows how to deal with them. There are probably plenty of engineered nanomaterials I could do the same with. I know that a single NP won’t kill me – probably a few billion wouldn’t be enough to do much damage. But I’m under no illusion that all engineered NPs will be safe, just because I’m breathing in incidental NPs all the time. We need to get the science right and avoid speculation if possible. Now, where’s my coffee... REFERENCES 1. Maynard, A. D., and Kuempel, E. D., J. Nanoparticle Res. (2005) 7, 587 2. Work-related lung disease surveillance report 2002, 2003-111, DHHS (NIOSH), 2003 3. Late lessons from early warnings: The precautionary principle 1896-2000, European Environment Agency, Denmark, (2001) 4. Dooley, E. E., Environ. Health Perspect. (2002) 110, A748 5. Mills, N. L., et al., N. Engl. J. Med. (2007) 357, 1075