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THE ENEMY WITHIN?Transmission electron micrographs of multi-walled carbon nanotubes in human epidermal keratinocytes. (From N. Monteiro-Riviere et al., Toxicol Lett, 155:377–84, March 15, 2005.)
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It's not often that an industry volunteers for tighter regulation and oversight. But that's just what happened this past June, when the Environmental Protection Agency hosted a meeting in Washington, DC, to discuss a voluntary pilot program aimed at collecting information on existing nanoscale materials in order to evaluate potential risks and exposures. The attendees, 150 scientists and officials representing industry, academia, government, and environmental and health advocacy groups, unanimously agreed such a system should be implemented.
But it won't be easy. Conventional approaches to risk assessment, toxicity screening, and ADME (absorption, distribution, metabolism, and excretion) modeling don't necessarily apply to nanoscale materials. Even nomenclature is a problem: Existing measures for regulating new chemical substances distinguish materials by name, not size. Thus, the Toxic Substances Control Act (TSCA) inventory, a listing of the more than 80,000 industrial chemicals currently produced or imported into the United States, classifies carbon nanotubes as a material chemically identical to diamond.
Yet nanoparticles (those smaller than 100 nanometers in diameter) often acquire properties absent from their macroscale counterparts; they may become stronger, lighter, more heat-resistant, or better electrical conductors, for instance. But they also can be more toxic, being readily inhaled into the lungs, absorbed through the skin, or transported across cell membranes. And nobody knows how long such materials may linger in or be cleared from the environment.
"While there is concern that the nanostructure-dependent properties of many engineered nanomaterials may lead to them being hazardous, the direct risk they present to human health will depend on the probability of exposures occurring, and the extent to which materials entering the body exhibit behavior associated with their nanostructure," says Julie W. Fitzpatrick, a scientist with the International Life Sciences Institute, who is developing toxicity screening strategies.
Too few studies have been completed, says Kristin Kulinowski, executive director for education and public policy for the National Science Foundation-funded Center for Biological and Environmental Nanotechnology (CBEN) at Rice University. "What we do know is that what may be true for one particular nanoparticle in one form or one application, may not be true for another," she says. "There have been some studies that have pointed out particular effects of nanoparticles on certain systems, such as cells in culture, fish, and rodents. But they have been pretty limited, and there are still many gaps in our knowledge about nanoparticle safety."
In one widely publicized 2004 report, Southern Methodist University researcher Eva Oberdörster found that nanoparticles called buckyballs can cause brain damage in fish. [ 1]
Later that year, Vicki Colvin and Christy Sayes at CBEN found that buckyballs are also toxic in vitro, causing 50% of cultured human cells to die at a concentration of 20 parts per billion. [ 2]
"The findings from those [CBEN] experiments were interesting in that they showed that the toxicity varied dramatically, according to what was happening at the surface of those particles," says Kulinowski.
Similarly, Mark Banaszak Holl of the University of Michigan has found that a particle's surface chemistry can govern whether a particle works well for biomedical applications. [ 3]
And North Carolina State University toxicologist Nancy Monteiro-Riviere showed that, depending on how they're made, some nanoscale materials that may otherwise irritate the skin can be rendered nontoxic. [ 4]
Her group is now studying quantum dots, carbon fullerenes, and iron oxide nanocrystals to see if these nanomaterials can also penetrate to the dermis.
While participants generally lauded the group's effort, some said its proposal doesn't go far enough. In a report statement presented at the meeting, a coalition of 17 environmental and health advocacy groups, including the Natural Resources Defense Council, the Sierra Club, and the Breast Cancer Fund, proposed classifying nanomaterials as "new" chemical substances under TSCA, because they are new organic or inorganic substances of a particular molecular identity.
The coalition backed recommendations from the Royal Society and the Royal Academy of Engineering, that nanoparticle release into the environment be minimized until more is known about how they would affect ecosystems.
The EPA is now formulating its strategy, and preliminary plans for the voluntary reporting scheme could arrive later this year. Charles Auer, director of the EPA's Office of Prevention, Pesticides, and Toxic Substances, says, "When we will have all these issues resolved, I don't know. There are a lot of wrinkles here to be sorted through, but there's a lot of work underway."
References
| 1. | | Oberdörster E:
"Manufactured nanomaterials (fullerenes, C60) induce oxidative stress in the brain of juvenile largemouth bass,".
Environ Health Perspect 2004, 112:1058-62. [Publisher Full Text]
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[1]
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| 2. | | Sayes C, et al.:
"The differential cytotoxicity of water-soluble fullerenes,".
Nano Lett 2004, 4:1881-7.
[Publisher Full Text]
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[1]
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| 3. | | Mecke A, et al.:
"Direct observation of lipid bilayer disruption by poly(amidoamine) den-drimers,".
Chem Phys Lipids 2004, 132:3-14. [Publisher Full Text]
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[1]
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| 4. | | Monteiro-Riviere N, et al.:
"Multi-walled carbon nanotube interactions with human epidermal keratinocytes,".
Toxicol Lett 155:377-84. [Publisher Full Text]
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| | | March 15, 2005
Return to citation in text:
[1]
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