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April 17, 2003 — A survey of 27 toxicology studies released this week concluded that ultrafine particles can enter the body through the skin, breathing and ingestion, leading to reactions such as inflammation. C. Vyvyan Howard, a pathologist at the University of Liverpool in England and author of the review, suggested particle size more than composition caused the toxic effect.
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Some environmental researchers questioned whether the particles under review were more akin to soot and other urban pollutants than manufactured nanomaterials, and whether the exposure levels used for those particulate studies made sense for nanomaterials.
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All agreed more work needs to be done to identify what risks might exist and ensure they are minimized.
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“This is not a totally exhaustive survey,” said Howard, co-author of a book on particulates and health and past president of the multidisciplinary Royal Microscopical Society. “It shows there are things to worry about and things to take notice of. … Regulators need to take a look, mainly for the protection of industrial workers.”
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The survey accompanies a report posted online Monday by ETC Group, a Canadian-based social advocacy organization that calls for a moratorium on nanotechnology. ETC asked Howard to conduct the survey to assess health issues, said Pat Mooney, ETC’s executive director.
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“We believe we need the moratorium because we don’t see enough safety (protocols),” Mooney said. “This will contribute to the momentum toward a moratorium.”
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In his review, Howard outlined the most probable transmission pathways for particulates smaller than 100 nanometers. He explained how small particles may evade the body’s various defense mechanisms: a coating of mucus in the air passageways that can trap and remove larger particles such as dust; cells that normally scour for invaders but seem unable to recognize threats smaller than 70 nanometers; and the skin, which can be penetrated by nanoscale molecules. Membrane openings that allow proteins and other biological molecules to enter cells serve as entry portals for nanomaterials, too, he said.
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Some nanotechnologists say nanoscale materials could be a blessing for the industry and society, but they also have the potential to be a curse. “Finely divided solids have access to areas of the body and interact with biological systems in completely unexpected ways, which is exactly why they are so powerful in medical applications,” said Vicki Colvin, director of the federally funded Center for Biological and Environmental Nanotechnology at Rice University in recent testimony before the U.S. House of Representatives.
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“The converse of this is that unintended exposures — of research workers, factory workers, and the general public — to nanoscale solids could have … dire consequences. … Or they could turn out to be benign. We just don’t know.”
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Various toxicology studies found that ultrafine particulates, once in the body, triggered reactions. Howard speculated that the smallness of the particulates made them more reactive because they offered highly charged surface areas.
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“The precise mechanism isn’t known,” he said. “Nanoparticles seem to generate free radicals (atoms with unpaired electrons). The theory is, they set up an inflammation reaction.”
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Certain small particles in the atmosphere have been shown to be problematic, said Nora Savage, an environmental engineer with the Environmental Protection Agency. She is spearheading efforts with the National Nanotechnology Initiative to fund up to $5 million in research on toxicological effects of nanomaterials, including how they interact with the environment and people.
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“What’s true with atmospheric particles is not necessarily true with nanomaterials, especially the ones that are manufactured,” Savage said. “I’m not sure there is a clear correlation between the two.”
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Colvin pointed out that typical toxicology studies rely on exposure levels that are unrealistic for nanomaterials, and the exposure in those studies is through an aerosol, which is not a naturally occurring form for many nanomaterials. “What’s clear is that most nanoengineered materials don’t occur in the quantities you find in something like diesel fumes,” Colvin said. “And they are not aerosolized.”
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Savage agreed with Howard that some materials approved by the U.S. Food and Drug Administration for commercial use should be re-evaluated as nanomaterials. One of the arguments for developing nanotechnology is it allows industry to exploit properties that don’t exist on a larger scale. Nanoscale titanium dioxide, for instance, is now used in some sunscreens because it can block damaging ultraviolet rays while appearing clear on the skin.
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“It does make sense for us at the EPA to revisit these materials,” she said. “The whole point is they have different properties.”
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The ETC Group’s report, “No Small Matter II: A Case for a Global Moratorium,” includes references to several unpublished studies on nanomaterials. Howard’s analysis does not incorporate those studies; instead he used peer-reviewed publications and literature from the drug industry.
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ETC helped defray the cost of three days of work by an assistant, Howard said, but did not pay him for his contribution. He plans to include his findings in an overview paper during a Royal Microscopical Society meeting in January 2004.
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“I want a lot more science done on this to make sure there is no dangers to our health,” Howard said, adding that he sees the advantages of nanotechnology but wants to ensure workers and the public are protected.
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Savage added that industry is also in favor of the toxicology studies she is soliciting. “The companies aren’t averse to this,” she said. “They don’t want to be caught manufacturing something that will be restricted.”