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Nanotoxicology is the study of the toxicity of nanomaterials. Because of the small size and large surface area of nanomaterials, these materials have unique properties compared with their larger counterparts. The nanomaterials, even when they are made of inert elements like gold, become very active at a nanometer range. Nanotoxicological studies are intended to determine whether and to what extent these may pose a threat to the environment and to human beings. For instance, Diesel nanoparticles have been found to damage the cardiovascular system in a mouse model.
Contents
- 1 Human health and safety
- 2 Toxicology of nanoparticles
- 3 No Fullerene toxicity reported
- 4 References
- 5 Further reading
- 6 External links
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Human health and safety
Calls for tighter regulation of nanotechnology have occurred alongside a growing debate related to the human health and safety risks associated with nanotechnology. The Royal Society identifies the potential for nanoparticles to penetrate the skin, and recommend that the use of nanoparticles in cosmetics be conditional upon a favorable assessment by the relevant European Commission safety advisory committee. Andrew Maynard also reports that ‘certain nanoparticles may move easily into sensitive lung tissues after inhalation, and cause damage that can lead to chronic breathing problems’.
Carbon nanotubes – characterized by their microscopic size and incredible tensile strength – are frequently likened to asbestos, due to their needle-like fiber shape. In a recent study that introduced carbon nanotubes into the abdominal cavity of mice, results demonstrated that long thin carbon nanotubes showed the same effects as long thin asbestos fibers, raising concerns that exposure to carbon nanotubes may lead to mesothelioma (cancer of the lining of the lungs caused by exposure to asbestos). Given these risks, effective and rigorous regulation has been called for to determine if, and under what circumstances, carbon nanotubes are manufactured, as well as ensuring their safe handling and disposal.
The Woodrow Wilson Centre’s Project on Emerging Technologies conclude that there is insufficient funding for human health and safety research, and as a result there is currently limited understanding of the human health and safety risks associated with nanotechnology. While the US National Nanotechnology Initiative reports that around four percent (about $40 million) is dedicated to risk related research and development, the Woodrow Wilson Centre estimate that only around $11 million is actually directed towards risk related research. They argued in 2007 that it would be necessary to increase funding to a minimum of $50 million in the following two years so as to fill the gaps in knowledge in these areas.
The potential for workplace exposure was highlighted by the 2004 Royal Society report which recommended a review of existing regulations to assess and control workplace exposure to nanoparticles and nanotubes. The report expressed particular concern for the inhalation of large quantities of nanoparticles by workers involved in the manufacturing process.
Stakeholders concerned by the lack of a regulatory framework to assess and control risks associated with the release of nanoparticles and nanotubes have drawn parallels with bovine spongiform encephalopathy (‘mad cow’s disease), thalidomide, genetically modified food),) nuclear energy, reproductive technologies, biotechnology, and asbestosis. In light of such concerns, the Canadian based ETC Group have called for a moratorium on nano-related research until comprehensive regulatory frameworks are developed that will ensure workplace safety.
Toxicology of nanoparticles
Nanotoxicology is a sub-specialty of particle toxicology. It addresses the toxicology of nanoparticles (particles <100 nm diameter) which appear to have some toxic effects that are unusual and not seen with larger particles. Nanoparticles can be divided into combustion-derived nanoparticles (like diesel soot), manufactured nanoparticles like carbon nanotubes and naturally occurring nanoparticles from volcanic eruptions, atmospheric chemistry etc. Typical nanoparticles that have been studied are titanium dioxide, alumina, zinc oxide, carbon black, and carbon nanotubes, and “nano-C60“. Nanoparticles seem to have some different properties from larger particles that are known to have pathogenic effects, like asbestos or quartz. These differences seem to be a result of their size. They have a larger surface area per unit mass, so that in some cases they may have more pro-inflammatory effects (in, for example, lung tissue). In addition, some nanoparticles seem to be able to translocate from their site of deposition to distant sites such as the blood and the brain. This has resulted in a sea-change in how particle toxicology is viewed- instead of being confined to the lungs, nanoparticle toxicologists study the brain, blood, liver, skin and gut. Nanotoxicology has revolutionised particle toxicology and rejuvenated it.
The smaller a particle is, the greater its surface area to volume ratio and the higher its chemical reactivity and biological activity. The greater chemical reactivity of nanomaterials results in increased production of reactive oxygen species (ROS), including free radicals. ROS production has been found in a diverse range of nanomaterials including carbon fullerenes, carbon nanotubes and nanoparticle metal oxides. ROS and free radical production is one of the primary mechanisms of nanoparticle toxicity; it may result in oxidative stress, inflammation, and consequent damage to proteins, membranes and DNA.
The extremely small size of nanomaterials also means that they much more readily gain entry into the human body than larger sized particles do. How these nanoparticles behave inside the body is a major question that needs to be resolved. The behavior of nanoparticles is a function of their size, shape and surface reactivity with the surrounding tissue. In principle, a large number of particles could overload the body’s phagocytes, cells that ingest and destroy foreign matter, thereby triggering stress reactions that lead to inflammation and weaken the body’s defense against other pathogens. In addition to questions about what happens if non-degradable or slowly degradable nanoparticles accumulate in bodily organs, another concern is their potential interaction with biological processes inside the body. Because of their large surface area, nanoparticles will, on exposure to tissue and fluids, immediately adsorb onto their surface some of the macromolecules they encounter. This may, for instance, affect the regulatory mechanisms of enzymes and other proteins.
Nanomaterials are able to cross biological membranes and access cells, tissues and organs that larger-sized particles normally cannot. Nanomaterials can gain access to the blood stream following inhalation or ingestion. At least some nanomaterials can penetrate the skin; even larger microparticles may penetrate skin when it is flexed. Broken skin is an ineffective particle barrier, suggesting that acne, eczema, shaving wounds or severe sunburn may accelerate skin uptake of nanomaterials. Then, once in the blood stream, nanomaterials can be transported around the body and be taken up by organs and tissues, including the brain, heart, liver, kidneys, spleen, bone marrow and nervous system. Nanomaterials have proved toxic to human tissue and cell cultures, resulting in increased oxidative stress, inflammatory cytokine production and cell death. Unlike larger particles, nanomaterials may be taken up by cell mitochondria and the cell nucleus. Studies demonstrate the potential for nanomaterials to cause DNA mutation and induce major structural damage to mitochondria, even resulting in cell death. Size is therefore a key factor in determining the potential toxicity of a particle. However it is not the only important factor.
Other properties of nanomaterials that influence toxicity include: chemical composition, shape, surface structure, surface charge, aggregation and solubility, and the presence or absence of functional groups of other chemicals. The large number of variables influencing toxicity means that it is difficult to generalise about health risks associated with exposure to nanomaterials – each new nanomaterial must be assessed individually and all material properties must be taken into account.
Since there is no authority to govern nanotech-based products, there are many products that could possibly be dangerous to humans. Scientific research has indicated the potential for some nanomaterials to be toxic to humans or the environment. In March 2004 tests conducted by environmental toxicologist Eva Oberdörster, Ph.D. working with Southern Methodist University in Texas, found extensive brain damage to fish exposed to fullerenes for a period of just 48 hours at a relatively moderate dose of 0.5 parts per million (commensurate with levels of other kinds of pollution found in bays). The fish also exhibited changed gene markers in their livers, indicating their entire physiology was affected. In a concurrent test, the fullerenes killed water fleas, an important link in the marine food chain. The extremely small size of fabricated nanomaterials also means that they are much more readily taken up by living tissue than presently known toxins. Nanoparticles can be inhaled, swallowed, absorbed through skin and deliberately or accidentally injected during medical procedures. They might be accidentally or inadvertently released from materials implanted into living tissue.
Researcher Shosaku Kashiwada of the National Institute for Environmental Studies in Tsukuba, Japan, in a more recent study, intended to further investigate the effects of nanoparticles on soft-bodied organisms. His study allowed him to explore the distribution of water-suspended fluorescent nanoparticles throughout the eggs and adult bodies of a species of fish, known as the see-through medaka (Oryzias latipes). See-through medaka were used because of their small size, wide temperature and salinity tolerances, and short generation time. Moreover, small fish like the see-through medaka have been popular test subjects for human diseases and organogenesis for other reasons as well, including their transparent embryos, rapid embryo development, and the functional equivalence of their organs and tissue material to that of mammals. Because the see-through medaka have transparent bodies, analyzing the deposition of fluorescent nanoparticles throughout the body is quite simple. For his study, Dr. Kashiwada evaluated four aspects of nanoparticle accumulation. These included the overall accumulation and the size-dependent accumulation of nanoparticles by medaka eggs, the effects of salinity on the aggregation of nanoparticles in solution and on their accumulation by medaka eggs, and the distribution of nanoparticles in the blood and organs of adult medaka. It was also noted that nanoparticles were in fact taken up into the bloodstream and deposited throughout the body. In the medaka eggs, there was a high accumulation of nanoparticles in the yolk; most often bioavailibility was dependent on specific sizes of the particles. Adult samples of medaka had accumulated nanoparticles in the gills, intestine, brain, testis, liver, and bloodstream. One major result from this study was the fact that salinity may have a large influence on the bioavailibility and toxicity of nanoparticles to penetrate membranes and eventually kill the specimen.
As the use of nanomaterials increases worldwide, concerns for worker and user safety are mounting. To address such concerns, the Swedish Karolinska Institute conducted a study in which various nanoparticles were introduced to human lung epithelial cells. The results, released in 2008, showed that iron oxide nanoparticles caused little DNA damage and were non-toxic. Zinc oxide nanoparticles were slightly worse. Titanium dioxide caused only DNA damage. Carbon nanotubes caused DNA damage at low levels. Copper oxide was found to be the worst offender, and was the only nanomaterial identified by the researchers as a clear health risk.
No Fullerene toxicity reported
Nanoparticles can also be made of C60, as is the case with almost any room temperature solid, and several groups have done this and studied toxicity of such particles. The results in the work of Oberdörster at Southern Methodist University, published in “Environmental Health Perspectives” in July 2004, in which questions were raised of potential cytotoxicity, has now been shown by several sources to be likely caused by the tetrahydrofuran used in preparing the 30 nm - 100 nm particles of C60 used in the research. Isakovic, et al., Biomaterials, 27, 5049-5058, 2006, who review this phenomenon, gives results showing that removal of THF from the C60 particles resulted in a loss of toxicity. Sayes, et al. Nanoletters, 2007. 7, (8), pp. 2399 - 2406, also show that particles prepared as in Oberdorster caused no detectable inflammatory response when instilled intratracheally in rats after observation for 3 months, suggesting that even the particles prepared by Oberdorster do not exhibit markers of toxicity in mammalian models. This work used as a benchmark quartz particles, which did give an inflammatory response.
A comprehensive and recent review of work on fullerene toxicity is available in “Toxicity Studies of Fullerenes and Derivatives,” a chapter from the book “Bio-applications of Nanoparticles” (Chan ed., Landes Bioscience, 2007). In this work, the authors review the work on fullerene toxicity beginning in the early 1990’s to present, and conclude that the evidence gathered since the discovery of fullerenes overwhelmingly points to C60 being non-toxic. As is the case for toxicity profile with any chemical modification of a structural moiety, the authors suggest that individual molecules be assessed individually.
References
- ^ http://www.bloomberg.com/apps/news?pid=washingtonstory&sid=aBt.yLf.YfOo study Pollution Particles Lead to Higher Heart Attack Risk (Update1)
- ^ Andrew Maynard. “Nanotechnology: A Research Strategy for Addressing Risks“.
- ^ Poland C, et al (2008). “Carbon Nanotubes Introduced into the Abdominal Cavity of Mice Show Asbestos-Like Pathogenicity in a Pilot-Study”. Nature Nanotechnology. doi:10.1038/nnano.2008.111, http://www.nature.com/nnano/journal/vaop/ncurrent/abs/nnano.2008.111.html.
- ^ Woodrow Wilson Centre for International Scholars Project on Emerging Nanotechnologies
- ^ . “An Issues Landscape for Nanotechnology Standards. Report of a Workshop“. Institute for Food and Agricultural Standards, Michigan State University, East Lansing.
- ^ Royal Society and Royal Academy of Engineering (2004). “Nanoscience and nanotechnologies: opportunities and uncertainties“. Retrieved on 2008-05-18.
- ^ Rowe G, Horlick-Jones T, Walls J, Pidgeon N, (2005). “Difficulties in evaluating public engagement initiatives: reflections on an evaluation of the UK GM Nation?”. Public Understanding of Science 14: 331–352. doi:10.1177/0963662505056611, http://pus.sagepub.com/cgi/content/abstract/14/4/331.
- ^ a b c Nel, Andre; et al. (3 February 2006). “Toxic Potential of Materials at the Nanolevel”. Science 311 (5761): 622–627. doi:10.1126/science.1114397. PMID 16456071. doi:10.1126/science.1114397
- ^ Holsapple, Michael P.; et al. (2005). “Research Strategies for Safety Evaluation of Nanomaterials, Part II: Toxicological and Safety Evaluation of Nanomaterials, Current Challenges and Data Needs”. Toxicological Sciences 88 (1): 12–17. doi:10.1093/toxsci/kfi293. PMID 16120754. doi:10.1093/toxsci/kfi293
- ^ a b c Oberdörster, Günter; et al. (2005). “Principles for characterizing the potential human health effects from exposure to nanomaterials: elements of a screening strategy”. Particle and Fibre Toxicology 2: 8. doi:10.1186/1743-8977-2-8. doi:10.1186/1743-8977-2-8
- ^ a b Hoet, Peter HM; et al. (2004). “Nanoparticles – known and unknown health risks”. Journal of Nanobiotechnology 2: 12. doi:10.1186/1477-3155-2-12. doi:10.1186/1477-3155-2-12
- ^ Ryman-Rasmussen, Jessica P.; et al. (2006). “Penetration of Intact Skin by Quantum Dots with Diverse Physicochemical Properties”. Toxicological Sciences 91 (1): 159–165. doi:10.1093/toxsci/kfj122. PMID 16443688. doi:10.1093/toxsci/kfj122
- ^ Tinkle, Sally S.; et al. (July 2003). “Skin as a Route of Exposure and Sensitization in Chronic Beryllium Disease”. Environmental Health Perspectives 111 (9): 1202–1208.
- ^ a b c “Nanotoxicology: An Emerging Discipline Evolving from Studies of Ultrafine Particles”. Environmental Health Perspectives 113 (7): 823–839. July 2005. doi:10.1289/ehp.7339
- ^ a b Li, Ning; et al. (April 2003). “Ultrafine particulate pollutants induce oxidative stress and mitochondrial damage”. Environmental Health Perspectives 111 (4): 455–460.
- ^ Porter, Alexandra E.; et al. (2007). “Visualizing the Uptake of C60 to the Cytoplasm and Nucleus of Human Monocyte-Derived Macrophage Cells Using Energy-Filtered Transmission Electron Microscopy and Electron Tomography”. Environmental Science and Technology 41 (8): 3012–3017. doi:10.1021/es062541f. doi:10.1021/es062541f
- ^ a b Geiser, Marianne; et al. (November 2005). “Ultrafine Particles Cross Cellular Membranes by Nonphagocytic Mechanisms in Lungs and in Cultured Cells”. Environmental Health Perspectives 113 (11): 1555–1560. doi:10.1289/ehp.8006
- ^ Savic, Radoslav; et al. (25 April 2003). “Micellar Nanocontainers Distribute to Defined Cytoplasmic Organelles”. Science 300 (5619): 615–618. doi:10.1126/science.1078192. PMID 12714738. doi:10.1126/science.1078192
- ^ Magrez, Arnaud; et al. (2006). “Cellular Toxicity of Carbon-Based Nanomaterials”. Nano Letters 6 (6): 1121–1125. doi:10.1021/nl060162e. doi:10.1021/nl060162e
- ^ Kashiwada, Shosaku. “Distribution of Nanoparticles in the See-through Medaka (Oryzias latipes).” Environmental Health Perspectives. November 2006: Volume 114.
- ^ Chemical & Engineering News Vol. 86 No. 35, 1 Sept. 2008, “Study Sizes up Nanomaterial Toxicity”, p. 44
Further reading
- Donaldson, K., Stone, V., Tran, C. L., Kreyling, W., and Borm, P. J. (2004). Nanotoxicology. Occup. Environ Med. 61(9), 727-728.
- Singh, S. and Nalwa H. S. (2007) Nanotechnology and Health Safety - Toxicity and Risk Assessments of Nanostructured Materials on Human Health. Journal of Nanoscience and Nanotechnology 7, 3048-3070.
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