Abstract  Nanotechnology has emerged at the forefront of science research and technology development. Carbon nanotubes (CNTs) are major building blocks of this new technology. They possess unique electrical, mechanical, and thermal properties, with potential wide applications in the electronics, computer, aerospace, and other industries. CNTs exist in two forms, single-wall (SWCNTs) and multi-wall (MWCNTs). They are manufactured predominately by electrical arc discharge, laser ablation and chemical vapor deposition processes; these processes involve thermally stripping carbon atoms off from carbon-bearing compounds. SWCNT formation requires catalytic metals. There has been a great concern that if CNTs, which are very light, enter the working environment as suspended particulate matter (PM) of respirable sizes, they could pose an occupational inhalation exposure hazard. Very recently, MWCNTs and other carbonaceous nanoparticles in fine (< 2.5 mu m) PM aggregates have been found in combustion streams of methane, propane, and natural-gas flames of typical stoves; indoor and outdoor fine PM samples were reported to contain significant fractions of MWCNTs. Here we review several rodent studies in which test dusts were administered intratracheally or intrapharyngeally to assess the pulmonary toxicity of manufactured CNTs, and a few in vitro studies to assess biomarkers of toxicity released in CNT-treated skin cell cultures. The results of the rodent studies collectively showed that regardless of the process by which CNTs were synthesized and the types and amounts of metals they contained, CNTs were capable of producing inflammation, epithelioid granulomas (microscopic nodules), fibrosis, and biochemical/toxicological changes in the lungs. Comparative toxicity studies in which mice were given equal weights of test materials showed that SWCNTs were more toxic than quartz, which is considered a serious occupational health hazard if it is chronically inhaled; ultrafine carbon black was shown to produce minimal lung responses. The differences in opinions of the investigators about the potential hazards of exposures to CNTs are discussed here. Presented here are also the possible mechanisms of CNT pathogenesis in the lung and the impact of residual metals and other impurities on the toxicological manifestations. The toxicological hazard assessment of potential human exposures to airborne CNTs and occupational exposure limits for these novel compounds are discussed in detail. Environmental fine PM is known to form mainly from combustion of fuels, and has been reported to be a major contributor to the induction of cardiopulmonary diseases by pollutants. Given that manufactured SWCNTs and MWCNTs were found to elicit pathological changes in the lungs, and SWCNTs (administered to the lungs of mice) were further shown to produce respiratory function impairments, retard bacterial clearance after bacterial inoculation, damage the mitochondrial DNA in aorta, increase the percent of aortic plaque, and induce atherosclerotic lesions in the brachiocephalic artery of the heart, it is speculated that exposure to combustion-generated MWCNTs in fine PM may play a significant role in air pollution-related cardiopulmonary diseases. Therefore, CNTs from manufactured and combustion sources in the environment could have adverse effects on human health.

Abstract  Carbon nanotubes (CNT) are expected to be applied in a wide range of industrial applications and consumer products. As a consequence of widespread usage and their supposed persistence against degradation, human and environmental exposure to CNT is likely to increase. There are still many open questions regarding the effects of human or ecological exposure. However, the results of toxicological studies suggest that nanotubes may affect human health. Here we study possible sources of CNT-release on the basis of two case studies. In order to investigate whether and under which conditions CNT may be released from applications, we track the CNT throughout their life cycle as part of two types of consumer products: lithium-ion secondary batteries and synthetic textiles. The findings of the case studies suggest that a release of nanotubes can occur not only in the production phase, but also in the usage and disposal phases of nanotube applications. The likelihood and form of release is determined by the way CNT are incorporated into the material. A considerable part of all CNT used may finally be dispersed somewhere in the technosphere or the environment, e.g. by cross-product contamination during recycling. As long as potential adverse effects of CNT cannot be ruled out, we recommend implementing precautionary measures along the value chain (including the end-of-life treatment) in order to reduce the release and possible negative environmental or human health effects of CNT. (c) 2007 Elsevier Ltd. All rights reserved.

Abstract  The purpose of this report is to provide an updated analysis of the bioaccumulation and environmental transformation of decabromodiphenyl ether (decaBDE), to be considered in the context of the information and analyses already published in the final screening assessment on polybrominated diphenyl ethers (PBDEs) (Canada 2006). This evaluation is considered a state of the science review. While this report does not critique individual studies, it considers the reliability of individual studies when forming a weight of evidence for persistence, bioaccumulation or inherent toxicity to non-human biota. This report considers materials published up to August 25, 2009.

Abstract  Polybrominated diphenyl ethers, PBDEs, are a class of brominated flame retardants that, like other persistent organic pollutants (POPs), have been found in humans, wildlife, and biota worldwide. Unlike other POPs, however, the key routes of human exposure are thought to be from their use in household consumer products, and their presence in house dust, and not from dietary routes. The exposure of Americans to PBDEs was systematically evaluated in this study. The production and lifecycle of the formulated PBDE products were examined. Literature on their fate and presence in the environment was reviewed. Exposure media data on brominated diphenyl ether (BDE) congeners were combined with estimates of adult, childhood, and infant intake factors to estimate a total intake of PBDEs for these receptors. The exposure pathways evaluated included food and water ingestion, inhalation, and ingestion of and dermal contact with house dust. For the adult intakes, a body burden of PBDEs was simulated using a simple pharmacokinetic model. The predicted body burdens were compared with representative adult profiles of PBDEs in blood and milk.

Abstract  The purpose of this Toxicological Review is to provide scientific support and rationale for the hazard and dose-response assessment in IRIS pertaining to chronic exposure to decabromodiphenyl ether. It is not intended to be a comprehensive treatise on the chemical or toxicological nature of decabromodiphenyl ether (BDE-209). This health assessment deals with BDE-209 of relatively high purity (=94%) and does not deal with earlier commercial decabromodiphenyl ether mixtures containing lower proportions of decabromodiphenyl ether (e.g., 75% purity). In addition to BDE-209, IRIS health assessments have also been prepared for three other polybrominated diphenyl ether congeners: tetraBDE-47, pentaBDE-99, and hexaBDE-153. These four congeners are those for which toxicological studies suitable for dose-response assessments were available and are the ones most commonly found in the environment and human biological media. The intent of Section 6, Major Conclusions in the Characterization of Hazard and Dose Response, is to present the major conclusions reached in the derivation of the reference dose, reference concentration and cancer assessment, where applicable, and to characterize the overall confidence in the quantitative and qualitative aspects of hazard and dose response by addressing the quality of data and related uncertainties. The discussion is intended to convey the limitations of the assessment and to aid and guide the risk assessor in the ensuing steps of the risk assessment process.

Abstract  Polybrominated diphenyl ethers (PBDEs) are a class of recalcitrant and bioaccumulative halogenated compounds that have emerged as a major environmental pollutant. PBDEs are used as a flame-retardant and are found in consumer goods such as electrical equipment, construction materials, coatings, textiles and polyurethane foam (furniture padding). Similar in structure to polychlorinated biphenyls (PCBs), PBDEs resist degradation in the environment. Less brominated PBDEs like tetra-, penta- and hexa- demonstrate high affinity for lipids and can accumulate in the bodies of animals and humans. Breast milk from North American women contained much higher amounts of PBDEs than levels in breast milk from Swedish women, indicating that North American exposures to PBDEs may be particularly high. Evidence to date suggests that tetra- and penta-BDEs are likely to be the more toxic and bioaccumulative of the PBDE compounds, compared to octa- and deca-congeners. PBDEs are sold as mixtures, under names such as "pentabromodiphenyl ether" and "octabromodiphenyl ether." The pentabromo product is a mixture of tetra-BDEs and penta-BDEs in approximately equal amounts. Pentabromo consists of PBDEs that are believed to be the most toxic. This mixture has been banned by the European Union, but is still used in North America. The United States is the leading producer and user of pentabromo. In August 2003, the State of California passed a bill to phase out the use of penta- and octa-PBDE by 2008. The toxicology of PBDEs is not well understood, but PBDEs have been associated with tumors, neurodevelopmental toxicity and thyroid hormone imbalance. The neurotoxic effects of PBDEs are similar to those observed for PCBs. Children exposed to PBDEs are prone to subtle but measurable developmental problems. It is presumed that PBDEs are endocrine disruptors, but research in this area is scant. Further studies are imperative in a multitude of health and environmental disciplines to determine the adverse effects and mode of action of this widespread emerging pollutant on human health.

Abstract  This study explores whether nanoparticles incorporated in polymers always act as synergists of conventional flame-retardant additives. For this purpose, two different filler nanoparticles, namely organically modified layered-silicate clay minerals or nanoclays and multi-walled carbon nanotubes, were incorporated in poly(methyl methacrylate) filled with an organophosphorus flame-retardant that acts through intumescence. Effective dispersion techniques specific to each nanoparticle were utilized and prepared samples were thoroughly characterized for their nanocomposite morphologies. Nanoclays were shown to outperform carbon nanotubes in respect of improving the fire properties of intumescent formulations assessed by cone calorimeter analysis. An intriguing explanation for the observed behaviour was the restriction of intumescence by strong carbon nanotube networks formed on the flaming surfaces during combustion contrary to enhanced intumescent chars by nanoclays. Carbon nanotubes surpassed nanoclays considering the thermal stability of intumescent formulations in thermogravimetry whereas mechanical properties were significantly superior with nanoclays to those with carbon nanotubes.