Abstract  Carbon nanotubes represent a relatively recently discovered allotrope of carbon that exhibits unique properties. While commercial interest in the material is leading to the development of mass production and handling facilities, little is known of the risk associated with exposure. In a two-part study, preliminary investigations have been carried out into the potential exposure routes and toxicity of single-walled carbon nanotube material (SWCNT)--a specific form of the allotrope. The material is characterized by bundles of fibrous carbon molecules that may be a few nanometers in diameter, but micrometers in length. The two production processes investigated use-transition metal catalysts, leading to the inclusion of nanometer-scale metallic particles within unrefined SWCNT material. A laboratory-based study was undertaken to evaluate the physical nature of the aerosol formed from SWCNT during mechanical agitation. This was complemented by a field study in which airborne and dermal exposure to SWCNT was investigated while handling unrefined material. Although laboratory studies indicated that with sufficient agitation, unrefined SWCNT material can release fine particles into the air, concentrations generated while handling material in the field were very low. Estimates of the airborne concentration of nanotube material generated during handling suggest that concentrations were lower than 53 microg/m(3) in all cases. Glove deposits of SWCNT during handling were estimated at between 0.2 mg and 6 mg per hand.

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  With a surge in technological advancements and the needs of diverse communities such as consumers, military and navy, the textile industry is shifting its focus to fabrication of next-generation textiles that not only meet the basic conventional requirements, but also serve a host of other functions. In this pursuit of fabricating next-generation textiles, called here e-textiles (electronic textiles), a novel technique is presented to produce nanocomposite fabrics made from carbon nanotubes (CNTs) with enhanced sensing capabilities. Catering to the ever increasing demand of improved sensors, this work discusses the electrospinning fabrication scheme that has been employed to develop novel CNT-based piezoelectric strain sensors. The resulting sensors have been characterized by performing structural vibration experiments to evaluate their strain-sensing performance. When these new CNT-based piezopolymer composites are electrospun into smart fabrics, the strain-sensing ability (as measured by voltage across the sensor) is increased by a dramatic 35 times, from 2.4 to 84.5 mV for 0.05 wt% of the nanotubes. The dominant mechanism responsible for such improvement is found to be the alignment of dipoles in the piezoelectric material. Such alignment is mainly attributed due to ability of the electrospinning process to generate very thin fibers from polymer-nanotube solution. The direct and reverse conversion of electrical energy into mechanical energy in the proposed sensors can create a platform for developing next-generation smart fabric with applications in membrane structures, distributed shape modulation and energy harvesting.

Abstract  The progress of flame retarded polymer nanocomposites and coatings in China over the past decades are described in this review. Emphasis on flammability performance of polymer nanocomposites containing nanofillers, mainly layered inorganic compounds, nanofibers and nanoparticles, combined with conventional flame retardant additives are addressed based on the open literature. Polymeric coatings with improved flame retardancy prepared using a wide variety of additives and UV-curing technology are also introduced. Derived from this research, the combination of multiple methods and technologies including catalyst and nanotechnology, is predicted to have a high probability to enhance char formation and improve the flame retardancy of polymeric materials. Copyright (C) 2011 John Wiley & Sons, Ltd.

Abstract  To investigate the effect of leachant on the leachability of polybrominated diphenyl ethers (PBDEs), we determined the leaching concentrations of PBDEs from flame-retardant plastic samples (TV housings and raw materials before molding processing) that are regarded as a source of PBDEs in landfill sites. The leachants used were distilled water, 20% methanol solution, and dissolved humic solution (DHS) of 1000 mg/l based on organic carbon. The leaching test conditions were a liquid-to-solid ratio of 100:1, and a contact period of five days, with twice-daily agitation in a temperature-controlled room of 30 degrees C without pH or ionic strength control. The leaching concentrations of PBDEs increased with increased content, and were found to be remarkably enhanced when methanol and DHS were used instead of distilled water. The enhancement of leachability in the presence of the latter was attributed to the cosolvency effect, and complex formations between the PBDEs and dissolved humic matter (DHM). PBDE concentrations in the leachate obtained from the leaching test and an actual landfill site revealed a significant presence of congeners below heptabromodiphenyl ethers (H7BDEs), detected in the leachate of the actual landfill, while significant amounts of nonabromodiphenyl ethers (N9BDEs) and decabromodiphenyl ether (D10BDE) were detected in the leachate of the leaching test.

Abstract  Environmental impacts due to engineered nanomaterials arise both from releases of the nanomaterials themselves as well as from their synthesis. In this work, we employ the USEtox model to quantify and compare aquatic ecotoxicity impacts over the life cycle of carbon nanotubes (CNTs). USEtox is an integrated multimedia fate, transport, and toxicity model covering large classes of organic and inorganic substances. This work evaluates the impacts of non-CNT emissions from three methods of synthesis (arc ablation, CVD, and HiPco), and compares these to the modeled ecotoxicity of CNTs released to the environment. Parameters for evaluating CNT ecotoxicity are bounded by a highly conservative "worst case" scenario and a "realistic" scenario that draws from existing literature on CNT fate, transport, and ecotoxicity. The results indicate that the ecotoxicity impacts of nanomaterial production processes are roughly equivalent to the ecotoxicity of CNT releases under the unrealistic worst case scenario, while exceeding the results of the realistic scenario by 3 orders of magnitude. Ecotoxicity from production processes is dominated by emissions of metals from electricity generation. Uncertainty exists for both production and release stages, and is modeled using a combination of Monte Carlo simulation and scenario analysis. The results of this analysis underscore the contributions of existing work on CNT fate and transport, as well as the importance of life cycle considerations in allocating time and resources toward research on mitigating the impacts of novel materials.

Abstract  Polybrominated diphenyl ether (PBDE) flame retardants have become distributed ubiquitously in the environment. High concentrations have been reported in U.S. sewage sludge (biosolids). The burgeoning practice of land-applying biosolids as fertilizer creates an avenue for reintroduction of PBDEs to surface waters and aquatic sediments. Bioavailability of biosolids- and sediment-associated PBDEs was assessed using the freshwater oligochaete, Lumbriculus variegatus. Oligochaetes were exposed to composted biosolids (1,600 ng/g total PBDEs) and artificial sediment spiked with penta- and deca-brominated diphenyl ether (BDE) formulations (1,300 ng/g total PBDEs). Uptake (28-d exposure) and depuration (21 d) of eight congeners were studied. Polybrominated diphenyl ethers in both substrates were bioavailable, but bioaccumulation was 5 to 10 times greater from spiked artificial sediment. The congeners BDE 47 and BDE 99 were the most prevalent congeners in oligochaetes after exposure. Congener BDE 47 was more bioaccumulative, possibly due to the threefold greater depuration rate of BDE 99. Bioaccumulation of penta- and hexa-brominated congeners appeared to be affected more strongly by substitution pattern than degree of bromination. Uptake of BDE 209, the dominant congener in deca-BDE, was minimal. Accumulation of certain PBDE congeners from biosolids and sediments by benthos provides a pathway for transfer to higher trophic levels, and congener discrimination may increase with each trophic transfer.

Abstract  Flame-resistant composite materials containing carbon nanotubes are described herein. The flame-resistant composite materials contain an outer layer and at least one inner layer, containing a first polymer matrix and a second polymer matrix, respectively. The outer layer has an exterior surface and a first carbon nanotube-infused fiber material that contains a first fiber material and a first plurality of carbon nanotubes greater than about 50 .mu.m in length. In some embodiments, the at least one inner layer also contains a second fiber material and/or a second carbon nanotube-infused fiber material containing a second fiber material and a second plurality of carbon nanotubes. When present, the second plurality of carbon nanotubes are generally shorter in length than the first plurality of carbon nanotubes. Alignment of the carbon nanotubes in the outer layer can transfer heat away from the composite material's inner layer(s). Flame-resistant articles containing carbon nanotube-infused fiber materials are also described.

Abstract  Cumene production process is gaining importance and so the process needs to be studied and better ideas suggested such that the production cost is reduced. With the advent of computers and simulating software like ASPEN PLUS® it is possible to design and optimize a particular process. Proper design can significantly reduce production cost as well as provide make the process safe and reduce environmental hazards. It has been identified from previous research papers that the cost of materials used is much higher than the cost of energy needed for the process. The materials, unit operations and processes involved are identified. Steady state simulation is done. Each unit is taken into consideration and the variables are optimized. The units are sequentially optimized in the order in which they appear in the rough flow sheet. Use of newer equipments in the process is suggested. The reactor system on being optimised by an equilibrium based approach gave the operating temperature as 360 C and 6:1 Benzene: Propylene ratio in feed. The distillation columns were optimised and the number of trays for benzene column was found to be 20 by 8 and that for cumene column to be 20 by 10. The reflux ratio values were found to be 0.5 and 0.8 respectively for the columns. The optimised temperature for flashing was identified as 92.5 C. The modified flow sheet of the optimised process was prepared which gives the values of all the optimised variables in detail.

Abstract  Municipal recycling coordinators do not fully understand some of the market dynamics of bulky goods because this has been a small portion of their responsibilities in the past. However, with increased attention being given to reuse, recycling, and composting in all aspects of the waste stream, municipal recyclers are trying to better understand and expand the markets for these products. These efforts are often in partnership with charities and the private sector that have been operating for a long time in this arena. Some of the products in which significant progress is taking place are highlighted below.

Abstract  Recent progress in chemical vapour deposition and aerosol synthesis of single-walled carbon nanotubes (SWCNTs) is reviewed with an emphasis on the role of metal nanoparticles in the processes. The effect of the various parameters on SWCNT formation is reported on the basis of published experiments. Evolution of the catalyst particle size distribution due to collision, sintering and evaporation of metal during SWCNT synthesis is discussed. The active catalyst has been demonstrated to be in a reduced metal form by comparison of the experimental data and calculations regarding the equilibrium concentration of carbon and oxygen in iron. Also the effect of the catalyst particle size on melting temperature and carbon solubility in metal is discussed. The stability of different carbon precursors (hydrocarbons and carbon monoxide) is considered thermodynamically. Furthermore, estimation of the maximum length of 1 and 2.5 nm diameter SWCNTs as a function of carbon solubility is conducted to determine whether carbon dissolution and precipitation are simultaneous or subsequent process steps.

Abstract  Goal, Scope, and Background The paper describes the integration of the economic input-output life cycle assessment (EIO-LCA) model and the environmental fate and transport model (CHEMGL) with a risk assessment tool. Utilizing the EIO-LCA, instead of a traditional LCA, enables a rapid, screening-level analysis of an emerging chemical of concern, decabromodiphenyl ether (DecaBDE). The risk assessment in this study is evaluated based on the mass of chemical released, estimated concentrations, exposure, and chemical toxicity.

Methods The relative risk from ten economic sectors identified within the EIO-LCA model, 55 chemicals utilized in those sectors and DecaBDE along with four potential DecaBDE breakdown products, were evaluated for the life cycle stages and exposure pathways. The relative risk (expressed as toluene equivalents) of the different chemicals, sectors, and life cycle stages were compared to assess those representing the greatest overall relative risks to humans (via inhalation and ingestion) and fish.

Results The greatest overall risk to human health resulted from the manufacturing and production stages. For fish, the manufacturing stage represented virtually all of the risk. Of the 56 chemicals evaluated, DecaBDE represented the majority of the total risk to humans. However, DecaBDE posed the least risk compared to its potential breakdown products.

Discussion The risk to humans from ingestion, which represented the greatest risk, from the production, manufacturing, and consumption stages can be controlled and reduced through various safety precautions in the workplace. Additionally, the increasing concentration of DecaBDE in anaerobic compartments represents a threat to humans and fish via the higher risk DecaBDE breakdown products.

Conclusions Overall, the manufacturing and production life cycle stages pose the greatest risk to humans and fish. The sediment compartment received the highest DecaBDE concentration for the production, manufacturing, and consumption stages. This case study demonstrates that the integrated EIO-LCA with risk assessment is suitable for screening-level analysis of emerging chemicals due to rapid life cycle inventory analysis.

Recommendations The production and manufacturing stages allow for greater industry control and government regulation, compared to the consumption stage, because there are fewer point sources. This integrated life cycle methodology may allow chemical designers to evaluate each stage and assess areas where risks can be minimized.

Abstract  Various applications of multiwalled carbon nanotubes (MWCNT) have been developed. One of these applications is an efficient sheet heating element that is woven from MWCNT-coated yarn. In this research, we assessed the exposure to MWCNT and/or the probability of particle release from broken MWCNT-coated yarn during the weaving process. This was accomplished using particle concentrations, microscopic observation, and carbon analysis. In the weaving process, neither an increase in the number of particles nor a difference in particle-size distribution was observed. In the scanning electron micrographic observation, nanosize MWCNT particles were not detected, but there were micron-size particles containing MWCNT as fragments of the yarn. Carbon analysis showed the concentration of micron-size particles containing MWCNT did not exceed 0.0053 mg-C/m(3) around the loom. This value was much lower than the respirable dust mass concentration. Most of micron-size particles seemed to originate from polyester yarn without MWCNT coating. It is recommended that workers use conventional (even not specialized for nanoparticles) personal protective equipment such as respirators and gloves to prevent exposure to respirable-size MWCNT-containing particles. The probability of MWCNT fall-off from the MWCNT-coated yarn was not detected by transmission electron microscopic observation of MWCNT-coated yarn before or after the weaving process.

Abstract  The environmental assessment of nanomanufacturing during the initial process design phase should lead to the development of competitive, safe, and environmentally responsible engineering and commercialization. Given the potential benefits and concerns regarding the use of single-walled carbon nanotubes (SWNTs), three SWNT production processes have been investigated to assess their associated environmental impacts. These processes include arc ablation (arc), chemical vapor deposition (CVD), and high-pressure carbon monoxide (HiPco). Without consideration of the currently unknown impacts of SWNT dispersion or other health impacts, life cycle assessment (LCA) methodology is used to analyze the environmental impact and provide a baseline for the environmental footprint of each manufacturing process. Although the technical attributes of the product resulting from each process may not be fully comparable, this study presents comparisons that show that the life cycle impacts are dominated by energy, specifically the electricity used in production. Under base case yield conditions, HiPco shows the lowest environmental impact, while the arc process has the lowest impact under best case yield conditions.

Abstract  Commercially available carbon nanotubes (CNT) often contain some quantities of metallic and carbonaceous impurities. These impurities influence their physicochemical properties and performance, and accordingly a number of potential applications. The lack of information of metal impurities may also preclude accurate environmental and health risk assessments for specific CNT materials. To address these needs, a quantitative analysis of the metal contents has been made in a number of commercial carbon nanotubes produced by different manufacturers. More than 20 metals or metalloids were determined by neutron activation analysis. The results indicate arranging from 0.44 to 3 wt% of catalyst residues remained although the producers claim to provide a catalyst-free product. Most of the impurity elements are transition metals, such as Fe, Ni, Mo, Y, Co and Cr. In addition to the expected catalyst residues, other unexpected impurity elements were detected including As, Gd, W, Yb, Sm and so on. Metallic impurities in carbon nanotube materials should come from the large-scale production procedures, post fabrication and post-purification treatments. The analytical results determined by inductively-coupled plasma mass spectrometry show that a further deep purification using conventional acid reflux cannot completely remove the metallic impurities from carbon nanotubes. Post-production clean up is difficult and often incompletely.

Abstract  It is suggested that assessments of chemicals of emerging concern can be rationally structured around a multistage process in which fate and risk are evaluated with increasing accuracy as new data become available. An initial tentative and approximate assessment of fate and risk can identify key data gaps and justify and direct further investigations, which progressively improve the reliability of the assessment. This approach is demonstrated for a class of chemicals, the polybrominated diphenyl ethers (PBDEs), which is of increasing concern, but about which there is presently a lack of comprehensive data on properties, sources, fate and effects. Specifically, 20 PBDE congeners are investigated using the suggested approach and research needs are identified.

Abstract  The National Institute for Occupational Safety and Health (NIOSH) conducted field studies at 12 sites using the Nanoparticle Emission Assessment Technique (NEAT) to characterize emissions during processes where engineered nanomaterials were produced or used. A description of the NEAT appears in Part A of this issue. Field studies were conducted in research and development laboratories, pilot plants, and manufacturing facilities handling carbon nanotubes (single-walled and multi-walled), carbon nanofibers, fullerenes, carbon nanopearls, metal oxides, electrospun nylon, and quantum dots. The results demonstrated that the NEAT was useful in evaluating emissions and that readily available engineering controls can be applied to minimize nanomaterial emissions.

Abstract  Quantification of natural and engineered carbon nanotubes (CNT) in the environment is urgently needed to study their occurrence and fate and to enable a proper risk assessment. Currently, such methods are lacking. Here, we tested the resistance of 15 structurally different CNTs to chemothermal oxidation at 375 degrees C (CTO-375), a method used to isolate soots from environmental samples. Depending on their structure, CNTs survived CTO-375 in proportions ranging from 26 to 93%. Standard addition of CNTs to soil and sediment yielded recoveries between 66 and 171%, demonstrating the capability of CTO-375 to isolate CNTs from complex environmental matrices. These data of pure and added CNTs correspond to recoveries obtained with "ordinary" soots under similar experimental conditions. Hence, soot fractions commonly isolated with CTO-375 from environmental matrices most probably encompass CNTs. Future work should attempt to enhance the method's selectivity, i.e., its capability to separate CNTs from other forms of soot.

Abstract  Carbon nanotubes (CNTs) are currently incorporated into various consumer products, and numerous new applications and products containing CNTs are expected in the future. The potential for negative effects caused by CNT release into the environment is a prominent concern and numerous research projects have investigated possible environmental release pathways, fate, and toxicity. However, this expanding body of literature has not yet been systematically reviewed. Our objective is to critically review this literature to identify emerging trends as well as persistent knowledge gaps on these topics. Specifically, we examine the release of CNTs from polymeric products, removal in wastewater treatment systems, transport through surface and subsurface media, aggregation behaviors, interactions with soil and sediment particles, potential transformations and degradation, and their potential ecotoxicity in soil, sediment, and aquatic ecosystems. One major limitation in the current literature is quantifying CNT masses in relevant media (polymers, tissues, soils, and sediments). Important new directions include developing mechanistic models for CNT release from composites and understanding CNT transport in more complex and environmentally realistic systems such as heteroaggregation with natural colloids and transport of nanoparticles in a range of soils.