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.

Systematic reviews of scientific literature are important for mapping the existing state of research and highlighting further growth channels in a field of study, but systematic reviews are inherently tedious, time consuming, and manual in nature. In recent years, keyword co-occurrence networks (KCNs) are exploited for knowledge mapping. In a KCN, each keyword is represented as a node and each co-occurrence of a pair of words is represented as a link. The number of times that a pair of words co-occurs in multiple articles constitutes the weight of the link connecting the pair. The network constructed in this manner represents cumulative knowledge of a domain and helps to uncover meaningful knowledge components and insights based on the patterns and strength of links between keywords that appear in the literature. In this work, we propose a KCN-based approach that can be implemented prior to undertaking a systematic review to guide and accelerate the review process. The novelty of this method lies in the new metrics used for statistical analysis of a KCN that differ from those typically used for KCN analysis. The approach is demonstrated through its application to nano-related Environmental, Health, and Safety (EHS) risk literature. The KCN approach identified the knowledge components, knowledge structure, and research trends that match with those discovered through a traditional systematic review of the nanoEHS field. Because KCN-based analyses can be conducted more quickly to explore a vast amount of literature, this method can provide a knowledge map and insights prior to undertaking a rigorous traditional systematic review. This two-step approach can significantly reduce the effort and time required for a traditional systematic literature review. The proposed KCN-based pre-systematic review method is universal. It can be applied to any scientific field of study to prepare a knowledge map.

Summary 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.

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