Search

Unlike conventional antimicrobials, the study of bacterial resistance to silver nanoparticles (AgNPs) remains in its infancy and the mechanism(s) through which it evolves are limited and inconclusive. The central question remains whether bacterial resistance is driven by the AgNPs, released Ag(I) ions or a combination of these and other factors. Here, we show a specific resistance in an Escherichia coli K-12 MG1655 strain to subinhibitory concentrations of AgNPs, and not Ag(I) ions, as indicated by a statistically significant greater-than-twofold increase in the minimum inhibitory concentration occurring after eight repeated passages that was maintained after the AgNPs were removed and reintroduced. Whole-population genome sequencing identified a cusS mutation associated with the heritable resistance that possibly increased silver ion efflux. Finally, we rule out the effect of particle aggregation on resistance and suggest that the mechanism of resistance may be enhanced or mediated by flagellum-based motility. Bacterial motility may be used as an important predictor of whether a particular bacteria strain can develop AgNP resistance and could inform design of nanoenabled antimicrobials that mechanistically target specific types of bacteria.

While the antibacterial potency of metal and metal oxide engineered nanomaterials (MMO ENMs) has been well-established in the literature, the underlying mechanisms of antibacterial activity are regarded by many as uncertain, despite a considerable volume of publications on this subject. In order to illuminate sources of perceived uncertainty and disagreement, 318 articles pertaining to the mechanism of antimicrobial activity of Ag, Cu, CuO, TiO2 and ZnO ENMs were analyzed. The 318 studies all aimed to assess one or more of eight mechanistic questions, and both positive (i.e. affirmative) and negative conclusions were reported for each mechanistic question for each of the five core compositions. Differences in study design, including the exposure conditions and experimental methods used, were found to statistically significantly correlate with differences in reported mechanistic conclusions. Further analysis of studies which investigated two or more mechanisms revealed how assumptions about which mechanisms predominate for a given core composition may influence study design and, in turn, conclusions. Finally, 181 distinct experimental methods were identified, many of which are relatively untested and have not been evaluated in the published literature, while many frequently-used methods were found to have limitations that may obscure interpretation and mechanistic insight.

The toxicity of graphene oxide (GO) has been documented for multiple species. However, GO has variable surface chemistry, and it is currently unclear whether changes in oxygen content impact GO-organism interactions the same way across species. In this study, a modified Hummer's GO (ARGO) was systematically reduced by thermal annealing at 200, 500, or 800 °C and toxicity towards bacteria (Escherichia coli), alga (Scenedesmus obliquus), cyanobacteria (Microcystis aeruginosa), and invertebrates (Daphnia magna) was assessed by measuring the effective concentrations inducing 50% inhibition (EC50). The EC50–carbon/oxygen ratio relationships show similar trends for bacteria and invertebrates, where toxicity increases as the material is reduced. Conversely, cyanobacterial inhibition decreases as GO is reduced. Further testing supports differences in cell-GO interactions between bacteria and cyanobacteria. Cyanobacteria showed a decrease in metabolic activity, evidenced by a 69% reduction in esterase activity after ARGO exposure but no oxidative stress, measured by 2′,7′-dichlorodihydrofluorescein diacetate (H2DCFDA) fluorescence and catalase activity. In contrast, ARGO induced a 55% increase in H2DCFDA fluorescence and 342% increase in catalase activity in bacteria. These changes in cell–material interactions propose different mechanisms of action, a physical mechanism occurring in cyanobacteria, and a chemical mechanism in bacteria. The differences in GO toxicity observed in different organisms emphasize the need to differentiate the safe-by-design guidelines made for GO in relation to the potential organisms exposed.

This is the first report of an atomic-scale direct oxidation mechanism of the thiol group in glutathione (GSH) by epoxides on graphene oxide (GO) at room temperature. The proposed reaction mechanism is determined using a coupled experimental and computational approach; active sites for the reaction are determined through examination of GO surface chemistry changes before and after exposure to GSH, and density functional theory (DFT) calculations determine the reaction barriers for the possible GO-GSH reaction schemes. The findings build on the previously established catalytic mechanism of GSH oxidation by graphenic nanocarbon surfaces and importantly identify the direct reaction mechanism which becomes important in low-oxygen environments. Experimental results suggest epoxides as the active sites for the reaction with GSH, which we confirm using DFT calculations of reaction barriers and further identify a synergism between the adjacent epoxide and hydroxyl groups on the GO surface. The direct oxidation mechanism at specific oxygen sites offers insight into controlling GO chemical reactivity through surface chemistry manipulations. This insight is critical for furthering our understanding of GO oxidative stress pathways in cytotoxicity as well as for providing rational material design for GO applications that can leverage this reaction.

Graphitic carbon nitride (g-C3N4) is a promising photocatalyst for bacterial disinfection. Herein, carbon doping (C-doping) was employed to manipulate g-C3N4 physicochemical properties and demonstr...

Nanotechnology offers potential solutions for sustainable agriculture, including increasing nutrient utilization efficiency, improving the efficacy of pest management, mitigating the impacts of climate change, and reducing adverse environmental impacts of agricultural food production. Many promising nanotechnologies have been proposed and evaluated at different scales, but several barriers to implementation must be addressed for technology to be adopted, including efficient delivery at field scale, regulatory and safety concerns, and consumer acceptance. Here we explore these barriers, and rank technology readiness and potential impacts of a wide range of agricultural applications of nanotechnology. We propose pathways to overcome these barriers and develop effective, safe and acceptable nanotechnologies for agriculture. Nanotechnology holds great application potential in plant agriculture. This Review Article identifies the technological readiness, addresses the primary barriers to adopting nano-enabled technologies and proposes a roadmap to advance nanotechnology-enabled agriculture.

Purpose The purpose of this study was to assess particular student outcomes when design thinking was integrated into an environmental engineering course. The literature is increasingly promoting design thinking for addressing societal and environmental sustainability engineering challenges. Design thinking is a human-centered approach that identifies needs upfront. Design/methodology/approach In an undergraduate engineering course, Design for the Environment, students have begun to obtain hands-on experience in applying design thinking to sustainability challenges. This case study investigates the association between the use of design thinking and student creativity with sustainability design solutions. Student perspectives on their own creativity and future sustainable design practices as a result of the course were also investigated. Findings The findings were favorable for design thinking, being associated with a significant difference and medium-to-large effect with regards to solution novelty. A qualitative analysis showed a positive association between design thinking and students’ perceptions of their creativity and future anticipated sustainability practices. Using a content analysis of reflective writings, students’ application of design thinking was assessed for comprehensiveness and correctness. A two-week introductory design-thinking module and significant use of in-class active learning were the course elements that most notably impacted students’ use of design thinking. Practical implications This case study preliminarily demonstrates that application of design thinking within an environmental engineering course may be associated with beneficial outcomes related to creativity and sustainability. Originality/value A review of the literature did not uncover studies of the use of design thinking for undergraduate socio-environmental challenges to promote creativity and sustainable-practices outcomes, although the literature has been calling for the marrying of these two areas.

Polycyclic aromatic hydrocarbons (PAHs) are a complex group of environmental contaminants, many having long environmental half-lives. As these compounds degrade, the changes in their structure can result in a substantial increase in mutagenicity compared to the parent compound. Over time, each individual PAH can potentially degrade into several thousand unique transformation products, creating a complex, constantly evolving set of intermediates. Microbial degradation is the primary mechanism of their transformation and ultimate removal from the environment, and this process can result in mutagenic activation similar to the metabolic activation that can occur in multicellular organisms. The diversity of the potential intermediate structures in PAH-contaminated environments renders hazard assessment difficult for both remediation professionals and regulators. A mixture of structural and energetic descriptors has proven effective in existing studies for classifying which PAH transformation products will be mutagenic. However, most existing studies of environmental PAH mutagens primarily focus on nitrogenated derivatives, which are prevalent in the atmosphere and not as relevant in soil. Additionally, PAH products commonly found in the environment can range from as large as five rings to as small as a single ring, requiring a broadly inclusive methodology to comprehensively evaluate mutagenic potential. We developed a combination of supervised and unsupervised machine learning methods to predict environmentally induced PAH mutagenicity with improved performance over currently available tools. K-means clustering with principal component analysis allows us to identify molecular clusters that we hypothesize to have similar mechanisms of action. Recursive feature elimination identifies the most influential descriptors. The cluster-specific regression outperforms available classifiers in predicting direct-acting mutagens resulting from the microbial biodegradation of PAHs and provides direction for future studies evaluating the environmental hazards resulting from PAH biodegradation.

While nitrogen doping greatly broadens graphene applications, relatively little is known about the influence of this heteroatom on the biological activity of graphene. A set of systematically modified nitrogen-doped graphene (NG) materials was synthesized using the hydrothermal method in which the degree of N-doping and N-bonding type is manipulated using two nitrogen precursors (urea and uric acid) and different thermal annealing temperatures. The bioactivity of the NG samples was evaluated using the oxidation of the intracellular antioxidant glutathione (GSH) and bacterial viability (of Escherichia coli K12), and oxidative stress was identified as the predominant antibacterial mechanism. Two key energy-relevant electrochemical reactions, oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), were used to characterize the influence of different N-types on the electronic properties of the NG materials. Electron-donating graphitic-N and electron-withdrawing pyridinic-N were identified as effective promoters for ORR and OER, respectively. The similar mechanisms between the GSH oxidation (indicative of oxidative stress) and ORR mechanisms reveal the role of graphitic-N as the active site in oxidative stress related bioactivity, independent of other consequential properties (e.g., defect density, surface area). This work advances a growing rational design paradigm for graphene family materials using chemical composition and further provides valuable insight into the performance-hazard tradeoffs of NG applications in related fields.

At all length scales, the stability of materials is impacted by their surrounding environment. However, it has now been observed that materials with different dimensions can exhibit markedly different responses to their environment, even for the same material composition. For example, the deterioration of nanomaterials is complicated by the unique chemical and physical properties that arise from changes to their size, shape, and/or surface chemistry. A first step in understanding and predicting nanomaterial stabilities is to leverage the decades of work dedicated to understanding the environment-specific deterioration mechanisms of analogous bulk materials. Then, unique nanoscale properties can be accounted for and used to understand both similarities and differences in deterioration behavior across these length scales. In this review, we specifically consider the stability of group 11 coinage metal surfaces: copper, silver, and gold. We first summarize the chemical mechanisms of environmentally-driven deterioration of these metals in the bulk. We then apply this knowledge to interpret stability studies of nanoparticles made from the same elements. Ultimately, we find that while the reactivity of gold and copper is relatively consistent across length scales, the composition of products formed on silver surfaces differs significantly. These results have important implications for predicting and controlling both desirable and undesirable metal nanoparticle deterioration processes.

Unlike conventional antimicrobials, the study of bacterial resistance to silver nanoparticles (AgNPs) remains in its infancy and the mechanism(s) through which it evolves are limited and inconclusive. The central question remains whether bacterial resistance is driven by the AgNPs, released Ag(I) ions or a combination of these and other factors. Here, we show a specific resistance in an Escherichia coli K-12 MG1655 strain to subinhibitory concentrations of AgNPs, and not Ag(I) ions, as indicated by a statistically significant greater-than-twofold increase in the minimum inhibitory concentration occurring after eight repeated passages that was maintained after the AgNPs were removed and reintroduced. Whole-population genome sequencing identified a cusS mutation associated with the heritable resistance that possibly increased silver ion efflux. Finally, we rule out the effect of particle aggregation on resistance and suggest that the mechanism of resistance may be enhanced or mediated by flagellum-based motility.

In photosynthetic microorganisms, the toxicity of carbon nanomaterials (CNMs) is typically characterized by a decrease in growth, viability, photosynthesis, as well as the induction of oxidative stress. However, it is currently unclear how the shape of the carbon structure in CNMs, such as in the 1-dimensional carbon nanotubes (CNTs) compared to the two-dimensional graphene oxide (GO), affects the way they interact with cells. In this study, the effects of GO and oxidized multi-walled CNTs were compared in the cyanobacterium Microcystis aeruginosa to determine the similarities or differences in how the two CNMs interact with and induce toxicity to cyanobacteria. Using change in Chlorophyll a concentrations, the effective concentrations inducing 50% inhibition (EC50) at 96 h are found to be 11.1 μg/mL and 7.38 μg/mL for GO and CNTs, respectively. The EC50 of the two CNMs were not found to be statistically different. Changes in fluorescein diacetate and 2′,7′-dichlorodihydrofluorescein diacetate fluorescence, measured at the EC50 concentrations, suggest a decrease in esterase enzyme activity but no oxidative stress. Scanning and transmission electron microscopy imaging did not show extensive membrane damage in cells exposed to GO or CNTs. Altogether, the decrease in metabolic activity and photosynthetic activity without oxidative stress or membrane damage support the hypothesis that both GO and CNTs induced indirect toxicity through physical mechanisms associated with light shading and cell aggregation. This indirect toxicity explains why the intrinsic differences in shape, size, and surface properties between CNTs and GO did not result in differences in how they induce toxicity to cyanobacteria.

Polycyclic aromatic hydrocarbons (PAHs) are a diverse group of environmental contaminants released during the combustion of organic materials and the production and utilization of fossil fuels. Once released, PAHs deposit in soil and water bodies where they are subjected to environmental transport and transformations. As they degrade, intermediate transformation products may play an important role in their environmental impact. However, studying the effects of these degradation products has proven challenging because of the complexity, transience, and low concentration of many intermediates. Herein, a novel integration of a pathway prediction system and network theory was developed and applied to a set of four PAHs to demonstrate a possible solution to this challenge. Network analysis techniques were employed to refine the thousands of potential outputs and elucidate compounds of interest. Using these tools, we determined correlations between PAH degradation network data and intermediate metabolite structures, gaining information about the chemical characteristics of compounds based on their placement within the degradation network. Upon applying our developed filtering algorithm, we are able to predict up to 48% of the most common transformation products identified in a comprehensive empirical literature review. Additionally, our integrated approach uncovers potential metabolites which connect those found by past empirical studies but are currently undetected, thereby filling in the gaps of information in PAH degradation pathways.

The use of agrochemicals—fertilizers and pesticides—in crop production is inefficient, resulting in cascading adverse impacts on the environment and public health. Engineered nanomaterials have the...

Engineered nanomaterials (ENMs) and ENM-enabled products have emerged as potentially high-performance replacements to conventional materials and chemicals. As such, there is an urgent need to incorporate environmental and human health objectives into ENM selection and design processes. Here, an adapted framework based on the Ashby material selection strategy is presented as an enhanced selection and design process, which includes functional performance as well as environmental and human health considerations. The utility of this framework is demonstrated through two case studies, the design and selection of antimicrobial substances and conductive polymers, including ENMs, ENM-enabled products and their alternatives. Further, these case studies consider both the comparative efficacy and impacts at two scales: (i) a broad scale, where chemical/material classes are readily compared for primary decision-making, and (ii) within a chemical/material class, where physicochemical properties are manipulated to tailor the desired performance and environmental impact profile. Development and implementation of this framework can inform decision-making for the implementation of ENMs to facilitate promising applications and prevent unintended consequences.

Agriculture fertilization suffers from inefficiencies that carry significant environmental and economic consequences. These consequences include high fertilizer production energy demand, on-field greenhouse gas emissions, and eutrophication. Additionally, inefficient fertilizer use is responsible for billions of dollars in annual economic losses in the form of resource loss as well as environmental burdens. Furthermore, the unsustainability of current fertilization practices and the reliance upon finite resources calls into question the ability of agriculture to meet projected increases in global demand. Herein, critical fertilizer system inefficiencies are highlighted and quantified with a new proposed metric, atom conversion efficiency (ACE), which captures inefficiencies of primary nutrient atoms (N and P) at each stage of the fertilizer life cycle, from synthesis to farm gate, for the model crop, corn. Conversion efficiencies for the most common forms of N and P used in conventional fertilizers range ...

Engineered nanomaterials (ENMs) used as fertilizers, pesticides and growth regulators will involve direct application of large quantities of ENMs to the environment and products intended for human consumption. Assessing their life cycle environmental impacts to mitigate unintended consequences poses several challenges. In this perspective, we identify obstacles to the application of life cycle assessment (LCA) for evaluating environmental tradeoffs of nano-enabled agrochemical applications. These include: (1) defining functional units that represent the function provided by nano-enabled agrochemicals and that are proportional to the scale of the study (nano-scale vs. field scale), (2) limitations in availability of comprehensive data necessary to inform life cycle material flow (resource use and emissions) for inventory development specific to nano-enabled agrochemical applications,(3) human and environmental exposure and effects data relevant to the agricultural context for impact assessment models, (4) spatial and temporal dependent components that can affect the results of an LCA of nano-enabled agrochemicals, and (5) high data uncertainties and the possibility of their reduction through collaborative efforts between life cycle practitioners and experimental researchers using anticipatory decision-based models. While several of these challenges are experienced in LCA of emerging technologies generally, they are highlighted herein due to their unique or heightened relevance to the use of ENMs in agriculture applications. Addressing challenges in these areas are intended to inform research prioritization to ensure safe and sustainable design, development, and implementation of nano-enabled agrochemicals.

Silver nanoparticles (AgNPs) and other ionizing engineered nanomaterials (ENMs) are candidates for the development of antimicrobial agents due to their efficacy, multiple modes of bacterial inactivation, and tunability with respect to both the magnitude and mechanisms of antimicrobial activity. Exploiting this versatility requires elucidating the bacterial inactivation pathway(s) of the ENM, and in particular, the link between material properties and the desired biological endpoint. The mechanisms of antimicrobial activity for macrosilver, Ag salts, and AgNPs have been widely studied, and largely attribute this activity to the release of Ag ions via oxidation and dissolution of the surface Ag atoms. However, it has also been established that Ag ion exposure alone does not elicit the same bacterial response as exposure to AgNPs, which suggests that the observed antimicrobial activity is induced not only by solubilized ions but also by the ENM itself. Resolving the role of the AgNP is critical to informing design of nano-enabled antimicrobials a priori. Herein, we present a systematic review of the AgNP antimicrobial activity literature and specifically focus on studies that scale Ag ion controls to the likely quantities of bioavailable Ag released from AgNPs. This literature selection criterion reveals the critical role of scaled ion controls in distinguishing ion and particle contributions to the observed antimicrobial activity. Overall, our analysis of this literature indicates that in most cases of bacteria exposure to AgNPs, particle-specific activity is observed and acts in concert with and/or independently from solubilized Ag ions alone. These results are exciting and suggest that more efficacious Ag- and ENM-enabled antimicrobials can be obtained through ENM design.

Here, we determine the impact of bacterial growth media on silver nanoparticle (diameter = 24.0 ± 3.2 nm) surface chemistry, the relationship of this surface chemistry to silver ion release from these nanoparticles, and ultimately the antimicrobial implications of those parameters. Importantly, we investigate the effects of multiple broths, as well as the isolated influence of individual broth components and their bicombinations. Our findings indicate that, in combination, broth components may exhibit additive, synergistic, and/or antagonistic effects on silver ion release. In addition, we find that the silver ion release does not always inversely correlate with ligand density, and interestingly, that the type of correlation (negative or positive) is dependent on the broth media. Finally, the impact of these media-dependent silver ion release profiles on bacterial cytotoxicity is studied using the model organism Escherichia coli. Overall, we establish the specific impacts of silver nanoparticle environment on silver nanoparticle surface chemistry, as well as the influence of those outcomes on bacteria growth in the presence of silver nanoparticles.

It is increasingly realized that rational design is critical to advance potential applications and proactively preclude adverse consequences of carbon nanomaterials (CNMs). Central to this approach is the establishment of parametric relationships that correlate material properties to both their functional performance and inherent hazard. This work aims to decouple the causative mechanisms of material structure and surface chemistry as it relates to the electrochemical and biological activities of graphene oxide (GO). The results are evaluated in the context of established relationships between surface chemistry and oxygen functionalized multi-walled carbon nanotubes (O-MWCNTs), a carbon allotrope. Systematic manipulation of GO surface chemistry is achieved through thermal annealing (under inert conditions, 200–900 °C). To further elucidate the contribution of several properties, chemical reduction was also used as an approach to differentially modify the surface chemistry. Physicochemical properties of GO and reduced GO (rGO) samples were comprehensively characterized using multiple techniques (AFM, TGA, XPS, ATR-FTIR, Raman, and DLS). The results indicate that surface chemistry is a viable design handle to control both activities. Rather than a single direct property (i.e., relative presence of carbonyl-containing moieties), it is a balance of multiple consequential properties, (extent of dispersion, defect density, and electrical conductivity) in combination with the relative presence of carbonyl moieties that synergistically contribute to electrochemical and biological activities. The identification of these governing physicochemical properties aims to inform the establishment of design parameters to guide the rational and safe design of CNMs.

Accurate measurement of engineered nanomaterial (ENM) release from diverse product lines and matrices during use is critical to evaluating environmental impacts across the life cycle of a nano-enabled product. While indoor accelerated weathering and a handful of outdoor weathering case studies exist, there has not been a standard methodology applied to characterize ENM release during outdoor weathering suitable for simultaneous use in multiple geographic locations. Such an approach has been established and is presented herein, to quantify ENM release and product transformations with the additional goal of improving life cycle assessments (LCA) of nano-enabled products. A team of experimentalists and life cycle practitioners engaged in the development of the methodology to ensure the data collected is useful to inform improved LCA and environmental impact characterization. While the method was developed to be broadly applicable, the examples included here are representative polymer nanocomposite (PNC) platforms, including multiple ENMs (i.e., nano-silver and carbon nanotubes) within different polymer matrices (i.e., polystyrene, poly(methyl methacrylate), and polycaprolactone). This unique methodology enables the study of ENM release under real climate conditions (i.e., composites are weathered outside) that coordinates: (i) multiple locations with distinct climates, (ii) the application of appropriate techniques to quantify ENM release at low (μg) released masses, (iii) tracking changes in efficacy as a function of weathering, and (iv) acquiring data to inform life cycle assessment. Initial findings (following one year of weathering polymer matrices) are included to demonstrate the type of data acquired and utility of the analysis enabled by this method.

The upstream and downstream environmental impacts of engineered nanomaterials (ENMs) are increasingly realized, and have motivated research to advance promising applications while precluding adverse impacts. Life-cycle assessment (LCA) is a comprehensive tool that considers the entire lifetime of a material, product or process—from raw material acquisition to end-of-life—and can be used to characterize these impacts as various environmental and human health categories. The motivation for this highlight stems from the curiosity of experimentalists and theorists researching the environmental and biological impacts that could result from widespread implementation of nanotechnology. In particular, we are motivated to identify how our research on the nano–bio interface can liaise with the nano-LCA community to advance nano-LCA in a safe and sustainable manner. As such, this highlight focuses on four recent nano-LCA publications that survey across several system levels and address the topics of: (i) upstream impacts from nanoparticle synthesis, (ii) extended lifetimes through the incorporation of ENMs in paints, (iii) integration of nano-specific data into existing life-cycle models, and (iv) the establishment of a nano-specific LCA framework.

Graphene oxide (GO) is an antimicrobial agent with tunable surface chemistry. To identify the physicochemical determinants of GO's antimicrobial activity, we generated different modified Hummer's GO materials thermally annealed at 200, 500, or 800 °C (TGO200, TGO500, and TGO800, respectively) to modify the surface oxygen groups on the material. Plating assays show that as-received GO (ARGO) and TGO200, TGO500, and TGO800 reduce

The globally recognized need to advance more sustainable agriculture and food systems has motivated the emergence of transdisciplinary solutions, which include methodologies that utilize the properties of materials at the nanoscale to address extensive and inefficient resource use. Despite the promising prospects of these nanoscale materials, the potential for large-scale applications directly to the environment and to crops necessitates precautionary measures to avoid unintended consequences. Further, the effects of using engineered nanomaterials (ENMs) in agricultural practices cascade throughout their life cycle and include effects from upstream-embodied resources and emissions from ENM production as well as their potential downstream environmental implications. Building on decades-long research in ENM synthesis, biological and environmental interactions, fate, transport and transformation, there is the opportunity to inform the sustainable design of nano-enabled agrochemicals. Here we perform a screening-level analysis that considers the system-wide benefits and costs for opportunities in which ENMs can advance the sustainability of crop-based agriculture. These include their on-farm use as (1) soil amendments to offset nitrogen fertilizer inputs, (2) seed coatings to increase germination rates and (3) foliar sprays to enhance yields. In each analysis, the nano-enabled alternatives are compared against the current practice on the basis of performance and embodied energy. In addition to identifying the ENM compositions and application approaches with the greatest potential to sustainably advance crop production, we present a holistic, prospective, systems-based approach that promotes emerging alternatives that have net performance and environmental benefits. A screening-level analysis that considers system-wide benefits and costs is used to identify opportunities where engineered nanomaterials can advance the sustainability of crop-based agriculture.

Current agricultural practices, developed during the green revolution, are becoming unsustainable, especially in the face of climate change and growing populations. Nanotechnology will be an important driver for the impending agri-tech revolution that promises a more sustainable, efficient and resilient agricultural system, while promoting food security. Here, we present the most promising new opportunities and approaches for the application of nanotechnology to improve the use efficiency of necessary inputs (light, water, soil) for crop agriculture, and for better managing biotic and abiotic stress. Potential development and implementation barriers are discussed, emphasizing the need for a systems approach to designing proposed nanotechnologies.

Alternatives assessment (AA) provides a framework for selection of safer substitutes for problematic chemicals. This study assesses alternatives for flame retardants (FR) in electrical and electronic equipment (EEE), including two common brominated FR, decabromodiphenyl ether (deca-BDE) and tetrabromobisphenol A (TBBPA). Although deca-BDE is restricted in the EU and undergoing phase-out in the US, TBBPA is still widely used. However, concerns about potential hazards are driving a search for halogen-free alternatives. Nonhalogenated organic chemical alternatives (e.g., phosphorus-based FRs) as well as minerals (e.g., montmorillonite) and nanomaterials (e.g., carbon nanotubes) have been proposed, yet it is unclear whether current frameworks can be used to systematically compare such heterogeneous alternatives. This study aims to (i) identify technologically and economically viable alternative FRs and (ii) evaluate each under the current AA frameworks, to (iii) elucidate challenges and shortcomings to adopti...

Shape of engineered nanomaterials (ENMs) can be used as a design handle to achieve controlled manipulation of physicochemical properties. This tailored material property approach necessitates the establishment of relationships between specific ENM properties that result from such manipulations (e.g., surface area, reactivity, or charge) and the observed trend in behavior, from both a functional performance and hazard perspective. In this study, these structure-property-function (SPF) and structure-property-hazard (SPH) relationships are established for nano-cupric oxide (n-CuO) as a function of shape, including nanospheres and nanosheets. In addition to comparing these shapes at the nanoscale, bulk CuO is studied to compare across length scales. The results from comprehensive material characterization revealed correlations between CuO surface reactivity and bacterial toxicity with CuO nanosheets having the highest surface reactivity, electrochemical activity, and antimicrobial activity. While less active than the nanosheets, CuO nanoparticles (sphere-like shape) demonstrated enhanced reactivity compared to the bulk CuO. This is in agreement with previous studies investigating differences across length-scales. To elucidate the underlying mechanisms of action to further explain the shape-dependent behavior, kinetic models applied to the toxicity data. In addition to revealing different CuO material kinetics, trends in observed response cannot be explained by surface area alone. The compiled results contribute to further elucidate pathways toward controlled design of ENMs.

Commercially available lumber, pressure-treated with micronized copper azole (MCA), has largely replaced other inorganic biocides for residential wood treatment in the USA, yet little is known about how different outdoor environmental conditions impact the release of ionic, nano-scale, or larger (micron-scale) copper from this product. Therefore, we weathered pressure treated lumber for 18 months in five different climates across the continental United States. Copper release was quantified every month and local weather conditions were recorded continuously to determine the extent to which local climate regulated the release of copper from this nano-enabled product during its use phase. Two distinct release trends were observed: In cooler, wetter climates release occurred primarily during the first few months of weathering, as the result of copper leaching from surface/near-surface areas. In warmer, drier climates, less copper was initially released due to limited precipitation. However, as the wood dried and cracked, the exposed copper-bearing surface area increased, leading to increased copper release later in the product lifetime. Single-particle-ICP-MS results from laboratory prepared MCA-wood leachate solutions indicated that a) the predominant form of released copper passed through a filter smaller than 0.45 micrometers and b) released particles were largely resistant to dissolution over the course of 6 wks. Toxicity Characteristic Leaching Procedure (TCLP) testing was conducted on nonweathered and weathered MCA-wood samples to simulate landfill conditions during their end-of-life (EoL) phase and revealed that MCA wood released

A cotreatment process for produced water and abandoned mine drainage (AMD) has been established and demonstrated at the pilot-scale. The present study evaluates the potential of the proposed process to aid in management of two high volume wastewater resources in Pennsylvania. A systems-level approach is established to evaluate the primary trade-offs, including cotreatment process environmental impacts, transportation impacts, and environmental benefits realized from precluding direct AMD release to the environment. Life cycle impact assessment was used to quantify the environmental and human health impacts as well as to identify "hot spots" of the cotreatment process. Electricity use was found to be the dominant contributor to all impact categories. Extending the system boundary to include transportation of the two wastewaters to a to-be-determined cotreatment site revealed the important impact of transportation. An optimization approach was employed (using the region of Southwest Pennsylvania) to evaluate minimization of transportation distance considering the location and number of treatment sites. Finally, a quantitative analysis of environmental benefits realized by precluding direct AMD release to the environment was performed. The results suggest that the magnitude of benefit realized in treating a highly polluted AMD is greater than the magnitude of impacts from the cotreatment process.

A method for enhancing electronic performance of single-walled carbon nanotube (SWCNT) thin films through enhanced dispersion of SWCNTs in aqueous solutions is presented. The best dispersion enhancement is obtained by covalent attachment of urea to the acid functionalized SWCNTs. Dispersion properties of urea treatment are compared to conventional chemical and physical treatment techniques, such as surfactants. The treatment type and time significantly influence SWCNT surface functionalization, which determines the dispersion effectiveness as described by the SWCNT aggregate size, morphology and stability. The findings suggest that urea-SWCNTs, as compared to surfactant dispersed-SWCNTs, resulted in the most effective dispersion method among chemical treatments, yielding the smallest monodispersed aggregates with the most rod-like morphology that were stable over the greatest range in pH. Thin films prepared with SWCNT samples were evaluated for their transparency and resistance, two metrics that are important for electronics device applications. The urea-SWCNT films exhibited superior optoelectrical properties compared to SWCNT films prepared with conventional chemicals as well as surfactants. This indicates a correlation between degree of dispersibility and optoelectrical properties.

A safe, scalable method for producing highly conductive aligned films of single-walled carbon nanotubes (SWNTs) from water suspensions is presented. While microfluidic assembly of SWNTs has received significant attention, achieving desirable SWNT dispersion and morphology in fluids without an insulating surfactant or toxic superacid is challenging. We present a method that uniquely produces a noncorrosive ink that can be directly applied to a device in situ, which is different from previous fabrication techniques. Functionalized SWNTs (f-SWNTs) are dispersed in an aqueous urea solution to leverage binding between the amine group of urea and the carboxylic acid group of f-SWNTs and obtain urea-SWNT. Compared with SWNTs dispersed using conventional methods (e.g., superacid and surfactants), the dispersed urea-SWNT aggregates have a higher aspect ratio with a rodlike morphology as measured by light scattering. The Mayer rod technique is used to prepare urea-SWNT, highly aligned films (two-dimensional nematic order parameter of 0.6, 5 μm spot size, via polarized Raman) with resistance values as low as 15-1700 Ω/sq in a transmittance range of 2-80% at 550 nm. These values compete with the best literature values for conductivity of SWNT-enabled thin films. The findings offer promising opportunities for industrial applications relying on highly conductive thin SWNT films.

The Twelve Principles of Green Chemistry were first published in 1998 and provide a framework that has been adopted not only by chemists, but also by design practitioners and decision-makers (e.g., materials scientists and regulators). The development of the Principles was initially motivated by the need to address decades of unintended environmental pollution and human health impacts from the production and use of hazardous chemicals. Yet, for over a decade now, the Principles have been applied to the synthesis and production of engineered nanomaterials (ENMs) and the products they enable. While the combined efforts of the global scientific community have led to promising advances in the field of nanotechnology, there remain significant research gaps and the opportunity to leverage the potential global economic, societal and environmental benefits of ENMs safely and sustainably. As such, this tutorial review benchmarks the successes to date and identifies critical research gaps to be considered as future opportunities for the community to address. A sustainable material design framework is proposed that emphasizes the importance of establishing structure-property-function (SPF) and structure-property-hazard (SPH) relationships to guide the rational design of ENMs. The goal is to achieve or exceed the functional performance of current materials and the technologies they enable, while minimizing inherent hazard to avoid risk to human health and the environment at all stages of the life cycle.

Life cycle assessment (LCA) – a comprehensive modeling framework used to identify environmental and human health impacts associated with products, processes, and technologies – is increasingly recommended for emerging nanotechnologies. LCA applied prospectively can guide design decisions and enable reduction of future impacts. A growing literature describes the potential for LCA to inform development of safer nanotechnologies, for example by identifying the manufacturing inputs or processes with the greatest potential for improvement. However, few published studies to date include all life cycle stages in part because of uncertainty regarding engineered nanomaterial (ENM) releases and impacts, which precludes comprehensive environmental assessment of nano-enabled products. Life cycle impact assessment (LCIA) converts emissions into environmental damages through linked fate-exposure-effect models that require robust experimental data and a mechanistic understanding for each of these components. In the case of ENMs, there are pertinent knowledge gaps, high uncertainties in experimental data, and disagreement regarding the suitability of existing fate, exposure, and effect models. This frontier review summarizes recent advances in human and aquatic ecotoxicity LCIA for ENMs and calls for greater coordination between LCA modelers and experimentalists, including those that study fate and transport, environmental transformations, occupational exposure, and toxicology, to inform responsible development of nanotechnology, enabling ENMs to reach their full potential.

Engineered nanomaterials (ENMs) and ENM-enabled products have emerged as potentially high-performance replacements to conventional materials and chemicals. As such, there is an urgent need to incorporate environmental and human health objectives into ENM selection and design processes. Here, an adapted framework based on the Ashby material selection strategy is presented as an enhanced selection and design process, which includes functional performance as well as environmental and human health considerations. The utility of this framework is demonstrated through two case studies, the design and selection of antimicrobial substances and conductive polymers, including ENMs, ENM-enabled products and their alternatives. Further, these case studies consider both the comparative efficacy and impacts at two scales: (i) a broad scale, where chemical/material classes are readily compared for primary decision-making, and (ii) within a chemical/material class, where physicochemical properties are manipulated to tailor the desired performance and environmental impact profile. Development and implementation of this framework can inform decision-making for the implementation of ENMs to facilitate promising applications and prevent unintended consequences.

As for any emerging technology, it is critical to assess potential life cycle impacts prior to widespread adoption to prevent future unintended consequences. The subject of this life cycle study is a carbon nanotube-enabled chemical gas sensor, which is a highly complex, low nanomaterial-concentration application with the potential to impart significant human health benefits upon implementation. Thus, the net lifecycle trade-offs are quantified using an impact-benefit ratio (IBR) approach proposed herein, where an IBR1 indicates that the downstream benefits outweigh the upstream impacts. The cradle-to-gate assessment results indicate that the midpoint impacts associated with producing CNTs are marginal compared with those associated with the other manufacturing stages. The cumulative upstream impacts are further aggregated to units of disability-adjusted life years (DALYs) using ReCiPe end point analysis method and quantitatively compared with the potential downstream DALY benefits, as lives saved, during the use phase. The approach presented in this study provides a guiding framework and quantitative method intended to encourage the development of nanoenabled products that have the potential to realize a net environmental, health, or societal benefit.

The Twelve Principles of Green Chemistry were first published in 1998 and provide a framework that has been adopted not only by chemists, but also by design practitioners and decision-makers (e.g., materials scientists and regulators). The development of the Principles was initially motivated by the need to address decades of unintended environmental pollution and human health impacts from the production and use of hazardous chemicals. Yet, for over a decade now, the Principles have been applied to the synthesis and production of engineered nanomaterials (ENMs) and the products they enable. While the combined efforts of the global scientific community have led to promising advances in the field of nanotechnology, there remain significant research gaps and the opportunity to leverage the potential global economic, societal and environmental benefits of ENMs safely and sustainably. As such, this tutorial review benchmarks the successes to date and identifies critical research gaps to be considered as future opportunities for the community to address. A sustainable material design framework is proposed that emphasizes the importance of establishing structure–property–function (SPF) and structure–property–hazard (SPH) relationships to guide the rational design of ENMs. The goal is to achieve or exceed the functional performance of current materials and the technologies they enable, while minimizing inherent hazard to avoid risk to human health and the environment at all stages of the life cycle.

Silver was utilized throughout history to prevent the growth of bacteria in food and wounds. Recently, nanoscale silver has been applied to consumer textiles (nAg-textiles) to eliminate the prevalence of odor-causing bacteria. In turn, it is proposed that consumers will launder these items less frequently thus, reducing the life cycle impacts. While previous studies report that laundering processes are associated with the greatest environmental impacts of these textiles, there is no data available to support the proposed shift in consumer laundering behavior. Here, the results from a comprehensive literature review of nAg-textile life cycle studies are used to inform a cradle-to-grave life cycle impact assessment. Rather than assuming shifts in consumer behavior, the impact assessment is conducted in such a way that considers all laundering scenarios to elucidate the potential for reduced laundering to enable realization of a net life cycle benefit. In addition to identifying the most impactful stages of the life cycle across nine-midpoint categories, a payback period and uncertainty analysis quantifies the reduction in lifetime launderings required to recover the impacts associated with nanoenabling the textile. Reduction of nAg-textile life cycle impacts is not straightforward and depends on the impact category considered.

Given the increased utility and lack of consensus regarding carbon nanotube (CNT) environmental and human health hazards, there is a growing demand for guidelines that inform safer CNT design. In this study, the zebrafish (Danio rerio) model is utilized as a stable, sensitive biological system to evaluate the bioactivity of systematically modified and comprehensively characterized multi-walled carbon nanotubes (MWNTs). MWNTs were treated with strong acid to introduce oxygen functional groups, which were then systematically thermally reduced and removed using an inert temperature treatment. While 25 phenotypic endpoints were evaluated at 24 and 120 hours post-fertilization (hpf), high mortality at 24 hpf prevented further resolution of the mode of toxicity leading to mortality. Advanced multivariate statistical methods are employed to establish a model that identifies those MWNT physicochemical properties that best estimate the probability of observing an adverse outcome. The physicochemical properties considered in this study include surface charge, percent surface oxygen, dispersed aggregate size and morphology and electrochemical activity. Of the five physicochemical properties, surface charge, quantified as the point of zero charge (PZC), was determined as the best predictor of mortality at 24 hpf. From a design perspective, the identification of this property–hazard relationship establishes a foundation for the development of design guidelines for MWNTs with reduced hazard.

Multiwalled carbon nanotubes (MWNTs) are utilized in a number of sectors as a result of their favorable electronic properties. In addition, MWNT antimicrobial properties can be exploited or considered a potential liability depending on their intended application and handling. The ability to tailor electrochemical and antimicrobial properties using economical and conventional treatment processes introduces the potential to significantly enhance product performance. Oxygen functional groups are known to influence several MWNT properties, including redox activity. Here, MWNTs were functionalized with oxygen groups using standard acid treatments followed by selective reduction via annealing. Chemical derivatization coupled to X-ray photoelectron spectroscopy was utilized to quantify specific surface oxygen group concentration after variable treatment conditions, which were then correlated to observed trends in electrochemical and antimicrobial activities. These activities were evaluated as the potential for MWNTs to participate in the oxygen reduction reaction and to have the ability to promote the oxidation of glutathione. The compiled results strongly suggest that the reduction of surface carboxyl groups and the redox activity of carbonyl groups promote enhanced MWNT reactivity and elucidate the opportunity to design functional MWNTs for enhanced performance in their intended electrochemical or antimicrobial application.