Fate Of Engineered Nanomaterials Research Articles

Role of root exudates on the transformation and ecological effect of engineering nanomaterials in soil system: A critical review

AbstractDue to the widespread use of engineered nanomaterials (ENMs) for soil remediation and nano‐enabled sustainable agriculture, there is a growing concern regarding the behavior and fate of ENMs released into soil systems in the presence of natural root exudates (REs). Herein, we investigate the influence of REs on the fate and ecological effect of ENMs from a comprehensive perspective. We summarize the key roles reported in the literature for REs in physical changes (e.g., adsorption, dispersion/aggregation), chemical changes (e.g., oxidation/redox reactions, and dissolution), and biotransformation of ENMs, which will further determine the ecological risk of ENMs in natural soil systems. Moreover, this review highlights the potential adverse effects of ENMs on different soil organisms (e.g., bacteria, plants, and eisenia foetida) in the presence of REs. The remaining unclear mechanisms (e.g., oxidative stress and DNA damage) of ENMs toxicity at the cellular level influenced by REs are reviewed and presented. Finally, the review concludes by addressing the current knowledge gaps and challenges in this field.

Analytical chemistry of engineered nanomaterials: Part 2. analysis in complex samples (IUPAC Technical Report)

Abstract Recently, the scope, regulation, legislation, and metrology of the analytical chemistry of engineered nanomaterials (ENMs) have been reviewed in the Part 1 of the IUPAC Technical Report. Chemical analysis of nanomaterials in complex sample matrices presents a substantial challenge for analytical science and regulatory agencies. The purpose of the present Part 2 is to discuss the detection, characterization, and quantification of nanomaterials in samples of complex matrices including methods for sample preparation and fitness for purpose. Analytical methods applied to analysis in matrices of environmental samples, food, cosmetics, and biological samples as well as those used to monitor the fate of ENMs in the environment and biological systems are reported. Tables of numerous recently published works on analyses of typical ENMs with detailed protocols and conclusive comments are presented. There is a rapid development in the field mostly in the stage of accumulation of factual material. The single-particle inductively coupled plasma mass spectrometry is already widely used at the chemical analysis of metal-containing nanoparticles.

Lipid Composition of the Cell Membrane Outer Leaflet Regulates Endocytosis of Nanomaterials through Alterations in Scavenger Receptor Activity.

Understanding the principles that guide the uptake of engineered nanomaterials (ENMs) by cells is of interest in biomedical and occupational health research. While evidence has started to accumulate on the role of membrane proteins in ENM uptake, the role of membrane lipid chemistry in regulating ENM endocytosis has remained largely unexplored. Here, we have addressed this issue by altering the plasma membrane lipid composition directly in live cells using a methyl-α-cyclodextrin (MαCD)-catalyzed lipid exchange method. Our observations, in an alveolar epithelial cell line and using silica nanoparticles, reveal that the lipid composition of the plasma membrane outer leaflet plays a significant role in ENM endocytosis and the intracellular fate of ENMs, by affecting nonspecific ENM diffusion into the cell, changing membrane fluidity, and altering the activity of scavenger receptors (SRs) involved in active endocytosis. These results have implications for understanding ENM uptake in different subsets of cells, depending on cell membrane lipid composition.

The impacts of metal-based engineered nanomaterial mixtures on microbial systems: A review.

The last decade has witnessed tremendous growth in the commercial use of metal-based engineered nanomaterials (ENMs) for a wide range of products and processes. Consequently, direct and indirect release into environmental systems may no longer be considered negligible or insignificant. Yet, there is an active debate as to whether there are real risks to human or ecological health with environmental exposure to ENMs. Previous research has focused primarily on the acute effects of individual ENMs using pure cultures under controlled laboratory environments, which may not accurately reveal the ecological impacts of ENMs under real environmental conditions. The goal of this review is to assess our current understanding of ENM effects as we move from exposure of single to multiple ENMs or microbial species. For instance, are ENMs' impacts on microbial communities predicted by their intrinsic physical or chemical characteristics or their effects on single microbial populations; how do chronic ENM interactions compare to acute toxicity; does behavior under simplified laboratory conditions reflect that in environmental media; finally, is biological stress modified by interactions in ENM mixtures relative to that of individual ENM? This review summarizes key findings and our evolving understanding of the ecological effects of ENMs under complex environmental conditions on microbial systems, identifies the gaps in our current knowledge, and indicates the direction of future research.

A Review on the Environmental Fate Models for Predicting the Distribution of Engineered Nanomaterials in Surface Waters.

Exposure assessment is a key component in the risk assessment of engineered nanomaterials (ENMs). While direct and quantitative measurements of ENMs in complex environmental matrices remain challenging, environmental fate models (EFMs) can be used alternatively for estimating ENMs’ distributions in the environment. This review describes and assesses the development and capability of EFMs, focusing on surface waters. Our review finds that current engineered nanomaterial (ENM) exposure models can be largely classified into three types: material flow analysis models (MFAMs), multimedia compartmental models (MCMs), and spatial river/watershed models (SRWMs). MFAMs, which is already used to derive predicted environmental concentrations (PECs), can be used to estimate the releases of ENMs as inputs to EFMs. Both MCMs and SRWMs belong to EFMs. MCMs are spatially and/or temporally averaged models, which describe ENM fate processes as intermedia transfer of well-mixed environmental compartments. SRWMs are spatiotemporally resolved models, which consider the variability in watershed and/or stream hydrology, morphology, and sediment transport of river networks. As the foundation of EFMs, we also review the existing and emerging ENM fate processes and their inclusion in recent EFMs. We find that while ENM fate processes, such as heteroaggregation and dissolution, are commonly included in current EFMs, few models consider photoreaction and sulfidation, evaluation of the relative importance of fate processes, and the fate of weathered/transformed ENMs. We conclude the review by identifying the opportunities and challenges in using EFMs for ENMs.

Nanomaterial Transformation in the Soil-Plant System: Implications for Food Safety and Application in Agriculture.

Engineered nanomaterials (ENMs) have huge potential for improving use efficiency of agrochemicals, crop production, and soil health; however, the behavior and fate of ENMs and the potential for negative long-term impacts to agroecosystems remain largely unknown. In particular, there is a lack of clear understanding of the transformation of ENMs in both soil and plant compartments. The transformation can be physical, chemical, and/or biological, and may occur in soil, at the plant interface, and/or inside the plant. Due to these highly dynamic processes, ENMs may acquire new properties distinct from their original profile; as such, the behavior, fate, and biological effects may also differ significantly. Several essential questions in terms of ENMs transformation are discussed, including the drivers and locations of ENM transformation in the soil-plant system and the effects of ENM transformation on analyte uptake, translocation, and toxicity. The main knowledge gaps in this area are highlighted and future research needs are outlined so as to ensure sustainable nanoenabled agricultural applications.

Differential Reactivity of Copper- and Gold-Based Nanomaterials Controls Their Seasonal Biogeochemical Cycling and Fate in a Freshwater Wetland Mesocosm.

Reliable predictions of the environmental fate and risk of engineered nanomaterials (ENMs) require a better understanding of ENM reactivity in complex, biologically active systems for chronic low-concentration exposure scenarios. Here, simulated freshwater wetland mesocosms were dosed with ENMs to assess how their reactivity and seasonal changes in environmental parameters influence ENM fate in aquatic systems. Copper-based ENMs (Kocide), known to dissolve in water, and gold nanoparticles (AuNPs), stable against dissolution in the absence of specific ligands, were added weekly to mesocosm waters for 9 months. Metal accumulation and speciation changes in the different environmental compartments were assessed over time. Copper from Kocide rapidly dissolved likely associating with organic matter in the water column, transported to terrestrial soils and deeper sediment where it became associated with organic or sulfide phases. In contrast, Au accumulated on/in the macrophytes where it oxidized and transferred over time to surficial sediment. A dynamic seasonal accumulation and metal redox cycling were found between the macrophyte and the surficial sediment for AuNPs. These results demonstrate the need for experimental quantification of how the biological and chemical complexity of the environment, combined with their seasonal variations, drive the fate of metastable ENMs.

Inventory of country-specific emissions of engineered nanomaterials throughout the life cycle

This study presents a country-specific European release dataset for engineered nanomaterials (ENMs) for 2015, featuring updated products containing ENMs and distribution over countries. The main goal is to assist ENM fate and risk assessments.

Modeling the transport of titanium dioxide nanomaterials from combined sewer overflows in an urban river

Combined sewer overflows (CSOs) occur frequently in the United States, discharging an estimated 3.2 billion cubic meters of untreated sewage into receiving waters every year. These discharges contain a variety of contaminants including engineered nanomaterials (ENMs), yet ENMs discharged through CSOs have not been taken into account in ENM fate and transport models. This study fills this knowledge gap by developing a new integrated model that links an urban hydrologic-hydraulic model, using the Storm Water Management Model (SWMM), with a three-dimensional hydrodynamic and water quality model of rivers, using the Environmental Fluid Dynamics Code (EFDC). The modeling framework was applied to predict the concentrations of titanium dioxide (TiO2) ENMs in the Buffalo River in Buffalo, New York, as a result of CSO events. CSOs are shown to have a potential for transient high concentrations of ENMs and thus potentially high localized risk near the CSO outfalls and deposition zones in the river. The present approach provides a promising modeling framework to simulate ENM fate and transport in urban waterways. The model presented in this study can help build a management tool to predict temporally and spatially varying concentrations of ENMs introduced into receiving waters through CSOs.

The Nano-Bio Interactions of Nanomedicines: Understanding the Biochemical Driving Forces and Redox Reactions.

Engineered nanomaterials (ENMs) have been developed for imaging, drug delivery, diagnosis, and clinical therapeutic purposes because of their outstanding physicochemical characteristics. However, the function and ultimate efficiency of nanomedicines remain unsatisfactory for clinical application, mainly because of our insufficient understanding of nanomaterial/nanomedicine-biology (nano-bio) interactions. The nonequilibrated, complex, and heterogeneous nature of the biological milieu inevitably influences the dynamic bioidentity of nanoformulations at each site (i.e., the interfaces at different biological fluids (biofluids), environments, or biological structures) of nano-bio interactions. The continuous interplay between a nanomedicine and the biological molecules and structures in the biological environments can, for example, affect cellular uptake or completely alter the designed function of the nanomedicine. Accordingly, the weak and strong driving forces at the nano-bio interface may elicit structural reconformation, decrease bioactivity, and induce dysfunction of the nanomaterial and/or redox reactions with biological molecules, all of which may elicit unintended and unexpected biological outcomes. In contrast, these driving forces also can be manipulated to mitigate the toxicity of ENMs or improve the targeting abilities of ENMs. Therefore, a comprehensive understanding of the underlying mechanisms of nano-bio interactions is paramount for the intelligent design of safe and effective nanomedicines. In this Account, we summarize our recent progress in probing the nano-bio interaction of nanomedicines, focusing on the driving force and redox reaction at the nano-bio interface, which have been recognized as the main factors that regulate the functions and toxicities of nanomedicines. First, we provide insight into the driving force that shapes the boundary of different nano-bio interfaces (including proteins, cell membranes, and biofluids), for instance, hydrophobic, electrostatic, hydrogen bond, molecular recognition, metal-coordinate, and stereoselective interactions that influence the different nano-bio interactions at each contact site in the biological environment. The physicochemical properties of both the nanoparticle and the biomolecule are varied, causing structure recombination, dysfunction, and bioactivity loss of proteins; correspondingly, the surface properties, biological functions, intracellular uptake pathways, and fate of ENMs are also influenced. Second, with the help of these driving forces, four kinds of redox interactions with reactive oxygen species (ROS), antioxidant, sorbate, and the prosthetic group of oxidoreductases are utilized to regulate the intracellular redox equilibrium and construct synergetic nanomedicines for combating bacteria and cancers. Three kinds of electron-transfer mechanisms are involved in designing nanomedicines, including direct electron injection, sorbate-mediated, and irradiation-induced processes. Finally, we discuss the factors that influence the nano-bio interactions and propose corresponding strategies to manipulate the nano-bio interactions for advancing nanomedicine design. We expect our efforts in understanding the nano-bio interaction and the future development of this field will bring nanomedicine to human use more quickly.

Sewage spills are a major source of titanium dioxide engineered (nano)-particles into the environment.

Sanitary sewer overflows (SSOs) are a common problem across the United States. An estimated 23,000-75,000 SSOs occurred annually in 2004 discharging between 11 and 38 billion liters of untreated wastewater to receiving waters. SSOs release many contaminants, including engineered nanomaterials (ENMs), to receiving water bodies. Measuring ENM concentrations in environmental samples remains a key challenge in environmental nanotechnology and requires the distinction between natural and engineered particles. This distinction between natural and engineered particles is often hampered by the similarities in the intrinsic properties of natural and engineered particles such as particle size, composition, density, surface chemistry, and by the limitations of the available nanometrology tools. To overcome these challenges, we applied a multi-method approach to measure the concentrations and properties of TiO2 engineered particles (e.g., ENMs and pigments) including 1) multi-element single particle-inductively coupled plasma-mass spectrometry (ME-SP-ICP-MS) to identify elemental associations and to determine elemental ratios in natural particles, 2) total elemental concentrations and ratios calculated from total metal concentrations measured following total sample digestion to estimate engineered particle concentrations, and 3) transmission electron microscopy (TEM) to characterize engineered particle size and morphology. ME-SP-ICP-MS analysis revealed that natural TiO2 particles are often associated with at least one of the following elements Al, Fe, Ce, Si, La, Zr, Nb, Pb, Ba, Th, Ta, W and U, and that elemental ratios of Ti to these elements is typical of riverine particulates and the average crustal ratios, except for Pb likely due to anthropogenic Pb contamination. High TiO2 engineered particle concentrations up to 100 μg L-1 were found in SSOs-impacted surface waters. TEM analysis demonstrated the presence of regular-shape TiO2 particles in SSOs-impacted surface waters. This study provides a comprehensive approach for measuring TiO2 engineered particle concentrations in surface waters. The quantitative data produced in this work can be used as input for modeling studies and pave the road toward routine monitoring of ENMs in environmental systems, validation of ENM fate models, and more accurate ENM exposure and risk assessment.

Colloidal stabilization of CeO2 nanomaterials with polyacrylic acid, polyvinyl alcohol or natural organic matter

Engineered nanomaterials (ENM) such as nano-sized cerium dioxide (CeO2) are increasingly applied. Meanwhile, concerns on their environmental fate are rising. Understanding the fate of ENM within and between environmental compartments such as surface water and groundwater is crucial for the protection of drinking water resources. Therefore, the colloidal stability of CeO2 ENM (2 mg L−1) was assessed with various surface coatings featuring different physico-chemical properties such as weakly anionic polyvinyl alcohol (PVA), strongly anionic polyacrylic acid (PAA) or complex natural organic matter (NOM) at various water compositions in batch experiments (pH 2–12, ionic strength 0–5 mM KCl or CaCl2). While uncoated CeO2 ENM aggregate in the range of pH 4–8 in 1 mM KCl solution, the results show that PAA, PVA and NOM surface coatings stabilize CeO2-ENM at neutral and alkaline pH in 1 mM KCl solution. Stabilization by PAA and NOM is associated with strongly negative zeta potentials below −20 mV, suggesting electrostatic repulsion as stabilization mechanism. No aggregation was detected up to 5 mM KCl for PAA- and NOM-coated CeO2 ENM. In contrast, CaCl2 induced aggregation at >2.2 mM CaCl2 for PAA and NOM-coated CeO2 ENM respectively. PVA-coated ENM showed zeta potentials of −15 mV to −5 mV in the presence of 0–5 mM ionic strength, suggesting steric effects as stabilization mechanism. The hydrodynamic diameter of PVA-coated ENM was larger compared to PAA and NOM at low ionic strength, but the size did not increase with ionic strength of the suspensions. The effect of ionic strength and counter ion valency (pH 7) on the colloidal stability of ENM depends on the prevailing stabilization mechanism of the organic coating. NOM can be similarly effective in colloidal stabilization of CeO2-ENM as PAA. Our results suggest natural Ca-rich waters will lead to ENM agglomeration even of coated CeO2-ENM.

Modeling the fate and end-of-life phase of engineered nanomaterials in the Japanese construction sector

To date construction materials that contain engineered nanomaterials (ENMs) are available at the markets, but at the same time very little is known about their environmental fate. Therefore, this study aimed at modeling the potential fate of ENMs by using the example of the Japanese construction sector and by conducting a dynamic material flow analysis. Expert interviews and national reports revealed that about 3920–4660 tons of ENMs are annually used for construction materials in Japan. Nanoscale TiO2, SiO2, Al2O3 and carbon black have already been applied for decades to wall paints, road markings or concrete. The dynamic material flow model indicates that in 2016 about 95% of ENMs, which have been used since their year of market penetration, remained in buildings, whereas only 5% ended up in the Japanese waste management system or were diffusely released into the environment. Considering the current Japanese waste management system, ENMs were predicted to end up in recycled materials (40–47%) or in landfills (36–41%). It was estimated that only a small proportion was used in agriculture (5–7%, as ENM-containing sewage sludges) or was diffusely released into soils, surface waters or the atmosphere (5–19%). The results indicate that ENM release predominantly depend on their specific applications and characteristics. The model also highlights the importance of adequate collection and treatment of ENM-containing wastes. In future, similar dynamic flow models for other countries should consider, inasmuch as available, historical data on ENM production (e.g. like declaration reports that are annually published by relevant public authorities or associations), as such input data is very important regarding data reliability in order to decrease uncertainties and to continuously improve model accuracy. In addition, more environmental monitoring studies that aim at the quantification of ENM release and inadvertent transfer, particularly triggered by waste treatment processes, would be needed in order to validate such models.

Interactions, Transformations, and Bioavailability of Nano-Copper Exposed to Root Exudates.

Due to the potential for interactions between crop plants and engineered nanomaterials (ENMs), there is increasing interest in understanding the bioavailability and effects of ENMs released into soil systems. Here, we investigate the influence of root exudates on the fate of ENMs from a thermodynamic perspective. Nano isothermal titration calorimetry was applied to determine thermodynamic parameters for the interaction between nanocopper (nCu) and synthetic root exudate (SRE) and its components (including sugars, organic acids, amino acids, and phenolic acids), as well as Cu2+ and SRE. The measured binding constant (Kd = 5.645 × 103 M-1) indicated strong interactions between nCu particles and SRE, as well as with individual organic acids. The interaction between Cu2+ and SRE was stronger (Kd = 7.181 × 104 M-1) but varies for the individual SRE components. nCu dissolution in the presence of SRE was the predominant interaction. In addition, SRE resulted in a complex transformation of nCu, where Cu2+, Cu+, and Cu0 were formed via oxidation and reduction. Plant-nCu exposure experiments indicate that the binding of SRE with nCu and dissolved Cu ions can significantly decrease Cu uptake and bioaccumulation in plants. nITC provides a fundamental thermodynamic understanding of interactions between nCu and plant root exudates, providing an important tool for understanding plant NP-interactions.

Effect of surfactants on the aggregation and sedimentation of zinc oxide nanomaterial in natural water matrices.

The wide application of surfactants and engineered nanomaterials (ENMs) in industrial and consumer products lead to the high possibility of their co-presence in natural water environment, making it important to study the effect of surfactants on the environmental behavior and fate of ENMs. In this work, we selected an anionic sodium dodecyl sulfate (SDS) and a nonionic nonylphenol ethoxylate (NPEO, Tergitol NP-9) to study their effects on the aggregation and sedimentation of a 20nm ZnO ENM in different water matrices. The adsorption of SDS and NP-9 by ZnO ENM were fitted with Langmuir model, and the maximum adsorption capacities were 43.73±4.62mg/g and 13.79±1.09 respectively. As the surfactant concentration increased from 0 to 0.030% (m:v), SDS reduced the zeta potential of ZnO ENM from 17.56±2.13 to -27.96±2.59mV, whereas NP-9 did not affect the zeta potential. After a 24-h batch reactor experiment, SDS and NP-9 reduced 93.02% and 80.26% of the aggregate size of ZnO ENM (50mgL-1) in maximum at surfactant concentrations≥0.015%. The ZnO ENM was not stable in natural aqueous matrices, mainly because of the relatively high ionic strength. However, surfactants were found to reduce the aggregation and sedimentation of ZnO ENM in six natural water matrices in different degrees. With the presence of 0.030% SDS in tap water, maximum reduction rates of aggregate size and sedimentation were recorded as 69.54% and 26.69%, respectively. The results of this study indicate that the presence of surfactants may alter the behaviors and fate of ENMs in natural water environment.

Leaching of nano-ZnO in municipal solid waste

Despite widespread use of engineered nanomaterials (ENMs) in commercial products and their potential disposal in landfills, the fate of ENMs in solid waste environments are still not well understood. In this study, the leaching behavior of nano ZnO -one of the most used ENMs- in fresh municipal solid waste (MSW) was investigated. Batch reactors containing municipal solid waste samples were spiked with three different types of nano ZnO having different surface stabilization. The leaching of ZnO was examined under acidic, basic and elevated ionic strength (IS) conditions. The results of the 3-day batch tests showed that the percent of the added nano-ZnO mass retained within the solid waste matrix ranged between 80% and 93% on average for the three types of nano-ZnO tested. The pH and IS conditions did not significantly influence the leaching behavior of ZnO. To further analyze the behavior of ZnO in the MSW matrix, a kinetic particle deposition/detachment model was developed. The model was able to reproduce the main trends of the batch experiments. Reaction rate constants for the batch tests ranged from 0.01 to 0.4 1/hr, reflecting the rapid deposition of nano-ZnO within the MSW matrix.

SEM analysis of particle size during conventional treatment of CMP process wastewater

Engineered nanomaterials (ENMs) are currently employed by many industries and have different physical and chemical properties from their bulk counterparts that may confer different toxicity. Nanoparticles used or generated in semiconductor manufacturing have the potential to enter the municipal waste stream via wastewater and their ultimate fate in the ecosystem is currently unknown. This study investigates the fate of ENMs used in chemical mechanical planarization (CMP), a polishing process repeatedly utilized in semiconductor manufacturing. Wastewater sampling was conducted throughout the wastewater treatment (WWT) process at the fabrication plant's on-site wastewater treatment facility. The goal of this study was to assess whether the WWT processes resulted in size-dependent filtration of particles in the nanoscale regime by analyzing samples using scanning electron microscopy (SEM). Statistical analysis demonstrated no significant differences in particle size between sampling points, indicating low or no selectivity of WWT methods for nanoparticles based on size. All nanoparticles appeared to be of similar morphology (near-spherical), with a high variability in particle size. EDX verified nanoparticles composition of silicon- and/or aluminum-oxide. Nanoparticle sizing data compared between sampling points, including the final sampling point before discharge from the facility, suggested that nanoparticles could be released to the municipal waste stream from industrial sources.

Nanotoxicity and Life Cycle Assessment: First attempt towards the determination of characterization factors for carbon nanotubes

Carbon materials, whether at macro, micro or at nanoscale, play an important role in the battery industry, as they can be used as electrodes, electrode enhancers, bipolar separators, or current collectors. When conducting a Life Cycle Assessment (LCA) of novel batteries manufacturing processes, we also need to consider the fate of potentially emitted carbon based nanomaterials. However, the knowledge generated in the last decade regarding the behavior of such materials in the environment and its toxicological effects has yet to be included in the Life Cycle Impact Assessment (LCIA) methodologies. Conventional databases of chemical products (e.g. ECHA, ECOTOX) offer little information regarding engineered nanomaterials (ENM). It is thus necessary to go one step further and compile physicochemical and toxicological data directly from scientific literature. Such studies do not only differ in their results, but also in their methodologies, and several calls have been made towards a more consistent approach that would allow us model the fate of ENM in the environment as well as their potentially harmful effects. Trying to overcome these limitations we have developed a tool based on Microsoft Excel® combining several methods for the estimation of physicochemical properties of carbon nanotubes (CNT). The information generated with this tool is combined with degradation rates and toxicological data consistent with the methods followed by the USEtox methodology. Thus, it is possible to calculate the characterization factors of CNTs and integrate them as a first proxy in future LCA of products including these ENM.

Emerging patterns for engineered nanomaterials in the environment: a review of fate and toxicity studies

A comprehensive assessment of the environmental risks posed by engineered nanomaterials (ENMs) entering the environment is necessary, due in part to the recent predictions of ENM release quantities and because ENMs have been identified in waste leachate. The technical complexity of measuring ENM fate and transport processes in all environments necessitates identifying trends in ENM processes. Emerging information on the environmental fate and toxicity of many ENMs was collected to provide a better understanding of their environmental implications. Little research has been conducted on the fate of ENMs in the atmosphere; however, most studies indicate that ENMs will in general have limited transport in the atmosphere due to rapid settling. Studies of ENM fate in realistic aquatic media indicates that in general, ENMs are more stable in freshwater and stormwater than in seawater or groundwater, suggesting that transport may be higher in freshwater than in seawater. ENMs in saline waters generally sediment out over the course of hours to days, leading to likely accumulation in sediments. Dissolution is significant for specific ENMs (e.g., Ag, ZnO, copper ENMs, nano zero-valent iron), which can result in their transformation from nanoparticles to ions, but the metal ions pose their own toxicity concerns. In soil, the fate of ENMs is strongly dependent on the size of the ENM aggregates, groundwater chemistry, as well as the pore size and soil particle size. Most groundwater studies have focused on unfavorable deposition conditions, but that is unlikely to be the case in many natural groundwaters with significant ionic strength due to hardness or salinity. While much still needs to be better understood, emerging patterns with regards to ENM fate, transport, and exposure combined with emerging information on toxicity indicate that risk is low for most ENMs, though current exposure estimates compared with current data on toxicity indicates that at current production and release levels, exposure to Ag, nZVI, and ZnO may cause toxicity to freshwater and marine species.

Identification and Avoidance of Potential Artifacts and Misinterpretations in Nanomaterial Ecotoxicity Measurements

Novel physicochemistries of engineered nanomaterials (ENMs) offer considerable commercial potential for new products and processes, but also the possibility of unforeseen and negative consequences upon ENM release into the environment. Investigations of ENM ecotoxicity have revealed that the unique properties of ENMs and a lack of appropriate test methods can lead to results that are inaccurate or not reproducible. The occurrence of spurious results or misinterpretations of results from ENM toxicity tests that are unique to investigations of ENMs (as opposed to traditional toxicants) have been reported, but have not yet been systemically reviewed. Our objective in this manuscript is to highlight artifacts and misinterpretations that can occur at each step of ecotoxicity testing: procurement or synthesis of the ENMs and assessment of potential toxic impurities such as metals or endotoxins, ENM storage, dispersion of the ENMs in the test medium, direct interference with assay reagents and unacknowledged indirect effects such as nutrient depletion during the assay, and assessment of the ENM biodistribution in organisms. We recommend thorough characterization of initial ENMs including measurement of impurities, implementation of steps to minimize changes to the ENMs during storage, inclusion of a set of experimental controls (e.g., to assess impacts of nutrient depletion, ENM specific effects, impurities in ENM formulation, desorbed surface coatings, the dispersion process, and direct interference of ENM with toxicity assays), and use of orthogonal measurement methods when available to assess ENMs fate and distribution in organisms.