Geographically distributed classification of surface water chemical parameters influencing fate and behavior of nanoparticles and colloid facilitated contaminant transport

Combined toxicity of fluorescent silica nanoparticles with cadmium in Ceriodaphnia dubia: Interactive effects of natural organic matter and green algae feeding

The environmental risks of silica nanoparticles (SiNP) reported in the literature are contradictory and bring into question its safety for use in consumer applications. Organisms are never exposed to NPs alone in the real environment, while studies of the combined toxicity of SiNP are limited. To address this, we compared the acute toxicity of fluorescent core-shell SiNPs alone and in mixtures with Cd2+ to Ceriodaphnia dubia in the absence and presence of NOM. We identified biodistribution and feeding behaviour in addition to the traditional endpoints. NOM increased the colloidal stability of SiNPs in reconstituted water. In immobility tests, no significant effects were observed from Cd2+ exposure with NOM and varying concentrations of SiNPs. A similar pattern of curve dose-response was observed for varying concentrations of SiNPs and increasing Cd2+ concentration and constant NOM. Fluorescence microscopy verified a dose-dependent bioaccumulation of SiNPs in C. dubia. Co-exposure to 10 mg L-1 SiNP with NOM and Cd2+ resulted in a stimulated stress feeding response at the lower Cd2+ concentrations which declined at the higher dose due to a functional impairment of the digestive tract. Alterations in feeding behaviour and the increasing bioaccumulation of SiNP indicate a potential ecological risk for Ceriodaphnia dubia from the mixture exposure.

Influence of humic acid and bovine serum albumin on colloid-associated heavy metal transport in saturated porous media

Colloid-facilitated contaminant transport in porous media has been widely observed in laboratory and field studies. In this study, the influence of two dissolved organic matters (DOMs), humic acid (HA) and bovine serum albumin (BSA), on the colloid-associated heavy metal transport, was investigated. Soil colloids with particle sizes <2 μm were prepared from bentonite. Glass bead was used as porous media for the column tests. The influence of DOM on the adsorption of Pb2+ and Cu2+ onto colloids was tested. Colloid mobility and colloid-metal co-transport in the presence/absence of DOMs were investigated by breakthrough tests. The test results showed that DOMs facilitated colloid mobility. The measured ζ-potentials showed that DOMs enhanced the electrostatic repulsion between colloids and glass beads and reduced colloid deposition. These findings were further confirmed by calculating the interaction energy using the DLVO theory. Batch tests showed the strong adsorption of Pb2+ and Cu2+ on the colloid, and the adsorption was enhanced by DOMs. The colloid-metal co-transport tests showed that colloids can significantly facilitate the transport of Pb2+ and Cu2+ and that the facilitation was further enhanced by DOMs. By heavy metals, the colloid mobility was retarded, mainly due to the increased deposition. The transport of Cu2+ facilitated by DOM was more obvious than that of Pb2+. Compared to BSA, the effect of HA on enhancing colloid mobility, increasing colloid adsorption to heavy metals, and hence on the facilitation of colloid-associated heavy metals transport was more prominent.

The environmental fate of nanoplastics: What we know and what we need to know about aggregation

The presence of nanoplastics in the environment has been proven. There is now an urgent need to determine how nanoplastics behave in the environment and to assess the risks they may pose. Here, we examine nanoplastic homo- and heteroaggregation, with a focus on environmentally relevant nanoplastic particle models. We made a systematic analysis of experimental studies, and ranked the environmental relevance of 377 different solution chemistries, and 163 different nanoplastic particle models. Since polymer latex spheres are not environmentally relevant (due to their monodisperse size, spherical shape, and smooth surface), their aggregation behavior in natural conditions is not transferable to nanoplastics. A few recent studies suggest that nanoplastic particle models that more closely mimic incidentally produced nanoplastics follow different homoaggregation pathways than latex sphere particle models. However, heteroaggregation of environmentally relevant nanoplastic particle models has seldom been studied. Despite this knowledge gap, the current evidence suggests that nanoplastics may be more sensitive to heteroaggregation than previously expected. We therefore provide an updated hypothesis about the likely environmental fate of nanoplastics. Our review demonstrates that it is essential to use environmentally relevant nanoplastic particle models, such as those produced with top-down methods, to avoid biased interpretations of the fate and impact of nanoplastics. Finally, it will be necessary to determine how the heteroaggregation kinetics of nanoplastics impact their settling rate to truly understand nanoplastics' fate and effect in the environment.

Influence of Soil Colloids on Ni Adsorption and Transport in the Saturated Porous Media: Effects of pH, Ionic Strength, and Humic Acid

Natural colloids are widely distributed in soil and groundwater. Due to their specific characteristics, colloids can actively involve various transport contaminants, resulting in a complicated fate and the transport of heavy metals to the environment. This study investigated the effects of soil colloids on the adsorption and transport of Ni2+ in saturated porous media under different conditions, including pH, ion strength (IS), and humic acid (HA), because these indexes are non-negligible in the fates of various organic or inorganic matters in the subsurface environment. The results indicate that Ni2+ adsorption by soil colloids slightly increased from 17% to 25% with the increase of pH from 5.5 to 7.5 at the IS of 30 mmol·L−1, whilst it significantly reduced from 55% to 17% with the increase of IS from 0 to 30 mmol·L−1 at a pH of 5.5. Both Langmuir and Freundlich models can fit the adsorption isotherms of Ni2+ on soil colloids and quartz sand. According to the column experiment, the presence of soil colloids increased the initial penetration rate, but could not increase the final transport efficiency of Ni2+ in the effluent. The presence of soil colloids has weakened the effect of IS on Ni2+ transport in the sand column. Moreover, this experiment implies that HA remarkably decreased the Ni2+ transport efficiency from 71.3% to 58.0% in the presence of soil colloids and that there was no significant difference in the HA effect on the Ni2+ transport in the absence of soil colloids.

A review on the generation, discharge, distribution, environmental behavior, and toxicity (especially to microbial aggregates) of nano-TiO2 in sewage and surface-water and related research prospects

This article reviews the nano-effects and applications of different crystalline nano‑titanium dioxide (nano-TiO₂), identifies their discharge, distribution, behavior, and toxicity to aquatic organisms (focusing on microbial aggregates) in sewage and surface-water, summarizes related toxicity mechanisms, and critically proposes future perspectives. The results show that: 1) based on crystal type, application boundaries of nano-TiO₂ have become clear, extending from traditional manufacturing to high-tech fields; 2) concentration of nano-TiO₂ in water is as high as hundreds of thousands of μg/L (sewage) or several to dozens of μg/L (surface-water) due to direct application or indirect release; 3) water environmental behaviors of nano-TiO₂ are mainly controlled by hydration conditions and particle characteristics; 4) aquatic toxicities of nano-TiO₂ are closely related to their water environmental behavior, in which crystal type and tested species (such as single species and microbial aggregates) also play the key role. Going forward, the exploration of the toxicity mechanism will surely become a hot topic in the aquatic-toxicology of nano-TiO₂, because most of the research so far has focused on the responses of biological indicators (such as metabolism and damage), while little is known about the stress imprint caused by the crystal structures of nano-TiO₂ in water environments. Additionally, the aging of nano-TiO₂ in a water environment should be heeded to because the continuously changing surface structure is bound to have a significant impact on its behavior and toxicity. Moreover, for microbial aggregates, comprehensive response analysis should be conducted in terms of the functional activity, surface features, composition structure, internal microenvironment, cellular and molecular level changes, etc., to find the key point of the interaction between nano-TiO₂ and microbial aggregates, and to take mitigation or beneficial measures to deal with the aquatic-toxicity of nano-TiO₂. In short, this article contributes by 1) reviewing the research status of nano-TiO₂ in all aspects: application and discharge, distribution and behavior, and its aquatic toxicity; 2) suggesting the response mechanism of microbial aggregates and putting forward the toxigenic mechanism of nanomaterial structure; 3) pointing out the future research direction of nano-TiO₂ in water environment.

Novel multimethod approach for the determination of the colloidal stability of nanomaterials in complex environmental mixtures using a global stability index: TiO2 as case study

A systematic study on the colloidal behavior of uncoated and polyvinylpyrrolidone (PVP) coated TiO₂ engineered nanomaterials (ENMs) in simulated aqueous media is herein reported, in which conditions representative for natural waters (pH, presence of divalent electrolytes (i.e. Ca²⁺/Mg²⁺ and SO₄^2-), of natural organic matter (NOM) and of suspended particulate matter (SPM)) were systematically varied. The colloidal stability of the different dispersions was investigated by means of Dynamic and Electrophoretic Light Scattering (DLS and ELS) and Centrifugal Separation Analysis (CSA), and a global stability index based on these three techniques was developed. The index allows to quantitatively classify the nano-based dispersions according to their colloidal stability affected by the different parameters studied. This multimethod approach clearly identifies inorganic SPM followed by divalent electrolytes as the main natural components destabilizing TiO₂ ENMs upon entering in simulated natural waters, while it highlights a moderate stabilization induced by NOM, depending mainly on pH. Moreover, the PVP coating was found to attenuate the influence of these parameters on the colloidal stability. The obtained results show how the global stability index developed is influenced by the complexity of the system, suggesting the importance of combining the information gathered from all the techniques employed to better elucidate the fate and behavior of ENMs in natural surface waters.

Ecotoxicological read-across models for predicting acute toxicity of freshly dispersed versus medium-aged NMs to Daphnia magna

Nanoinformatics models to predict the toxicity/ecotoxicity of nanomaterials (NMs) are urgently needed to support commercialization of nanotechnologies and allow grouping of NMs based on their physico-chemical and/or (eco)toxicological properties, to facilitate read-across of knowledge from data-rich NMs to data-poor ones. Here we present the first ecotoxicological read-across models for predicting NMs ecotoxicity, which were developed in accordance with ECHA's recommended strategy for grouping of NMs as a means to explore in silico the effects of a panel of freshly dispersed versus environmentally aged (in various media) Ag and TiO₂ NMs on the freshwater zooplankton Daphnia magna, a keystone species used in regulatory testing. The dataset used to develop the models consisted of dose-response data from 11 NMs (5 TiO₂ NMs of identical cores with different coatings, and 6 Ag NMs with different capping agents/coatings) each dispersed in three different media (a high hardness medium (HH Combo) and two representative river waters containing different amounts of natural organic matter (NOM) and having different ionic strengths), generated in accordance with the OECD 202 immobilization test. The experimental hypotheses being tested were (1) that the presence of NOM in the medium would reduce the toxicity of the NMs by forming an ecological corona, and (2) that environmental ageing of NMs reduces their toxicity compared to the freshly dispersed NMs irrespective of the medium composition (salt only or NOM-containing). As per the ECHA guidance, the NMs were grouped into two categories - freshly dispersed and 2-year-aged and explored in silico to identify the most important features driving the toxicity in each group. The final predictive models have been validated according to the OECD criteria and a QSAR model report form (QMRF) report included in the supplementary information to support adoption of the models for regulatory purposes.

Comparison of the effects of large-grained and nano-sized biochar, ferrihydrite, and complexes thereof on Cd and As in a contaminated soil-plant system

Cd and As are difficult to co-remediate in co-contaminated soils. In this study, remediation materials comprising large-grained and nano-sized biochar (BC), ferrihydrite (FH), and complexes thereof were added to Cd- and As-contaminated soil. The uptake of Cd and As by pak choi (Brassica chinensis L.) was then evaluated using a pot experiment and the Cd and As concentrations of the soil pore water and leaching water were measured. The Cd and As concentrations of the pore and leaching water were slightly increased with the addition of BC, and decreased with addition of FH and the biochar-ferrihydrite complex (BC-FH). However, nano-sized BC (BC_N), FH (FH_N), and BC-FH (BC-FH_N) had little influence on the decreases in Cd and As of the two monitored water types. Large-grained remediation materials, rather than nanomaterials, decreased the Cd and As concentrations of the two monitored water types. Nonetheless, nanomaterial treatments more effectively decreased the Cd and As concentrations in plants by an average of >10% relative to the large-grained treatments. The DLVO theory analysis suggested that BC_N, FH_N, and BC-FH_N, immobilized in the topsoil, adsorbed heavy metals in the rhizosphere soil. The remainder of the nano-sized materials was dispersed in the rhizosphere soil pores, shielding the uptake of Cd and As by the roots. Although the doses of nanomaterials used in this study were less than one-fortieth of those of the large-grained materials, changes in the plant rhizosphere microenvironment caused by the nanomaterials decreased the risk of toxicity transfer from the soil to the plants.

Morphology, structure, and composition of sulfidized silver nanoparticles and their aggregation dynamics in river water

The sulfidized form represents an environmentally relevant transformation state of silver nanoparticles (Ag-NPs) released into natural systems via wastewater route. However, the detailed characterization of sulfidized silver nanoparticles (S-Ag-NPs) is missing and their colloidal stability in aquatic systems is only insufficiently studied. The aim of this study was to systematically evaluate the surface properties, morphology, structure, composition, as well as aggregation dynamics of S-Ag-NPs in synthetic and natural river water. The S-Ag-NPs were prepared by sulfidation of citrate-coated silver nanoparticles (Cit-Ag-NPs). The sulfidation of Ag-NPs was accompanied by the formation of fiber-like Ag₂S nano-bridges, Ag⁰-Ag₂S core-shell structures, and hollow regions. In contrast to the published literature, the nano-bridges were thinner (2-9 nm) and longer (up to 60 nm), they formed at higher S^2-/Ag molar ratio (2.041), and the formation of the core-shell structures was observed even in the absence of natural organic matter (NOM). Furthermore, we observed selective sulfidation of nanoparticles which can induce the hot spots for the release of toxic Ag⁺ ions. The critical coagulation concentration (CCC) of Ca²⁺ determined for S-Ag-NPs in reconstituted river water was 2.47 ± 0.23 mmol/L and thus higher than the CCC obtained for Cit-Ag-NPs in our earlier study revealing higher colloidal stability of S-Ag-NPs. In natural river water, S-Ag-NPs were also colloidally more stable compared to the Cit-Ag-NPs. Furthermore, the stabilizing effect of NOM was much higher for S-Ag-NPs than for Cit-Ag-NPs. For S-Ag-NPs stabilized by a low amount of citrate, we expect longer residence times in the water phase of rivers and thus higher risk for aquatic organisms. In contrast to this, the pristine Cit-Ag-NPs are expected to be accumulated faster in the sediments representing higher risk for benthic organisms. This study contributes to better understanding of environmental fate and effects of Ag-NPs released via wastewater route.

Development of Deep Learning Models for Predicting the Effects of Exposure to Engineered Nanomaterials on Daphnia magna

This study presents the results of applying deep learning methodologies within the ecotoxicology field, with the objective of training predictive models that can support hazard assessment and eventually the design of safer engineered nanomaterials (ENMs). A workflow applying two different deep learning architectures on microscopic images of Daphnia magna is proposed that can automatically detect possible malformations, such as effects on the length of the tail, and the overall size, and uncommon lipid concentrations and lipid deposit shapes, which are due to direct or parental exposure to ENMs. Next, classification models assign specific objects (heart, abdomen/claw) to classes that depend on lipid densities and compare the results with controls. The models are statistically validated in terms of their prediction accuracy on external D. magna images and illustrate that deep learning technologies can be useful in the nanoinformatics field, because they can automate time-consuming manual procedures, accelerate the investigation of adverse effects of ENMs, and facilitate the process of designing safer nanostructures. It may even be possible in the future to predict impacts on subsequent generations from images of parental exposure, reducing the time and cost involved in long-term reproductive toxicity assays over multiple generations.

Multigenerational Exposures of Daphnia Magna to Pristine and Aged Silver Nanoparticles: Epigenetic Changes and Phenotypical Ageing Related Effects

Engineered nanoparticles (NPs) undergo physical, chemical, and biological transformation after environmental release, resulting in different properties of the "aged" versus "pristine" forms. While many studies have investigated the ecotoxicological effects of silver (Ag) NPs, the majority focus on "pristine" Ag NPs in simple exposure media, rather than investigating realistic environmental exposure scenarios with transformed NPs. Here, the effects of "pristine" and "aged" Ag NPs are systematically evaluated with different surface coatings on Daphnia magna over four generations, comparing continuous exposure versus parental only exposure to assess recovery potential for three generations. Biological endpoints including survival, growth and reproduction and genetic effects associated with Ag NP exposure are investigated. Parental exposure to "pristine" Ag NPs has an inhibitory effect on reproduction, inducing expression of antioxidant stress related genes and reducing survival. Pristine Ag NPs also induce morphological changes including tail losses and lipid accumulation associated with aging phenotypes in the heart, abdomen, and abdominal claw. These effects are epigenetic remaining two generations post-maternal exposure (F2 and F3). Exposure to identical Ag NPs (same concentrations) aged for 6 months in environmentally realistic water containing natural organic matter shows considerably reduced toxicological effects in continuously exposed generations and to the recovery generations.

Silica colloids as non-carriers facilitate Pb2+ transport in saturated porous media under a weak adsorption condition: effects of Pb2+ concentrations

Transport of environmental pollutants in groundwater systems can be greatly influenced by colloids. In this study, the cotransport of Pb²⁺ and silica (SiO₂) colloids at different Pb²⁺ concentrations was systematically investigated by batch adsorption and saturated sand column experiments. Results showed that SiO₂ colloids had low adsorption capacity for Pb²⁺ (less than 1% of the input) compared with sands. In saturated porous media, SiO₂ colloids showed a high mobility; however, with the increase of Pb²⁺ concentration in the sand column, the mobility of SiO₂ colloids gradually decreased. Notably, SiO₂ colloids could facilitate Pb²⁺ transport, although they did not serve as effective carriers of Pb²⁺. Under the condition of low Pb²⁺ concentration, SiO₂ colloids promoted the Pb²⁺ transport mainly through the way of "transport channel," while changing the porosity of the medium and masking medium adsorption sites were the main mechanisms of SiO₂ colloid-facilitated Pb²⁺ transport under the condition of high Pb²⁺ concentration. The discovery of this non-adsorption effect of colloids would improve our understanding of colloid-facilitated Pb²⁺ transport in saturated porous media, which provided new insights into the role of colloids, especially colloids with weak Pb²⁺ adsorption capacity, in Pb²⁺ occurrence and transport in soil-groundwater systems.

Water discrimination based on the kinetic variations of AgNP spectrum

The assessment of water quality and its classification have considerable importance on public health. This requires monitoring of a wide range of physical, chemical and biological parameters. Here, an array of sensors composed of absorbances in different wavelengths in a kinetic process was used for classification. The data were obtained in the kinetic absorbance variations of silver nanoparticles (AgNPs) in the presence of different mineral waters. Spectral variations with time for each water sample were vectorized, and the matrix composed of these vectors was analyzed using principal component analysis (PCA) and hierarchical cluster analysis (HCA) as unsupervised clustering methods. The distinct clusters of nine different water samples were obtained using PCA and clustering by HCA resulted in an error rate of only 14.8%, which corresponds to misclassification of 4 water samples out of 27. The ability of the method for the discrimination of water samples using AgNP as the sole reagent can be attributed to the high dimensionality of data and the influence of the chemical environment in each water sample on the absorbance variations of AgNPs.

Water samples can be classified by AgNPs.

In the Search for Nanospecific Effects of Dissolution of Metallic Nanoparticles at Freshwater-Like Conditions: A Critical Review

Knowledge on relations between particle properties and dissolution/transformation characteristics of metal and metal oxide nanoparticles (NPs) in freshwater is important for risk assessment and product development. This critical review aims to elucidate nanospecific effects on dissolution of metallic NPs in freshwater and similar media. Dissolution rate constants are compiled and analyzed for NPs of silver (Ag), copper (Cu), copper oxide/hydroxide (CuO, Cu(OH)₂), zinc oxide (ZnO), manganese (Mn), and aluminum (Al), showing largely varying (orders of magnitude) constants when modeled using first order kinetics. An effect of small primary sizes (<15 nm) was observed, leading to increased dissolution rate constants and solubility in some cases. However, the often extensive particle agglomeration can result in reduced nanospecific effects on dissolution and also an increased uncertainty related to the surface area, a parameter that largely influence the extent of dissolution. Promising ways to model surface areas of NPs in solution using fractal dimensions and size distributions are discussed in addition to nanospecific aspects related to other processes such as corrosion, adsorption of natural organic matter (NOM), presence of capping agents, and existence of surface defects. The importance of the experimental design on the results of dissolution experiments of metal and metal oxide NPs is moreover highlighted, including the influence of ionic metal solubility and choice of particle dispersion methodology.

Enhanced cadmium immobilization in saturated media by gradual stabilization of goethite in the presence of humic acid with increasing pH

Goethite (Gt) and humic acid (HA) are important components of soil that significantly affect Cd mobility. In this study, the co-transport of Cd²⁺ and Gt with/without HA in saturated sand columns was investigated by monitoring the breakthrough curves at different pH values. A solute transport model was used to study Cd²⁺ transport and retention in the saturated sand in the presence of Gt and HA, and a colloid transport model was used to describe the Gt colloid (Gt_C) transport in the columns. Our results showed that the transport behaviors of Cd²⁺ and Gt colloids/aggregates were regulated by pH. Cadmium transport was significantly inhibited at high pH due to its adsorption on the sand and Gt. Moreover, Gt retention was gradually stabilized with increasing pH regardless of its forms, i.e., individual colloids (Gt_C) or larger assemblages of particles due to aggregation (Gt_A). This retention was obviously enhanced in the presence of HA. Thus, the superposition of increased Cd²⁺ adsorption on Gt and Gt retention (stabilization) enhanced the immobilization of Cd²⁺ at high pH. In addition to stabilizing Gt, HA further enhance Cd²⁺ adsorption on Gt, thus promoting Cd²⁺ immobilization. However, only a small amount of organic-matter-bound Cd²⁺ was observed in the columns with injected HA. The major fractions of retained Cd²⁺ were exchangeable Cd²⁺ and Fe-oxide-bound Cd²⁺. Our results provide new insights into the roles of Gt and HA in the transport and mobilization of Cd²⁺ in soil-groundwater systems.

Simulating graphene oxide nanomaterial phototransformation and transport in surface water

The production of graphene-family nanomaterials (GFNs) has increased appreciably in recent years. Graphene oxide (GO) has been found to be the most toxic nanomaterial among GFNs and, to our knowledge, no studies have been conducted to model its fate and transport in the environment. Lab studies show that GO undergoes phototransformation in surface waters under sunlight radiation resulting in formation of photoreduced GO (rGO). In this study, the recently updated Water Quality Analysis Simulation Program (WASP8) is used to simulate time-dependent environmental exposure concentrations of GO and its major phototransformation product, rGO, for Brier Creek, GA, USA at two flow scenarios under a constant loading of GO to the river for a period of 20 years. Analysis shows that the degree of phototransformation is closely associated with river flow condition: up to of 40% of GO undergoes phototransformation at low flow condition, whereas only 2.5% of GO phototransformation occurs at mean flow condition. River flow and heteroaggregation exhibit a 'competing' effect in determining the formation of rGO heteroagglomerates. Mass fraction analysis indicates that the vast majority of rGO heteroagglomerates settle to the sediment layers due to the settling of suspended solids. Simulation of natural recovery after removal of the GO source suggests that free GO and rGO are the immediate contaminants of concern in the studied surface water system, while rGO heteroaggregated with suspended solids can have a long-term ecological impact on both the water column and sediments.

An overview of graphene materials: Properties, applications and toxicity on aquatic environments

Due to unique chemical and physical properties, nanomaterials from the Graphene family are being increasingly introduced in all fields of science. The specific roles they can occupy within different applications are attracting increased attention by several industrial sectors. These carbon nanoparticles are released into the environment especially accumulating in aquatic systems. Since the discovery of graphene, a number of research actives are being conducted to find out the toxic potential of the Graphene family materials to different organism's models. Although their toxicity effects are well described for biomedical applications, few data were produced with the specific aim of assessing the toxic effects of these carbon nanomaterials in the aquatic environment. The purpose of this review is to compile up-to-date information on properties, applications and characterization methods of graphene family materials in aquatic environments and identified biological toxic impacts of these NMs, with special focus on graphene oxide based on the most recent literature.

Modeling of the transport and deposition of polydispersed particles: Effects of hydrodynamics and spatiotemporal evolution of the deposition rate

A time-distance-dependent deposition model is built to investigate the effects of hydrodynamic forces on the transport and deposition of polydispersed particles and the evolution of deposition rates with time and distance. Straining and the heterogeneity of the particle population are considered to play important roles in the decreasing distribution of deposition rates. Numerical simulations were applied in a series of sand column experiments at different fluid velocities for three different porous media. The effects of hydrodynamics forces are elaborated with the systematic variations of deposition dynamic parameters of the proposed model. With retention distributions with particle size as well as temporal and spatial evolutions of deposition rates, the transport and deposition mechanisms of polydispersed particles will be elucidated through the interplay of the variation of the particle size distribution of mobile particle populations and the geometrical change of the porous medium due to retention (straining and blocking).

Impact of water chemistry on the behavior and fate of copper nanoparticles

A full-factorial test design was applied to systematically investigate the contribution and significance of water chemistry parameters (pH, divalent cations and dissolved organic carbon (DOC) concentration) and their interactions on the behavior and fate of copper nanoparticles (CuNPs). The total amount of Cu remaining in the water column after 48 h of incubation was mostly influenced by divalent cation content, DOC concentration and the interaction of divalent cations and DOC. DOC concentration was the predominant factor influencing the dissolution of CuNPs, which was far more important than the effect of pH in the range from 6 to 9 on the dissolution of the CuNPs. The addition of DOC at concentrations ranging from 5 to 50 mg C/L resulted in a 3-5 fold reduction of dissolution of CuNPs after 48 h of incubation, as compared to the case without addition of DOC. Divalent cation content was found to be the most influential factor regarding aggregation behavior of the particles, followed by DOC concentration and the interaction of divalent cations and DOC. In addition, the aggregation behavior of CuNPs rather than particulate dissolution explained most of the variance in the sedimentation profiles of CuNPs. These results are meaningful for improved understanding and prediction of the behavior and fate of metallic NPs in aqueous environments.

Impact of water chemistry on the particle-specific toxicity of copper nanoparticles to Daphnia magna

Toxicity of metallic nanoparticle suspensions (NP_(total)) is generally assumed to result from the combined effect of the particles present in suspensions (NP_(particle)) and their released ions (NP_(ion)). Evaluation and consideration of how water chemistry affects the particle-specific toxicity of NP_(total) are critical for environmental risk assessment of nanoparticles. In this study, it was found that the toxicity of Cu NP_(particle) to Daphnia magna, in line with the trends in toxicity for Cu NP_(ion), decreased with increasing pH and with increasing concentrations of divalent cations and dissolved organic carbon (DOC). Without the addition of DOC, the toxicity of Cu NP_(total) to D. magna at the LC50 was driven mainly by Cu NP_(ion) (accounting for ≥53% of the observed toxicity). However, toxicity of Cu NP_(total) in the presence of DOC at a concentration ranging from 5 to 50mg C/L largely resulted from the NP_(particle) (57%-85%), which could be attributable to the large reduction of the concentration of Cu NP_(ion) and the enhancement of the stability of Cu NP_(particle) when DOC was added. Our results indicate that water chemistry needs to be explicitly taken into consideration when evaluating the role of NP_(particle) and NP_(ion) in the observed toxicity of NP_(total).

Crystalline phase-dependent eco-toxicity of titania nanoparticles to freshwater biofilms

The potential toxic impacts of different crystal phases of titania nanoparticles (TNPs) on freshwater biofilms, especially under ultraviolet C irradiation (UVC), are unknown. Here, adverse impacts of three phases (anatase, rutile, and P25, 50 mg L^-1 respectively) with UVC irradiation (An-UV, Ru-UV, and P25-UV) on freshwater biofilms were conducted. Characterization experiments revealed that rutile TNPs had a higher water environment stability than anatase and P25 TNPs, possessing a stronger photocatalytic activity under UVC irradiation. Phase-dependent inhibition of cell viability and significant decreases of four- and five-fold in algal biomass at 12 h of exposure were observed compared with unexposed biofilms. Moreover, phase-dependent oxidative stress resulted in remarkably significant reductions (P < 0.01) of the photosynthetic yields of the biofilms, to 40.32% (P25-UV), 48.39% (An-UV), and 46.77% (Ru-UV) of the plateau value obtained in the unexposed biofilms. A shift in community composition that manifested as a strong reduction in diatoms, indicating cyanobacteria and green algae were more tolerant than diatoms when exposed to TNPs. In terms of the toxic mechanisms, rutile TNPs resulted in apoptosis by inducing excessive intracellular reactive oxygen species (ROS) production, whereas P25 and anatase TNPs tended to catalyze enormous acellular ROS lead to cell necrosis under UVC irradiation.

Microplastic Exposure Assessment in Aquatic Environments: Learning from Similarities and Differences to Engineered Nanoparticles

Microplastics (MPs) have been identified as contaminants of emerging concern in aquatic environments and research into their behavior and fate has been sharply increasing in recent years. Nevertheless, significant gaps remain in our understanding of several crucial aspects of MP exposure and risk assessment, including the quantification of emissions, dominant fate processes, types of analytical tools required for characterization and monitoring, and adequate laboratory protocols for analysis and hazard testing. This Feature aims at identifying transferrable knowledge and experience from engineered nanoparticle (ENP) exposure assessment. This is achieved by comparing ENP and MPs based on their similarities as particulate contaminants, whereas critically discussing specific differences. We also highlight the most pressing research priorities to support an efficient development of tools and methods for MPs environmental risk assessment.

Comparative study on toxicity of ZnO and TiO2 nanoparticles on Artemia salina: effect of pre-UV-A and visible light irradiation

This study evaluated the toxicity potential of ZnO and TiO₂ nanoparticles under pre-UV-A irradiation and visible light condition on Artemia salina. The nanoparticle suspension was prepared in seawater medium and exposed under pre-UV-A (0.23 mW/cm²) and visible light (0.18 mW/cm²) conditions. The aggregation profiles of both nanoparticles (NPs) and dissolution of ZnO NPs under both irradiation conditions at various kinetic intervals (1, 24, 48 h) were studied. The 48-h LC₅₀ values were found to be 27.62 and 71.63 mg/L for ZnO NPs and 117 and 120.9 mg/L for TiO₂ NPs under pre-UV-A and visible light conditions. ZnO NPs were found to be more toxic to A. salina as compared to TiO₂ NPs. The enhanced toxicity was observed under pre-UV-A-irradiated ZnO NPs, signifying its phototoxicity. Accumulation of ZnO and TiO₂ NPs into A. salina depends on the concentration of particles and type irradiations. Elimination of accumulated nanoparticles was also evident under both irradiation conditions. Other than ZnO NPs, the dissolved Zn²⁺ also had a significant effect on toxicity and accumulation in A. salina. Increased catalase (CAT) activity in A. salina indicates the generation of oxidative stress due to NP interaction. Thus, this study provides an understanding of the toxicity of photoreactive ZnO and TiO₂ NPs as related to the effects of pre-UV-A and visible light irradiation.

Environmental dynamics of metal oxide nanoparticles in heterogeneous systems: A review

Metal oxide nanoparticles (MNPs) have been used for many purposes including water treatment, health, cosmetics, electronics, food packaging, and even food products. As their applications continue to expand, concerns have been mounting about the environmental fate and potential health risks of the nanoparticles in the environment. Based on the latest information, this review provides an overview of the factors that affect the fate, transformation and toxicity of MNPs. Emphasis is placed on the effects of various aquatic contaminants under various environmental conditions on the transformation of metal oxides and their transport kinetics - both in homogeneous and heterogeneous systems - and the effects of contaminants on the toxicity of MNPs. The presence of existing contaminants decreases bioavailability through hetero-aggregation, sorption, and/or complexation upon an interaction with MNPs. Contaminants also influence the fate and transport of MNPs and exhibit their synergistic toxic effects that contribute to the extent of the toxicity. This review will help regulators, engineers, and scientists in this field to understand the latest development on MNPs, their interactions with aquatic contaminants as well as the environmental dynamics of their fate and transformation. The knowledge gap and future research needs are also identified, and the challenges in assessing the environmental fate and transport of nanoparticles in heterogeneous systems are discussed.

Modelling the Release, Transport and Fate of Engineered Nanoparticles in the Aquatic Environment - A Review

Engineered nanoparticles, that is, particles of up to 100 nm in at least one dimension, are used in many consumer products. Their release into the environment as a consequence of their production and use has raised concern about the possible consequences. While they are made of ordinary substances, their size gives them properties that are not manifest in larger particles. It is precisely these properties that make them useful. For instance titanium dioxide nanoparticles are used in transparent sunscreens, because they are large enough to scatter ultraviolet light but too small to scatter visible light.To investigate the occurrence of nanoparticles in the environment we require practical methods to detect their presence and to measure the concentrations as well as adequate modelling techniques. Modelling provides both a complement to the available detection and measurement methods and the means to understand and predict the release, transport and fate of nanoparticles. Many different modelling approaches have been developed, but it is not always clear for what questions regarding nanoparticles in the environment these approaches can be applied. No modelling technique can be used for every possible aspect of the release of nanoparticles into the environment. Hence it is important to understand which technique to apply in what situation. This article provides an overview of the techniques involved with their strengths and weaknesses. Two points need to be stressed here: the modelling of processes like dissolution and the surface activity of nanoparticles, possibly under influence of ultraviolet light, or chemical transformation has so far received relatively little attention. But also the uncertainties surrounding nanoparticles in general-the amount of nanoparticles used in consumer products, what constitutes the appropriate measure of concentration (mass or numbers) and what processes are relevant-should be explicitly considered as part of the modelling.

Combining exposure and effect modeling into an integrated probabilistic environmental risk assessment for nanoparticles

There is a growing need for good environmental risk assessment of engineered nanoparticles (ENPs). Environmental risk assessment of ENPs has been hampered by lack of data and knowledge about ENPs, their environmental fate, and their toxicity. This leads to uncertainty in the risk assessment. To deal with uncertainty in the risk assessment effectively, probabilistic methods are advantageous. In the present study, the authors developed a method to model both the variability and the uncertainty in environmental risk assessment of ENPs. This method is based on the concentration ratio and the ratio of the exposure concentration to the critical effect concentration, both considered to be random. In this method, variability and uncertainty are modeled separately so as to allow the user to see which part of the total variation in the concentration ratio is attributable to uncertainty and which part is attributable to variability. The authors illustrate the use of the method with a simplified aquatic risk assessment of nano-titanium dioxide. The authors' method allows a more transparent risk assessment and can also direct further environmental and toxicological research to the areas in which it is most needed. Environ Toxicol Chem 2016;35:2958-2967. © 2016 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Stability of uncoated and fulvic acids coated manufactured CeO2 nanoparticles in various conditions: From ultrapure to natural Lake Geneva waters

Understanding the behavior of engineered nanoparticles in natural water and impact of water composition in changing conditions is of high importance to predict their fate once released into the environment. In this study we investigated the stability of uncoated and Suwannee River fulvic acids coated CeO2 manufactured nanoparticles in various environmental conditions. The effect of pH changes on the nanoparticle and coating stability was first studied in ultrapure water as well as the variation of zeta potentials and sizes with time in presence of fulvic acids at environmental pH. Then the stability of CeO2 in synthetic and natural Lake Geneva waters was investigated as a function of fulvic acids concentration. Our results indicate that the adsorption of environmentally relevant concentrations of Suwannee River fulvic acids promotes CeO2 stabilization in ultrapure water as well as synthetic water and that the coating stability is high upon pH variations. On the other hand in natural Lake Geneva water CeO2 NPs are found in all cases aggregated due to the effect of heterogeneous organic and inorganic compounds.

Blocking effect of colloids on arsenate adsorption during co-transport through saturated sand columns

Transport of environmental pollutants through porous media is influenced by colloids. Co-transport of As(V) and soil colloids at different pH were systematically investigated by monitoring breakthrough curves (BTCs) in saturated sand columns. A solute transport model was applied to characterize transport and retention sites of As(V) in saturated sand in the presence of soil colloids. A colloid transport model and the DLVO theory were used to reveal the mechanism and hypothesis of soil colloid-promoted As(V) transport in the columns. Results showed that rapid transport of soil colloids, regulated by pH and ionic strength, promoted As(V) transport by blocking As(V) adsorption onto sand, although soil colloids had low adsorption for As(V). The promoted transport was more significant at higher concentrations of soil colloids (between 25 mg L(-1) and 150 mg L(-1)) due to greater blocking effect on As(V) adsorption onto the sand surfaces. The blocking effect of colloids was explained by the decreases in both instantaneous (equilibrium) As adsorption and first-order kinetic As adsorption on the sand surface sites. The discovery of this blocking effect improves our understanding of colloid-promoted As transport in saturated porous media, which provides new insights into role of colloids, especially colloids with low As adsorption capacity, in As transport and mobilization in soil-groundwater systems.

Influence of siloxane on the transport of ZnO nanoparticles from different release pathways in saturated sand

The production of nanomaterials (NMs) is expected to grow continuously, yet their transformation, transport, release mechanisms, and interactions with contaminants under environmental conditions remain poorly understood. Few studies have investigated the effects of contaminants on fate and transport of NMs, especially siloxanes that are widely found in products. It is hypothesized that the model contaminant, siloxane (e.g., 1,1,3,3-tetramethyldisiloxane (TMDS)) may influence the mechanisms and transport kinetics of NMs under different release pathways. Sand column experiments were carried out under two different scenarios: the release from a mixed TMDS and nano-ZnO suspension (A) and the release of nano-ZnO from sand contaminated with TMDS (B). Results show that interparticle reactions are dominant in (A) and particle-porous interactions are responsible for blocking effects governing in (B). Insights, especially the kinetics of nano-ZnO from co-transport by a contaminant and from porous media preloaded with a contaminant, and environmental factors affecting the release and retention of nano-ZnO in saturated sand are unveiled. These two dominant transport mechanisms (e.g., interparticle reactions and blocking effects) were derived. This study indicates that the release of ZnO NPs is influenced by the presence of TMDS; the extent of mobility and their transport pathways depend on the pre-existence of TMDS in porous media.

Impact of TiO₂ nanoparticles on freshwater bacteria from three Swedish lakes

Due to the rapidly rising production and usage of nano-enabled products, aquatic environments are increasingly exposed to engineered nanoparticles (ENPs), causing concerns about their potential negative effects. In this study we assessed the effects of uncoated titanium dioxide nanoparticles (TiO2NPs) on the growth and activity of bacterial communities of three Swedish lakes featuring different chemical characteristics such as dissolved organic carbon (DOC) concentration, pH and elemental composition. TiO2NP exposure concentrations were 15, 100, and 1000 μg L(-1), and experiments were performed in situ under three light regimes: darkness, photosynthetically active radiation (PAR), and ambient sunlight including UV radiation (UVR). The nanoparticles were most stable in lake water with high DOC and low chemical element concentrations. At the highest exposure concentration (1000 μg L(-1) TiO2NP) the bacterial abundance was significantly reduced in all lake waters. In the medium and high DOC lake waters, exposure concentrations of 100 μg L(-1) TiO2NP caused significant reductions in bacterial abundance. The cell-specific bacterial activity was significantly enhanced at high TiO2NP exposure concentrations, indicating the loss of nanoparticle-sensitive bacteria and a subsequent increased activity by tolerant ones. No UV-induced phototoxic effect of TiO2NP was found in this study. We conclude that in freshwater lakes with high DOC and low chemical element concentrations, uncoated TiO2NPs show an enhanced stability and can significantly reduce bacterial abundance at relatively low exposure concentrations.

Aggregation and resuspension of graphene oxide in simulated natural surface aquatic environments

A series of experiments were performed to simulate the environmental behavior and fate of graphene oxide nanoparticles (GONPs) involved in the surface environment relating to divalent cations, natural organic matter (NOM), and hydraulics. The electrokinetic properties and hydrodynamic diameters of GONPs was systematically determined to characterize GONPs stability and the results indicated Ca(2+) (Mg(2+)) significantly destabilized GONPs with high aggregate strength factors (SF) and fractal dimension (FD), whereas NOM decreased aggregate SF with lower FD and improved GONPs stability primarily because of increasing steric repulsion and electrostatic repulsion. Furthermore, the GONPs resuspension from the sand bed into overlying water with shear flow confirmed that the release would be restricted by Ca(2+) (Mg(2+)), however, enhanced by NOM. The interaction energy based on Derjaguin-Landau-Verwey-Overbeek theory verifies the aggregation and resuspension well. Overall, these experiments provide an innovative look and more details to study the behavior and fate of GONPs.

Agglomeration of Ag and TiO2 nanoparticles in surface and wastewater: Role of calcium ions and of organic carbon fractions

This study aims to investigate factors leading to agglomeration of citrate coated silver (AgNP-Cit), polyvinylpyrrolidone coated AgNPPVP and titanium dioxide (TiO2) nanoparticles in surface waters and wastewater. ENPs (1 mg/L) were spiked to unfiltered, filtered, ultrafiltered (<10 kDa and <1 kDa) samples. Z-average particle sizes were measured after 1 h, 1 day and 1 week. AgNP-PVP was stable in all fractions of the samples and kept their original size around 60 nm over 1 week. Agglomeration of AgNP-Cit and TiO2 was positively correlated with Ca(2+) concentration, but dissolved organic carbon concentrations > 2 mg/L contributed to stabilizing these NP. Moreover, agglomeration of AgNP-Cit in the various organic matter fractions showed that high molecular weight organic compounds such as biopolymers provide stabilization in natural water. A generalized scheme for the agglomeration behavior of AgNP-Cit, AgNP-PVP and TiO2 in natural waters was proposed based on their relation with Ca(2+), Mg(2+) and DOC concentration.

Stream dynamics and chemical transformations control the environmental fate of silver and zinc oxide nanoparticles in a watershed-scale model

Mathematical models are needed to estimate environmental concentrations of engineered nanoparticles (NPs), which enter the environment upon the use and disposal of consumer goods and other products. We present a spatially resolved environmental fate model for the James River Basin, Virginia, that explores the influence of daily variation in streamflow, sediment transport, and stream loads from point and nonpoint sources on water column and sediment concentrations of zinc oxide (ZnO) and silver (Ag) NPs and their reaction byproducts over 20 simulation years. Spatial and temporal variability in sediment transport rates led to high NP transport such that less than 6% of NP-derived metals were retained in the river and sediments. Chemical transformations entirely eliminated ZnO NPs and doubled Zn mobility in the stream relative to Ag. Agricultural runoff accounted for 23% of total metal stream loads from NPs. Average NP-derived metal concentrations in the sediment varied spatially up to 9 orders of magnitude, highlighting the need for high-resolution models. Overall, our results suggest that "first generation" NP risk models have probably misrepresented NP fate in freshwater rivers due to low model resolutions and the simplification of NP chemistry and sediment transport.

Modeling flows and concentrations of nine engineered nanomaterials in the Danish environment

Predictions of environmental concentrations of engineered nanomaterials (ENM) are needed for their environmental risk assessment. Because analytical data on ENM-concentrations in the environment are not yet available, exposure modeling represents the only source of information on ENM exposure in the environment. This work provides material flow data and environmental concentrations of nine ENM in Denmark. It represents the first study that distinguishes between photostable TiO₂ (as used in sunscreens) and photocatalytic TiO₂ (as used in self-cleaning surfaces). It also provides first exposure estimates for quantum dots, carbon black and CuCO₃. Other ENM that are covered are ZnO, Ag, CNT and CeO₂. The modeling is based for all ENM on probability distributions of production, use, environmental release and transfer between compartments, always considering the complete life-cycle of products containing the ENM. The magnitude of flows and concentrations of the various ENM depends on the one hand on the production volume but also on the type of products they are used in and the life-cycles of these products and their potential for release. The results reveal that in aquatic systems the highest concentrations are expected for carbon black and photostable TiO₂, followed by CuCO₃ (under the assumption that the use as wood preservative becomes important). In sludge-treated soil highest concentrations are expected for CeO₂ and TiO₂. Transformation during water treatments results in extremely low concentrations of ZnO and Ag in the environment. The results of this study provide valuable environmental exposure information for future risk assessments of these ENM.

Nano silver and nano zinc-oxide in surface waters - exposure estimation for Europe at high spatial and temporal resolution

Nano silver and nano zinc-oxide monthly concentrations in surface waters across Europe were modeled at ~6 x 9 km spatial resolution. Nano-particle loadings from households to rivers were simulated considering household connectivity to sewerage, sewage treatment efficiency, the spatial distribution of sewage treatment plants, and their associated populations. These loadings were used to model temporally varying nano-particle concentrations in rivers, lakes and wetlands by considering dilution, downstream transport, water evaporation, water abstraction, and nano-particle sedimentation. Temporal variability in concentrations caused by weather variation was simulated using monthly weather data for a representative 31-year period. Modeled concentrations represent current levels of nano-particle production.Two scenarios were modeled. In the most likely scenario, half the river stretches had long-term average concentrations exceeding 0.002 ng L(-1) nano silver and 1.5 ng L(-1) nano zinc oxide. In 10% of the river stretches, these concentrations exceeded 0.18 ng L(-1) and 150 ng L(-1), respectively. Predicted concentrations were usually highest in July.

A systematic evaluation of agglomeration of Ag and TiO2 nanoparticles under freshwater relevant conditions

This study aims to investigate effects of freshwater components in order to predict agglomeration behavior of silver nanoparticles coated with citrate (AgNP-Cit), polyvinylpyrrolidone (AgNP-PVP), and of TiO2 nanoparticles. Agglomeration studies were conducted in various media based on combinations of ions, natural organic matter (humic, fulvic acid) and surfactants (sodium dodecyl sulfate, alkyl ethoxylate), at a constant ionic strength of 10 mM over time for up to 1 week. Agglomeration level of AgNP-Cit and TiO2 was mostly dependent on the concentration of Ca(2+) in media, and their size strongly increased to micrometer scale over 1 week. However, AgNP-Cit and TiO2 were stabilized to particle size around 500 nm in the presence of NOM, surfactants and carbonate over 1 week. AgNP-PVP maintained their original size in all media except in the presence of Mg(2+) ions which led to significant agglomeration. Behavior of these engineered nanoparticles was similar in a natural freshwater medium.

Stability and Transport of Graphene Oxide Nanoparticles in Groundwater and Surface Water

The effects of groundwater and surface water constituents (i.e., natural organic matter [NOM] and the presence of a complex assortment of ions) on graphene oxide nanoparticles (GONPs) were investigated to provide additional insight into the factors contributing to fate and the mechanisms involved in their transport in soil, groundwater, and surface water environments. The stability and transport of GONPs was investigated using dynamic light scattering, electrokinetic characterization, and packed bed column experiments. Stability results showed that the hydrodynamic diameter of the GONPs at a similar ionic strength (2.1±1.1 mM) was 10 times greater in groundwater environments compared with surface water and NaCl and MgCl2 suspensions. Transport results confirmed that in groundwater, GONPs are less stable and are more likely to be removed during transport in porous media. In surface water and MgCl2 and NaCl suspensions, the relative recovery was 94%±3% indicating that GONPs will be very mobile in surface waters. Additional experiments were carried out in monovalent (KCl) and divalent (CaCl2) salts across an environmentally relevant concentration range (0.1-10 mg/L) of NOM using Suwannee River humic acid. Overall, the transport and stability of GONPs was increased in the presence of NOM. This study confirms that planar "carbonaceous-oxide" materials follow traditional theory for stability and transport, both due to their response to ionic strength, valence, and NOM presence and is the first to look at GONP transport across a wide range of representative conditions found in surface and groundwater environments.