Aggregation, Sedimentation, Dissolution, and Bioavailability of Quantum Dots in Estuarine Systems

An update on the biological effects of quantum dots: From environmental fate to risk assessment based on multiple biological models

Quantum dots (QDs) are zero-dimension nanomaterials with excellent physical and chemical properties, which have been widely used in environmental science and biomedicine. Therefore, QDs are potential to cause toxicity to the environment and enter organisms through migration and bioenrichment effects. This review aims to provide a comprehensive and systematic analysis on the adverse effects of QDs in different organisms based on recently available data. Following PRISMA guidelines, this study searched PubMed database according to the pre-set keywords, and included 206 studies according to the inclusion and elimination criteria. CiteSpace software was firstly used to analyze the keywords of included literatures, search for breaking points of former studies, and summarize the classification, characterization and dosage of QDs. The environment fate of QDs in the ecosystems were then analyzed, followed with comprehensively summarized toxicity outcomes at individual, system, cell, subcellular and molecular levels. After migration and degradation in the environment, aquatic plants, bacteria, fungi as well as invertebrates and vertebrates have been found to be suffered from toxic effects caused by QDs. Aside from systemic effects, toxicity of intrinsic QDs targeting to specific organs, including respiratory system, cardiovascular system, hepatorenal system, nervous system and immune system were confirmed in multiple animal models. Moreover, QDs could be taken up by cells and disturb the organelles, which resulted in cellular inflammation and cell death, including autophagy, apoptosis, necrosis, pyroptosis and ferroptosis. Recently, several innovative technologies, like organoids have been applied in the risk assessment of QDs to promote the surgical interventions of preventing QDs' toxicity. This review not only aimed at updating the research progress on the biological effects of QDs from environmental fate to risk assessment, but also overcame the limitations of available reviews on basic toxicity of nanomaterials by interdisciplinarity and provided new insights for better applications of QDs.

Impacts of dissolved organic matter on the aggregation and photo-dissolution of cadmium pigment nanoparticles in aquatic systems

Cadmium pigments are a group of inorganic pigments used in consumer products. The aggregation behavior and photo-dissolution process of cadmium pigment nanoparticles in aquatic systems control their environmental fate, which is largely unknown. Herein, we investigated the influence of dissolved organic matter (DOM) on the aggregation behavior and photo-dissolution process of CdS nanoparticles in aquatic systems. Bare CdS nanoparticles are prone to aggregation in both NaCl and CaCl₂ solutions. DOM can remarkably increase the colloidal stability of CdS nanoparticles owing to the steric hindrance and enhanced electrostatic repulsion. With 10 mg/L Suwannee River natural organic matter (SRNOM), the colloidal stability of CdS nanoparticles is significantly enhanced in NaCl solutions (i.e., the critical coagulation concentration, CCC_Na, is 707.2 mM). Suwannee River humic acid (SRHA) has a stronger stabilization effect than SRNOM due to its higher molecular weight and aromaticity. The Ca²⁺ cations can induce charge neutralization and structural compacting of DOM corona, efficiently reducing the colloidal stability of CdS nanoparticles. The CCC_Ca is 10.8 mM and 14.9 mM with 10 mg/L SRNOM and SRHA, respectively. Upon solar irradiation, the presence of a low concentration of SRNOM (3 mg/L) can enhance the photo-dissolution of CdS nanoparticles and the consequent Cd²⁺ leaching. This is caused by the facilitated electron transfer from CdS nanoparticles to O₂ induced by SRNOM corona, leading to better electron-hole separation. However, a high concentration of SRNOM inhibited the photo-dissolution of CdS nanoparticles due to the strong inner filter effect and the scavenging of phototransients. The colloidal stability of SRNOM-coated CdS nanoparticles increases in NaCl but decreases in CaCl₂ solutions after irradiation owing to the oxidation of SRNOM corona. Our results highlight the decisive role of DOM in the environmental fate of cadmium pigments.

Surface defects and particle size determine transport of CdSe quantum dots out of plastics and into the environment

Polymers incorporating quantum dots (QDs) have attracted interest as components of next-generation consumer products, but there is uncertainty about how these potentially hazardous materials may impact human health and the environment. We investigated how the transport (migration) of QDs out of polymers and into the environment is linked to their size and surface characteristics. Cadmium selenide (CdSe) QDs with diameters ranging from 2.15 to 4.63 nm were incorporated into low-density polyethylene (LDPE). Photoluminescence was used as an indicator of QD surface defect density. Normalized migration of QDs into 3% acetic acid over 15 days ranged from 13.1 ± 0.6-452.5 ± 31.9 ng per cm² of polymer surface area. Migrated QD mass was negatively correlated to QD diameter and was also higher when QDs had photoluminescence consistent with larger surface defect densities. The results imply that migration is driven by oxidative degradation of QDs originating at surface defect sites and transport of oxidation products along concentration gradients. A semi-empirical framework was developed to model the migration data. The model supports this mechanism and suggests that QD surface reactivity also drives the relationship between QD size and migration, with specific surface area playing a less important role.

Parental exposure to CdSe/ZnS QDs affects cartilage development in rare minnow (Gobiocypris rarus) offspring

Cartilage development is a sensitive process that is easily disturbed by environmental toxins. In this study, the toxicity of CdSe/ZnS quantum dots on the skeleton of the next generation (F1) was evaluated using rare minnows (Gobiocypris rarus) as model animals. Four-month-old sexually mature parental rare minnows (F0) were selected and treated with 0, 100, 200, 400 and 800 nmol/L CdSe/ZnS quantum dots for 4 days. Embryos of F1 generation rare minnows were obtained by artificial insemination. The results showed that with increasing maternal quantum dots exposure, the body length of F1 embryos decreased, the overall calcium content decreased, and the deformity and mortality rates increased. Alcian blue staining results showed that the lengths of the craniofacial mandible, mandibular arch length, mandibular width, and CH-CH and CH-PQ angles of larvae of rare minnows increased; histological hematoxylin-eosin staining further indicated that quantum dots affected the development of chondrocytes. Furthermore, high concentrations of CdSe/ZnS quantum dots inhibited the transcript expression of the bmp2b, bmp4, bmp6, runx2b, sox9a, lox1 and col2α1 genes. In conclusion, CdSe/ZnS quantum dots can affect the skeletal development of F1 generation embryos of rare minnows at both the individual and molecular levels, the damage to the craniofacial bone is more obvious, and the toxic effect of high concentrations of quantum dots (400 nmol/L and 800 nmol/L) is more significant.

Assessing the Environmental Effects Related to Quantum Dot Structure, Function, Synthesis and Exposure

Quantum dots (QDs) are engineered semiconductor nanocrystals with unique fluorescent, quantum confinement, and quantum yield properties, making them valuable in a range of commercial and consumer imaging, display, and lighting technologies. Production and usage of QDs are increasing, which increases the probability of these nanoparticles entering the environment at various phases of their life cycle. This review discusses the major types and applications of QDs, their potential environmental exposures, fates, and adverse effects on organisms. For most applications, release to the environment is mainly expected to occur during QD synthesis and end-product manufacturing since encapsulation of QDs in these devices prevents release during normal use or landfilling. In natural waters, the fate of QDs is controlled by water chemistry, light intensity, and the physicochemical properties of QDs. Research on the adverse effects of QDs primarily focuses on sublethal endpoints rather than acute toxicity, and the differences in toxicity between pristine and weathered nanoparticles are highlighted. A proposed oxidative stress adverse outcome pathway framework demonstrates the similarities among metallic and carbon-based QDs that induce reactive oxygen species formation leading to DNA damage, reduced growth, and impaired reproduction in several organisms. To accurately evaluate environmental risk, this review identifies critical data gaps in QD exposure and ecological effects, and provides recommendations for future research. Future QD regulation should emphasize exposure and sublethal effects of metal ions released as the nanoparticles weather under environmental conditions. To date, human exposure to QDs from the environment and resulting adverse effects has not been reported.

Monitoring the Cd2+ release from Cd-containing quantum dots in simulated body fluids by size exclusion chromatography coupled with ICP-MS

Quantification of Cd²⁺ release from Cd-containing quantum dots (QDs) is of fundamental importance to elucidate its toxicity to organisms, but remains a great challenge due to the lack of appropriate analytical method. Herein, a facile method based on size exclusion chromatography (SEC) combined with inductively coupled plasma mass spectrometry (ICP-MS) was developed for separating and quantifying the QDs and counterpart ions. By using the mixture of sodium dodecyl sulfate (SDS) and ethylenediaminetetraacetic acid tetrasodium salt (EDTA) as the mobile phase, the defect of QD and ion adsorption onto the SEC column was overcome, thus realizing the accurate quantification of ionic species. Besides, the concentration of QDs was achieved through subtracting the ion concentration from the total concentration. Selecting CdSe@ZnS as the typical QDs, the Cd²⁺ release process in four typical simulated body fluids, namely, simulated gastric fluid, simulated sweat, Gamble's solution, and artificial lysosomal fluid, was monitored using the developed SEC-ICP-MS method. The media pH is identified as the decisive factor which controls the dissolution of ZnS shells and also the Cd²⁺ release kinetics and final concentration. Our results suggest that the oral pathway for QD uptake poses the biggest risk to human health.

Current trends and challenges in analysis and characterization of engineered nanoparticles in seawater

With the increasingly wide use of engineered nanoparticles (ENPs), their release into the environment makes it important to determine in what quantitates they occur in aquatic systems and to understand their fate therein. In particular, detection and quantification of ENPs in seawater is challenging and often requires analytical methods to perform close to the feasibility confines. This review is aimed at critical analysis of current and emerging capabilities of analytical methods as have been employed for the analysis and characterization of ENPs in seawater in the last decade. An emphasis is given to the most reliable experimental strategies focused on avoiding the high-salt matrix effect and isolation and enrichment of the nanoparticulate fraction prior to analysis. Advanced analytical methodology in use basically relies on the application of elemental mass spectrometry to determine various particle-core metals and its single-particle mode to characterize the seawater-mediated transformation of ENPs, including dissolution, aggregation, etc. On the other hand, common microscopy, light scattering or X-ray based techniques are not sensitive enough to acquire the transformation information from real seawater samples. Finally, attention is pinpointed upon an acute shortcoming of the current research which is in the overwhelming majority of cases restricted to samples spiked with ENPs and often at excessive concentration levels.

Mobility and transformation of CdSe/ZnS quantum dots in soil: Role of the capping ligands and ageing effect

The increasing application of Quantum Dots (QDs) is cause of concern for the potential negative effects for the ecosystem, especially in soils that may act as a sink. In this study, soil leaching experiments were performed in quartz sand packed columns to investigate the behavior of core-shell CdSe/ZnS QDs coated with either small ligands (TGA-QDs) or more complex polymers (POAMA-QDs). Fluorescence emission was compared to mass spectrometric measurements to assess the nanoparticles (NPs) state in both the leachate (transported species) and porous media (deposited amounts). Although both QDs were strongly retained in the column, large differences were observed depending on their capping ligand stability. Specifically, for TGA-QDs elution was negligible and the retained fraction accumulated in the top-columns. Furthermore, 74% of the NPs were degraded and 38% of the Se was found in the leachate in non-NPs state. Conversely, POAMA-QDs were recovered to a larger extent (78.1%), and displayed a higher transport along the soil profile. Further experiments with altered NPs showed that homo-aggregation of the QDs prior injection determined a reduced mobility but no significant changes in their stability. Eventually, ageing of the NPs in the column (15 days) caused the disruption of up to 92% of the original QDs and the immobilization of NPs and metals. These results indicate that QDs will accumulate in top-soils, where transformations phenomena will determine the overall transport, persistency and degradation of these chemicals. Once accumulated, they may act as a source for potentially toxic Cd and Se metal species displaying enhanced mobility.

Assessing cadmium-based quantum dots effect on the gonads of the marine mussel Mytilus galloprovincialis

This study assesses the sex-specific effects induced by CdTe QDs, on the marine mussel Mytilus galloprovincialis in comparison to its dissolved counterpart. A 14 days exposure to CdTe QDs and dissolved Cd was conducted (10 μg Cd L^-1), analysing Cd accumulation, oxidative stress, biotransformation, metallothionein and oxidative damage in the gonads. Both Cd forms caused significant antioxidant alterations, whereby QDs were more pro-oxidant, leading to oxidative damage, being females more affected. Overall, biochemical impairments on gonads of M. galloprovincialis demonstrate that the reproductive toxicity induced by CdTe QDs in mussels are sex-dependent and mediated by oxidative stress and lipid peroxidation. It is crucial to acknowledge how gametes are affected by metal-based nanoparticles, such as Cd-based QDs. As well as understanding the potential changes they may undergo at the cellular level during gametogenesis, embryogenesis and larval development potentially leading to serious impacts on population sustainability and ecosystem health.

Water chemistry influences on long-term dissolution kinetics of CdSe/ZnS quantum dots

Widespread usage of engineered metallic quantum dots (QDs) within consumer products has evoked a need to assess their fate within environmental systems. QDs are mixed-metal nanocrystals that often include Cd²⁺ which poses a health risk as a nanocrystal or when leached into water. The goal of this work is to study the long-term metal cation leaching behavior and the factors affecting the dissolution processes of mercaptopropionic acid (MPA) capped CdSe/ZnS QDs in aphotic conditions. QD suspensions were prepared in different water conditions, and release of Zn²⁺ and Cd²⁺ cations were monitored over time by size exclusion chromatography-inductively coupled plasma-mass spectrometry. In most conditions with dissolved O₂ present, the ZnS shell degraded fairly rapidly over ~1 week, while some of the CdSe core remained up to 80 days. Additional MPA, Zn²⁺, and Cd²⁺ temporarily delayed dissolution, indicating a moderate role for capping agent detachment and mineral solubility. The presence of H₂O₂ and the ligand ethylenediaminetetraacetate accelerated dissolution, while NOM had no kinetic effect. No dissolution of CdSe core was observed when O₂ was absent or when QDs formed aggregates at higher concentrations with O₂ present. The shrinking particle model with product layer diffusion control best describes Zn²⁺ and Cd²⁺ dissolution kinetics. The longevity of QDs in their nanocrystal form appears to be partly controlled by environmental conditions, with anoxic, aphotic environments preserving the core mineral phase, and oxidants or complexing ligands promoting shell and core mineral dissolution.

Tracing multi-isotopically labelled CdSe/ZnS quantum dots in biological media

The strengths and limits of isotopically labelled Engineered Nanoparticles (spiked ENPs) spread in biological media have been assessed. Multi-spiked CdSe/ZnS quantum dots (QDs), measuring 7 nm and coated with thioglycolic acid (TGA), were synthesized and enriched in 68Zn, 77Se and 111Cd. These QDs were dispersed at very low concentrations (0.1 to 5000 ppt) in diverse biological matrices (synthetic saliva, synthetic urine, plasma and Dulbecco's phosphate buffered saline - DPBS growth medium) and the isotopic compositions were determined by HR-ICP-MS. The initial QDs concentrations were calculated to assess the limit of quantification (QD-LOQ) according to the matrix and the isotopically enriched element. The obtained results demonstrated the advantages of the isotopic labelling method in order to work at very low concentrations: the QD-LOQ values for the spiked Zn, Cd and Se originated from the QDs were 10, 0.3 and 6 ppt, respectively, which is below the conventional LOQ of the HR-ICP-MS used (30, 3 and 60 ppt for Zn, Cd and Se, respectively). Conversely, in complex matrices such as saliva, urine, plasma and DPBS growth medium, the QD-LOQ values increased significantly, with values ranging from 16 to 32 ppt for Cd, 446 to 10598 ppt for Zn and 1618 to 8317 ppt for Se. These QD-LOQs are dependent on factors as the elemental background concentration already present in the matrices, and the dilution factor. In this study, the QD-LOQs are expressed for the first time with respect to the background concentration in biological media (QD-RLOQ), which can be used to better assess and then predict the efficiency of the spiking method.

Toxicity Evaluation of Quantum Dots (ZnS and CdS) Singly and Combined in Zebrafish (Danio rerio)

The exponential growth of nanotechnology has led to the production of large quantities of nanomaterials for numerous industrial, technological, agricultural, environmental, food and many other applications. However, this huge production has raised growing concerns about the adverse effects that the release of these nanomaterials may have on the environment and on living organisms. Regarding the effects of QDs on aquatic organisms, existing data is scarce and often contradictory. Thus, more information is needed to understand the mechanisms associated with the potential toxicity of these nanomaterials in the aquatic environment. The toxicity of QDs (ZnS and CdS) was evaluated in the freshwater fish Danio rerio. The fishes were exposed for seven days to different concentrations of QDs (10, 100 and 1000 µg/L) individually and combined. Oxidative stress enzymes (catalase, superoxide dismutase and glutathione S-transferase), lipid peroxidation, HSP70 and total ubiquitin were assessed. In general, results suggest low to moderate toxicity as shown by the increase in catalase activity and lipid peroxidation levels. The QDs (ZnS and CdS) appear to cause more adverse effects singly than when tested combined. However, LPO results suggest that exposure to CdS singly caused more oxidative stress in zebrafish than ZnS or when the two QDs were tested combined. Levels of Zn and Cd measured in fish tissues indicate that both elements were bioaccumulated by fish and the concentrations increased in tissues according to the concentrations tested. The increase in HSP70 measured in fish exposed to 100 µg ZnS-QDs/L may be associated with high levels of Zn determined in fish tissues. No significant changes were detected for total ubiquitin. More experiments should be performed to fully understand the effects of QDs exposure to aquatic biota.

Fate and Transformation of Graphene Oxide in Estuarine and Marine Waters

The possibility of graphene oxide (GO) exposure to the environment has spurred several studies investigating the fate of this nanoparticle (NP). However, there is currently little or no data on the fate of GO in estuarine and marine waters. This study investigated the aggregation, sedimentation, and transformation of GO in saline waters, considering the roles of salinity (0-50 ‰), light (visible light and solar irradiation), and aging, among others. The attachment efficiency of GO reached unity at 1.33 ‰. The sedimentation rate of GO increased with salinity up to 10 ‰ after which it decreased due to formation of ramified GO agglomerates and media density. On the basis of the sedimentation rate determined at 30 ‰ (0.121 m/d), the residence time of GO agglomerates in the euphotic zone of typical open oceans will exceed 500 days. Aging in the presence of visible light increased the relative abundance of the GO's aromatic (C-C/C=C) fraction, reducing the NP. Reduction of GO in visible light was confirmed via UV-vis and Raman spectroscopic techniques. Reduction of GO was faster under solar irradiation. This study demonstrates that when introduced into saline waters, GO will undergo a range of transformations affecting its fate and potential effects to aquatic organisms.

Isotopically Labeled Nanoparticles at Relevant Concentrations: How Low Can We Go? The Case of CdSe/ZnS QDs in Surface Waters

Analytical barriers impose work at nanoparticles (NPs) concentrations orders of magnitude higher than the expected NPs concentrations in the environment. To overcome these limitations, the use of nontraditional stable isotope tracers incorporated in NPs (spiked-NPs) coupled with HR-ICP-MS has been proposed. The performance and efficiency of this analytical method was assessed in the case of quantum dots (QDs). Multi-isotopically labeled ¹¹¹Cd⁷⁷Se/⁶⁸ZnS QDs were synthesized and their dissemination in natural aquatic matrices (river, estuarine and sea waters) was modeled at very low concentrations (from 0.1 to 5000 ppt). The QD limits of quantification (QD-LOQ) in each matrix were calculated according to the isotopic tracer. In ultrapure and simple medium (HNO₃ 2%), Zn, Cd, and Se originated from the QDs were quantifiable at concentrations of 10, 0.3, and 6 ppt, respectively, which are lower than the conventional HR-ICP-MS LOQs. In aquatic matrices, the QD-LOQs increase 10-, 130-, and 250-fold for Zn, Cd, and Se, respectively, but remain relevant of environmental concentrations (3.4 ppt ≤ QD-LOQs ≤ 2.5 ppb). These results validate the use of isotopically labeled ENPs at relevant concentrations in experimental studies related to either their fate, behavior, or toxicity in most aquatic matrices.

Ligands and media impact interactions between engineered nanomaterials and clay minerals

The exponential growth in technologies incorporating engineered nanomaterials (ENMs) requires plans to handle waste ENM disposal and accidental environmental release throughout the material life cycle. These scenarios motivate efforts to quantify and model ENM interactions with diverse background particles and solubilized chemical species in a variety of environmental systems. In this study, quantum dot (QD) nanoparticles and clay minerals were mixed in a range of water chemistries in order to develop simple assays to predict aggregation trends. CdSe QDs were used as a model ENM functionalized with either negatively charged or zwitterionic small molecule ligand coatings, while clays were chosen as an environmentally relevant sorbent given their potential as an economical water treatment technology and ubiquitous presence in nature. In our unbuffered experimental systems, clay type impacted pH, which resulted in a change in zwitterionic ligand speciation that favored aggregation with kaolinite more than with montmorillonite. With kaolinite, the zwitterionic ligand-coated QD exhibited greater than ten times the relative attachment efficiency for QD-clay heteroaggregation compared to the negatively charged ligand coated QD. Under some conditions, particle oxidative dissolution and dynamic sorption of ions and QDs to surfaces complicated the interpretation of the removal kinetics. This work demonstrates that QDs stabilized by small molecule ligands and electrostatic surface charges are highly sensitive to changes in water chemistry in complex media. Natural environments enable rapid dynamic physicochemical changes that will influence the fate and mobility of ENMs, as seen by the differential adsorption of water-soluble QDs to our clay media.

Strategies for robust and accurate experimental approaches to quantify nanomaterial bioaccumulation across a broad range of organisms

One of the key components for environmental risk assessment of engineered nanomaterials (ENMs) is data on bioaccumulation potential. Accurately measuring bioaccumulation can be critical for regulatory decision making regarding material hazard and risk, and for understanding the mechanism of toxicity. This perspective provides expert guidance for performing ENM bioaccumulation measurements across a broad range of test organisms and species. To accomplish this aim, we critically evaluated ENM bioaccumulation within three categories of organisms: single-celled species, multicellular species excluding plants, and multicellular plants. For aqueous exposures of suspended single-celled and small multicellular species, it is critical to perform a robust procedure to separate suspended ENMs and small organisms to avoid overestimating bioaccumulation. For many multicellular organisms, it is essential to differentiate between the ENMs adsorbed to external surfaces or in the digestive tract and the amount absorbed across epithelial tissues. For multicellular plants, key considerations include how exposure route and the role of the rhizosphere may affect the quantitative measurement of uptake, and that the efficiency of washing procedures to remove loosely attached ENMs to the roots is not well understood. Within each organism category, case studies are provided to illustrate key methodological considerations for conducting robust bioaccumulation experiments for different species within each major group. The full scope of ENM bioaccumulation measurements and interpretations are discussed including conducting the organism exposure, separating organisms from the ENMs in the test media after exposure, analytical methods to quantify ENMs in the tissues or cells, and modeling the ENM bioaccumulation results. One key finding to improve bioaccumulation measurements was the critical need for further analytical method development to identify and quantify ENMs in complex matrices. Overall, the discussion, suggestions, and case studies described herein will help improve the robustness of ENM bioaccumulation studies.

Cotransport of nanoplastics (NPs) with fullerene (C60) in saturated sand: Effect of NPs/C60 ratio and seawater salinity

Nanoplastics (NPs) have been identified as newly emerging particulate contaminants. In marine environments, the interaction between NPs and other engineered nanoparticles remains unknown. This study investigated the cotransport of NPs with fullerene (C₆₀) in seawater-saturated columns packed with natural sand as affected by the mass concentration ratio of NPs/C₆₀ and the hydrochemical characteristics. In seawater with 35 practical salinity units (PSU), NPs could remarkably enhance C₆₀ dispersion with a NPs/C₆₀ ratio of 1. NPs behaved as a vehicle to facilitate C₆₀ transport by decreasing colloidal ζ-potential and forming stable primary heteroaggregates. As the NPs/C₆₀ ratio decreased to 1/3, NPs mobility was progressively restrained because of the formation of large secondary aggregates. When the ratio continuously decreased to 1/10, the stability and transport of colloids were governed by C₆₀ rather than NPs. Under this condition, the transport trend of binary suspensions was similar to that of single C₆₀ suspension, which was characterized by a ripening phenomenon. Seawater salinity is another key factor affecting the stability and associated transport of NPs and C₆₀. In seawater with 3.5 PSU, NPs and C₆₀ (1:1) in binary suspension exhibited colloidal dispersion, which was driven by a high-energy barrier. Thus, the profiles of the cotransport and retention of NPs/C₆₀ resembled those of single NPs suspension. This work demonstrated that the cotransport of NPs/C₆₀ strongly depended on their mass concentration ratios and seawater salinity.

Interpreting the effects of natural organic matter on antimicrobial activity of Ag2S nanoparticles with soft particle theory

Natural organic matter (NOM) ubiquitously exists in natural waters and would adsorb onto the particle surface. Previous studies showed that NOM would alleviate the toxicity of nanomaterials, while the mechanism is seldom quantitatively interpreted. Herein, the effects of humic substances [Suwannee River fulvic acid (SRFA) and Suwannee River humic acid (SRHA)] and biomacromolecules [alginate and bovine serum albumin (BSA)] on the aggregation and antimicrobial effects of silver sulfide nanoparticles (Ag₂S-NPs) were investigated. The aggregation kinetics of Ag₂S-NPs in electrolyte solutions were in agreement with the results based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The dynamic light scattering (DLS) results showed that the SRFA, SRHA, alginate and BSA molecules coated on the Ag₂S-NPs surfaces. The NOM coating layer prevented salt-induced coagulation of Ag₂S-NPs, and the effects of BSA and SRHA on Ag₂S-NPs stabilizing were more obvious than that of SRFA and alginate. Flow cytometry analysis results suggested that BSA and SRHA were more effective on alleviating the Ag₂S-NPs induced cell (Escherichia coli) membrane damage than SRFA and alginate. After interpreting the electrophoretic mobility (EPM) data of the NOM coated Ag₂S-NPs by Ohshima's soft particle theory, it was found that the thickness of the NOM coating layers followed the orders of BSA > SRHA > alginate > SRFA. The E.coli cell membrane damage level was negatively correlated with the thickness and softness of the coating layer. NOM coating may physically alleviate the contact between NPs and E. coli cells and thus attenuate the extent of cell membrane damage caused by the NP-cell interaction. This work provides a new perspective for quantitatively interpreting the influence of NOM on the environmental behaviors and risks of nanomaterials.

Size-dependent transport and retention of micron-sized plastic spheres in natural sand saturated with seawater

A series of one-dimensional column experiments were conducted to investigate the transport and retention of micron-sized plastic spheres (MPs) with diameters of 0.1-2.0 μm in seawater-saturated sand. In seawater with salinity of 35 PSU (practical salinity units), the mass percentages recovered from the effluent (M_eff) of the larger MPs increased from 13.6% to 41.3%, as MP size decreased from 2.0 μm to 0.8 μm. This occurred because of the gradual reduction of physical straining effect of MPs in the pores between sands. The smaller MPs (0.6, 0.4, and 0.1 μm) showed the stronger inhibition of MPs mobility, with M_eff values of 11.5%, 11.9%, and 9.8%, respectively. This was due to the lower energy barriers (from 108 k_BT to 16 k_BT) between the smaller MPs and the sand surface, when compared with the larger MPs (from 296 k_BT to 161 k_BT). In particular, the aggregation of MPs (0.6 or 0.4 μm) triggered a progressive decrease in MP concentration in the effluent. Retention experiments showed that the vertical migration distance of most MP colloids was 0-4 cm at the inlet of column. For 0.6 or 0.4 μm MPs, the particles were concentrated over a 0-2 cm vertical distance. Moreover, the salinity (35-3.5 PSU) did not affect the transport of the larger MPs (2.0-0.8 μm). However, as seawater salinity decreased from 35 PSU to 17.5 or 3.5 PSU, the aggregation of the smaller MPs (0.6-0.1 μm) was dramatically inhibited or completely prevented. Meanwhile, ripening of the sand surface by the MPs (0.6 and 0.4 μm) no longer occurred. By contrast, all MPs in deionized water (0 PSU) achieved complete column breakthroughs because of the strong repulsive energy barrier (from 218 k_BT to 4192 k_BT) between the MPs and the sand surface. Consequently, we find that the transport and retention of MPs in sandy marine environment strongly relies on both the MP size and the salinity levels.

Assessing the release of copper from nanocopper-treated and conventional copper-treated lumber into marine waters II: Forms and bioavailability

One application of nanocopper is as a wood-preserving pesticide in pressure-treated lumber. Recent research has shown that pressure-treated lumber amended with micronized copper azole (MCA), which contains nanosized copper, releases copper under estuarine and marine conditions. The form of copper released (i.e., ionic, nanocopper [1-100 nm in size]) is not fully understood but will affect the bioavailability and toxicity of the metal. In the present study, multiple lines of evidence, including size fractionation, ion-selective electrode electrochemistry, comparative toxicity, and copper speciation were used to determine the form of copper released from lumber blocks and sawdust. The results of all lines of evidence supported the hypothesis that ionic copper was released from MCA lumber and sawdust, with little evidence that nanocopper was released. For example, copper concentrations in size fractionations of lumber block aqueous leachates including unfiltered, 0.1 μm, and 3 kDa were not significantly different, suggesting that the form of copper released was in the size range operationally defined as dissolved. These results correlated with the ion-selective electrode data which detects only ionic copper. In addition, comparative toxicity testing resulted in a narrow range of median lethal concentrations (221-257 μg/L) for MCA lumber blocks and CuSO4 . We conclude that ionic copper was released from the nanocopper pressure-treated lumber under estuarine and marine conditions. Environ Toxicol Chem 2018;37:1969-1979. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Assessing the release of copper from nanocopper-treated and conventional copper-treated lumber into marine waters I: Concentrations and rates

Little is known about the release of metal engineered nanomaterials (ENMs) from consumer goods, including lumber treated with micronized copper. Micronized copper is a recent form of antifouling wood preservative containing nanosized copper particles for use in pressure-treated lumber. The present study investigated the concentrations released and the release rate of total copper over the course of 133 d under freshwater, estuarine, and marine salinity conditions (0, 1, 10, and 30‰) for several commercially available pressure-treated lumbers: micronized copper azole (MCA) at 0.96 and 2.4 kg/m3 , alkaline copper quaternary (ACQ) at 0.30 and 9.6 kg/m3 , and chromated copper arsenate (CCA) at 40 kg/m3 . Lumber was tested as blocks and as sawdust. Overall, copper was released from all treated lumber samples. Under leaching conditions, total release ranged from 2 to 55% of the measured copper originally in the lumber, with release rate constants from the blocks of 0.03 to 2.71 (units per day). Generally, measured release and modeled equilibrium concentrations were significantly higher in the estuarine conditions compared with freshwater or marine salinities, whereas rate constants showed very limited differences between salinities. Furthermore, organic carbon was released during the leaching and demonstrated a significant relationship with released copper concentrations as a function of salinity. The results indicate that copper is released into estuarine/marine waters from multiple wood treatments including lumber amended with nanoparticle-sized copper. Environ Toxicol Chem 2018;37:1956-1968. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Assessment of toxicity of selenium and cadmium selenium quantum dots: A review

This paper reviews the current understanding of the toxicity of selenium (Se) to terrestrial mammalian and aquatic organisms. Adverse biological effects occur in the case of Se deficiencies, associated with this element having essential biological functions and a narrow window between essentiality and toxicity. Several inorganic species of Se (-2, 0, +4, and +6) and organic species (monomethylated and dimethylated) have been reported in aquatic systems. The toxicity of Se in any given sample depends not only on its speciation and concentration, but also on the concomitant presence of other compounds that may have synergistic or antagonistic effects, affecting the target organism as well, usually spanning 2 or 3 orders of magnitude for inorganic Se species. In aquatic ecosystems, indirect toxic effects, linked to the trophic transfer of excess Se, are usually of much more concern than direct Se toxicity. Studies on the toxicity of selenium nanoparticles indicate the greater toxicity of chemically generated selenium nanoparticles relative to selenium oxyanions for fish and fish embryos while oxyanions of selenium have been found to be more highly toxic to rats as compared to nano-Se. Studies on polymer coated Cd/Se quantum dots suggest significant differences in toxicity of weathered vs. non-weathered QD's as well as a significant role for cadmium with respect to toxicity.

Quantitative Particle-Cell Interaction: Some Basic Physicochemical Pitfalls

There are numerous reports about particle-cell interaction studies in the literature. Many of those are performed in two-dimensional cell cultures. While the interpretation of such studies seems trivial at first sight, in fact for quantitative analysis some basic physical and physicochemical bases need to be considered. This starts with the dispersion of the particles, for which gravity, Brownian motion, and interparticle interactions need to be considered. The respective strength of these interactions determines whether the particles will sediment, are dispersed, or are agglomerated. This in turn largely influences their interaction with cells. While in the case of well-dispersed particles only a fraction of them will come into contact with cells in a two-dimensional culture, (agglomeration-induced) sedimentation drives the particles toward the cell surface, resulting in enhanced uptake.