Nanocolloids in Natural Water: Isolation, Characterization, and Toxicity

Nanocolloids in the soil environment: Transformation, transport and ecological effects

Nanocolloids (Ncs) are ubiquitous in natural systems and play a critical role in the biogeochemical cycling of trace metals and the mobility of organic pollutants. However, the environmental behavior and ecological effects of Ncs in the soil remain largely unknown. The accumulation of Ncs may have detrimental or beneficial effects on different compartments of the soil environment. This review discusses the major transformation processes (e.g., agglomeration/aggregation, absorption, deposition, dissolution, and redox reactions), transport, bioavailability of Ncs, and their roles in element cycles in soil systems. Notably, Ncs can act as effective carriers for other pollutants and contribute to environmental pollution by spreading pathogens, nutrients, heavy metals, and organic contaminants to adjacent water bodies or groundwater. Finally, the key knowledge gaps are highlighted to better predict their potential risks, and important new directions include exploring the geochemical process and mechanism of Ncs's formation; elucidating the transformation, transport, and ultimate fate of Ncs, and their long-term effect on contaminants, organisms, and elemental cycling; and identifying the impact on the growth and quality of important crops, evaluating its dominant effect on agro-ecosystems in the soil environment.

Ubiquitous nanocolloids suppress the conjugative transfer of plasmid-mediated antibiotic resistance in aqueous environment

Nanocolloids (Nc) are widespread in natural water environment, whereas the potential effects of Nc on dissemination of antibiotic resistance remain largely unknown. In this study, Nc collected from the Yellow River in Henan province was tested for its ability to influence the conjugative transfer of resistant plasmid in aqueous environment. The results revealed that the conjugative transfer of RP4 plasmid between Escherichia coli was down-regulated by 52%-91% upon exposure to 1-10 mg/L Nc and the reduction became constant when the dose became higher (20-200 mg/L). Despite the exposure of Nc activated the anti-oxidation and SOS response in bacteria through up-regulating genes involved in glutathione biosynthesis and DNA recombination, the inhibition on the synthesis and secretion of extracellular polysaccharide induced the prevention of cell-cell contact, leading to the reduction of plasmid transfer. This was evidenced by the decreased bacterial adhesion and lowered levels of genes and metabolites relevant to transmembrane transport and D-glucose phosphorylation, as clarified in phenotypic, transcriptomics and metabolomics analysis of E. coli. The significant down-regulation of glycolysis/gluconeogenesis and TCA cycle was associated with the shortage of ATP induced by Nc. The up-regulation of global regulatory genes (korA and trbA) and the reduction of plasmid genes (trfAp, trbBp, and traG) expression also contributed to the suppressed conjugation of RP4 plasmid. The obtained findings remind that the role of ubiquitous colloidal particles is nonnegligible when practically and comprehensively assessing the risk of antibiotic resistance in the environment.

Nanoplastics increase algal absorption and toxicity of Cd through alterations in cell wall structure and composition

Nanoplastics (NPs) may act as carriers of heavy metals and cause complex toxicity to aquatic organisms, while the exact role of NPs in the joint toxicity remains unclear. Here, we investigated the joint toxicity of polystyrene NPs (PS-NPs) and Cd to freshwater algae (Chlorella vulgaris). It was found that PS-NPs (1 mg L-1) could hardly enter algal cells and slightly inhibit algal growth (p < 0.01). The effect of PS-NPs as carriers on the joint toxicity of PS-NPs and heavy metals could be neglected because of the limited adsorption of Cd by PS-NPs, while the PS-NPs altered the cell wall structure and composition, which resulted in the increased algal absorption and toxicity of Cd. Compared to the low dose Cd (0.4 mg L-1) treatment alone, the extracellular and intracellular Cd contents in the cotreatment were significantly increased by 27.3 % and 18.0 %, respectively, due to the increased contents of cell wall polysaccharides (pectin and hemicellulose in particular) by the PS-NPs. Furthermore, after the high dose Cd (2 mg L-1) exposure, the inhibited polysaccharide biosynthesis and the loosen cell wall structure weakened the tolerance of cell wall to abiotic stress, facilitating the entry of PS-NPs into the algal cells and inducing the higher toxicity. These results elucidate the mechanism by which NPs enhance heavy metal toxicity to algae, providing a novel insight into environmental risks of NPs.

Nanoplastics inhibit carbon fixation in algae: The effect of aging

Despite the considerable efforts devoted to the toxicological assessment of nanoplastics, the effect of UV-irradiation induced aging, a realistic environmental process, on the toxicity of nanoplastics toward microalgae and its underlying mechanisms remain largely unknown. Herein, this study comparatively investigated the toxicities of polystyrene nanoplastics (nano-PS) and the UV-aged nano-PS on the eukaryotic alga Chlorella vulgaris, focusing on evaluating their inhibitory effects on carbon fixation. Exposure to environmentally relevant concentrations (0.1-10 mg/L) of nano-PS caused severe damage to chloroplast, inhibited the photosynthetic efficiency and electron transport, and suppressed the activities of carbon fixation related enzymes. Multi-omics results revealed that nano-PS interfered with energy supply by disrupting light reactions and TCA cycle and hindered the Calvin cycle, thereby inhibiting the photosynthetic carbon fixation of algae. The above alterations partially recovered after a recovery period. The aged nano-PS were less toxic than the pristine ones as evidenced by the mitigated inhibitory effect on algal growth and carbon fixation. The aging process introduced oxygen-containing functional groups on the surface of nano-PS, increased the hydrophilicity of nano-PS, limited their attachment on algal cells, and thus reduced the toxicity. The findings of this work highlight the potential threat of nanoplastics to the global carbon cycle.

Insight interactions of engineered nanoparticles with aquatic higher plants for phytoaccumulation, phytotoxicity, and phytoremediation applications: A review

With the growing age of human civilization, industrialization has paced up equally which is followed by the innovation of newer concepts of science and technology. One such example is the invention of engineered nanoparticles and their flagrant use in widespread applications. While ENPs serve their intended purposes, they also disrupt the ecological balance by contaminating pristine aquatic ecosystems. This review encompasses a comprehensive discussion about the potent toxicity of ENPs on aquatic ecosystems, with a particular focus on their impact on aquatic higher plants. The discussion extends to elucidating the fate of ENPs upon release into aquatic environments, covering aspects ranging from morphological and physiological effects to molecular-level phytotoxicity. Furthermore, this level of toxicity has been correlated with the determination of competent plants for the phytoremediation process towards the mitigation of this ecological stress. However, this review further illustrates the path of future research which is yet to be explored. Determination of the genotoxicity level of aquatic higher plants could explain the entire process comprehensively. Moreover, to make it suitable to be used in natural ecosystems phytoremediation potential of co-existing plant species along with the presence of different ENPs need to be evaluated. This literature will undoubtedly offer readers a comprehensive understanding of the stress induced by the irresponsible release of engineered nanoparticles (ENP) into aquatic environments, along with insights into the resilience characteristics of these pristine ecosystems.

Blockage of ATPase-mediated energy supply inducing metabolic disturbances in algal cells under silver nanoparticles stress

Adenosine triphosphate (ATP) generation of aquatic organisms is often subject to nanoparticles (NPs) stress, involving extensive reprogramming of gene expression and changes in enzyme activity accompanied by metabolic disturbances. However, little is known about the mechanism of energy supply by ATP to regulate the metabolism of aquatic organisms under NPs stress. Here, we selected extensively existing silver nanoparticles (AgNPs) to investigate their implications on ATP generation and relevant metabolic pathways in alga (Chlorella vulgaris). Results showed that ATP content significantly decreased by 94.2% of the control (without AgNPs) in the algal cells at 0.20 mg/L AgNPs, which was mainly attributed to the reduction of chloroplast ATPase activity (81.4%) and the downregulation of ATPase-coding genes atpB and atpH (74.5%-82.8%) in chloroplast. Molecular dynamics simulations demonstrated that AgNPs competed with the binding sites of substrates adenosine diphosphate and inorganic phosphate by forming a stable complex with ATPase subunit beta, potentially resulting in the reduced binding efficiency of substrates. Furthermore, metabolomics analysis proved that the ATP content positively correlated with the content of most differential metabolites such as D-talose, myo-inositol, and L-allothreonine. AgNPs remarkably inhibited ATP-involving metabolic pathways, including inositol phosphate metabolism, phosphatidylinositol signaling system, glycerophospholipid metabolism, aminoacyl-tRNA biosynthesis, and glutathione metabolism. These results could provide a deep understanding of energy supply in regulating metabolic disturbances under NPs stress.

Effect of natural soil nanocolloids on the fate and toxicity of cadmium to rice (Oryza sativa L.) roots

Toxic heavy metals are common contaminants and will most likely interact with ubiquitous natural nanocolloids (Ncs) in the soil environment. However, the effect of soil Ncs on the fate and health risk of cadmium (Cd) have not been well addressed. Here, the interaction between Ncs and Cd is investigated using two-dimensional correlation spectroscopy (2DCOS) combined with synchronous fluorescence and Fourier transform infrared spectroscopy. Our results reveal that Cd binding to the soil Ncs surface is mainly driven through strong hydrophilic effects and π - π interactions, which contribute to a high adsorption capacity (366-612 mg/g) and strong affinity (K_L = 4.3-9.7 L/mg) of Cd to soil Ncs. Interestingly, soil Ncs and Cd coexposure can significantly mediate the phytotoxicity (e.g., uptake, root growth, and oxidative stress) of Cd to rice (Oryza sativa L.) roots after 7 days of exposure. At the molecular level, metabolomic analysis reveals that the downregulated metabolic pathways (e.g., isoquinoline alkaloid and aminoacyl-tRNA biosynthesis, glycine, serine and threonine metabolism) may contribute to the above adverse phytotoxicity. This study provides new insight into the effect of natural Ncs on the fate and health risks of toxic heavy metals in soil environments.

Natural nanocolloids regulate the fate and phytotoxicity of hematite particles in water

Hematite (the most abundant iron oxide polymorph) is widely detected in the water environment and has attracted considerable attention. Natural nanocolloids (Ncs) exist ubiquitously in surface waters and play critical roles in biogeochemical processes. However, the influences of Ncs on the fate and phytotoxicity of hematite remain unknown. In this study, the infrared absorption spectra coupled with two-dimensional correlation spectroscopy analysis reveal that the specific binding interactions between Ncs and hematite primarily occur via hydrophilic effects and π-π interactions with an increase in the Ncs contact time. Moreover, binding with Ncs slightly promoted the aggregation rates of hematite particles in the BG-11 medium. Interestingly, Ncs remarkably mitigate the phytotoxicity (e.g., growth inhibition, oxidative stress, and mitochondrial toxicity) of nanosized and submicrosized hematite particles to Chlorella vulgaris after a 96 h exposure. The integrating metabolomic and transcriptomic analysis reveals that the regulated urea cycle, amino acids, and fatty acid-related metabolites (e.g., urea, serine, glutamate, and hexadecenoic acid) and genes (e.g., ACY1, CysC, and GLA) contribute to persistent phytotoxicity. This study provides new insights into the roles and mechanisms of natural Ncs in regulating the environmental risk of iron oxide minerals in aqueous media.

Effects of natural nanoparticles on the acute toxicity, chronic effect, and oxidative stress response of phenicol antibiotics in Daphnia magna

Natural nanoparticles (NNP) are ubiquitous in natural water and can interact with other contaminants, causing ecotoxic effects on aquatic nontarget organisms. However, the impact of NNPs on the ecotoxicity of antibiotics remains largely unknown. This work investigated the acute toxicity, chronic effect, and oxidative response and damage in Daphnia magna co-exposed to phenicol antibiotics (chloramphenicol, thiamphenicol) and different concentrations of NNPs (10 mg/L: environmentally relevant concentration; 100 mg/L: a high concentration that caused no apparent immobilization in D. magna). The results showed that the acute toxicity of chloramphenicol was increased by 10 mg/L NNPs but decreased by 100 mg/L NNPs; both concentrations of NNPs increased and decreased acute toxicities of thiamphenicol and chloramphenicol + thiamphenicol treatments, respectively. After long-term exposure, phenicol antibiotics (1 μg/L) and NNP (10 mg/L) mixtures in environmentally relevant concentrations significantly affected the reproduction of D. magna but did not influence their growth. The catalase activity, reduced glutathione level, and malonaldehyde content in D. magna also varied with the NNPs concentrations. Notably, the lowest concentration of thiamphenicol and chloramphenicol + thiamphenicol combined with NNPs significantly increased the malondialdehyde content in D. magna compared with the control, indicating membrane lipid peroxidation occurred in daphnids. This study suggests that the toxic effects of contaminants and NNPs on aquatic organisms should be considered thoroughly to avoid underestimating the hazard of these pollutants in the actual aquatic environment.

Affinity-based alleviation of dissolved organic matter (DOM) on tetracycline toxicity to photosynthesis of green algae Chlorella vulgaris: roles of hydrophilic and hydrophobic DOM

The environmental fate and toxic effects of antibiotics such as tetracycline (TC) could be influenced by the ubiquitous dissolved organic matter (DOM). However, DOM from different origins has different hydrophilic and hydrophobic properties. It is still unknown the effects of hydrophilic and hydrophobic DOM on the toxic effect of TC. In this study, DOM with hydrophilicity and hydrophobicity was separated and used to investigate their roles in affecting TC toxicity to the photosynthesis of green algae Chlorella vulgaris. Results showed that 10 mg L^-1 TC inhibited the efficiency of photosystem II (PSII) of C. vulgaris using light by hindering electron transfer from Q_A^- to Q_B/Q_B^-, and the O₂ release rate of C. vulgaris decreased by a third after 12-h treatment of 10 mg L^-1 TC, while both hydrophilic and hydrophobic DOM (20 mg L^-1 TOC) alleviated TC toxicity to the photosynthesis of C. vulgaris. In the presence of hydrophilic or hydrophobic DOM, stable complex of TC-hydrophilic DOM or TC-hydrophobic DOM was formed immediately, due to the good affinity of both DOM for TC. Fourier transform infrared spectroscopy result showed that both hydrophilic and hydrophobic DOM could reduce C=O in TC to C-O, and isothermal titration calorimetry result suggested that reactions of both DOM with TC were exothermic (△H < 0) and spontaneous (△G < 0). Thereinto, the reaction constant (K_a) of TC reacting with hydrophobic DOM (K_a=9.70) was higher than that with hydrophilic DOM (K_a=8.93), indicating hydrophobic DOM with more chemical binding sites and accessible fractions for TC. The present study suggests that DOM, especially the hydrophobic DOM, is an important consideration in the environmental impact assessment of antibiotics.

Physiological and morphological responses of Chlorella pyrenoidosa to different exposure methods of graphene oxide quantum dots

Graphene oxide quantum dots (GOQDs) can convert the ultraviolet (200- 380 nm) into available wavelength (400- 700 nm) for microalgae cultivation. However, it has not been applied in large-scale microalgae culture due to its high cost and difficulties in recovery. This study proposed a new strategy for the sustainable use of GOQDs, namely, GOQDs solution was added to the outer sandwich of the reactor. Herein, the effects of direct and indirect exposure of different GOQDs concentrations (0, 100, and 1000 mg/L) on the microalgae culture were compared. When microalgae were directly exposed to the GOQDs, 100 mg/L of GOQDs increased the biomass production of microalgae by 24.0 %, while 1000 mg/L of GOQDs decreased biomass production by 31 %. High concentration of GOQDs (direct exposure) could cause extra oxidative stress in the microalgae cells and result in a significant reduction of pigment content. When microalgae were indirectly exposed to the GOQDs, the increased concentration of GOQDs enhanced the growth of microalgae. Compared to the blank group, 1000 mg/L of GOQDs increased the microalgae biomass production and bioenergy by 14.1 % and 40.17 %, respectively. The indirect exposure of GOQDs can effectively avoid photo-oxidation and organelle damage to the microalgae cells. Overall, the indirect exposure of GOQDs is a sustainable way for effectively promoting microalgae growth and reducing the application cost.

Composite Membrane Dressings System with Metallic Nanoparticles as an Antibacterial Factor in Wound Healing

Wound management is the burning problem of modern medicine, significantly burdening developed countries’ healthcare systems. In recent years, it has become clear that the achievements of nanotechnology have introduced a new quality in wound healing. The application of nanomaterials in wound dressing significantly improves their properties and promotes the healing of injuries. Therefore, this review paper presents the subjectively selected nanomaterials used in wound dressings, including the metallic nanoparticles (NPs), and refers to the aspects of their application as antimicrobial factors. The literature review was supplemented with the results of our team’s research on the elements of multifunctional new-generation dressings containing nanoparticles. The wound healing multiple molecular pathways, mediating cell types, and affecting agents are discussed herein. Moreover, the categorization of wound dressings is presented. Additionally, some materials and membrane constructs applied in wound dressings are described. Finally, bacterial participation in wound healing and the mechanism of the antibacterial function of nanoparticles are considered. Membranes involving NPs as the bacteriostatic factors for improving wound healing of skin and bones, including our experimental findings, are discussed in the paper. In addition, some studies of our team concerning the selected bacterial strains’ interaction with material involving different metallic NPs, such as AuNPs, AgNPs, Fe₃O₄NPs, and CuNPs, are presented. Furthermore, nanoparticles’ influence on selected eukaryotic cells is mentioned. The ideal, universal wound dressing still has not been obtained; thus, a new generation of products have been developed, represented by the nanocomposite materials with antibacterial, anti-inflammatory properties that can influence the wound-healing process.

Environmental decomposition and remodeled phytotoxicity of framework-based nanomaterials

Zeolitic imidazole frameworks (ZIFs) have attracted a considerable amount of attention for use in environmental applications (e.g., pollutant adsorption and photocatalysis in water treatments). The environmental stability and toxicity of ZIFs are key prerequisites for their practical applications, but information about these factors is largely lacking. The present work finds that pristine ZIFs (ZIF-8 and ZIF-67) photodegrade from frame structures into two-dimensional nanosheets and are oxidized to zinc carbonate (ZIF-8) and Co₃O₄ (ZIF-67) under visible-light irradiation. The photoinduced electrons, holes and free radicals promote dissolution of the metal cores and organic ligands, leading to collapse of the frame structure. The photodegradation of ZIF-8 alleviates developmental inhibition, oxidative stress, plasmolysis, and photosynthetic toxicity, while the photodegradation of ZIF-67 aggravates nanotoxicity. The integration of metabolomics and transcriptomics analysis reveals that unsaturated fatty acid biosynthesis and metal ion-binding transcription contribute to the altered toxicity of ZIF photodegradation. These findings highlight the roles of photodegradation in structural transformation and alteration of the toxicity of ZIFs, alarming the study of pristine metal-organic frameworks (MOFs).

Selectively Tracking Nanoparticles in Aquatic Plant Using Core-Shell Nanoparticle-Enhanced Raman Spectroscopy Imaging

Nanoparticles contribute to enormous environmental processes, but, due to analytical challenges, the understanding of nanoparticle fate remains elusive in complex environmental matrices. To address the challenge, a core-shell nanoparticle-enhanced Raman spectroscopy (CSNERS) imaging method was developed to selectively track prevalent SiO₂ nanoparticles in an aquatic plant, Lemna minor. By encapsulating gold nanoparticles and Raman reporters inside, the resonance Raman signature was enhanced, thus enabling the sensitive and selective detection of SiO₂ nanoparticles at an environmentally relevant concentration. The panoramic visualization of the translocation pathway of nanoparticles shows an unexpected, fast (in hours) and a preferential accumulation of nanoparticles on the node, leaf edge, root cap, etc., implying the ability of CSNERS to spectroscopically determine nanotoxicity. The core-shell design in CSNERS was capable of multiplex labeling two differently charged nanoparticles and distinguishing their biobehavior simultaneously. Meanwhile, the CSNERS method can be further applied for a variety of nanoparticles, implying its promising applications for nanotoxicity research and biogeochemical study.

Transcriptomics and Metabolomics Revealed the Biological Response of Chlorella pyrenoidesa to Single and Repeated Exposures of AgNPs at Different Concentrations

Increased release of engineered nanoparticles (ENPs) from widely used commercial products has threatened environmental health and safety, particularly the repeated exposures to ENPs with relatively low concentration. Herein, we studied the response of Chlorella pyrenoidesa (C. pyrenoidesa) to single and repeated exposures to silver nanoparticles (AgNPs). Repeated exposures to AgNPs promoted chlorophyll a and carotenoid production, and increased silver accumulation, thus enhancing the risk of AgNPs entering the food chain. Notably, the extracellular polymeric substances (EPS) content of the 1-AgNPs and 3-AgNPs groups were dramatically increased by 119.1% and 151.5%, respectively. We found that C. pyrenoidesa cells exposed to AgNPs had several significant alterations in metabolic process and cellular transcription. Most of the genes and metabolites are altered in a dose-dependent manner. Compared with the control group, single exposure had more differential genes and metabolites than repeated exposures. 562, 1341, 4014, 227, 483, and 2409 unigenes were differentially expressed by 1-0.5-AgNPs, 1-5-AgNPs, 1-10-AgNPs, 3-0.5-AgNPs, 3-5-AgNPs, and 3-10-AgNPs treatment groups compared with the control. Metabolomic analyses revealed that AgNPs altered the levels of sugars and amino acids, suggesting that AgNPs reprogrammed carbon/nitrogen metabolism. The changes of genes related to carbohydrate and amino acid metabolism, such as citrate synthase (CS), isocitrate dehydrogenase (IDH1), and malate dehydrogenase (MDH), further supported these results. These findings elucidated the mechanism of biological responses to repeated exposures to AgNPs, providing a new perspective on the risk assessment of nanomaterials.

Metals and Metal-Nanoparticles in Human Pathologies: From Exposure to Therapy

An increasing number of pathologies correlates with both toxic and essential metal ions dyshomeostasis. Next to known genetic disorders (e.g., Wilson's Disease and β-Thalassemia) other pathological states such as neurodegeneration and diabetes are characterized by an imbalance of essential metal ions. Metal ions can enter the human body from the surrounding environment in the form of free metal ions or metal-nanoparticles, and successively translocate to different tissues, where they are accumulated and develop distinct pathologies. There are no characteristic symptoms of metal intoxication, and the exact diagnosis is still difficult. In this review, we present metal-related pathologies with the most common onsets, biomarkers of metal intoxication, and proper techniques of metal qualitative and quantitative analysis. We discuss the possible role of drugs with metal-chelating ability in metal dyshomeostasis, and present recent advances in therapies of metal-related diseases.

Environmental factors-mediated behavior of microplastics and nanoplastics in water: A review

The release of plastics in nature is an increasing global concern due to their degradation from microplastics (MPs) and even to nanoplastics (NPs), which are being recognized as a potential global threat to humans and environment. This paper summarizes the current knowledge on the effect of different environmental factors on the aggregation of MPs and NPs in aquatic environment. Stability (or extent of aggregation) of MPs and NPs varies with pH, ionic strength, ion type (monovalent, divalent, and trivalent), kind of minerals, and natural organic matter (NOM) of the aquatic environment. Electrostatic interactions between particles at different pH and ionic strength caused by salts of different valents govern the aggregation. In the presence of minerals (or inorganic colloids), net surface charge of mineral and surface potential of MPs and NPs (i.e., positive or negative surface functionality) play important roles in the heteroaggregation of MPs and NPs. In the presence of NOM, additional complex interactions including hydrophobic interactions and bridging are also involved in the aggregation of particles. Understanding the interactions of MPs and NPs of different surface charge with diverse environmental factors at a wide range of environmental conditions is pivotal to assess the mobility and the fate of degraded plastic particles and their risk to human health and ecological systems.

Nanotechnology Development for Formulating Essential Oils in Wound Dressing Materials to Promote the Wound-Healing Process: A Review

Wound healing refers to the replacement of damaged tissue through strongly coordinated cellular events. The patient’s condition and different types of wounds complicate the already intricate healing process. Conventional wound dressing materials seem to be insufficient to facilitate and support this mechanism. Nanotechnology could provide the physicochemical properties and specific biological responses needed to promote the healing process. For nanoparticulate dressing design, growing interest has focused on natural biopolymers due to their biocompatibility and good adaptability to technological needs. Polysaccharides are the most common natural biopolymers used for wound-healing materials. In particular, alginate and chitosan polymers exhibit intrinsic antibacterial and anti-inflammatory effects, useful for guaranteeing efficient treatment. Recent studies highlight that several natural plant-derived molecules can influence healing stages. In particular, essential oils show excellent antibacterial, antifungal, antioxidant, and anti-inflammatory properties that can be amplified by combining them with nanotechnological strategies. This review summarizes recent studies concerning essential oils as active secondary compounds in polysaccharide-based wound dressings.

Nanocolloids, but Not Humic Acids, Augment the Phytotoxicity of Single-Layer Molybdenum Disulfide Nanosheets

Engineered nanomaterials (ENMs), especially transition metal dichalcogenide (TMDC), have received great attention in recent years due to their advantageous properties and applications in various fields and are inevitably released into the environment during their life cycle. However, the effect of natural nanocolloids, widely distributed in the aquatic environment, on the environmental transformation and ecotoxicity of ENMs remains largely unknown. In this study, the effects of natural nanocolloids were compared to humic acid on the environmental transformation and ecotoxicity of single-layer molybdenum disulfide (SLMoS₂), a representative TMDC. SLMoS₂ with nanocolloids or humic acid (HA) enhanced their dispersion and Mo ion release in deionized water. Nanocolloids induced growth inhibition, reactive oxygen species (ROS) elevation, and cell permeability. Low-toxicity SLMoS₂ combined with nanocolloids will enhance the above adverse effects. SLMoS₂-nanocolloids induced serious damage (cell distortion and deformation), SLMoS₂ internalization, and metabolic perturbation on Chlorella vulgaris (C. vulgaris). In contrast, the addition of HA induced the growth promotion and lower ROS level, inhibited the internalization of SLMoS₂, and mitigated metabolic perturbation on C. vulgaris. This work provides insights into the effect of natural nanocolloids on the behaviors and biological risks of ENMs in aquatic environments, deserving substantial future attention.

Nanocolloids in drinking water increase the risk of obesity in mice by modulating gut microbes

Both gut microbes and environmental contamination may cause metabolic disorders and obesity. However, the relationships among gut microbes, environmental contamination and obesity remain obscure. The drinking water on a national scale (31 cities in China) contained nanocolloid-pattern contamination at the mg/L level, a concentration that is 10- to 100-fold higher than commonly reported pollutants. Exposure to nanocolloids (environmentally related dose, 0.15 mg/kg) for three weeks increased the body weight and leptin levels of mice and decreased the expression of adiponectin. Nanocolloids increased the ratio of Firmicutes to Bacteroidetes, a typical obesity-related phenomenon, in the obese individuals. Oral administration of resveratrol verified the role of gut microbes in the tendency toward obesity induced by nanocolloids. The ratio of Firmicutes to Bacteroidetes is positively correlated with body weight and leptin levels. Compared to the control, the levels of triglycerides and high-density lipoprotein cholesterol were up- and downregulated by the tested nanocolloids at 0.15 mg/kg, respectively. Long-chain fatty acids, lipid metabolites and the expression of lipid synthesis-related genes (Fas, Srebp-1 and ACC-1) were also significantly increased by nanocolloids. The present study provides new insights that improve our understanding the risks of obesity associated with drinking water contamination that are mediated by gut microbes.

The dual effect of natural organic matter on the two-step internalization process of Au@Sio2 in freshwater

Dissolved organic matter (DOM) in aquatic ecosystems reshapes the surface of nanoparticles (NPs) greatly. Understanding how these changes influence the bioavailability of NPs is critical for accurately predicting the ecological risks of NPs. A quantitative model based on the two-step internalization process enabled the differentiation between the adhesion ability of NPs to membranes and the internalization capacity. Using protozoa Tetrahymena thermophila as the test organism, fluorescein isothiocyanate-modified silica NPs (FITC-SiO₂) and silica-coated gold NPs (Au@SiO₂) were prepared to validate the model and study the influence of DOM on uptake. DOM reduced the ability of Au@SiO₂ to adhere onto cell membranes and the inhibitory effect of bovine serum albumin (BSA) and β-lactoglobulin was higher due to their higher molecular weights and the weaker interaction. Moreover, DOM increased the internalization capacity. 80% Au@SiO₂ was internalized in the presence of humic acid (HA), over 90% Au@SiO₂ was internalized in the presence of the two proteins, whereas only 60% were internalized by the control group. Next, the specific recognition of the cell internalization in the presence of DOM was confirmed. We concluded that the traditional "accumulation" may misestimate the true biological effect caused by NPs coated with DOM. NPs coated with highly bioavailable DOM pose a greater risk to aquatic ecosystems because they are more likely to be internalized by living organisms.

Barrier function of zebrafish embryonic chorions against microplastics and nanoplastics and its impact on embryo development

Embryonic stage is important for the development of aquatic animals, and embryonic chorion is an efficient barrier against exogenous pollutants. The efficient barrier function of zebrafish (Danio rerio) embryonic chorions against micro- and nano- polystyrene (PS) particles was observed. Embryonic chorions presented high affinity to PS particles. The covering layer of PS particles on the outer surface of chorions affected the patency of pores in chorions, and the nano- PS particles exerted a considerable effect. The accelerated heart rate and blood flow velocity in the embryos indicated that the PS particles adhering to embryonic chorions might cause an internal hypoxic microenvironment in the embryos. The coating of PS particles on embryonic chorions also resulted in delayed hatching of the embryos. The observed development toxicity induced by the nano- and micro-PS particles was confirmed via the expressions of metabolic pathways related to antioxidant system. The pathways of biosynthesis of unsaturated fatty acid, linoleic acid metabolism and alanine, and aspartate and glutamate metabolism extensively altered when the embryos were exposed to PS particles, especially to the nano- PS particles. Although micro- and nano- plastic particles can be efficiently blocked by embryonic chorions, they can still affect the early development of aquatic organisms.

Effects of graphene oxide on algal cellular stress response: Evaluating metabolic characters of carbon fixation and nutrient removal

The effects of different concentrations of graphene oxide (GO) on intracellular metabolism in Chlorella vulgaris (C. vulgaris) and removal of nitrogen and phosphorus nutrients by C. vulgaris from synthetic wastewater were studied. The results demonstrated that cell division of Chlorella vulgaris increased at 24 h and decreased at 96 h after exposure to different concentrations of GO. The removal rates of total nitrogen (TN), ammoniacal nitrogen (NH₃-N), phosphate (PO₄^3--P), and chemical oxygen demand (COD) were 24.1%, 70.0%, 37.0%, and 39.6%, respectively, when the concentration of GO was 0.01 mg/L 10 mg/L GO induced severe plasmolysis and cytoplasmic contraction. Furthermore, the protein-like exopolysaccharide (EPS) content of algal cells exposed to 10 mg/L GO decrease to 10.8% of the control group. Simultaneously, the reactive oxygen species (ROS) level was 175.4% of control group. The biological responses to 10 mg/L GO included increase in ROS level, inhibition of saccharide metabolism, and degradation of amino acids. In addition, high concentrations of 10 mg/L GO weakened the carbon fixation process in algal cells. These stress-response behaviors increased cell permeability and oxidative stress. Overall, these findings provide new insights regarding the effects of GO on algal cellular stress responses.

Natural Nanocolloids Mediate the Phytotoxicity of Graphene Oxide

Nanocolloids (Ncs) are ubiquitous in natural surface waters. However, the effects of Ncs on the fate and ecotoxicity of graphene oxide (GO, a popular engineered nanomaterial (ENM)) remain largely unknown. Ncs exhibit strong adsorption affinity (K_L = 1.93 L/mg) and high adsorption capacity (176.2 mg/g) for GO. After Ncs hybridization, GO nanosheets became scrolls, and the aggregation rate of GO decreased. The influence of humic acid and Ncs on GO toxicity was compared. Humic acid mitigated the phytotoxicity of GO. However, GO and GO-Ncs were found to have an envelopment effect on algal cells, and both could enter algal cells. GO-Ncs induced higher reactive oxygen species (ROS) generation, stronger DNA damage and plasmolysis, and more obvious inhibition of photosynthesis compared to GO. Proteomic analysis revealed that photosystem I- and II-related proteins (e.g., E1ZQR2 and E1ZPG5) were regulated more significantly in the GO-Ncs groups than in the GO groups. A combined proteomic and metabolomic analysis showed that inhibition of carbohydrate, fatty acid, and amino acid metabolism contributed to ROS generation. Given the high concentrations and activity of Ncs, the above results highlight the need for reconsideration of the Ncs-mediated environmental behaviors and risks of ENMs and other pollutants.

A preliminary study of the interactions between microplastics and citrate-coated silver nanoparticles in aquatic environments

Microplastics and silver nanoparticles (AgNPs) are considered two emerging environmental contaminants that have adverse effects on aquatic environments. Knowledge on the interactions between AgNPs and microplastics may improve our understanding of these pollutants, posing to surrounding environments and public health. However, current knowledge regarding this issue is limited. Here, we investigate, for the first time, the interactions between AgNPs and the microplastics polyethylene (PE), polypropylene (PP), and polystyrene (PS) in aquatic environments. Results showed no significant interactions between AgNPs and PE or PP microplastics. However, AgNPs were efficiently removed by PS microplastics. These differences are mainly attributed to the presence of π-π interactions. Meanwhile, AgNPs aggregations were generated due to higher concentrations of leaching additives derived from PS microplastics. Interestingly, AgNPs are significantly captured on PS microplastic surfaces in the form of Ag⁰ rather than Ag⁺. The capture process is a monolayer adsorption and influenced greatly by the mass ratio of AgNPs and PS microplastics. These observations may provide a novel environmental fate of AgNPs, and indicate a new potential method for their removal to some degree. These findings demonstrate the complexities of AgNPs absorption onto microplastics and enhance present understanding of interactions between nanoparticles and microplastics in aquatic environments.

Nanoholes Regulate the Phytotoxicity of Single-Layer Molybdenum Disulfide

Single-layer molybdenum disulfide (SLMoS₂) are applied as a hot 2D nanosheet in various fields involving water treatments. Both intentional design and environmental or biological processes induce many nanoholes in SLMoS₂. However, the effects of nanoholes on the environmental stability and ecotoxicity of SLMoS₂ remain largely unknown. The present work discovered that visible-light irradiation induced nanoholes (diameters, approximately 20 nm) in the plane of SLMoS₂, with irregular edges and increased interplanar crystal spacing. The ratios of Mo to S in pristine and transformed SLMoS₂ were 0.53 and 0.33, respectively. After 96 h exposure at concentrations from 0.1 to 1 mg/L, the above nanoholes promoted algal division, induced a stress-response hormesis, decreased the generation of •OH, and mitigated the cell shrinkage and wall rupture of Chlorella vulgaris induced by SLMoS₂. In terms of stress response, the nanohole-bearing SLMoS₂ induced fewer vacuoles and polyphosphate bodies of Chlorella vulgaris than the pristine form. Metabolomic analysis revealed that nanoholes perturbed the metabolisms of energy, carbohydrates, and fatty acids. This work proposes that nanoholes cause obvious effects on the environmental fate and ecotoxicity of SLMoS₂ and that the environmental risks of engineered nanomaterials should be reevaluated using nanohole-bearing rather than pristine forms for testing.

Phytotoxicity induced by engineered nanomaterials as explored by metabolomics: Perspectives and challenges

Given the wide applications of engineered nanomaterials (ENMs) in various fields, the ecotoxicology of ENMs has attracted much attention. The traditional plant physiological activity (e.g., reactive oxygen species and antioxidant enzymes) are limited in that they probe one specific process of nanotoxicity, which may result in the loss of understanding of other important biological reactions. Metabolites, which are downstream of gene and protein expression, are directly related to biological phenomena. Metabolomics is an easily performed and efficient tool for solving the aforementioned problems because it involves the comprehensive exploration of metabolic profiles. To understand the roles of metabolomics in phytotoxicity, the analytical methods for metabolomics should be organized and discussed. Moreover, the dominant metabolites and metabolic pathways are similar in different plants, which determines the universal applicability of metabolomics analysis. The analysis of regulated metabolism will globally and scientifically help determine the ecotoxicology that is induced by ENMs. In the past several years, great developments in nanotoxicology have been achieved using metabolomics. However, many knowledge gaps remain, such as the relationships between biological responses that are induced by ENMs and the regulation of metabolism (e.g., carbohydrate, energy, amino acid, lipid and secondary metabolism). The phytotoxicity that is induced by ENMs has been explored by metabolomics, which is still in its infancy. The detrimental and defence mechanisms of plants in their response to ENMs at the level of metabolomics also deserve much attention. In addition, owing to the regulation of metabolism in plants by ENMs affected by multiple factors, it is meaningful to uniformly identify the key influencing factor.

Widely distributed nanocolloids in water regulate the fate and risk of graphene oxide

The environmental behaviors and risks associated with graphene oxide (GO, a popular 2D nanomaterial) have attracted considerable attention. GO released to aquatic systems will most likely interact with ubiquitous nanocolloids (Nc) in surface water. However, the effects of Nc on the fate and risk of GO remain largely unknown in water. Herein, the binding of Nc onto GO was investigated via electron microscopy, electron paramagnetic resonance, 2D correlation spectroscopy and biolayer interferometry. The results revealed that electron charge transfers, hydrophilic effects and π-π stacking contributed to a strong affinity (K_D = 5.6 nM) and high adsorption capacity (159.8 mg/g) of Nc onto the GO surface. Moreover, GO nanosheets transformed to a scroll morphology or multiple GO particles bridging by Nc, which remarkably reduced the aggregation and sedimentation rates after binding with Nc. Interestingly, co-exposure with Nc greatly alleviated the toxicity (e.g., tail malformation, yolk sac edema and oxidative stress) of GO to zebrafish embryos. Morphological and structural alterations of GO after binding to Nc contributed to the mechanisms for the antagonistic effects on the zebrafish embryos toxicity. The present work provides insights into the environmental fate and risk of GO by ubiquitous Nc in natural water.

Shape-dependent toxicity of alumina nanoparticles in rat astrocytes

Nanosized alumina (Al₂O₃-NPs), a widely used nanoparticle in numerous commercial applications, is released into environment posing a threat to the health of wildlife and humans. Recent research has revealed essential roles of physicochemical properties of nanoparticles in determining their toxicity potencies. However, influence of shape on neurotoxicity induced by heterogeneous Al₂O₃-NPs remains unknown. We herein compared the neurotoxicity of two shapes of γ-Al₂O₃-NPs (flake versus rod) and their effects on metabolic profiles of astrocytes in rat cerebral cortex. While exposed to both shapes caused significant cytotoxicity and apoptosis in a dose-dependent manner after 72 h exposure, a significantly stronger response was observed for nanorods than for nanoflakes. These effects were associated with significantly greater ROS accumulation and inflammation induction, as indicated by increased concentrations of IL-1β, IL-2 and IL-6. Using untargeted metabolomics, significant alternations in metabolism of amino acids, lipids and purines, and pyrimidines were observed after exposure to both types. Moreover, changes in the metabolome caused by nanorods were significantly greater than those by nanoflakes as also indicated by physiological stress responses to ROS, inflammation, and apoptosis. Taken together, these findings demonstrated the critical role of morphology in determining toxic potencies of nano-alumina and its underlying mechanisms of toxic actions.

Effects of carboxyl single-walled carbon nanotubes on synthetic wastewater nutrient removal by an algal-bacterial consortium: Regulation and interaction

In this study, the morphology, ultrastructure, nutrient removal, metabolite levels, and interaction of an algal-bacterial consortium exposed to different concentrations of carboxylic single-walled carbon nanotubes (C-SWCNT) were investigated. At a C-SWCNT concentration of 0.05 mg·L^-1, the removal rates of TN, NH₃-N, PO₄^3--P, and COD were 94.7%, 94.8%, 86.4% and 84.3%, respectively. When cells were exposed to 50 mg·L^-1 C-SWCNT, its intracellular levels in individual algae and the algal-bacterial consortium were 23.6 μg·g^-1 and 12.1 μg·g^-1, respectively. C-SWCNT (0.05 mg·L^-1) promoted the metabolism of fatty acids, amino acids, small molecules, and acid in the algal-bacterial consortium. The main response to the interaction of C-SWCNT and the consortium was the change in extracellular carbohydrate levels. C-SWCNT also increased chlorophyll a and glycine levels. These findings reveal new insights into our understanding of the biological responses and interactions between C-SWCNT and algal-bacterial consortium.

Study of the Persistence of the Phytotoxicity Induced by Graphene Oxide Quantum Dots and of the Specific Molecular Mechanisms by Integrating Omics and Regular Analyses

Although increasing attention has been paid to the nanotoxicity of graphene oxide quantum dots (GOQDs) due to their broad range of applications, the persistence and recoverability associated with GOQDs had been widely ignored. Interestingly, stress-response hormesis for algal growth was observed for Chlorella vulgaris as a single-celled model organism. Few physiological parameters, such as algal density, plasmolysis, and levels of reactive oxygen species, exhibited facile recovery. In contrast, the effects on chlorophyll a levels, permeability, and starch grain accumulation exhibited persistent toxicity. In the exposure stage, the downregulation of genes related to unsaturated fatty acid biosynthesis, carotenoid biosynthesis, phenylpropanoid biosynthesis, and binding contributed to toxic effects on photosynthesis. In the recovery stage, downregulation of genes related to the cis-Golgi network, photosystem I, photosynthetic membrane, and thylakoid was linked to the persistence of toxic effects on photosynthesis. The upregulated galactose metabolism and downregulated aminoacyl-tRNA biosynthesis also indicated toxicity persistence in the recovery stage. The downregulation and upregulation of phenylalanine metabolism in the exposure and recovery stages, respectively, reflected the tolerance of the algae to GOQDs. The present study highlights the importance of studying nanotoxicity by elucidation of stress and recovery patterns with metabolomics and transcriptomics.

Integrating Biolayer Interferometry, Atomic Force Microscopy, and Density Functional Theory Calculation Studies on the Affinity between Humic Acid Fractions and Graphene Oxide

The interactions between nanoparticles and humic acid (HA) are critical to understanding the environmental risks and applications of nanoparticles. However, the interactions between HA fractions and graphene oxide (GO, a popular carbon nanosheet) at the molecular level remain largely unclear. Four HA fractions with molecular weights ranging from 4.6 to 23.8 kDa were separated, and the large HA fractions presented low oxygen contents and many aromatic structures. The binding constants of the large HA fractions on GO were 2.6- to 3551-fold higher than those of the small HA fractions, while the maximum adsorption capacities of the larger HA fractions onto GO were much higher. Atomic force microscopy (AFM) found that the small and large HA fractions were spread over the center and the edge of the GO nanosheets, respectively. Density functional theory (DFT) simulation and nuclear magnetic resonance spectroscopy confirmed the above phenomena (three adsorption patterns, "vs", "ps", and "pea") and revealed that HA bonded to the GO nanosheets mainly through van der Waals force and π-π interactions. The integrating analysis of binding affinity, AFM, and DFT provides new insights into the environmental behavior of GO and the applications of GO in pollutant removal under exposure from HA.

Interactions between silver nanoparticles and other metal nanoparticles under environmentally relevant conditions: A review

Global production of engineered nanoparticles (ENPs) continues to increase due to the demand of enabling properties in consumer products and industrial applications. Release of individual or aggregates of ENPs have been shown to interact with one another subsequently resulting in adverse biological effects. This review focuses on silver nanoparticles (AgNPs), which are currently used in numerous applications, including but not limited to antibacterial action. Consequently, the release of AgNPs into the aquatic environment, the dissociation into ions, the binding to organic matter, reactions with other metal-based materials, and disruption of normal biological and ecological processes at the cellular level are all potential negative effects of AgNPs usage. The potential sources of AgNPs includes leaching of intact particles from consumer products, disposal of waste from industrial processes, intentional release into contaminated waters, and the natural formation of AgNPs in surface and ground water. Formation of natural AgNPs is greatly influenced by different chemical parameters including: pH, oxygen levels, and the presence of organic matter, which results in AgNPs that are stable for several months. Both engineered and natural AgNPs can interact with metal and metal oxide particles/nanoparticles. However, information on the chemical and toxicological interactions between AgNPs and other nanoparticles is limited. We have presented current knowledge on the interactions of AgNPs with gold nanoparticles (AuNPs) and titanium dioxide nanoparticles (TiO₂ NPs). The interaction between AgNPs and AuNPs result in stable bimetallic Ag-Au alloy NPs. Whereas the interaction of AgNPs with TiO₂ NPs under dark and light conditions results in the release of Ag⁺ ions, which may be subsequently converted back into AgNPs and adsorb on TiO₂ NPs. The potential chemical mechanisms and toxic effects of AgNPs with AuNPs and TiO₂ NPs are discussed within this review and show that further investigation is warranted.

The Phases of WS2 Nanosheets Influence Uptake, Oxidative Stress, Lipid Peroxidation, Membrane Damage, and Metabolism in Algae

Application of transition metal dichalcogenide (TMDC) nanosheets with different phases have attracted much attention in various fields. However, the effects of TMDC phases on environmental biology remain largely unknown. In this study, chemically exfoliated WS₂ nanosheets (Ce-WS₂, mainly the 1T phase) and annealed exfoliated WS₂ nanosheets (Ae-WS₂, 2H phase) were fabricated to serve as representative TMDC nanomaterials. Ce-WS₂ showed higher levels of cellular uptake, oxidative stress, lipid peroxidation, membrane damage, and inhibition of photosynthesis than Ae-WS₂ in Chlorella vulgaris. These differences were attributed to the higher electron conductivity and higher separation efficiency of electrons and holes in the 1T phase, a typical feature of Ce-WS₂. Correspondingly, 2H-phase Ae-WS₂ exhibited lower photooxidation/reduction activity and a lower ability to generate reactive oxygen species (mainly •OH) under visible-light irradiation. 1T-phase Ce-WS₂ dissolved more readily than Ae-WS₂ and released more W ions into aqueous environments, but the W ions exhibited negligible toxicity. Metabolomic analysis revealed that Ce-WS₂ induced more obvious alterations in metabolites (e.g., amino acids and fatty acids) and metabolic pathways (e.g., starch and sucrose metabolism) than Ae-WS₂. These alterations correlated with cell membrane damage, oxidative stress and photosynthesis inhibition. The present work provides insights into the environmentally friendly design of two-dimensional TMDCs.