Se Wang

Impacts of low-molecular-weight organic acids on aquatic behavior of graphene nanoplatelets and their induced algal toxicity and antioxidant capacity

Knowledge of the interaction between graphene-based materials and low-molecular-weight organic acids (LOAs) is essential to understand fate and effects of graphene-based materials in the aquatic environment, but this interaction remains poorly elucidated. In this study, the effects of LOAs on the physicochemical properties of graphene nanoplatelets (GNPs) in an aqueous medium and on the GNP toxicity to algae were studied. The unicellular green alga Scenedesmus obliquus was exposed to GNP suspensions in the presence of benzoic acid or gallic acid at various concentrations. The GNPs had smaller hydrodynamic sizes and the GNP suspensions were more stable and had higher or lower surface zeta potentials in the presence of LOAs than when LOAs were not present. The toxic effects in S. obliquus cultures incubated with GNP suspensions containing LOAs were related to the LOA concentration, and the presence of LOAs caused three effects: stimulation, alleviation, and synergistic inhibition. The intensities of the effects mainly correlated with the LOA concentration, the extent of agglomeration, and particle-induced oxidative stress. The results indicate that the environmental fates and toxicities of GNPs are strongly affected by the binding of GNPs to LOAs.

Assessment and prediction of joint algal toxicity of binary mixtures of graphene and ionic liquids

Graphene and ionic liquids (ILs) released into the environment will interact with each other. So far however, the risks associated with the concurrent exposure of biota to graphene and ILs in the environment have received little attention. The research reported here focused on observing and predicting the joint toxicity effects in the green alga Scenedesmus obliquus exposed to binary mixtures of intrinsic graphene (iG)/graphene oxide (GO) and five ILs of varying anionic and cationic types. The isolated ILs in the binary mixtures were the main contributors to toxicity. The binary GO-IL mixtures resulted in more severe joint toxicity than the binary iG-IL mixtures, irrespective of mixture ratios. The mechanism of the joint toxicity may be associated with the adsorption capability of the graphenes for the ILs, the dispersion stability of the graphenes in aquatic media, and modulation of the binary mixtures-induced oxidative stress. A toxic unit assessment showed that the graphene and IL toxicities were additive at low concentration of the mixtures but antagonistic at high concentration of the mixtures. Predictions made using the concentration addition and independent action models were close to the observed joint toxicities regardless of mixture types and mixture ratios. These findings provide new insights that are of use in the risk assessment of mixtures of engineered nanoparticles and other environmentally relevant contaminants.

Combined ecotoxicity of binary zinc oxide and copper oxide nanoparticles to Scenedesmus obliquus

ABSTRACT A combined ecotoxicity study was carried out with nano-zinc oxide (nZnO) and nano-copper oxide (nCuO) to freshwater algae Scenedesmus obliquus. Concentration–response analysis indicated that the dissolved metal fraction was not the major source of individual and combined toxicity of the metal-oxide nanoparticles (MONPs). Moreover, the contribution of the nCuO (based on metallic mass) to the combined toxicity was greater than that of the nZnO. The observed combined toxicity can be predicted by the pharmacological concepts of concentration addition (CA) and independent action (IA). Combined toxicity prediction (in terms of median effect concentration) based on both concepts tends to overestimate the overall observed toxicity of the MONP mixtures. CA was more accurate for predicting the combined toxicity than IA. It may be concluded that CA gives a valid estimation of the overall ecotoxicity for mixtures comprising of similar acting MONPs.

Physicochemical properties and ecotoxicological effects of yttrium oxide nanoparticles in aquatic media: Role of low molecular weight natural organic acids.

Understanding how engineered nanoparticles (ENPs) interact with natural organic acids is important to ecological risk assessment of ENPs, but this interaction remains poorly studied. Here, we investigate the dispersion stability, ion release, and toxicity of yttrium oxide nanoparticles (nY2O3) suspensions after exposure to two low molecular weight natural organic acids (LOAs), namely benzoic acid and gallic acid. We find that in the presence of LOAs the nY2O3 suspensions become more stable with surface zeta potential more positive or negative, accompanied by small agglomerated size. LOA interaction with nY2O3 is shown to promote the release of dissolved yttrium from the nanoparticles, depending on the concentrations of LOAs. Toxic effects of the nY2O3 suspensions incubated with LOAs on Scenedesmus obliquus as a function of their mixture levels show three types of signs: stimulation, inhibition, and alleviation. The mechanism of the effects of LOAs on the nY2O3 toxicity may be mainly associated with the degree of agglomeration, particle-induced oxidative stress, and dissolved yttrium. Our results stressed the importance of LOA impacts on the fate and toxicity of ENPs in the aquatic environment.

Simulating Molecular Interactions of Carbon Nanoparticles with a Double-Stranded DNA Fragment

Molecular interactions between carbon nanoparticles (CNPs) and a double-stranded deoxyribonucleic acid (dsDNA) fragment were investigated using molecular dynamics (MD) simulations. Six types of CNPs including fullerenes (C60 and C70), () single-walled carbon nanotube (SWNT), () double-walled carbon nanotube (DWNT), graphene quantum dot (GQD), and graphene oxide quantum dot (GOQD) were studied. Analysis of the best geometry indicates that the dsDNA fragment can bind to CNPs through pi-stacking and T-shape. Moreover, C60, DWNT, and GOQD bind to the dsDNA molecules at the minor groove of the nucleotide, and C70, SWNT, and GQD bind to the dsDNA molecules at the hydrophobic ends. Estimated interaction energy implies that van der Waals force may mainly contribute to the mechanisms for the dsDNA-C60, dsDNA-C70, and dsDNA-SWNT interactions and electrostatic force may contribute considerably to the dsDNA-DWNT, dsDNA-GQD, and dsDNA-GOQD interactions. On the basis of the results from large-scale MD simulations, it was found that the presence of the dsDNA enhances the dispersion of C60, C70, and SWNT in water and has a slight impact on DWNT, GQD, and GOQD.

TiO2, SiO2 and ZrO2 Nanoparticles Synergistically Provoke Cellular Oxidative Damage in Freshwater Microalgae

Metal-based nanoparticles (NPs) are the most widely used engineered nanomaterials. The individual toxicities of metal-based NPs have been plentifully studied. However, the mixture toxicity of multiple NP systems (n ≥ 3) remains much less understood. Herein, the toxicity of titanium dioxide (TiO2) nanoparticles (NPs), silicon dioxide (SiO2) NPs and zirconium dioxide (ZrO2) NPs to unicellular freshwater algae Scenedesmus obliquus was investigated individually and in binary and ternary combination. Results show that the ternary combination systems of TiO2, SiO2 and ZrO2 NPs at a mixture concentration of 1 mg/L significantly enhanced mitochondrial membrane potential and intracellular reactive oxygen species level in the algae. Moreover, the ternary NP systems remarkably increased the activity of the antioxidant defense enzymes superoxide dismutase and catalase, together with an increase in lipid peroxidation products and small molecule metabolites. Furthermore, the observation of superficial structures of S. obliquus revealed obvious oxidative damage induced by the ternary mixtures. Taken together, the ternary NP systems exerted more severe oxidative stress in the algae than the individual and the binary NP systems. Thus, our findings highlight the importance of the assessment of the synergistic toxicity of multi-nanomaterial systems.

Impacts of dissolved organic matter on aqueous behavior of nano/micron-titanium nitride and their induced enzymatic/non-enzymatic antioxidant activities in Scenedesmus obliquus

ABSTRACT Freshwater dispersion stability and ecotoxicological effects of titanium nitride (TiN) with particle size of 20 nm, 50 nm, and 2–10 μm in the presence of dissolved organic matter (DOM) at various concentrations were studied. The TiN particles that had a more negative zeta potential and smaller hydrodynamic size showed more stable dispersion in an aqueous medium when DOM was present than when DOM was absent. Biochemical assays indicated that relative to the control, the TiN particles in the presence of DOM alleviated to some extent the antioxidative stress enzyme activity in Scenedesmus obliquus. In addition, it was found that the TiN with a primary size of 50 nm at a high concentration presented a significant impact on non-enzymatic antioxidant defense in algal cells.

Co-exposure of Freshwater Microalgae to Tetrabromobisphenol A and Sulfadiazine: Oxidative Stress Biomarker Responses and Joint Toxicity Prediction

Combined toxicity and oxidative stress biomarker responses were determined for tetrabromobisphenol A (TBBPA) and sulfadiazine (SDZ) to the unicellular green alga Scenedesmus obliquus. Concentration–response analyses were performed for single toxicants and for mixtures containing TBBPA and SDZ with two different mixture ratios. The effect concentrations and the observed effects of the mixtures were compared to the predictions of the joint toxicity by the concentration addition (CA) model and independent action (IA) model. Results showed that the observed joint toxicity was within the scope of the highest (TBBPA) and lowest (SDZ) toxicity observed for the individual components. Furthermore, co-exposure of S. obliquus to TBBPA and SDZ provided preliminary evidence that the mixtures induced oxidative stress leading to cell damage. The CA and IA models proved to be valid for the prediction of the joint toxicity of TBBPA and SDZ. This study highlights a combined environmental risk assessment for two emerging pollutants.

Dissolved organic matter and aluminum oxide nanoparticles synergistically cause cellular responses in freshwater microalgae

ABSTRACT This study investigated the impact of dissolved organic matters (DOM) on the ecological toxicity of aluminum oxide nanoparticles (Al2O3NPs) at a relatively low exposure concentration (1 mg L−1). The unicellular green alga Scenedesmus obliquus was exposed to Al2O3NP suspensions in the presence of DOM (fulvic acid) at various concentrations (1, 10, and 40 mg L−1). The results show that the presence of DOM elevated the growth inhibition toxicity of Al2O3NPs towards S. obliquus in a dose-dependent manner. Moreover, the combination of DOM at 40 mg L−1 and Al2O3NPs resulted in a synergistic effect. The relative contribution of Al-ions released from Al2O3NPs to toxicity was lower than 5%, indicating that the presence of the particles instead of the dissolved ions in the suspensions was the major toxicity sources, regardless of the presence of DOM. Furthermore, DOM at 10 and 40 mg L−1 and Al2O3NPs synergistically induced the upregulation of intercellular reactive oxygen species levels and superoxide dismutase activities. Analysis of the plasma malondialdehyde concentrations and the observation of superficial structures of S. obliquus indicated that the mixtures of DOM and Al2O3NPs showed no significant effect on membrane lipid peroxidation damage. In addition, the presence of both DOM and Al2O3NPs contributed to an enhancement in both the mitochondrial membrane potential and the cell membrane permeability (CMP) in S. obliquus. In particular, Al2O3NPs in the presence of 10 and 40 mg L−1 DOM caused a greater increase in CMP compared to Al2O3NPs and DOM alone treatments. In conclusion, these findings suggest that DOM at high concentrations and Al2O3NPs synergistically interrupted cell membrane functions and triggered subsequent growth inhibition toxicity.

Algal toxicity of binary mixtures of zinc oxide nanoparticles and tetrabromobisphenol A: Roles of dissolved organic matters

The present study investigated the impacts of dissolved organic matters (DOM) on joint toxicity involved in zinc oxide nanoparticles (ZnO NPs) and tetrabromobisphenol A (TBBPA) at relevant low-exposure concentrations (<1 mg/L). It was found that ZnO NPs in single and combined systems exhibited severe inhibition effects on a freshwater microalgae Scenedesmus obliquus. However, the presence of DOM slightly alleviated the growth inhibition toxicity induced by the binary mixtures of ZnO NPs and TBBPA. Ultrastructure analysis revealed that ZnO NPs caused structural damage to cells, including plasmolysis, membrane destruction, and the disruption of thylakoid in the chloroplast, regardless of the presence of coexisting substances. Oxidative stress biomarker quantitative analysis and in situ observations indicated that the massive accumulation of reactive oxygen species in the binary mixtures of ZnO NPs and TBBPA caused severe oxidative damage, but the presence of DOM significantly mitigated the damage.