Interactions between Algal Extracellular Polymeric Substances and Commercial TiO₂ Nanoparticles in Aqueous Media

The implications of engineered nanomaterials (ENMs) in the environment are often investigated using pristine particles. However, there are several biogenic and geogenic materials in natural waters that interact with and modify the surface of ENMs, thereby influencing their fate and effects. Here we studied the influence of soluble extracellular polymeric substances (sEPS) produced by freshwater and marine algae on the surface properties and fate of three commercial TiO₂ nanoparticles (<i>n</i>TiO₂) with different coatings. Adsorption of sEPS by the various <i>n</i>TiO₂ is dependent on particle surface area, intrinsic <i>n</i>TiO₂ surface charge, and hydrophobicity. Interactions between sEPS and <i>n</i>TiO₂ were driven by electrostatic interactions and chemical bonding (bridge-coordination) between the COO^– group of sEPS and <i>n</i>TiO₂. Charge reversal of positively charged <i>n</i>TiO₂ was observed at pH 7 in the presence of 0.5 mg-C/L sEPS. In addition, the critical coagulation concentration (CCC) of <i>n</i>TiO₂ increased in the presence of sEPSfrom both freshwater and marine sources. CCC of all <i>n</i>TiO2 increased as sEPS concentrations increased. This study shows that naturally occurring sEPS can modify the surface properties and fate of <i>n</i>TiO₂ in natural waters, and should be accounted for when predicting the fate and effects of engineered nanomaterials in the environment

Metabolomics Reveals Cu(OH)₂ Nanopesticide-Activated Anti-oxidative Pathways and Decreased Beneficial Antioxidants in Spinach Leaves

While the use of nanopesticides in modern agriculture continues to increase, their effects on crop plants are still poorly understood. Here, 4 week old spinach plants grown in an artificial medium were exposed via foliar spray to Cu­(OH)₂ nanopesticide (0.18 and 18 mg/plant) or Cu ions (0.15 and 15 mg/plant) for 7 days. A gas chromatography-time-of-flight-mass spectrometry metabolomics approach was applied to assess metabolic alterations induced by Cu­(OH)₂ nanopesticide in spinach leaves. Exposure to Cu­(OH)₂ nanopesticide and copper ions induced alterations in the metabolite profiles of spinach leaves. Compared to the control, exposure to 18 mg of Cu­(OH)₂ nanopesticide induced significant reduction (29–85%) in antioxidant or defense-associated metabolites including ascorbic acid, α-tocopherol, threonic acid, β-sitosterol, 4-hydroxybutyric acid, ferulic acid, and total phenolics. The metabolic pathway for ascorbate and aldarate was disturbed in all exposed spinach plants (nanopesticide and Cu²⁺). Cu²⁺ is responsible for the reduction in antioxidants and perturbation of the ascorbate and aldarate metabolism. However, nitrogen metabolism perturbation was nanopesticide-specific. Spinach biomass and photosynthetic pigments were not altered, indicating that metabolomics can be a rapid and sensitive tool for the detection og earlier nanopesticide effects. Consumption of antioxidants during the antioxidant defense process resulted in reduction of the nutritional value of exposed spinach

¹H NMR and GC-MS Based Metabolomics Reveal Defense and Detoxification Mechanism of Cucumber Plant under Nano-Cu Stress

Because copper nanoparticles are being increasingly used in agriculture as pesticides, it is important to assess their potential implications for agriculture. Concerns have been raised about the bioaccumulation of nano-Cu and their toxicity to crop plants. Here, the response of cucumber plants in hydroponic culture at early development stages to two concentrations of nano-Cu (10 and 20 mg/L) was evaluated by proton nuclear magnetic resonance spectroscopy (¹H NMR) and gas chromatography–mass spectrometry (GC-MS) based metabolomics. Changes in mineral nutrient metabolism induced by nano-Cu were determined by inductively coupled plasma-mass spectrometry (ICP-MS). Results showed that nano-Cu at both concentrations interferes with the uptake of a number of micro- and macro-nutrients, such as Na, P, S, Mo, Zn, and Fe. Metabolomics data revealed that nano-Cu at both levels triggered significant metabolic changes in cucumber leaves and root exudates. The root exudate metabolic changes revealed an active defense mechanism against nano-Cu stress: up-regulation of amino acids to sequester/exclude Cu/nano-Cu; down-regulation of citric acid to reduce the mobilization of Cu ions; ascorbic acid up-regulation to combat reactive oxygen species; and up-regulation of phenolic compounds to improve antioxidant system. Thus, we demonstrate that nontargeted ¹H NMR and GC-MS based metabolomics can successfully identify physiological responses induced by nanoparticles. Root exudates metabolomics revealed important detoxification mechanisms

Influence of Phytoplankton on Fate and Effects of Modified Zerovalent Iron Nanoparticles

Nanoscale zerovalent iron (nZVI) and its derivatives hold promise for remediation of several pollutants but their environmental implications are not completely clear. In this study, the physicochemical properties and aggregation kinetics of sulfide/silica-modified nZVI (FeSSi) were compared in algal media in which <i>Chlamydomonas reinhardtii</i> had been cultured for 1, 2, or 11 days in order to elicit the effects of organic matter produced by the freshwater algae. Furthermore, transformation of FeSSi particles were investigated in <i>C. reinhardtii</i> cultures in exponential (1-d) and slowing growth (11-d) phases while monitoring the response of algae. We found evidence for steric stabilization of FeSSi by algal organic matter, which led to a decrease in the particles’ attachment efficiency. Transformation of FeSSi was slower in 11-d cultures as determined via inductively coupled plasma and X-ray analyses. High concentrations of FeSSi caused a lag in algal growth, and reduction in steady state population size, especially in cultures in exponential phase. The different outcomes are well described by a dynamic model describing algal growth, organic carbon production, and FeSSi transformations. This study shows that feedback from algae may play important roles in the environmental implications of engineered nanomaterials

Developmental effects of two different copper oxide nanomaterials in sea urchin (<i>Lytechinus pictus</i>) embryos

<p>Copper oxide nanomaterials (nano-CuOs) are widely used and can be inadvertently introduced into estuarine and marine environments. We analyzed the effects of different nano-CuOs (a synthesized and a less-pure commercial form), as well as ionic copper (CuSO₄) on embryo development in the white sea urchin, a well-known marine model. After 96 h of development with both nano-CuO exposures, we did not detect significant oxidative damage to proteins but did detect decreases in total antioxidant capacity. We show that the physicochemical characteristics of the two nano-CuOs play an essential role in their toxicities. Both nano-CuOs were internalized by embryos and their differential dissolution was the most important toxicological parameter. The synthesized nano-CuO showed greater toxicity (EC₅₀ = 450 ppb of copper) and had increased dissolution (2.5% by weight over 96 h) as compared with the less-pure commercial nano-CuO (EC₅₀ = 5395 ppb of copper, 0.73% dissolution by weight over 96 h). Copper caused specific developmental abnormalities in sea urchin embryos including disruption of the aboral-oral axis as a result in changes to the redox environment caused by dissolution of internalized nano-CuO. Abnormal skeleton formation also occurred.</p

Detection and Quantification of Graphene-Family Nanomaterials in the Environment

An increase in production of commercial products containing graphene-family nanomaterials (GFNs) has led to concern over their release into the environment. The fate and potential ecotoxicological effects of GFNs in the environment are currently unclear, partially due to the limited analytical methods for GFN measurements. In this review, the unique properties of GFNs that are useful for their detection and quantification are discussed. The capacity of several classes of techniques to identify and/or quantify GFNs in different environmental matrices (water, soil, sediment, and organisms), after environmental transformations, and after release from a polymer matrix of a product is evaluated. Extraction and strategies to combine methods for more accurate discrimination of GFNs from environmental interferences as well as from other carbonaceous nanomaterials are recommended. Overall, a comprehensive review of the techniques available to detect and quantify GFNs are systematically presented to inform the state of the science, guide researchers in their selection of the best technique for the system under investigation, and enable further development of GFN metrology in environmental matrices. Two case studies are described to provide practical examples of choosing which techniques to utilize for detection or quantification of GFNs in specific scenarios. Because the available quantitative techniques are somewhat limited, more research is required to distinguish GFNs from other carbonaceous materials and improve the accuracy and detection limits of GFNs at more environmentally relevant concentrations

Effects of TiO₂ and Ag Nanoparticles on Polyhydroxybutyrate Biosynthesis By Activated Sludge Bacteria

Manufactured nanomaterials (MNMs) are increasingly incorporated into consumer products that are disposed into sewage. In wastewater treatment, MNMs adsorb to activated sludge biomass where they may impact biological wastewater treatment performance, including nutrient removal. Here, we studied MNM effects on bacterial polyhydroxyalkanoate (PHA), specifically polyhydroxybutyrate (PHB), biosynthesis because of its importance to enhanced biological phosphorus (P) removal (EBPR). Activated sludge was sampled from an anoxic selector of a municipal wastewater treatment plant (WWTP), and PHB-containing bacteria were concentrated by density gradient centrifugation. After starvation to decrease intracellular PHB stores, bacteria were nutritionally augmented to promote PHB biosynthesis while being exposed to either MNMs (TiO₂ or Ag) or to Ag salts (each at a concentration of 5 mg L^–1). Cellular PHB concentration and PhyloChip community composition were analyzed. The final bacterial community composition differed from activated sludge, demonstrating that laboratory enrichment was selective. Still, PHB was synthesized to near-activated sludge levels. Ag salts altered final bacterial communities, although MNMs did not. PHB biosynthesis was diminished with Ag (salt or MNMs), indicating the potential for Ag-MNMs to physiologically impact EBPR through the effects of dissolved Ag ions on PHB producers