Rute F. Domingos

Bioaccumulation and Effects of CdTe/CdS Quantum Dots on Chlamydomonas reinhardtii – Nanoparticles or the Free Ions?

In order to properly assess the environmental risk of engineered nanoparticles (ENP), it is necessary to determine their fate (including dissolution, aggregation, and bioaccumulation) under representative environmental conditions. CdTe/CdS quantum dots (QD), such as those used in medical imaging, are known to release Cd(2+) due (mainly) to the dissolution of their outer shell. In this study, Chlamydomonas reinhardtii was exposed to either a soluble Cd salt or QD at similar concentrations of total Cd. Free Cd concentrations were measured using the Absence of Gradients and Nernstian Equilibrium Stripping technique. QD dissolution increased with decreasing pH and with increasing QD concentration. When exposed to QD, bioaccumulation was largely accounted for by dissolved Cd. Nonetheless, QD were shown to be taken up by the cells and to provoke unique biological effects. Whole transcriptome screening using RNA-Seq analysis showed that the free Cd and the QD had distinctly different biological effects.

Deposition of TiO2 nanoparticles onto silica measured using a quartz crystal microbalance with dissipation monitoring.

Titanium dioxide (TiO2) nanoparticles introduced into subsurface environments may lead to contamination of drinking water supplies and can act as colloidal carriers for sorbed contaminants. A model laboratory system was used to examine the influence of water chemistry on the physicochemical properties of TiO2 nanoparticles and their deposition. Deposition rates of TiO2 particles onto a silica surface were measured over a broad range of solution conditions (pH and ionic strength) using a quartz crystal microbalance with energy dissipation monitoring (QCM-D). Higher particle deposition rates were observed under favorable interaction conditions (i.e., in the presence of attractive electrostatic interactions) in comparison to unfavorable deposition conditions where electrostatic repulsion dominates particle-surface interactions. Nanoparticle sizes were characterized by fluorescence correlation spectroscopy (FCS), dynamic light scattering (DLS), and atomic force microscopy (AFM). These analyses confirmed the nanoscale of the system under study as well as the presence of TiO2 aggregates in some cases. TiO2 deposition behavior onto silica measured using QCM-D was generally found to be in qualitative agreement with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability.

Aggregation of titanium dioxide nanoparticles: role of calcium and phosphate

FCS Technique A laser light is focussed into a sample of interest using confocal optics. In this manner, an open, illuminated volume element with dimensions of ~0.5–1.0 μm 3 (confocal volume) is created. At any point in time, the confocal volume is occupied by one or only a few fluorescent molecules. In the absence of chemical reactions or other dynamic processes, temporal fluctuations in the measured fluorescence intensity in the confocal volume can be attributed solely to the translational diffusion of the fluorescent particle. Variations in the fluorescence intensity are analysed using an autocorrelation function that assumes a three-dimensional Gaussian

Transcriptome Sequencing (RNA-seq) Analysis of the Effects of Metal Nanoparticle Exposure on the Transcriptome of Chlamydomonas reinhardtii

ABSTRACT The widespread use of nanoparticles (NPs) raises concern over their potential toxicological effects in humans and ecosystems. Here we used transcriptome sequencing (RNA-seq) to evaluate the effects of exposure to four different metal-based NPs, nano-Ag (nAg), nano-TiO2 (nTiO2), nano-ZnO (nZnO), and CdTe/CdS quantum dots (QDs), in the eukaryotic green alga Chlamydomonas reinhardtii. The transcriptome was characterized before and after exposure to each NP type. Specific toxicological effects were inferred from the functions of genes whose transcripts either increased or decreased. Data analysis resulted in important differences and also similarities among the NPs. Elevated levels of transcripts of several marker genes for stress were observed, suggesting that only nZnO caused nonspecific global stress to the cells under environmentally relevant conditions. Genes with photosynthesis-related functions were decreased drastically during exposure to nTiO2 and slightly during exposures to the other NP types. This pattern suggests either toxicological effects in the chloroplast or effects that mimic a transition from low to high light. nAg exposure dramatically elevated the levels of transcripts encoding known or predicted components of the cell wall and the flagella, suggesting that it damages structures exposed to the external milieu. Exposures to nTiO2, nZnO, and QDs elevated the levels of transcripts encoding subunits of the proteasome, suggesting proteasome inhibition, a phenomenon believed to underlie the development and progression of several major diseases, including Alzheimers disease, and used in chemotherapy against multiple myeloma.

Manufactured nanoparticles in the aquatic environment-biochemical responses on freshwater organisms: A critical overview.

The enormous investments in nanotechnology have led to an exponential increase of new manufactured nano-enabled materials whose impact in the aquatic systems is still largely unknown. Ecotoxicity and nanosafety studies mostly resulted in contradictory results and generally failed to clearly identify biological patterns that could be related specifically to nanotoxicity. Generation of reactive oxygen species (ROS) is one of the most discussed nanotoxicity mechanism in literature. ROS can induce oxidative stress (OS), resulting in cyto- and genotoxicity. The ROS overproduction can trigger the induction of anti-oxidant enzymes such as catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidases (GPx), which are used as biomarkers of response. A critical overview of the biochemical responses induced by the presence of NPs on freshwater organisms is performed with a strong interest on indicators of ROS and general stress. A special focus will be given to the NPs transformations, including aggregation, and dissolution, in the exposure media and the produced biochemical endpoints.

Copper removal by algal biomass : Biosorbents characterization and equilibrium modelling

The general principles of Cu(II) binding to algal waste from agar extraction, composite material and algae Gelidium, and different modelling approaches, are discussed. FTIR analyses provided a detailed description of the possible binding groups present in the biosorbents, as carboxylic groups (D-glucuronic and pyruvic acids), hydroxyl groups (cellulose, agar and floridean starch) and sulfonate groups (sulphated galactans). Potentiometric acid-base titrations showed a heterogeneous distribution of two major binding groups, carboxyl and hydroxyl, following the quasi-Gaussian affinity constant distribution suggested by Sips, which permitted to estimate the maximum amount of acid functional groups (0.36, 0.25 and 0.1 mmol g(-1)) and proton binding parameters (pK(H)=5.0, 5.3 and 4.4; m(H)=0.43, 0.37, 0.33), respectively for algae Gelidium, algal waste and composite material. A non-ideal, semi-empirical, thermodynamically consistent (NICCA) isotherm fitted better the experimental ion binding data for different pH values and copper concentrations, considering only the acid functional groups, than the discrete model. Values of pK(M) (3.2; 3.6 and 3.3), n(M) (0.98, 0.91, 1.0) and p (0.67, 0.53 and 0.43) were obtained, respectively for algae Gelidium, algal waste and composite material. NICCA model reflects the complex macromolecular systems that take part in biosorption considering the heterogeneity of the biosorbent, the competition between protons and metals ions to the binding sites and the stoichiometry for different ions.

Agglomeration and dissolution of zinc oxide nanoparticles: role of pH, ionic strength and fulvic acid

The increasing use of engineered nanoparticles (ENPs) in industrial and household applications has led to their release into the environment and increasing concern about their effects. Proper assessment of the ecological risks of ENPswillrequiredataontheirbioavailability,persistenceandmobilityoverabroadrangeofphysicochemicalconditions, including environmentally relevant pH, ionic strength and concentrations of natural organic matter (NOM). In this study, fluorescencecorrelationspectroscopywasusedtodeterminetheagglomerationofaZnOENP(nZnO)withanominalsize of 20nm. Particle dissolution was followed using scanned stripping chronopotentiometry. The effects of Suwannee River fulvic acid (SRFA, 0-60mgL � 1 ) and the roles of pH (4-10) and ionic strength (0.005-0.1M) were carefully evaluated. Agglomeration of the bare nZnO increased for pH values near the zero point of charge, whereas the dissolution of the particles decreased. At any given pH, an increase in ionic strength generally resulted in a less stable colloidal system. The role of SRFA was highly dependent upon its concentration with increased agglomeration observed at low SRFA:nZnO massratiosanddecreasedagglomerationobservedathigherSRFA:nZnOmassratios.Theresultsindicatedthatinnatural systems, both nZnO dispersion and dissolution will be important and highly dependent upon the precise conditions of pH and ionic strength.

The effects of different coatings on zinc oxide nanoparticles and their influence on dissolution and bioaccumulation by the green alga, C. reinhardtii.

Determining the environmental risk of nanoparticles (NPs) requires an in-depth understanding of the NP core, the particle surface coatings and the interactions of the two with environmental matrices. Non-coated ZnO NPs (nZnO) are known to release ionic Zn, contributing directly to the toxicity of these particles. On the other hand, relatively less data are available for particles that have coatings designed to increase particle stability. In this study, Chlamydomonas reinhardtii was exposed to either a soluble Zn salt or nZnO with different stabilizers: (i) bare nZnO, (ii) polyacrylic acid-stabilized, nZnO-PAA, or a (iii) sodium hexametaphosphate-stabilized, nZnO-HMP. Multiple techniques were used to quantify particle agglomeration and dissolution. The dissolution of the NPs depended on the stabilizer, with the largest dissolution obtained for the bare nZnO (near total dissolution), followed by the nZnO-PAA. When exposed to the bare and PAA-stabilized nZnOs, bioaccumulation was largely accounted for by free Zn. On the other hand, the bioaccumulation of nZnO-HMP was greater than could be attributed to the release of free Zn from the particles. The increased Zn bioaccumulation was hypothesized to have resulted from the biological stimulation of C. reinhardtii due to phosphate from the particle coating.

Metals in the Aquatic Environment—Interactions and Implications for the Speciation and Bioavailability: A Critical Overview

In most case scenarios, individual metals exist as components in mixtures with organic and inorganic substances and/or particulate matter. While the concepts encompassing mixture toxicity and modeling have been around for decades, only recently have new approaches (dynamic speciation techniques and fate and bioavailability models) been expanded to consider metal mixture scenarios. For example, the kinetic features of humic substances and inorganic colloids on the complexation of metals are generally considered. Although current environmental regulations rarely require an assessment of chemicals mixtures, research on these mixtures in the environment is essential for future regulatory demands and is vital for ensuring adequate environmental protection. Interpretation of speciation and bioavailability data from metal mixtures can be very complex and demanding, due to the existence of kinetic physicochemical transformations of the dynamic components. This kinetic effect largely affects metals’ dynamic speciation, culminating in different transformed metal-containing products with different contributions for the metal uptake by a consuming interface. This manuscript is focused on the environmental fate of metal mixtures, which determines how the mixture is biogeochemically processed and which receptors are most exposed (organisms and exposure route), with a special focus on their dynamic speciation, including a critical evaluation of the current challenges and available dynamic speciation techniques as well as computer codes and models.

Trace metal dynamic speciation studied by scanned stripping chronopotentiometry (SSCP)

Environmental context. Natural aquatic systems are subject to changing conditions and practically never reach chemical equilibrium. Therefore, a quantitative understanding of the interaction of the trace metals with heterogeneous samples and their kinetic characteristics requires the dynamic characterisation of trace metal speciation. We show that scanned stripping chronopotentiometry (SSCP) is able to discriminate the dynamic nature of the complexes, although it still overestimates the average stability constants obtained from the SSCP wave characteristics using the Freundlich isotherm to account for the chemical heterogeneity. Abstract. The ability of scanned stripping chronopotentiometry (SSCP) to obtain dynamic information for metal complexation with heterogeneous colloidal ligands was evaluated by measurements of lead(II) and cadmium(II) complexation by humic and fulvic acids extracted from an ombrotrophic peat bog. Average stability constants were calculated, using a first order chemical heterogeneity approach, and compared with those obtained by an ion selective electrode (ISE). SSCP average stability constants were overestimated in comparison to those obtained by the ISE, which suggests that the first order heterogeneity approach did not fully account for the ligand heterogeneity. However, the comparison of the stability constants obtained from the two SSCP signals (the shift of the half-wave potential and the decrease of transition time) provides information about the dynamic nature of the metal complexes formed with the humic matter. These results were in reasonable agreement with the theoretical predictions of the dynamic theory for colloidal systems.