Vera I. Slaveykova

Oxidative stress induced by inorganic nanoparticles in bacteria and aquatic microalgae – state of the art and knowledge gaps

Abstract Nanotechnology has revolutionised many areas of modern life, technology and research, which is reflected in the steadily increasing global demand for and consumption of engineered nanomaterials and the inevitable increase of their release into the environment by human activity. The overall long-term impact of engineered nanomaterials on ecosystems is still unknown. Various inorganic nanoparticles have been found to exhibit bactericidal properties and cause growth inhibition in model aquatic microalgae, but the mechanisms of toxicity are not yet fully understood. The causal link between particle properties and biological effects or reactive oxygen species generation is not well established and represents the most eminent quest of nanoecotoxicological investigation. In this review, the current mechanistic understanding of the toxicity of inorganic metal and metal oxide engineered nanomaterials towards bacterial and aquatic microalgal model organisms based on the paradigm of oxidative stress is presented along with a detailed compilation of available literature on the major toxicity factors and research methods.

Mechanisms of toxic action of Ag, ZnO and CuO nanoparticles to selected ecotoxicological test organisms and mammalian cells in vitro: A comparative review

Abstract Silver, ZnO and CuO nanoparticles (NPs) are increasingly used as biocides. There is however increasing evidence of their threat to “non-target” organisms. In such a context, the understanding of the toxicity mechanisms is crucial for both the design of more efficient nano-antimicrobials, i.e. for “toxic by design” and at the same time for the design of nanomaterials that are biologically and/or environmentally benign throughout their life-cycle (safe by design). This review provides a comprehensive and critical literature overview on Ag, ZnO and CuO NPs’ toxicity mechanisms on the basis of various environmentally relevant test species and mammalian cells in vitro. In addition, factors modifying the toxic effect of nanoparticles, e.g. impact of the test media, are discussed. Literature analysis revealed three major phenomena driving the toxicity of these nanoparticles: (i) dissolution of nanoparticles, (ii) organism-dependent cellular uptake of NPs and (iii) induction of oxidative stress and consequent cellular damages. The emerging information on quantitative structure–activity relationship modeling of nanomaterials’ toxic effects and the challenges of extrapolation of laboratory results to the environment are also addressed.

Permanent modification in electrothermal atomic absorption spectrometry-Advances, anticipations and reality

Abstract Permanent modification is an important recent development in chemical modification techniques which is promising in view of increasing sample throughput with ‘fast’ programs, reducing reagent blanks, preliminary elimination of unwanted modifier components, compatibility with on-line and in situ enrichment, etc. An overview of this approach based on the authors’ recent research and scarce literature data is given, revealing both success and failure in studies with permanently modified surfaces (carbides, non-volatile noble metals, noble metals on carbide coatings, etc.), as demonstrated in examples of direct electrothermal atomic absorption spectrometric (ETAAS) applications to biological and environmental matrices and vapor generation (VG)–ETAAS coupling with in-atomizer trapping of hydrides and other analyte vapors. Permanent modifiers exhibit certain drawbacks and limitations such as: poorly reproducible treatment technologies — eventually resulting in poor tube-to-tube repeatability and double or multiple peaks; impaired efficiency compared with modifier addition to each sample aliquot; relatively short lifetimes; limitations imposed on temperature programs, the pyrolysis, atomization and cleaning temperatures being set somewhat lower to avoid excessive loss of modifier; applicability to relatively simple sample solutions rather than to high-salt matrices and acidic digests; side effects of overstabilization, etc. The most important niches of application appear to be the utilization of permanently modified surfaces in coupled VG–ETAAS techniques, analysis of organic solvents and extracts, concentrates and fractions obtained after enrichment and/or speciation separations and direct ETAAS determinations of highly volatile analytes in relatively simple sample matrices.

Some fundamental (and often overlooked) considerations underlying the free ion activity and biotic ligand models

Trace metal bioavailability is often evaluated on the basis of steady-state models such as the free ion activity model (FIAM) and the biotic ligand model (BLM). Some of the assumptions underlying these models were verified by examining Pb and Zn uptake by the green microalga Chlorella kesslerii. Transporter bound metal ([M-Rcell]) and free ion concentrations ([M(Z+)]) were related to experimentally determined uptake fluxes (Jint). Although the BLM and FIAM correctly predicted Pb uptake in the absence of competing ions, they failed to predict competitive interactions with Ca2+, likely because of modifications of the algal surface charge and the active nature of Ca2+ transport. Zinc transport is also active; in this case, both the internalization rate constant (kint) and the equilibrium constant for the binding of Zn to the transport sites (K(Zn-Rcell)) varied as a function of [Zn2+] in the bulk solution. For this reason, Zn uptake could not be modeled by the steady-state models either in the presence or absence of competitors (Cd and Ca). Furthermore, the role of Cu on Pb and Zn adsorption and uptake could not be predicted by either model because of secondary effects on the algal physiology and membrane permeability. Finally, a 17 degree C reduction in temperature resulted in a two- to fivefold decrease in membrane permeability of the metals, an observation that also is unaccounted for by either the FIAM or BLM. This paper emphasizes the limitations of the models in well-controlled laboratory systems with the goal of extrapolating the results to complex environmental systems.

The biouptake and toxicity of arsenic species on the green microalga Chlorella salina in seawater

The present study focuses on the biouptake, biotransformations, and toxicity of arsenic species on the marine green alga Chlorella salina in seawater from the Bulgarian Black Sea coast. Exposure to equal concentrations of As(III) or As(V) led to equivalent levels of toxicity and total intracellular arsenic content. Biouptake and toxicity of methylated arsenic species, monomethylarsonate (MMA) and dimethylarsinate (DMA), were approximately three orders of magnitude lower than those for inorganic arsenic species. Seawater enrichment with phosphate (up to 1.3 mg P L(-1)) resulted in a significant reduction of both intracellular As content and toxicity due to As(III) and As(V). In contrast, the toxicity and intracellular content of MMA and DMA were unaffected by the presence of phosphate. We measured the distribution and excretion of intracellular arsenic species, and demonstrated that the release of As(V) and/or As(III), together with the bio-reduction of As(V) and the subsequent methylation of As(III) may be a detoxification mechanism for these algae. The implications of the results with respect to arsenic species bioavailability and toxicity in marine water are further discussed.

Colloidal organic matter from wastewater treatment plant effluents: Characterization and role in metal distribution

Colloidal organic matter from wastewater treatment plants was characterized and examined with respect to its role in metal distribution by using tangential flow ultrafiltration, liquid chromatography coupled with organic carbon and UV detectors, and an asymmetrical flow field-flow fractionation (AFlFFF) multidetection platform. Results revealed that a humic-like fraction of low aromaticity with an average molar mass ranging from 1600 to 2600Da was the main colloidal component. High molar mass fractions (HMM), with molar mass ranges between 20 and 200kDa, were present in lower proportions. Ag, Cd, Cu, Cr, Mn and Zn were found mainly in the dissolved phase (<0.45microm) and their distribution between colloidal and truly dissolved fractions was strongly influenced by the distribution of dissolved organic carbon. AFlFFF coupled to ICP-MS showed that Ag, Cd, Cu, Cr, Mn and Zn associate to the low molar mass fraction of the colloidal pool, whereas Al, Fe and Pb were equally bound to low and high molar mass fractions.

Comparative study of ruthenium, rhodium and palladium as chemical modifiers in graphite furnace atomic absorption spectrometry

Abstract Comparative study on the efficiency of ruthenium, rhodium and palladium as chemical modifiers for thermal stabilization of 18 analyte elements with high and moderate volatility has been performed. Addition of ascorbic acid provided higher temperatures of thermal pretreatment by +50 to +250°C for the analytes: As, Ge, P, Pb, Se, Sn and Tl, as well as better performence for Ga, In and Tl. Possible mechanisms and trends in stabilization are discussed.

Potential of hyperspectral imaging microscopy for semi-quantitative analysis of nanoparticle uptake by protozoa.

Hyperspectral imaging with enhanced darkfield microscopy (HSI-M) possesses unique advantages in its simplicity and non-invasiveness. In consideration of the urgent need for profound knowledge on the behavior and effects of engineered nanoparticles (NPs), here, we determined the capability of HSI-M for examining cellular uptake of different metal-based NPs, including nanosized metals (silver and gold, both citrate stabilized), metal oxides (copper oxide and titanium dioxide), and CdSe/ZnS core/shell quantum dots at subtoxic concentrations. Specifically, we demonstrated that HSI-M can be used to detect and semi-quantify these NPs in the ciliated protozoan Tetrahymena thermophila as a model aquatic organism. Detection and semi-quantification were achieved on the basis of spectral libraries for the NPs suspended in extracellular substances secreted by this single-celled organism, accounting for matrix effects. HSI-M was able to differentiate between NP types, provided that spectral profiles were significantly different from each other. This difference, in turn, depended upon NP type, size, agglomeration status, and position relative to the focal plane. As an exception among the NPs analyzed in this study, titanium dioxide NPs showed spectral similarities compared to cell material of unexposed control cells, leading to false positives. High biological variability resulted in highly variable uptake of NPs in cells of the same sample as well as between different exposures. We therefore encourage the development of techniques able to reduce the currently long analysis times that still hamper the acquisition of statistically strong data sets. Overall, this study demonstrates the potential and challenges of HSI-M in monitoring cellular uptake of synthetic NPs.

Interactions between mercury and phytoplankton: Speciation, bioavailability, and internal handling

The present review describes and discusses key interactions between mercury (Hg) and phytoplankton to highlight the role of phytoplankton in the biogeochemical cycle of Hg and to understand direct or indirect Hg effects on phytoplankton. Phytoplankton are exposed to various Hg species in surface waters. Through Hg uptake, phytoplankton affect the concentration, speciation, and fate of Hg in aquatic systems. The mechanisms by which phytoplankton take up Hg are still not well known, but several studies have suggested that both facilitated transport and passive diffusion could be involved. Once internalized, Hg will impact several physiological processes, including photosynthesis. To counteract these negative effects, phytoplankton have developed several detoxification strategies, such as the reduction of Hg to elemental Hg or its sequestration by intracellular ligands. Based on the toxicological studies performed so far in the laboratory, Hg is unlikely to be toxic to phytoplankton when they are exposed to environmentally relevant Hg concentrations. However, this statement should be taken with caution because questions remain as to which Hg species control Hg bioavailability and about Hg uptake mechanisms. Finally, phytoplankton are primary producers, and accumulated Hg will be transferred to higher consumers. Phytoplankton are a key component in aquatic systems, and their interactions with Hg need to be further studied to fully comprehend the biogeochemical cycle of Hg and the impact of this ubiquitous metal on ecosystems.

Study of Some Tungsten Containing Chemical Modifiers in Graphite-Furnace Atomic Absorption Spectrometry

Abstract Several chemical modifiers based on tungsten have been evaluated: the individual modifiers W(VI) as WO3 in aq. 0.2 M NH3 and W(V) as W in H2O2 and the mixed modifiers W(VI)/NH3 + Pd(II), W(V)/H2O2 + Pd(II), and W(V)/H2O2 + PO4 3-. High efficiency of thermal stabilization for 18 analyte elements of high and moderate volatility has been demonstrated and possible mechanisms of stabilization are discussed.