1,720,988 research outputs found
Zinc oxide nanorods-decorated graphene nanoplatelets: A promising antimicrobial agent against the cariogenic bacterium Streptococcus mutans
No full textNanomaterials are revolutionizing the field of medicine to improve the quality of life due to the myriad of applications stemming from their unique properties,including the antimicrobial activity against pathogens. In this study,the antimicrobial and antibiofilm properties of a novel nanomaterial composed by zinc oxide nanorods-decorated graphene nanoplatelets (ZNGs) are investigated. ZNGs were produced by hydrothermal method and characterized through field-emission scanning electron microscopy (FE-SEM),energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) techniques. The antimicrobial activity of ZNGs was evaluated against Streptococcus mutans,the main bacteriological agent in the etiology of dental caries. Cell viability assay demonstrated that ZNGs exerted a strikingly high killing effect on S. mutans cells in a dose-dependent manner. Moreover,FE-SEM analysis revealed relevant mechanical damages exerted by ZNGs at the cell surface of this dental pathogen rather than reactive oxygen species (ROS) generation. In addition,inductively coupled plasma mass spectrometry (ICP-MS) measurements showed negligible zinc dissolution,demonstrating that zinc ion release in the suspension is not associated with the high cellmortality rate. Finally,our data indicated that also S. mutans biofilm formation was affected by thepresence of graphene-zinc oxide (ZnO) based material,as witnessed by the safranin staining andgrowth curve analysis. Therefore,ZNGs can be a remarkable nanobactericide against one of the maindental pathogens. The potential applications in dental care and therapy are very promising. © 2016 by the authors; licensee MDPI,Basel,Switzerland
High geochemical background of potentially harmful elements. The “geochemical risk” and “natural contamination” of soils and water: awareness and policy approach in Europe with a focus on Italy
No full textA brief review on the occurrence of high natural concentrations of potentially toxic elements (PHEs) in soils and water is presented, analysing also various approaches and strategies applied in different Countries to address the problem of “natural” contamination. Starting from the well known case of arsenic, the situation for other elements such as beryllium, uranium and nickel, among the most interesting, is analysed. The analysis is based on already evidenced geochemical anomalies and on the possible evolution both in the estimate of their toxicological effects and the redefinition (lowering) of the limits at the moment imposed by legislation or suggested by guidelines. New data obtained in the ENEA laboratory in the last years on arsenic and beryllium are presented. The growing need of “geochemical maps” at regional, national and European level and of a continuous monitoring activity is highlighted. At the same time the importance of considering concentration and speciation of elements and how an element is bound and under what circumstances it may be bioavailable and able to damage the ecosystem, is recalled. Finally it is suggested to concentrate efforts on the development of screening methodologies that could play a key role in the characterisation of contamination and on standardising fast procedures that enable a guided real-time survey. The clear definition of a “geochemical risk” requires a complex and multidisciplinary approach, so the emerging role of Medical Geology is underlined. © 2015, Accademia Nazionale dei Lincei
Understanding uranium behaviour in a natural rock–water system: leaching and adsorption tests on the Tufo Rosso a Scorie Nere ignimbrite (Viterbo area, central Italy)
No full textBased on both chemical leaching and adsorption tests and a simple modelling using PHREEQC, geochemical behaviours of uranium during the ignimbrite–water interaction were evaluated mainly as a function of temperature, pH, and solution chemistry (esp., alkalinity). The main results of this work are: (1) uranium is more easily mobilized by slightly basic solution (pH 7.5) than by acidified water (pH 4.5) when relative concentrations of the main uranyl ion–calcium–carbonate species, Ca2UO2(CO3)3, increase from 0.6 to 90%; (2) the greatest leaching of uranium occurs at 50 °C (not at higher temperature) because the first dissociation constant of H2CO3 is directly correlated with temperature up to about 50 °C, but decreases from 50 to 80 °C. This directly influences the concentration of HCO3 − which is mirrored by dissolved CO2 variations; (3) the presence of alkalinity, total C-species and calcium controls the saturation index of sorbate solution with respect to calcite, influencing also speciation, solubility, and sorption of dissolved U; and (4) higher adsorption of uranium is obtained in tests with deionized water (90.0 ± 0.7 mg/kg, at equilibrium) compared to those performed with the natural water (26.0 ± 1.5 mg/kg, at equilibrium), strengthening the role of complexes between uranyl, HCO3 −, and Ca2+ ions in solution to explain the corresponding decrease in uranium adsorption. © 2017, Springer-Verlag GmbH Germany
Toxicity of the readily leachable fraction of urban PM2.5 to human lung epithelial cells: Role of soluble metals
No full textFine airborne particulate matter (PM2.5) has been repeatedly associated with adverse health effects in humans. The PM2.5 soluble fraction, and soluble metals in particular, are thought to cause lung damage. Literature data, however, are not consistent and the role of leachable metals is still under debate. In this study, Winter and Summer urban PM2.5 aqueous extracts, obtained by using a bio-compatible solution and different contact times at 37 °C, were used to investigate cytotoxic effects of PM2.5 in cultured lung epithelial cells (A549) and the role played by the leachable metals Cu, Fe, Zn, Ni, Pb and Cd. Cell viability and migration, as well as intracellular glutathione, extracellular cysteine, cysteinylglycine and homocysteine concentrations, were evaluated in cells challenged with both PM2.5 extracts before and after ultrafiltration and artificial metal ion solutions mimicking the metal composition of the genuine extracts. The thiol oxidative potential was also evaluated by an abiotic test. Results demonstrate that PM2.5 bioactive components were released within minutes of PM2.5 interaction with the leaching solution. Among these are i) low MW (<3 kDa) solutes inducing oxidative stress and ii) high MW and/or water-insoluble compounds largely contributing to thiol oxidation and to increased homocysteine levels in the cell medium. Cu and/or Ni ions likely contributed to the effects of Summer PM2.5 extracts. Nonetheless, the strong bio-reactivity of Winter PM2.5 extracts could not be explained by the presence of the studied metals. A possible role for PM2.5 water-extractable organic components is discussed. © 2017 Elsevier Lt
Content, mineral allocation and leaching behavior of heavy metals in urban PM2.5
No full textTo clarify the relationship between airborne particulate exposure and negative impacts on human health, focusing on the heavy metal content alone might not be sufficient. To address this issue, in the present work, mineral allocation and leaching behavior of heavy metals in the PM2.5 were investigated. This work, therefore, provides a novel perspective in the field of urban airborne particle investigation that is not currently found in the literature. Four sampling campaigns were performed in the urban area of Rome (Central Italy) during the winter and summer seasons (February and July 2013 and 2014, respectively). The measured concentrations of the regulated elements of As, Cd, Ni and Pb were consistent with those reported by the local Environmental Agency (ARPA Lazio), but non-regulated heavy metals, including Fe, Cu, Cr and Zn, were also found in PM2.5 and analyzed in detail. As a novelty, heavy metals were associated with the host-identified mineral phases, primarily oxides and alloys, and to a lesser extent, other minerals, such as sulfates, carbonates and silicates. Leaching tests of the collected samples were conducted in a buffered solution mimicking the bodily physiological environment. Despite the highest concentration of heavy metals found during the winter sampling period, all of the elements showed a leaching trend leading to major mobility during the summer period. To explain this result, an interesting comparative analysis between the leaching test behavior and innovative mineral allocation was conducted. Both the heavy metal content and mineral allocation in PM2.5 might contribute to the bioavailability of toxic elements in the pulmonary environment. Hence, for regulatory purposes, the non-linear dependency of heavy metal bioavailability on the total metal content should be taken into account. © 2017 Elsevier Lt
A field screening test for the assessment of concentrations and mobility of potentially toxic elements in soils: a case study on urban soils from Rome and Novi Sad
No full textThe increasing demand for environmental pollution control results in the development and use of new procedures for the determination of dangerous chemicals. Simple screening methods, which can be used directly in the field for a preliminary assessment of soil contamination, seem to be extremely advantageous. In our laboratory, we developed and optimized a rapid test for a preliminary evaluation of both the concentration and the mobility of some potentially toxic metals in soils. This screening test consists of a single extraction of the soil sample with a buffer solution, followed by the titration of the extracted solution with dithizone to determine the contents of bi-valent heavy metals (such as Pb, Cu, Zn, and Cd). This screening method was then directly applied in the field during the sampling campaign in the framework of an Italian–Serbian collaborative project, finalized in the study of metal availability in soils. The results obtained in the field with the rapid test were compared with those obtained in the laboratory following the conventional procedure commonly used to evaluate metal bioavailability (diethylenetriaminepentaacetic extraction). Moreover, selected samples were analyzed sequentially in the laboratory using the standardized BCR three-step sequential extraction procedure. The screening test gave results conceptually in good agreement with those obtained via the BCR procedure. These preliminary data show that the proposed screening test is a reliable method for the preliminary rapid evaluation of metal total concentrations and of potential metal mobility in soils, supporting sampling activities directly in the field. © 2017, Springer International Publishing AG
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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