1,720,958 research outputs found
Transformations of silver nanoparticles in wastewater effluents: links to Ag bioavailability
No full textAs a result of the burgeoning nanotechnology industry, the number of uses of engineered silver nanoparticles (Ag NPs) in consumer products has risen significantly in recent years. Despite their utility as anti-bacterial agents, the 'nano-scale' properties of these materials may lead to eco-toxicological problems when they end up in the environment. Wastewater effluents represent one of the main routes through which Ag NPs can reach an aquatic environment, where they may potentially interact with aquatic life. However, in wastewaters, Ag NPs may undergo different chemical and physical transformations, which may alter the potential toxicity of these NPs towards aquatic organisms. The main objectives of this study are to characterize the Ag NPs in wastewater effluents and then to assess their interactions with a model organism, the green alga Chlamydomonas reinhardtii. Experiments were conducted to distinguish the effect(s) of the wastewater matrix on the dissolution of Ag NPs and to determine whether the transformed NPs or the dissolved Ag species would be most bioavailable to C. reinhardtii. It was shown that in environmental matrices such as wastewater, the bioavailability of Ag+ could be significantly or completely reduced—a conclusion that is in contrast with experiments performed with Ag+ ions in simple biological media. The substantial reduction in the bioavailability of Ag+ in wastewaters could be explained by the presence of high concentrations of organic/inorganic ligands, which would bind to Ag+ and render it non-bioavailable. Another plausible explanation is the presence of various types of ions in wastewaters that would compete with Ag for biouptake. Nonetheless, Ag NPs did appear to be bioavailable to C. reinhardtii cells at higher concentrations, as observed from bioaccumulation experiments comparing dissolved Ag and Ag NPs. Since the biouptake of Ag NPs could not be explained by free Ag+ alone, it was speculated that complexed Ag+ and/or small NPs could have contributed to biouptake. Overall, the results suggested that the water chemistry of wastewaters had a significant effect on the biouptake of ionic or particulate Ag, by changing their physicochemical states.Durant ces dernières années, l'utilisation des nanoparticules manufacturées d'argent (Ag NPs) a augmenté considérablement suite au plein essor qu'a connu l'industrie de la nanotechnologie. Malgré leur grande utilité comme agents antibactériens, les propriétés de ces nanomatériaux peuvent conduire à de sérieux problèmes éco-toxicologique s'ils se retrouvent dans l'environnement. Les eaux usées constituent l'une des principales voies que les Ag NPs peuvent emprunter pour atteindre l'environnement aquatique et interagir avec les différents (mico)organismes qui y vivent. Cependant, dans les eaux usées les Ag NPs peuvent subir diverses transformations physicochimiques qui peuvent modifier leur toxicité potentielle vis-à-vis des organismes aquatiques. Les objectifs principaux de cette étude étaient de caractériser les Ag NPs dans des effluents d'eaux usées et ensuite évaluer leurs interactions avec une algue verte Chlamydomonas reinhardtii considérée comme un organisme modèle. Nous avons étudié l'effet de la matrice des eaux usées sur la dissolution des Ag NPs et la biodisponibilité des différentes formes (particulaire et dissoute) des Ag NPs pour C. reinhardtii. Dans les matrices environnementales telles que les eaux usées la biodisponibilité de Ag+ serait réduite de façon significative, si ce n'est complète; une conclusion qui va à l'encontre les résultats des études similaires faites dans des matrices biologiques simples. Cette réduction notable de biodisponibilité de Ag+ dans les eaux usées peut être expliquée par la présence de concentrations élevées de ligands organiques et inorganiques qui peuvent se lier fortement aux ions Ag+ et inhiber ainsi l'interaction de ces derniers avec les organismes aquatiques. Une autre explication plausible serait la présence d'autres types d'ions qui entreraient en compétition avec Ag+ pour la bioaccumulation par les (micro)organismes. Toutefois, à des concentrations élevées, les expériences de bioaccumulation comparative de Ag NPs et Ag dissous ont montré une certaine biodisponibilité des Ag NPs pour les cellules de C. reinhardtii. La bioaccumulation des Ag NPs ne pouvant être expliquée par Ag+ seul, on peut admettre que les complexes de Ag et/ou des nanoparticules de petites tailles peuvent contribuer à la bioaccumulation. En général, les résultats ont montré que la chimie des eaux usées a un effet significatif sur la bioaccumulation de l'argent ionique ou particulaire en modifiant leurs états physicochimiques
AF4/ICP-ToF-MS for the investigation of species-specific adsorption of organometallic contaminants on natural colloidal particles
No full textOrganotin (OT) compounds, while crucial in many industrial applications, pose substantial risks to the environment and human health. The toxicity and environmental behaviour of OTs depend on their chemical form, i.e., the type and number of organic substituents. Each species thus exhibits distinct toxicity profiles and varying binding affinities to environmental colloids, which influence their mobility, bioavailability, and environmental impacts. To date, however, most studies addressed speciation and colloidal characterization separately, leaving the combined determinations of organometallics along with their carrier colloids largely elusive. Here, we develop and validate an on-line measurement system to quantify the adsorption dynamics of 10 OT species on natural colloidal particles (<500 nm). The approach integrates a versatile fractionation technique (AF4), with a state-of-the-art multi-element analyzer (ICP-ToF-MS), achieving Sn detection limits as low as 6.0 ng/L. The method separates colloid-free OT species from those bound to colloids and enables the determination of OT interactions with distinct colloidal fractions. Validated in both fractionation and detection, the method provides reliable data that could elucidate the species-specific and temporal aspects of species-colloids adsorption processes. The results feature comparative studies of 10 OT species, offering critical insights into OT mobility and distribution in environmental systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Transformations of Silver Nanoparticles in Wastewater Effluents: Links in Ag Bioavailability
No full textWastewater effluents represent one of the main routes through which silver nanoparticles (Ag NPs) can reach natural aquatic environments, where they may interact with a range of organisms. However, in wastewaters, Ag NPs may undergo different chemical and physical transformations, which may alter NP toxicity towards aquatic organisms. The main objectives of this study are to characterize the dissolution and speciation of a Ag NP in a wastewater effluent and to assess its interactions with a model organism, Chlamydomonas reinhardtii (green alga), in the same medium. Experiments were conducted to distinguish the effect(s) of the wastewater matrix on the dissolution of Ag NPs and to determine whether the transformed NPs or the dissolved Ag species would be more bioavailable to C. reinhardtii. It was shown that in the wastewater effluent, Ag bioavailability was significantly reduced with respect to experiments using similar Ag concentrations in simple media. The substantial reduction in Ag bioavailability in wastewaters could be explained by the presence of high concentrations of organic/inorganic ligands, which complexed the Ag and the presence of substantial competing ions.[...
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
