1,720,977 research outputs found
Human health risk assessment for nanoparticle-contaminated aquifer systems
Full text linkNanosized particles (NPs), such as TiO2, Silver, graphene NPs, nanoscale zero-valent iron, carbon nanotubes, etc., are increasingly used in industrial processes, and releases at production plants and from landfills are likely scenarios for the next years. As a consequence, appropriate procedures and tools to quantify the risks for human health associated to these releases are needed. The tiered approach of the standard ASTM procedure (ASTM-E2081-00) is today the most applied for human health risk assessment at sites contaminated by chemical substances, but it cannot be directly applied to nanoparticles: NP transport along migration pathways follows mechanisms significantly different from those of chemicals; moreover, also toxicity indicators (namely, reference dose and slope factor) are NP-specific. In this work a risk assessment approach modified for NPs is proposed, with a specific application at Tier 2 to migration in groundwater. The standard ASTM equations are modified to include NP-specific transport mechanisms. NPs in natural environments are typically characterized by a heterogeneous set of NPs having different size, shape, coating, etc. (all properties having a significant impact on both mobility and toxicity). To take into account this heterogeneity, the proposed approach divides the NP population into classes, each having specific transport and toxicity properties, and simulates them as independent species. The approach is finally applied to a test case simulating the release of heterogeneous Silver NPs from a landfill. The results show that taking into account the size-dependent mobility of the particles provides a more accurate result compared to the direct application of the standard ASTM procedure. In particular, the latter tends to underestimate the overall toxic risk associated to the nP release
Estensione dell'analisi di rischio sanitario ambientale a contaminazioni di nanomateriali in sistemi acquiferi
Full text linkIl largo impiego dei nanomateriali in numerosi processi industriali ha sollevato particolare attenzione attorno alle questioni sanitarie connesse ad una loro potenziale diffusione in ambiente. Tuttavia, a causa della natura polidispersa dei nanomateriali, il rischio sanitario ambientale associato ad una contaminazione da nanoparticelle (NP) non può essere quantificato tramite la procedura ASTM comunemente applicata per le altre sostanze chimiche. NP di dimensione diverse sono infatti caratterizzate da differente tossicità e mobilità nei comparti ambientali. In questo studio viene proposto un approccio per l’adattamento della procedura ASTM al caso di acquiferi contaminati da NP. Le soluzioni analitiche usate per l’analisi di rischio di Livello 2 di sostanze disciolte sono qui adattate ed estese per tenere conto dei meccanismi di trasporto propri delle NP. Vengono infine presentati due casi applicativi della procedura proposta, uno teorico ed uno sperimentale-modellistico, facendo particolare riferimento al ruolo dell’eterogeneità granulometrica delle NP nella quantificazione del rischio sanitario ambientale
Exploring the potential of graphene oxide nanosheets for porous media decontamination from cationic dyes
Full text linkGraphene oxide (GO) nanosheets, often embedded in nano-composites, have been studied as promising materials for waste water purification, in particular to adsorb heavy metals and cationic organic contaminants. However, a broader range of potential applications of GO is still unexplored. This work investigated the potential applicability of GO for enhanced in-situ soil washing of secondary sources of groundwater contamination (i.e. the controlled recirculation of a washing GO suspension via injection/extraction wells). The laboratory study aimed at quantifying the capability of GO to effectively remove adsorbed methylene blue (MB) from contaminated sand. The tests were conducted in simplified conditions (synthetic groundwater at NaCl concentration of 20 mM, silica sand) to better highlight the key mechanisms under study. The results indicated a maximum sorption capacity of 1.6 mgMB/mgGO in moderately alkaline conditions. Even though the adsorption of MB onto GO slightly reduced the GO mobility in the porous medium, a breakthrough higher than 95% was obtained for MB/GO mass ratios up to 0.5. This suggests that a very high recovery of the injected particles should be also expected in the field
Mobility of solid and porous hollow SiO2 nanoparticles in saturated porous media: Impacts of surface and particle structure
Full text linkSilica nanoparticles (SiO2 NPs) are of increasing interest in nano-enabled agriculture, particularly as nanocarriers for the targeted delivery of agrochemicals. Their direct application in agricultural soils may lead to the release of SiO2 NPs in the environment. Although some studies have investigated transport of solid SiO2 NPs in porous media, there is a knowledge gap on how different SiO2 NP structures incorporating significant porosities can affect the mobility of such particles under different conditions. Herein, we investigated the effect of pH and ionic strength (IS) on the transport of two distinct structures of SiO2 NPs, namely solid SiO2 NPs (SSNs) and porous hollow SiO2 NPs (PHSNs), of comparable sizes (~200 nm). Decreasing pH and increasing ionic strength reduced the mobility of PHSNs in sand-packed columns more significantly than for SSNs. The deposition of PHSNs was approximately 3 times greater than that of SSNs at pH 4.5 and IS 100 mM. The results are non-intuitive given that PHSNs have a lower density and the same chemical composition of SSNs but can be explained by the greater surface roughness and ten-fold greater specific surface area of PHSNs, and their impacts on van der Waals and electrostatic interaction energies
Alginate nanohydrogels as a biocompatible platform for the controlled release of a hydrophilic herbicide
Full text linkThe large-scale application of volatile and highly water-soluble pesticides to guarantee crop production can often have negative impacts on the environment. The main loss pathways are vapor drift, direct volatilization, or leaching of the active substances. Consequently, the pesticide can either accumulate and/or undergo physicochemical transformations in the soil. In this scenario, we synthesized alginate nanoparticles using an inverse miniemulsion template in sunflower oil and successfully used them to encapsulate a hydrophilic herbicide, i.e., dicamba. The formulation and process conditions were adjusted to obtain a unimodal size distribution of nanohydrogels of about 20 nm. The loading of the nanoparticles with dicamba did not affect the nanohydrogel size nor the particle stability. The release of dicamba from the nanohydrogels was also tested: the alginate nanoparticles promoted the sustained and prolonged release of dicamba over ten days, demonstrating the potential of our preparation method to be employed for field application. The encapsulation of hydrophilic compounds inside our alginate nanoparticles could enable a more efficient use of pesticides, minimizing losses and thus environmental spreading. The use of biocompatible materials (alginate, sunflower oil) also guarantees the absence of toxic additives in the formulation
Studying the effect of sea level rise on nuisance flooding due to groundwater in a coastal urban area with aging infrastructure
No full textIn this paper, we present a study focused on the effect of sea level rise (SLR) on nuisance flooding due to groundwater (or groundwater flooding). A densely populated coastal urban area along a river estuary was selected for this work. We developed a three-dimensional (3D) shallow unconfined aquifer model of the site. We calibrated it with field measurements and used it to predict areas prone to groundwater flooding under different SLR scenarios. Results show that the water table is controlled by the river level as well as by aging infrastructure such as aging combined sewer and drinking water networks which drain and recharge the unconfined aquifer. Steady-state simulations run considering current river level scenarios show a very shallow aquifer throughout the area and simulations under different SLR scenarios predict that the water table starts to emerge from the ground in the low-lying parts of the site for 0.4 m of SLR. Overall, this work suggests that groundwater in coastal urban areas is regulated by anthropogenic and natural systems and is susceptible to climate change contributing to inundation together with marine flooding and intense precipitation
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
Zerovalent iron nanoparticles for groundwater remediation: Surface and magnetic properties, colloidal stability, and perspectives for field application
No full textIn the context of groundwater remediation, the use of zero-valent metals is known to be successful for the degradation of a wide range of contaminants. In particular, granular iron filings in permeable reactive barriers (PRBs) are a consolidated technology applied on a number of sites. Nevertheless, the realization and construction limitations restrain, in some cases, the applicability of this technology. In order to overcome some of these restrictions, the use of nanoscale zerovalent iron (nZVI) was proposed. NZVI particles, thanks to their reduced size, can be dispersed in aqueous slurries, and directly injected in the subsoil slurry, thus allowing to directly target the contaminant close to the source of contamination. However, critical points for successfully full-scale applications are stability against aggregation, mobility in subsurface environments, and longevity under subsurface conditions. Iron nanoparticles should remain in suspension for a time sufficient to allow slurry preparation, handling and injection in the subsurface. Also, they should have a sufficient mobility in the subsurface to be transported for some extent around the injection point. However, several studies have shown nZVI to be scarcely mobile and stable in both laboratory studies and field-scale tests, due to the strong tendency of nZVI particles to aggregate when dispersed in water, forming big dendritic flocs and subsequently network structures, which may widely exceed the micron. Such aggregates could also significantly limit transport by plugging the pores of the aquifer, and exhibit reduced specific surface area, and consequently reactivity. Reasons for nZVI aggregation are to be found in the balance of repulsive and attractive forces acting between particles. Iron nanoparticles, being mainly composed by Fe0 and iron oxides are subject to long-ranged attractive magnetic forces. Magnetic interactions have been stated to be the cause for the abatement of the energy barrier in the inter-particle interaction potential, promoting aggregation. Therefore, strong long-ranged repulsive forces among particles are needed to overcome this magnetic attraction. Coating of the iron nanoparticles with hydrophilic polymers and increasing the viscosity of the nZVI slurry were found successful approaches for improving both colloidal stability and mobility in lab-scale experiments.
The particles can be delivered into the subsurface using both permeation and fracturing technologies. When injected into natural aquifers, highly concentrated nZVI slurries (usually between 10 - 20 g/L) will need to move from the wells to the contaminated zone, coming in contact with the contaminants. At the same time, they should not disperse in the environment or leave the contaminated area with a residual reactivity. As a consequence, the mobility of the particles is to be predicted with a sufficient precision before designing any injection at the field scale. Although it is unfeasible to draw absolute conclusions for nZVI mobility in natural subsurface environments from results of laboratory tests, numerical transport models can be developed from column tests, and used to simulate nZVI transport in porous media at the field scale. Such models can represent a tool in the development of an efficient injection technology for field-scale applications of nZVI slurries
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
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