1,721,144 research outputs found
Heavy metal in sediments and bioaccumulation in the bivalve Corbula gibba in a drilling discharge area
No full textThe longterm bioavailability of heavy metals in sediments of a Northern Adriatic Sea shelf area affected by drilling mud and Cutting discharges was discussed. Levels of Mn, Cu, Cr, Zn and Pb in different geochemical phases of the sediment and in soft tissues of the bivalve Corbula gibba were recorded and the relationships between biological and geochemical metal investigated. Total metal content, acetic acid extractable-, exchangeable-, carbonate-, easily reducible-, moderately reducible-, oxidable- and residual-fractions were determined oil sediment samples. Corbula gibba was collected from wet sediments at the same times and sites, and the soft-tissue metal contents were determined. Correlations show that the fractions with greatest bioavailability are the exchangeable and carbonate for Cr and the exchangeable, carbonate, easily and moderately reducible fractions for Zn. Data also show a possible bioavailability of Pb only from the residual fraction, consisting of very resistant matter of more recent anthropogenic origin. Near the platform, total Mn content in sediments and in C. gibba tissues show a strong correlation suggesting that this organism is sensitive to variations of the Mn-oxi-hydroxides superficial film. No relationships were found between biological and sediment-bound Cu, however the discharged muds did not cause Cu enrichment. The metal fraction determined by weak acetic acid extraction at no point seems related to metal levels in Corbula gibba
Electrochemistry and spectroelectrochemistry of polypyridine ligands: A theoretical approach
No full textThe 2,3-bis(2-pyridyl)pyrazine (2,3-dpp) and 2,5-bis(2'-pyridyl)pyrazine (2,5-dpp) have been successfully used as bridging ligands for building up ruthenium (II) and osmium (II) polypyridyl redox and luminescent active dendrimers. Such ligands have been herein investigated by ab initio and DFT theoretical calculations both in gas phase and with the solvent effect. The different molecular conformations exhibited by 2,3-dpp, which depend on whether it is free or coordinated to one or two metal centres, have been explored by performing the scan of the potential energy surface. The spectra of the neutral and the radical anion species of the relevant conformers have been calculated at DFT and semiempirical level of the theory. The results have been assessed by correlating them with electrochemical and UV-Vis-NIR spectroelectrochemical experimental ones, obtained in highly aprotic and dry conditions. (c) 2006 Elsevier B.V. All rights reserved
Arsenic fractioning in natural solid matrices sampled in a deep groundwater body
Full text linkWe investigate arsenic (As) fractioning in four natural solid matrices collected in a deep alluvial aquifer body which constitutes a typical example of an alluvial system characterized by large values of local As concentrations in groundwater. Samples are collected at diverse depths within the aquifer and the underlying aquitard. Their composition ranges from sand to silt, including vegetal matter, the latter being particularly abundant within the analyzed host porous formation. Selective sequential extractions (SSE) are performed and allow quantifying and comparing As partitioning within all tested natural solid matrices. SSE evidenced that As content in vegetal-rich sediments is one order of magnitude larger than that observed in the other matrices; solid matrices with similar composition in terms of sand texture and collected at different depths may display diverse As content and partitioning; and amorphous and crystalline phases constitute the most critical fractions governing As partitioning for all tested matrices. Amongst all the collected matrices the key dynamics of As release from the silty matrix to groundwater are then experimentally evaluated by subjecting the solid matrix to alternating aerobic/anaerobic settings under a range of redox and pH conditions consistent with field values. Arsenic mobilization from the silty matrix was triggered by abrupt changes in redox conditions and displays a clear relationship with the temporal dynamics of the oxidation/reduction potential. Our study suggests that the environmentally critical As concentrations detected in the investigated aquifer are consistent with the occurrence of hot-spots of high natural As content associated with vegetal matter and the potentially significant role of the silty matrix on As dynamics
The interaction between displacements and water level changes due to natural and anthropogenic effects in the Po Plain (Italy): The different point of view of GNSS and piezometers
No full textLike other sedimentary plains, the Po Plain in Northern Italy has largely subsided due to natural processes and human activities. Displacements of the Earth surface of hydrological origin are caused by groundwater changes, which in turn, are expected to be related to rainfall changes. In the Bologna metropolitan area (located in the Southeastern border of Po Plain), the 2010 politic decision of dismissing civil water supply from the groundwater withdrawal has provided us the opportunity to test a methodology for the retrieval of an anthropic effect in two different data sets: vertical displacements measured by continuous GNSS sites and piezometric water table fluctuations. The data sets have been analyzed by means of the Principal Component Analysis (PCA) and compared to rainfall time series from the Po Plain rain gauges. Several piezometers undergo a clear increase in the water level following the withdrawal decrease. Differently, the anthropic induced surface displacements are significantly smaller than the ones induced by rainfall. Accordingly, without a multivariate analysis such an effect on vertical displacements would have remained hidden in the raw time series. Only looking at the spatial distribution of the principal components we have highlighted that anthropic effects are local and present even in GNSS data, entailing for the 2010 case a decrease of about 4 mm/y of vertical velocity in some sites closest the withdrawal wells. Moreover, the multivariate analysis allowed us to assess that, on time scales larger than months, the rainfall-related hydrological response of vertical displacement depends on the geological setting. In the Apennines chain a water level increase causes subsidence, in agreement with the predictions of elastic models, whereas in the Po Plain it causes uplift, suggesting a dominant poro-elastic response, in agreement with the guess that the subsidence of the Po Plain is related to soil compaction. Our results suggest that in cases of the aquifers over-exploitation, a PCA analyses and the combined use of different observables such as GNSS, piezometers time series, rainfall data, geological setting allow getting a correct identification of the anthropic and natural signals
Electrochemistry and spectroelectrochemistry of polypyridine ligands: A theoretical approach
No full textElectron transfer in polyaromatic hydrocarbons and molecular carbon nanostructures
Full text linkPlanar and curved polycyclic aromatic hydrocarbons (PAHs)
represent an interesting class of compounds with physical
chemical properties particularly appealing, as good organic
semiconductors and molecular model of larger carbon nano-
structures. Investigation of the heterogeneous electron transfer
in these systems lets to probe their electronic properties and
the reactivity of the corresponding generated carbanions and
carbocations that can form new bonds, thus leading to different
carbon systems. A particular focus is on the intrinsically high
reactivity of carbocations which induces a series of reactions
building up new carbon–carbon bonds, thus allowing to
enlarge the initial molecular unit into a nanostructure. This
represents a new and convenient way to exploit the electro-
chemically triggered reactivity into the synthesis of carbon
nanostructured materials
Geostatistical multimodel approach for the assessment of the spatial distribution of natural background concentrations in large-scale groundwater bodies
Full text linkQuantification of the (spatially distributed) natural contributions to the chemical signature of groundwater resources is an emerging issue in the context of competitive groundwater uses as well as water regulation and management frameworks. Here, we illustrate a geostatistically-based approach for the characterization of spatially variable Natural Background Levels (NBLs) of target chemical species in large-scale groundwater bodies yielding evaluations of local probabilities of exceedance of a given threshold concentration. The approach is exemplified by considering three selected groundwater bodies and focusing on the evaluation of NBLs of ammonium and arsenic, as detected from extensive time series of concentrations collected at monitoring boreholes. Our study is motivated by the observation that reliance on a unique NBL value as representative of the natural geochemical signature of a reservoir can mask the occurrence of localized areas linked to diverse strengths of geogenic contributions to the groundwater status. We start from the application of the typical Pre-Selection (PS) methodology to the scale of each observation borehole to identify local estimates of NBL values. The latter are subsequently subject to geostatistical analysis to obtain estimates of their spatial distribution and the associated uncertainty. A multimodel framework is employed to interpret available data. The impact of alternative variogram models on the resulting spatial distributions of NBLs is assessed through probabilistic weights based on model identification criteria. Our findings highlight that assessing possible impacts of anthropogenic activities on groundwater environments with the aim of designing targeted solutions to restore a good groundwater quality status should consider a probabilistic description of the spatial distribution of NBLs. The latter is useful to provide enhanced information upon which one can then build decision-making protocols embedding the quantification of the associated uncertainty
Detecting natural and anthropic effects on displacements and water level changes: a combined observation from rain gauges, piezometers, and CGNSS
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