1,721,025 research outputs found
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
Iron within the erionite cavity and its potential role in inducing its toxicity: Evidence of Fe (III) segregation as extra-framework cation
No full textIn this work we report the results of the crystal chemical, structural and surface characterization of erionite-K fibres from Rome (Oregon, USA) after interaction with Fe (III) chloride solutions at different concentrations. In addition, Fe (III) loaded samples were investigated after incubation in ascorbic acid in order to monitor the mobility of reduced Fe (II) and to highlight its possible incorporation as EF cation through ion exchange. Comparison between released and acquired charges under the form of Fe confirms, in perfect agreement with previous studies that Fe (III) is mainly fixed at the fibre surface. Nevertheless, in very diluted Fe (III) solutions (below 50 μM FeCl3) a significant fraction of Fe (III) is segregated by an ion-exchange mechanism in the erionite cavity at the Ca3 site, albeit with a significantly lower efficiency with respect to Fe (II). It is worth mentioning that, as a result of the catalytic properties of zeolites, the location of iron in well-defined crystallographic positions is the prerequisite for behaving as a very active site in the generation of reactive oxygen species. Incubation in ascorbic acid revealed that only Fe (III) residing at the fibres surface and characterized by low nuclearity is significantly reduced, whereas this reaction does not occur (or possibly occurs very marginally) in the case of the ion-exchanged metal. Considering that the total iron in lung fluids occurs at very low concentration (ca. 0.21 μM), our results strongly suggest that the physiological environment unfortunately represents the optimum condition for iron to behave as a very active site. © 2016 Elsevier Inc
The mechanism of iron binding processes in erionite fibres
No full textFibrous erionite-Na from Rome (Oregon, USA) was K-exchanged and characterized from the structural point of view. In addition, the modifications experienced after contact with a Fe(II) source were investigated for evaluating if the large potassium ions, blocking off nearly all the erionite cavity openings, might prevent the Fe(II) binding process, which is currently assumed to be one of the reasons of the toxicity of erionite. The K-exchanged sample had a 95% reduction of the BET surface area indicating that it behaves as a mesoporous material. Exchanged K is segregated at K2 and at OW sites commonly occupied by H2O. The latter K cations provide a relevant contribution to the reduction of the surface area. Surprisingly, despite the collapse of its surface area the sample preserves the tendency to bind Fe(II). Therefore, yet in the case of a peculiar and potentially hostile structural environment the Fe(II) ion-exchange process has essentially the same kinetics observed in a typical erionite sample. This is a clear evidence of the very limited effect of the chemical composition of erionite on the Fe(II) binding process and reasonably it does not play a significant role in its toxicity. © 2017 The Author(s)
Cartografia Geochimica d'Italia. Workshop di medio termine del progetto GEOBASI
No full textpresentazione status di progetto strategic
Thermally induced behavior of the K-exchanged erionite: A further step in understanding the structural modifications of the erionite group upon heating
No full textFibrous erionite is a naturally occurring zeolite considered to be highly carcinogenic upon inhalation, even more than crocidolite. Since no iron is typically present in erionite, its toxicity has been attributed to ion-exchanged Fe participating in Fenton chemistry. Recently, a study aimed at investigating possible fiber inactivation routes surprisingly showed that, despite having completely occluded all available pores with K ions, the erionite-Na sample preserved the property to upload Fe (II) within the structure. In this work, the thermal behavior of the K-exchanged erionite-Na was investigated by TG/ DSC and in situ XRPD analyses in order to provide relevant information for modeling the thermally induced behavior of the erionite group. Rietveld refinement results evidenced a general trend of cell parameters and volume with temperature similar to that observed for erionite-K from Rome (Oregon, USA). However, the dependence of Tdehydr and Tbreak from Si/Si+Al ratio observed in zeolites (high Si content favours a lower Tdehydr and a higher Tbreak) is not observed, possibly due to the effect of the relevant amount of large K ions dispersed within the erionite cage, acting as reinforcing blocks for the framework. Heating produces a progressive emptying of the Ca sites, common effect previously observed in erionite samples showing different chemistry. In addition, K1 s.s. remains unchanged evidencing the absence of any “internal ion exchange” process, whereas s.s. at K2 increases in the range 438-573 K and then slowly decreases in the range 700-1218 K. Both Rietveld and DSC data suggest the motion of K ions from OW sites toward the walls of the erionite cavity during dehydration. © 2018 Edizioni Nuova Cultura. All Rights Reserved
Different erionite species bind iron into the structure: A potential explanation for fibrous erionite toxicity
No full textIn this investigation, the crystal chemical characterization of one sample of woolly erionite-K (Lander County, NV, USA) was examined after suspension in a FeCl2 solution, in anaerobic conditions. The aim of this study was to determine the effect of the chemical composition of erionite on its efficiency to bind iron. Inductively coupled plasma (ICP) results showed that the sample bound Fe(II) through an ion-exchange mechanism mainly involving Ca. In addition, chemical and structural data indicated that Fe(II) is fixed at the Ca3 site, six-fold coordinated to water molecules. According to Brunauer–Emmett–Teller (BET) sample surface area the amount of Fe(II) bound by the fibers was comparable with that retrieved for fibrous erionite-Na sample from Rome (OR, USA) for which the ion-exchange process mainly affected Na. This finding provides clear evidence of a strong tendency of Fe(II) to bind to the erionite structure. Furthermore, considering that the woolly erionite-K from Langer County differs markedly from erionite-Na from Rome in the extra-framework cation content, our observations indicate that the Fe binding efficiency is not significantly modulated by the chemical composition. Notably, Fe ion-exchanged and/or accumulated on the fiber surface can generate hydroxyl radicals via the Fenton reaction, thus influencing the potential carcinogenicity of the different erionite species. © 2018 by the authors. Licensee MDPI, Basel, Switzerland
Chemical characterization and surface properties of a new bioemulsifier produced by Pedobacter sp. strain MCC-Z
No full textA novel biopolymer was described in the form of an extracellular polysaccharide (EPS) by Pedobacter sp. strain MCC-Z, a member of a bacterial genus not previously described as an emulsifier producer. The new biomolecule was extracted, purified and characterized, and its surface and emulsifying properties were evaluated. The purified bioemulsifier, named Pdb-Z, showed high emulsifying activity (E24%=64%) and reduced the surface tension of water up to 41mN/m with a critical micelle concentration value of 2.6mg/mL. The chemical characterization of Pdb-Z was performed using 1H NMR, FT-IR, HPLC/MS/MS and GC/MS. Pdb-Z was found to contain 67% of carbohydrates, consisting mainly of galactose and minor quantities of talose, 30% of lipids, being pentadecanoic acid the major lipidic constituent, and 3% of proteins. The bioemulsifier was a glycolipids-protein complex with an estimated molecular mass of 106Da. Furthermore, Pdb-Z emulsified pure aliphatic and aromatic hydrocarbons as well as diesel more efficiently than commercial synthetic surfactants, used for comparison. Our results suggest Pdb-Z has interesting properties for applications in remediation of hydrocarbon-contaminated environments and bioremediation processes. © 2014 Elsevier B.V.
Surface alteration mechanism and topochemistry of iron in tremolite asbestos: A step toward understanding the potential hazard of amphibole asbestos
No full textNon-occupational, environmental and unintentional exposure to fibrous tremolite, one of the most widespread naturally occurring asbestos, represents a potentially significant geological risk in several parts of the world. The toxicity of amphibole asbestos is commonly related to iron content and oxidation state, but information available on surface iron topochemistry and amphibole alteration mechanism is still rather poor. With the aim to shed a light on this mechanism, two tremolite samples, one from Italy (Castelluccio) and one from USA (Maryland), immersed in a buffer solution (pH7.4) with H2O2 were characterized by a multi-technique approach. X-ray photoelectron spectroscopy (XPS) and high resolution-transmission electron microscopy (HR-TEM) were used to investigate the surface chemistry of the incubated samples and to detect structural modifications of the fibres, while inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the concentration of dissolved elements.An original four-step model for amphibole alteration pathway is proposed. The alteration process starts with an incongruent dissolution of the amphiboles that produces an amorphous, altered surface layer and that is followed by iron oxidation and formation of FeOOH species. Then the congruent dissolution of the altered layer starts and, subsequently, the residual Fe oxi-hydroxides aggregates and insoluble, Fe-rich, amorphous nanoparticles on top of the fibres are formed. The results are compared to those obtained on crocidolite, a highly toxic amphibole asbestos with a 10 to 20 times higher iron content than tremolite. The high chemical reactivity observed in the literature for tremolite appears to be related not only to its iron content and oxidation state, but also to the low nuclearity of iron on the altered surfaces, in contrast to pronounced Fe clusterization at crocidolite surfaces. This is a significant step toward a conceivable explanation of why asbestos tremolite is potentially as toxic as crocidolite. © 2015 Elsevier B.V
Dissolution reaction and surface iron speciation of UICC crocidolite in buffered solution at pH 7.4: A combined ICP-OES, XPS and TEM investigation
No full textThe dissolution reaction and the surface modifications of crocidolite asbestos fibres incubated for 0.5, 1, 24, 48, 168 and 1440h in a phosphate buffered solution at pH 7.4 with and without hydrogen peroxide were investigated. Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) was used to monitor the ion release into solution, X-ray Photoelectron Spectroscopy (XPS) was performed to unveil the chemistry of the leached surface, and High Resolution Transmission Electron Microscopy (HR-TEM) was carried out to monitor the structural modifications of the fibres. No significant differences were observed between dissolution experiments carried out with and without H2O2 with the exception of results after the first hour, from which it may be inferred that the dissolution proceeds faster in the presence of H2O2 but only in its very early steps. Congruent mobilization of Si and Mg from crocidolite was observed, increasing with time especially in the range between 1 and 48h, while Ca decreased after 48h and Fe was not detected at any incubation time. In the undersaturated conditions (0-48h), dissolution rate of UICC crocidolite fibres has been estimated to be d(Si)/dt=0.079μmolh-1. The fibre surface modification is continuous with time: XPS results showed a regular depletion of Si and Mg and enrichment of Fe along dissolution. The Fe2p3/2 signal on the surface was fitted with four components at 709.0, 710.5, 711.6 and 712.8eV binding energy values corresponding to: (i) Fe(II)-O and (ii) Fe(III)-O surrounded by oxygen atoms in the silicate structure, (iii) Fe(III)-OOH as a product of the dissolution process, and (iv) Fe in a phosphate precipitate (Fe-P), respectively. The evolution of Fe speciation on the crocidolite surface was followed by integrating the four photoemission peaks, and results showed that the oxidative environment promotes the formation of Fe(III)-O (up to 37% Fetot) and of Fe-P species (up to 16% Fetot), which are found on the fibre surface at the end of the dissolution experiment. HR-TEM showed that the crocidolite lattice structure, the fibrous habit and the high aspect ratio are preserved upon leaching, while Fe-bearing nanoparticles, likely amorphous and possibly displaced on top of the fibres, become clearly visible. As a conclusion, coating of the crocidolite fibres was demonstrated to occur due to precipitation of Fe-rich phases (both phosphates and oxide-hydroxides). The occurrence of such iron armouring may modulate asbestos toxicity and possibly be the initial step in the formation of asbestos ferruginous bodies. © 2013 Elsevier Ltd
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