Residual soil pollution from the Aznalcóllar mine spill is still a problem in some parts of the affected area, today converted in the Guadiamar Green Corridor. Dispersed spots of polluted soils, ...identified by the absence of vegetation, are characterized by soil acid pH and high concentrations of As, Pb, Cu and Zn. Ex situ remediation techniques were performed with unrecovered soil samples. Landfarming, Composting and Biopiles techniques were tested in order to immobilize pollutants, to improve soil properties and to promote vegetation recovery. The effectiveness of these techniques was assessed by toxicity bioassays: Lactuca sativa L. root elongation test, Vibrio fischeri bioluminescence reduction test, soil induced respiration test, and Eisenia andrei survival and metal bioaccumulation tests. Landfarming and Composting were not effective techniques, mainly due to the poor improvement of soil properties which maintained high soluble concentrations of Zn and Cu after treatments. Biopile technique, using adjacent recovered soils in the area, was the most effective action in the reduction of soil toxicity; the improvement of soil properties and the reduction in pollutants solubility were key to improve the response of the tested organisms. Therefore, the mixture of recovered soils with polluted soils in the areas affected by residual contamination is considered a more suitable technique to reduce the residual pollution and to promote the complete soil recovery in the Guadiamar Green Corridor.
•Residual soil pollution in Guadiamar Green Corridor is still a problem 18 years after contamination.•Soil toxicity bioassays were key tools for the assessment of remediation techniques applied.•Landfarming and Composting were not effective due to the high soluble concentrations of Zn and Cu after treatment.•Biopiles, using recovered soils in the area, were the most effective treatment for soil remediation.
Context. The maximum size of the Galactic stellar disk is not yet known. Some studies have suggested an abrupt drop-off of the stellar density of the disk at Galactocentric distances R ≳ 15 kpc, ...which means that in practice no disk stars or only very few of them should be found beyond this limit. However, stars in the Milky Way plane are detected at larger distances. In addition to the halo component, star counts have placed the end of the disk beyond 20 kpc, although this has not been spectroscopically confirmed so far. Aims. Here, we aim to spectroscopically confirm the presence of the disk stars up to much larger distances. Methods. With data from the LAMOST and SDSS-APOGEE spectroscopic surveys, we statistically derived the maximum distance at which the metallicity distribution of stars in the Galactic plane is distinct from that of the halo populations. Results. Our analysis reveals the presence of disk stars at R > 26 kpc (99.7% C.L.) and even at R > 31 kpc (95.4% C.L.).
Controlling graphene conductivity is crucial for its potential applications. With this focus, this paper shows the effect of the non-covalent bonding of a pyrimidine derivative (HIS) on the ...electronic properties of graphene (G). Several G-HIS hybrids are prepared through mild treatments keeping unaltered the structures of both G and HIS. The attachment of HIS to G occurs by π–π stacking of the HIS-aromatic residue with the G surface. This partially blocks the p z electrons of G, giving rise to the splitting of both the valence and conduction bands. Moreover, the width of the splitting is directly related to the HIS content. This fact allows the fine-tuning of the band gap of G-HIS hybrids. Furthermore, HIS keeps its metal-complexing ability in the G-HIS hybrids. Taking advantage of this, a G-HIS–Cu(0) composite was prepared by H2 plasma reduction of a precursor of the G-HIS–Cu(II) type. G-HIS−Cu(0) contains Cu(0) clusters stabilized on the G surface due to interactions with the COO– functions of HIS. In an analogous hybrid, G-HIS–Au(0), the Au(0) NPs are also stabilized by COO– functions. This material, consisting of the coupling of Au(0) NPs and G-HIS, photocatalyzed water reduction under visible light radiation producing 12.5 μmol·g–1·h–1of hydrogen.
Our purpose is to adapt a statistical method for the analysis of discrete numerical series to the keywords appearing in scientific articles of a given area. As an example, we apply our methodological ...approach to the study of the keywords in the Library and Information Sciences (LIS) area. Our objective is to detect the new author keywords that appear in a fixed knowledge area in the period of 1 year in order to quantify the probabilities of survival for 10 years as a function of the impact of the journals where they appeared. Many of the new keywords appearing in the LIS field are ephemeral. Actually, more than half are never used again. In general, the terms most commonly used in the LIS area come from other areas. The average survival time of these keywords is approximately 3 years, being slightly higher in the case of words that were published in journals classified in the second quartile of the area. We believe that measuring the appearance and disappearance of terms will allow understanding some relevant aspects of the evolution of a discipline, providing in this way a new bibliometric approach.
Residual pollution in the Guadiamar Green Corridor still remains after Aználcollar mine spill in 1998. The polluted areas are identified by the absence of vegetation, soil acidic pH and high ...concentrations of As, Pb, Zn and Cu. Soil toxicity was assessed by lettuce root elongation and induced soil respiration bioassays. In bare soils, total As and Pb concentrations and water-extractable levels for As, Zn and Cu exceeded the toxicity guidelines. Pollutants responsible for toxicity were different depending on the tested organism, with arsenic being most toxic for lettuce and the metal mixture to soil respiration. Soil properties, such as pH or organic carbon content, are key factors to control metal availability and toxicity in the area. According to our results, there is a risk of pollution to living organisms and the soil quality criteria established in the area should be revised to reduce the risk of toxicity.
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•15 years after the Aznalcóllar mine spill residual pollution remains in some areas.•Toxic levels were exceeded for total As and Pb and for soluble As, Zn and Cu.•Metals responsible for soil toxicity are different depending on the tested organism.•pH and organic carbon content reduce metal availability and therefore soil toxicity.•Regulatory guidelines in the area should be revised to reduce the risk of toxicity.
Residual pollution in the Guadiamar Green Corridor remains in some areas after long-term stabilization, with some risk of pollution according to toxicity bioassays.
This study evaluates the potential toxicity of the soils of the Guadiamar Green Corridor (GGC) affected by the Aznalcóllar mine spill (Andalusia, Spain), one of the most important mining accidents in ...Europe in recent decades. Twenty years after the accident, although the area is considered to be recovered, residual contamination in soils persists, and the bioavailability of some contaminants, such as As, is showing trends of increasing. Therefore, the potential residual toxicity in 84 soil samples was evaluated by bioassays with lettuce (Latuca sativa L.), earthworms (Eisenia andrei) and determining the microbial activity by basal respiration and metabolic quotient. The selected soils sampled along the GGC were divided into 4 types according to their physicochemical properties. In the closest part of the mine two soil types appear (SS1 and SS2), originally decarbonated and loamy, with a reduction in lettuce root elongation of 57% and 34% compared to the control, as well as a the highest metabolic quotient (23.9 and 18.1 ng CcO2 μg Cmicrob−1 h−1, respectively) with the highest risk of Pb and As toxicity. While, located in the middle and final part of the affected area of the spill (SS3 and SS4), soils presented alkaline pH, finer textures and the lowest metabolic quotient (<9.5 ng CcO2 μg Cmicrob−1 h−1). In addition, due to Pb and As exceeded the Guideline values established in the studied area, the human toxicity risk was determined according to US-EPA methodology. Although the total contents were higher than the Guidelines established, the obtained hazard quotients for both contaminants were less than one, so the risk for human health was discarded. However, monitoring over time of the toxicity risks of the GGC soils would be advisable, especially due to the existence of areas where residual contamination persist, and soil hazard quotient obtained for As in children was higher and close to unity.
•Two decades after the accident soils are not completed recovered.•Pb and As still exceeded the regional guideline values.•There is remobilization of As in recovered soils.•Arsenic risk to children health for the recreational use.
Highly porous homoleptic Ni(bpb) and Zn(bpb) materials have been obtained by reaction of nickel(II) and zinc(II) salts with the deprotonated form of the 1,4-(4-bispyrazolyl)benzene ligand (H2bpb). ...Ab-initio structure solution methods and thermodiffractometry have allowed the determination of their crystal structures, framework flexibility, and thermal stability. The different stereochemical requirements of the Ni(II) and Zn(II) ions induce, in Ni(bpb) and Zn(bpb), rhombic and square channels, respectively, accounting for 57 and 65% of the total cell volume. The two materials feature high adsorption capacities toward small gaseous molecules (N2 and Ar at 77 K, CO2 and CH4 at 273 K), peaking at 22 mmol g−1 of N2 in the case of the zinc(II) derivative, which is reflected by a very large surface area (above 2000 m2 g−1). The flexibility, size, and hydrophobic nature of their channels are adequate also for the incorporation of organic vapors. In this regard, the adsorption of benzene and cyclohexane has been studied under static conditions at 303 K, while that of thiophene has been investigated in dynamic conditions, by measurement, at 298 K, of the breakthrough curves of a flow of CH4/CO2 containing 30 ppm of thiophene. Ni(bpb) and Zn(bpb) are outperforming adsorbents, uptaking up to 0.34 g of thiophene per gram of material. The presence of humidity (60%), which is a major drawback for practical applications of MOFs, does not significantly affect the performance of Ni(bpb) in the removal of thiophene, at variance with Zn(bpb) and HKUST-1, Cu3(btc)2 (btc = benzene-1,3,5-tricarboxylate), which become ineffective in the presence of moisture. Additional XRPD studies have been performed on benzene-loaded Ni(bpb) samples in order to shed some light on the affinity of this material for aromatic guests.
DNA molecules containing a 1D silver array may be applied for nanotechnology applications, but first their conducting and photoluminescence behavior must be enhanced. Here we have synthesized and ...characterized three new helical compounds based on stacked silver-mediated cytosine base pairs Ag(mC)
X (mC = N1-methylcytosine; X = NO
(
), BF
(
) and ClO
(
)), that contain uninterrupted polymeric Ag
chains that run through the center of the helixes, comparable to related silver-DNA structures. The exposure of nanostructures of Ag(mC)
BF
(
) to cold hydrogen plasma stimulates the reduction of the prearranged Ag
polymeric chains to metallic silver along the material. This solvent-free reduction strategy leads to the compound Ag
(mC)
X@Ag
(
) that contains uniformly well-distributed silver metallic nanostructures that are responsible for the new conducting and photoluminescence properties of the material. The presence of silver nanostructures alongside compound
has been evaluated by means of X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, and X-ray powder diffraction (XRPD). The conducting and photoactive properties of
were studied by electrostatic force microscopy (EFM) and conducting-AFM (c-AFM), and photoluminescence microscopy (PL), respectively. The results demonstrate that the presence of well-organized metallic silver nanoentities on the material is responsible for the novel conductivity and photoactive properties of the material. This methodology can be employed for the generation of multifunctional silver-DNA related materials with tailored properties.
This paper reports a new method to obtain ultra-small Pd and Pt nanoparticles (0.5-1 nm) supported on multi-walled carbon nanotubes (MWCNTs). Even at high loadings of both metals (22.3 and 31.5% ...(wt/wt) of Pd
2+
and Pt
2+
, respectively), very narrow and unimodal particle size distributions are achieved. The complexing capabilities of polyethyleneimine covalently attached to the surface of the tubes are optimal for the retention of Pd
2+
and Pt
2+
from solution. We have addressed the reduction of the retained ions by two approaches: a classical treatment with NaBH
4
in aqueous solution, and a novel method using hydrogen cold plasma to preserve the structural features of the material. Cold plasma produced degrees of reduction similar or even larger than NaBH
4
, supporting the advantage of hydrogen cold plasma as reducing agent as it is a simple, clean and fast (15 minutes) procedure. XPS analysis of the reduced materials show an increase in the electron density near the Fermi level. Pt/MWCNT materials have been tested as anode for methanol electrooxidation, showing a catalytic profile typical of that observed for platinum nanoparticles. The stability after 1000 cycles of the plasma-reduced materials is much larger than these reported for Pt/carbon materials, indicating the stability of the ultra-small nanoparticles.
This paper reports a new method to obtain ultra-small Pd and Pt nanoparticles (0.5-1 nm) supported on multi-walled carbon nanotubes (MWCNTs).
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