Valentina Pinto

One century sedimentary record of Hg and Pb pollution in the Sagua estuary (Cuba) derived from 210Pb and 137Cs chronology

The vertical distribution of Hg and Pb were determined in a sediment core collected from the Sagua estuary (North Cuba) that receives input from the Sagua river, one of the most polluted rivers discharging into the Cuban coastal environment. Depth profiles of metal concentrations were converted to time-based profiles using the (210)Pb dating method and confirmed with the (137)Cs fallout peak. The mean mass accumulation rate was estimated to be 0.17+/-0.04 g cm(-2)y(-1) (mean sediment accumulation rate 0.52+/-0.13 cm y(-1)) and the core bottom was estimated to date back about 130 years. The historical sedimentary record showed a strong enrichment of mercury concentrations in the past decades, caused by the incomplete treatment of industrial wastes from a chlor-alkali plant with mercury-cell technology in the Sagua river basin. Lead fluxes to sediments showed a gradual increase from the 1920s to present, which agrees with a population increase in Sagua la Grande City. Fluxes of both metals have increased the past 25 years, with values reaching a maximum of 0.5 and 3.9 microg cm(-2)y(-1) for Hg and Pb, respectively.

Assessment of the applicability of a “toolbox” designed for microbially assisted phytoremediation: the case study at Ingurtosu mining site (Italy)

The paper describes the fieldwork at the Italian test site of the abandoned mine of sphalerite and galena in Ingurtosu (Sardinia), with the aim to assess the applicability of a “toolbox” to establish the optimized techniques for remediation of soils contaminated by mining activities. A preliminary characterization—including (hydro)geochemistry, heavy metal concentration and their mobility in soil, bioprospecting for microbiology and botany—provided a data set for the development of a toolbox to deliver a microbially assisted phytoremediation process. Euphorbia pithyusa was selected as an endemic pioneer plant to be associated with a bacterial consortium, established with ten selected native strains, including metal-tolerant bacteria and producers of plant growth factors. The toolbox was firstly assessed in a greenhouse pot experiment. A positive effect of bacterial inoculum on E. pithyusa germination and total plant survival was observed. E. pithyusa showed to be a well-performing metallophyte species, and only inoculated soil retained a microbial activity with a high functional diversity, expanding metabolic affinity also towards root exudates. These results supported the decision to proceed with a field trial, investigating different treatments used singly or in combination: bioaugmentation with bacterial consortia, mycorrhizal fungi and a commercial mineral amendment. Microbial activity in soil, plant physiological parameters and heavy metal content in plants and in soil were monitored. Five months after the beginning, an early assessment of the toolbox under field conditions was carried out. Despite the cold season (October–March), results suggested the following: (1) the field setup as well as the experimental design proved to be effective; (2) plant survival was satisfactory; (3) soil quality was increased and bioaugmentation improved microbial activity, expanding the metabolic competences towards plant interaction (root exudates); and (4) multivariate analysis supported the data provided that the proposed toolbox can be established and the field trial can be carried forward.

Mercury contamination of riverine sediments in the vicinity of a mercury cell chlor-alkali plant in Sagua River, Cuba

Sediment is a great indicator for assessing coastal mercury contamination. The objective of this study was to assess the magnitude of mercury pollution in the sediments of the Sagua River, Cuba, where a mercury-cell chlor-alkali plant has operated since the beginning of the 1980s. Surface sediments and a sediment core were collected in the Sagua River and analyzed for mercury using an Advanced Mercury Analyser (LECO AMA-254). Total mercury concentrations ranged from 0.165 to 97 μg g(-1) dry weight surface sediments. Enrichment Factor (EF), Index of Geoaccumulation (Igeo) and Sediment Quality Guidelines were applied to calculate the degrees of sediment contamination. The EF showed the significant role of anthropogenic mercury inputs in sediments of the Sagua River. The result also determined that in all stations downstream from the chlor-alkali plant effluents, the mercury concentrations in the sediments were higher than the Probable Effect Levels value, indicating a high potential for adverse biological effects. The Igeo index indicated that the sediments in the Sagua River are evaluated as heavily polluted to extremely contaminated and should be remediated as a hazardous material. This study could provide the latest benchmark of mercury pollution and prove beneficial to future pollution studies in relation to monitoring works in sediments from tropical rivers and estuaries.

Analysis of the Growth Process and Pinning Mechanism of Low-Fluorine MOD YBa 2 Cu 3 O 7-δ Films With and Without BaZrO 3 Artificial Pinning Centers

A YBa2Cu3O7-δ (YBCO) film grown by metal organic decomposition (MOD) is a promising candidate in the realization of high-performance superconducting wires with high critical current density. Moreover, artificial pinning centers (APCs) inclusions improve the current transport performance of the films in both high magnetic fields and temperatures. YBCO films with and without artificial pinning centers were successfully obtained on single-crystal SrTiO3 (STO) by an environmental friendly low-fluorine coating solution approach. Percentages of 5% and 10% of BaZrO3 (BZO) are used as APCs. X-ray diffraction analyses have been performed to characterize the structural properties of the as-obtained structure. Current-voltage (I-V) characteristics have been collected at different magnetic fields to investigate the superconducting properties.

Analysis of Transport Properties of MOD YBCO Films With BaZrO3 as Artificial Vortex Pinning Centers

The transport properties of nanocomposite YBa2Cu3O7-x (YBCO) films grown by metal-organic decomposition (MOD) and prepared with a low-fluorine-coating solution on SrTiO3 single-crystal substrates were studied with dc and microwave measurement techniques. As demonstrated in previous studies, the combination of these two techniques is a powerful tool for vortex pinning investigation. The BaZrO3 inclusions (BZO) as artificial pinning centers were introduced into the YBCO matrix by the excess of corresponding Ba and Zr precursor salts to the initial YBCO precursor solution up to 5 mol%. The effect of BZO was clearly observed in magnetic field dependence relations of critical current density (Jc) and the complex surface impedance, i.e., ΔZ, at fixed temperature and magnetic field parallel to the c-axis. The result shows that BZO particles mainly act as isotropic pinning centers. The short-range vortex dynamics was probed by the ~47.7-GHz microwave surface impedance technique. The derived vortex parameters r and kp were sensitive to the presence of nanoparticles, indicating the effect of BZO on pinning. The joint field dependence relations of Jc and kp help in elucidating the pinning regime in our nanocomposite MOD YBCO/BZO films.

Aging of Precursor Solutions Used for YBCO Films Chemical Solution Deposition: Study of Mechanisms and Effects on Film Properties

The proposed study investigates the aging of two precursor solutions used for the chemical solution deposition of YBa2Cu3O7-x (YBCO) and composite YBCO films with nanostructured inclusions of BaZrO3 (YBCO-BZO). The stability of precursor solutions plays a crucial role in determining the crystalline quality and the superconducting properties of YBCO films. Although low-or free-fluorine solutions are promising in order to improve the synthesis route and to reduce the environmental impact, the poor stability of the solution is the major drawback of the low-fluorine precursors since they degrade faster (4-6 weeks) than other precursor solutions for superconducting layers (e.g., trifluoroacetates solutions are stable up to 6 months) or buffer layers (stable for several months). Therefore, a deeper comprehension of the degradation mechanisms is fundamental to properly optimize the composition of the precursor solution. The current work studies two precursor solutions (for YBCO and YBCO-BZO) that are complex systems, in which different interactions need to be considered: most of all, the nature of ligands (acetate, propionate, ammonia) that complex each metal and influence not only the solution stability but also the quality of the deposited film. Thus, information obtained from different analyses is correlated with morphological, structural, and superconducting properties of the deposited film in order to understand the underlying chemical mechanisms of aging (salts precipitation, oxidation, polymerization) and its effects.

Enhanced 77 K vortex-pinning in Y Ba2Cu3O7−x films with Ba2Y TaO6 and mixed Ba2Y TaO6 + Ba2Y NbO6 nano-columnar inclusions with irreversibility field to 11 T

Pulsed laser deposited thin Y Ba2Cu3O7−x (YBCO) films with pinning additions of 5 at. % Ba2Y TaO6 (BYTO) were compared to films with 2.5 at. % Ba2Y TaO6 + 2.5 at. % Ba2Y NbO6 (BYNTO) additions. Excellent magnetic flux-pinning at 77 K was obtained with remarkably high irreversibility fields greater than 10 T (YBCO-BYTO) and 11 T (YBCO-BYNTO), representing the highest ever achieved values in YBCO films.

Development of Biaxially Textured LZO Film on Cold-Rolled Metal Substrate

La2Zr2O7 (LZO) film grown by the chemical solution deposition (CSD) technique is a widely studied buffer layer for YBa2Cu3O7-x film growth on a rolling-assisted biaxially textured (RABiT) substrate. A biaxially textured LZO film is epitaxially grown on a cube-textured metal substrate. In a RABiT substrate, cube texture is obtained as primary recrystallization of heavily cold-rolled fcc metals and is normally developed before CSD film deposition to obtain an oriented film growth. In this paper, we show that a biaxially textured LZO film can be grown by depositing the precursor solution directly on a cold-rolled fcc metal substrate and performing a single heat treatment. In fact, we show that if the recrystallization temperature of the metallic substrate is lower than the nucleation temperature of the film, a biaxially textured film is obtained as a result of transient cube texture transfer. Biaxially textured LZO films grown on cold-rolled substrates are compared with films grown on recrystallized substrates. In particular, the growth of LZO on either pure-Cu- or Ni-based substrate was studied. Compared with the LZO film grown on a cube-textured substrate, LZO grown on a cold-rolled substrate shows similar structural properties and morphology. Moreover, films are well adherent without cracks or delamination, suggesting that grain boundary migration in the metallic substrate has no detrimental influence on the film. In some cases, secondary recrystallization of the substrate occurs, without affecting the quality of the LZO film.

Development of Low Aspect Ratio Coated Conductor

ReBa2Cu3O7-x (ReBCO, Re = Y or rare earth) coated conductors are currently available as ribbon-shaped conductors. The high aspect ratio of such conductors is often regarded as a limitation for many electrotechnical applications due to the anisotropy of the electrical and mechanical properties and high ac losses. In this view, a method for the development of cube-textured, low aspect ratio wire substrate for ReBCO coated conductor is presented. The method is derived from the conventional cold-rolling and recrystallization process and modified to obtain a cube-textured wire with low aspect ratio rectangular cross section. To show the feasibility of the method, pure copper was used as raw material. Cube-textured copper substrate with a square cross section and a thickness around 0.5 mm was realized by longitudinally cutting a heavily cold-rolled thick tape. All 4 sides of the wire show a strong cube texture development. Cube texture development is comparable with the one obtained in standard tapes, with a fraction of cube-oriented area above 95% and a full width at half maximum of (002) ω-scan ranging from 6.5° to 7.5°. The quality of the obtained surfaces was tested through the epitaxial growth of MgO/Pd bilayer. Preliminary results indicate that all 4 sides of the wire are equally available for epitaxial film growth and lead to a comparable film quality.

Microwave Measurements of Pinning Properties in Chemically Deposited YBCO/BZO Films

We present a comparative study of vortex pinning in chemically deposited YBa2Cu3O7-x/BaZrO3 nanocomposite films, with the aim of correlating the preparation method to the superconducting properties. Two sets of samples have been prepared by different low fluorine routes (one set followed the in situ approach), with different starting YBCO coating solution and with a different amount of BaZrO3. The short-range vortex pinning properties have been assessed using a contactless microwave (48 GHz) technique, which yielded the vortex pinning constant (Labusch parameter) kp and the vortex viscosity θ as a function of the applied field up to 0.8 T, and for temperatures between 60 K and Tc. The results were compared to more usual (long-range vortex motion) Jc measurements. Despite the supposed similarity in pinning as determined from Jc, we found significant differences between the pinning properties of the two sets of samples. It appears that the in situ approach results in stronger pinning at microwaves in the whole temperature range explored, and that this behavior is due to the smaller dimensions of BaZrO3 nanoparticles. This information can be very useful in the search of optimized chemical route to strong pinning superconducting nanocomposite materials.