Organochlorine pesticides sequestered in the aquatic macrophyte Schoenoplectus californicus (C.A. Meyer) Soják from a shallow lake in Argentina

This study was conducted in Los Padres Lake from Argentina in order to assess the ability of Schoenoplectus californicus to bioconcentrate organochlorine pesticides (OCPs). Bulrush tissues, superficial and near root sediments were collected from the input and the output creek areas. OCP analyses were carried out by GC-ECD. Samples from the input creek area showed the higher OCP levels as a result of contaminants washed down from upstream agricultural fields. Bulrush roots accumulated the highest concentrations of pollutants (30.2-45.7ngg(-1) dry weight). DDTs and chlordanes predominated in sediments and roots besides endosulfan sulfate. The sediments constitute the main source for these OCPs partitioning to bulrush. Stems mainly exposed to water column accumulated preferentially the less hydrophobic pesticides, such as HCHs and endosulfans. We have confirmed the important role of S. californicus in the contaminant removal from sediments. Therefore, this macrophyte can be used as a tool for field studies of OCP pollution monitoring and remediation.     

Mercury speciation in the Valdeazogues River-La Serena Reservoir system: Influence of Almadén (Spain) historic mining activities

Mercury (Hg) speciation and partitioning have been investigated in a river-reservoir system impacted by the Almadén mining activities, the world's largest Hg district. This study is the first to simultaneously investigate Hg dynamics from above the mining district and into the La Serena Reservoir (3219 Hm³), being the third largest reservoir in Europe and the largest in Spain.Water, sediment and biota were sampled at different seasons during a 2-year study from the Valdeazogues River, which flows east-west from the mining District, to La Serena Reservoir. Simultaneously, a comprehensive study was undertaken to determine the influence of some major physico-chemical parameters that potentially influence the fate of Hg within the watershed.Concentrations of dissolved Hg in water were below 0.14 µg/L, whereas particulate Hg ranged from 0.1 to 87 µg/g, with significant seasonal variation. Total Hg concentrations varied from 7 to 74 µg/g in sediment from the Valdeazogues River, while in sediments from La Serena Reservoir were below 2 µg/g. On the other hand, methyl-Hg reached concentrations up to 0.3 ng/L in water and 6 ng/g in sediment from La Serena Reservoir, whereas maximum concentrations in Valdeazogues River were 5 ng/L and 880 ng/g in water and sediment, respectively. The distribution of Hg species in the Valdeazogues River-La Serena Reservoir system indicated a source of Hg from the mine waste distributed along the river. Total Hg in water was strongly correlated with total dissolved solids and chlorophyll a concentrations, whereas organic carbon and Fe concentrations seem to play a role in methylation of inorganic Hg in sediment. Total Hg concentrations were low in fish from Valdeazogues River (0.8-8.6 ng/g, wet weight) and bivalves from La Serena Reservoir (10-110 ng/g, wet weight), but most was present as methyl-Hg.     

Self-cleaning in an estuarine area formerly affected by 226Ra anthropogenic enhancements: numerical simulations

A numerical model of the Odiel-Tinto estuary (Spain) has been developed to study the self-cleaning process that was evidenced from 226Ra measurements in water and sediments collected in the period 1999-2002, after direct releases from a fertilizer complex ceased (in 1998). The hydrodynamic model is first calibrated, and standard tidal analysis is carried out to calculate tidal constants required by the dispersion code to determine instantaneous water currents and elevations over the estuary. In this way, long-term simulations may be carried out. The dispersion code includes advective/diffusive transport of radionuclides plus exchanges with bottom sediments described through a kinetic approach. The dispersion model is first tested by comparing computed and measured 226Ra concentrations over the estuary resulting after releases in the Odiel and Tinto rivers. Next, it is applied to simulate the self-cleaning process of the estuary. The time evolution of radium concentrations in bed sediments is in generally good agreement with observations. The computed sediment halving time of the estuary is 510 days, which also is in good agreement with that estimated from measurements.     

Biodeterioration of the Lions Fountain at the Alhambra Palace, Granada (Spain)

Stone works of art exposed to the environment are liable to be deteriorated by the action of biological agents such as bacteria, fungi, mosses, etc. In ornamental fountains, the microorganisms present in water can contribute to these biodeterioration processes. This paper assesses the biodeterioration experienced by the Lions Fountain at the Alhambra Palace in Granada (Spain). Analyses have been made of the biodeterioration of Lions 4, 5 and 9, the biofouling of the fountain basin, and the water supply system. Conventional and molecular biology techniques have identified microorganisms belonging to various microbial groups (-, β- and γ-Protebacteria, Chlamydiae/Verrucomicrobia and Eukaryota). Additionally, on the mortar in the sculptures the presence of algae and bryophytes has been observed. X-ray diffraction allowed both the detection of neoformation mineral products that can be related with the presence of microorganisms and the corrosion products in the Lions Fountain. A number of recommendations are made regarding the prevention and control of biodeterioration in this important work of art.     

A Heat-Conduction Flow Microcalorimeter for Solute Transfer Enthalpy Determinations. Design And Calibration

Abstract

The construction of a heat-conduction flow microcalorimeter of the twin type, that uses thermopiles to detect thermal changes in the reference and reaction cells, is described. For comparative purposes, gold and silver cells, with different geometric shapes, are used. The calorimetric set is immersed in a water thermostat at a temperature of 25.000 ± 0.005°C. The thermostat is placed in a room whose temperature is controlled to 25.0 ± 0.2°C by an air thermostat.

The calibration constant of the apparatus is determined for several values of electric work and power. Values of 22 WV¹ and 14 WV¹ are obtained for the gold and silver cells, respectively.

The influence of the flow rate on the potential signal is studied. Chemical calibrations are performed with HCl-NaOH, THAM-HCl (trihidroxymethylaminomethane), and urea-water systems at different flow rates. The results are in good agreement with those reported in the literature.     

Combustion synthesis and electrochemical characterisation of Pt–Ru–Ni anode electrocatalyst for PEMFC

The present work studies the synthesis by the combustion method of an anode catalyst for protonic exchange membrane fuel cell (PEMFC) employing two different fuels, that is, urea and sucrose. The unsupported pure solid solution Pt_0.6Ru_0.3Ni_0.1 was selected from a calculated and empirical ternary phase diagram, which was previously studied. Theoretically, this particular composition exhibited single-phase features without the presence of secondary phases as RuO₃ and NiO, regarding the oxygen partial pressure conditions generated during the combustion synthesis. In the X-ray diffraction (XRD) analysis of the nanoparticles synthesized by using two different fuels, a single-phase Pt_0.6Ru_0.3Ni_0.1 alloy was detected. However, the X-ray photoelectron spectroscopy (XPS) studies showed that the nanoparticles prepared could present an onion-shell structure, in the case of the sample synthesized with sucrose as fuel, the external layers are partially constituted by Ni hydroxides, which can exhibit an active role in the hydrogen oxidation reaction. The electrochemical behaviour of this unsupported catalyst was performed by preparing MEAs, which were evaluated using a I–V polarisation curve test. The results obtained indicated that the nanoparticles prepared by sucrose have better performance, 260 mW/cm², than those prepared using urea, 170 mW/cm². These results are discussed in relation with the hydrogen oxidation mechanism. The results obtained reveal combustion synthesis as an appropriate method for preparing PEMFC electrocatalysts, due to its versatility, simplicity and fastness.     

Rheological Behavior and Slip Casting of Al2O3–Ni Aqueous Suspensions

A strong effort has been devoted recently toward processing of metal–ceramic composites with tailored microstructure by colloidal methods. The aim of this work is to optimize the rheological behavior of concentrated Al₂O₃–nickel (Ni) aqueous suspensions and further slip casting in order to obtain dense green composites. Compositions with Ni relative contents ranging from 5 to 75 vol% were prepared from suspensions with high solids loadings (50 vol%) by adjusting the colloidal stability of each component in terms of pH, mobility, dissolution conditions, and influence of polyelectrolytes. The rheological properties were measured under controlled rate and controlled stress conditions at different basic pH conditions and contents of polyelectrolyte. Better rheological conditions of the mixtures were found for pH 10 and 1.0 wt% polyelectrolyte. Minimum viscosity was obtained for suspensions containing 15 vol% of Ni. The analysis of flow curves demonstrates that the suspensions form a structure at very low shear, hindering sedimentation. Homogeneous slip cast bodies with green densities up to 70% of theoretical and up to 75 vol% Ni were sintered in Ar to achieve dense biphasic composites.     

Synthesis of Mullite Powders Through a Suspension Combustion Process

This work reports on the synthesis of mullite powders by a suspension combustion process. Aluminum nitrate, as a source of Al, and a colloidal silica suspension, as a source of Si, are used as reagents, and urea serves as the fuel. This colloidal suspension allows a complete mixing of the reactants, thus promoting a core-shell reaction to produce the mullite. The powders obtained need to be treated at a high temperature to form the mullite. However, when ammonium nitrate is also added as a combustion aid, the mullite phase is directly obtained without any further treatment. A chemical reaction involving all these compounds is proposed, and the thermodynamic parameters are calculated in order to predict the temperature reached during the combustion process. The addition of ammonium nitrate reduces the temperature of the reaction by ca. 150°C. Once the conditions for the combustion reaction are optimized, the Al/Si ratio is modified in an attempt to obtain monophasic mullite.     

Flow-induced degradation of hydrolyzed polyacrylamide in porous media

Summary In this work we present an experimental study of flow-induced degradation of hydrolyzed polyacrylamide in aqueous solutions flowing through porous media. The degradation is analyzed by passing the solution repeatedly through the medium at a constant flow velocity and the degraded solution is then characterized by porous media and opposed jets flows. When the polyacrylamide is dissolved in deionized water, it exhibits a gradual extension thickening in the flow through porous media and opposed jets. In this case, the polymer degrades as it passes through the porous medium even at relatively low flow rates. When the polyacrylamide is dissolved in an NaCl solution, it exhibits critical extension thickening in porous media flows, and it only degrades at Reynolds numbers that are higher than the onset of the extension thickening behavior. Chain degradation is therefore only encountered when extension thickening is produced. The results also show that the extent of degradation decreases as the pore size decreases.     

The Use of Ultrasonic Echo Pulse Velocity as an NDT Method to Predict the Concrete Strength and Uniformity

Russian Journal of Nondestructive Testing - The ultrasonic approach is one of the non-destructive testing methods that most technologically progressed in past few years. This study aims to validate...