F. Prado

Oxygen Reduction Reaction on Ruddlesden–Popper Phases Studied by Impedance Spectroscopy

The oxygen reduction mechanism of Ruddlesden-Popper phases Sr 3 FeMO 6+δ (M = Fe, Co, Ni) has been investigated by impedance spectroscopy at 500, 600, and 700°C under oxygen partial pressure pO 2 between 10 -5 and 1 atm using both He and Ar as gas carriers. Thick porous electrodes were sprayed on dense Ce 0.9 Gd 0.1 O 2-x and impedance spectra data were collected on symmetrical cells. An equivalent circuit was proposed considering the electrolyte resistances R el , a Warburg element W HF , and two parallel elements RCpe (RCpe IF and RCpe LF ). For the three compounds, W HF has been assigned to the oxygen vacancies diffusion in the bulk, the intermediate component, RCpe IF , to oxygen dissociative adsorption in the electrode surface, and the low frequency element, RCpe LF , to oxygen diffusion in the gas phases. In the case of the Sr 3 Fe 2 O 6+δ and Sr 3 FeCoO 6+δ compounds, the p0 2 dependence of Warburg high frequency component suggests a complex process involving both oxygen bulk diffusion and charge transfer. The results of Sr 3 FeMO 6+δ (M = Fe, Co, Ni) compared with those of La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3-δ perovskite electrodes, allowing us to discuss the effect of the crystal structure on the electrochemical behavior of these layered compounds.

Detoxification of Cr(VI) in Salvinia minima is related to seasonal-induced changes of thiols, phenolics and antioxidative enzymes

In this study, protein- and non-protein-thiol-containing compounds (THCC), soluble phenolics (SP), proline (Pro), proteins and malondialdehyde (MDA) contents, and antioxidative enzyme activities were analyzed in floating and submerged leaves of Salvinia minima to establish their role against Cr-induced oxidative stress. We analyzed relationships among biochemical responses to different Cr(VI) concentrations to explore underlying mechanisms of Cr detoxification in plants growing under field conditions during summer and winter seasons. Significant increases in THCC were observed in submerged leaves from both seasons, while in floating leaves THCC increased only in summer being decreased in winter. Contrarily SP increased in floating leaves and decreased in submerged ones. MDA increased significantly in winter-leaves, but in summer-leaves remained unchanged. Antioxidative enzymes, i.e. guaiacol peroxidase (G-POD), superoxide dismutase (SOD) and catalase (CAT) showed different activity patterns. G-POD significantly increased in Cr-treated leaves from both seasons, while SOD increased in submerged leaves only, remaining practically unchanged in floating ones. CAT activity increased in floating leaves from both seasons, whereas in submerged ones was decreased or increased. Proteins increased in both leaf types during summer whereas decreased or remained unchanged in winter. Pro increased in winter-submerged leaves only. Results show that seasonal-induced changes occur in all measured parameters.

Phytoremediation: Strategies of Argentinean Plants Against Stress by Heavy Metals

Environmental pollution by organic and inorganic contaminants is an increasing global problem, but mostly affects both poor and developing countries. The effects of environmental pollution on biota and human health are reaching intolerable limits, so urgent actions are required to address their remediation before it is too late to generate a less polluted world and better life quality to next generations. In Argentina the environmental pollution has already been installed in regions once considered non-contaminated sites such as the Andean mountain range and fertile plains (Pampas). For a long time several Argentinean laboratories are working on phytoremediation technologies to clean polluted soils and water bodies. However, most of these studies are carried out at small-scale under laboratory conditions and/or in small-sized confined environments. In fact to date no more than one full-scale experiment has been carried out to decontaminate sewage and industrial effluents from a metallurgical factory. Strikingly, most studies have focused on a few toxic heavy metals, i.e., chromium (Cr), cadmium (Cd), lead (Pb), zinc (Zn), copper (Cu), manganese (Mn), and nickel (Ni), but ongoing investigations have not considered the most widespread of all: arsenic (As). It affects more than half of the Argentine territory, including large areas of the Chaco-Pampean plains and also numerous rivers that provide water for both human and animal consumption, as well as for crop irrigation. Studies on phytoremediation of organic pollutants are less developed.

Effect of seasonality and Cr(VI) on starch-sucrose partitioning and related enzymes in floating leaves of Salvinia minima

Effects of seasonality and increasing Cr(VI) concentrations on leaf starch-sucrose partitioning, sucrose- and starch-related enzyme activities, and carbon allocation toward leaf development were analyzed in fronds (floating leaves) of the floating fern Salvinia minima. Carbohydrates and enzyme activities of Cr-exposed fronds showed different patterns in winter and summer. Total soluble sugars, starch, glucose and fructose increased in winter fronds, while sucrose was higher in summer ones. Starch and soluble carbohydrates, except glucose, increased under increasing Cr(VI) concentrations in winter fronds, while in summer ones only sucrose increased under Cr(VI) treatment. In summer fronds starch, total soluble sugars, fructose and glucose practically stayed without changes in all assayed Cr(VI) concentrations. Enzyme activities related to starch and sucrose metabolisms (e.g. ADPGase, SPS, SS and AI) were higher in winter fronds than in summer ones. Total amylase and cFBPase activities were higher in summer fronds. Cr(VI) treatment increased enzyme activities, except ADPGase, in both winter and summer fronds but no clear pattern changes were observed. Data of this study show clearly that carbohydrate metabolism is differently perturbed by both seasonality and Cr(VI) treatment in summer and winter fronds, which affects leaf starch-sucrose partitioning and specific leaf area (SLA) in terms of carbon investment.