Composición de los agregados no dispersables de sedimentos pampeanos

Dispersion by conventional treatrnents for grain-size analysis do not work efficiently when used in Pampean sediments modified either by pedogenesis or groundwater circulation. Although aggregation decreases when free Fe oxides are removed, most of the sedirnent remains aggregated by a Si-Al rich cement which forms sand size nodules made up of smaller size particles. Total dispersion of samples is obtained with a 0,5 M NaOH dispersing agent on a hot plate. This produces the remo val of amorphous and poorly crystallized aluminosilicate cements. However, trus procedure is not generally used due lo lhe high alkali-sample ratio required. The origin of silica cement found in nodules is probably related to Si02 leaching during pedogenesis.Los sedimentos pampeanos que presentan rasgos paleopedológicos o reestructuración por acción ácuea son difíciles de dispersar con los tratamientos convencionales previos al análisis granulométrico. Con la remoción de los óxidos de hierro libre disminuye la agregación; no obstante, gran parte del material persiste aglutinado por un cemento rico en sílice y alúmina constituyendo verdaderos durinódulos; los mismos son de tamaño arena y engloban partículas de menor tamaño. Para obtener la dispersión total de las muestras es necesario aplicar un tratamiento con NaOH 0,5 M en caliente, con el cual se eliminan los cementantes amorfos o pobremente cristalinos de composición aluminosilicática; sin embargo, este método no es aplicable en forma rutinaria por la alta relación álcali! muestra requerida. La formación de estos durinódulos (agregados) se relacionaría con la lixiviación de sílice durante los procesos pedológicos sufridos por los materiales

Geochemistry of heavy metals in bottom sediments from streams of the western coast of the Rio de la Plata Estuary, Argentina

The fluvial system within the southwestern coastal sector of the Río de la Plata interacts with a very large and efficient mixing basin known as the Río de la Plata estuary. The region is a densely populated and productive sector of Argentina and is characterised by a temperate humid climate. The streams Carnaval, Martín, Del Gato and El Pescado of the study area drain two main geomorphologic units: a higher inner zone and the low lands of the coastal plain. In particular, the Del Gato stream receives heavily polluted discharges from agricultural, urban and industrial point and non-point sources of pollution, while the other streams collect a lower and variable discharge input. As a part of an initial assessment of the role of fluvial bottom sediments in the fate of metals through the stream ecosystems, the spatial distribution of trace and major elements related to particles in the accumulation areas was examined. Concentration of Cr, Ni, Cu, Zn, Cd, Hg, Pb, Fe, and Mn, grain size, mineralogy (clay-X ray diffraction) and organic matter content were analysed in the four streams considering both geomorphologic units at different depositional time. Untreated and iron-normalised trace metal concentrations in the most polluted streams show higher levels in the upper layers of most contaminated sectors and accumulation areas associated to topographic low lands. The coastal plain sector behaves as a regional sink between the upstream area and the estuary.Fil: Ronco, Alicia Estela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química; ArgentinaFil: Camilión, C.. Centro de Investigaciones de Suelos y Aguas de Uso Agropecuario; ArgentinaFil: Manassero, Marcelo Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentin

A 3.3-Ma impact in Argentina and possible consequences

Enigmatic glassy materials (escorias) and red bricklike materials (tierras cocidas) occur at a restricted stratigraphic level (the top of the Chapadmalal Formation). Materials from one locality near Mar del Plata are attributed to a mid-Pliocene impact event with a radiometric and magnetostratigraphic age of 3.3 million years ago (Ma). An extinction of endemic fauna (including the glyptodonts and flightless cariamid birds) correlates with the unit containing the impact glasses. Moreover, the age of the glasses is coincident within dating uncertainties with a pulselike change in the oxygen isotope marine record in the Atlantic and Pacific Oceans just before the late Pliocene deterioration of the climate

Ozone and UV radiation over southern South America: Climatology and anomalies

Ozone and UV radiation were analyzed at eight stations from tropical to sub-Antarctic regions in South America. Ground UV irradiances were measured by multichannel radiometers as part of the Inter American Institute for Global Change Radiation network. The irradiance channels used for this study were centered at 305 nm (for UV-B measurements) and 340 nm (for UV-A measurements). Results were presented as daily maximum irradiances, as monthly averaged, daily integrated irradiances and as the ratio of 305 nm to 340 nm. These findings are the first to be based on a long time series of semispectral data from the southern region of South America. As expected, the UV-B channel and total column ozone varied with latitude. The pattern of the UV-A channel was more complex because of local atmospheric conditions. Total column ozone levels of <220 Dobson Units were observed at all sites. Analysis of autocorrelations showed a larger persistence of total column ozone level than irradiance. A decreasing cross-correlation coefficient between 305 and 340 nm and an increasing cross-correlation coefficient between 305 nm and ozone were observed at higher latitudes, indicating that factors such as cloud cover tend to dominate at northern sites and that ozone levels tend to dominate at southern sites. These results highlight the value of long-term monitoring of radiation with multichannel radiometers to determine climatological data and evaluate the combination of factors affecting ground UV radiation.Fil: Diaz, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Camilión, C.. Centro Austral de lnvestigaciones Cientifica; ArgentinaFil: Deferrari, Guillermo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Fuenzalida, H.. Universidad de Chile; ChileFil: Armstrong, R.. Universidad de Puerto Rico; Puerto RicoFil: Booth, C.. Biospherical Instruments Inc.; Estados UnidosFil: Paladini, Alejandro Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Cabrera, S.. Universidad de Chile; ChileFil: Casiccia, C.. Universidad de Magallanes; ChileFil: Lovengreen, C.. Universidad Austral de Chile; ChileFil: Pedroni, J.. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Rosales, A.. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Zagarese, Horacio Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Vernet, M.. University of California at San Diego; Estados Unido

The electrogenic Na+/HCO3− cotransport modulates resting membrane potential and action potential duration in cat ventricular myocytes

Perforated whole-cell configuration of patch clamp was used to determine the contribution of the electrogenic Na+/HCO3− cotransport (NBC) on the shape of the action potential in cat ventricular myocytes. Switching from Hepes to HCO3− buffer at constant extracellular pH (pHo) hyperpolarized resting membrane potential (RMP) by 2.67 ± 0.42 mV (n = 9, P < 0.05). The duration of action potential measured at 50% of repolarization time (APD50) was 35.8 ± 6.8% shorter in the presence of HCO3− than in its absence (n = 9, P < 0.05). The anion blocker SITS prevented and reversed the HCO3−-induced hyperpolarization and shortening of APD. In addition, no HCO3−-induced hyperpolarization and APD shortening was observed in the absence of extracellular Na+. Quasi-steady-state currents were evoked by 8 s duration voltage-clamped ramps ranging from −130 to +30 mV. A novel component of SITS-sensitive current was observed in the presence of HCO3−. The HCO3−-sensitive current reversed at −87 ± 5 mV (n = 7), a value close to the expected reversal potential of an electrogenic Na+/HCO3− cotransport with a HCO3−:Na+ stoichiometry ratio of 2: 1. The above results allow us to conclude that the cardiac electrogenic Na+/HCO3− cotransport has a relevant influence on RMP and APD of cat ventricular cells