Release and mobility of hexavalent chromium in contaminated soil with chemical factory waste: Experiments, Cr isotope analysis and reactive transport modeling.

Our study focused on the leaching processes in soil contaminated with hexavalent chromium (Cr(VI)), traced to industrial waste from a disused site and resulting in groundwater contamination. Mineral and geochemical characterization of the soil by means of XRD, SEM-EDS, total digestion and sequential extractions revealed that the main Cr content was from solid waste located in the upper meter of the soil profile. Flow-through and column experiments were carried out to investigate the processes responsible for Cr(VI) release. Cr(VI) mobility along the soil profile was also assessed. Moreover, Cr isotope signatures were used to evaluate a potential Cr(VI) reduction process, which preferably could immobilize toxic Cr(VI) complexes. One-dimensional (1D) numerical simulations reproduced the Cr(VI) release from the flow-through experiment containing the Cr(VI) rich-solid waste and also the Cr(VI) mobility along the column experiment. These results enabled us to interpret quantitatively the processes resulting in Cr(VI) contamination and mobility along the soil profile. Cr(VI) was released from dissolving Cr(VI)-rich phases (e.g., sodium chromate, Cr(VI)-hydrocalumite and Cr(VI)-ettringite) of the solid waste layer. Cr(VI) reduction and Cr(VI) adsorption did not take place along the column. Such accurate characterization of these processes is necessary for the mitigation of Cr(VI) mobility in contaminated soils.

Characterisation of the natural attenuation of chromium contamination in the presence of nitrate using isotopic methods. A case study from the Matanza-Riachuelo River basin, Argentina.

The groundwater contamination by hexavalent chromium (Cr(VI)) in a site of the Matanza-Riachuelo River basin (MRB), Argentina, has been evaluated by determining the processes that control the natural mobility and attenuation of Cr(VI) in the presence of high nitrate (NO3-) contents. The groundwater Cr(VI) concentrations ranged between 1.9E-5 mM and 0.04 mM, while the NO3- concentrations ranged between 0.5 mM and 3.9 mM. In order to evaluate the natural attenuation of Cr(VI) and NO3- in the MRB groundwater, Cr and N isotopes were measured in these contaminants. In addition, laboratory batch experiments were performed to determine the isotope fractionation (ε) during the reduction of Cr(VI) under denitrifying conditions. While the Cr(VI) reduction rate is not affected by the presence of NO3-, the NO3- attenuation is slower in the presence of Cr(VI). Nevertheless, no significant differences on ε values were observed when testing the absence or presence of each contaminant. The ε53Cr determined in the batch experiments describe a two- stage trend, in which Stage I is characterized by ε53Cr ~-1.8‰ and Stage II by ε53Cr ~-0.9‰. The respective ε15NNO3 obtained is -23.9‰ whereas ε18ONO3 amount to -25.7‰. Using these ε values and a Rayleigh fractionation model we estimate that an average of 60% of the original Cr(VI) is removed from the groundwater of the contaminated site. Moreover, the average degree of NO3- attenuation by denitrification is found to be about 20%. This study provides valuable information about the dynamics of a complex system that can serve as a basis for efficient management of contaminated groundwater in the most populated and industrialized basin of Argentina.

Epilepsia en menores de 3 anos / Epilepsy in children under 3 years old

Se estudiaron 96 pacientes de 3 anos, ingresados en el Servicio de Neurologia Pediatrica de nuestro Centro, con diagnostico de epilepsia, con el objetivo de evaluar la aplicacion de la clasificacion de los ataques, la de Epilepsia y Sindromes de Epilepticos aceptados actualmente por la Liga Internacional Contra la Epilepsia (ILAE). En ellos se observo con mayor frecuencia la presentacion de ataques parciales (58,3 por ciento), seguido de los generalizados (36,5 por ciento) e indeterminados (5 por ciento); no se presentaron diferencias significativas respecto a la distribucion de estos entre menores de 1 ano y los comprendidos en edades entre 1 y 3 anos. En 28 pacientes se encontraron dificultades para clasificarlos acorde con la de Epilepsia y Sindromes Epilepticos, y se analizaron su distribucion y caracteristicas. Se comentan brevemente los resultados del electroencefalograma (EEG) en relacion con la actividad paroxistica y se presentan los sindromes mas frecuentemente observados

Epilepsia en menores de 3 años / Epilepsy in children under 3 years old

Se estudiaron 96 pacientes de 3 años, ingresados en el Servicio de Neurología Pediátrica de nuestro Centro, con diagnóstico de epilepsia, con el objetivo de evaluar la aplicación de la clasificación de los ataques, la de Epilepsia y Síndromes de Epilépticos aceptados actualmente por la Liga Internacional Contra la Epilepsia (ILAE). En ellos se observó con mayor frecuencia la presentación de ataques parciales (58,3 por ciento), seguido de los generalizados (36,5 por ciento) e indeterminados (5 por ciento); no se presentaron diferencias significativas respecto a la distribución de éstos entre menores de 1 año y los comprendidos en edades entre 1 y 3 años. En 28 pacientes se encontraron dificultades para clasificarlos acorde con la de Epilepsia y Síndromes Epilépticos, y se analizaron su distribución y características. Se comentan brevemente los resultados del electroencefalograma (EEG) en relación con la actividad paroxística y se presentan los síndromes más frecuentemente observados(AU)