Biocorrosión de muestras de hormigón en condiciones controladas de laboratorio

57 páginas.Trabajo Fin de Máster Universitario en Tecnología Ambiental (2023/24). Tutor: Dr. D. Francisco Córdoba García. La Faja Pirítica es considerada como una de las mayores concentraciones de sulfuros masivos de la corteza terrestre. En un escenario ambiental inusual que refleja la belleza de un ambiente geológico que durante siglos ha sido testigo de extracciones de los minerales que se concentran en sus depósitos y donde, la presencia de estructuras de hormigón asociados a la minería y las actividades de la construcción y geológicas han progresado, se hace evidente la degradación de cientos de kilómetros de la red fluvial por el Drenaje Ácido de Mina (AMD) que transporta una serie de minerales que en contacto con el oxígeno produce reacciones químicas capaces de liberar al medio cantidades ingentes de metales como el hierro que le otorga al río su color característico. Estas reacciones catalizadas por la acción de agentes químicos y de organismos extremófilos que encuentran las condiciones ideales en estos ecosistemas para multiplicarse, provocan la acidez a partir de un proceso que durante miles de años ha provocado la oxidación de los sulfuros que afloran. Por tanto, en este contexto la vulnerabilidad de estructuras de hormigón asociadas a las actividades mineras es alta puesto que la oxidación microbiológica está incidiendo negativamente sobre los elementos estructurales manifestándose en estos: agrietamientos, pérdida de volumen y la oxidación anticipada en acero y hormigón. Con el objetivo de analizar el potencial oxidativo de los consorcios bacterianos propios de las aguas afectadas por AMD se investigó su actividad sobre probetas de hormigón bajo condiciones controladas de laboratorio. En los experimentos realizados se midieron la evolución del pH, conductividad y potencial redox, la proporción de Fe2+/Fe3+, la concentración de diversos elementos químicos mediante ICP-óptico. También se analizaron los precipitados formados mediante SEM-EDS y se realizó un seguimiento macro- y microscópico de las muestras. Los resultados obtenidos muestran efectos diferenciales cuando el hormigón se cultivó en medios que contenían bacterias con relación a los medios esterilizados por filtración. Estos resultados se discuten sobre la función catalítica de las bacterias quimiolitotrofas oxidantes de hierro y/o azufre (como Acidithiobacillus o Leptospirillum) así como de otras bacterias heterótrofas que pueden oxidar compuestos orgánicos usando iones férricos como aceptores de electrones (ej. Acidiphillium sp)The Pyritic Belt is considered one of the largest concentrations of massive sulfides in the Earth's crust. In an unusual environmental scenario that reflects the beauty of a geological environment that has witnessed mineral extractions concentrated in its deposits for centuries, the presence of concrete structures associated with mining, construction activities, and geological advancements highlights the degradation of hundreds of kilometers of river networks due to Acid Mine Drainage (AMD). This drainage carries a series of minerals that, upon contact with oxygen, trigger chemical reactions capable of releasing vast amounts of metals into the environment, such as iron, which gives the river its characteristic color. These reactions, catalyzed by chemical agents and extremophilic organisms finding ideal conditions in these ecosystems to multiply, cause acidity through a process that, for thousands of years, has resulted in the oxidation of the exposed sulfides. Consequently, in this context, the vulnerability of concrete structures associated with mining activities is high, given that microbiological oxidation is negatively impacting the structural elements, leading to cracking, volume loss, and premature oxidation in both steel and concrete. To analyze the oxidative potential of bacterial consortia present in waters affected by AMD, their activity on concrete test specimens was investigated under controlled laboratory conditions. The experiments measured the evolution of pH, conductivity, redox potential, the Fe2+/Fe3+ ratio, the concentration of various chemical elements via Optical ICP, and analyzed the precipitates formed using SEM-EDS. Macro- and microscopic monitoring of the samples was also conducted. The results obtained revealed differential effects when concrete was cultivated in media containing bacteria compared to media sterilized by filtration. These results are discussed concerning the catalytic function of iron- and sulfur-oxidizing chemolithotrophic bacteria (such as Acidithiobacillus or Leptospirillum) as well as other heterotrophic bacteria capable of oxidizing organic compounds using ferric ions as electron acceptors (e.g., Acidiphilium sp)

Changes in Physiology before, during, and after Yawning

The ultimate function of yawning continues to be debated. Here, we examine physiological measurements taken before, during, and after yawns in humans, in an attempt to identify key proximate mechanisms associated with this behavior. In two separate studies we measured changes in heart rate, lung volume, eye closure, skin conductance, ear pulse, respiratory sinus arrhythmia, and respiratory rate. Data were depicted from 75 s before and after yawns, and analyzed at baseline, during, and immediately following yawns. Increases in heart rate, lung volume, and eye muscle tension were observed during or immediately following yawning. Patterns of physiological changes during yawning were then compared to data from non-yawning deep inhalations. In one study, respiration period increased following the execution of a yawn. Much of the variance in physiology surrounding yawning was specific to the yawning event. This was not the case for deep inhalation. We consider our findings in light of various hypotheses about the function of yawning and conclude that they are most consistent with the brain cooling hypothesis

Quality of Cohort Studies Reporting Post the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement

The quality of reporting of cohort studies published in the most prestigious scientific medical journals was investigated to indicate to what extent the items in the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) checklist are addressed. Six top scientific medical journals with high impact factor were selected including New England Journal of Medicine, Journal of the American Medical Association, Lancet, British Medical Journal, Archive of Internal Medicine, and Canadian Medical Association Journal. Ten cohort studies published in 2010 were selected randomly from each journal. The percentage of items in the STROBE checklist that were addressed in each study was investigated. The total percentage of items addressed by these studies was 69.3 (95% confidence interval: 59.6 to 79.0). We concluded that reporting of cohort studies published in the most prestigious scientific medical journals is not clear enough yet. The reporting of other types of observational studies such as case-control and cross-sectional studies particularly those being published in less prestigious journals expected to be much more imprecise