Hexavalent Chromium in Waters for Human Consumption and Irrigation in the Guano Canton

Introduction: Considering the geographical location and industrial activities of the county Guano, which lies on an aquifer that supply water for both consumption and crop irrigation, it is necessary to examine the levels of chromium (Cr) in its watershed and tributaries. Objective: To evaluate the amount of Cr existing in the surface waters of the Guano river basin and aquifer. Methods: Several samples of the river and aquifer were taken and the amount of Cr present was measured. Using Z-test, Cr levels found in the water were compared with those recommended as normal by the World Health Organization (WHO), national standards of the Texto Unificado de Legislación Secundaria de Medio Ambiente (TULSMA) and the Servicio Ecuatoriano de Normalización 1108 ( INEN 1108). Results: Relatively high Cr values were found when compared with those established by the WHO. However, they were normal when compared with TULSMA and INEN 1108. Conclusion: The levels of Cr found in the Guano river and the aquifer were higher than those recommended by the WHO. It is recommended to replicate our findings in order to corroborate the results and to take appropriate measures in order to reduce water contamination. Keywords: chromium, water, Guano, Ecuador. Resumen Introducción: Considerando la ubicación geográfica y actividades industriales del cantón Guano el cual yace sobre un acuífero que sustenta las necesidades de agua tanto para consumo y riego de la población es necesario examinar los niveles de Cromo (Cr) en su vertiente como sus afluentes. Objetivo: Evaluar la cantidad de Cr existente en las aguas superficiales de la cuenca del río Guano y en pequeños ojos de agua provenientes del acuífero. Métodos: Se tomó varias muestras de agua del río y ojos de agua y se midió la cantidad de Cr presente. Por medio de la prueba Z se comparó los niveles de Cr con los recomendados como normales por la Organización Mundial de la Salud (OMS), normas nacionales del Texto Unificado de Legislación Secundaria de Medio Ambiente (TULSMA) y Servicio Ecuatoriano de Normalización 1108 (INEN 1108). Resultados: Se encontró valores relativamente altos de Cr al compararlos con los establecidos por la OMS. Sin embargo, estos se encontraron dentro de rangos normales al compararlos con TULSMA e INEN 1108. Conclusiones: Los niveles de Cr encontrados en el río Guano y ojos de agua del acuífero son superiores a los recomendados por la OMS. Se recomienda replicar los hallazgos para corroborar los resultados y tomar las medidas adecuadas para reducir la contaminación del agua. Palabras clave: cromo, agua, Guano, Ecuador

Limitations on the superposition principle: superselection rules in non-relativistic quantum mechanics

The superposition principle is a very basic ingredient of quantum theory. What may come as a surprise to many students, and even to many practitioners of the quantum craft, is tha superposition has limitations imposed by certain requirements of the theory. The discussion of such limitations arising from the so-called superselection rules is the main purpose of this paper. Some of their principal consequences are also discussed. The univalence, mass and particle number superselection rules of non-relativistic quantum mechanics are also derived using rather simple methods.Comment: 22 pages, no figure

A low steady HBsAg seroprevalence is associated with a low incidence of HBV-related liver cirrhosis and hepatocellular carcinoma in Mexico: a systematic review

To address the relationship between hepatitis B virus (HBV) endemicity and HBV-related liver diseases in Mexico. Research literature reporting on HBsAg and antibody to hepatitis B core antigen (anti-HBc) prevalence in Mexican study groups were searched in NLM Gateway, PubMed, IMBIOMED, and others. Weighted mean prevalence (WMP) was calculated from the results of each study group. A total of 50 studies were analyzed. Three nationwide surveys revealed an HBsAg seroprevalence of less than 0.3%. Horizontal transmission of HBV infection occurred mainly by sexual activity and exposure to both contaminated surgical equipment and body fluids. High-risk groups exposed to these factors included healthcare workers, pregnant women, female sex workers, hemodialysis patients, and emergency department attendees with an HBsAg WMP ranging from 1.05% (95% confidence interval [CI], 0.68–1.43) to 14.3% (95% CI, 9.5–19.1). A higher prevalence of anti-HBc in adults than those younger than 20 years was associated with the main risk factors. Anti-HBc WMP ranged from 3.13% (95% CI, 3.01–3.24) in blood donors to 27.7% (95% CI, 21.6–33.9) in hemodialysis patients. A heterogeneous distribution of HBV infection was detected, mainly in native Mexican groups with a high anti-HBc WMP of 42.0% (95% CI, 39.5–44.3) but with a low HBsAg WMP of 2.9% (95% CI 2.08–3.75). Estimations of the Mexican population growth rate and main risk factors suggest that HBsAg seroprevalence has remained steady since 1974. A low HBsAg prevalence is related to the low incidence of HBV-related liver cirrhosis and hepatocellular carcinoma (HCC) previously reported in Mexico

A Paleogeographic Overview of Tropical Fossil Sloths: Towards an Understanding of the Origin of Extant Suspensory Sloths?

Modern sloths are among the more characteristic mammals of South and Central American faunas. Recent discovery in four Paleogene, 22 Neogene, and dozens of Pleistocene fossiliferous localities in the tropics has revealed an unexpected paleobioversity constituted by some 81 fossil sloth species. Probably originating in southern South America near the Eocene/Oligocene transition, sloths were represented in the tropics during the late Oligocene by Pseudoglyptodon, Mylodontidae, and Megalonychidae. The latter occupied the West Indies between at least the late early Miocene and late Pleistocene, and two mylodontid clades, Octodontobradyinae and Urumacotheriinae, were characteristic of Amazonian localities from the Colhuehuapian and the Laventan periods, respectively, until the end of the Miocene. Megatheriinae and Nothrotheriidae appeared during the middle Miocene, colonizing the tropics and then North America, where Mylodontidae and Megalonychidae had already been present since the early late Miocene. Nothrotheriids are more abundant and diversified during the late Miocene in the tropics than in southern South America. Remains closely related to either of the modern sloths are absent from the fossil record, including those in the tropics. The characteristic suspensory posture of Bradypus and Choloepus appeared independently and likely after the Miocene epoch, and thus well after the hypothesized split suggested by molecular studies of the respective clades of these genera. Given their current widespread distribution in and reliance on the tropics, prospecting efforts for the direct fossil kin of suspensory sloths should concentrate on deposits in the Amazonian region, as this area has shown promise in producing fossil sloths.Fil: Pujos, François Roger Francis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: De Iuliis, G.. University of Toronto; Canadá. Royal Ontario Museum; CanadáFil: Cartelle, C.. Pontifícia Universidade Católica de Minas Gerais ; Brasi