El sistema de control interno y su incidencia en la baja recaudación del impuesto predial de la Municipalidad Distrital de Pocollay, periodo 2017

La presente investigación tiene por finalidad comprobar si el sistema de control interno incide en la baja recaudación del impuesto predial de la Municipalidad Distrital de Pocollay, periodo 2017. El tema fue elegido porque existe irregularidades por parte de los funcionarios y servidores respecto a la conclusión prevista. La recolección de la información, los procedimientos desarrollados y el informe de investigación se efectuó en el año 2017, con la información obtenida durante el año mencionado se llegó a los resultados que demuestran que el sistema de control interno incide en la baja recaudación del impuesto predial de la Municipalidad Distrital de Pocollay, periodo 2017. Como también se demuestra que el ambiente de control, la actividad de control y la información y comunicaciones incide positivamente en la baja recaudación del impuesto predial de la Municipalidad Distrital de Pocollay, periodo 2017. Cumpliendo con los objetivos y metas trazadas por la Municipalidad.Tesi

Cycle biogéochimique du Hg dans l’hydrosystème tropical d’altitude lac Uru-Uru, Altiplano bolivien

This thesis is dedicated to the study of the biogeochemical cycle of Hg (Hg) in the high altitude (3800m a.s.l.) and tropical aquatic ecosystem Uru-Uru, located on the Bolivian Altiplano. The aim of this study is to gather information about the concentration levels of different Hg species, and to understand the mechanisms involved in the formation of methylHg (MMHg) which bioaccumulates in trophic food webs. In this environment, Hg methylation is mediated predominantly by sulphate-reducing bacteria. Floating bio-inorganic aggregates and surface sediments contributes significantly to the MMHg pool of the ecosystem. The partition coefficients of MMHg and inorganic Hg (iHg) suggest that sediments are the main source of MMHg to the water column. High percentages of dissolved MMHg (~50%) suggest this compound to be highly stable in the water, probably due to the important attenuation of UV radiation and the occurrence of complexing colloidal material. Eventually, analyses of correlation factors Hg/Sb and Hg/W in the sediments show that the main source of Hg is probably from mining origin.Cette thèse est consacrée à l’étude du cycle biogéochimique du Hg (Hg) dans l’écosystème aquatique tropical Uru-Uru, situé sur l’Altiplano bolivien à 3800m. L’objectif était de documenter les niveaux de concentrations pour différentes espèces de Hg, et de comprendre les mécanismes mis en jeu dans la formation du méthylHg (MMHg), qui se bioaccumule dans la chaine trophique. Dans cet environnement, la methylation du Hg résulte majoritairement de l’activité des bactéries sulfato-réductrices. Les agrégats bio-inorganiques flottants et les sédiments de surface contribuent significativement au pool de MMHg de l’écosystème. Les coefficients de partition du MMHg et du Hg inorganique (iHg) suggèrent que les sédiments sont la source principale du MMHg vers la colonne d’eau. Les fortes proportions en MMHg dissous (~50%) suggèrent une grande stabilité de ce composé dans l‘eau, probablement influencé par l’atténuation forte du rayonnement UV et la présence de matériel colloïdal complexant. Finalement, les analyses de coefficients de corrélation Hg/Sb et Hg/W dans les sédiments, indiquent que la source principale du Hg est probablement d’origine minière

Association of a Specific Algal Group with Methylmercury Accumulation in Periphyton of a Tropical High-Altitude Andean Lake

International audiencePeriphyton relevance for methylmercury (MeHg) production and accumulation are now well known in aquatic ecosystems. Sulfate-reducing bacteria and other microbial groups were identified as the main MeHg producers, but the effect of periphyton algae on the accumulation and transfer of MeHg to the food web remains little studied. Here we investigated the role of specific groups of algae on MeHg accumulation in the periphyton of Schoenoplectus californicus ssp. (Totora) and Myriophyllum sp. in Uru Uru, a tropical high-altitude Bolivian lake with substantial fishing and mining activities accruing around it. MeHg concentrations were most strongly related to the cell abundance of the Chlorophyte genus Oedogonium (r2 = 0.783, p = 0.0126) and to no other specific genus despite the presence of other 34 genera identified. MeHg was also related to total chlorophyll-a (total algae) (r2 = 0.675, p = 0.0459), but relations were more significant with chlorophyte cell numbers, chlorophyll-b (chlorophytes), and chlorophyll-c (diatoms and dinoflagellates) (r2 = 0.72, p = 0.028, r2 = 0.744, p = 0.0214, and r2 = 0.766, p = 0.0161 respectively). However, Oedogonium explains most variability of chlorophytes and chlorophyll-c (r2 = 0.856, p = < 0.001 and r2 = 0.619, p = 0.002, respectively), suggesting it is the most influential group for MeHg accumulation and periphyton algae composition at this particular location and given time

Exposición a metil mercurio de mujeres y niños de comunidades del río Beni con relación a problemas de salud endémicos en el área

Colloque international dans le cadre de l'ACTION THEMATIQUE INTERDEPARTEMENTALE IRD – U2SISRESUMEN: La disponibilidad del mercurio en el medio ambiente ha contaminado el ecosistema de la Amazonia, por lo tanto numerosos estudios han reportado exposiciones a través del consumo de los peces en forma de metil mercurio en niveles dañinos para la gente. Los estudios en Bolivia son escasos. Por este motivo, se planificó un estudio para determinar la importancia de la contaminación por el metil mercurio en la salud en comunidades que viven a orillas del río Beni. OBJETIVO: Evaluar la exposición con metil-Hg en mujeres, niños y adolescentes, y su efecto en la salud teniendo en cuenta otros factores patológicos frecuentes del área como la anemia, estado nutricional, tipos de infecciones y parasitismo. MÉTODOS: Se examinaron 631 personas (174 madres y 457 niños) en 15 comunidades que se encuentran a orillas del río Beni desde Rurrenabaque hasta 110 km río abajo. Fueron recolectados datos sobre consumo de alimentos, estado clínico y nutricional, se realizó un examen hematológico y coproparasitológico. La exposición al mercurio se evaluó mediante análisis de cabellos. La concentración de mercurio se midió con Espectrometría de Absorción Atómica en el Laboratorio de Calidad Ambiental de la UMSA RESULTADOS: Se examinaron 174 madres (edad promedio: 34,8 ± 13.3 años). Más de la mita de las madres perdieron al menos un niño. El 39.8% presentaron anemia. El 61.1% presentaron concentraciones de mercurio total 10μg /g. Los consumos mas frecuentes de pescados, se observaron en madres con niveles altos de Hg, Un total de 450 niños y adolescentes (240 niñas y 210 niños) de 0 a 15años fue examinado. Se observó una prevalencia elevada de retrazo de crecimiento (el 38.8% están por debajo de 2 z-scores del índice talla para la edad) y el 68.6% de los niños fueron positivos a protozoarios y el 83.5% fueron positivos a helmintos. El 61.1% tenían concentración de mercurio total 10 μg/g en cabellos. Finalmente, se observó que los niños de 5 a 10 años con niveles elevados de mercurio, tenían mejores índices nutricionales. CONCLUSIÓN: Dentro del área de estudio se encontró niveles de concentraciones de mercurio leves a moderados, teniendo una relación positiva con la frecuencia de consumo de pescados. Por lo tanto estos niveles de mercurio no parecen generar efectos muy dañinos en la población en estudio. La presencia de un alta carga parasitaria, y de prevalencias elevadas de infecciones, anemias y malnutrición, parecen en la actualidad, más preocupantes para la salud de estas comunidades

Sulfate-Reducing Bacteria in Floating Macrophyte Rhizospheres from an Amazonian Floodplain Lake in Bolivia and Their Association with Hg Methylation

Five subgroups of sulfate-reducing bacteria (SRB) were detected by PCR in three macrophyte rhizospheres (Polygonum densiflorum, Hymenachne donacifolia, and Ludwigia helminthorriza) and three subgroups in Eichhornia crassipes from La Granja, a floodplain lake from the upper Madeira basin. The SRB community varied according to the macrophyte species but with different degrees of association with their roots. The rhizosphere of the C(4) plant Polygonum densiflorum had higher frequencies of SRB subgroups as well as higher mercury methylation potentials (27.5 to 36.1%) and carbon (16.06 ± 5.40%), nitrogen (2.03 ± 0.64%), Hg (94.50 ± 6.86 ng Hg g(−1)), and methylmercury (8.25 ± 1.45 ng Hg g(−1)) contents than the rhizosphere of the C(3) plant Eichhornia crassipes. Mercury methylation in Polygonum densiflorum and Eichhornia crassipes was reduced when SRB metabolism was inhibited by sodium molybdate

Riverine Li isotope fractionation in the Amazon River basin controlled by the weathering regimes.

We report Li isotope composition (δ7Li) of river-borne dissolved and solid material in the largest River system on Earth, the Amazon River basin, to characterize Li isotope fractionation at a continental scale. The δ7Li in the dissolved load (+1.2‰ to +32‰) is fractionated toward heavy values compared to the inferred bedrock (−1‰ to 5‰) and the suspended sediments (−6.8‰ to −0.5‰) as a result of the preferential incorporation of 6Li into secondary minerals during weathering. Despite having very contrasted weathering and erosion regimes, both Andean headwaters and lowland rivers share similar ranges of dissolved δ7Li (+1.2‰ to +18‰). Correlations between dissolved δ7Li and Li/Na and Li/Mg ratios suggest that the proportion of Li incorporated in secondary minerals during weathering act as the main control on the δ7Lidiss across the entire Amazon basin. A “batch” steady-state fractionation model for Andean and lowland rivers satisfactorily reproduces these variations, with a fractionation factor between weathering products and dissolved load (αsec-dis) of 0.983 ± 0.002. Two types of supply-limited weathering regimes can be identified for the lowlands: “clearwaters” with dominant incorporation of Li in secondary minerals, and “black waters” (e.g., Rio Negro) where dissolution of secondary minerals enhanced by organic matter produces low δ7Li. Apart from the black waters, the δ7Li of Andean and lowland rivers is negatively correlated to the denudation rates with the lowest δ7Li corresponding to the rivers having the highest denudation rates. In contrast, the main tributaries draining both the Andes and the lowlands have higher δ7Li compared to other rivers. We propose that part of the dissolved Li derived from weathering in the Andes is re-incorporated in sediments during transfer of water and sediments in floodplains and that this results in an increase of the dissolved δ7Li along the course of these rivers. Unlike other rivers, the dissolved δ7Li in the main tributaries is best described by a Rayleigh fractionation model with a fractionation factor αsec-dis of 0.991. Altogether, the control imposed by residence time in the weathering zone and floodplain processes results in (i) a non-linear correlation between dissolved δ7Li and the weathering intensity (defined as W/D) and (ii) a positive relationship between the dissolved Li flux and the denudation rate. These results have important implications for the understanding of past ocean δ7Li and its use as a paleo weathering proxy

Synergistic effects of mining and urban effluents on the level and distribution of methylmercury in a shallow aquatic ecosystem of the Bolivian Altiplano

International audienceLake Uru Uru (3686 m a.s.l.) located in the Bolivian Altiplano region receives both mining effluents and urban wastewater discharges originating from the surrounding local cities which are under rapid development. We followed the spatiotemporal distribution of different mercury (Hg) compounds and other metal(oid)s (e.g.{,} Fe{,} Mn{,} Sb{,} Ti and W) in both water and sediments during the wet and dry seasons along a north-south transect of this shallow lake system. Along the transect{,} the highest Hg and metal(oid) concentrations in both water and sediments were found downstream of the confluences with mining effluents. Although a dilution effect was found for major elements during the wet season{,} mean Hg and metal(oid) concentrations did not significantly differ from the dry season due to the increase in acid mine drainage (AMD) inputs into the lake from upstream mining areas. In particular{,} high filtered (<0.45 [small mu ]m) mono-methylmercury (MMHg) concentrations (0.69 +/- 0.47 ng L-1) were measured in surface water representing 49 +/- 11% of the total filtered Hg concentrations (THgF) for both seasons. Enhanced MMHg lability in relation with the water alkalinity{,} coupled with abundant organic ligands and colloids (especially for downstream mining effluents){,} are likely factors favoring Hg methylation and MMHg preservation while inhibiting MMHg photodegradation. Lake sediments were identified as the major source of MMHg for the shallow water column. During the dry season{,} diffusive fluxes were estimated to be 227 ng m-2 d-1 for MMHg. This contribution was found to be negligible during the wet season due to a probable shift of the redox front downwards in the sediments. During the wet season{,} the results obtained suggest that various sources such as mining effluents and benthic or macrophytic biofilms significantly contribute to MMHg inputs in the water column. This work demonstrates the seasonally dependent synergistic effect of AMD and urban effluents on the shallow{,} productive and evaporative high altitude lake ecosystems which promotes the formation of natural organometallic toxins such as MMHg in the water column

Biogeoquímica del mercurio en el lago tropical de altura Uru Uru (Altiplano boliviano)

International audienceEn la región del Altiplano boliviano, de condiciones ambientales extremas (3700 m.s.n.m. de altitud, elevada radiación UV, menor disponibilidad de O2), se encuentra el lago Uru Uru. De aguas poca profundas (0-1 m), elevada gradiente en la salinidad de sus aguas y alta productividad primaria, es impactado por descargas de afluentes mineros y urbanos. Las elevadas concentraciones de monometilmercurio (MMHg), un neurotóxico muy potente, medidas en peces y aves (Molina et al., 2012), ha cuestionando la fuente y transformaciones del Hg para la producción de MMHg en los ecosistemas de altura. La producción de MMHg es un proceso clave que dirige la bioacumulación del Hg en la cadena alimentaria y los procesos de metilación y demetilación, son los mayores patrones de transformación que regulan la producción neta de MMHg. Para dar respuesta a estas preguntas concentraciones de metales, metaloides (Fe, Mn, Sb, Ti y W), elementos mayoritarios, especies de mercurio (mercurio inorgánico (IHg), MMHg, mercurio vapor (Hg°) y dimetilmercurio (DMHg)) fueron medidas en muestras de aguas; MMHg y mercurio total (THg) en sedimentos y aguas intersticiales de sedimentos del lago Uru Uru. Al mismo tiempo se realizó un seguimiento de la distribución espacio temporal de Norte a Sur del lago, para todos estos parámetros, durante las épocas seca y húmeda (octubre, 2010 y mayo 2011). Además se determinó los potenciales de metilación (M) y demetilación (D) en situ en muestras de sedimentos, aguas, periphyton y agregados bio-orgánicos flotantes en los sitios norte (NS) y sur (SS) del lago Uru Uru, utilizando trazadores isotópicos estables de 199Hg y MM201Hg. Entre los resultados más importantes se encuentra la elevada concentración de metales pesados y de MMHg en forma disuelta, la cual llega hasta el 49 ± 11 % con respecto al mercurio total disuelto (THgd). Se identifica a los sedimentos como la fuente principal de MMHg, cuyo flujo difusivo alcanzan hasta 227 ng m-2 day-1 de MMHg durante la época seca. Esta aseveración es sustentada con la medición de los potenciales de M/D en las diferentes matrices. Los potenciales Netos de M, medidos en el sitio Norte, indican que los efluentes mineros y urbanos promueven la producción de MMHg en las aguas y en los sedimentos (3,4±1,2 ng g−1 day−1) durante la época seca. Si bien se identifica a los agregados bio-orgánicos como los mayores productores de MMHg (5,8 ng MMHg g−1 day−1, época seca), son los sedimentos los mayores representantes de producción de esta sustancia tóxica, tomando en cuenta la diferencia de masa total de cada matriz en el lago. Se determina también que el rol del periphyton de las totoras es el de la descomposición de MMHg (-2,1 ng MMHg g−1 day−1), pero también el de almacenamiento de MMHg. En suma se demuestra que existe un efecto sinérgico de los drenajes ácidos mineros (DAM) según la temporada y los efluentes urbanos en los ecosistemas productivos, al cual la evaporación superficial promueven las elevadas emisiones de contaminantes organometálicos como MMHg en la columna de agua, cuya producción y la estabilidad se nutre de la abundante materia orgánica y de los ligandos presentes en el medio

Diurnal variability and biogeochemical reactivity of mercury species in an extreme high-altitude lake ecosystem of the Bolivian Altiplano

International audienceAbstr act Methylation and demethylation represent major transformation pathways regulating the net production of methylmercury (MMHg). Very few studies have documented Hg reactivity and transformation in extreme high-altitude lake ecosystems. Mercury (Hg) species concentrations (IHg, MMHg, Hg°, and DMHg) and in situ Hg methylation (M) and MMHg demethylation (D) potentials were determined in water, sediment, floating organic aggregates, and periphyton compartments of a shallow productive Lake of the Bolivian Altiplano (Uru Uru Lake, 3686 m). Samples were collected during late dry season (October 2010) and late wet season (May 2011) at a north (NS) and a south (SS) site of the lake, respectively. Mercury species concentrations exhibited significant diurnal variability as influenced by the strong diurnal biogeochemical gradients. Particularly high methylated mercury concentrations (0.2 to 4.5 ng L −1 for MMHg T) were determined in the water column evidencing important Hg methylation in this ecosystem. Methylation and D potentials range were, respectively, <0.1–16.5 and <0.2–68.3 % day −1 and were highly variable among compartments of the lake, but always higher during the dry season. Net Hg M indicates that the influence of urban and mining effluent (NS) promotes MMHg pro duction in both water (up to 0.45 ng MMHg L −1 day −1) and sediment compartments (2.0 to 19.7 ng MMHg g −1 day −1). While the sediment compartment appears to represent a major source of MMHg in this shallow ecosystem, floating organic aggregates (dry season, SS) and Totora's periphyton (wet season, NS) were found to act as a significant source (5.8 ng MMHg g −1 day −1) and a sink (−2.1 ng MMHg g −1 day −1) of MMHg, respectively. This work demonstrates that high-altitude productive lake ecosystems can promote MMHg formation in various compartments supporting recent observations of high Hg contents in fish and water birds

Mercury contamination level and speciation inventory in Lakes Titicaca & Uru-Uru (Bolivia): Current status and future trends

International audienceAquatic ecosystems of the Bolivian Altiplano (∼3800 m a.s.l.) are characterized by extreme hydro-climatic constrains (e.g., high UV-radiations and low oxygen) and are under the pressure of increasing anthropogenic activities, unregulated mining, agricultural and urban development. We report here a complete inventory of mercury (Hg) levels and speciation in the water column, atmosphere, sediment and key sentinel organisms (i.e., plankton, fish and birds) of two endorheic Lakes of the same watershed differing with respect to their size, eutrophication and contamination levels. Total Hg (THg) and monomethylmercury (MMHg) concentrations in filtered water and sediment of Lake Titicaca are in the lowest range of reported levels in other large lakes worldwide. Downstream, Hg levels are 3-10 times higher in the shallow eutrophic Lake Uru-Uru than in Lake Titicaca due to high Hg inputs from the surrounding mining region. High percentages of MMHg were found in the filtered and unfiltered water rising up from <1 to ∼50% THg from the oligo/hetero-trophic Lake Titicaca to the eutrophic Lake Uru-Uru. Such high %MMHg is explained by a high in situ MMHg production in relation to the sulfate rich substrate, the low oxygen levels of the water column, and the stabilization of MMHg due to abundant ligands present in these alkaline waters. Differences in MMHg concentrations in water and sediments compartments between Lake Titicaca and Uru-Uru were found to mirror the offset in MMHg levels that also exist in their respective food webs. This suggests that in situ MMHg baseline production is likely the main factor controlling MMHg levels in fish species consumed by the local population. Finally, the increase of anthropogenic pressure in Lake Titicaca may probably enhance eutrophication processes which favor MMHg production and thus accumulation in water and biota