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This study identifies causes of rising arsenic (As) concentrations over 17 years in an inter-montane aquifer system located just north of the Trans-Mexican-Volcanic-Belt in the Mesa central physiographic region that is extensively developed by long-screened production wells. Arsenic concentrations increased by more than 10 µg/L in 14% (3/22) of re-sampled wells. Similarly, in a larger scale analysis wherein As concentrations measured in 137 wells in 2016 were compared to interpolated, baseline concentrations from 246 wells in 1999, As concentrations rose more than 10 µg/L in 30% of wells. Between 1999 and 2016, the percentage of all wells sampled in each basin-wide sampling campaign exceeding the World Health Organization's 10 µg/L drinking water limit increased from 38 to 64%. Principal Components Analysis (PCA), step-wise multiple regression, and Random Forest modeling (RF) revealed that high As concentrations are closely associated with high pH and temperature, and high concentrations of fluoride (F), molybdenum (Mo), lithium (Li), sodium (Na) and silica (Si), but low calcium (Ca) and nitrate (NO3) concentrations. Pumping-induced mixing with hot, geothermally impacted groundwater generates alkaline water through hydrolysis of silicate minerals. The rising pH converts oxyanion sorption sites from positive to negative releasing As (and Mo) to pore waters. The negative correlation between nitrate and As concentrations can be explained by conservative mixing of shallow, young groundwater with geothermally influenced groundwater. Therefore water carrying an anthropogenic contaminant dilutes water carrying geogenic contaminants. This process is enabled by long well screens. Over-exploitation of aquifers in geothermal regions for agriculture can drive As concentrations in water from production wells to toxic levels even as the total dissolved solids remain low.

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RESUMO

Fluoride (F), naturally found in aquifers around the world at toxic concentrations, causes disease in millions of people. The long-term stability, however, of those concentrations within intensively pumped aquifers is poorly characterized. We assessed long-term stability in the spatial distribution of F concentrations in an intensively pumped aquifer within the semi-arid, inter-montane Independence Basin in central Mexico between 1999 and 2016. Although stable in 16 re-sampled wells, F concentrations increased in some localities across the basin by as much as 4mg/L. Changes in recharge pathways to the deep aquifer were identified by analyzing changes in δ2H, δ18O and Cl/Br mass ratios. In 1999, δ2H and δ18O values suggested the aquifer was recharged in the mountains. In 2016, however, substantial increases in δ18O values in the center of the basin suggest recharge water is derived from rainfall that had experienced increased evaporation. In 1999, the mass ratio Cl/Br in groundwater was slightly enriched over local rainfall, and followed a single mixing line on a plot of Cl. vs. Cl/Br. In 2016, however, three distinct groupings of wells were evident, all following different mixing lines. These changes suggest input from new sources including urban sewage, evaporate dissolution, connate sea water and geothermal waters. Step-wise multiple regression was used to quantify the impact of physical and chemical parameters on F concentrations. In 1999, Li (6.8±1.7) and Na (0.01±0.004) drove F concentrations (R2=0.54). In 2016, Na (0.013±0.0018), HCO3 (0.004±0.001), Ca (-0.0018±0.00045), and Mg (-0.055±0.023) drove F concentrations (0.78). Irrigation pumping and urban expansion within semi-arid, groundwater-dependent, inter-montane basins drive mixing of disparate groundwater chemistries and introduces new sources of recharge to aquifers inducing changes in aquifer chemistry including increasing concentrations of geogenic toxic elements.

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The aim of this paper is to study the behavior of an earth fill dam, analyzing the deformations determined by high precision geodetic techniques and those obtained by the Finite Element Method (FEM). A large number of control points were established around the area of the dam, and the measurements of their displacements took place during several periods. In this study, high-precision leveling and GNSS (Global Navigation Satellite System) techniques were used to monitor vertical and horizontal displacements respectively. Seven surveys were carried out: February and July 2008, March and July 2013, August 2014, September 2015 and September 2016. Deformations were predicted, taking into account the general characteristics of an earth fill dam. A comparative evaluation of the results derived from predicted (FEM) and observed deformations shows the differences on average being 20 cm for vertical displacements, and 6 cm for horizontal displacements at the crest. These differences are probably due to the simplifications assumed during the FEM modeling process: critical sections are considered homogeneous along their longitude, and the properties of the materials were established according to the general characteristics of an earth fill dam. These characteristics were taken from the normative and similar studies in the country. This could also be due to the geodetic control points being anchored in the superficial layer of the slope when the construction of the dam was finished.

RESUMO

This study was designed to determine whether calreticulin (CRT), a chaperone protein, is present in in vitro-matured (IVM) pig oocytes and to study its potential role in the block to polyspermy. Western blot analysis, using an anti-CRT antibody, of oocyte lysate showed an immunoreactive band of ∼60  kDa. Simultaneous labeling of IVM oocytes with anti-CRT antibody and peanut agglutinin lectin (PNA lectin, a porcine cortical granules (CG)-specific binding lectin) revealed localization of CRT in the subplasmalemmal region with a 27.7% colocalization with PNA staining. After IVF, PNA labeling was not observed and anti-CRT labeling decreased significantly in zygotes and disappeared in two-cell embryos. Western blot analysis of oocyte exudate obtained from zona pellucida (ZP)-free oocytes activated with calcium ionophore confirmed the presence of a band that reacted with an anti-CRT antibody. Anti-CRT antibody and PNA labeling were not observed in activated oocytes despite being detectable in non-activated oocytes. The presence of CRT in vesicles located under the oolemma was demonstrated using immunogold cytochemistry at the ultrastructural level. To study the role of CRT in fertilization, ZP-enclosed and ZP-free oocytes were incubated with exogenous CRT and then inseminated. Whereas ZP-free oocytes showed fewer penetrating sperm and lower polyspermy rates than untreated oocytes, the opposite effect was observed in ZP-enclosed oocytes. In conclusion, CRT is confined to subplasmalemmal vesicles partially overlapping with CG contents. Its exocytosis after the oocyte activation seems to participate in the membrane block to polyspermy in pigs but is not involved in the ZP block.

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