The origin of rare alkali metals in geothermal fluids of southern Tibet, China: A silicon isotope perspective.

Geothermal waters from the Semi, Dagejia and Kawu hot springs in the Shiquanhe-Yarlung Zangbo geothermal field of southern Tibet (China) are highly enriched in rare alkali metals (RAM). However, the enrichment mechanism is still hotly debated. Here, we report the first silicon isotope data of these geothermal waters to unravel the origin of the extreme RAM enrichments. Sinter precipitation in the spring vents and water-rock interaction in the deep reservoir controlled both the silicon budget and silicon isotope fractionation. The rates of water-rock interaction and sinter precipitation in three spring sites decrease in the sequences Semi > Kawu > Dagejia, and Dagejia > Kawu > Semi respectively. Silicon isotope fractionation during sinter precipitation (i.e. Δ30Siprecipitate-solution < -0.1‰) is less than that due to water-rock interaction (i.e. Δ30Sisolution-rocks at least as high as -0.47‰), which makes it possible to use the δ30Si signatures of springs to evaluate the intensity of water-rock interaction. Based on the available evidence, a conceptual model of RAM enrichment is proposed: (i) persistent magmatic activity in southern Tibet provided the initial enrichment of the RAM in host rocks and a heat sources for the deep reservoirs of geothermal systems; (ii) the high Cl- content and long residence time (thousands of years) promote the leaching of RAM from the silicate host rocks.

Isotope fractionation of sandy-soil water during evaporation - an experimental study.

Soil samples containing water with known stable isotopic compositions were prepared. The soil water was recovered by using vacuum/heat distillation. The experiments were held under different conditions to control rates of water evaporation and water recovery. Recoveries, δ18O and δ2H values of the soil water were determined. Analyses of the data using a Rayleigh distillation model indicate that under the experimental conditions only loosely bound water is extractable in cases where the recovery is smaller than 100 %. Due to isotopic exchange between vapour and remaining water in the micro channels or capillaries of the soil matrix, isotopic fractionation may take place under near-equilibrium conditions. This causes the observed relationship between δ2H and δ18O of the extracted water samples to have a slope close to 8. The results of this study may indicate that, in arid zones when soil that initially contains water dries out, the slope of the relationship between δ2H and δ18O values should be close to 8. Thus, a smaller slope, as observed by some groundwater and soil water samples in arid zones, may be caused by evaporation of water before the water has entered the unsaturated zone.

[High-concentration palmitic acid inhibits the proliferation of peripheral blood-derived human endothelial progenitor cells in vitro].

OBJECTIVE: To study the effects of palmitic acid (PA) on the proliferation of peripheral blood-derived endothelial progenitor cells (EPCs) in vitro. METHODS: The mononuclear cells (MNCs) were isolated from the peripheral blood by Ficoll density-gradient centrifugation. The isolated EPCs were characterized by Di-LDI uptake and FITC-lectin binding assay using laser confocal microscope, and further identified by detection of CD34, CD133 and VEGFR2 expression using flow cytometry. The cultured EPCs were incubated in the presence of PA at the concentrations of 0, 50, 100, 200, 400 and 800 micromol/L for different durations (0, 12, 24, 36, 48 and 60 h). The cell morphology was observed and cell proliferation determined with CCK-8 assay. RESULTS: Incubation with 400 and 800 micromol/L of PA significantly inhibited the proliferative ability of EPCs as compared with the control group (P < 0.05). PA at 400 micromol/L had the strongest effect on the cell proliferation, and this effect was intensified with the passage of time, reaching the peak at 48 h with the growth inhibition rate of 58.59% (P < 0.05). CONCLUSION: High-concentration PA can significantly inhibit the proliferation of EPCs in vitro.