RESUMEN

Hydrous fluids play a vital role in the chemical and rheological evolution of ductile, quartz-bearing continental crust, where fluid percolation pathways are controlled by grain boundary domains. In this study, widths of grain boundary domains in seven quartzite samples metamorphosed under varying crustal conditions were investigated using Atomic Force Microscopy (AFM) which allows comparatively easy, high magnification imaging and precise width measurements. It is observed that dynamic recrystallization at higher metamorphic grades is much more efficient at reducing grain boundary widths than at lower temperature conditions. The concept of force-distance spectroscopy, applied to geological samples for the first time, allows qualitative estimation of variations in the strength of grain boundary domains. The strength of grain boundary domains is inferred to be higher in the high grade quartzites, which is supported by Kernel Average Misorientation (KAM) studies using Electron Backscatter Diffraction (EBSD). The results of the study show that quartzites deformed and metamorphosed at higher grades have narrower channels without pores and an abundance of periodically arranged bridges oriented at right angles to the length of the boundary. We conclude that grain boundary domains in quartz-rich rocks are more resistant to fluid percolation in the granulite rather than the greenschist facies.

RESUMEN

Fluoride contamination in groundwater is a major problem throughout the world as well as in India. High-fluoride content was reported in the hot springs of Atri and Tarbalo sites in Odisha, India, and residents of nearby villages showed the manifestations of fluorosis. Around 39% of the groundwater samples showed fluoride concentration > 1 mg/l, higher than the desirable limit specified by the WHO. The dominant chemical facies of groundwaters were ions of Ca-Mg-HCO3 and Ca-Na-Cl, which infers the lithological control over the hydrochemistry of this area. A strong correlation between fluoride and other major ions could not be found, suggesting that multiple processes are responsible for the enriched fluoride concentration observed in the study area. The major geochemical processes include dissolution of fluoride-bearing minerals from the rocks, evapotranspiration, agricultural input and mixing of cold groundwater with hot spring water containing high fluoride. The maximum fluoride exposure doses through drinking water from fluoride-contaminated tube wells were estimated to be 0.07 mg/kg/d for infants, 0.125 mg/kg/d for children and 0.06 mg/kg/d for adults, which are higher than the minimum risk level (0.05 mg/kg/d). Exposure doses of fluoride indicate that exposure risk is doubled for children in comparison to infants and adults, which might cause severe dental fluorosis and other ailments. Considering the environmental and hydrological set up of the study area, membrane defluoridation process can be suggested as the best remediation method. Nalgonda technique, dilution of fluoride-rich groundwater and better nutrition containing calcium and vitamin C are other possible options that can be included for early mitigation of fluoride contamination.

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RESUMEN

Existence of wide spread elevated concentrations of groundwater arsenic (As) across South Asia, including India, has endangered a huge groundwater-based drinking water dependent population. Here, using high-spatial resolution As field-observations (~3 million groundwater sources) across India, we have delineated the regional-scale occurrence of elevated groundwater As (≥10 µg/L), along with the possible geologic-geomorphologic-hydrologic and human-sourced predictors that influence the spatial distribution of the contaminant. Using statistical and machine learning method, we also modeled the groundwater As concentrations probability at 1 Km resolution, along with probabilistic delineation of high As-hazard zones across India. The observed occurrence of groundwater As was found to be most strongly influenced by geology-tectonics, groundwater-fed irrigated area (%) and elevation. Pervasive As contamination is observed in major parts of the Himalayan mega-river Indus-Ganges-Brahmaputra basins, however it also occurs in several more-localized pockets, mostly related to ancient tectonic zones, igneous provinces, aquifers in modern delta and chalcophile mineralized regions. The model results suggest As-hazard potential in yet-undetected areas. Our model performed well in predicting groundwater arsenic, with accuracy: 82% and 84%; area under the curve (AUC): 0.89 and 0.88 for test data and validation datasets. An estimated ~90 million people across India are found to be exposed to high groundwater As from field-observed data, with the five states with highest hazard are West Bengal (28 million), Bihar (21 million), Uttar Pradesh (15 million), Assam (8.6 million) and Punjab (6 million). However it can be much more if the modeled hazard is considered (>250 million). Thus, our study provides a detailed, quantitative assessment of high groundwater As across India, with delineation of possible intrinsic influences and exogenous forcings. The predictive model is helpful in predicting As-hazard zones in the areas with limited measurements.

RESUMEN

High groundwater arsenic (As) across the globe has been one of the most well researched environmental concerns during the last two decades. Consequently, a large scientific knowledge-base has been developed on As distributions from local to global scales. However, differences in bulk sediment As concentrations cannot account for the As concentration variability in groundwater. Instead, in general, only aquifers in sedimentary basins adjacent to mountain chains (orogenic foreland basins) along continental convergent tectonic margins are found to be As-enriched. We illustrate this association by integrating observations from long-term studies of two of the largest orogenic systems (i.e., As sources) and the aquifers in their associated foreland basins (As sinks), which are located in opposite hemispheres and experience distinct differences in climate and land-use patterns. The Andean orogenic system of South America (AB), an active continental margin, is in principle a modern analogue of the Himalayan orogenic system associated with the Indus-Ganges-Brahmaputra river systems in South Asia (HB). In general, the differences in hydrogeochemistry between AB and HB groundwaters are conspicuous. Major-solute composition of the arid, oxic AB groundwater exhibits a mixed-ion hydrochemical facies dominated by Na-Ca-Cl-SO4-HCO3. Molar calculations and thermodynamic modeling show that although groundwater of AB is influenced by cation exchange, its hydrochemical evolution is predominated by feldspar dissolution and relationships with secondary clays. In contrast, humid, strongly reducing groundwater of HB is dominated by Ca-HCO3 facies, suggestive of calcite dissolution, along with some weathering of silicates (monosiallitization). This work demonstrates that although hydrogeochemical evolutionary trends may vary with local climate and lithology, the fundamental similarities in global tectonic settings can still lead to the elevated concentrations of groundwater As.

RESUMEN

More than 100 million people around the world are endangered by geogenic arsenic (As) in groundwater, residing in sedimentary aquifers. However, not all sedimentary aquifers are groundwater As enriched, and the ultimate source of As in enriched aquifer sediments is yet-unknown, globally. A reconnaissance of the major aquifers suggests that major As enriched aquifers are predictably systematic on a global scale, existing in sedimentary foreland basins in the vicinity of modern or ancient orogenic systems. In conformity with the Principle of Uniformitarianism, we demonstrate that the groundwater As comes from magmatic arcs (primary source) in present (e.g. Andes) or ancient (e.g. Himalaya) continental convergent margins of some of the most prominent orogenic systems across the globe, and ends up in sediments (secondary source) in adjoining foreland or related basins that eventually act as aquifers. These arc magmas scavenge As while rising through the deep continental crust. Erosion of such orogens ultimately increases the bulk As content in sediments of adjoining basins, leading to groundwater As enrichment in downstream aquifers. Such As-polluted aquifers are eventually extensively used for groundwater exploitation, for drinking and other human purposes. Surface geological and biogeochemical processes, like redox reactions, are conducive to such groundwater As enrichment. We suggest this model by integrating our study of long-time observations in Himalayan and Andean basin aquifers, and generalizing 63 major aquifers across the globe, to demonstrate the source-to-sink transport of As, thereby delineating it's geogenic cycling in the subsurface. This work outlines the specifics of the mechanisms that would drive the processes of groundwater As enrichment across spatio-temporal scales, i.e. tectonic-scale taking place over millions of years on continental-scale and groundwater pollution taking place at human time-scales on village to household scale. Thus, in this work, we demonstrate a direct evidence of connectivity between global geological processes and individual human health.

RESUMEN

Forensic medicine deals both the living (eg, sexual assaults) as well as dead (eg, rape followed by murder) and drug induced death cases. In drug induced death or sexual assault cases some of the victims are sufferers of AIDS. HIV transmission occurs more in free and unlimited sex. Some points are to be remembered as the safety devices while a case of suspected HIV person is examined or autopsy is conducted. These points are elaborated in this article. Some legal implications are looked into while handling such cases with evidence of AIDS. These are also discussed.

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