Arsenic contamination of groundwater: A global synopsis with focus on the Indian Peninsula

More than 2.5 billion people on the globe rely on groundwater for drinking and providing high-quality drinking water has become one of the major challenges of human society.Although groundwater is considered as safe,high concentrations of heavy metals like arsenic(As) can pose potential human health concerns and hazards.In this paper, we present an overview of the current scenario of arsenic contamination of groundwater in various countries across the globe with an emphasis on the Indian Peninsula.With several newly affected regions reported during the last decade, a significant increase has been observed in the global scenario of arsenic contamination.It is estimated that nearly 108 countries are affected by arsenic contamination in groundwater(with concentration beyond maximum permissible limit of 10 ppb recommended by the World Health Organization.The highest among these are from Asia(32) and Europe(31), followed by regions like Africa(20), North America(11), South America(9) and Australia(4).More than 230 million people worldwide, which include 180 million from Asia, are at risk of arsenic poisoning.Southeast Asian countries, Bangladesh, India, Pakistan,China, Nepal, Vietnam, Burma, Thailand and Cambodia, are the most affected.In India, 20 states and 4 Union Territories have so far been affected by arsenic contamination in groundwater.An attempt to evaluate the correlation between arsenic poisoning and aquifer type shows that the groundwater extracted from unconsolidated sedimentary aquifers, particularly those which are located within the younger orogenic belts of the world, are the worst affected.More than 90% of arsenic pollution is inferred to be geogenic.We infer that alluvial sediments are the major source for arsenic contamination in groundwater and we postulate a strong relation with plate tectonic processes, mountain building, erosion and sedimentation.Prolonged consumption of arsenic-contaminated groundwater results in severe health issues like skin, lung, kidney and bladder cancer; coronary heart disease;bronchiectasis; hyperkeratosis and arsenicosis.Since the major source of arsenic in groundwater is of geogenic origin, the extend of pollution is complexly linked with aquifer geometry and aquifer properties of a region.Therefore, remedial measures are to be designed based on the source mineral, climatological and hydrogeological scenario of the affected region.The corrective measures available include removing arsenic from groundwater using filters, exploring deeper or alternative aquifers, treatment of the aquifer itself, dilution method by artificial recharge to groundwater, conjunctive use, and installation of nano-filter, among other procedures.The vast majority of people affected by arsenic contamination in the Asian countries are the poor who live in rural areas and are not aware of the arsenic poisoning and treatment protocols.Therefore, creating awareness and providing proper medical care to these people remain as a great challenge.Very few policy actions have been taken at international level over the past decade to reduce arsenic contamination in drinking water, with the goal of preventing toxic impacts on human health.We recommend that that United Nations Environment Programme(UNEP) and WHO should take stock of the global arsenic poisoning situation and launch a global drive to create awareness among people/medical professionals/health workers/administrators on this global concern.     

Garnet-staurolite-mica schist from Rangli Rangliot,Eastern Himalaya: Constraints from phase equilibria and Thermobarometry

Rangli Rangliot is an integral part of lesser Himalaya. The area around Rangli Rangliot consists of garnetstaurolite-mica schist and it is characterized by mineral assemblage garnet-biotite-muscovite-staurolite-quartz± plagioclase. Different reaction textures are of particular interest as they reflect discontinuous or continuous reactions under changing physical conditions. The relative X_Mg in the minerals varies in the order: muscovite> biotite> staurolite> garnet, and the X_Mn decreases in the order: garnet>staurolite>biotite>muscovite. The P-T evolution of the garnet-staurolite-mica schist has been constrained through the use of internally consistent TWEEQU programme and Perple_X software in the KFMASH model system. The combination of these two approaches demonstrates that the garnet-staurolite-mica schist experienced peak pressure and temperature at 5.8 kbar and 590 °C. The proposed clockwise P-T path implies that rocks from the study area could have resulted from thickened continental crust undergoing decompression.     

Solid sedimentation rates history of the Southern African continental margins: Implications for the uplift history of the South African Plateau

The Cretaceous and Cenozoic fill of the continental margins of southern Africa (South‐East Atlantic and Agulhas Margins) contains a continuous record of sediment supplied from the South African Plateau (SAP) for the past 134 million years. Estimates of solid sediment volumes deposited offshore were calculated from isopach maps and extrapolated vertical cross‐sections derived from a large amount of industrial geophysical data. Solid phase volumes and accumulation rates were calculated for six epochs: Lower Cretaceous (134–113 Ma), Mid Cretaceous (113–93.5 Ma), Upper Cretaceous (93.5–81 and 81–66 Ma), Palaeogene (66–25 Ma), Neogene (25–0 Ma). Our new compilation demonstrates the existence of two periods of elevated flux. The most important one occurs in the late Cretaceous (93.5–66 Ma) and was synchronous with an acceleration of onshore denudation as shown by thermochronometric data. After a period of extremely low accumulation rate, the second phase of elevated flux started in the Oligocene (~30–25 Ma) until present‐day. From these observations we suggest that the main phase of uplift of the SAP took place during the Upper Cretaceous. Two mechanisms, namely uplift caused by lithospheric delamination or by dynamic topography caused by the continent moving over the African Superplume, are viable explanations for our observations. The more recent and lower amplitude episode of enhanced accumulation rates is likely to correspond to a second period of uplift, potentially associated with the onset of uplift and extension along the East African Rift System.     

Stratigraphic responses to a major tectonic event in a foreland basin: the Ecuadorian Oriente Basin from Eocene to Oligocene times

The Eocene to Oligocene sediments of the Ecuadorian Oriente Basin record two kinds of second-order stratigraphic response to the tectonic evolution. Lower Eocene shows evidences of local scale syntectonic deposits. This tectonic activity can be related to right lateral convergent movements inverting pre-cretaceous extensional structures. Upper Eocene and Oligocene sediments are integrated as the expression of an isostatic rebound characterizing a basin scale syntectonic deposition. This response is evidenced by a reciprocal architecture of the depositional sequences identified in the sedimentary formations. These data have allowed us to propose a new geodynamic model for the Paleogene evolution of the Oriente Basin.     

Materializing post-colonial geographies: examining the textural landscapes of migration in the South Asian home

This paper considers the role of visual cultures in understanding the value of landscape to post-colonial migrants living in Britain. The paper also considers these visual cultures as prismatic devices which refract lived landscapes of South Asia and East Africa into British domestic scene. The visual cultures are investigated using a materialist lens. They are positioned as materials that allow embodied connections to landscapes experienced pre-migration, including sensory connections with past homes, natures and family life. These then become artefacts symbolising relationships with past landscapes, made meaningful in their presence in Britain homes. Using this materialist lens, visual cultures in the British Asian home, such as photographs, pictures, and paintings, are given meaning and value beyond their textual content. This paper is an exercise in reading visual cultures in the everyday through a materialist lens which allows for an examination of their place in the process of ‘making home' for South Asian women in Britain. In particular, objects presence the migratory experience of the South Asian community, importing ‘other' landscapes (previously shaped by colonial governance) into Britain, and help to shape environmental values, landscape imaginaries and South Asian landscapes of belonging in the post-colonial period.     

Miocene tidal-influenced sedimentation to continental Pliocene sedimentation in the forebulge–backbulge depozones of the Beni–Mamore foreland Basin (northern Bolivia)

Mio-Pliocene deposits of the forebulge–backbulge depozones of the Beni-Mamore foreland Basin indicate tidally to fluvially dominated sedimentation. Seven facies assemblages have been recognized: FAA–FAG. FAA represents a distal bottom lake assemblage, FAB and FAD are interpreted as tidal flat deposits, FAC and FAG are interpreted as fluvial systems, FAE sediments are deposited in a subtidal/shoreface setting, and FAG represents a meandering fluvial system. The identification of stratigraphic surfaces (SU, MFS, and MRS) and the relationship among the facies assemblages permit the characterization of several systems tracts: a falling-stage systems tract (FSST) followed by a lowstand systems tract (LST), a transgressive systems tract (TST), and a highstand systems tract (HST). The FSST and LST may have been controlled by the uplift of the Beni-Mamore forebulge, whereas TST may result from a quiescent stage in the forebulge. Subaerial unconformity two (SU2) records the passage from a tide-influenced depositional system to a fully continental depositional system. The Miocene tidal-influenced deposits in the Beni–Mamore Basin suggest that it experienced a connection, either with the South Atlantic Ocean or the Caribbean Sea or both.     

Tracing ionic sources and geochemical evolution of groundwater in the Intermountain Una basin in outer NW Himalaya,Himachal Pradesh,India

The present research aims to identify sources of ions and factors controlling the geochemical evolution of groundwater in an intermountain basin, comprising hill and valley fill region, of Outer Himalaya in Himachal Pradesh, India. The groundwater samples collected from 81 tubewells and handpumps are analyzed for major ions, trace metals and stable isotopes (δ¹⁸O and δD). Geochemically the dominant hydrochemical facies in the Una basin are Ca–HCO₃, Ca–Mg–HCO₃ and Na–Cl types at few locations. A relatively lower ionic concentration in the valley fills indicates dilution and low residence time of water to interact with the aquifer mass due to high porosity and permeability. The ionic ratios of 0.9, 0.8 and 3.8 to 5.7, respectively, for (Ca?+?Mg): HCO₃, (Ca?+?Mg): (HCO₃?+?SO₄) and Na: Cl, suggests that ionic composition of groundwater is mainly controlled by rock weathering of, particularly by dissolution/precipitation of calcrete and calcite hosted in rock veins and Ca–Na feldspar hosted in conglomerate deposits derived from the Higher and Lesser Himalaya during the formation of Siwalik rocks. Although Na, K, NO₃ and SO₄ are introduced in the groundwater through agricultural practices, Na has also been introduced through ion exchange processes that have occurred during water–rock interaction, as indicated by negative CAI values. Factor analysis further suggests three major factors affecting the water chemistry of the area. The first two factors are associated with rock weathering while the third is anthropogenic processes associated with high nitrate and iron concentration. High concentrations of Fe and Mn ions that are exceeded that of WHO and BIS standards are also present at few locations. The recharge of groundwater in the Outer Himalaya is entirely through Indian Southwest Monsoon (ISM) and depleted ratios of δ¹⁸O/δD in valley region indicate infiltration from irrigation in recharging the groundwater and fractionation of isotopes of precipitation due to evaporation before infiltration. High d-excess values and inverse relation with δ¹⁸O are indicative of secondary evaporation of precipitation during recharge of groundwater.     

Chemical weathering and carbon dioxide consumption in a small tropical river catchment,southwestern India

Aquatic Geochemistry - Studies done on small tropical west-flowing river catchments located in the Western Ghats in southwestern India have suggested very intense chemical weathering rates and...