Groundwater Quality beneath an Asian Megacity on a Delta: Kolkata's (Calcutta's) Disappearing Arsenic and Present Manganese.

Kolkata, the capital city of West Bengal, exploits groundwater for public water-supply. The groundwater has been reported to be widely polluted by arsenic (As). Analysis for As in 280 groundwaters from across Kolkata, failed to detect As concentrations >10 µg/L from natural processes. Arsenic concentrations between 10 and 79 µg/L found in 14 of the 280 groundwaters are remnant from a pollution-plume emanating from a single factory site where Paris Green, an arsenical pesticide, was manufactured between 1965 and 1985. In 45% of groundwaters sampled, concentrations of Mn exceed 0.4 mg/L, a putative health guideline value for drinking water. Sporadic minor hazards are posed by Pb > 10 µg/L introduced into groundwater from well-fittings, from 4% of groundwaters with F concentrations between 0.75 and 1 mg/L, and the 14% of groundwaters containing more than 500 mg/L Na, concentrations that might contribute to excessive daily intake of Na. Compounding hazards from As, F, Mn, Na, and Pb, shows that 64% of public wells and 40% of municipal wells supply groundwater of suspect quality. Groundwaters comply with WHO Guideline Values for drinking water in terms of Cr, Cu, Co, NO2, NO3, Sb, Se, and U. Aesthetic guideline values for Fe, Mn, SO4, and Cl are exceeded for many groundwaters.

Arsenic in Groundwater: The Deep Late Pleistocene Aquifers of the Western Bengal Basin.

in groundwaters from 145 wells across central West Bengal, India, those from Pleistocene aquifers at depths >70 m beneath paleo-interfluves contain <10 µg/L As. Pleistocene aquifers beneath deep paleo-channels typically host groundwaters containing 10-100 µg/L As at depths between 120 and 180 m. The depth profiles of As and SO4 and the conservative tracers Cl/Br, δ(18)O, and δ(2)H show that the As in Pleistocene groundwater beneath deep paleo-channels is relict and does not arise from migration downward of As-polluted groundwater in overlying aquifers. We postulate that the As was liberated in situ by reduction of minimal iron oxyhydroxides in the gray Pleistocene sands by organic matter infiltrating from riverbeds during late Pleistocene or earliest Holocene times. Mitigation of the widespread As-pollution in shallow aquifers through exploitation of deep Pleistocene aquifers would improve if guided by an understanding of the distribution of buried paleo-channels and paleo-interfluves and the knowledge that As may be present naturally in groundwater at depths >150 m beneath deep paleo-channels.

Palaeosol Control of Arsenic Pollution: The Bengal Basin in West Bengal, India.

Groundwater in the Bengal Basin is badly polluted by arsenic (As) which adversely affects human health. To provide low-As groundwater for As mitigation, it was sought across 235 km(2) of central West Bengal, in the western part of the basin. By drilling 76 boreholes and chemical analysis of 535 water wells, groundwater with <10 µg/L As in shallow aquifers was found under one-third of a study area. The groundwater is in late Pleistocene palaeo-interfluvial aquifers of weathered brown sand that are capped by a palaeosol of red clay. The aquifers form two N-S trending lineaments that are bounded on the east by an As-polluted deep palaeo-channel aquifer and separated by a shallower palaeo-channel aquifer. The depth to the top of the palaeo-interfluvial aquifers is mostly between 35 and 38 m below ground level (mbgl). The palaeo-interfluvial aquifers are overlain by shallow palaeo-channel aquifers of gray sand in which groundwater is usually As-polluted. The palaeosol now protects the palaeo-interfluvial aquifers from downward migration of As-polluted groundwater in overlying shallow palaeo-channel aquifers. The depth to the palaeo-interfluvial aquifers of 35 to 38 mbgl makes the cost of their exploitation affordable to most of the rural poor of West Bengal, who can install a well cheaply to depths up to 60 mbgl. The protection against pollution afforded by the palaeosol means that the palaeo-interfluvial aquifers will provide a long-term source of low-As groundwater to mitigate As pollution of groundwater in the shallower, heavily used, palaeo-channel aquifers. This option for mitigation is cheap to employ and instantly available.

Stable groundwater quality in deep aquifers of Southern Bangladesh: the case against sustainable abstraction.

In forty six wells >150 m deep, from across the arsenic-polluted area of south-central Bangladesh, groundwater composition remained unchanged between 1998 and 2011. No evidence of deteriorating water quality was found in terms of arsenic, iron, manganese, boron, barium or salinity over this period of 13 years. These deep tubewells have achieved operating lives of more than 20 years with minimal institutional support. These findings confirm that tubewells tapping the deep aquifers in the Bengal Basin provide a safe, popular, and economic, means of arsenic mitigation and are likely to do so for decades to come. Nevertheless, concerns remain about the sustainability of a resource that could serve as a source of As-safe water to mitigate As-pollution in shallower aquifers in an area where tens of millions of people are exposed to dangerous levels of arsenic in well water. The conjunction of the stable composition in deep groundwater and the severe adverse health effects of arsenic in shallow groundwater lead us to challenge the notion that strong sustainability principles should be applied to the management of deep aquifer abstraction in Bangladesh is, the notion that the deep groundwater resource should be preserved for future generations by protecting it from adverse impacts, probably of a minor nature, that could occur after a long time and might not happen at all. Instead, we advocate an ethical approach to development of the deep aquifer, based on adaptive abstraction management, which allows possibly unsustainable exploitation now in order to alleviate crippling disease and death from arsenic today while also benefiting future generations by improving the health, education and economy of living children.

Waste-water impacts on groundwater: Cl/Br ratios and implications for arsenic pollution of groundwater in the Bengal Basin and Red River Basin, Vietnam.

Across West Bengal and Bangladesh, concentrations of Cl in much groundwater exceed the natural, upper limit of 10 mg/L. The Cl/Br mass ratios in groundwaters range up to 2500 and scatter along mixing lines between waste-water and dilute groundwater, with many falling near the mean end-member value for waste-water of 1561 at 126 mg/L Cl. Values of Cl/Br exceed the seawater ratio of 288 in uncommon NO(3)-bearing groundwaters, and in those containing measurable amounts of salt-corrected SO(4) (SO(4) corrected for marine salt). The data show that shallow groundwater tapped by tube-wells in the Bengal Basin has been widely contaminated by waste-water derived from pit latrines, septic tanks, and other methods of sanitary disposal, although reducing conditions in the aquifers have removed most evidence of NO(3) additions from these sources, and much evidence of their additions of SO(4). In groundwaters from wells in palaeo-channel settings, end-member modelling shows that >25% of wells yield water that comprises ≥10% of waste-water. In palaeo-interfluvial settings, only wells at the margins of the palaeo-interfluvial sequence contain detectable waste water. Settings are identifiable by well-colour survey, owner information, water composition, and drilling. Values of Cl/Br and faecal coliform counts are both inversely related to concentrations of pollutant As in groundwater, suggesting that waste-water contributions to groundwater in the near-field of septic-tanks and pit-latrines (within 30 m) suppress the mechanism of As-pollution and lessen the prevalence and severity of As pollution. In the far-field of such sources, organic matter in waste-water may increase groundwater pollution by As.

The palaeosol model of arsenic pollution of groundwater tested along a 32 km traverse across West Bengal, India.

The distribution of As-pollution in groundwater of the deltaic aquifers of south-eastern Asia may be controlled by the subsurface distribution of palaeo-channel sediments (As-polluted groundwaters) and palaeo-interfluvial sediments (As-free groundwaters). To test this idea, termed the palaeosol model of As-pollution, we drilled 10 sites, analysed groundwater from 249 shallow wells (screened <107 mbgl), field-tested another 149 for As, and used colour as a guide to the presence or absence of As-pollution in a further 531 wells. Our work was conducted along a 32-km traverse running W to E across southern West Bengal, India. At seven drill sites we logged a palaeo-interfluvial sequence, which occurs as three distinct units that together occupy 20 km of the traverse. These palaeo-interfluvial sequences yield As-free groundwaters from brown sands at depth<100 m. The palaeo-interfluvial sequences are separated by two deep palaeo-channels, which were logged at 3 sites. The palaeo-channel deposits host As-polluted groundwater in grey sands. Our findings confirm the predictions of the palaeosol model of As-pollution. We show again that well-colour can be used both to successfully predict the degree of As-pollution in groundwater, and to locate regions of buried palaeo-interfluve that will yield As-free groundwater for the foreseeable future.

Sedimentological control on Mn, and other trace elements, in groundwater of the Bengal delta.

To reveal what controls the concentration and distribution of possibly hazardous (Mn, U, Se, Cd, Bi, Pb) and nonhazardous (Fe, V, Mo, PO(4)) trace elements in groundwater of the Bengal delta, we mapped their concentrations in shallow groundwater (<60 mbgl) across 102 km(2) of West Bengal. Only Mn is a potential threat to health, with 55% of well water exceeding 0.3 mg/L, the current Indian limit for drinking water in the absence of an alternate source, and 75% exceeding the desirable limit of 0.1 mg/L. Concentrations of V are <3 µg/L. Concentrations of U, Se, Pb, Ni, Bi, and Cd, are below WHO guideline values. The distributions of Fe, Mn, As, V, Mo, U, PO(4), and δ(18)O in groundwater reflect subsurface sedimentology and sources of water. Areas of less negative δ(18)O reveal recharge by sources of evaporated water. Concentrations of Fe, As, Mo, and PO(4) are high in palaeo-channel groundwaters and low in palaeo-interfluvial groundwaters. Concentrations of U, V, and Mn, are low in palaeo-channel groundwaters and high in palaeo-interfluvial groundwaters. Concentrations of Fe and Mn are highest (18 and 6 mg/L respectively) at dual reduction-fronts that form strip interfaces at depth around the edges of palaeo-interfluvial aquifers. The fronts form as focused recharge carries dissolved organic carbon into the aquifer margins, which comprise brown, iron-oxide bearing, sand. At the Mn-reduction front, concentrations of V and Mo reach peak concentrations of 3 µg/L. At the Fe-reduction front, concentrations of PO(4) and As reach concentrations 3 mg/L and 150 µg/L respectively. Many groundwaters contain >10 mg/L of Cl, showing that they are contaminated by Cl of anthropogenic origin and that organic matter from in situ sanitation may contribute to driving reduction.

Migration of As, and (3)H/(3)He ages, in groundwater from West Bengal: Implications for monitoring.

From 2002 to 2010 inclusive we monitored concentrations of arsenic (As) and major ions (Ca, Mg, Sr, Na, K, Fe, Mn, Cl, and SO(4)) in groundwater from 14 domestic wells and three piezometer nests in a shallow aquifer (<60 m depth), and 3 wells in a deep aquifer (>70 m depth), in southern West Bengal, India. In the deep aquifer, concentrations of As did not change over time despite increases in the concentration of Fe in two wells. The shallow aquifer occurs in two sedimentological settings: palaeo-channel and palaeo-interfluve. At the top of the shallow aquifer of the palaeo-channel, decreases in all constituent concentrations with time, and an (3)H/(3)He age of 1.4 years, proves that the aquifer is beginning to be flushed of pollutants. In As-polluted groundwater (>50 microg/L As) tapped from deeper grey sands of the shallow, palaeo-channel, aquifer, concentrations of As were mostly stable over time, but both increases and decreases occurred with time in response to downward migration of the chemically-stratified water column. In groundwater tapped from Pleistocene brown sands, the concentration of As remained either low and stable (<2 microg/L As), or increased at rates up to 34 microg/L per year. The increases were caused by the flow of As-rich groundwater either downward into brown sand at the base of palaeo-channels, or laterally into a confined, unpolluted, palaeo-interfluvial, aquifer of brown sand that lies regionally beneath a palaeosol. Under the present pumping regime, the prognosis for As-pollution in the shallow aquifer is complex. Wells in brown sand may become polluted over timescales of as little as 2 years, whilst some wells tapping As-polluted groundwater from grey sand will become fit for potable use (<50 microg/L) within a few decades. The evidence of flushing, and of declining As in some of the groundwater from palaeo-channels, which are conduits for recharge of the confined, As-free, palaeo-interfluve aquifer, and probably also the deeper aquifer, offers hopes that the spread of As-pollution will be limited.

Do ponds cause arsenic-pollution of groundwater in the Bengal basin? An answer from West Bengal.

We report time-series data collected over two years for delta18O, delta2H, and Ca, Mg, K, and Cl, concentrations for 10 ponds in, and upflow of, an As-polluted region of southern West Bengal. We compare the compositions of As-polluted groundwaters from wells with the compositions of waters in ponds upflow, and within the range of influence, of the wells. Conservative tracers (delta18O, delta2H, K), and other tracers (Ca, Mg) that are likely conservative in the waters, showthat pondwater and groundwater are distinct and do not overlap in composition. These data show that water from ponds cannot be identified in As-polluted groundwater, so putative DOC in pondwater cannot be mixing into the As-polluted groundwater we have sampled. Separate estimates of the degree of recharge from ponds to groundwater, using calculations based on temporal variations in salt content and isotopic composition in ponds, and salt-balance, show that insignificant amounts of As-polluted groundwater are derived via pond recharge. It follows that pondwater in the study area does not contribute significant mass to arsenic-polluted groundwater and so does not provide organic matterto aquifers in amounts sufficientto drive reduction of iron oxyhydroxides and hence arsenic pollution.

Effects of electromyographic biofeedback on reaction time and movement time.

The effects of electromyographic (EMG) biofeedback on reaction time (RT) and movement time (MT) were investigated utilizing 42 right-handed, male subjects from a university population. Subjects were randomly divided into three groups, a control group and two experimental groups. Both experimental groups were exposed to their EMG signals from their triceps brachii during the task, one experimental group received written information explaining the purpose of the EMG was to improve performance through biofeedback. Reaction times of the first block of 25 trials were significantly faster than those on the subsequent three blocks of trials for all groups. This provided evidence of learning. No other significant effects for reaction times were observed. Mean movement time for the EMG-only group was significantly slower than the means of either the Control group or EMG-Biofeedback group, with no difference between the latter two. The differences between experimental groups may have been related to alteration of strategy, anxiety, motivation.