Amit K. Kundu

Hydrogeochemical contrast between brown and grey sand aquifers in shallow depth of Bengal Basin: consequences for sustainable drinking water supply.

Delineation of safe aquifer(s) that can be targeted by cheap drilling technology for tubewell (TW) installation becomes highly imperative to ensure access to safe and sustainable drinking water sources for the arsenic (As) affected population in Bengal Basin. This study investigates the potentiality of brown sand aquifers (BSA) as a safe drinking water source by characterizing its hydrogeochemical contrast to grey sand aquifers (GSA) within shallow depth (<70 m) over an area of 100 km(2) in Chakdaha Block of Nadia district, West Bengal, India. The results indicate that despite close similarity in major ion composition, the redox condition is markedly different in groundwater of the two studied aquifers. The redox condition in the BSA is delineated to be Mn oxy-hydroxide reducing, not sufficiently lowered for As mobilization into groundwater. In contrast, the enrichments of NH(4)(+), PO(4)(3-), Fe and As along with lower Eh in groundwater of GSA reflect reductive dissolution of Fe oxy-hydroxide coupled to microbially mediated oxidation of organic matter as the prevailing redox process causing As mobilization into groundwater of this aquifer type. In some portions of GSA the redox status even has reached to the stage of SO(4)(2-) reduction, which to some extent might sequester dissolved As from groundwater by co-precipitation with authigenic pyrite. Despite having low concentration of As in groundwater of the BSA the concentration of Mn often exceeds the drinking water guidelines, which warrants rigorous assessment of attendant health risk for Mn prior to considering mass scale exploitation of the BSA for possible sustainable drinking water supply.

Shallow hydrostratigraphy in an arsenic affected region of Bengal Basin : implication for targeting safe aquifers for drinking water supply

To delineate arsenic (As) safe aquifer(s) within shallow depth, the present study has investigated the shallow hydrostratigraphic framework over an area of 100 km(2) at Chakdaha Block of Nadia District, West Bengal. Drilling of 29 boreholes and subsequent hydrostratigraphic modeling has identified three types of aquifer within 50 m below ground level (bgl). Aquifer-1 represents a thick paleochannel sequence, deposited parallel to the River Hooghly and Ichamati. Aquifer-2 is formed locally within the overbank deposits in the central floodplain area and its vertical extension is strictly limited to 25 m bgl. Aquifer-3 is distributed underneath the overbank deposits and represents an interfluvial aquifer of the area. Aquifer-3 is of Pleistocene age (~70 ka), while aquifer-1 and 2 represent the Holocene deposits (age <9.51 ka), indicating that there was a major hiatus in the sediment deposition after depositing the aquifer-3. Over the area, aquifer-3 is markedly separated from the overlying Holocene deposits by successive upward sequences of brown and olive to pale blue impervious clay layers. The groundwater quality is very much similar in aquifer-1 and 2, where the concentration of As and Fe very commonly exceeds 10 μg/L and 5 mg/L, respectively. Based on similar sediment color, these two aquifers have jointly been designated as the gray sand aquifer (GSA), which constitutes 40% (1.84×10(9) m(3)) of the total drilled volume (4.65×10(9) m(3)). In aquifer-3, the concentration of As and Fe is very low, mostly <2 μg/L and 1mg/L, respectively. This aquifer has been designated as the brown sand aquifer (BSA) according to color of the aquifer materials and represents 10% (4.8×10(8) m(3)) of the total drilled volume. This study further documents that though the concentration of As is very low at BSA, the concentration of Mn often exceeds the drinking water guidelines.

Is Saliva a Potential Biomarker of Arsenic Exposure? A Case-Control Study in West Bengal, India

Saliva is a biological fluid that has not been used extensively as a biomonitoring tool in epidemiological studies. This study presents the arsenic (As) concentrations in saliva and urine samples collected from populations of West Bengal, India who had been previously exposed to high As levels in their drinking water. We found a significant (p < 0.05) association between the Log transformed Daily Ingestion of As (μg day(-1)) and the As concentration in saliva (r = 0.68). Additionally, As concentration of saliva and urine also had a significant positive correlation (r = 0.60, p < 0.05). Male participants, smokers, and cases of skin lesion were independently and significantly associated with an increase in salivary As. Thus our findings show that saliva is a useful biomarker of As exposure in the study population. The study also advocates that measurement of the forms of As in saliva may additionally provide insight into the internal dose and any individual differences in susceptibility to As exposure.

Assessment of toxic metals in groundwater and saliva in an arsenic affected area of West Bengal, India: A pilot scale study

Communities in many parts of the world are unintentionally exposed to arsenic (As) and other toxic metals through ingestion of local drinking water and foods. The concentrations of individual toxic metals often exceed their guidelines in drinking water but the health risks associated with such multiple-metal exposures have yet to receive much attention. This study examines the co-occurrence of toxic metals in groundwater samples collected from As-rich areas of Nadia district, West Bengal, India. Arsenic in groundwater (range: 12-1064 µg L(-1); mean ± S.D: 329±294 µg L(-1)) was the most important contaminant with concentrations well above the WHO guideline of 10 µg L(-1). Another important toxic metal in the study area was manganese (Mn) with average concentration of 202±153 µg L(-1), range of 18-604 µg L(-1). The average concentrations (µg L(-1)) of other elements in groundwater were: Cr (5.6±5.9), Mo (3.5±2.1), Ni (8.3±8.7), Pb (2.9±1.3), Ba (119±43), Zn (56±40), Se (0.60±0.33), U (0.50±0.74). Saliva collected from the male participants of the area had mean concentrations of 6.3±7.0 µg As L(-1) (0.70-29 µg L(-1)), 5.4±5.5 µg Mn L(-1) (0.69-22 µg L(-1)), 2.6±3.1 µg Ni L(-1) (0.15-13 µg L(-1)), 0.78±1.0µg Cr L(-1) (<DL-5.9 µg L(-1)), 0.94±0.90 µg Pb L(-1) (<DL-4.2 µg L(-1)), 0.56±0.37 µg Se L(-1) (0.11-1.5 µg L(-1)) and 194±54 µg Zn L(-1) (112-369 µg L(-1)). The high concentrations of salivary As and Mn are believed to be indicative of intake from the groundwater. The clustering of salivary As and Mn in principal component analysis further indicated influence of the common exposure source. Zinc and selenium comprised a separate component presumably reflecting the local deficiencies in intakes of these essential elements from drinking water and foodstuff. Thus the study reveals that the concentration of other metals beside As must be monitored in drinking water before implementation of any policies to provide safe water to the affected communities.

Arsenic retention in cooked rice: Effects of rice type, cooking water, and indigenous cooking methods in West Bengal, India

This study evaluated the concentration of arsenic in paired raw and cooked rice prepared by individual households in arsenic-endemic rural area of West Bengal. The aim was to investigate how the cooking habits of rural villagers of West Bengal might influence the arsenic content of rice meals. It was found that the use of arsenic-rich groundwater for cooking could elevate the arsenic concentration in cooked rice (up to 129% above the raw sample), thereby enhancing the vulnerability of the rural population of West Bengal to arsenic exposure through rice consumption. The risk is heightened by the habit of drinking the stewed rice water (gruel) in the local communities. The cooking method employed, rice variety, background arsenic concentration in raw rice and cooking water arsenic concentration were found to be important predisposing factors that could affect the accumulation of arsenic in cooked form. The fundamental indigenous cooking practice followed by the villagers requires use of low-arsenic water for cooking as a necessary strategy to alleviate arsenic exposure in their staple food.

Arsenic in Groundwater: Distribution and Geochemistry in Nadia District, West Bengal, India

Groundwater in Bengal Delta Plain (BDP; West Bengal and Bangladesh) is contaminated with geogenic arsenic (As). Shallow aquifers ( 10 µg L−1) for community water supply. In this context, deeper aquifer is the most reliable source of safer water as remediation technologies are in many cases incapable of yielding arsenic-safe water.

Optimisation of laboratory arsenic analysis for groundwaters of West Bengal, India and possible water testing strategy

ABSTRACT Regular monitoring of arsenic (As) in groundwater is crucial from public health perspectives as millions of people are suffering due to use of contaminated aquifer water for drinking purposes. The routine analyses, especially in developing nations, are mostly done in localised government/non-government laboratories with limited resources, having the target of analysing large number of samples in each run. Thus apart from analytical sensitivity, cost-effectiveness of the method and eco-friendliness of the experimental operation are key surreptitious factors. This demands optimisation of total As measurement methods and finding a method that gives ‘optimum benefit’ considering all these factors together. The present study therefore evaluates four common As (total) measurement methods [iodometric-colorimetric method, silver diethyl dithiocarbamate method, molybdenum blue method and hydride generation atomic absorption spectrophotometric (HG-AAS) method] practised in the Bengal Delta Plain, in view of their analytical sensitivity, related environmental hazard and experimental costs. It was found that the HG-AAS method is analytically more sensitive, whereas the iodometric-colorimetric method and the molybdenum blue method are better choices in terms of eco-friendliness and cost-effectiveness, respectively. However, when all three factors (analytical reliability, environmental hazard and cost) are considered simultaneously, the molybdenum blue method was found to be placed first in the ‘optimum performance rank’ list. It was also found that both environmental hazard and cost play a more crucial role than analytical reliability, although this is case specific and would differ from place to place around the globe. Finally based on the results, we have hypothesised a water testing strategy for developing countries such as India where the molybdenum blue method can be adapted as a screening method and later the HG-AAS method can be used to precisely identify the groundwater samples with As concentration below the WHO drinking water guideline value of 10 μg/L.