Debashis Chatterjee

Role of metal-reducing bacteria in arsenic release from Bengal delta sediments

The contamination of ground waters, abstracted for drinking and irrigation, by sediment-derived arsenic threatens the health of tens of millions of people worldwide, most notably in Bangladesh and West Bengal. Despite the calamitous effects on human health arising from the extensive use of arsenic-enriched ground waters in these regions, the mechanisms of arsenic release from sediments remain poorly characterized and are topics of intense international debate. We use a microscosm-based approach to investigate these mechanisms: techniques of microbiology and molecular ecology are used in combination with aqueous and solid phase speciation analysis of arsenic. Here we show that anaerobic metal-reducing bacteria can play a key role in the mobilization of arsenic in sediments collected from a contaminated aquifer in West Bengal. We also show that, for the sediments in this study, arsenic release took place after Fe(iii) reduction, rather than occurring simultaneously. Identification of the critical factors controlling the biogeochemical cycling of arsenic is one important contribution to fully informing the development of effective strategies to manage these and other similar arsenic-rich ground waters worldwide.

Occurrence of Arsenic-contaminatedGroundwater in Alluvial Aquifers from Delta Plains, Eastern India: Options for Safe Drinking Water Supply

Abstract Arsenic contamination in groundwater used for drinking purposes has been envisaged as a problem of global concern. Exploitation of groundwater contaminated with arsenic within the delta plains in West Bengal has caused adverse health effects among the population within a span of 8-10 years. The sources of arsenic in natural water are a function of the local geology, hydrology and geochemical characteristics of the aquifers. The retention and mobility of different arsenic species are sensitive to varying redox conditions. The delta plains in West Bengal are characterized by a series of meander belts formed by the fluvial processes comprising different cycles of complete or truncated fining upward sequences (sand-silt-clay). The arseniferous groundwater belts are mainly located in the upper delta plain and in abandoned meander channels. Mineralogical investigations have established that arsenic in the silty clay as well as in the sandy layers occurs as coatings on mineral grains. Clayey sediments i...

Remediation of inorganic arsenic in groundwater for safe water supply: a critical assessment of technological solutions.

Arsenic contaminations of groundwater in several parts of the world are the results of natural and/or anthropogenic sources, and have a large impact on human health. Millions of people from different countries rely on groundwater containing As for drinking purposes. This paper reviews removal technologies (oxidation, coagulation flocculation, adsorption, ion exchange and membrane processes) with attention for the drawbacks and limitations of these applied technologies. The technologies suggested and applied for treatment of As rich water have various problems, including the need for further treatment of As containing secondary waste generated from these water treatment processes. More efficient technologies, with a lower tendency to generate waste include the removal of As by membrane distillation or forward osmosis, instead of using pressure driven membrane processes and subsequently reducing soluble As to commercially valuable metallic As are surveyed. An integrated approach of two or more techniques is suggested to be more beneficial than a single process. Advanced technologies such as membrane distillation, forward osmosis as well as some hybrid integrated techniques and their potentials are also discussed in this review. Membrane processes combined with other process (especially iron based technologies) are thought to be most sustainable for the removal of arsenic and further research allowing scale up of these technologies is suggested.

Hydrogeochemical comparison and effects of overlapping redox zones on groundwater arsenic near the Western (Bhagirathi sub-basin, India) and Eastern (Meghna sub-basin, Bangladesh) margins of the Bengal Basin

Although arsenic (As) contamination of groundwater in the Bengal Basin has received wide attention over the past decade, comparative studies of hydrogeochemistry in geologically different sub-basins within the basin have been lacking. Groundwater samples were collected from sub-basins in the western margin (River Bhagirathi sub-basin, Nadia, India; 90 samples) and eastern margin (River Meghna sub-basin; Brahmanbaria, Bangladesh; 35 samples) of the Bengal Basin. Groundwater in the western site (Nadia) has mostly Ca-HCO(3) water while that in the eastern site (Brahmanbaria) is much more variable consisting of at least six different facies. The two sites show differences in major and minor solute trends indicating varying pathways of hydrogeochemical evolution However, both sites have similar reducing, postoxic environments (p(e): +5 to -2) with high concentrations of dissolved organic carbon, indicating dominantly metal-reducing processes and similarity in As mobilization mechanism. The trends of various redox-sensitive solutes (e.g. As, CH(4), Fe, Mn, NO(3)(-), NH(4)(+), SO(4)(2-)) indicate overlapping redox zones, leading to partial redox equilibrium conditions where As, once liberated from source minerals, would tend to remain in solution because of the complex interplay among the electron acceptors.

Microcosm depth profiles of arsenic release in a shallow aquifer, West Bengal

Abstract Arsenic mobilization and Fe(III) reduction in acetate-amended sediments collected from a range of depths from an aquifer with elevated groundwater arsenic concentrations in West Bengal were monitored over a 1 month period. Significant arsenic release was noted in sediment collected from 24 m and 45 m depth, with some Fe(III) reduction also observed in the 24 m sample. The structure of the microbial communities present in the sediments prior to incubation showed marked differences down the sediment column. Profiling of the microbial community in the 24 m and 45 m samples revealed a relatively complex make-up, with Acinetobacter species comprising the bulk of the 24 m sedimentary bacterial population, but no previously characterized As(V)-reducers were detected in either sample.

Assessment of arsenic exposure from groundwater and rice in Bengal Delta Region, West Bengal, India.

Arsenic (As) induced identifiable health outcomes are now spreading across Indian subcontinent with continuous discovery of high As concentrations in groundwater. This study deals with groundwater hydrochemistry vis-à-vis As exposure assessment among rural population in Chakdaha block, West Bengal, India. The water quality survey reveals that 96% of the tubewells exceed WHO guideline value (10 μg/L of As). The groundwaters are generally anoxic (-283 to -22 mV) with circum-neutral pH (6.3 to 7.8). The hydrochemistry is dominated by HCO(3)(-) (208 to 440 mg/L), Ca(2+) (79 to 178 mg/L) and Mg(2+) (17 to 45 mg/L) ions along with high concentrations of As(T) (As total, below detection limit to 0.29 mg/L), Fe(T) (Fe total, 1.2 to 16 mg/L), and Fe(II) (0.74 to 16 mg/L). The result demonstrates that Fe(II)-Fe(III) cycling is the dominant process for the release of As from aquifer sediments to groundwater (and vice versa), which is mainly controlled by the local biogeochemical conditions. The exposure scenario reveals that the consumption of groundwater and rice are the major pathways of As accumulation in human body, which is explained by the dietary habit of the surveyed population. Finally, regular awareness campaign is essential as part of the management and prevention of health outcomes.

Groundwater As mobilization in the Bengal Delta Plain, the use of ferralite as a possible remedial measure—a case study

Abstract High As groundwater (50–1600 μg l−1) poses the greatest threat to human health in the Holocene alluvial aquifers of the Bengal Delta Plain (BDP) with increasing global concern in recent years. This study deals with groundwater quality and As mobilization vis-a-vis employing ferralite as a remedial option for removal of As from groundwater. The investigation suggests that Fe-rich As traps undergo degeneration to produce Fe oxyhydroxide (HFO) as coating/precipitation on the fine-grained sediment surface and release redox sensitive species (As, Fe and Mn) as well as PO43− into the groundwater under local reducing conditions. Sediment analysis reveals the presence of AsT (average 17.2 mg/kg), FeT (average 0.93 g/kg) and organic matter (average 7.6 g/kg). Sediment AsT and FeT content cannot validate the presence of high groundwater As/Fe. FeII catalysed FeIII reduction, induced by dissimilatory Fe reducing bacteria liberate the more toxic AsIII than AsV. The release of redox sensitive species (As, Fe and Mn) are the functions of bio-available forms of Fe oxides, concentration and distribution of fresh organic matter and availability of electron donors within the sediment. Further attempt is made to establish the role of ferralite, enriched with natural HFO as an As scavenger. Batch studies demonstrate the competency of the material over the natural/commonly used chemical coagulants generally used for water treatment. The high pHpzc value, 8.5 of ferralite along with the adsorption studies over a wide range of pH elucidate the effectiveness of the material in adsorbing both AsIII and AsV from the well-buffered groundwater. The presence of FeII in the system enhances the As removal process. The Langmuir adsorption isotherm further confirms the merit of ferralite as an efficient As scavenger. The material has been shaped for a fixed bed filter medium to remove As from groundwater (both laboratory and field scale). Ferralite is also cost effective (US

Characterization of aquifers conducting groundwaters with low and high arsenic concentrations: a comparative case study from West Bengal, India

8/metric ton of ferralite with a density 1.17 kg/dm3). Transportation cost for ferralite (from ferralitic bed to the affected area) is US

Consumption of Brown Rice : A Potential Pathway for Arsenic Exposure in Rural Bengal

16/ton/1000 km whereas US

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

0.6/100 l is required for treatment of contaminated water.