Elevated arsenic and manganese in groundwaters of Murshidabad, West Bengal, India.
High levels of geogenic arsenic (As) and manganese (Mn) in drinking water has led to widespread health problems for the population of West Bengal, India. Here we delineate the extent of occurrences of As and Mn in Murshidabad, where the contaminated aquifers occur at shallow depths between 35 and 40 m and where access to safe drinking water is a critical issue for the local population. A total of 78 well-water samples were taken in 4 blocks on either side of the river Bhagirathi: Nabagram and Kandi (west, Pleistocene sediments), Hariharpara and Beldanga (east, Holocene sediments). High As, total iron (FeT) and low Mn concentrations were found in waters from the Holocene gray sediment aquifers east of the river Bhagirathi, while the opposite was found in the Pleistocene reddish-brown aquifer west of the river Bhagirathi in Murshidabad. Speciation of As in water samples from Holocene sediments revealed the dominant species to be As(III), with ratios of As(III):AsT ranging from 0.55 to 0.98 (average 0.74). There were indications from saturation index estimations that Mn solubility is limited by the precipitation of MnCO3. Tubewells from high As areas in proximity to anthropogenic waste influx sources showing high molar Cl/Br ratios, low SO4(2-) and low NO3(-) demonstrate relatively lower As concentrations, thereby reducing As pollution in those wells. Analyses of core samples (2 in each of the blocks) drilled to a depth of 45 m indicate that there is no significant variation in bulk As (5-20mg/kg) between the Holocene and Pleistocene sediments, indicating that favorable subsurface redox conditions conducive to mobilization are responsible for the release of As. The same applies to Mn, but concentrations vary more widely (20-2000 mg/kg). Sequential extraction of Holocene sediments showed As to be associated with 'specifically sorbed-phosphate-extractable' phases (10-15%) and with 'amorphous and well crystalline Fe-oxyhydroxide' phases (around 37%) at As-contaminated well depths, suggesting that the main As release mechanisms could be either competitive ion exchange with PO4(3-), or the dissolution of Fe oxyhydroxides. In the Pleistocene sediments Mn is predominantly found in the easily exchangeable fraction.
Department of Geology, Kansas State University, Manhattan, KS 66506, USA.
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Sankar
Department of Geology, Kansas State University, Manhattan, KS 66506, USA.
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Vega
Department of Agronomy, Kansas State University, Manhattan, KS 66506, USA.
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Defoe
Department of Geology, Kansas State University, Manhattan, KS 66506, USA.
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Kibria
Department of Geology, Kansas State University, Manhattan, KS 66506, USA.
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Ford
Department of Earth and Environmental Sciences, Tulane University, New Orleans 70118, USA.
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Telfeyan
Virginia Water Resources Research Center, Virginia Tech, VA 24061, USA.
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Neal
Department of Earth and Environmental Sciences, Tulane University, New Orleans 70118, USA.
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Mohajerin
Department of Agronomy, Kansas State University, Manhattan, KS 66506, USA.
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Hettiarachchi
Department of Geology, Kansas State University, Manhattan, KS 66506, USA.
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Barua
Department of Geology, Kansas State University, Manhattan, KS 66506, USA.
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Hobson
Department of Earth and Environmental Sciences, Tulane University, New Orleans 70118, USA.
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Johannesson
Department of Geology, Kansas State University, Manhattan, KS 66506, USA. Electronic address: sdatta@ksu.edu.
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Datta
D001151:Arsenic / Q000032:analysis*; D060766:Drinking Water / Q000737:chemistry; D004784:Environmental Monitoring; D060587:Groundwater / Q000737:chemistry*; D007194:India; D008345:Manganese / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014881:Water Supply / Q000706:statistics & numerical data
D060766:Drinking Water; D014874:Water Pollutants, Chemical; D008345:Manganese; D001151:Arsenic
Arsenic; Contamination; Geogenic; Groundwater; India; Manganese; Murshidabad