STOTEN-15926; No of Pages 10 Science of the Total Environment xxx (2014) xxx–xxx

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Elevated arsenic and manganese in groundwaters of Murshidabad, West Bengal, India M.S. Sankar a, M.A. Vega a, P.P. Defoe b, M.G. Kibria a, S. Ford a, K. Telfeyan c, A. Neal d, T.J. Mohajerin c, G.M. Hettiarachchi b, S. Barua a, C. Hobson a, K. Johannesson c, S. Datta a,⁎ a

Department of Geology, Kansas State University, Manhattan, KS 66506, USA Department of Agronomy, Kansas State University, Manhattan, KS 66506, USA Department of Earth and Environmental Sciences, Tulane University, New Orleans 70118, USA d Virginia Water Resources Research Center, Virginia Tech, VA 24061, USA b c

H I G H L I G H T S • • • • •

Identification of high occurrences of As in groundwaters of Eastern India. Identification of mechanisms of release of Mn in groundwaters. Both these occurrences are estimated east and west of NS flowing Bhagirathi river. We postulate processes that concentrate natural As, Mn in fluvio-deltaic settings. Concentrations of Mn and As are to some extent inversely related to each other.

a r t i c l e

i n f o

Article history: Received 11 May 2013 Received in revised form 14 February 2014 Accepted 14 February 2014 Available online xxxx Keywords: Arsenic Manganese Geogenic Groundwater Contamination Murshidabad India

a b s t r a c t 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 SO2− 4 and low NO− 3 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 (5–20 mg/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 PO3− 4 , or the dissolution of Fe oxyhydroxides. In the Pleistocene sediments Mn is predominantly found in the easily exchangeable fraction. © 2014 Published by Elsevier B.V.

1. Introduction

⁎ Corresponding author. Tel.: +1 785 532 2241. E-mail address: [email protected] (S. Datta).

Large populations in the Bengal Basinal Delta system, roughly 43 million in West Bengal (Eastern India) and roughly 22 million in Bangladesh, are exposed to arsenic (As) poisoning by consumption of high arsenic (As) groundwaters (Bhattacharya et al., 1997; Nickson

http://dx.doi.org/10.1016/j.scitotenv.2014.02.077 0048-9697/© 2014 Published by Elsevier B.V.

Please cite this article as: Sankar MS, et al, Elevated arsenic and manganese in groundwaters of Murshidabad, West Bengal, India, Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.02.077

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M.S. Sankar et al. / Science of the Total Environment xxx (2014) xxx–xxx

et al., 1998; Smith et al., 2000; McArthur et al., 2001; Dowling et al., 2002; Roychowdhury et al., 2002; Ravenscroft et al., 2005; Acharyya and Shah, 2006; Datta et al., 2009; PHED, 2010 and references therein). Arsenic is extremely toxic and a Class-I carcinogen (Ghosh et al., 2013; Pandey et al., 2012; Datta et al., 2011; McArthur et al., 2012a,b) and the World Health Organization (WHO) guideline value for drinking water is 10 μg/L (WHO, 2011). Elevated concentrations of manganese (Mn) are also found in the groundwaters of this region (McArthur et al., 2012a,b; Biswas et al., 2012). The ingestion of Mn is known to cause adverse health effects, and in excessive quantities it is a neurotoxin (McArthur et al., 2012a,b). The young and unborn are particularly at risk from Mn contamination (Hafeman et al., 2007). It has also been shown that maternal environmental exposure to Mn is associated with a reduced activity of the newborn's erythrocyte Ca-pump (Yazbeck et al., 2006). Moreover, Mn in drinking water is associated with neurotoxic effects in children, for example with a diminished intellectual function (Wasserman et al., 2006). The WHO guideline value for drinking water is set at b 0.4 mg/L (WHO, 2011). The predominant mechanisms by which sediment-bound arsenic is released into groundwater are thought to be through microbially mediated reductive dissolution of FeOOH(s) (McArthur et al., 2001, 2004; Dowling et al., 2002). Reducing conditions are also responsible for the release of manganese (Mn) through the reduction of Mn(III,IV)

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(hydr)oxides to soluble Mn(II) species. Manganese(III,IV) are reduced under less reducing conditions than Fe(III) (hydr)oxides (Morgan and Stumm, 1964). Thus elevated arsenic and manganese concentrations in chemically reduced groundwaters may be related. Farooq et al. (2011) found a mean Mn value of 0.9 mg/L from 35 sampled tubewells throughout Murshidabad, and numerous studies have found similar results in the neighboring regions of Bangladesh (Frisbie et al., 2002; Agusa et al., 2006., Van Geen et al., 2007; Hafeman et al., 2007). These studies have found, however, that Mn values frequently have little to no relationship with As. In Murshidabad groundwater is the major drinking water source and 19 out of 26 blocks are at the risk of As contamination, making it one of the most densely affected districts in West Bengal (PHED, 2010). People utilize (hand pumped) shallow level tubewells drilled via local drilling companies. The contaminated aquifers occur at depths of ~35–40 m. Surface waters from Murshidabad are highly contaminated by anthropogenic pollutants, including enteric bacteria, due to overuse and additions of waste streams to the streams/channels as shown for Nadia, West Bengal (McArthur et al., 2012a,b). Health impacts associated with the use of As and Mn contaminated groundwaters for drinking, have been observed (McArthur et al., 2012a) and malnutrition, which is prevalent in the region (Deb et al., 2013; Mandal et al., 2012; Mondal et al., 2012; Arlappa et al., 2011) may aggravate the situation. The sustainable provision of water of sufficient quantity and

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Fig. 1. Sites for arsenic: State of West Bengal, district of Murshidabad, 4 locations are chosen for the current study: Beldanga (BM), Hariharpara (HK) on the eastern side (high As and low Mn) and Nabagram (NB) and Kandi (KHN) on the western side (low As and high Mn) of the river Bhagirathi. This figure is reproduced from Mohajerin et al., 2014.

Please cite this article as: Sankar MS, et al, Elevated arsenic and manganese in groundwaters of Murshidabad, West Bengal, India, Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.02.077

M.S. Sankar et al. / Science of the Total Environment xxx (2014) xxx–xxx

quality is a major challenge (e.g., Ravenscroft et al., 2009). The provision of water from uncontaminated aquifers at different depths requires understanding of release mechanisms underlying groundwater As and Mn contamination. The current study investigates groundwater contamination in the shallow aquifers of the eastern part of the Bengal Basin (Murshidabad district, Fig. 1). In this paper we outline the geochemical controls of As and Mn within Holocene–Pleistocene sedimentary aquifers mostly deposited under fluvial deltaic conditions (Mukherjee et al., 2012). Four study locations with high and low As and Mn contamination were chosen east and west of the River Bhagirathi (Fig. 1). To the east groundwater in Beldanga and Hariharpara abstracted from Holocene aquifers has As in the concentration range 700 to 4500 μg/L. To the west in Nabagram and Kandi, where water is abstracted from Pleistocene sediments, As concentrations are low (6–18 μg/L, Datta et al., 2011; Mohajerin et al., 2014). At these sites groundwater composition has been investigated as a function of depth and interpreted in terms of both the geological depositionary environment and the geochemical mechanisms underlying the release of As and Mn. 2. Materials and methods 2.1. Location The Murshidabad district is located at the south-central part of the Bengal Basin and is transected north to south by the river Bhagirathi, a distributary of river Ganges (Fig. 1). The district covers an area of roughly 5550 km2 (study area ~ 497 km2) and has a population of approximately 7.1 million people (Census, 2011). The region has a tropical wet–dry climate. The average precipitation during the monsoon is about 1400 mm during the year, with 70% of rainfall occurring during monsoonal months (Jun–Aug) (Supplementary Table 1). 2.2. Geology and geography The Bengal Basin is located in the Himalayan foreland, within the southeastern part of the Indo-Gangetic alluvial plain, and is composed of Quaternary sediments deposited within paleo-channels and paleointerfluves formed by the Ganges and Brahmaputra, the meandering Himalayan rivers (Morgan and McIntire, 1959; McArthur et al., 2011; Hoque et al., 2011., Mukherjee et al., 2012). The Bengal Basin is bounded to the north by the Himalayan mountain ranges and in the southwest by the Precambrian Peninsular Indian craton. The basin extends to the Bay of Bengal in the south, forming the great Bengal fan. Chronostratigraphically the basin holds two major types of sedimentary units; the older Pleistocene unit and the younger Holocene unit (Mukherjee et al., 2008; McArthur et al., 2008, 2011, 2012a). During the Last Glacial Maximum (~ 20 ka before present), when sea level was substantially lower, the current highlands in the basin (i.e., current paleo-interfluvial areas) were exposed and a thin layer of paleosol was deposited over on top (McArthur et al., 2008). However, the low-lying areas (current paleo-channels) were devoid of such deposits (McArthur et al., 2008; Hoque et al., 2011, references therein). The Murshidabad district forms part of the lower Ganges valley and is covered by extensive deposits of Quaternary alluvium (Biswas and Roy, 1976; Mukherjee et al., 2008). Regions of Murshidabad west of the river Bhagirathi are occupied by the Suja Formation, which consists of Pleistocene alluvium composed of oxidized ferruginous sand, silt, and clay with caliche (calcium carbonate cemented sediments). Groundwaters from aquifers in this region are low in As but high in Mn. To the east of the river Bhagirathi is the extensive alluvial deposits of the Bhagirathi-Ganga (flood plain-deltaic deposits) formation, which is of Holocene age and composed of fine sand, silt, and clay (Datta et al., 2011). Groundwaters from aquifers in this region are high in As and low in Mn. The contaminated aquifers of the Murshidabad district (Bengal Basin) exist mostly at depths between 35 and 40 m and are

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mainly composed of fine to medium grained sand with substantial amount of clays and sedimentary organic matter (~ 10–20% organic matter by weight) (Datta et al., 2011; Mohajerin et al., 2014).

2.3. Sample collection and analysis Monitoring of groundwaters and surface waters along with sediment sampling was conducted from December 2009 through January 2013 in Murshidabad: pre-monsoon (2009), post-monsoon (2010, 2011, 2012). There were no significant monsoonal effects observed on As and Mn distribution. Water samples were collected from shallow tubewells (25–40 m) from As-contaminated wells in Beldanga (23 wells) and Hariharpara (28 wells), and 15 of the low-As wells in Nabagram (which has 18 wells) and Kandi (with 12 wells). These wells already existed and were constructed by local drillers to a depth of ~20–40 m at the request of the inhabitants. In addition, 2 cores were taken to a depth of 45 m at each of the 4 sampling sites. The location of all samples was recorded by handheld GPS and referenced to WGS 84 coordinate system. Unacidified and unfiltered fresh water samples for major anion analyses were collected in 500 mL HDPE narrow mouth plastic bottles (Fisherbrand® Cat no. 12-100-317). Filtered (0.45 μm, polyether sulfone membranes) and acidified (250 μL of 0.2% ultrapure nitric acid) water samples for analyses of major cations and As concentrations were collected in 125 mL amber plastic narrow mouthed bottles (Fisherbrand® Cat no. 02-923-5c). Filtered groundwater samples were first acidified to pH ~ 3.5 with ultra-pure HNO− 3 prior to passing through the anion-exchange columns. Arsenite (H 3AsO 3 °) passed through the column and was collected in pre-cleaned, amber HDPE bottles, whereas As(V) (H2 AsO − 4 ) was retained on the column (Wilkie and Hering, 1998; Haque and Johannesson, 2006). Arsenite was quantified in the eluted fractions and total dissolved As was measured on separate aliquots by high-resolution magnetic sector ICP-MS (Haque et al., 2008). Arsenate was then determined by difference between total dissolved As and As(III). Subsurface sediment cores were collected close to wells with known high and low dissolved As concentrations from shallow (2–~ 15 m), intermediate (15–~25 m), and deeper (25–~40 m) aquifers in Nabagram (2 cores), Kandi (1 core), Beldanga (3 cores) and Hariharpara (2 cores) using the local percussion hand drilling method (hand operated river circulation method). All samples were collected at regular depth intervals (usually ~2–3 m; within separate transparent core liners and capped on both ends) and at noticeable changes in lithology (i.e. grain size, color, etc.) in each borehole (See Supplementary Fig. 1). Samples were immediately placed in an O2-impermeable Remel® bag (Mitsubishi Gas Company, Remel®, Cat no. 2019-11-02), along with an O2 absorber pouch (Mitsubishi Gas Company, AnaeroPouch® Anaero; Cat no. 23-246-379), flushed with high-purity N2 gas, and sealed. Major cations and anions (including Cl−, NO23 −, SO24 − and PO3− 4 ) were analyzed by high resolution inductively coupled plasma mass spectrometry (HR-ICPMS) and ion chromatography (IC) respectively. Bromine and Mn were analyzed by ICP-MS. Total dissolved Fe (FeT) and Mn concentrations were also measured using UV/vis spectrophotometric techniques in the field (e.g., Haque et al., 2008). Groundwater samples were analyzed for As within 1–2 weeks of sample collection by sector field ICP-MS (Thermofisher ELEMENT 2) at Tulane University (Datta et al., 2011; Mohajerin et al., 2014). Total digestions of aquifer sediments were performed prior to the analysis of As, Mn and FeT. Micro-wave digestion (CEM MARS5 (Matthews, NC)) using 70% trace metal grade HNO3 (Fisher Scientific) as the matrix to dissolve sediment was employed to obtain an estimate of total extractable As. The NIST standard reference material (SRM) Montana II soil standard was also digested for quality assurance. A 6 mL aliquot was analyzed via ICP-OES for total As, Mn and Fe concentrations.

Please cite this article as: Sankar MS, et al, Elevated arsenic and manganese in groundwaters of Murshidabad, West Bengal, India, Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.02.077

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The 5-step sequential extraction method of He et al. (2010) (modified from Wenzel et al., 2001; Keon et al., 2001) was chosen to determine concentrations of As and Mn in various sediment fractions. Aquifer samples from each location were selected for the study. A total of 27 samples, 2 duplicates and one standard reference material (Montana II 2711, www.nist.gov/srm) were used for the experiment (Beldanga: 8 samples, 1 duplicate: Hariharpara: 7 samples, 1 duplicate; Nabagram: 6 samples; Kandi: 6 samples). The samples were selected based on the values obtained from microwave total digestion results. A detailed description of the methodologies behind this procedure is described in the supplementary text (Supplementary Text 3).

3. Results 3.1. Water quality

Dissolved As (µg/l)

3.1.1. Groundwater Water Quality Parameters that were analyzed in the field from tubewells at an average of ~20 m depth were: temperature (24–27 °C), salinity (0.01–12 ppt), TDS (98 mg/L–10 g/L), conductivity (2.6–990 μS/cm), pH (6.6 to 8.2) and alkalinity (375–630 mg/L). The TDS and conductivity do not show considerable variation among the high and low As areas. The high As areas showed a pH of 6.6–7.8 while pH in the low As areas was 6.6–8.2.

The major distribution of dissolved As and Mn in three of the four sampling locations in Murshidabad are depicted in a google-based map (Fig. 3). The groundwater data reveals that regions where As concentrations are high, such as Beldanga (b10 ≤ As ≤ 4622 μg/L; ~ 35–45 m depth) and Hariharpara (5 ≤ As ≤ 695 μg/L; 6–37 m depth), also have relatively low to moderate Mn concentrations (182–1291 μg/L, Beldanga; 602.3–1232 μg/L, Hariharpara) (Fig. 3). In the regions characterized by low groundwater As concentrations, Nabagram (0 b As ≤ 16 μg/L; 20–45 m depth) and Kandi (5 ≤ As ≤ 50 μg/L; 20–55 m depth) appear to have higher Mn concentrations (i.e., Nabagram: 75.6 ≤ Mn ≤ 2327 μg/L; Kandi: Mn ≤ 1500 μg/L). We note that one groundwater sample from the Kandi block exhibited a relatively low Mn concentration (40 μg/L), suggesting that more sampling of groundwaters from this site could reveal substantial variation in Mn concentrations (Fig. 4B). As variation with depth in the high and low As locations have also been defined (Fig. 4G, H). Speciation of As executed on 23 samples in the field revealed the dominant species to be As(III). As(III):AsT ratios ranged from 0.55 to 0.98 for wells east of Bhagirathi, with an average ratio of 0.74 (Fig. 2). West of Bhagirathi, the one well on which As speciation was done contained only 36% As(III). Overall, total dissolved As (and As(III)) increased from west to east. Ammonium ion concentrations in Murshidabad groundwaters range from 0.01–0.06 mg/L. Nitrate content in groundwaters from the high As areas of Beldanga and Hariharpara are typically lower than those

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Tubewells from West to East of river Bhagirathi Fig. 2. Total dissolved As (AsT) and As(III) concentrations (μg/L) from 23 tubewells and one shallow irrigation well from Murshidabad. AsT in groundwater collected west of river Bhagirathi was 36% As(III). The site's nomenclatures are as follows: BM = Beldanga; HK and HB = Hariharpara; NR and NRJ = Naoda; JB = Jalangi; KB = Kandi. Sites Naoda and Jalangi are not discussed in this context. IRW stands for irrigation well at 60′ (~18 m) at Hariharpara.

Please cite this article as: Sankar MS, et al, Elevated arsenic and manganese in groundwaters of Murshidabad, West Bengal, India, Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.02.077

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Please cite this article as: Sankar MS, et al, Elevated arsenic and manganese in groundwaters of Murshidabad, West Bengal, India, Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.02.077

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measured in groundwaters from the low As regions of Nabagram and Kandi (Fig. 4D). The concentration of chloride (Cl−) in groundwaters is higher (29–200 mg/L) in low As areas like Nabagram and Kandi compared to the high As areas like Beldanga and Hariharpara. Molar Cl/Br ratios for the groundwaters from the latter sites show a ratio i.e. N1561 (Fig. 5). By comparison, molar Cl/Br ratios in groundwaters from the low Nabagram and Kandi are highly variable, ranging between 92 and 12,340 for the Nabagram groundwaters and from 280–560 in the Kandi groundwaters (Fig. 5). The groundwaters demonstrated SO24 − concentrations (1–75 mg/L) throughout the field areas (Fig. 4E). Phosphate concentrations of groundwaters from the high As (i.e., Beldanga, Hariharpara) and low As sites show similar ranges (0.4–2.2 mg/L) (Fig. 4F). The concentrations of FeT are higher in groundwaters with high As concentrations (Beldanga; 0.09 ≤ FeT ≤ 13.6 mg/L; Hariharpara; 0.04 ≤ Fe T ≤ 7.2 mg/L) compared to the low As areas like Nabagram (0.007–1.2 mg/L) and Kandi (0.07–1.03 mg/L) (Fig. 4C). Fluoride concentrations range from 0.17 to 1.76 mg/L and only a few samples from the low As areas exceed the WHO guideline value (Fig. 4A). Not all wells were tested for F− in Murshidabad. Hence, more systematic depthwise analysis is needed for these waters. There is a positive correlation of arsenic with FeT, PO34 − and TDS content in most of the high As areas, whereas the Mn+2 and Cl− ions are usually negatively correlated with high As (Fig. 4B, C, F and Appendix A, B, F and H). 3.2. Aquifer sediment composition At Beldanga, total As ranges from 9.35 to 18.09 mg/kg, Mn from 151.4 to 1840.7 mg/kg, and Fe from 10,689 to 32,972 mg/kg. At Hariharpara the maximum As, Mn and Fe are observed within the initial 10 m depth, which is also dominantly composed of dark gray silty clay (Appendix G; Supplementary Fig. 1). In the low-As areas

of Nabagram and Kandi, the majority of As, Mn and Fe are concentrated in the clay fractions (Supplementary Fig. 1). Supplementary Fig. 2(A, B and C) also show depth profiles of total As, Fe and Mn extracted from bulk sediment samples from low As areas of Nabagram and Kandi. The total As, as seen from total extractions, indicates similar total bulk As in the low and high As areas within the range between 8 and 23 mg/L, hence there is no significant variation in total As among the sediments from the low and high As areas. The sequential extraction (semi-quantitative estimate) methods followed here provide an indication of how strongly As is bound to the sediments. The results for Beldanga, as an example of a high-As area, and Nabagram, as a high-Mn area, are shown in Fig. 6A and B. In the shallow sediments [10′ (3 m)–70′ (21 m); Fig. 6A] of Beldanga, no As was observed in the ‘nonspecifically sorbed phases’, up to 30% was observed in P-extractable (specifically sorbed) phases, a considerable portion of As was associated with Fe hydroxides: ~ 10–15% (with an exception of ~ 30% at 3 m depth) for amorphous and poorly crystalline phases and ~ 5–20% for well-crystallized phases, while a dominant ~ 30–50% was determined to be in the residual phases. Intermediate depth sediments [90′ (27 m)] of Beldanga (high As) had no easily exchangeable As, but 15% of total As was specifically sorbed. ~25% and ~15% of total As was associated with the amorphous/ poorly twb=0.27w?>crystalline Fe hydroxide and well-crystallized phases, respectively, with over 45% in the residual phases. Deep sediments [100′ (30 m)–110′ (33 m)] showed the majority of As was again in the residual phase (~ 40–55%), along with minimal As in the easily-exchangeable phases (~ 10–20% of As was P-extractable and ~10–20% was found to be in poorly crystalline/amorphous Fe hydroxide phases; ~ 15–30% of total As was in well-crystallized Fe hydroxide phases (Fig. 6A)). Sequential extractions from shallow sediments [10′ (3 m)–50′ (15 m) depth] of Nabagram (low As) showed that up to 40% of Mn was in

Please cite this article as: Sankar MS, et al, Elevated arsenic and manganese in groundwaters of Murshidabad, West Bengal, India, Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.02.077

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Fig. 5. (A) Plot showing molar Cl/Br ratio vs As in Murshidabad groundwaters; and (B) molar Cl/Br ratio vs depth in Murshidabad groundwaters.

the easily exchangeable phases (~12% at 10′ (3 m); ~40% at both 40′ (12 m) and 50′ (15 m)). ~10 to 20% of Mn was P-extractable. Varying percentages of Mn were found in the poorly crystalline/amorphous Fe-hydroxide phases (10′ (3 m) = 50%; 40′ (12 m) = ~ 15% and 50′ (15 m) = ~ 15%), and ~ 8–18% was found in well-crystallized Fe-hydroxide phases. 10% was in the residual phase at 10′ (3 m) with ~ 25–30% at depths of 40′ (12 m) and 50′ (15 m). Intermediate depth sediments (90′ (27 m)) from Nabagram showed that Mn predominantly existed in the easily exchangeable phases (~ 47%). Deep sediment samples (130′ (40 m)–140′ (43 m) depth) showed a similar dominance with Mn existing at ~50% in the easily exchangeable phases. ~19% was P-extractable and b10% Mn was found in both the

poorly crystalline and well-crystallized Fe-hydroxide phases. ~24% was in the residual phases (Fig. 6B). 4. Discussions 4.1. Arsenic and manganese in drinking water Arsenic occurrence in the groundwaters of Murshidabad appears to be associated with groundwater redox conditions as found many times previously (e.g. Nickson et al., 1998; McArthur et al., 2001, 2004; Dowling et al., 2002; Datta et al., 2011). This is evidenced by the predominance of reduced As and the presence of dissolved Fe in

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NB-40 NB-50 NB-90 NB-130 NB-140 % Non specifically sorbed % Specifically sorbed % Amorphous & poorly crystalline hydrous oxides of Fe & Al % Well crystalline hydrous oxides of Fe and Al % Residual phases

Fig. 6. (A) Distribution of As in various sediment fractions in Drill Core CS-103 BM from Beldanga, total depth of core 34 m (e.g. BM-10 = 10 ft (~3 m) depth; BM-110 = 110 ft (~43 m) depth). (B) Distribution of Mn in various sediment fractions in Drill Core CS-104 NB from Nabagram. Total depth of the core is 43 m (e.g. NB-10 = 10 ft (~3 m) depth; NB-140 = 110 ft (~43 m) depth).

Please cite this article as: Sankar MS, et al, Elevated arsenic and manganese in groundwaters of Murshidabad, West Bengal, India, Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.02.077

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samples with elevated As. In fact in both the As-contaminated blocks As and Fe are highly correlated. Maximum concentrations of these ions are found at 30–40 m in the Beldanga samples and 10–30 m in the Hariharpara samples. The solid-phase Fe concentrations range from 0.5 to 4 wt.% but trends as a function of depth that correlate in some way to water composition are not observed. Arsenic speciation is dominated by As(III) in the majority of groundwaters in Murshidabad. This is likely a reflection of the general anoxic conditions of the local groundwaters and because As(III) is thought to be more mobile in circum-neutral pH groundwaters as it occurs as uncharged arsenious acid, H3AsO03 (Polizzotto et al., 2006). The accumulation of As(III), coupled with possible microbial reduction of Fe3+ and As(V) along specific flow paths, could explain some of the highest As(III):AsT ratios. It is interesting to note that water samples from the Pleistocene aquifer still have measureable, though low, concentrations of As and Fe. At these sites some depths exhibited suboxic conditions (mean Eh ~ 301 mV), low As concentrations (mean 12.6 μg/L), and at the same time higher Mn concentrations (mean 1.7 mg/L). The Eh values are not low enough to entirely reduce sediment-bound Fe(III)-hydroxides, which therefore still offer strong binding sites for As and PO34 −. The absence of nitrate or low nitrate concentrations in most of the wells are in agreement with suboxic conditions as is the presence of reduced Mn(II) (e.g. Buschmann et al., 2007). This type of redox environment indicates the observed relationship of high Mn and low As in the district of Nabagram. The underlying process that leads to the high As but low Mn is a matter of speculation. From the redox perspective if conditions are reducing enough to release As, they are certainly reducing enough to release Mn. We hypothesize that in Holocene sediments, since biodegradation is still active, higher PCO2, resulting in elevated dissolved carbonate content controls the solubility of Mn through the precipitation of rhodochrosite (MnCO3). Indeed, logarithmic saturation indices for rhodochrosite in high As–low-Mn waters range from − 0.8 to + 0.97. In the Pleistocene sediments, which presumably have less biodegradation and thus lower carbonate content (alkalinity), higher Mn is found but does not reach that high reducing state to release As into the shallow aquifer. When alkalinity (as CO2− 3 ) is plotted against dissolved Mn concentrations between the high and low As sites, a negative correlation is observed in both areas, however a steeper gradient is demonstrated in the high Mn, low As area. This may indicate more dissolution of Mn into the groundwater (Supplementary Fig. 3). The alkalinity of the suboxic and highly reducing conditions are 6.3 meq/L (Beldanga) and 6.0 meq/L (Hariharpara) as HCO 3 respectively, which also supports this hypothesis. The high Mn and low As area Nabagram showed much lower values (4.8 meq/L as HCO− 3 ), which is ~22% lower (statistically significant) when compared to a combined average of high As, low Mn sites. McArthur et al. (2012a) determined that groundwater recharge into paleo-interfluvial aquifers from paleo-channels are controlled by overlying impermeable Last Glacial Maximum paleosols in parts of West Bengal, creating dual Fe and Mn reduction fronts that promote elevated concentrations of Mn and Fe along pre-Last Glacial Maximum (LGM) and post LGM sediment boundaries. Black stains of Mn-oxide and red stains of Fe-oxide were observed in wells along both of these respective fronts. In our study area, some tubewell platforms conspicuously show reddish stains (high As), while some with low As show black stains, as also observed in Nadia as by Biswas et al. (2012). McArthur et al. (2012a) suggest that the primary redox driver was found to be DOC, where both fronts maintain similar sources, such as river-bank and wastewater derived DOC infiltration. The northern, upstream interface demonstrated notably higher concentrations of Fe (up to 18 mg/L) and Mn (up to 6 mg/L) (McArthur et al., 2012a). Since the Bengal Basin is a part of the highly cultivated Indo-Gangetic alluvial plains, PO3− 4 in local groundwaters could be due to extensive use of phosphate fertilizers. For example, the presence of dissolved PO3− in 4

groundwaters can cause replacement of As sorbed onto FeOOHs (Acharyya and Shah, 2010). Alternatively, sorbed PO3− 4 could be released during disintegration of organic rich peat layers which also enhances reductive dissolution of FeOOHs (McArthur et al., 2001). The second hypothesis is still somewhat (even if it has been discredited) relevant to the present study because during our field work, shallow drilling operations were conducted to recover aquifer sediments. The sediment analyses reveal the presence of several layers of organic rich clays and sands which produce groundwaters with up to 3 mg/L of PO3− 4 . This area in Murshidabad has extensive agricultural practices and application of various phosphatic fertilizers during the rice cultivation months were seen during our field campaigns. Hence, oxidation of this organic matter contained within the clay and sand layers (Bhattacharya et al., 2011) and addition of phosphates during agriculture could contribute higher PO3− to the groundwaters. This was part of an exploratory study where 4 the effect of P could not be quantified during those field campaigns. Further investigation is required to understand the role of anthropogenic P addition to the groundwater. von Bromssen et al. (2007) postulates 2− from their study in Matlab, Bangladesh that high PO3− 4 , high NO3 , and high SO2− 4 , indicate possible contamination from surface sources. Similarly, this is applicable to the present study in Murshidabad. The presence of elevated Cl− could be due to high evaporation rates during the dry season or may reflect an effect of anthropogenic inputs from, for example, pit latrines, septic tanks and contaminated ponds (McArthur et al., 2012b; Xie et al., 2012). Higher molar Cl/Br ratios from the high As wells as in Beldanga and Hariharpara exhibited a ratio that exceeds waste-water values (1561) as reported by McArthur et al. (2012b). On the other hand molar Cl/Br ratios in Nabagram are highly variable whereas Kandi consistently is very low. It is interesting to note that some groundwater samples with high molar Cl/Br ratios collected from Beldanga and Hariharpara have shown comparatively low As concentrations (Fig. 5A, B). We posit that this observation is consistent with the suppression of Fe(III)-oxides and oxyhydroxide reductions and subsequent release of sorbed/coprecipitated As by waste water influence derived from pit latrines, and other anthropogenic sources. The majority (75%) of tubewells from Beldanga and Hariharpara that produce groundwaters with high molar Cl/Br ratios and relatively low As concentrations are constructed close to pit latrines as well as ponds (Figs. 3 and 5). Because excess water from local tubewells can drain into local ponds, these ponds are also subject to an influx of anthropogenic organic matter originally sourced from pit latrines. We conclude that the variation of the Cl/Br ratios could be due to the location of tubewells near anthropogenic waste sources such as pit latrines. The differences in nitrate concentrations could reflect more reducing conditions that characterize the Holocene aquifers east of the river Bhagirathi that produce high groundwater As concentrations (Datta et al., 2011; Mohajerin et al., 2014). Sulfate concentrations are also generally low in groundwaters from the high As areas of Beldanga and Hariharpara, but typically higher in groundwaters from the low As site of Nabagram. Even Bangladeshi groundwaters (e.g. Matlab Upazila in Chandpur) have high As (352 to 600 μg/L) but low SO24 − b5 mg/L (von Bromssen et al., 2007). There are several indicators that support the hypothesis of an anthropogenic influence on reducing conditions in these underlying aquifers. In the current study, we see groundwaters from the high As areas demonstrate anthropogenic effluent contamination (e.g. human or sewage wastes), that is exhibited by high values of Cl−, molar Cl/Br ratios, but low sulfate and nitrates where these two later constituents are partially eliminated due to prevalent reducing conditions in the aquifers. 4.2. Arsenic and manganese in sediments Overall, the bulk As content of the sediments from the low and high groundwater As areas are similar. We suggest that the distribution of As, Fe, and Mn in aquifer sediments in Murshidabad indicates that As occurs in similar mineral phases across the district (e.g. FeIII-oxides and -

Please cite this article as: Sankar MS, et al, Elevated arsenic and manganese in groundwaters of Murshidabad, West Bengal, India, Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.02.077

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oxyhydroxides), but favorable subsurface redox conditions conducive to mobilization occur in sediments from east of the river Bhagirathi. It is interesting to note that no easily exchangeable phases of As were found in the sequential extractions from high As sediments (Beldanga). With over approximately 50% of As in these sediments residing in specifically sorbed phase, amorphous and crystalline Fe, it may be suggested that the main As-releasing mechanisms in this area are: 1) Competitive ion exchange processes by which As in the specifically sorbed phases are replaced by PO3− present in the circulating ground4 water (Acharyya et al., 1999; McArthur et al., 2001); and 2) The dissolution of Fe and Mn oxyhydroxides, thus releasing their adsorbed As into the groundwater due to high reducing conditions present in the subsurface (Cummings et al., 1999; Dowling et al., 2002; McArthur et al., 2001, 2004; van Geen et al., 2007). In turn both of these processes could act together and aid in causing the observed high concentrations of dissolved As in these areas. Reza et al. (2010a,b) states that their sequential extraction results from Chapai-Nawabganj, NW Bangladesh exhibit a dominance of Mn and Fe hydroxides, organic matter and sulfides as the major leachable As solid phases in the sediments, and indicating the presence of siderites within the sediments. They show a poor correlation between dissolved Fe and As in groundwater, which can be related to the loss of Fe by precipitation of carbonate phases of Fe (Nickson et al., 2000), implying that other geochemical processes can control the As and Fe levels in West Bengal groundwaters. Contrary to this idea, it should be noted that siderites were not essentially found in the current sediments, and might also indicate that this is due to a fluctuation in water table leading to noticeable changes in redox conditions. High concentrations of As and Mn in residual phases in all areas could be due to the release of organic-matter bound As and Mn while digesting with H2O2. So part of the As and Mn concentrations in residual phases could be from organic matter also. The total and sequential extractions of the sediments show that As and Mn are in considerable proportion within the sediments, and for As we see the shallow to intermediate depth sediments to be in poorly crystalline/well crystalline Fe-oxides and the residual phases. The dissolved As in the water in the shallow and intermediate depth indicates that even in less bioavailable to more bioavailable phases As can be extracted out rather readily. Mn sequential extraction results in Nabagram show that Mn is mostly present in the easily exchangeable phase (nonspecifically sorbed; 10–50%) at all depths and can therefore easily be released into solution by reacting with percolating groundwater. This was evident by the presence of high concentration of dissolved Mn in groundwaters of Nabagram. 5. Conclusions Geogenically derived As and Mn contamination is causing an immense problem in shallow drinking waters for the population of Eastern India. The present work confirms the distribution of As and Mn pollution of groundwater across the southern part of West Bengal. Reduced As is the predominant As species in wells to the east of Bhagirathi. Arsenic is mobilized from the clay rich gray sediments within the low-relief Holocene aquifers. Tubewells with high molar Cl/Br ratios possibly impacted by anthropogenic sewage influx and pit latrine wastes suppress As concentrations in waters, even when associated with Fe-(III) oxide and oxyhydroxide reduction. Notably high concentrations of PO3− in groundwaters indicate agricultural practices 4 which may help in oxidation of organic matter contained within the sediments. It is probable that subsurface redox conditions conducive to mobilization of As by competitive ion exchange processes in the specifically sorbed phases are replaced by PO3− and/or the dissolution 4 of Fe oxyhydroxides, releasing adsorbed As into the groundwater. The presence of high Mn in low As sediments as nonspecifically sorbed or easily exchangeable phases provides ready opportunity for release of

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Mn into percolating groundwater. The presence of high Mn and low As in groundwaters of Nabagram can be explained by redox conditions conducive to Mn reduction (and therefore aqueous release) yet not quite reducing enough to support As release. Holocene sediments, whose waters are reducing enough to contain elevated dissolved As and total Fe concentrations, are probably controlled by the precipitation of Mn-carbonates. Acknowledgments The authors are thankful to the National Science Foundation (NSF) and Kansas State University for support for field trips and overall project design in West Bengal. The authors also thankfully acknowledge immense help from the villagers in Murshidabad (and people of Lalbagh) where field work was done. We also thank the Department of Geology for field support to India. The authors are also immensely thankful to the reviewers especially Reviewer 1 and specifically the helpful comments and suggested edits by the managing editor Dr. Annette Johnson to comment at many aspects of this article in great details and pointing out places to improve the manuscript in many ways. Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.scitotenv.2014.02.077. References Acharyya SK, Shah BA. Arsenic-contaminated groundwater from parts of Damodar fandelta and west of Bhagirathi River, West Bengal, India: influence of fluvial geomorphology and Quaternary morphostratigraphy. Environ Geol 2006;52:489–501. Acharyya SK, Shah BA. Groundwater arsenic pollution affecting deltaic West Bengal, India. Curr Sci 2010;99(12):1787–94. Acharyya SK, Chakraborty P, Lahiri S, Raymahashay BC, Guha S, Bhowmik A. Arsenic poisoning in the Ganges delta. Nature 1999;401(6753):545-545. Agusa T, Kunito T, Fujihara J, Kubota R, Minh TB, Trang TK, et al. Contamination by arsenic and other trace elements in tube-well water and its risk assessment to humans in Hanoi, Vietnam. Environ Pollut 2006;139:95–106. Arlappa N, Laxmaiah A, Balakrishna N, Harikumar R, Kodavanti MR, Reddy CG, et al. Micronutrient deficiency disorders among the rural children of West Bengal, India. Ann Hum Biol 2011;38(3):281–9. Bhattacharya P, Chatterjee D, Jacks G. Occurrence of As-contaminated groundwater in alluvial aquifers from the Delta Plains, Eastern India: option for safe drinking water supply. Water Resour Dev 1997;13:79–92. Bhattacharya P, Mukherjee A, Mukherjee AB. Arsenic in groundwater of India. Encyl Environ Health 2011:150–64. Biswas AB, Roy RN. A study on the depositional processes and heavy mineral assemblages of the Quaternary sediments from Murshidabad district, West Bengal. Proc Indian Natl Sci Acad 1976;42(5):372–86. Biswas A, Nath B, Bhattacharya P, Halder D, Kundu AK, Mandal U, et al. Testing tubewell platform color as a rapid screening tool for arsenic and manganese in drinking water wells. Environ Sci Technol 2012;46:434–40. Buschmann J, Berg M, Stengel C, Sampson ML. Arsenic and manganese contamination of drinking water resources in Cambodia: coincidence of risk areas with low relief topography. Environ Sci Technol 2007;41(7):2146–52. Census, 2011. http://www.census2011.co.in/census/district/7-murshidabad.html. Cummings DE, Caccavo F, Fendorf S, Rosenzweig RF. Arsenic mobilization by the dissimilatory Fe(III)-reducing bacterium Shewanella alga BrY. Environ Sci Technol 1999;33(5):723–9. Datta S, Mailloux B, Jung HB, Hoque MA, Stute M, Ahmed KM, et al. Redox trapping of arsenic during groundwater discharge in sediments from the Meghna riverbank in Bangladesh. Proc Natl Acad Sci 2009;106(40):16930–5. Datta S, Neal AW, Mohajerin TJ, Ocheltree T, Rosenheim BE, White CD, et al. Perennial ponds are not an important source of water or dissolved organic matter to groundwaters with high arsenic concentrations in West Bengal, India. Geophys Res Lett 2011;38:L20404. Deb D, Majumdar KK, Mazumder DNG. Arsenicosis and dietary nutrient intake among men and women. Proc Acad Sci 2013;83(3):405–13. Dowling CB, Poreda RJ, Basu AR, Peters SL. Geochemical study of arsenic release mechanisms in the Bengal Basin groundwater. Water Resour Res 2002;38:12-1–12-18. Farooq SH, Chandrasekharam D, Norra S, Berner Z, Eiche E, Thambidurai P, et al. Temporal variations in arsenic concentration in the groundwater of Murshidabad district, West Bengal, India. Environ Earth Sci 2011;62:223–32. Frisbie SH, Ortega R, Maynard DM, Sarkar B. The concentrations of arsenic and other toxic elements in Bangladesh's drinking water. Environ Health Perspect 2002;110: 1147–53. Ghosh SK, Bandyopadhyay D, Bandyopadhyay SK, Debbarma K. Cutaneous malignant and premalignant conditions caused by chronic arsenicosis from contaminated ground

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Please cite this article as: Sankar MS, et al, Elevated arsenic and manganese in groundwaters of Murshidabad, West Bengal, India, Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.02.077

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, Ind...
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