geochemistry and mobilization of arsenic in shuklaganj area of kanpur–unnao district, uttar...

Geochemistry and mobilization of arsenic in Shuklaganjarea of Kanpur–Unnao district, Uttar Pradesh, India

Vivek Singh Chauhan & M. Yunus &

Nalini Sankararamakrishnan

Received: 2 February 2011 /Accepted: 24 August 2011 /Published online: 14 September 2011# Springer Science+Business Media B.V. 2011

Abstract The level of arsenic (As) contamination andthe geochemical composition of groundwater in Shu-klaganj area located on the banks of the Ganges Delta ofKanpur–Unnao district were elucidated. Samples(n=59) were collected from both India Mark II handpumps (depth, 30–33 m) and domestic hand pump tubewells (10–12 m) located within 5 km from the banks ofGanges. Samples were analyzed for various parame-ters, including total inorganic As, sulfate, nitrate,alkalinity, ammonia, and iron. Hydrochemistry of thegroundwater aquifer was studied through the trilinearplots between monovalent and divalent cations andanions. In Indian mark II hand pumps, arsenicconcentration ranged from below detection limit to448 μg/L. Most of the samples contained both As(III)and As(V). The pH of the samples ranged from 7.1 to8.2. Except for a few, most of the samples werereducing in nature as evident by their negativeoxidation reduction potentials. A positive correlationfor arsenic with iron, ammonia, and dissolved organiccarbon shows the probability of biodegradation of

organic matter and reductive dissolution of Fe oxy-hydroxide processes to leach As in aquifers. Forconfirmation of the suggested arsenic mobilizationmechanism, the presence and absence of sulfate-reducing bacteria and iron-reducing bacteria were alsotested.

Keywords Arsenic .Mobilization . Kanpur district

Introduction

Natural arsenic contamination of groundwater isincreasingly recognized as a threat to human healthworldwide. The presence of arsenic in groundwaterhas been reported from many parts of the world,particularly in the Bengal Delta of India and Bangla-desh (BGS/DPHE 2001), China (Kinniburgh andSmedley 2001), Vietnam (UNESCAP-UNICEF-WHO 2001), and Nepal (Tandukar et al. 2001).Arsenic contamination in India is well documentedespecially in Ganga–Meghna–Brahmaputra plain(Garai et al. 1984; Dhar et al. 1997; Chakraborti etal. 2002). The WHO guideline as well as the Bureauof Indian Standard (BIS) allowable limits for arsenicin drinking water is 10 μg/L. Presently, an interimstandard of 50 μg/L is retained by the Ministry ofRural Development (MHRD) in India.

Mobilization of arsenic occurs in the environ-ment through a combination of several complexnatural processes (Smedley and Kinniburgh 2002).

Environ Monit Assess (2012) 184:4889–4901DOI 10.1007/s10661-011-2310-5

V. S. Chauhan :N. Sankararamakrishnan (*)Center for Environmental Sciences and Engineering,Indian Institute of Technology,Kanpur UP-208016, Indiae-mail: [email protected]

V. S. Chauhan :M. YunusDepartment of Environmental Sciences,Babasaheb Bhimrao Ambedkar University,Lucknow UP-226025, India

Though there are several reports on the variousmobilization routes of arsenic to the environment,some of the most widely accepted hypotheses aredetailed below.

a. Reductive dissolution. In this mechanism(Bhattacharya et al. 1997; Nickson et al. 1998),the reduction of As-rich Fe oxides, due to buriedpeat (McArthur et al. 2001) and other organicdeposits, leads to arsenic release to the aquifer.

b. Alkali desorption. At pH >8, the desorption ofarsenic from metal oxides, especially Fe and Mn,can lead to a high arsenic concentration in thegroundwater (Smedley and Kinniburgh 2002,2005).

c. Sulfide oxidation. Oxidation of arsenical pyritein the alluvial sediments as aquifer drawdownpermits atmospheric oxygen to invade theaquifer (Mallick and Rajagopal 1996; Mandalet al. 1998; Chowdhury et al. 1999). Thismechanism is commonly referred to as the“oxidation hypothesis.”

d. Geothermal action. Mixing of geothermal solu-tions and fresh groundwater can lead to high arsenicconcentrations in some locations (Smedley andKinniburgh 2002).

In the state of Uttar Pradesh, India, few inves-tigations have been carried out on the distribution ofarsenic contamination (Nickson et al. 2007; Chauhanet al. 2009; Chakraborti et al. 2009; Kumar et al.2010). However, the mechanism of release of arsenicin Kanpur district is still unexplored. Arsenic mobi-lization mechanism may vary with the locationdepending on hydrogeological conditions. Hence, itis important to study the correlation of arsenic withvarious species including nitrate, sulfate, iron, bicar-bonate, dissolved oxygen, phosphate, etc., for assess-ing the likely mechanism of arsenic mobilization.This paper delineates the hydrogeochemistry of theshallow aquifers with new data from Kanpur–Unnaodistrict. The objectives of this study were to investi-gate the distribution of arsenic with redox-sensitiveparameters and their redox chemistry in groundwaterand to elucidate possible As release mechanisms inthe groundwater of Shuklaganj area of Kanpurdistrict. Understanding the mechanism for mobiliza-tion may elucidate the predominant arsenic species toplan for proper mitigation steps in arsenic-affectedareas of Kanpur–Unnao districts.

Site description, materials, and methods

Site description and geomorphology of Shuklaganjarea

Unnao industrial areas are parts of Kanpur and UnnaoDistricts of Uttar Pradesh, located at longitude 80°15′–80°34′ E and latitude 26°24′–26°35′ N; it is achronic polluted area and one of the biggest exportingcenters of tanned leather. It is situated on the rightbank of the Ganga River and the left bank of itstributary, the Pandu River, as shown in Fig. 1.

The Ganga River enters the town from the NW andleaves it in the SE direction. The Pandu River enters thecity from the west and joins the Ganga River at adistance of 156 km downstream of Kanpur city. TheKanpur–Unnao region is one of the largest industrialcomplexes of the Ganga Plain in which a number ofindustries such as cotton and wool textile mills, tanningand leather manufacturing industries, large fertilizerfactories, and several arms factories are situated. Thesefactories are producing large amounts of industrialwaste, which are indiscriminately spread in the region.Furthermore, with a population of about 2.4 million inKanpur city and 0.2 million in Unnao city, a largeamount of untreated municipal waste is also dischargedin this region. The area is traversed by the Ganga River,and there are a number of smaller rivers of varyingchannel characteristics (Ansari et al. 2002).

Sample collection, preservation, and analysis

A total of 59 groundwater samples were collectedfrom both India Mark II (30–35 m) and private tubewells (12–15 m) in March–April 2010. A GPS devicewas used for the positioning of each location (Fig. 2).

Prior to sampling, the hand pumps were flushed with30–40 L of water. During sampling, water was filled tothe brim of the bottle without any air bubbles. Those forthe analysis of cations and sulfate were acidified to 1%(v/v) HNO3. Samples were acidified with 2% (v/v) HClfor the analysis of total As (AsT), As(III), and iron.Samples for anion analysis were left unacidified.

In the field, after collection, the samples wereimmediately analyzed for oxidation reduction potential(ORP) and pH measurements by a Wagtech ORP/pHelectrode. The procedures used for the analysis were asper the Standard Methods for Water and Wastewateranalysis APHA 1998. Since most of the techniques are

4890 Environ Monit Assess (2012) 184:4889–4901

of routine type, they are not described here. Totalinorganic arsenic analysis was carried out using silverdiethyldithiocarbamate (APHA 1998). In brief, arsenitewas reduced selectively by aqueous sodium borohy-dride solution to arsine at pH 6. Arsenate, methylar-sonic acid, and dimethylarsenic acid were not reduced

under these conditions. The generated arsine was sweptby a stream of nitrogen from the reduction vesselthrough a scrubber containing glass wool impregnatedwith lead acetate solution into an absorber tubecontaining silver diethyldithiocarbamate and morpho-line dissolved in chloroform. A red color developed,

Fig. 1 Location of the study area in Kanpur–Unnao zone and regional surface geological characteristics (Gowda et al. 2010)

Fig. 2 GPS samplinglocation of Shuklaganj area

Environ Monit Assess (2012) 184:4889–4901 4891

the intensity of which was measured at 520 nm. Todetermine total arsenic in the absence of methyl arseniccompounds, another sample portion was reduced atpH 1. Arsenate concentration was determined by thedifference between the total arsenic concentration andAs(III) concentration. The lower limit of detection wasfound to be 4 μg L−1. Each sample was analyzedtwice. The coefficient of variation in the duplicatesamples was 2.5%. The average total arsenic level in20 aqueous calibration check samples spiked with50 μg L−1As was 52±4.0 μg L−1. All chemicals andsolvents used were of analytical reagents grade. TheSDDC was used from Sigma-Aldrich and E Merck.The procedures for detecting the presence and absenceof sulfate-reducing bacteria (SRB) and iron-reducingbacteria (IRB) are described in brief as follows (Guhaet al. 2005).

For testing the presence of SRB, eleven 100-mLsterilized culture bottles were taken with 50 mL ofautoclaved deoxygenated (using nitrogen purging)enrichment medium (Lovley and Phillips 1988). Inten bottles, a 50-mL aliquot of field sample wasadded. The samples were devoid of dissolved oxygenand were transported in sealed condition. In onebottle, which served as a control, 50 mL of sterilizedand deoxygenated distilled water was added. Thus, allbottles were completely filled with no headspace.Bottles were incubated in an anaerobic incubator at37°C. After 7 days, the results were observedaccording to the color obtained. A highly intenseblack color (+++) indicated a rich active SRB colony;a minus sign (−) sign indicates the absence of SRB.For testing the presence of IRB, the samples (kept at37°C for 7 days) were tested for Fe(II) concentration.

Result and discussion

Geochemistry of major ions

The physicochemical analyses and major ionic concen-trations of 59 groundwater samples were determined(data not shown); the summary of statistical data foreach parameter is presented in Table 1.

Physicochemical parameters

The groundwater samples had a pH range between 7.11and 8.24, with a mean value of 7.74. The temperature

was found to be almost uniform in all the samples,which ranged from 25.7°C to 27.5°C. Like severalprevious studies of Bangladesh aquifers (BGS/DPHE2001; Kinniburgh and Smedley 2001), the redoxpotential data demonstrate a mild oxidizing (onesample showing the positive value of 5.4 mV) to amoderately and/or strongly reducing character (nega-tive ORP values ranging from 0 to −197 mV) of theaquifer of study area.

Major ion chemistry

The concentration variations of major ions ingroundwater samples were analyzed, and it wasfound that HCO3

− (median=350 mg/L) and Na+

(median=98.3 mg/L) were the dominant ions in allgroundwater samples, followed by Cl− (median=78.92 mg/L), SO4

2− (median=65.92 mg/L), Ca2+

(median=55 mg/L), and Mg2+ (median=53 mg/L).The concentration of HCO3

− in groundwaterranged from 210 to 680 mg/L, and relatively highHCO3

− concentrations were observed in shallowwells. The source of HCO3

− could be attributed tothe oxidation of dissolved organic matter present ingroundwater (Smedley et al. 2003).

Organic matter ðCH2OÞ þ O2 ! H2Oþ CO2 ð1Þ

CaMgðCO3Þ2þ CO2þH2O ! Mg2þ þ 2HCO3� þ CaCO3

ð2ÞCaCO3þ CO2 þH2O ! Ca2þ þ 2HCO3

� ð3Þ

Table 1 Summary statistics for analyzed groundwater samplesfrom tube wells (n=9)

Min Max Mean Median SD

Na+ 44.2 365 115.39 98.3 59.42

K+ 3.2 14.68 7.79 7.37 2.61

Ca2+ 28 148 60.52 55 23.48

Mg2+ 21 103 55.15 53 20.72

HCO3− 210 680 364.57 350 105.33

Cl− 83.9 474.85 103.27 78.92 81.47

NO3− 1 54 17.91 12 16.01

PO42− 0 1 0.26 0.2 0.25

SO42− 4.95 248 77.88 65.92 49.94

Concentrations of cations and anions are presented in milligramsper liter


The concentration of Ca2+ and HCO3− in ground-

water could be increased by calcite dissolution(Smedley et al. 2003). Due to this effect, the pH ofgroundwater was found to be slightly alkaline (7.8–8.2). The concentration differences of the chemicalconstituents of groundwater are determined (graph notshown). It is evident that major ions in groundwaterwere quite variable in concentration.

A Na+-normalized Ca2+ versus HCO3− plot

(Fig. 3a) showed that the groundwater samples wereinfluenced by carbonate dissolution. Calciumwas foundto be somewhat linearly related to Mg2+ (R2=0.63;Fig. 3b). Similarly, the Na+-normalized Ca2+ versusMg 2+ plot (Fig. 3c) showed that most of the Mg2+

might have been derived from carbonate dissolution.Groundwater in this study did not show a correlationbetween HCO3

− and (Na+K) excess (i.e., [Na+K]−Cl), as noted by Mukherjee and Fryar (2008).However, a bivariate plot (Fig. 3d) of (Ca2+ + Mg2+)versus HCO3

− showed a positive correlation betweenthem, which further suggested that most parts of thesesolutes might be derived from carbonate mineraldissolution through microbial degradation of organicmatter in the shallow aquifer (Ahmed et al. 2004).

Among the other anions, SO42−

, NO3−, and PO4

2−

were the major inorganic components that might affectthe groundwater as drinking water. Groundwatershowed a wide variability in the concentration of Cl−

and NO3− in the water samples. Phosphate and sulfate

concentrations ranged from 0.0 to 1.0 mg/L and from4.95 to 248 mg/L, respectively. The source of nitrateand phosphate in groundwater in agricultural areascould be due to the application of fertilizer. Even inthese areas, low nitrate in a few samples could beattributed to a bacterial-mediated reduction of nitrate inthe presence of organic matter. Iron(III) reduction iscontrolled by the presence of nitrate. In the presence ofhigh nitrate, iron(III) reduction is thermodynamicallynot feasible. Our results have also shown that there is anegative correlation between nitrate and arsenic.

To classify the major ions for groundwater and tosummarize the major contrasts in hydrogeochemicalcomposition between different water sources, Piperdiagrams were found to be widely used. Plots ofmajor ions on a Piper diagram (Fig. 4) showed thatmost of the samples that fall in the field alkalis exceedalkaline earth. The data plot suggested that thegroundwater in the area was Na–Ca and Cl–SO4–

0 1 2 3 4 5 6 7 8 90.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0 Ca/Na

Ca

/Na

Bicarbonate/Na20 40 60 80 100 120 140 160

20

40

60

80

100Mg

Mg

(mg

/L)

Ca (mg/L)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8Mg/Na

Mg

/Na

Ca/Na200 300 400 500 600 700

40

60

80

100

120

140

160

180

200

220

240 Ca+Mg

Ca+

Mg

(mg

/L)

Bicarbonate (mg/L)

a b

c d

Fig. 3 Bivariate plots show-ing the relationships betweenNa+-normalized Ca2+ andHCO3

− (a), Ca2+ andMg2+ (b), Na+-normalizedCa2+ and Mg2+ (c), and(Ca2+ +Mg2+) and HCO− (d)


HCO3 facies dominant. The trilinear diagram revealedthat majority of the sample was enriched with Na+

and Cl− ions.

Arsenic

In the study area, groundwater arsenic concentrationswere found to be as high as 448 μg L−1. It was alsoobserved that most of the private shallow hand pumpscontained high levels of arsenic. Out of 59 samples inShuklaganj, 44 samples exceeded the BIS and WHOpermission limit (10 μg L−1), and 21 samples exceedthe MHRD (50 μg L−1) permissible limit. Sevensamples exceeded the concentration of 100 μg L−1 ingroundwater. Arsenic(III) concentrations were vari-able in the shallow groundwater, ranging betweenbelow detection limit and 151 μg L−1 (median=7.0 μg L−1). The distributions of As(III) and As(V)are depicted in Fig. 5. It is evident from the figure thatamong the 59 samples analyzed, both As(III) and As(V) were present in 39 samples, while As(V) alonewas found in 14 samples. However, there were nosamples in which As(III) alone was present. Sixsamples contained arsenic below the detection limit(BDL). The ratio of As(III) to As(V) ranged from

BDL to 10.33. The ratio between As(III) with totalarsenic concentration ranged between BDL and 0.91.

Correlation of arsenic with other parameters

Spearman’s rank correlation coefficients have beencalculated to examine the possible relationshipsamong the measured parameters (Table 2). Theconcentrations of arsenic were plotted as a functionof different selected parameters (Fig. 6). Arsenicexhibited a significant correlation with NH3, PO4

3−,and Fe and a negative correlation with nitrate andsulfate. There was no significant correlation of arsenicwith HCO3

−.The positive correlation between PO4

3−, NH4, andAs (Fig. 6) could be associated with the reductivedissolution of Fe (hydr)oxides because PO4

3− com-petes with As for the same adsorption sites of Fe(hydr)oxides (Stollenwerk et al. 2007). Under strongreducing conditions with sufficient SO4, HS

− gener-ated from SO4

2− reduction precipitated dissolved Fe2+

ions as sulfide minerals, leading to low As concen-trations by co-precipitation with Fe sulfide minerals(Appelo and Postma 2005). The reduction of Fe (hydr)oxides could occur at more oxidizing conditions than

Fig. 4 Piper diagram show-ing the level differencebetween major ions of thegroundwater (all theconcentrations are inmilliequivalents)


the sulfate reduction. However, the redox potentialranges of both reactions overlap to a large extent.Therefore, the increase in As concentration by Fe(hydr)oxide reduction could be largely suppressedby the SO4

2− reduction.Figure 7 shows the variations of water quality

parameters with increasing total arsenic concentrationin Shuklaganj. The samples with high As concen-trations (>50 μg/L) generally show very low SO4

2−

levels (Fig. 7c), an indication that the spatial variationin As concentration is closely related to the SO4

2−

concentration. This explanation is supported by other

observations that have shown that alluvial ground-waters with high As concentrations (>100 μg/L) arenormally very low in SO4

2− (<1 μg/L; Ahmed et al.2004). The low concentrations of SO4

2− in ground-water samples and the negative correlation betweenAs and SO4

2− (Fig. 6c) indicated that As has not beendirectly mobilized from sulfide minerals (Harvey etal. 2005).

The relation between As and NO3− indicates that

the low As levels are observed at shallow depths withhigh concentrations of NO3

− (Fig. 6a). The samerelation was also reported in the Bengal Basin byNickson (1998). It is well known that NO3

− stronglybuffers the redox potential and that the reductivedissolution of Fe (hydr)oxides is largely suppressed(Senn and Hemond 2002). As a result, As concen-trations can be very low in the presence of NO3

−.The presence of organic matter in the aquifer

sediments of the Bengal Basin has been reported inseveral studies (McArthur et al. 2001; Ahmed et al.2004). The degradation of this organic matter coulddrive the sequence of redox reactions in the aquifer andmay thereby enhance As mobilization (Ravenscroft etal. 2001; McArthur et al. 2004). Elevated levels ofPO4

3− and iron due to the biodegradation of organicmatter (Harvey et al. 2002; Bhattacharya et al. 2006)are indicated by a positive correlation (R2=0.75 and

500

400

300

200

100

100

20 30 40 50

Ars

enic

con

cent

ratio

n (µ

g/L)

No. of samples

As(V)As(III)

Fig. 5 Distribution As(III) and As(V) in Shuklaganj

Table 2 Correlation matrix among various water quality parameters for Shukalganj (Kanpur–Unnao) area

As(t) pH ORP Hard HCO3 Na K Ca Cl SO4 NH3 NO3 DO PO4 Fe Mg

As(t) 1.00 −0.11 −0.02 0.04 0.28 0.15 −0.12 −0.14 −0.13 −0.21 0.67 −0.42 −0.53 0.75 0.67 −0.03pH 1.00 0.10 0.22 0.03 −0.18 −0.04 0.04 0.13 0.40 −0.06 −0.02 0.03 0.06 −0.14 −0.30ORP 1.00 0.24 0.19 −0.16 0.06 0.19 −0.10 0.09 0.02 0.11 0.19 0.06 −0.10 0.15

Hard 1.00 0.16 −0.11 0.14 0.28 −0.15 0.07 0.14 −0.13 0.21 0.24 −0.05 −0.04HCO3 1.00 −0.18 −0.09 −0.19 −0.17 0.04 0.21 −0.11 −0.03 0.17 0.00 −0.08Na 1.00 0.00 0.05 0.04 −0.04 −0.01 −0.11 −0.01 −0.13 0.06 0.02

K 1.00 0.06 0.06 0.05 −0.01 0.08 0.23 −0.13 −0.21 0.08

Ca 1.00 0.11 0.05 −0.13 −0.02 0.15 −0.11 −0.11 0.25

Cl 1.00 0.17 −0.04 0.00 −0.03 −0.19 0.09 0.23

SO4 1.00 −0.21 0.08 0.33 −0.16 −0.27 −0.09NH3 1.00 −0.46 −0.27 0.71 0.51 −0.04NO3 1.00 0.04 −0.51 −0.24 −0.09DO 1.00 −0.29 −0.50 0.08

PO4 1.00 0.59 −0.02Fe 1.00 −0.07Mg 1.00


0 100 200

250

200

150

100

300 400 500

0

0

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8

0.0

0.2

0.4

0.6

0.8

1.0

10

20

30

40

50

50

60

0

1

2

3

4

5

6

Nitr

ate

(mg/

l)

Arsenic (µg/L)

0 100 200 300 400 500

Arsenic (µg/L)

0 100 200 300 400 500Arsenic (µg/L)

0 100 200 300 400 500

Arsenic (µg/L)

0 100 200 300 400 500

Arsenic (µg/L)

Am

mon

ia (

mg/

l)

Sulphate

Sul

phat

e (m

g/l)

Pho

spha

te (

mg/

L)

0.0

0

0.2

0.4

0.6

0.8

1.0

Pho

spha

te (

mg/

L)

iron

(mg/

l)

Iron (mg/L)

a b

c d

e f

Fig. 6 Plots of As concentration as functions of various chemical parameters


R2=0.67, respectively) with total As. DO in thegroundwater is normally consumed by the decomposi-tion of organic matter. After the DO is completelydepleted, denitrification, reduction of Fe (hydr)oxides,

and sulfate reduction start to occur successively bymicrobes as the redox conditions become morereducing. Alkalinity and pH generally show increasingtrends due to these reactions (Kim et al. 2008).

5 10 15 20 25 30 35 40 45 50 55 600.00.20.40.60.81.0

0123450

2

4

6

80

50100150200250

010203040500

100200300400

Pho

spha

te (

mg/

L)

Number of Samples

Am

mon

ia

(m

g/l)

Iron

(mg/

L)

Sul

phat

e (

mg/

L) N

itrat

e (

mg/

L) A

rsen

ic (

µg/L

)

b

a

c

d

e

f

Fig. 7 Variation of other water quality parameters with increasing total arsenic concentration in Shuklaganj, Kanpur (n=59


Elevated levels of PO43− in groundwater indicated

a moderately strong positive correlation (R2=0.556)with As (Fig. 6e). Sorption of phosphate and arsenategenerally decreases with high pH conditions (Gao andMucci 2001). It is also reported that if the As-to-phosphate ratio is 1:10, then As(V) and As(III)sorption decreased by 40% and 50%, respectively(Dixit and Hering 2003). In the present scenario, thepH of the groundwater ranged from 7.11 to 8.24, witha mean value of 7.74. Hence, in the presence of highlevels of phosphate, desorption of arsenic occurs,leading to a positive correlation. Microbial degrada-tion of organic matter could lead to elevated levels ofPO4

3− in groundwater (Ravenscroft et al. 2001;Bhattacharya et al. 2006). Acharyya (1999) speculat-ed that PO4

3− in the groundwater resulted from theapplication of fertilizers; however, this is not con-vincing because the amount of dissolved and sorbedPO4

3− over the aquifer volumes would exceed theamount of PO4

3− applied as fertilizers (Bhattacharyaet al. 2002). A significantly strong correlationbetween Fe and PO4

3− (R2=0.59; Fig. 6f) is a clearevidence for the release of PO4

3− in the groundwaterthrough a microbial-mediated reductive dissolutionof Fe(III) oxyhydroxide (McArthur et al. 2004;Bhattacharya et al. 2006).

A good positive correlation (R2=0.65376) betweendissolved organic carbon (DOC) and As (Fig. 8) ingroundwater suggested that microbial degradation oforganic matter in the sediment resulted in an overallreducing environment and facilitated the release of Asin groundwater (McArthur et al. 2001). It is also

known that microbial degradation of DOC resulted inthe formation of HCO3

−. Bacteria mediated therelease of As of younger sediments into groundwaterunder reducing conditions. Enhanced microbial ac-tivity accelerated the digenetic process involving themobilization of As from sediments with high organicmatter (Akai et al. 2004).

Presence and absence of SRB/IRB

SRB reduced sulfate to form hydrogen sulfide. Ferricammonium sulfate reacted with hydrogen sulfide toproduce ferrous sulfide, an insoluble black precipitate.This reaction was found to be responsible for theobserved blackening of the vials. Sample 5 and 17,which turned highly black within 24 h, were found tohave low arsenic concentrations (6 and 1 μg/L,respectively) compared with samples having higharsenic concentrations of 260 and 192 μg/L (samples16 and 4, respectively). However, sulfate as well asORP in samples 5 and 6, and 16 and 17 were similar.The observed ORP in these samples indicated thatthis is not conducive to sulfate reduction. Thus, itmay not be possible to explain the correlationbetween sulfate, sulfate-reducing bacteria, and arse-nic. The results obtained are shown in Table 3.Thus, the presence of SRB indicated that theseanaerobes that obtain their energy from the enzymaticreduction of sulfates produced hydrogen sulfidewhich reacted with arsenic, leading to the formationof arsenic sulfide and their immobilization in theaquifer. This explains the reverse correlation of SRBand arsenic concentration.

The most significant electron acceptors remainingin the aquifer are ferric iron and sulfate. It is generallyobserved that IRB preferentially reduced and dis-solved the least crystalline discrete phases of hydratediron oxide, with a consequent release of its sorbedarsenic and other trace elements to groundwater(Lovley and Chapelle 1995). It is evident from Table 4that samples 4 and 16 with total arsenic concen-trations of 192 and 260 ppb, respectively, contained ahigh concentration of Fe(II) (around 0.40 mg/L),indicating higher IRB activity. Furthermore, themeasured ORP of these samples also showed thatiron reduction is possible. Thus, these observationssuggested that Fe(III) reduction to ferrous oxyhydr-oxide, releasing arsenic in due course, could be thepossible mechanism.

50

40

30

20

40

00 100 200 300 400 500

DO

C (m

g/L)

Arsenic concentration (µg/L)

r = 0.65376

Fig. 8 Plot between arsenic concentration versus DOC


From the aforementioned observations, the geo-chemistry of Shuklaganj area is summarized below:

1. All groundwater samples were found to be reducingin nature (as indicated by negative ORP values), andthe pH of all samples were below 8.5.

2. There existed a positive correlation betweenarsenic with iron, ammonium, and phosphate ionand a weak negative correlation between arsenicnitrate and sulfate.

3. In most of the samples, As(III) and As(V)coexisted; among the 59 analyzed samples, bothAs(III) and As(V) were present in 39 samples,while As(V) was present alone in 14 samples.There are six samples in which arsenic concen-tration was BDL.

4. A good positive correlation between DOC and Asin groundwater suggested that microbial degrada-tion of organic matter in the sediment resulted inan reducing environment.

5. The bivariate plot of (Ca2+ + Mg2+) versusHCO3

− showed a positive correlation betweenthem, which suggested that most parts of thesesolutes may be derived from carbonate mineraldissolution through microbial degradation oforganic matter in the shallow aquifer.

6. The data plot in trilinear plot suggested that thegroundwater in the area is Na–Ca and Cl–SO4–HCO3 facies dominant.

7. Tests for the presence and absence of SRB andIRB showed the active role of microorganism forarsenic release.

Based on the above results and taking into accountthe redox chemistry of arsenic, it could be suggestedthat arsenic is released by the reductive dissolution offerric oxide hydroxide.

Conclusions

A systematic study was conducted in the Shuklaganjarea of Kanpur–Unnao district, UP, to investigate thegeochemistry of arsenic in groundwater with the viewof obtaining a better understanding regarding themechanisms governing the mobilization of arsenicinto the groundwaters of this district. The studyinvolved the collection of groundwater in and aroundShuklaganj area. Samples were collected from IndiaMark II hand pumps (depth, 30–33 m) and domestichand-pumped tube wells (10–12 m) located within5 km from the banks of Ganges. Except for a few,most of the samples were reducing in nature, asevident from their negative ORPs. A bivariate plot ofCa2+ and Mg2+ versus HCO3

− showed a positive

Sample no. Total arsenic (μg/L) Presence or absence of sulfate-reducing bacteria Note

1 15 +++ (+3)

4 192 ++ (+2)

5 6 ++++++++++ (+10) Highly black

7 57 +++++ (+5)

9 38 ++++ (+4)

11 62 ++++++ (+6)

12 14 ++++++++ (+8)

16 260 + (+1)

17 1 ++++++++++ (+10) Highly black

19 15 +++++++ (+7)

Table 3 Presence orabsence of sulfate-reducingbacteria

+, Very light black color; ++, Prominent black color; +++, Very dark black color;More than 3+, Highly black

Table 4 Presence or absence of iron-reducing bacteria

Sample no. Total arsenic(μg/L)

Fe (tot.)(mg/L)

Fe(II)(mg/L)

4 192 3.5 0.40

5 6 0.5 0.08

7 57 1.57 0.14

9 38 0.63 0.09

11 62 6.06 0.11

12 14 0.56 0.16

14 4 0.18 0.18

16 260 4.7 0.42

18 50 1.65 0.38


correlation between them, suggesting the carbonatemineral dissolution through microbial degradation oforganic matter in the shallow aquifer. The trilineardiagram revealed that majority of the samples areenriched with Na+ and Cl− ions. Arsenic concen-trations ranged from <4 to 448 μg/L. Most of thesamples contained both As(III) and As(V). Theconcentration of As(III) was found to be equal/higherthan As(V) in most of the samples. Correlationstudies among various water quality parameters andthe tests for SRB and IRB revealed a reductionmechanism as the most probable mechanism for therelease of arsenic to groundwater.

Acknowledgments NS is thankful to Council of Scientificand Industrial Research (scheme no. 24(306)09-EMR-II) forfinancial support to carry out this work. VS Chauhan is gratefulto CSIR for providing the SRF (File No. 9/92(738)10-EMRI).We are also thankful to www.gpsvisualizer.com for plotting thegps locations in the map.

References

Acharyya, S. K. (1999). Arsenic poisoning in the Ganges Delta.Nature, 401, 545.

Ahmed, K. M., Bhattacharya, P., Hasan, M. A., Akhter, S. H.,Alam, S. M. M., & Bhuyian, M. A. H. (2004). Arsenicenrichment in groundwater of the alluvial aquifers inbangladesh: An overview. Applied Geochemistry, 19(2),181–200.

Akai, J., Izumi, K., Fukuhara, H., Masuda, H., Nakano, S., &Yoshimura, T. (2004). Mineralogical and geomicrobiolog-ical investigations on groundwater arsenic enrichment inBangladesh. Applied Geochemistry, 19(2), 215–230.

Ansari, A. A., Singh, I. B., & Tobschall, H. J. (2002).Importance of geomorphology and sedimentation process-es for metal dispersion in sediments and soils of the gangaplain: Identification of geochemical domains. ChemicalGeology, 162(3–4), 245–266.

APHA. (1998). Standard methods for water and wastewater (20thed.). Washington: American Public Health Association.

Appelo, C. A. J., & Postma, D. (2005). Geochemistry,groundwater and pollution (2nd ed.). Rotterdam: A.A.Bakelma.

BGS/DPHE (2001). Arsenic contamination of groundwater inBangladesh. In: Kinniburgh, D. G., Smedley, P. L. (Eds.),Final Report, BGS Technical Report WC/00/19. BritishGeological Survey, Keyworth, UK.

Bhattacharya, P., Chatterjee, D., & Jacks, G. (1997). Occurrenceof arsenic-contaminated groundwater in alluvial aquifersfrom delta plains, Eastern India: Options for safe drinkingwater supply. International Journal of Water ResourcesDevelopment, 13, 79–92.

Bhattacharya, P., Jacks, G., Ahmed, K. M., Routh, J., & Khan,A. A. (2002). Arsenic in groundwater of the Bengal Delta

plain aquifers in Bangladesh. Bulletin of EnvironmentContamination and Toxicology, 69(4), 538–545.

Bhattacharya, P., Claesson, M., Bundschu, J., Srace, O.,Fagerberg, J., & Jacks, G. (2006). Distribution andmobility of arsenic in the Río Dulce alluvial aquifers inSantiago del Estero province, Argentina. Science of theTotal Environment, 358(1), 97–120.

Chakraborti, D., Ghorai, S. K., Das, B., Pal, A., Nayak, B., &Shah, B. A. (2009). Arsenic exposure through groundwaterto the rural and urban population in the allahabad-kanpurtrack in the upper ganga plain\ supplementary informat.Journal of Environmental Monitoring, 11(8), 1455–1459.

Chakraborti, D., Rahman, M. M., Chowdhury, U. K., Paul, K.,Sengupta, M. K., & Lodh, D. (2002). Arsenic calamity inthe Indian subcontinent: What lessons have been learned?Talanta, 58, 3–22.

Chauhan, V. S., Nickson, R. T., Chauhan, D., Iyengar, L., &Sankararamakrishnan, N. (2009). Ground water geochem-istry of Ballia district, Uttar Pradesh, India and mechanismof arsenic release. Chemosphere, 75(1), 83–91.

Chowdhury, T. R., Basu, G. K., Mandal, B. K., Biswas, B. K.,Samanta, G., & Chowdhury, U. K. (1999). Arsenicpoisoning in the Ganges Delta. Nature, 401, 545–546.

Dhar, R. K., Biswas, B. K., Samanta, G., Mandal, B. K.,Chakraborti, D., Roy, S., et al. (1997). Groundwaterarsenic calamity in Bangladesh. Current Science, 73(1),48–59.

Dixit, S., & Hering, J. G. (2003). Comparison of As(III) and As(V) sorption onto iron oxide minerals: Implications forarsenic mobility. Environment Science and Technology, 37,4182–4189.

Gao, Y., & Mucci, A. (2001). Acid base reactions, phosphateand arsenate complexation, and their competitive adsorp-tion at the surface of goethite in 0.7 M NaCl solution.Geochimica et Cosmochimica Acta, 65, 2361–2378.

Garai, R., Chakraborty, A. K., Dey, S. B., & Saha, K. C. (1984).Chronic arsenic poisoning from tubewell water. Journal ofthe Indian Medical Association, 82(1), 34–35.

Gowda, S. S., Reddy, R. M., & Govil, P. K. (2010). Assessment ofheavy metal contamination in soils at Jajmau (Kanpur) andUnnao industrial areas of the Ganga Plain, Uttar Pradesh,India. Journal of Hazardous Materials, 174, 113–121.

Guha, S., Raymahashay, B. C., Banerjee, A., Acharyya, S. K.,& Gupta, A. (2005). Collection of depth specific groundwater samples from an arsenic contaminated aquifer inWest Bengal, India. Environmental Engineering Science,22, 870–881.

Harvey, C. F., Swartz, C. H., Badruzzaman, A. B. M., Keon-Blute, N., Yu, W., Ali, M. A., et al. (2002). Arsenicmobility and groundwater extraction in Bangladesh.Science, 298, 1602–1606.

Harvey, C. F., Swartz, C. H., Badruzzaman, A. B. M., Keon-Blute, N., Yu, W., & Ali, M. A. (2005). Groundwaterarsenic contamination on the Ganges Delta: Biogeochem-istry, hydrology, human perturbations, and human suffer-ing on a large scale. Comptes Rendus Geoscience, 337(2),285–296.

Kim, K., Kim, H., Choi, B., Kim, S., Park, K., & Park, E.(2008). Fe and Mn levels regulated by agriculturalactivities in alluvial groundwaters underneath a floodedpaddy field. Applied Geochemistry, 23(1), 44–57.


Kinniburgh, D. G., & Smedley, P. L. (2001). Arsenic contam-ination of groundwater in Bangladesh. Tech. Rep. WC/00/19. British Geological Survey, Keyworth.

Kumar, M., Kumar, P., Ramanathan, A. L., Bhattacharya, P.,Thunvik, R., & Singh, U. K. (2010). Arsenic enrichmentin groundwater in the middle Gangetic Plain of Ghazipurdistrict in Uttar Pradesh, India. Journal of GeochemicalExploration, 105(3), 83–94.

Lovley, D. R., & Chapelle, F. H. (1995). Deep subsurfacemicrobial processes. Reviews of Geophysics, 33, 365–381.

Lovley, D. R., & Phillips, E. J. P. (1988). Novel mode of microbialenergy metabolism: Organic carbon oxidation coupled todissimilatory reduction of iron or manganese. Applied andEnvironmental Microbiology, 54(6), 1472–1480.

Mallick, S., & Rajagopal, N. R. (1996). Groundwater develop-ment in the arsenic affected alluvial belt of West Bengal—Some questions. Current Science, 70, 956–958.

Mandal, B. K., Chowdhury, T. R., Samanta, G., Mukherjee, D. P.,Chanda, C. R., Saha, K. C., et al. (1998). Impact of safe waterfor drinking on five families for 2 years inWest Bangal, India.Science of the Total Environment, 218, 185–201.

McArthur, J. M., Ravenscroft, P., Safiullah, S., & Thirlwall, M.F. (2001). Arsenic in groundwater: Testing pollutionmechanisms for sedimentary aquifer in Bangladesh. WaterResources Research, 37, 109–117.

McArthur, J. M., Banerjee, D. M., Hudson-Edwards, K. A.,Mishra, R., Purohit, R., Ravenscroft, P., et al. (2004).Natural organic matter in sedimentary basins and itsrelation to arsenic in anoxic ground water: The exampleof West Bengal and its worldwide implications. AppliedGeochemistry, 19, 1255–1293.

Mukherjee, A., & Fryar, A. E. (2008). Deeper groundwaterchemistry and geochemical modeling of the arsenicaffected western Bengal Basin, West Bengal, India.Applied Geochemistry, 23(4), 863–894.

Nickson, R., McArthur, J., Burgess, W., Ahmed, K. M.,Ravenscroft, P., & Rahman, M. (1998). Arsenic poisoningof Bangladesh groundwater. Nature, 395, 338 (Letter).

Nickson, R. T., Sengupta, C., Mitra, P., Dave, S. N., Banerjee,A. K., Bhattacharya, B., et al. (2007). Current knowledgeon the distribution of arsenic in groundwater in five statesof India. Journal of Environmental Science and Health,Part A Environmental Science A, 42, 1–12.

Ravenscroft, P., McArthur, J. M., & Hoque, B. A. (2001).Geochemical and palaeohydrological controls on pollutionof groundwater by arsenic. In W. R. Chappell, C. O.Abernathy, & R. L. Calderon (Eds.), Arsenic exposure andhealth effects, vol. IV (pp. 53–57). Oxford: Elsevier.

Senn, D. B., & Hemond, H. F. (2002). Nitrate controls on ironand arsenic in an urban lake. Science, 296(5577), 2373–2376.

Smedley, P. L., & Kinniburgh, D. G. (2002). A review of thesource, behaviour and distribution of arsenic in naturalwaters. Applied Geochemistry, 17(5), 517–568.

Smedley, P. L., & Kinniburgh, D. G. (2005). Arsenic ingroundwater and the environment. In: Selinus, Olle,Alloway, B. (Eds.), Essentials of medical geology. Impactsof natural environment on public health (pp. 263–299).Amsterdam: Academic.

Smedley, P. L., Zhang, M., Zhang, G., & Luo, Z. (2003).Mobilisation of arsenic and other trace elements in fluviola-custrine aquifers of the huhhot basin, inner mongolia.Applied Geochemistry, 18, 1453–1477.

Stollenwerk, K. G., Breit, G. N., Welch, A. H., Yount, J. C.,Whitney, J. W., Foster, A. L., et al. (2007). Arsenicattenuation by oxidized aquifer sediments in Bangladesh.Science of the Total Environment, 379(3), 133–150.

Tandukar, N., Bhattacharya, P., & Mukherjee, A. B. (2001).Managing arsenic for our future. Proceedings of theInternational Conference on Arsenic in the Asia–Pacificregion, Adelaide, South Australia, 21–23 November, pp.103–105.

UNESCAP-UNICEF-WHO. (2001). Expert Group Meeting.United Nations Economic and Social Commission forAsia and Pacific. In: Geology and health: Solving thearsenic crisis in the Asia–Pacific region, Bangkok.


geochemistry and mobilization of arsenic in shuklaganj area of kanpur–unnao district, uttar...

Documents