NATURAL ARSENIC IN GROUNDWATER: OCCURRENCE, REMEDIATION AND MANAGEMENT - CHAPTER 17 ppt

Microbial processes and arsenic mobilization in mine tailings
and shallow aquifers
J. Routh
Department of Geology and Geochemistry, Stockholm University, Stockholm, Sweden
A. Saraswathy
Department of Biology, West Virginia State College, West Virginia, USA
ABSTRACT: Microbial processes play an important role in transforming and mobilizing As in
the sub-surface. Enrichment cultures indicated several As tolerant species, which actively reduced
As(V) to As(III). No change in As speciation occurred in the controls, thereby confirming As(V)
reduction was biologically mediated, and active metabolism was a prerequisite for reduction.
Different growth and As(V) reduction rates were noted under oxic to sub-oxic conditions, and a
zero-order model best fits the As(V) reduction data. Arsenic concentrations in the microcosms
seem to affect biomass yield and As(V) reduction rates in some of the strains. Arsenic reduction
in these microorganisms probably occurs for respiratory or detoxification purposes. It is likely that
microbial mobilization of As may have an impact on groundwater remediation treatment in these
environments.
1 INTRODUCTION
Arsenic (As) compounds are highly toxic (Nriagu 2002). People have known about its lethal proper-
ties since antiquity, and have often used arsenic trioxide (As
2
O
3
) for homicide purposes. Renewed
interest in the metalloid has increased dramatically, but for different reasons. A recent paper by
Bhattacharya et al. (2002) details the As crisis, which affects the lives of general population
en masse in several countries. The problem is nowhere as serious as it is in Bangladesh and India,
where more than 70 million people are at risk from drinking As-rich groundwater (Harvey et al.
2003). The first reports on clinical manifestation of As toxicity from this region came up around
1978, and thereafter, chronic cases of As poisoning (including fatalities) have been reported since
1982 (Saha 1984, Goriar 1984).
Arsenic commonly occurs in the environment as inorganic trivalent As(III) and pentavalent

As(V) species (Cullen & Reimer 1989). The trivalent arsenous acid is more dominant under reducing
conditions, whereas its pentavalent counterpart, in the form of arsenic acid is common under oxi-
dizing conditions. Mobility of As(III) is higher compared to As(V) in sedimentary and aqueous
environments. The difference in mobility is attributed to the high affinity of As(V) for insoluble
species such as hydrous ferric and manganese oxides (Cullen & Reimer 1989). Additionally, several
methylated forms of organoarsenicals (e.g., methylarsonic, methylarsonus, and dimethylarsenic
acid) are also found in water as breakdown or excretory byproducts (Cullen & Reimer 1989,
Sohrin et al. 1997). Although As(III) is not thermodynamically stable under oxidizing conditions,
there are several incidences where As(III) occurs as the dominant species in the water column
(Aurillo et al. 1994, Sohrin et al. 1997). Prevalence of As(III) in these studies was correlated with
phytoplankton abundance suggesting non-equilibrium conditions were microbially mediated.
Arsenic enters the terrestrial and aquatic environments through both natural and anthropogenic
activities. Natural processes can contribute to the widespread distribution of As through weathering
145
Natural Arsenic in Groundwater: Occurrence, Remediation and Management –
Bundschuh, Bhattacharya and Chandrasekharam (eds)
© 2005, Taylor & Francis Group, London, ISBN 04 1536 700 X
Copyright © 2005 Taylor & Francis Group plc, London, UK
of As bearing rocks and minerals, microbial activity, and volcanic eruptions. In contrast, anthro-
pogenic point sources are localized and include inputs from mining of base metals, smelter slag,
coal combustion, production of paints and dyes, tanning, wood preservation, and pesticides. The net
output of As from anthropogenic processes is high compared to natural processes (Bhattacharya
et al. 2002), but ironically, it is the natural processes that are involved in dispersion of As, which
is of most concern to human beings.
1.1 Arsenic toxicity and microbial resistance
Arsenic compounds readily accumulate in living tissues due to their affinity for proteins and lipids
or cause breakdown of oxidative phosphorylation (Oremland & Stolz 2003). Many prokaryotes
and eukaryotes have however, developed unique inter-cellular reaction mechanisms to rid them-
selves of As, and excrete it as waste byproducts. Some even generate energy during this process.
For example, higher eukaryotes reduce As(V) to As(III) followed by methylation resulting in mono

and dimethylarsonoic acids (MMA, DMA). Fungi produce trimethylarsines and bacteria produce
MMA and DMA (Diorio et al. 1995, Sohrin et al. 1997). The physical excretion of these byproducts
often occur as encrustations on the cell wall (Saraswathy et al. 2004) or transferred into the water
column at the sediment-water interface (Ahmann et al. 1997, Martin & Pedersen, 2002, Routh et al.
2004). Additionally, As can be converted to benign products as arsenobetaine and As containing
sugars found in marine algae, animals, and higher plants (Cullen & Reimer 1989).
Reduction of As(V) to As(III) in anoxic environments primarily occurs via dissimilatory As
reduction (Ahmann et al. 1997, Newman et al. 1997a,b), whereby microorganisms utilize As(V)
as the terminal electron acceptor. The reaction is energetically favorable and coupled to oxidation
of organic matter. Two important prerequisites for such microorganisms are the presence of strict
anoxic conditions and high As levels (Newman et al. 1997b). Dissimilatory As reduction occurs in
bacteria scattered throughout the bacterial domain representing ␥-, ␦-, ␧-Proteobacteria, low-GC
gram-positive bacteria, thermophilic Eubacteria, and Crenoarchea (Oremland & Stolz 2003).
However, microorganisms may also possess reduction mechanisms that are not coupled to respi-
ratory processes, but instead, impart resistance to As toxicity (e.g., Jones et al. 2000, Macur et al.
2001). Enzymes involved in the detoxification pathway are transcribed by the ars operon resulting
in inter-cellular reduction of As(V), and the subsequent efflux of As(III) via a trans-membrane
pump (Cervantes et al. 1994, Rosen 2002).
1.2 Arsenic mobilization
Different biogeochemical mechanisms have been proposed to explain As mobilization in sedimen-
tary environments. These processes involve: (1) oxidation of pyrite, (2) reduction of Fe-oxyhydroxides
coupled to oxidation of organic matter and release of As(V), (3) exchange of As(V) with phosphate
based fertilizers (e.g., Roy Chowdury et al. 1999, Nickson et al. 1998, Harvey et al. 2003). More
recently, researchers have increasingly focused on the role of microorganisms in mobilizing As in
sedimentary environments (e.g., Ahmann et al. 1997, Cummings et al. 1999, Jones et al. 2000, Macur
et al. 2001, Islam et al. 2004). Transformation of As by microorganisms has important environ-
mental implications because As(V) and As(III) have different sorption and toxicological properties.
Primarily such studies have mostly focused on sites contaminated by mining, pesticides or other
related anthropogenic activities, and they all demonstrate enhanced microbial As mobilization on
short time scales.

Here, we present data from our ongoing investigations on mine tailings in northern Sweden and
shallow aquifers in West Bengal, India. The environments are completely different in terms of
physiographic settings, sub-surface geology, and environmental conditions, but both places indicate
high As concentrations in ground and surface water. Although different processes in the sub-surface
may substantially influence the biogeochemical cycling of As, we focused on microbial processes
and their affect As cycling. The different microbial processes important in As cycling underscore
the need for our continued inquiry regarding As transformations, in hopes, that we can develop
146
Copyright © 2005 Taylor & Francis Group plc, London, UK
greater predictability of its behavior. To the best of our knowledge, microbial processes affecting
As mobilization has not been investigated by other researchers at these sites, and may thus, pro-
vide new insights. Moreover, microbial processes involved in As(V) reduction and mobilization
are many times faster than chemical transformation (e.g., Sohrin et al. 1997, Jones et al. 2000). If
microbial processes are indeed active, this may have important environmental implications on As
remediation for groundwater treatment and management at these sites.
2MATERIALS AND METHODS
2.1 Sampling sites
Adak mine tailings: The abandoned mine tailings at Adak in Västerbotten district of northern
Sweden extends over 1500 m ϫ 2000 m ϫ 5 m. The site is affected by acid mine drainage and has
low pH (ϳ3–4). The tailings have high concentrations of As, Cu, and Zn, and they have been
mixed with glacial till to reduce surficial weathering (Jacks et al. 2003). The tailings are underlain
by peat bogs, and extend close to the shores of Lake Ruttjejaure. Shallow streams running adjacent
to the tailings deposits, drain into Lake Ruttjejaure carrying washouts of mine tailings. Sampling was
done using a gravity corer to extract undisturbed sediment cores from the lake. Details on sam-
pling and different geochemical and microbiological assays are further discussed in Bhattacharya
(2004).
Ambikanagar groundwater aquifer: Ambikanagar is located in the Deganga Block of North 24
Parganas in West Bengal, India. The water table occurs at a depth of 5-m, and rainfall in summer
is the principal source of recharge for aquifers. Reconnaissance work by our group indicated that
As concentrations in the shallow wells are often above the permissible drinking water limit

(50 ␮g/L; Routh et al. 2003). The underlying thick Quaternary alluvium consists of cycles of com-
plete or partly truncated fining-upward sequences dominated by coarse to medium sand, fine sand,
silt, and clay. Aquifer sediments in the deep wells are mostly coarse sands, whereas the shallow
wells usually consist of fine-to-medium grained sands. Air jet drilling was used to install an 18-m
deep well. The aquifer sediments were collected in Anero™ (Mitsubishi, Inc.) bags and shipped to
Stockholm for microbial assays. The experiments were started within 4-days after sampling.
2.2 Microcosm experiments
The microcosm experiments were a two-step process: (1) enrichment studies to isolate bacteria tol-
erant to high As levels, and (2) determination of the As mobilizing capacity of isolated pure microbial
cultures. The sediments were inoculated into sterile minimal medium (Turpeinen et al. 1999). The
medium contained lactate as the carbon source, and it was spiked with As. The microcosms were
sampled, and a specific volume of sample sacrificed periodically for different microbiological and
geochemical assays. The sediment slurries extracted under aseptic conditions through the rubber
septa were centrifuged at 907 G (3000 rpm). The aqueous and sediment phases obtained were sep-
arately analyzed for As(III) and As(V) species, and compared to the heterotrophic plate counts of
the corresponding day. The heterotrophic plate counts were performed by serially diluting the
samples using phosphate buffered saline solution. The bacterial culture was spread on Tryptic Soy
Agar plates spiked with As, and incubated for 72 hrs at 22°C. The bacterial colonies were selected
and replated until pure cultures were obtained. The isolates were identified using the API and 16S
rRNA techniques.
The pure cultures were inoculated into sterile basal salts medium under oxic to sub-oxic
(2–3 mg/L dissolved oxygen; obtained by bubbling Ar through the medium and storing samples in
N
2
filled box) conditions containing 1mM, 2mM, and 5mM As(V) and lactate. During sampling
Eh, pH, and oxygen were measured in the microcosms. Replicate samples were sacrificed period-
ically. Microbial growth was determined by measuring change in optical density (600 nm) and dry
weight over the duration of the microcosm experiment. As(III) and As(V) species in the medium
147
Copyright © 2005 Taylor & Francis Group plc, London, UK

was measured by modifying existing spectrophotometric methods (Johnson & Pilson 1972,
Cummings et al. 1999). Optical density was calibrated for each strain. Additional samples were set
up as controls after treating the samples with HgCl
2
and formaldehyde. Specific details of these
procedures are provided in Collins et al. (2004) and Routh et al. (2004).
3 RESULTS
3.1 Adak mine tailings
Microbes enhanced dissolution of As in enrichment cultures by increasing As(III) concentrations in
the aqueous phase and mobilizing ϳ27–51% of As present in contaminated sediments (Bhattacharya
et al. 2003). Several bacteria were isolated from the enrichment studies, and identification of
different microbial strains is ongoing. Here, we have focused on two microbial strains where we
have generated complete data for: (1) arsenic transformation and mobilization, and (2) API and
16S rRNA identification.
Arsenicicoccus bolidensis is hitherto a new species of actinomycete and it is a gram-positive,
facultatively anaerobic, coccus-shaped microorganism (Fig. 1; Collins et al. 2004). The microcosm
experiments indicated a fall in As(V) coupled to increase in As(III) and heterotrophic growth
(indicated as increase in optical density and dry weight). A. bolidensis reduced 0.06–0.20mM/day
As(V) under sub-oxic conditions (Saraswathy et al. 2004). Arsenic reduced by the bacteria occurs
as encrustations on bacterial cells as shown by EDAX X-emission spectrum (Fig. 1). The As(V)
reduction values are low compared to other As reducing microorganisms (Routh et al. 2004).
As(V) reduction is however, related to growth in A. bolidensis implying that respiration and/or
detoxification pathways may be involved in As(V) transformation. Notably, this is the first report
of an actinomycete involved in As reduction in sedimentary environments.
A novel species of facultatively anaerobic Chromobacterium occurring as rod-shaped microor-
ganisms were isolated from the Adak sediments (Fig. 1). Bacterial growth in the culture decreased
after 12 days corresponding to the conversion of 74% of 1mM As(V) to As(III). This bacterium
was able to reduce 0.7–0.22 mM/day of As(V) (Fig. 2). Oxygen levels as high as 0.025 mM did not
affect bacterial growth or As(V) reduction. In the presence of other electron acceptors in com-
petition experiments involving lactate and a combination of As(V) with sulfate or nitrate, only

As(V) concentrations varied.
3.2 Ambikanagar shallow aquifer
Enrichment cultures indicated several As tolerant species, which actively reduced As(V). Specific
details regarding the geochemical trends indicated by these bacteria are discussed in Routh et al.
(2004). Continued increase in As concentrations in the enrichment cultures affected bacterial
growth resulting in a decrease in plate counts and As(V) reduction. During the experiment, oxy-
gen and Eh levels decreased, whereas pH increased. Amongst the eleven microbial strains isolated
from the TSA plates, five of them were morphologically most distinct. These strains were selected
for 16S rRNA characterization and As mobilization experiments. The bacteria were identified as:
Acinetobacter johnsonii, Citrobacter freundii, Comamonas testosteroni, Enterobacter cloacae,
and Sphingobium yanoikuyae. These bacteria range from aerobic to facultative anaerobic species.
Similarity of the 16S rRNA sequence with GenBank varies between 98 and 100%.
Different growth and As(V) reduction rates were noted on inoculating the basal salts medium.
Maximum growth and As(V) reduction was noted in the bacteria A. johnsonii (Fig. 2), which cor-
responded with initial As(V) concentration and biomass yield. Compared to other As(V) reducing
microorganisms, bacteria isolated in this study indicated lower reduction rates (0.11–0.25 mM/day).
Notably, C. testosteroni and S. yanoikuyae did not indicate a direct correlation between As(V)
concentration versus growth rate and biomass yield. It is likely that As(V) reduction in these bacteria
was related to detoxification (e.g. Macur et al. 2001).
148
Copyright © 2005 Taylor & Francis Group plc, London, UK
4 DISCUSSION
4.1 As(V) reduction and growth
Our investigations on As cycling in the mine tailings and shallow aquifers show several interest-
ing results. First, in situ microorganisms play an important role in transforming and mobilizing As
at both locations. The microbial strains indicated general resistance to As toxicity under oxic to
sub-oxic conditions, and reduced As(V) to As(III). Increase in optical density and dry weight was
directly correlated to growth in the microcosms inoculated with individual microbial strains.
Notably, As speciation remained unchanged and no microbial growth occurred in the controls
(data not shown). This clearly confirms that As(V) reduction was ‘biologically mediated’ and

microorganisms play a role in As cycling. Because the enrichment cultures did not isolate iron and
sulfate reducing bacteria (which are also capable of mobilizing As e.g., Cummings et al. 2000,
Jones et al. 2000, Kuhn & Sigg 1993) their role in As cycling at these sites can only be specula-
tive. Although we have clearly established As(V) reduction and mobilization in the sediment
microcosms in absence of Fe and sulfur reducing bacteria, it is unknown if this process is affective
in natural environments. While some of these microorganisms isolated in this study are new (e.g.,
149
Figure 1. ESEM imaging in wet mode illustrating the Arsenicicoccus bolidensis and Chromobacterium
cluster. Representative EDAX X-emission spectrum quantification collected from electron dense particles
on bacterial surface as encrustations (inset). The S, O, and P speaks are due to background from the support-
ing grid.
0
1
2
3
4
5
6
0369121518
0.0
0.2
0.4
0.6
0.8
Chromobacterium
Conc. (mM)
Days
As(V)
As(III)
O.D

1.0
O.D. (600 nm)
024681012
0
1
2
3
4
5
6
Conc. (mM)
Days
As(V)
As(III)
O.D
0.0
0.2
0.4
0.6
0.8
1.0
O.D. (600 nm)
Acinetobacterjohnsonii
Figure 2. Growth of Chromobacterium and Acinetobacter johnsonii in minimal medium with 5 mM As(V).
Note that change in As speciation corresponds with enhanced growth represented as optical density measure-
ments in the microcosm cultures (experiments were conducted in duplicate).
Copyright © 2005 Taylor & Francis Group plc, London, UK
A. bolidensis and Chromobacterium), others have been associated with As cycling in sedimentary
environments (e.g. S. yanoikuyae; Macur et al. 2001).
Inasmuch as it is important to expect other biogeochemical conditions to play a role in affect-

ing As(V) reduction, in situ microbial processes are probably more affective on short-term basis.
Researchers have indicated that abiotic reduction of As(V) may occur due to sulfides (Kuhn &
Sigg 1993), but no odor for H
2
S was detected during sampling or change in color noted in the sed-
iments to suggest presence of iron sulfides. Moreover, both laboratory and field measurements
indicate that abiotic reduction of As(V) is kinetically a slow process (Kuhn & Sigg 1993, Newman
et al. 1997b), and does not match with the As transformation rates in these sediments (e.g. Routh
et al. 2004).
The effect of As(V) concentration on bacterial growth was evaluated. A zero-order model with
respect to As(V) concentration best fits our experimental data. The kinetic model applied to eval-
uate As(V) reduction is similar to U(VI) reduction involving sulfate reducing bacteria (Spear et al.
2000). The model is represented as:
(1)
where As ϭ is the model predicted As(V) concentration, As
0
ϭ initial concentration of As(V),
k
0
ϭ maximum specific reaction rate coefficient expressed as As(V) concentration/mg (dry
weight) of cells/ml/h, X ϭ bacterial cell concentration in mg (dry weight)/ml, and t ϭ time in hours.
Figure 3 indicates the trend for modeled and fitted k
0
values for Chromobacterium in microcosms
containing 1, 2, and 5 mM As(V). The zero-order model is a simplification of Michaelis-Menten
and Monod type kinetics at high substrate concentrations denoted by:
(2)
where V
max
ϭ Michaelis-Menten maximum substrate utilization rate constant expressed as the

As(V) concentration/mg (dry weight) of cells/ml/day, ␮m ϭ Monod maximum specific growth
rate constant/h, and Y ϭ cell yield expressed as mass of cells in mg per mg of substrate used.
150
0
1
2
3
4
5
6
0 3691215
Days
Observed 1 mM
Fitted 1 mM
Observed 2 mM
Fitted 2 mM
Observed 5 mM
Fitted 5 mM
As(V) reduction (mM)
Figure 3. Time course of As(V) reduction by Chromobacterium first with a zero-order model. The plot is
based on calculation of As concentration and k
0
values (see equations 1 and 2 in text). Each set of data points
represents at least two experiments conducted over a 15-days period.
Copyright © 2005 Taylor & Francis Group plc, London, UK
Microbial growth and reduction rates varied between individual species, but compared to other
microorganisms the reduction rates were low (Routh et al. 2004). In this context, an important
distinction from other laboratory simulated studies (e.g., Ahmann et al. 1997, Newman et al. 1997
a, b among others) is the fact that we used carbon levels (external inputs to the cultures) that was
substantially low (0.01mM versus 1 to 10mM in other studies). While the low organic carbon con-

centration is more reflective of the natural organic matter content in these environments, it may
have resulted in low As(V) reduction rates. Organic matter breakdown products in the microcosms
were not measured, but consistent increase in pH, As(III), and microbial numbers support reaction
pathways involving breakdown of lactate (e.g. Zobrist et al. 2000) or natural sedimentary organic
matter. Other researchers have also indicated fall in As(V) reduction with decrease in organic
substrate in microcosms (e.g. Ahmann et al. 1997, Harvey et al. 2003, Islam et al. 2004). The
results reiterate the importance of organic matter for the survival of these heterotrophic microbial
communities in the sub-surface.
One of the confounding issues in this study is underpinning whether these microorganisms
reduce As(V) for detoxification or respiratory purposes. This partly arises due to the aerobic or
strict anaerobic habitats preferred by the respective microbial colonies involved in As(V) reduc-
tion (Newman et al. 1997b). The general conditions in this study were sub-oxic, and some of the
microorganisms probably use As(V) as an alternate electron acceptor. Interestingly, recent studies
by other researchers imply that presence of an enzymatic detoxification pathway does not preclude
the As(V) respiration capability in bacteria. For example, both detoxifying and respiratory As
(V) reductases occur in the microaerophile Bacillus selenitireducens (Switzer-Blum et al. 1998)
and the As(V)-respiring anaerobe Shewanella ANA-3 strain (Saltikov & Newman 2003). Similar
possibilities may exist in some of the bacteria discussed here (e.g., A. johnsonii, A. bolidensis), but
genetic evidence (on same lines as in Saltikov & Newman 2003) is presently unavailable to
support this idea. Nonetheless, the fact that some these microorganisms are capable of using O
2
or switch to other terminal electron acceptor during respiration implies that they are generally
opportunistic by character. By means of complex inter-cellular processes these microorganism
are able to survive under conditions that are generally less preferable to others in the sub-surface.
The study implies the potential impact such microorganisms could have on As cycling at these
sites.
4.2 Environmental implications
Of late, the thrust by different regulatory agencies is on developing As remediation methods
that are supposed to be cost-affective and reaches out to a larger population. The most commonly
used in situ techniques involve maintaining aerobic conditions through aeration or using

chemical oxidants to convert As(III) to the less mobile and toxic As(V) species. In this context,
microbial transformation and mobilization of As in the sub-surface may have important impli-
cations on groundwater treatment. First, microbial As(V) reduction if it is common, then the pre-
diction of As valence, and thus behavior, based solely on redox status may be problematic. For
example, even under oxidizing conditions As(III) has been found as the predominant species
in the Adak tailings deposit (Bhattacharya et al. 2003) similar to other studies (Aurillo et al.
1994, Sohrin et al. 1997). Second, efforts made to chemically oxidize As(III) to As(V) during
groundwater treatment may be unproductive since As(V) is actively reduced to As(III) by in situ
bacteria.
This is largely bad news for researchers focusing on developing As remediation techniques.
Most methods up to date have focused on manipulating the redox states and converting As(III) to
As(V) (for review see Murcott 2001, Ahmed 2001). Many of these methods hardly take into
account the role of in situ microbial activity. Hence, it is not surprising many groundwater treat-
ment methods fail to work effectively under field conditions. Clearly, there is an urgent need to
assess the occurrence and efficiency of these microbial processes in field-based pilot studies as a
prerequisite to provide critical information before implementing specific remediation methods for
removing As.
151
Copyright © 2005 Taylor & Francis Group plc, London, UK
5 CONCLUSIONS
Microbial processes play a crucial role in As mobilization. Mobilization of As from sediments into
the aqueous phase is mediated by eukaryotes, fungi, and bacteria. This involves reduction of As(V)
into the more mobile and toxic As(III) species. Microbial reduction of As(V) mainly arises for
detoxification or respiratory purposes. They are different biochemical pathways occurring under
mostly oxic or strict anoxic conditions, respectively.
Here, we have indicated the role of microorganisms in mobilizing As at sites contaminated by mine
tailings (in northern Sweden) and shallow aquifers in West Bengal (India). We isolated several
microorganisms (including two new species) that are involved in As reduction under oxic to sub-
oxic conditions. These microorganisms are generally resistant to As toxicity. As (V) reduction in
the microcosms, correspond with increase in dry weight and optical density measurements. In

some of these microorganisms, the correspondence between As concentration, bacterial growth,
and biomass yield is high. This leads us to believe that some of these microorganisms are prob-
ably using As(V) for respiration in addition to detoxification purposes. Further genetic work is
required to understand such complex biochemical pathways. Nonetheless, the study proves that
the microorganisms whether they are present in mine tailings or groundwater aquifers; they are
generally opportunistic by character. The microorganisms have developed unique survival skills,
and in the process, created a microbial niche for themselves.
Enhanced mobilization of As from sediments has important implications on groundwater treat-
ment. Active microbial processes may result in disequilibrium conditions, whereby even under
oxidizing conditions As(III) species may predominate. Additionally, groundwater treatment based
on aeration and oxidation processes (if implemented at these sites) needs to be assessed critically.
Given the fact that in both places, we have a thriving microbial community in the sub-surface,
which is able to reduce As(V) under oxic to sub-oxic conditions, it raises questions about groundwater
treatment methods suitable for these sites.
ACKNOWLEDGEMENT
We thank the Geological Survey of Sweden (SGU) and Swedish International Development Agency
(Sida-SAREC) for providing the research funds to conduct our studies in Sweden and India. Gunnar
Jacks, Sisir Nag, S.P. Sinha Ray, and Prosun Bhattacharya helped us with fieldwork. We thank Roger
Herbert and Jim Saunders for their suggestions. Rolf Hallberg helped with the ESEM imaging.
REFERENCES
Ahmann, D., Krumholz, L.R., Hemond, H.F., Lovley, D.R. & Morel, F.M.M. 1997. Microbial mobilization of
arsenic from sediments of the Aberjona watershed. Environ. Sci. Tech. 31: 2923–2930.
Aurillo, A.C., Mason, R.P. & Hemond, H.F. 1994. Speciation and fate of arsenic in three lakes of the Aberjona
watershed. Environ. Sci. Tech. 28: 577–585.
Bhattacharya, P., Jacks, G., Frisbie, S.H., Smith, E., Naidu, R. & Sarkar, B. 2002. Arsenic in the Environment:
A Global Perspective. In B. Sarkar (ed.) Heavy Metals in the Environment: 147–215. NY: Marcel Dekker.
Bhattacharya, A., Routh, J., Saraswathy, A., Jacks, G. & Bhattacharya, P. 2003. Influence of microbes on
mobilization and speciation of arsenic from mine tailings in Adak, Västerbotten district, northern Sweden.
7th International Conference on Biogeochemistry of Trace Elements, Uppsala (Sweden), Vol. 2, pp. 58–59.
Bhattacharya, A. 2004. Mobilisation of arsenic and other trace elements from abandoned mine tailings in

Adak, Västerbotten district, northern Sweden. Licentiat thesis, Stockholm University.
Cervantes, C., Ji, G., Ramirez, J.L. & Silver, S. 1994. Resistance to arsenic compounds in microorganisms.
FEMS Microbiol. Rev. 15: 355–367.
Collins, M.D., Routh, J., Saraswathy, A., Lawson, P.A., Schumann, P., Welinder-Olsson, C. & Falsen, C. 2004.
Arsenicicoccus bolidensis gen. nov., sp. nov., a novel actinomycete isolated from contaminated lake sediment.
Int. J. Syst. Evolut. Microbiol. 54: 605–608.
Cullen, W.R. & Reimer, K.J. 1989. Arsenic speciation in the environment. Chem. Rev. 89: 713–764.
152
Copyright © 2005 Taylor & Francis Group plc, London, UK
Cummings, D.E., Caccavo, F.J., Fendorf, S. & Rosenzweig, R.F. 1999. Arsenic immobilization by dissimilatory
Fe(III)-reducing bacterium Shewanella alga BrY. Environ. Sci. Tech. 33: 723–729.
Diorio, C., Cai, J., Marmor, J., Shinder, R. & DuBow, M. 1995. An Escherichia coli chromosomal ars operon
homolog is functional in arsenic detoxification and gram-negative bacteria. J. Bacteriol. 177: 2050–2056.
Goriar, R., Chakraborty, K. & Pyne, R. 1984. Chronic arsenic poisoning from tubewell water. J. Indian Med.
Assoc. 82: 34–35.
Harvey, C.F., Swartz, C., Badruzzaman, A.B.M., Keon-Blute, N., Yu, W., Ali, M.A., Jay, J., Beckie, R.,
Niedan, V., Brabander, D., Oates, P., Ashfaque, K., Islam, S., Hemond, H. & Ahmed, M.F. 2003. Response
to comments on arsenic mobility and groundwater extraction in Bangladesh. Science 300: 584.
Islam, F.S., Gault, A.G., Boothman, C., Polya, D.A., Charnock, J.M., Chatterjee, D. & Lloyd, J.R. 2004. Role
of metal-reducing bacteria in arsenic release from Bengal delta sediments. Nature 430: 68–71.
Jacks, G., Bhattacharya, P., Routh, J. & Martin, M.T. 2003. Arsenic cycling in a covered mine tailings
deposit, Northern Sweden. In H.D. Schulz & A. Hadeler (eds.) Geochemical Processes in Soil and
Groundwater: 303–309. Weinheim: Wiley-VCH.
Johnson, D.L. & Pilson, M.E.Q. 1972. Spectrophotometric determination of arsenite, arsenate and phosphate
in natural waters. Anal. Chem. Acta 58: 289–299.
Jones, C.A., Langner, H.W., Anderson, K., McDermott, T.R. & Inskeep, W.P. 2000. Rates of microbially mediated
arsenate reduction and solubilization. Soil Sci. Soc. Am. J. 64: 600–608.
Kuhn, A. & Sigg, L. 1993. Arsenic cycling in eutrophic Lake Greifen, Switzerland: Influence of seasonal
redox processes. Limnol. Oceanogr. 38: 1052–1059.
Macur, R.E., Wheeler, J.T., McDermott, T.R. & Inskeep, W.P. 2001. Microbial populations associated with the

reduction and enhanced mobilization of arsenic in mine tailings. Environ. Sci. Tech. 35: 3676–3682.
Martin, A.J. & Pedersen, T.F. 2002. Seasonal and interannual mobility of arsenic in a lake impacted by metal
mining. Environ. Sci. Technol. 36: 1516–1523.
Newman, D.K., Beveridge, T.J. & Morel, F.M.M. 1997a. Precipitation of arsenic trisulfide by
Desulfotomaculum auripigmentum. Appl. Environ. Microbiol. 63: 2022–2028.
Newman, D.K., Ahmann, D. & Morel, F.M.M. 1997b. A brief review of dissimilatory arsenate reduction.
Geomicrobiol. J. 15: 255–268.
Nickson, R.T., McArthur, J.M., Burgess, W.G., Ahmed, K.M., Ravenscroft, P. & Rahman, M. 1998. Arsenic
poisoning of Bangladesh groundwater. Nature 395, 338.
Nriagu, J.O. 2002. In W.T. Frankenberger, Jr. (ed) Environmental Chemistry of Arsenic: 1–26. NY: Dekker.
Oremland, R.S. & Stolz, J.F. 2003. The ecology of arsenic. Science 300: 939–944.
Rosen, B.P. 2002. Biochemistry of arsenic detoxification. FEMS Letters 529: 86–92.
Routh, J., Saraswathy, A., Nag, S.K., Sinha Ray, S.P. & Jacks, G. 2004. Arsenic reduction by indigenous
bacteria in shallow aquifers from Ambikanagar, West Bengal (India). In Advances in Arsenic Research:
American Chem. Soc. Special Issue (in press).
Routh, J., Sinha Ray, S.P., Nag, S.K., Jacks, G., Bhattacharya, A., Datta, S. & Bhattacharya, P. 2003. Safe drink-
ing water – The issue of shallow versus deep wells in two arsenic affected areas in West Bengal, India. 7th
International Conference on Biogeochemistry of Trace Elements, Uppsala (Sweden), Vol. 2, pp. 462–463.
Roy Chowdhury, T., Basu, G.K., Mandal, B.K., Biswas, R.K., Chowdhury, U.K., Chanda, C.R., Lodh, D.,
Roy, S.L., Saha, K.C., Roy, S., Kabir, S., Quamruzzaman, Q. & Chakraborti, D. 1999. Arsenic poisoning in
the Ganges delta. Nature 401: 545–546.
Saltikov, C.W. & Newman, D.K. 2003. Genetic identification of a respiratory arsenate reductase. PNAS 100:
10983–10988.
Saha, K.C. 1984. Melanokeratosis from arsenic contaminated tubewell water. Ind. J. Dermat. 29: 37–46.
Saraswathy, A., Routh, J. & Collins, M.D. 2004. Arsenicicoccus bolidensis a novel arsenic reducing actino-
mycete. FEMS Letters (submitted).
Sohrin, Y., Matsui, M., Kawashima, M., Hojo, M. & Hasegawa, H. 1997. Arsenic biogeochemistry affected by
eutrophication in Lake Biwa, Japan. Environ. Sci. Tech. 31: 2712–2720.
Spear, J.R., Figueroa, L.A. & Honeyman, D. 2000. Modeling Reduction of Uranium U (VI) under variable
sulfate concentrations by sulfate-reducing bacteria. Appl. Environ. Microbiol. 66: 3711–3721.

Switzer-Blum, J., Bindi, B.A., Buzzelli, J., Stolz, J.F. & Oremland, R.S. 1998. Bacillus arseniocoselenatis, sp.
nov., and Bacillus selenitireducens, sp. nov. Two haloalkaliphiles from Mono Lake, California that respire
oxyanions of selenium and arsenic. Arch. Microbiol. 171: 19–30.
Turpeinen, R., Pantsar-Kallio, M., Häggblom, M. & Kairesalo, T. 1999. Influence of microbes on the mobi-
lization, toxicity and biomethylation of arsenic in the soil. Sci. of Tot. Environment 236: 173–180.
Zobrist, J., Dowdle, P.A., Davis, J.A. & Oremland, R.S. 2000. Mobilization of arsenite by dissimilatory reduction
of adsorbed arsenate. Environ. Sci. Technol. 34: 4747–4753.
153
Copyright © 2005 Taylor & Francis Group plc, London, UK