AGU Chapman Conference on Arsenic in Groundwater of Southern Asia
Siem Reap, Cambodia 24–27 March 2009
Conveners • Alexander van Geen, Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, USA, e-mail ([email protected]) • Scott Fendorf, Environmental Earth System Science, Stanford University, Stanford, California, USA, e-mail ([email protected])
Co-Host The conveners and planning committee wish to thank the Royal Government of Cambodia, Ministry of Rural Development for their support of this Chapman conference.
Program Committee • Kazi Matin Ahmed, Department of Geology, University of Dhaka, Bangladesh, e-mail ([email protected]) • Charles Harvey, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge Massachusetts, USA, e-mail ([email protected]) • Janet Hering, Swiss Federal Institute of Aquatic Science and Technology (Eawag), Duebendorf, Switzerland, e-mail ([email protected]) • Jonathan Lloyd, School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, UK, e-mail ([email protected]) • Andrew Meharg, Department of Plant and Soil Sciences, University of Aberdeen, UK, e-mail ([email protected]) • Pauline Smedley, British Geological Survey, Wallingford, Oxfordshire, UK, e-mail ([email protected])
1
AGU Chapman Conference on Arsenic in Groundwater of Southern Asia
Siem Reap, Cambodia 24–27 March 2009
Local Organizers • Jan Willem Rosenboom, Water and Sanitation Program, World Bank, Phnom Penh, Cambodia, email ([email protected]) • Mickey Sampson, Resource Development International, (Kean Svay, Kandal, Cambodia), email ([email protected])
The conference organizers wish to gratefully acknowledge the following sponsors for their generous support of this conference.
The CALIBRE Project, "Cambodia and Laos Initiative for Building human Resources for the Environment" is funded by the European Commission Asia-Link Programme Ref: KH/Asia- Link/04 142-966. This document has been produced with the financial assistance of the European Union. The contents of this document can under no circumstances be regarded as reflecting the position of the European Union.
2 AGU Chapman Conference on Arsenic in Groundwater in Southern Asia Siem Reap, Cambodia 24 – 27 March 2009
MEETING AT A GLANCE
Monday, 23 March 2009 0700h – 1400h Pre-Conference Field Trip to Kandal Province 1600h – 1700h Registration 1700h – 1900h Ice Breaker Reception
Tuesday, 24 March 2009 0530h – 0830h Buffet Breakfast Grandview Coffeehouse 0830h – 0900h Opening Remarks 0900h Session I Lunch Grandview Coffeehouse Dinner (On your own) 1900h Poster Presentations 2000h Oral Presentation Discussion and selection of posters
Wednesday, 25 March 2009 0530h – 0830h Buffet Breakfast Grandview Coffeehouse Lunch 0700h – 1400h FREE TIME Lunch Grandview Coffeehouse 1400h Session II Dinner (On your own) 1900h Poster Presentations 2000h Oral Presentation Discussion and selection of posters
Thursday, 26 March 2009 0530h – 0830h Buffet Breakfast Grandview Coffeehouse Session III Lunch Grandview Coffeehouse Dinner (On your own) 1900h Poster Presentation 2000h Discussion and selection of posters
Friday, 27 March 2009 0530h – 0830h Buffet Breakfast Grandview Coffeehouse Session IV Lunch Grandview Coffeehouse Round Table Discussion 1800h Press Conference 2000h Buffet Dinner Poolside, Grandview Coffeehouse
3 Program Overview
Sessions and events will take place at the Angkor Century Resort and Spa, Siem Reap, Cambodia. The Registration/Information Desk will be in the Lotus Ballroom foyer throughout the conference.
MONDAY, 23 MARCH 2009
0700h – 1400h Pre-Conference Field Trip – Kandal Province, Phnom Penh
1600h – 1700h Registration ♦ Lotus Ballroom Foyer
1700h – 1900h Welcome Reception ♦ Lotus Ballroom
TUESDAY, 24 MARCH 2009
0530h – 0830h Breakfast Buffet ♦ Grandview Coffeehouse
0830h – 0900h Opening Remarks JW Rosenboom, M Sampson
0900h Session I – Biogeochemistry♦Lotus Ballroom
J Lloyd The Microbial Ecology of Arsenic Mobilizing Aquifer Sediments
Coffee Break ♦ Lotus Ballroom
D Postma Mobilization of Arsenic and Iron from Red River Floodplain Sediments, Vietnam
B Bostick, B. Kocar Impacts of sulfur biogeochemistry on arsenic fate and transport in South/Southeast Asian Aquifers
Lunch ♦ Grandview Coffeehouse
Dinner (On your own)
1900h Poster Presentations ♦ Lotus Ballroom
2000h G Breit The geologic context of biogeochemical processes affecting arsenic in South Asia
J Hering – Discussion and Selection of Posters
4 WEDNESDAY, 25 MARCH 2009
0530h – 0830h Breakfast Buffet ♦ Grandview Coffeehouse
0700-1400h FREE TIME
Lunch ♦ Grandview Coffeehouse
1400h Session II – Hydrogeology ♦ Lotus Ballroom
C Harvey Ponds, Fields, and Rivers - Sources of Water and Solute Loads to Aquifers in the Ganges Delta
M Stute Environmental Tracer Applications in Floodplain Aquifers with Elevated Arsenic Concentrations
Coffee Break ♦ Lotus Ballroom
S Benner Hydrologic Constraints on Arsenic Behavior, Observations From a Field Site in Cambodia
F Larsen Geological and Hydrogeological Processes Affecting the Distribution of Arsenic Ground Water Concentrations in Holocene and Pleistocene Aquifers in the Red River Flood Plain, Vietnam.
Dinner (On your own)
1900h Poster Presentations
2000h R Beckie The geochemistry of high- and low-arsenic groundwaters and their association with an in-filled abandoned channel at a Field Site in Gotra, Nadia District, West Bengal, India
W Burgess – Discussion and selection of posters
THURSDAY, 26 MARCH 2009
0530h – 0830h Breakfast Buffet ♦ Grandview Coffeehouse
0900h Session III – Vulnerability of low-As aquifers ♦ Lotus Ballroom
H Michael Is Deep Groundwater a Sustainable Source of Arsenic-Safe Water in the Bengal Basin? Management Insights from a Regional Modeling Analysis
Y Zheng Equilibrium and Kinetics of As Sorption to Bangladesh Gray and Orange Sediments Determined by Batch Experiments
5 Coffee Break ♦ Lotus Ballroom
D McKnight Reduced Humic Substances Promote Iron Reduction and Mobilization of Arsenic in Aquifers in Bangladesh
D Polya Arsenic mobilization into shallow groundwaters of southern Asia? where, when and why does it occur - evidence from organic, isotopic and bio- geochemistry
Lunch ♦ Grandview Coffeehouse
Dinner (On your own)
1900h Poster Presentations ♦ Lotus Ballroom
2000h S Fendorf, A van Geen – Consensus
Discussion and selection of posters
FRIDAY, 27 MARCH 2009
0530h – 0830h Breakfast Buffet ♦ Grandview Coffeehouse
0900h Session IV – Open Questions and Mitigation ♦ Lotus Ballroom
A van Geen, S Fendorf – Future Experiments
KM Ahmed Groundwater Arsenic Occurrences in Bangladesh: Options for Management and Mitigation
M Berg, S Hug Predicting Groundwater Arsenic Contamination in Southeast Asia from Surface Parameters and from Geology at Depth
Lunch ♦ Grandview Coffeehouse
1400h A Smith Arsenic in Drinking Water Results in the Highest Known Toxic Substance Disease Risks
M Sampson Incomplete Arsenic-Removal by Iron-Amended BioSand Filters in Kandal Province, Cambodia
Round Table Discussion: Drinking water options Discussion leader: J W Rosenboom
1800h Press Conference ♦ Lotus Ballroom
2000h Buffet Dinner ♦ Poolside, Grandview Coffeehouse
6
Abstracts
Groundwater Arsenic Occurrences in there are safe aquifers at depths almost all Bangladesh: Options for Management over the country. However, there are and Mitigation certain constraints for deep groundwater development in specific geological [*K M Ahmed*] (Department of provinces of the country. Current arsenic Geology, University of Dhaka, Dhaka mitigation plan of the Government of 1000, Bangladesh. ph:+880-2-9661920 Bangladesh puts emphasis on certain Ex.7316; fax: +880-2-8615583; email: options without proper scientific [email protected], validation. The current mitigation strategy [email protected]) needs to be revised giving emphasis on the options which are safe and sustainable. Wide spread occurrences of arsenic in While doing this a review of the arsenic groundwater above the allowable limit for occurrence, distribution and mitigation is drinking water has emerged as a major necessary in order to modify the action public health issue in Bangladesh. The plan. The paper will present a review of extent of the problem is severe in the current situation and knowledge base Bangladesh as many million people have and outline a revised mitigation strategy been exposed to arsenic above the for sustainable management of water allowable limit. Intake through food chain supply in Bangladesh. has also been considered another major area of concern. Management of arsenic disaster in Bangladesh is a major challenge Variability in Dissolved Arsenic in in the field of water supply, sanitation and Shallow Aquifers Linked to Local irrigation. Current estimates show that Hydrology about one third of the country’s domestic drinking wells yield water above the [*Z Aziz*] (Lamont-Doherty Earth Bangladesh national drinking water limit Observatory of Columbia University, whereas more than half of the wells exceed Palisades, NY 10964, USA, ph. +1-845- the World Health Organisation provisional 365-8412; fax +1-845-365-8154; e-mail: guideline value. Efforts have been made to [email protected]); manage the problem since its detection in A. van Geen 1993. However, the pace of mitigation is ([email protected]); M. Stute slow compared to the magnitude of the ([email protected]); B.C. problem. There various different options Bostick for managing the problem. While ([email protected]); planning arsenic management strategy, M.W. Rahman both drinking and irrigation water should ([email protected]); M. M. be considered though the potable water Rahman ([email protected]); warrants the top priority. It has been found M.R. Huq ([email protected]); K M in various parts of the country that arsenic Ahmed (Department of Geology, safe groundwater can be abstracted from University of Dhaka, Dhaka 1000, various depths if well sitting is done based Bangladesh; ph. +880-2-966-1920 Ext. on based on certain geological and 7316; fax +880-2-861-5583; e-mail: hydrogeological criteria. Existing well [email protected]) testing data can also provide guidelines in delineating the safe depths. In general
7 Time series of groundwater composition sulfides in the solid phase at this depth have shown that concentrations of As in suggest that dissolved As is sequestered in groundwater of Bangladesh are by and sediments by the reduction of arsenate to large remarkably constant despite large arsenite followed by precipitation as seasonal variations in groundwater and arsenic sulfides in the presence of reduced river levels. Some temporal variations sulfur. In this setting, the sequestration of might be expected in particularly shallow As at the intermediate well significantly aquifers, however, based on recent studies dampen seasonal variations that would be showing that local recharge can play a role expected based on changes in groundwater in setting the spatial distribution of As. To level alone. explore the complex interactions between dissolved As levels in shallow aquifers and At Site Y, no sharp vertical gradient in recharge, nests of three very shallow (6-9 aquifer properties was observed and m deep) monitoring wells were monitored neither were there any significant bi-weekly over 2 years in three contrasting fluctuations in groundwater properties areas of Araihazar, Bangladesh. At control driven by the monsoon over the two year site Z, no vertical or temporal changes in period: Eh (-8±35 mV), SO4 (85±54 groundwater chemistry or hydrology were mg/L), Cl (115±55 mg/L), P (994±102 recorded over the entire monitoring period: ug/L), As (45±7 ug/L) in the shallowest Eh (29±38 mV), SO4 (6±5 mg/L), Cl well and Eh (-7±34 mV), SO4 (44±16 (24±7 mg/L), P (158±32 ug/L), As (26±4 mg/L), Cl (81±35 mg/L), P (137±44 ug/L), ug/L) in the shallowest well and Eh As (25±4 ug/L) at the deepest well. (22±42 mV), SO4 (1±1 mg/L), Cl (22±4 However, the time series show a gradual mg/L), P (98±65 ug/L), As (12±3 ug/L) in decline of ~5 ug/L per year in average As the deepest well. over the entire period at all depths. Relative hydraulic heads between sites Y At Site X, a strong vertical gradient in and control Site Z and a broad trend of redox conditions and groundwater increasing downward hydraulic gradients composition between the shallowest and at site Y parallel the declining average As. deepest well is indicated by Eh (+134±64 This suggests an enhancement of vertical mV vs. -4±43 mV, n=50), P (47±38 vs. recharge by irrigation pumping. Based on 1153±130 ug/L, n=50), As (3±1 vs. the observations at Site X, we postulate 230±24 ug/L, n=50), SO4 (160±54 vs. 9±8 that enhanced recharge driven by irrigation mg/L, n=50), and Cl concentrations pumping resulted in an enhanced supply of (267±54 vs. 60±14 mg/L, n=50). Whereas SO4 and therefore removal of dissolved the composition of groundwater at the As by arsenic sulfide formation. These shallowest and deepest well remained observations provide further evidence that relatively constant over two years, recharge can occasionally drive seasonal considerably larger seasonal fluctuations and longer-term variations in groundwater were observed at the intermediate well (7.6 composition including As in shallow m): 44±52 mV in Eh, 112±65 mg/L in aquifers of Bangladesh. SO4, 196±93 mg/L in Cl, 691±374 ug/L in P, and 15±11 ug/L in As. Hydraulic head measurements indicate that these changes Hydrologic Constraints on Arsenic reflect a combination of changes in the Behavior, Observations From a Field direction of groundwater flow and mixing Site in Cambodia of groundwater from above and below 7.6 [*S.G. Benner*] (Department of Geology, m depth. A non-conservative behavior of Boise State University, Boise, ID 83725, arsenic relative to its structural analogue USA; [email protected]; 208-426- phosphate, and the presence of arsenic 3629; 208-426-4061); M.L. Polizzotto
8 (School of Earth Sciences, Stanford setting for evaluating chemical changes University, Stanford, CA 94305 USA), along flow paths using vertically B.D. Kocar (School of Earth Sciences, incremented sampling through the clay. Stanford University, Stanford, CA 94305 Along these infiltration flow paths (over a USA); M. Sampson (Resource 5-10 m distance), we observe universal Development International, Kien Svay, increases in dissolved arsenic Kandal, Cambodia) S. Fendorf (School of concentrations from the surface infiltrating Earth Sciences, Stanford University, waters (As<10 gL-1) to the aquifer Stanford, CA 94305 USA) (As>500 gL-1). Based on associated changes in aqueous and solid phase The hydrologic tools of mass balance, geochemistry, this arsenic release to the gradient driven flux, and flow continuity pore water is attributed to reductive can provide rigorous constraints on arsenic dissolution of arsenic-bearing iron oxides behavior in groundwater. At a field site in at and below the depth of permanent Cambodia, where the shallow groundwater saturation. In this presentation, we will contains elevated arsenic concentrations, discuss the uncertainties associated with we have integrated these basic hydrologic this physical model, evaluate potential tools within a numerical model to hydrological perturbations on this flow investigate the influence of groundwater system and explore its relevance to arsenic flow on arsenic behavior. The dominant behavior at other sites in Asia. driver of groundwater flow at this site is hydraulic head differentials in the seasonal surface water levels of the Mekong River Predicting Groundwater Arsenic and the adjacent wetland systems that Contamination in Southeast Asia from overlie the aquifer. While the relative Surface Parameters and from Geology elevations of these two water bodies invert at Depth semi-annually, the net annual hydraulic head gradient is from the wetlands to the [*Michael Berg*], Lenny Winkel, river. Both the seasonal fluctuations and Manouchehr Amini, Stephan Hug, Annette the net hydraulic gradient are manifested Johnson (Eawag, Swiss Federal Institute of in the hydraulic head behavior for the Aquatic Science and Technology, 8600 aquifer; subsurface gradients invert Dübendorf, Switzerland, seasonally and the net annual subsurface [email protected]); gradient is towards the river. The Pham Thi Kim Trang, Vi Mai Lan, Dao subsurface stratigraphy can be idealized as Manh Phu, Pham Hung Viet, Nguyen Van a two layer system, clay overlying sand, Dan, Nguyen Thi Ha (CETASD, Hanoi with the clay 2-10 m thick forming an University of Science, Hanoi, Vietnam) aquitard overlying a sand aquifer that is approximately 60 m thick; this system Arsenic contamination of groundwater extends approximately 5000 m outwards resources threatens the health of millions from the river. Application of the observed of people worldwide, particularly in the gradients in this flow media geometry (low densely populated river deltas of Southeast hydraulic conductivity material overlying Asia. Although many arsenic-affected high conductivity material assembled as a areas have been identified in recent years, long thin flow system) produces flow a systematic evaluation of vulnerable areas paths from the wetlands to the aquifer that remains to be carried out. In order to are nearly vertical through the clay pinpoint untested areas at risk of aquitard, while flow through the aquifer groundwater arsenic concentrations, we sands is nearly horizontal to the river. produced a risk map by combining Such a flow system provides an optimal geological and surface soil parameters in a
9 logistic regression model, calibrated with results of this approach will be presented 1756 aggregated and geo-referenced and compared with the predictions groundwater data points from the Bengal, modeled entirely from surface parameters. Red River and Mekong deltas.
The model is based on three assumptions. Impacts of Fluvial Geomorphic First, sedimentary depositional Processes on the Distribution of environments are characterized by a Groundwater Arsenic Contamination in unique combination of chemical, physical the Mekong Delta and biological properties and can serve as indicators (proxies) for chemical and [*B C Bostick*] (Department of Earth physical conditions of the aquifers beneath Sciences, Dartmouth College, Hanover, the surface. Second, soil properties are NH 03755, United States; ph. 603-646- proxies for present and past drainage 3624; fax 603-646-3922; e-mail: conditions and they are also indicators of [email protected]); N C Papacostas recent depositional environments. Third, (Temple University, School of Medicine, soil textures, for example clay and silt, are Philadelphia PA 19122, United States; e- proxies for the chemical maturity of the mail: [email protected]); H M sediments, where clay is more mature than Nguyen (Department of Earth Sciences, silt. An important factor in the Dartmouth College, Hanover, NH 03755, development of soil textures is United States; e-mail: topography, which enables the delineation [email protected]); A N of areas where the model is applicable. Quicksall (University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556, We show that Holocene deltaic and United States; e-mail: organic-rich surface sediments are key [email protected]); J Sun indicators for arsenic risk areas and that (Department of Earth Sciences, Dartmouth the combination of surface parameters is a College, Hanover, NH 03755, United successful approach to predict States; ph. 603-646-0994; fax 603-646- groundwater arsenic contamination. 3922; e-mail: [email protected]); S Predictions are in good agreement with the Khim (Resource Development spatial distribution of known arsenic International, Royal Brick Road, Kien contamination but also indicate elevated Svay, Kandal, Cambodia; ph. 855-23-399- risks in Sumatra and Myanmar where no 577; fax 855-24-399-577; groundwater data existed. [email protected]); M L Sampson (Resource Development International, All the above is based on two-dimensional Royal Brick Road, Kien Svay, Kandal data (that is, surface maps). We are Cambodia; ph. 855-23-399-577; fax 855- currently exploring avenues of three- 24-399-577; [email protected]) dimensional predictions for the Red River delta, using a new set of regional Arsenic contamination is a widespread but geological maps at 1m depth intervals heterogeneous phenomenon in many large, (surface to 100 m depth) in combination sediment-laden deltas. Arsenic is released with As measurements from our from sediments through the coupling of groundwater survey of the delta area. microbial decomposition of organic matter Although, three- dimensional information and reductive dissolution of arsenic- could improve the performance of model, bearing iron minerals. In this work, we such data is generally not available at large examine how fluvial processes impact the scales and is technically difficult to be distribution of arsenic in the Mekong Delta included in geostatistical modeling. Latest of Cambodia. This dynamic region
10 changes rapidly in response to river stage, CA 94025; e-mail: [email protected]); H and erosion or deposition along active A Lowers (U.S. Geological Survey, Box channels. The variation in depositional 25046 MS 973, Denver, CO 80225; e- environment creates a number of unique mail: [email protected]); D W Clark geomorphic features, including scroll bars, (U.S. Geological Survey; e-mail: avulsions, crevasse splays, and docked [email protected]), and J C Yount (U.S. islands. Groundwater arsenic Geological Survey, Box 25046 MS 980, contamination is strongly correlated to Denver, CO; e-mail: these geomorphic features. The detailed [email protected]) characterization of transects of sediments, surface and ground water within these The variable composition of ground water young geomorphic features suggest that in the Bengal Basin is partly the product of they have several physical and chemical multiple depositional environments of characteristics conducive to arsenic aquifer sediments, temporally and spatially release. Organic matter quantity and variable biogeochemical processes, and quality differs in young features, as does passage of water ranging from river water their mineralogy. The wide variation in to sea water through the sediment. particle size from channel sands and Implicit in these variations are the impacts gravels to fine-grained overbank deposits of climate change, sea level, and more influences aquifer recharge and recently, human-induced land-use and groundwater hydrology. Each of these hydrologic changes. Evaluation of the factors impacts sediment redox chemistry, sustainability of ‘safe aquifers’ requires related arsenic release (or sequestration), consideration of this complex framework and thus the distribution of groundwater and the implications it has for content of arsenic. Such integrated approaches to dissolved arsenic as well as iron, identify affected areas are invaluable to manganese, and salinity in the resulting identify sustainable groundwater sources ground water. in affected areas. Within Bangladesh and West Bengal, India, potable water is produced from Characterizing Heterogeneity of Water- depths as little as a few meters to as great producing Sediments in the Bengal as 350 m; this interval is the product of Basin – A Challenge in Assessing more than 100,000 years of sediment Aquifer Vulnerability deposition. Ground water from the upper 50 m of Holocene sediment varies in [*G N Breit*] (U.S. Geological Survey, dissolved As, Mn, and Fe over 10s to 100s Box 25046 MS 964, Denver, CO 80225; of meters. Deeper ground water (150-350 ph 303-236-4951; e-mail: m) lacks As and varies in dissolved Fe, [email protected]); J W Whitney (U.S. Mn, and TDS on the scale of a few Geological Survey, Box 25046 MS 980, kilometers. Such heterogeneity challenges Denver, CO 80225; e-mail: the ability to predict the lateral uniformity [email protected]); K G Stollenwerk of ground water within ‘aquifers’. (U.S. Geological Survey, Box 25046 MS 413, Denver, CO 80225; e-mail: The distribution and abundance of arsenic [email protected]); Md N Uddin in ground water in the Holocene sediment (Geological Survey of Bangladesh, 153 is consistent with equilibration of recently Pioneer Road, Segunbagicha, Dahka 1000, oxidized sediment buried in a chemically Bangladesh; e-mail: [email protected]); reducing environment. Although sediment A L Foster (U.S. Geological Survey, 345 deeper than 100 m has been suggested to Middlefield Road, MS 901, Menlo Park, be ‘flushed’ of its labile arsenic, it is more
11 likely that arsenic has been redistributed Denver, CO; e-mail: such that a substantial portion is retained [email protected]) in phases stable in the ambient geochemical environment. These Samples of ground water from Holocene environments include pyrite and other sediments in the Kandal Province of ferrous iron phases in chemically reduced Cambodia contain as much as 1000 m g/L sediment and crystalline ferric oxides in arsenic. These high concentrations are oxidized units. The degradation of water attributed to the reductive dissolution of produced from ‘safe-aquifers’ can ferric oxyhydroxides coating detrital potentially result from flow of arsenic-rich grains within buried sediment. Detrital water into the producing interval, and organic matter is considered to be introduction of compounds that react with responsible for establishing reducing arsenic-containing minerals. Both conditions evident in the high contents of mechanisms can be promoted by human dissolved organic carbon, ammonium and, induced and natural alteration of flow locally, methane. In addition, ammonium regimes and reactant supplies. in the high-arsenic ground water has d 15N values of 2.8 to 4.8 per mil, values Laboratory experiments and field consistent with anaerobic release of observations have shown that shallow organically bound nitrogen in peat ‘safe aquifers’ have a significant but finite accumulations (2.3 to 3.7 per mil) within capacity to remove arsenic and other the study area. reactants from solution. Thus, the sustainability of safe aquifers is affected Analyses of sediment exposed in by rates and volumes of ground water excavations and along river banks revealed abstraction for domestic and irrigation that, in addition to release from sediment, purposes. Similar evaluation should be arsenic has accumulated locally in made for deep aquifers. Geochemical diagenetic pyrite and secondary goethite. solute-transport modeling can be used to Samples of peaty sediments contained 10 predict rates of ‘safe aquifer’ to 500 ppm arsenic; analyses of pyrite in contamination; however, detailed these sediments found up to 0.6 wt.% As. hydrologic information is required to In oxidized sediment, arsenic accumulates adequately define flow fields. to levels of 40 to 450 ppm through assimilation into neoformed ferric oxyhydroxides. The organic-rich and oxic Processes of Arsenic Accumulation sediments act as natural filters capable of within Holocene Alluvium of Kandal removing dissolved arsenic from Province, Cambodia: Implications for contaminated ground water, although the Land Use rate of accumulation relative to ground water transport remains unknown. [*G N Breit*] (U.S. Geological Survey, Box 25046 MS 964, Denver, CO 80225; Sediments with natural arsenic ph 303-236-4951; e-mail: enrichments should be considered in the [email protected]); J K Bohlke (U.S. management of arsenic contaminated areas Geological Survey, 12201 Sunrise Valley to minimize disruptions that might Drive, MS , Denver, CO 80225; e-mail: destabilize the arsenic-containing phases. [email protected]); H A Lowers (U.S. Land-use change in Kandal province is Geological Survey, Box 25046 MS 973, evident in excavation and dispersal of Denver, CO 80225; e-mail: peaty sediments, burial of aerated [email protected]); J C Yount (U.S. sediment, and drainage of wetlands. These Geological Survey, Box 25046 MS 980, modifications could result in local ‘hot-
12 spots’ of arsenic contamination even in of models, consistent with these data. areas with no prior arsenic contamination Model outcomes may be compared with as arsenic-rich phases are destabilized. In independent determinations of addition, disruption of the natural groundwater age, and are used to accumulation processes could result in a demonstrate the scale of uncertainty in the sustained increase in ground water arsenic implications for security of supply. concentrations where flow paths cross the disrupted sediments. The Interplay of Microbiology and Nanoparticle Chemistry in Arsenic Provenance and Travel Time of Mobilization Groundwater Pumped from ‘Arsenic- safe’ Depths in the Aquifer System of [*L. Charlet*] (LGIT, CNRS and Southern Bangladesh: Sources of University of Grenoble, BP 53, 38041 Uncertainty and Implications for Grenoble Cedex 9, France, 33-476635198, Security of Supply [email protected]); A.Burnol (BRGM and LGIT, 3, avenue Claude-Guillemin, [*W G Burgess*] (Department of Earth BP 6009, 45060 Orléans Cedex 2, Sciences, University College London, 33238644647, [email protected]); S. London WC1E 6BT, UK; ph. +44 (0) 207- Chakraborty LGIT, CNRS and University 679-7820; fax +44 (0) 207-387-1612; e- of Grenoble, BP 53, 38041 Grenoble mail: [email protected]; M A Cedex 9, France, 33-476635187, Hoque (Department of Earth Sciences, [email protected]); University College London, London J.M.Greneche (LPEC, CNRS and WC1E 6BT, UK; ph. +44 (0) 207-679- University of Le Mans, 72085 Le Mans 2364; fax +44 (0) 207-387-1612; e-mail: Cedex 9 France, 33 2 43 83 33 01, [email protected]) [email protected]); G. Morin (MPMC, 140 rue de Lourmel, 75015 Paris, Security, in relation to arsenic content, of France, 33 1 44 27 75 04, groundwater pumped from depth in [email protected]); B. Nath southern Bangladesh is a function of (School of Environmental Systems borehole catchment and time of travel Engineering, The University of Western from the recharge provenance. Borehole Australia, M015, 35 Stirling Highway, catchments in layered sedimentary systems Crawley 6009, Australia, are sensitive to basin geometry, hydro- [email protected]); C. Tournassat stratigraphy, anisotropy, sources and styles (BRGM, 3, avenue Claude-Guillemin, BP of recharge and the imposed pumping 6009, 45060 Orléans Cedex 2, regime. Representation of these factors in 33238644647, 33 2 38 64 47 44, models involves uncertainty on account of [email protected]) limitations of knowledge and data, and limitations inherent in the modeling The distribution pattern of arsenic process. These uncertainties have been concentrations in the Ganges Delta region investigated for a 5000 km2 region of SE is heterogeneous and there are numerous Bangladesh, using data from 11 petroleum As hotspots in Bengale. In this work, we exploration lithological logs to 1700 m, examine how field work combined with 600 lithological logs and 12 geophysical microbiological, chemical and logs to a depth of up to 350 m, and spectroscopical observation impact the sensitivity analysis of boundary distribution of arsenic in asian deltas, and conditions. A range of aquifer demonstrates the importance of representations has been applied to a series hydrogeochemical characteristics
13 (groundwater flow and recharge) of an the second month is due to its reduction aquifer in the release of As to to the more weakly adsorbed As(III) which groundwater. Our study site is located cannot compete against carbonate ions for along the Hooghly River, 60 km north of sorption onto ferrihydrite. Kolkota City, near the city of Chakdaha, in India West Bengale. The spatial The identity of the weekly As adsorbing distribution pattern of As is patchy with secondary Fe(II) rich solid phases formed areas containing groundwater that is high in this process is the topic of an intense in As (>200 µg L-1) found in close debate in the litterature. Analysis of the vicinity to low As (<50 µg L-1) As, Mn and Fe fluctuations observed with groundwaters (within 100 m). The river depth in our field site show groundwater to Hooghly, which forms the NW boundary be always at equilibrium with siderite, of the study site, shows dual behaviour carbonate green rust and rhodochrosite (effluent and influent during pre- and post- (MnCO3). However a separate Mössbauer monsoon periods, respectively), spectroscopic study performed on complicating the site hydrogeology. The analogue anoxic formations, shows these observed groundwater flow lines tend to (and other Fe(II) rich species such as be deflected away from the high As Fe(II) rich clays) to be extremly sensitive, portion of the aquifer, indicating that even to exposure to air at room groundwater movement is very sluggish in temperature just the time necessary to the As-rich area. This leads to a high record the Mössbauer spectra. These Fe(II) residence time for this groundwater rich phases are therfore systematically package, prolonging sediment–water underestimated in mineralogical studies interaction, and hence facilitating which do not include drilling under groundwater As release. nitrogen and transport in liquid nitrogen, conditions seldom encountered in field Mn and Fe concentrations are found to studies. Therefore the accurate fluctuate with depth. These fluctuations identification and size characterization of are shown to be, via solubility of solid Fe(II) secondary phases formed in the field carbonate phases, mostly by local PCO2 , (phyllosilicates, magnetite, carbonate, i.e. by respiration of microorganisms such oxycaerbonate and sulfides) as well their as the dissimilatory iron reductive bacteria solubility and As affinity are urgently (DIRB). We investigated DIRB dissolution needed in order to correctly model the of As(V) rich "ferrihydrite", and widespread heterogeneity in groundwater developped a biogeochemical kinetic and arsenic contamination. equilibrium model to simulate aqueous- and solid phase X-ray diffraction and X- ray absorption observations. The main Modeling Shallow Groundwater Flow in conclusions drawn from the model are an Arsenic-Impacted Aquifer at a Field the following. (1) As(V) is not reduced Site in Gotra, Nadia District, West during the first incubation month Bengal, India characterized by high Eh values, but rather re-adsorbed onto the ferrihydrite [*A J Desbarats*] (Geological Survey of surface, and this state remains until Canada, Ottawa, ON, K1A 0E8, Canada; arsenic reduction is energetically more ph. 613-995-5512; e-mail: favorable than iron reduction. (2) the [email protected]); decoupling of Fe and As release is C E M Koenig (Department of Earth and controlled by the solubility of the nano- Ocean Sciences, University of British sized initial As-rich ferrihydrite sub Columbia, Vancouver, BC, V6T 1Z4, particles and (3) the release of As during Canada; ph. 604-822-2764; e-mail:
14 [email protected]); T Pal (Central channel versus excavated) as sources of Petrological Laboratories, Geological aquifer recharge, and to assess their Survey of India, Kolkata-700016, India; potential as sources of organic carbon ph. 033-2286-1616 ext. 2705; Email: driving the reductive process associated [email protected]); P K Mukherjee with high arsenic concentrations. (Central Petrological Laboratories, Geological Survey of India, Kolkata- Based on subsurface information from 17 700016, India; ph. 033-2286-1615 ext. boreholes and surface geomorphology, the 2702; Email: shallow geology of the site is interpreted [email protected]); R D as a meander-belt fluvial fining-upwards Beckie (Department of Earth and Ocean sequence approximately 25m thick Sciences, University of British Columbia, overlying undifferentiated alluvial Vancouver, BC, V6T 1Z4, Canada; ph. deposits. The sequence consists of grey, 604-822-6462; e-mail: fining-upward, point-bar sands capped by [email protected]) oxidized, silty levee or crevasse splay deposits and a soil layer. The point bar The geological surveys of India and sands are the shallowest permeable unit Canada have established a field research and they represent the aquifer most site in the village of Gotra, West Bengal, commonly tapped by villagers for in order to investigate the occurrence of domestic purposes. Hydraulic elevated arsenic concentrations in local conductivities, measured by slug tests, are groundwater. The village is located in the in the range of 5E-04 m/s. Silty levee Bengal Delta Plain, approximately 55 km deposits form a leaky confining layer over north-east of Kolkata and 17 km east of the northeastern portion of the study area. the river Hooghly. It is situated on a However, towards the abandoned channel, natural levee forming the northeastern, the point-bar sands thin as overlying, low- concave, bank of an arcuate abandoned conductivity (K = 9E-08 m/s) channel-fill river channel which has been dammed into deposits thicken. These deposits, which a string of small ponds. Another series of consist of dark, organic-rich, clayey silts, ponds, excavated for building material, form an asymmetric plug in cross-section, borders the village to the northeast where and reach a maximum thickness of 22m in the levee gives way to lower-lying ground the thalweg of the abandoned channel. The used for vegetable and rice cultivation. highest observed groundwater arsenic concentrations (500 µg/L) are encountered The site is relatively unique in that in the aquifer adjacent to the string of repeated surveys of groundwater chemistry ponds that mark the final course of the in domestic wells have revealed a sharply- abandoned channel. defined zone of high arsenic, approximately 80m wide, extending sub- A conceptual model of the shallow parallel to the trend of the abandoned groundwater flow system is developed channel. The zone is characterized by from the hydrostratigraphy and highly reducing conditions with elevated hydrographs obtained from a network of alkalinity, iron, ammonium and phosphate. instrumented piezometers. It is The purpose of the groundwater modeling implemented in a transient, 3D numerical exercise is to establish a sound (MODFLOW) model calibrated to hydrogeological framework for piezometric data and constrained by mass interpreting this geochemical pattern. balance calculations and lines of evidence More specifically, modeling is used to from conservative tracers and stable determine the hydrogeological significance isotopes. The model is designed with a of contrasting pond types (abandoned discretization grid appropriate for
15 investigating the relatively short-scale and University of British Columbia have been shallow flow paths in the aquifer affected investigating naturally occurring arsenic in by arsenic contamination. It provides an groundwater at a field site near the village internally-consistent, quantitative, of Gotra, West Bengal, India. The site is hydrogeological context for interpreting located in a classical fluvial-deltaic the observed geochemical front in light of depositional environment and with an in- seasonal variations in the groundwater filled abandoned channel located between flow regime and the effects of irrigation relatively low permeability flood-plain pumping. Results of the modeling study deposits to the south and west and higher show that not all ponds are equal as permeability point-bar deposits to the sources of recharge and organic carbon, north and east. The distinguishing feature despite similarities in their water of the site is that groundwater with high chemistry. Although high-arsenic concentrations of arsenic (> 50 ppb) is groundwaters were recharged in ponds, the found in the aquifer below and proximal to source of organic carbon is demonstrated the in-filled channel and is separated by a to be in the underlying channel-fill sharp transition zone of less than 30 m sediments. width from groundwater with lower concentrations of arsenic to the north and east. Shallow wells completed in the low- The geochemistry of high- and low- permeability soft, gray silty-clay channel arsenic groundwaters and their fill within 5 m from the edge of a pond association with an in-filled abandoned show unambiguously that the arsenic is channel at a Field Site in Gotra, Nadia released within the channel fill and is District, West Bengal, India moving vertically downward into the aquifer sands where most domestic wells [*R D Beckie*] (Department of Earth and are completed. Water proximal to another Ocean Sciences, University of British pond away from the channel is not Columbia, Vancouver, BC, V6T 1Z4, associated with high arsenic. All Canada; ph. 604-822-6462; e-mail: geochemical indicators point to organic- [email protected]); A J Desbarats matter driven reductive release processes. (Geological Survey of Canada, Ottawa, Indeed, groundwater with high arsenic is ON, K1A 0E8, Canada; ph. 613-995-5512; associated with high phosphate, low e-mail: Alexandre.Desbarats@nrcan- sulfate, high ammonia, high alkalinity, rncan.gc.ca); T Pal (Central Petrological abundant methane, high dissolved organic Laboratories, Geological Survey of India, carbon and PCO2 between 10-1.2 and 10- Kolkata-700016, India; ph. 033-2286-1616 0.7 bars. The degree of super-saturation ext. 2705; Email: [email protected]); C with respect to vivianite and siderite E M Koenig (Department of Earth and increases with arsenic concentration. Ocean Sciences, University of British Sediments contained solid-phase arsenic Columbia, Vancouver, BC, V6T 1Z4, concentrations of 1 to several ppm As in Canada; ph. 604-822-2764; e-mail: sandy zones up to 20 ppm As in finer- [email protected]); P K Mukherjee grained channel material. In vertical (Central Petrological Laboratories, profiles, sediment arsenic peaks did not Geological Survey of India, Kolkata- coincide with dissolved-arsenic peaks 700016, India; ph. 033-2286-1615 ext. although the highest dissolved and 2702; Email: sediment arsenic was observed near the [email protected]); surface. The sediment geochemistry showed that solid-phase arsenic was Since 2004, the Geological Surveys of strongly correlated with solid-phase iron, India and Canada in collaboration with the manganese and the metals copper, nickel,
16 chromium and to a slightly lesser extent (Institute of Biogeochemistry and zinc. The correlation was stronger in the Pollutant Dynamics, ETH Zurich, CHN, low-dissolved-arsenic zone than in the CH-8092 Zürich; ph. +41-44-6336033; fax high-dissolved-arsenic zone. There was a +41-44-6331118; e-mail: poor correlation between solid-phase [email protected]) arsenic and sulfur, although any correlation could have been masked by the In Bangladesh, groundwater is extensively high solid-phase sulfur detection limits. used for irrigation of dry season Boro rice. Due to often high arsenic (As) concentrations in irrigation water, Estimating Long-Term Trends of approximately 1360 tons of As were Arsenic Accumulation in Irrigated estimated to be transferred to arable soils Paddy Soils in Bangladesh: A Mass in Bangladesh each year (1). Potential Balance Approach accumulation of As in paddy soils may have adverse effects on rice yield and [*J Dittmar*] (Institute of quality and consequently human health. Biogeochemistry and Pollutant Dynamics, ETH Zurich, CHN, CH-8092 Zürich; ph. We studied the fate of As in paddy fields +41-44-6336064; fax +41-44-6331118; e- in Munshiganj, where Boro rice is grown mail: [email protected]); A since the early 1990’s under irrigation with Voegelin (Institute of Biogeochemistry water containing ~ 400 μg As L-1. We and Pollutant Dynamics, ETH Zurich, found that irrigation leads to spatially CHN, CH-8092 Zürich; ph. +41-44- heterogeneous As input into paddy fields. 6336147; fax +41-44-6331118; e-mail: Soil As contents are highest in topsoils and [email protected]); L C decrease with increasing distance from the Roberts (Swiss Federal Institute of Aquatic point where the irrigation water enters the Science and Technology (Eawag), CH- field. On the field site the growth season is 8600 Dübendorf; ph. +41-44-8235418; fax followed by intense monsoon flooding and +41-44-8235210; e-mail: soil As is variable over the year, increasing [email protected]); S J Hug (Swiss during irrigation and decreasing during Federal Institute of Aquatic Science and monsoon. These high spatiotemporal As Technology (Eawag), CH-8600 variations complicate the reliable Dübendorf; ph. +41-44-8235454; fax +41- assessment of long term trends. First 44-8235210; e-mail: estimates suggested that As input may [email protected]); G C Saha partly be counteracted by As loss through (Department of Civil Engineering, Dhaka irrigation water percolation and/or As University of Engineering and diffusion into monsoon floodwater (2, 3). Technology, Gazipur-1700, Bangladesh; e- mail: [email protected]); M A Ali In order to asses the potential for long- (Department of Civil Engineering, term As accumulation, we measured soil Bangladesh University of Engineering and As contents in an individual field with Technology, Dhaka-1000, Bangladesh; ph. high spatial and temporal resolution (38 +8802-9665650-80 Ext. 7625; fax 880-2- soil cores, 4 sections down to 40 cm, 7 9663695; e-mail: [email protected]); A sampling campaigns over 3 years (4x after B M Badruzzaman (Department of Civil monsoon, 3x after irrigation)). We will Engineering, Bangladesh University of discuss the results from these sampling Engineering and Technology, Dhaka-1000, campaigns with respect to seasonal As Bangladesh; ph. +8802-9665650 Ext- fluxes and the As accumulation potential 7569; fax 880-2-9663695; e-mail: in paddy fields. [email protected]); R Kretzschmar
17 References cut from the middle of the stem and the (1) Ali et al., In Fate of Arsenic in the remaining half of the stem and roots are Environment; ITN: Dhaka, 2003, 7-20. ploughed back for the next cultivation. (2) Roberts et al., ES&T 2007, 41, 5960- This activity leaves a considerable amount 5966. of organic matter in the paddy field, which (3) Dittmar et al., ES&T 2007, 41, 5967- during monsoon starts decomposing and 5972. subsequently leads, among others, to the formation of organic acids. Organic acids thus produced percolates down with Role of Agricultural Practices in rainwater and on their way to the Mobilization of Arsenic From groundwater table reacts with the mineral Sediments to Groundwater surfaces and modifies their sorption behaviour. In the present work, a study has [*S H Farooq*] (Department of Earth been made to investigate the role of Sciences, Indian Institute of Technology organic acids produced in the paddy field Bombay, Powai, Mumbai, 400076, India; in mobilizing arsenic from sediments to ph. +91-9820376292; fax +91- groundwater. For this purpose, column 2225767253; e-mail: experiments on a 9 meter deep soil profile, [email protected]); D collected from a paddy field in West Chandrasekharam (Department of Earth Bengal have been conducted. In the Sciences, IIT Bombay, Powai, Mumbai, column filled with the material from the 400076, India; ph. +91-2225767263; fax uppermost 3 meters of the soil profile +91-2225767253; e-mail: results indicate a significant mobilization [email protected]); S Norra (Institute of of arsenic from the very beginning of the Mineralogy and Geochemistry, University experiment when leached with a solution Karlsruhe (TH), Karlsruhe 76131, containing 100 mg/L of indigenous Germany; ph. +49-7216086155, e-mail: organic acids. At depths between 3 to 9 [email protected]); Z Berner meters the sediments become coarser with (Institute of Mineralogy and increasingly larger grain size dominated by Geochemistry, University Karlsruhe (TH), sand fraction that apparently acts as Karlsruhe 76131, Germany; ph. +49- sorption media for arsenic. In the column 7216086374, e-mail: filled with this material, the release of [email protected]); D Stüben arsenic during six weeks of the experiment (Institute of Mineralogy and increases gradually in parallel with the Geochemistry, University Karlsruhe (TH), decrease of the redox values and the Karlsruhe 76131, Germany; ph. +49- availability of binding sites for adsorption. 7216083322, e-mail: In a control experiment, using tap water [email protected]). without addition of organic acids no significant release of arsenic could be Arsenic contamination in groundwater is observed during the same time interval. posing a major health threat to global The results of these experiments may be human population. The problem is helpful in better understanding of arsenic especially severe in many South Asian release mechanism especially in the South countries like West Bengal (India), Asian countries which have similar Bangladesh, Vietnam and Cambodia. agricultural practices, climate and Careful observation shows a striking sediment type (deltaic). similarity between all the affected areas of South Asia that follow similar agricultural practice i.e. traditional paddy cultivation method. In this method, harvested crop is
18 The Cause of Severe Arsenic pond recharge with aquifer sediments Contamination in Bangladesh results in the chemical composition observed in arsenic-contaminated [* C. F. Harvey *] (48-309, MIT, groundwater. These findings have a Cambridge MA, 02139, 617-258-0392, number of implications that are important [email protected]); K.N Ashfaque; R.B. for water management. First, arsenic Neumann concentrations will likely shift over decades, the time-scale of groundwater Biogeochemists have puzzled over the circulation and land-use change, so mechanisms that cause high arsenic monitoring programs will need to extend concentrations in the groundwater of over this time-scale. Second, our results Bangladesh since the severe health effects support Michael and Voss?s recent of contaminated drinking-water wells were suggestion to place drinking water wells first publicized. To describe all of the below irrigation wells because the biogeochemical processes that lead to high hydraulic barrier induced by the irrigation arsenic concentrations with certainty wells can prevent recent local surface would require tracking sediment-water water recharge from reaching drinking- interactions along a flow path from water wells. Third, the results emphasize recharge to contamination ? an endeavour the importance of understanding how land- that would require the detailed level of use changes can affect water quality. hydrogeologic characterization only Changes, such as the extensive excavation supported in economically developed of ponds and widespread adoption of countries. However, by combining groundwater irrigation, can alter physical understanding of groundwater groundwater chemistry by changing flow, with isotopic tracers and detailed patterns of groundwater flow as well as the chemical characterization of both recharge biogeochemical input to aquifers. water and groundwater, we demonstrate that recharge from constructed ponds leads to high arsenic concentrations at a site in Water Resources Quality (WRQ): Risk Munshiganj, Bangladesh. We show that Assessment and Mitigation for labile organic carbon that enters the Inorganic Contaminants in aquifer through pond sediments promotes Groundwater arsenic mobilization from aquifer minerals, and that the resulting high [*J G Hering*] (Eawag, Swiss Federal concentrations of arsenic are distributed Institute of Aquatic Science & through the aquifer by groundwater flow. Technology, Duebendorf, Switzerland, Three-dimensional numerical simulations CH-8600; ph. +41 44 823 5001; fax +41 of groundwater dynamics demonstrate that 44 823 5398; e-mail: recharge from ponds excavated during the [email protected]); WRQ team* last century is drawn laterally through the aquifer at the depth of peak arsenic As a sustainable source of safe drinking concentrations by irrigation withdrawals. water, groundwater has many advantages Isotopic tracking of groundwater sources over surface water, most notable its natural supports these results, and laboratory protection from the pathogens that are a experiments show that pond recharge leading cause of child mortality in contains biological degradable organic developing countries. As tragically carbon, whereas the organic carbon in illustrated in South and Southeast Asia, recharge through agricultural soils is however, consumption of groundwater can recalcitrant. Furthermore, likely reaction also pose health risks due to exposure to pathways suggest that the interaction of geogenic contaminants. These risks are
19 real and their impact on exposed chemical parameters such as alkalinity, populations must be acknowledged, but As(T), As(III), Fe(II), Mn, Na, K, Ca, Mg, they can also be managed. The WRQ NH4+, CH4 also reduced from 8.8mM; approach promotes the development of 232µg/L; 188 µg/L; 10.8; 0.4; 3.9; 3.3; risk awareness through use of GIS-based 111.5; 31.7; 0.5; 2.3 mg/L to the lowest maps of the probability of occurrence of point at the 33rd day with the the geogenic contaminants arsenic and concentration is 3.5mM; 160.8µg/L; fluoride. In locations where groundwater 141.9µg/L; 4.2; 0.2; 2.7; 2.1; 47.8; 12.6; containing geogenic contaminants is a 0.3; 0.38 mg/L. The mixing fraction, necessary component of the drinking water calculated based on EC, showed that when supply, WRQ focuses on risk mitigation river water level was highest, groundwater by water treatment for arsenic and fluoride was recharged by 69.4% of river water on removal. (*WRQ team at Eawag: C.A average. It means that, the major changes Johnson (coordinator) K. Abbaspour, M. in water chemistry of groundwater caused Berg, E. Hoehn, S. Hug, H.J. Mosler, K. by mixing with the river water infiltrated Mueller, H. Yang, to the adjacent aquifer. However the http://www.wrq.eawag.ch/index_EN ) whole process can be very complex due to the redox processes, the dissolution and precipitation of minerals such as FeS, Study on geochemical changes of bank CaCO3, etc. infiltration in Red River floodplain aquifer - Case study at Dan Phuong, Ha Tay Arsenic and Manganese Concentrations in Deep Tubewells in Munshiganj, 1Le Quynh Hoa, 3Søren Jessen, 1Nguyen Bangladesh Thi Minh Hue,3Dieke Postma, 3Flemming Larsen, 2Pham Quy Nhan, 1Pham Hung [*S J Hug*] (Swiss Federal Institute of Viet Aquatic Science and Technology (Eawag), 1Research Centre for Environmental CH-8600 Dübendorf, Switzerland; ph. Technology and Sustainable Development, +41-44-8235454; fax +41-44-8235210; e- Hanoi University of Science - Vietnam mail: [email protected]); A B M National University Badruzzaman (Department of Civil 2Hanoi University of Mining and Geology Engineering, Bangladesh University of 3Department of Environment and Engineering and Technology, Dhaka-1000, Resources, Denmark Technique University Bangladesh; ph. +8802-9665650 Ext- 7569; fax 880-2-9663695; e-mail: With the supposition that the artificial [email protected]); M A Ali recharge of high-arsenic groundwater by (Department of Civil Engineering, non-arsenic river water could be a feasible Bangladesh University of Engineering and strategy to produce low-arsenic Technology, Dhaka-1000, Bangladesh; ph. groundwater for human consumption in +8802-9665650-80 Ext. 7625; fax 880-2- the Red River floodplain, the pumping 9663695; e-mail: [email protected]); L infiltration experiment was installed C Roberts (Swiss Federal Institute of throughout rainy season (July to October) Aquatic Science and Technology (Eawag), to investigate the geochemical changes CH-8600 Dübendorf, Switzerland; ph. during this process. After 33 days of +41-44-8235418; fax +41-44-8235210; e- pumping, electric conductivity (EC) of mail: [email protected]); D groundwater reduce significantly from Gaertner (Swiss Federal Institute of about 780μS/cm to 350μS/cm (compare to Aquatic Science and Technology (Eawag), EC of river water is ~200 μS/cm), other CH-8600 Dübendorf, Switzerland; ph.
20 +41-44-8235454; fax +41-44-8235210; e- ph. +880-2-934-2485; e-mail: mail: [email protected]) [email protected]); SK Ghosh (Department of Public Health Engineering, Deep tubewells are installed in many Dhaka, Bangladesh; ph. +88-02-933-0061; regions in Bangladesh to avoid arsenic e-mail: [email protected]); RB contaminated groundwater from shallow Johnston (UNICEF, Dhaka, Bangladesh; tubewells. The necessary depth to reach ph. +880-2-933-6701; fax +880-2-933- 'arsenic-free' water is dependent on the 5641; e-mail: [email protected]). local stratigraphy. In the district of Munshiganj, where over 80% of the The Government of Bangladesh through shallow tubewells are affected by more its Environmental Technology Verification than 50 µg/L As, deep tubewells are programme has granted provisional typically screened at 180-230 m depth. In approval to four arsenic removal two small surveys in Sreenagar Upazila, technologies. These include three we found As concentrations below 10 household level filters (ALCAN, READ-F µg/L in almost all deep tubewells, but Mn and SONO) and one community plant concentrations reached 1-5 mg/L (greatly (SIDKO). As part of a broader evaluation, exceeding the WHO guideline value for nearly 20,000 filters have been distributed Mn of 0.4 mg/L) in most deep tubewells to arsenic-affected households since 2007, around Sreenagar town. To obtain more and more than 50 community plants have detailed information about the deeper been constructed. Water quality of the aquifers, we installed monitoring tubewells source wells and treated water has been down to 230 m depth, at a location ca. 1 monitored by NGO workers, and a social km east of the town of Sreenagar. The assessment is underway. Preliminary transition from gray Holocene to brown monitoring results are presented which Pleistocene sediments was observed at show that in most cases the household and 170-190 m. As concentrations peaked at community filters are able to remove around 30 m depth with over 500 µg/L and arsenic for at least one year. In some parts concentrations of around 200 µg/L of the country arsenic breakthrough has extended down to 100 m. Below 130 m, occurred earlier, this seems to be mainly As concentrations were lower than 20 due to a more challenging water matrix, µg/L. Mn concentrations were below 0.5 though in some cases physical damage to mg/L down to 180 m, but then rose sharply the filter caused during transport and to over 3 mg/L from 180-210 m. If installation has led to filter failure. planned pumping test show that water from 160-180 m depth (slightly above the Pleistocene sediments) can be pumped for In situ Removal of Arsenic: Column household use without the risk of Studies contamination with shallow water, deep tubewells screened in this depth range [*RB Johnston *] (UNICEF, Dhaka, could provide water with low As and Mn Bangladesh; ph. +880-2-933-6701; fax concentrations in this region. +880-2-933-5641; email: [email protected]); PC Singer (University of North Carolina, Chapel Hill, Arsenic Removal Technologies in NC 27516 USA; ph. +1-919-966-3865; Bangladesh: an Interim Progress fax:+1-919-966-791; email: Report [email protected]).
[*SMI Huq*] (Department of Public By injecting aerated water into an aquifer Health Engineering, Dhaka, Bangladesh; which contains elevated levels of dissolved
21 Fe(II), localized oxidizing conditions can that goethite has a substantially higher be created. Fe(II) is then oxidized in situ, capacity for Fe(II) than for As(III). creating fresh ferric surfaces which can subsequently adsorb Fe(II), allowing low- These experiments suggest that in situ Fe water to be abstracted for some time. A treatment is a promising approach for series of column experiments using obtaining safe drinking water from goethite-coated sand were conducted to aquifers containing elevated levels of simulate this process, and to determine if dissolved arsenic and iron. in situ treatment could simultaneously remove Fe(II) and As(III). Retardation factors for O2, Fe(II), and As(III) were Geochemistry of Arsenic during estimated by measuring the number of Groundwater Discharge in the Ganges- pore volumes at which 50% breakthrough Brahmaputra-Meghna Delta occurred. Experiments were conducted at pH 7.0, 7.5, and 8.0, and simulated using a [*H B Jung*] (Queens College and the geochemical model. Graduate School and University Center, The City University of New York, The observed retardation of oxygen, iron Flushing, New York, NY 11367; ph. 718- and arsenic was in good agreement with 702-3491; fax 718-997-3300; e-mail: theory. [email protected]); Y Zheng (Queens College and the Graduate School and Iron retardation during abstraction phases University Center, The City University of increased with increasing pH, and matched New York, Flushing, New York, NY stoichiometric mass balance calculations 11367; Lamont-Doherty Earth from oxygen retardation during injection Observatory, 61 Route 9W, Palisades, phases. Duplicate columns showed good New York, NY 10964; ph. 718-702-3491; agreement. Geochemical modeling fax 718-997-3300; predicts that retardation factors should [email protected]), B C Bostick increase with increasing treatment cycle (Department of Earth Sciences, Dartmouth numbers, as sediments become College, Hanover, NH 03755, United increasingly coated with fresh ferric States; ph. 603-646-3624; fax 603-646- surfaces. This 'ripening effect' was 3922; e-mail: [email protected]); K observed at pH 8.0 only. M Ahmed (Dhaka University, Department of Geology, Dhaka, 1000 Bangladesh; ph. Arsenic retardation showed less pH 880-2-9661920-72; fax 880-2-8615583; dependence, and a ripening effect was seen [email protected]) at pH 8.0 only. However, substantial retardation was consistently noted the first Shallow groundwaters in the Ganges- time Fe(II) and As(III) were co-injected on Brahmaputra-Meghna Delta (GBMD) are the column; this is interpreted as a frequently elevated in arsenic and iron. electrochemical effect, as adsorbed Fe(II) The large hydraulic gradient between increases the surface potential. This effect shallow groundwater and rivers at the did not persist in subsequent cycles, onset of dry season drives the flow from indicating that the product of Fe(II) groundwater to rivers, but little is known oxidation is different from the goethite regarding the fate of arsenic during originally present. discharge. Sporadic sedimentary As enrichment up to hundreds to thousands Mass balance calculations, as well as mg/kg in the shallow subsurface found independent batch experiments, indicate along the Meghna Riverbank from Northeastern Bangladesh (25 ºN) to the
22 Bay of Bengal (22.5 ºN), is associated with the rapid oxidation of Fe(II) at neutral pH, zones of discharge. This accumulation of is the dominant Fe mineral in Meghna arsenic suggests a plausible mechanism of Riverbank sediment enriched with As by trapping of As by a natural reactive barrier XAS. consisting of freshly precipitated Fe minerals formed at the redox boundary between reducing groundwater and oxic Arsenic contamination in ground water river water during discharge. samples of Rajnandgaon district, Central India To ascertain this hypothesis, shallow sediment core (n=14) and pore water 1Anand Kamavisdar, 2Rajmani Patel and profiles (n=7) were collected at sites along 3Shitikanth Rajaram Khanwalkar the Meghna River to ~ 7 m depth in 1National Institute of Miners’ Health, January 2006 and Oct-Nov 2007 for JNARDDC Campus, Amaravati Road, geochemical analysis. Groundwater WADI, Nagpur 440023 MS India discharge rate is 6.1±1.8 cm/d based on [email protected] seepage meter (n=19) deployed in Oct- 2Department of Applied Chemistry, Shri Nov 2007. Depth profiles of sediment Shankaracharya College of Engineering Fe(II)/Fe(II+III) ratios and pore water and Technology, Junwani, Bhilai, 490020 dissolved oxygen and Fe concentrations CG India [email protected] indicate that there is a redox transition 3Central Institute of Mining and Fuel zone from anoxic to suboxic from ~2 m Research, 17/c, Telangkhedi Area, Civil depth to the surface. Sediment As Lines, Nagpur MS 440001 India enrichment up to ~700 mg/kg is closely associated with this redox transition zone. Studies were carried out on ground water Concentrations of groundwater Fe, As, and samples (n = 50) collected near P decreased significantly along the flow Rajnandgaon district (21N06 81E08) of path from the upland shallow well newly formed Chhattisgarh state of Central groundwater to riverbank pore water, and India for the determination of arsenic. The finally to river water, while the decreases concentration of arsenic in the study area of concentrations of major cations are was found to be in the range of 10 – 800 much less. This indicates immobilization µg L-1. The median (µg L-1) and of groundwater As and P coupled with Fe standard deviation of the metal in ground at the point of discharge. Transects of water samples was calculated and found to sediment cores and high-resolution depth be 159.5 and (±) 233.02, respectively. The analysis of sediment indicate that the high variation in the range and standard arsenic enrichment zone in the riverbank is deviation of the concentration of arsenic in vertically thin, only 5~20 cm in a number ground water samples was recorded may of cores, but is wide horizontally spanning be due to wide variation in their natural a length of 10-15m from the river shore. availability in soil, scavenging potentiality, Arsenic speciation in sediment determined chemical forms, solubility etc. The by X-ray absorption spectroscopy (XAS) industrial emission (burning of coal in is dominated by mixed As(III) and As(V) steel and thermal power plants in the with on average, 23±23% and 68±20% of region) strength with wide range may also total As, respectively. In pore water, > be contributing factor in the statistical 90% of dissolved As in shallow variations of the metal concentration in groundwater is in the form of As(III). This ground water samples. The toxic form of suggests that dissolved As (III) is partially arsenic i.e. As (III) and As (V) were also oxidized during or after trapping. found to be present in the analyzed Ferrihydrite, which commonly forms from samples, predominantly. The sources of
23 arsenic in the study area may be due to contamination and risk. To achieve this rock weathering which in turn leaching the goal tubewell water, together with plant ground water samples with contributions and soil samples, from rural household and of atmospheric depositions. The people irrigation fields were collected and living nearby the study area may be subsequently As determination was carried affected from diseases related with arsenic out using ICP-MS. Laboratory pollution i.e. keratosis, melanosis, skin determination of As concentration shows cancer etc. that the overall mean As concentration in tubewell water across the landscape was 148 µg L-1 and ranged from 0 to 969 µg Spatial Variation of Arsenic in L-1. Analysis of As water surfaces Groundwater in the Rural Landscape of indicated that As concentrations were Bangladesh and the Impact on Human highly variable for water sources located Health within close proximity (50 m) of each other [*Nasreen Islam Khan*] (Centre for Environmental Risk Assessment and To identify spatial variability and patterns Remediation (CERAR), University of of As contamination across the landscape, South Australia and Department of geostatistical techniques were applied to Geography and Environment, Dhaka the As concentration database to create University, Bangladesh; ph. 61 8 concentration surfaces. Geostatistical 83025298; fax. 61 8 83023057; email: interpolation was of limited value for As [email protected]); David Bruce concentration surfaces due to inherit high (School of Nature Built and Environment, spatial variability in groundwater As University of South Australia; ph. 61 8 concentrations even over short distances (< 83021856; fax. 61 8 83022252 email: 50 m), but did indicate some trends and [email protected]); and Gary patterns of As concentration in Owens (Centre for Environmental Risk groundwater that varied between thanas. Assessment and Remediation (CERAR), To identify the causes of spatial variability University of South Australia; ph. 61 8 of As concentration in tubewell water the 83025043; fax. 61 8 83023057; email: depth-concentration relationship was [email protected]) investigated. While there was no significant linear relationship between Arsenic (As) contaminated groundwater tubewell depth and As concentration (r2 = commonly extracted through tubewells is 0.11), the negative correlation (r = -0.34) widely used for drinking and identified as exhibited between tubewell depth and As major As exposure pathways to the concentration, indicated that As population that live in the rural areas of concentration did tend to decrease with Bangladesh. Since As groundwater increasing tubewell depth. The frequency contamination and the associated human of exceedance of the Bangladesh drinking health risk are potentially spatially water guideline value (50 µg L-1) was connected, this research assesses and related to reported tubewell depth and quantifies the spatial variability of As indicated a peak when the tubewell depth concentrations in the rural landscape in was around 18.7 m. A small number of relation to As concentrations from tubewells exceeded the Bangladesh drinking and irrigation water sources. guideline of 50 µg L-1 at lower depth and Arsenic contamination and human health also at depths above 70 m suggesting that risk were treated as spatial phenomena and both shallow and deeper tubewells could methodology was developed to analyze be solutions to alleviate As exposure from and visualize the spatial variability of As water. Spatial analysis of As concentration
24 in water sources also indicated that the System Science, Stanford University, current Bangladesh drinking water Stanford CA 94305; ph. 650-723-5238; guideline of 50 μg L-1 underestimates the fax 650-725-2199; e- risk of As exposure and hence a large mail:[email protected]) fraction of the population and their water sources would not be targeted for the Weathering of As-bearing rocks in the remediation measures using this guideline. Himalayas has resulted in the transport of sediments down major river systems such This investigation was further extended by as the Brahmaputra, Ganges, Red, identifying the relationship between water- Irrawaddy, and Mekong. Groundwater in soil-plant (vegetables) As concentration these river basins commonly has As using GIS. Distance-concentration-impact concentrations exceeding the World analysis indicated that there was no direct Health Organization's recommended correlation between water As and surface drinking water limit (10 µg/L) by more soil As concentrations in the same location than an order of magnitude. Coupling of in the landscape. However, a positive hydrology and biogeochemical processes linear correlation (r = 0.4) was observed underlies the elevated concentrations of As between As concentration in groundwater in these aquifers. In particular, the spatial and rice grain, but no similar relationship distribution As within sediment profiles was observed between As concentration in must be examined to ascertain sources and groundwater and vegetables (r = -0.1). sinks of As and to predict future patterns of contamination in evolving aquifers. We therefore performed a comprehensive Measuring and Simulating the Near- analysis of near-surface and aquifer Surface Biogeochemical and Hydrologic biogeochemistry within an As-afflicted Processes Governing Arsenic Transport field area south of Phnom Penh, in the Mekong Delta, Cambodia Cambodia, bounded by the Bassac and Mekong Rivers and comprising [*B D Kocar*] (Department of approximately 50 km2. Biogeochemical Environmental Earth System Science, profiles of aqueous constituents including Stanford University, Stanford CA 94305; As, Fe, and DOC coupled with detailed ph. 650-723-4152; fax 650-725-2199; e- hydrologic measurements illustrate that As mail: [email protected]); M Polizzotto is released within near-surface (<12 m) (Department of Environmental Earth sediments within oxbow features. System Science, Stanford University, Stanford CA 94305; ph. 650-723-4152; To fully elucidate the biogeochemical fax 650-725-2199; e-mail: mechanisms of near-surface sedimentary [email protected]); S C Ying As release, we used a number of field, (Department of Environmental Earth laboratory, and spectroscopic System Science, Stanford University, measurements. Based on these Stanford CA 94305; ph. 650-723-4152; measurements, we assess the fax 650-725-2199; e-mail: thermodynamic potential for As, Fe, and S [email protected]); S Benner reduction to transpire—the major (Department of Geology, Boise State processes influencing As release and University, ID 83725; ph. 208-426-3629; mobility. Our results illustrate that e-mail: [email protected]); M sediments (0-12m deep) within oxbow and Sampson (Resource Development interior wetland environments are International, Cambodia; ph (855)24-399- seasonally inundated, exhibit saturated 577; email: [email protected]); S Fendorf conditions throughout the year, and (Department of Environmental Earth possess appreciable quantities of As-
25 bearing Fe-(hydr)oxide and organic Geological and hydrogeological processes carbon—conditions conducive for the affecting concentrations of arsenic (As) in mobilization of As through As(V) and As- Holocene and Pleistocene aquifers in the Fe-(hydr)oxide reduction. Ensuing Red River flood plain in Vietnam have reductive mobilization of As from As- been studied both on a regional and a local bearing Fe (hydr)oxides results in its scale. The geology was investigated using migration to the underlying sandy aquifer geophysical methods and drilling of (>12 m deep). Near-surface As release is exploratory boreholes. The hydrogeology linked to widespread aquifer was studied using: (i) water sampling in contamination with reactive transport monitoring boreholes in a 45 km transect modeling; simulations calibrated with across the southern and central part of the biogeochemical and hydraulic field data delta, (ii) time-series of hydraulic head demonstrate that continuous release from distributions in surface waters and near-surface sediments delivers sufficient aquifers; (iii) the stable isotope quantities of As to propagate widespread, composition of rain, surface and ground elevated As concentrations within the water, and (iv) numerical ground water aquifer for centuries to millennia. modeling. Results show relatively high As ground water concentrations in the shallow Holocene aquifers and lower Geological and Hydrogeological concentrations in underlying Pleistocene Processes Affecting the Distribution of aquifers. Arsenic Ground Water Concentrations in Holocene and Pleistocene Aquifers in The major mobilization of As to ground the Red River Flood Plain, Vietnam. water seems to occur in the Holocene sediments, with the reduction of As- [Flemming Larsen] (Geological Survey contaminated Fe-oxides controlled by of Denmark and Greenland, 10 natural organic matter degradation as the Ostervoldgade, 1350 Copenhagen K, controlling geochemical process. An Denmark, ph +45 38142777, fax estimated mobilization rate of As from the +38142050; e-mail: [email protected]); Dieke Holocene sediments of 14 µg/L/year is Postma (Geological Survey of Denmark comparable with estimated release rates and Greenland, 10 Ostervoldgade, 1350 from a previous Bangladesh study of As Copenhagen K, Denmark, ph +45 release from similar aquifer sediments. 38142000, fax +38142050, e-mail: Through most of the year, the ground [email protected]); Pham Quy Nhan (Hanoi water flow in the shallow Holocene University of Mining and Geology, Dich, aquifers is controlled by a regional flow Cau Giay, Hanoi, ph 0913546004, e-mail: towards the main rivers, whereas during [email protected]); Pham Hung the monsoon, the river water stages rises Viet (Hanoi University of Science and up to 6 m and stalls the regional ground Technology, 334 Nguyen Trai Street, ph water flow. In this high water stage period, 84-4-858 7964, e-mail: the interaction between the surface waters [email protected]); Nhan Duc Dang and shallow aquifer system is highly (Institute of Nuclear Science and dynamic with a succession of gaining and Technology, 79, Hoang Viet, Cau Giay, losing phases through high permeable Hanoi, ph 8448588152, e-mail: layers adjacent to the rivers. A mass [email protected]); Søren Jessen balance based on the numerical ground (Technical University of Denmark, water flow modeling, and average As Building 114, 2800 Lyngby Denmark; ph ground water concentrations, suggests that +45 45252525, e-mail: [email protected]). As is exported with the ground water from the Holocene aquifers to the rivers, where
26 is seems to be re-precipitated in bottom Ballentine (School of Earth Atmospheric sediments. Compared to the pool of As and Environmental Sciences, University of present in the aquifers sediments, the flux Manchester, Manchester, UK M13 9PL; of As into the rivers is small (0.01 %) and ph. +44 161 275 3832; fax +44 161 306 a timescale of thousands of years is 9361; e-mail: envisaged before the Holocene sediments [email protected]); A become depleted in As. Boyce (ICSF, SUERC, East Kilbride, UK, G75 0QF; ph. +44 1355 270143; fax +44 Observed low As groundwater 1355 229898; e-mail: concentrations in the Pleistocene aquifers [email protected]); C Bryant have been ascribed to a reduced reactivity (NERC Radiocarbon Laboratory, East of the organic matter in these older Kilbride, UK, G75 0QF UK M13 9PL; ph. sediments and in addition to a originally +44 1355 260037; fax +44 1355 229829; lower content of organic matter in these e-mail: [email protected]); D fluvial deposits. Localized elevated As Mondal (School of Earth Atmospheric and ground water concentrations in the Environmental Sciences, University of Pleistocene aquifers could therefore be Manchester, Manchester, UK M13 9PL; controlled by natural or pumping induced ph. downward flow from the Holocene +44 161 275 3818; fax +44 161 306 9361; aquifers into the underlying Pleistocene e-mail: aquifers. Observed stable isotopes [email protected] compositions (18O/16O and 2H/1H) and c.uk); C Davies (School of Earth As concentrations from these studies seem Atmospheric and Environmental Sciences, to confirm such a flow control on the As University of Manchester, Manchester, ground water distribution in the UK M13 9PL; ph. +44 161 275 0384; fax Pleistocene aquifer, but it still need to be +44 161 306 9361; e-mail: proven whether this is a widespread [email protected]); D phenomenon. Where high As containing Chatterjee (Department of Chemistry, ground water is flowing down into University of Kalyani, Kalyani, West Pleistocene aquifer, sorption of As to Bengal, India; ph. +91 033 2582 8750; sediment surfaces could reduce the As fax: +91 033 2582 8282; e-mail: concentrations in the water. [email protected]); S Majumder (Department of Chemistry, University of Kalyani, Kalyani, West Isotopic Tracing of Ground-Surface Bengal, India; ph. +91 033 2582 8750; Water Interaction and its Role in fax: +91 033 2582 8282; e-mail: Arsenic Release in West Bengal, India [email protected]); A Biswas (Department of Chemistry, University of [*M Lawson*] (School of Earth Kalyani, Kalyani, West Bengal, India; ph. Atmospheric and Environmental Sciences, +91 033 2582 8750; fax: +91 033 2582 University of Manchester, Manchester, 8282; e-mail: UK M13 9PL; ph. +44 161 275 3802; fax [email protected]) +44 161 306 9361; e-mail: [email protected] Arsenic in groundwaters utilised for k); D A Polya (School of Earth drinking, cooking and irrigation in many Atmospheric and Environmental Sciences, parts of southern Asia is adversely University of Manchester, Manchester, affecting the health of tens of millions of UK M13 9PL; ph. +44 161 275 3818; fax people. It is widely accepted (although not +44 161 306 9361; e-mail: universally held) that this arsenic is of [email protected]); C J natural origin and that it is mobilised under
27 reducing conditions via the microbially Kwei Liu (Department of Geosciences, mediated reductive dissolution of Fe(III) National Taiwan University, Taiwan, phases. This process is driven by the ROC; ph. 886-2-33662909; fax 886-2- consumption of organic matter (OM). 23657380; e-mail: [email protected]) However, the nature and provenance of this OM utilized by these microbes Groundwaters from deep aquifers (60- remains a subject of intense debate. 300m) in southwestern Taiwan are high in Harvey et al (2002) have suggested that concentrations of arsenic (As) and humic that modern OM, drawn in to reducing substances (with molecular weight larger aquifers from surface water bodies than 500 Dalton). Previous studies showed following the extensive pumping of that arsenic can be complexed with shallow groundwater over the last few dissolved humic substances, but the decades, has accelerated the rate of the existence of As-humic substances complex arsenic release process. If this is shown to in the Chianan groundwater has not been be the case, then it would have profound confirmed. Therefore, we analyzed the implications for management of contents of dissolved organic carbon groundwater resources in Southern Asia. (DOC), arsenic, major ions, and total alkalinity of 22 groundwater samples from We present here data collected from a field the plain. Moreover, the percentage of study site in Chakdaha, West Bengal, complexed arsenic in 13 samples was where massive groundwater abstraction further determined by ultrafiltration has been proceeding for decades. Tritium, methods. Analysis results obtained show 14C and noble gas data provide key that DOC and arsenic concentrations range constraints on groundwater ages and from 3.8 to 45.9 mgC/L and from 0.02 to provenance, whilst d18O, dD, d13CDIC 1.01 mg/L, respectively. A distinct and d13CDOC provide key positive correlation was found between complementary information with which to arsenic and DOC concentrations. Na+/Cl- determine the relative importance of molar ratios are essentially the same as surface water contributions to the seawater, but SO42-/Cl- molar ratios are groundwater and the nature and not, reflecting the occurrence of sulfate provenance of organic carbon present in reducing reaction. Besides, the values of the aqueous phase. This data directly total alkalinity increase with DOC addresses the issue of the role of surface concentrations, suggesting that DOC and waters and hence the source of OM in DIC resulted from microbial metabolism promoting arsenic mobilisation. of sedimentary organic carbon (SOC). Ultrafiltration analyses showed that almost all arsenic (more than 90%) of all but one Arsenic-Humic Substances Complex in samples analyzed were found to be Groundwater of the Chianan Coastal retained in the dissolved organic matters Plain, Taiwan which have the molecular weight greater than 500 Dalton, demonstrating that most [*Chih-Ping Lee*] (Department of arsenic was complexed with humic Geosciences, National Taiwan University, substances. Taiwan, ROC; ph. 886-2-33662909; fax 886-2-23657380; e-mail: [email protected]); Li-Chun Liu (Department of Geosciences, National Taiwan University, Taiwan, ROC; ph. 886-2-33662909; fax 886-2-23657380; e- mail: [email protected]); Tsung-
28 The Microbial Ecology of Arsenic Polya (School of Earth Atmospheric and Mobilizing Aquifer Sediments Environmental Sciences, University of Manchester, Manchester, UK M13 9PL; [*J R Lloyd*] (School of Earth ph. +44 161 275 3818; fax +44 161 306 Atmospheric and Environmental Sciences, 9361; e-mail: University of Manchester, Manchester, [email protected]) UK M13 9PL; ph. +44 161 275 7155; fax +44 161 306 9361; e-mail: The contamination of groundwaters, [email protected]); M Hery abstracted for drinking and irrigation, by (School of Earth Atmospheric and sediment-derived arsenic, threatens the Environmental Sciences, University of health of tens of millions worldwide. Manchester, Manchester, UK M13 9PL; Using the techniques of microbiology and ph. +44 161 275 7155; fax + 44 161 306 molecular ecology, in combination with 9361; e-mail: aqueous and solid phase speciation [email protected]); A G analysis of arsenic, we have used Gault (Department of Earth Sciences, microcosm and axenic culture-based University of Ottawa ,140 Louis Pasteur, approaches to provide evidence that Ottawa, ON, K1N 6N5, Canada,; ph. + anaerobic metal-reducing bacteria can play 613-562-5773 ; fax + 613-562-5192; e- a key role in the reductive mobilization of mail: [email protected]); J Charnock arsenic in sediments collected from (School of Earth Atmospheric and aquifers in West Bengal and Cambodia. Environmental Sciences, University of The critical controls on these activities will Manchester, Manchester, UK M13 9PL; by described, including the role of organic ph. +44 161 275 3814; fax +44 161 306 matter in promoting arsenic-mobilizing 9361; e-mail: respiratory processes, alongside the [email protected]); G. diversity of organisms involved in Lear (School of Biological Sciences, The mediating these transformations. The University of Auckland, Auckland City, impact of other competing anaerobic New Zealand; e-mail: processes, including sulfate reduction, on [email protected]); R Pancost arsenic speciation will also be discussed in (School of Chemistry, University of the context of mitigating arsenic Bristol, Bristol, UK BS8 1TS; ph. +44 mobilization. 117 9289178; fax +44 117 9251295; e- mail: [email protected]); H A L These biogeochemical processes have Rowland (eawag, Uberlandstraase 133, been investigated using culturing Duebendorf, CH-8600, Switzerland; ph. experiments and stable isotope probing +41 44 8235269; fax +41 44 8235028; e- (SIP) techniques in combination with mail: [email protected]); D J Vaughan functional gene analysis, to identify the Dongen (School of Earth Atmospheric and active fraction of subsurface microbial Environmental Sciences, University of communities responsible for mobilizing Manchester, Manchester, UK M13 9PL; arsenic. Using SIP we have shown that the ph. +44 161 275 3935; fax +44 161 306 introduction of a proxy for organic matter 9361; e-mail: (including 13C-labelled acetate and other [email protected]); B Van electron donors) stimulated As(V) Dongen (School of Earth Atmospheric and reduction in sediments collected from a Environmental Sciences, University of Cambodian aquifer that hosts arsenic-rich Manchester, Manchester, UK M13 9PL; groundwater. This was accompanied by an ph. +44 161 306 7460; fax +44 161 306 increase in the proportion of prokaryotes 9361; e-mail: closely related to the dissimilatory As(V)- [email protected]); D A reducing bacteria Sulfurospirillum NP-4
29 and Desulfotomaculum auripigmentum. areas are unique in that such deltas contain As(V) respiratory reductases genes (arrA) regions of rapid deposition, erosion, and, closely associated with those found in as a result, there are numerous lateral Sulfurospirillum barnesii and Geobacter unconformities that complicate their uraniireducens were also detected in active stratigraphy, which result in a complex bacterial communities utilising 13C- relationship between sediment age and labelled acetate in microcosms. Thus, this groundwater arsenic levels. While these SIP study suggests a direct link between areas of extensive arsenic contamination inputs of organic matter, and the increased appear to be quite young based on prevalence and activity of organisms landscape position, there is little which transform As(V) to the potentially information about the absolute age of more mobile As(III) via dissimilatory sediments, or the role of sediment As(V) reduction. deposition rates and age on the expression of groundwater arsenic. Here, we measure maximum sediment ages using Pb-210, Relationship between Sediment Cs-137 and other atmospherically-derived Depositional Age and Groundwater radionuclides, and to establish the recent Arsenic Levels in Cambodia. depositional history of different landscape surfaces. We find extreme heterogeneity in [*J D Landis*] (Department of Earth sediment ages, with many areas Sciences, Dartmouth College, Hanover, experiencing little or no significant NH 03755, United States; ph. 603-646- deposition immediately adjacent to areas 6564; fax 603-646-3922; e-mail: with rapid deposition. In isolated cases [email protected]); L Salmon- associated with areas of groundwater Legagneur (Ecole Nationale Supérieure de contamination, the presence of excess Pb- Géologie, Rue du Doyen Marcel Roubault, 210 at depths of >10 m indicates that 54 500 Vandoeuvre-lès-Nancy, France; e- sediment deposition is both very recent mail: [email protected]); G O and extensive. We attribute the presence of Cadwalader (Department of Earth excess lead at these depths to channel Sciences, Dartmouth College, Hanover, migration and rapid infilling during NH 03755, United States; ph. 603-646- subsequent flooding episodes. Despite the 0994; fax 603-646-3922; e-mail: presence of excess Pb-210 in some [email protected]); J environments, there are several limitations M Kaste (Department of Geology, College to using this methodology for the of William and Mary, Williamsburg VA characterization of depositional rates in 23187-8795, United States; ph. 757-221- these environments, most notably 2951; e-mail: [email protected]); M L extensive sediment redistribution, which Sampson (Resource Development dilutes radionuclide activities with International, Royal Brick Road, Kien relatively old sediments, and non-steady Svay, Kandal, Cambodia; ph. 855-23-399- state conditions, which limits the 577; fax 855-24-399-577; accumulation of atmospherically-derived [email protected]); B C Bostick radionuclides at the soil surface. (Department of Earth Sciences, Dartmouth College, Hanover, NH 03755, United States; ph. 603-646-3624; fax 603-646- 3922; e-mail: [email protected])
Arsenic contamination in groundwater is associated with regions of rapid change within the deltas of southern Asia. These
30 Biotite and its chemical weathering as a groundwater is determined by the reaction primary source and formation with detrital minerals especially feldspars mechanism of arsenic contaminated and biotite. Nitrogen stable isotope ratios groundwater in the Holocene aquifer in of ammonium, which was believed to be a Bangladesh product of microbial activity in reducing aquifer condition, indicate the chemical [*Harue Masuda*] (Department of fertilizers such as urea as the source of Geosciences, Osaka City University, ammonium. Osaka 558-8585 Japan; ph. 81-6-6605- 2591; fax. 81-6-6605-2522; e-mail. The sediments were taken from the surface [email protected]); Ashraf Ali and shallow depth around unsaturated and SEDDIQUE (Department of Geosciences, saturated zones of unconfined groundwater Osaka City University, Osaka 558-8585 and cored through arsenic contaminated Japan; ph. 81-6-6605-2591; fax. 81-6- Holocene aquifer (10 to 30 m depth) to 6605-2522; e-mail. uncontaminated Pleistocene aquifer (>45 [email protected]); Muneki m depth) up to 90 m depth. Arsenic MITAMURA (Department of concentration of all the studied sediments Geosciences, Osaka City University, is <12 mg/kg except one (50 mg/kg), and Osaka 558-8585 Japan; ph. 81-6-6605- gives the well positive correlation to the 2592; fax. 81-6-6605-2522; e-mail. concentration of aluminum, iron and [email protected]); Shinji magnesium, and XRD peak intensities of NAKAYA (Department of Civil mica (muscovite and biotite). Abundant Engineering, Shinshu University, Nagano biotite, which were partly altered to be 380-8553 Japan; ph. 81-26-269-5316; fax. hydrobiotite and not coated with iron 81-26-223-4480; e-mail. oxyhydroxides/oxides, is included in the [email protected]); Takaaki Holocene aquifer sediments comprising ITAI (Department of Earth and Planetary fine to medium sand. The separated Systems Science, Hiroshima University, biotite fractions contained 10~50 mg/kg Hiroshima 739-8526; arsenic. Those facts indicate that the ph. 81-824-24-7460; fax. 81-824-24-0735; biotite is a primary source of As in the e-mail. [email protected]) studied sediments.
The formation mechanism of arsenic The above facts strongly support the contaminated groundwater via microbial hypothesis that the arsenic contamination reduction and dissolution of iron occurs associating with vertical infiltration oxyhydroxides/oxides hosting arsenic must of surface water, promoting chemical be reconsidered based on the geochemical weathering of detrital minerals including data set of groundwater and cored arsenic-bearing biotite, into the aquifer sediments from the boundary between along outside of well pipes and/or holes of contaminated Holocene and abandoned well due to excess use of well uncontaminated Pleistocene aquifers in water. Sonargaon, Bangladesh. Arsenic accumulation in the surface and The major chemistry and oxygen and shallow sediments, in which the hydrogen isotope ratios of the groundwater decomposition of basic minerals and iron in the studied area suggest that highly hydroxides formation would occur in arsenic contaminated groundwater was association with changing surface and recharged from narrow areas around each groundwater level and following redox wells during the late rainy to early dry condition, were not observed in the studied seasons. Major cation composition of the area; i.e., organic matters and
31 silicates/sulfides, but not iron fluorescence spectroscopy. In the Ganges hydroxides/oxides, are the abundant host Brahmaputra Delta of Bangladesh, a phases of arsenic. Microbial activity greater understanding of iron-oxide would play an important role to be reduction in shallow groundwater is a demobilized and detoxicate arsenic as priority because this process drives arsenic producing organo-arsenic species, since mobilization in water supplies used by the arsenic in organic phases increases and millions of people. We used fluorescence that in silicate/sulfide phase decreases with spectroscopy to characterize the dissolved decreasing levels of arsenic contamination humic substances in several surface waters of groundwater of the areas. and groundwater from Bangladesh and modeled the spectra using parallel factor analysis (PARAFAC). In general the Reduced Humic Substances Promote surface water contained oxidized humic Iron Reduction and Mobilization of substances and high concentrations of Arsenic in Aquifers in Bangladesh labile DOM, as indicated by protein-like peaks in the fluorescence spectra. In [*D M McKnight *](Department of Civil contrast, in shallow groundwater where and Environmental Engineering, iron and arsenic concentrations are high, University of Colorado, Boulder, CO humic substances were in a reduced state 80309; ph. 303-492-4687; fax 303-492- and labile DOM was less abundant. These 6388; e-mail: results suggest that a humic-enhanced [email protected]); N electron shuttling cascade contributes to Mladenov (INSTAAR, University of iron reduction and arsenic mobilization in Colorado, Boulder CO 80309, ph. 303- the Bangladesh groundwater system. 492-1534; fax 303-492-6388; e-mail: [email protected]); K M Ahmed (Dept. of Geology, Dhaka Is Deep Groundwater a Sustainable University, Dhaka 1000, Bangladesh); Source of Arsenic-Safe Water in the Diana Nemergut (Department of Ecology Bengal Basin? Management Insights and Evolutionary Biology, University of from a Regional Modeling Analysis Colorado, Boulder, CO 80309; ph. 303- 735-1239; fax 303-492-6388); Yan Zheng [*H A Michael*] (Department of (Queens College, City University of New Geological Sciences, University of York, Flushing, NY 11367; ph 718-997- Delaware, Newark, DE 19716; ph. 302- 3329; fax 718-997-3299; e-mail: 831-4197; email: [email protected]); C I [email protected]) Voss (US Geological Survey, Reston, VA 20192; ph. 703-648-5885; email: Humic substances are heterogeneous [email protected]) organic compounds that can act as electron shuttles in the microbial utilization of Groundwater containing unsafe labile dissolved organic matter, enhancing concentrations of dissolved arsenic is the rates of electron transfer to iron oxides produced from shallow depths by domestic in anoxic sediments. This redox cascade and irrigation wells in the Bengal Basin can influence overall metal cycling in the aquifer system. Deeper groundwater, environment, as sorbed metals are released nearly universally low in arsenic, is a through reductive dissolution of iron potential source of safe water, but an oxides. The redox active moieties in humic understanding of the sustainability of the substances have quinone-like properties supply is critical for management of the and their redox state can be characterized resource. Unsustainable deep pumping by electron spin resonance and would induce vertical flow of water from
32 shallow depths, with associated transport timescale. This insight may assist water- of dissolved arsenic on a timescale of resources managers in alleviating one of management, contaminating the wells and the world’s largest groundwater destroying the deep resource. contamination problems. Sustainability assessment requires an understanding of the groundwater flow system and its potential response to Field Study of Arsenic Adsorption in changes in pumping rates and depths, Low-Arsenic Aquifers of Bangladesh by achieved through large-scale Simulating Shallow Groundwater hydrogeologic analysis and flow Intrusion simulation. [*I Mihajlov*] (Lamont-Doherty Earth Results from groundwater modeling, in Observatory of Columbia University, which the Bengal Basin aquifer system is Palisades, NY 10964, USA; ph. +1-845- represented as a single aquifer with higher 365-8926; e-mail: horizontal than vertical hydraulic [email protected]); K A conductivity, indicate that this anisotropy Radloff ([email protected]); M Stute is the primary hydrogeologic control on ([email protected]); Y Zheng the natural flowpath lengths, and despite ([email protected]); B J extremely low hydraulic gradients due to Mailloux ([email protected]); M minimal topographic relief, anisotropy Bounds ([email protected]); M R Huq implies large-scale (tens to hundreds of ([email protected]); K M Ahmed kilometers) flow at depth. Other (Department of Geology, University of hydrogeologic factors, including lateral Dhaka, Dhaka 1000, Bangladesh; ph. and vertical changes in hydraulic +880-2-966-1920 Ext. 7316; fax +880-2- conductivity, have minor effects on overall 861-5583; e-mail: flow patterns. However, because na tural [email protected]); A van Geen hydraulic gradients are low, the impact of ([email protected]) pumping on groundwater flow is overwhelming; modeling indicates that Deeper, mainly Pleistocene, aquifers pumping has substantially changed the currently provide a safe source of drinking shallow groundwater budget and flowpaths water for Bangladesh due to their from predevelopment conditions. ubiquitously low arsenic concentrations. However, evidence exists that downward Three pumping scenarios were considered hydraulic gradient is developing between as possible future management options the high As, shallow Holocene aquifer and within the high-arsenic region, with the low As aquifer around Dhaka as a associated sensitivity analysis. The result of increased pumping from deep scenarios are (1) deeper pumping for both wells. Increasing exploitation of deeper irrigation and domestic supply, (2) deeper aquifers raises concerns about the pumping only for domestic supply while possibility of leakages of shallow maintaining shallow pumping for groundwater on smaller scale around irrigation, and (3) deeper pumping for pumping wells, and on larger scales in domestic supply without groundwater areas where clay aquitard is thin or irrigation. Analysis indicates that limiting completely absent. In order to simulate the deep pumping to domestic supply only intrusion of shallow groundwater, four (scenarios 2 and 3) may provide a injections of ~1000 L of high As sustainable source of arsenic-safe drinking groundwater were performed in the deeper water to more than 90% of the arsenic- aquifer at our research site in Araihazar. impacted region over a 1000-year Deep groundwater with additions of ~200
33 g/L As(V) or As(III) was used for two of Temporal Indicators of Hydrochemical the injections, while the other two were Processes Including Cation Exchange in performed with unaltered high As shallow Arsenic Contaminated Groundwater of groundwater from two different depths. Nawalparashi, Nepal
As(V) added to deep groundwater [*A Neku*] (Department of Geosciences, adsorbed more rapidly than As(III), with The University of Texas at Dallas, P.O. 50% of As removed in 1.5 and 4 hours, Box 830688, Richardson, TX 75083, respectively. Shallow groundwater As USA; ph. 469-363-9908; fax 972-883- generally seemed to follow the adsorption 2537; e-mail: [email protected]); T patterns of As(III), aside from the slower H Brikowski (Department of Geosciences, initial rate observed with high P The University of Texas at Dallas, P.O. groundwater. We considered As Box 830688, Richardson, TX 75083, adsorption to proceed like a first order USA; ph. 972-883-6242; fax 972-883- reaction, which yielded fast adsorption 2537; e-mail: [email protected]) kinetics for the first 6-12 hours post injection, followed by a lower rate of The Nawalparashi district of Nepal lies in adsorption up to 2 days. After 2 days, a the headwaters of the South Asian arsenic slow rate of desorption occurred as the crisis region. Strong heterogeneity in ambient low-As water was drawn towards groundwater arsenic distribution is the wells. This simple approach does not, characteristic of this area for uncertain however, account for the complexity of a reasons. This study investigates the role of single well injection-withdrawal localized hydrologic differences in experiment with incomplete mixing within generating that heterogeneity by affecting the affected volume and with a the hydrochemical environment and contaminant that has a high partitioning arsenic mobility. coefficient (Kd). A numerical model was constructed instead to account for the role Six nested piezometer stations were that As retardation and flow patterns play established to monitor water levels, major in the observed adsorption, thus effectively cations and anions, arsenic, iron and separating kinetic and equilibrium aspects phosphate on a monthly basis. Three river of the breakthrough curves. points were also monitored for hydrochemical parameters and two were Overall, the performed experiments also monitored for discharge. Based on demonstrated fast kinetics of As water level variations and monsoon adsorption onto deeper aquifer sediments response these observation wells can be and confirmed their high Kd in situ. The categorized into two groups. One group results appear favorable to continued use (Group A) has the greatest and quickest of these aquifers as a sustainable source of monsoon response, representing wells at drinking water. However, further studies depths less than 30 m. Other group (Group are necessary to assess the capacity of B, consisting of wells having around 50m these sediments to adsorb As from a depth) has a delayed and subdued response prolonged leakage of shallow to monsoon. Each multi-level site exhibits groundwater. a downward hydraulic gradient.
All wells have bicarbonate-dominated water. Group B has sodium-dominated bicarbonate whereas most of Group A has calcium-dominated bicarbonate water. The highest sodium to calcium ratio is
34 observed in Group B, strongly suggesting Ocean Sciences, University of British a cation exchange process is active in Columbia, Vancouver, BC, V6T 1Z4, intervening clays. Six out of eight wells in Canada; ph. 604-822-2764; e-mail: Group A and one out of two wells in [email protected]); R D Beckie Group B have arsenic greater than WHO (Department of Earth and Ocean Sciences, guideline value of 10 ppb in all time series University of British Columbia, data. Arsenic was below detection limits Vancouver, BC, V6T 1Z4, Canada; ph. in the river points. Total dissolved solids 604-822-6462; e-mail: (TDS) in all wells declined to an almost [email protected]) uniform value of 650 ppm by monsoon end, indicating thorough flushing. TDS Groundwater arsenic hotspots exhibit a then increases steadily in shallow zones patchy distribution throughout the Bengal during the dry season up to about 1000 Delta Plain which straddles the state of ppm which is probably due to poor West Bengal, India, and adjacent sanitation. Considerable variability is Bangladesh. Reasons for the small-scale observed in major cations/anions, arsenic spatial variability of groundwater arsenic and water levels and their relationships concentrations are still not well remain uncertain. Lack of correlation understood. However, investigations by between Arsenic and Sulphate indicates the Geological Surveys of India and that Pyrite oxidation is not the cause for Canada at a field site in the arsenic Arsenic release. Good correlation between affected village of Gotra, Nadia District, Arsenic and Phosphate shows that West Bengal, are shedding new light on Phosphate is not exchanged for Arsenate. the geological controls that determine the Arsenic exhibits good correlation with pattern of groundwater arsenic bicarbonate and total iron indicating that contamination in a meandering fluvial reductive dissolution of ferric depositional environment. Measurements oxyhydroxides is the cause for Arsenic of arsenic in over fifty domestic tube-wells release in the wells having Arsenic greater and piezometers have delineated sharply than WHO guideline values. defined high and low arsenic zones which can be related to aquifer geology.
Geological Controls on Groundwater The village of Gotra is located on a natural Arsenic: New Insights from a Field Site levee adjacent to an abandoned river at Gotra, Nadia District, West Bengal, channel. The subsurface geology is India characterized by two 60m undisturbed cores and fifteen “hand flapper” boreholes [*T Pal*] (Central Petrological of 30m from which only samples of fine- Laboratories, Geological Survey of India, grained sediment could be recovered. The Kolkata-700016, India; ph. 033-2286-1616 deposits of the Bengal Delta Plain consist ext. 2705; Email: [email protected]); P of a thick sequence of fluvio-deltaic K Mukherjee (Central Petrological sediments of Quaternary age characterized Laboratories, Geological Survey of India, by successions of sand, silt and clay with Kolkata-700016, India; ph. 033-2286-1616 subtle variations in color, grain size, and to ext. 2702; Email: some extent, mineralogy. Generally, the [email protected]); A J lithologies intersected in the boreholes Desbarats (Geological Survey of Canada, consist of approximately 25m of grey, Ottawa, ON, K1A 0E8, Canada; ph. 613- coarse-to-fine grained Holocene sediments 995-5512; e-mail: underlain by brownish grey sediments [email protected]); tentatively dated as Pleistocene. The C E M Koenig (Department of Earth and sediment mineralogy is dominated by
35 quartz, chlorite, mica (muscovite) and tapped by deeper irrigation wells. smectite. Although ubiquitous locally, the paleosol and “Orange Sand” are discontinuous and In the village area, the shallow Holocene appear to have been incised by the younger sediments represent a classic meander-belt Holocene sequence in the channel vicinity. fluvial fining-upward sequence. There, the grey Holocene sediments are Subsurface information and the curvature immediately underlain by the brownish- of the abandoned channel indicate grey sands and they are found to contain southwesterly migration of point-bar moderate levels of dissolved arsenic. deposits which underlie the low-lying An understanding of the sedimentology cultivated area northeast of the village. and stratigraphy of the study area has The point-bars consist of thick grey established a clear spatial linkage between medium-to-fine sands capped by brownish groundwater arsenic contamination in the oxidized silts likely representing crevasse shallow Holocene aquifer and fine- splay deposits. Beneath the levee, the grained, organic-rich sediments filing an point-bar sands start to thin and are abandoned fluvial channel. This overlain by channel-fill deposits which understanding has also led to the thicken as the abandoned channel is identification of the “Orange Sand” aquifer approached. Being the shallowest that may provide a readily accessible safe transmissive unit, the point-bar sands form groundwater resource on the short term. the aquifer most often tapped by villagers Finally, these investigations point to the although arsenic contamination is clearly significance of the low-permeability related to proximity of the abandoned paleosol layer in protecting the quality of channel. The channel-fill deposits consist groundwater in deeper aquifers. of very fine-grained, dark-grey, organic- rich sediments that reach a maximum thickness of 22m beneath the remnant Coupled Hydrologic and ponds marking the final course of the Biogeochemical Processes Controlling abandoned channel. The highest sediment Arsenic in Cambodian Groundwater arsenic concentrations (26 ppm) are associated with the finest-grained (> 10% [*M L Polizzotto*] (Environmental Earth clay) and organic-rich (Corg up to 1.8% System Science, Stanford University, weight) of these sediments. Laterally, the Stanford, CA 94305; ph. 202-341-7386; channel incised earlier Holocene flood fax 650-725-2199; e-mail: plain deposits consisting of thinly-bedded, [email protected]); B D Kocar dark, organic-rich silts and clays with peat (Environmental Earth System Science, and gastropod horizons. The base of the Stanford University, Stanford, CA 94305; meander-belt fluvial sequence is generally ph. 650-723-4152; fax 650-725-2199; e- at around 28m bgs and is marked by a hard mail: [email protected]); S G Benner clayey paleosol layer containing calcrete (Department of Geosciences, Boise State (kankar) and woody debris. The upper University, Boise, ID 83725; ph. 208-426- portion of the layer is grey-blue in color 3629; fax 208-426-4061; e-mail: transitioning to oxidized brown in its [email protected]); M Sampson lower half. The layer grades downward in (Resource Development International, brown silty sands, and, at 35-37 m bgs, Cambodia; ph (855)24-399-577; e-mail: into a fine-to-medium grained unit known [email protected]); K Phan (Resource as the “Orange Sand” aquifer. This unit is Development International, Cambodia; ph being promoted as an immediate target for (855)24-399-577; e-mail: safe potable groundwater. It is underlain [email protected]); K Ouch by brownish-grey silty sands which are (Resource Development International,
36 Cambodia; ph (855)24-399-577; e-mail: observation of strong hydrologic influence [email protected]); S Fendorf on arsenic behavior indicates that release (Environmental Earth System Science, and transport of arsenic are sensitive to Stanford University, Stanford CA 94305; continuing and impending anthropogenic ph. 650-723-5238; fax 650-725-2199; e- disturbances. mail: [email protected])
Tens of millions of people in South and Arsenic mobilization into shallow Southeast Asia routinely consume groundwaters of southern Asia ? where, groundwater that has unsafe arsenic levels. when and why does it occur - evidence Arsenic is naturally derived from eroded from organic, isotopic and bio- Himalayan sediments, and is believed to geochemistry enter solution following reductive release from solid phases under anaerobic [*D A Polya*] (School of Earth conditions. However, the processes Atmospheric and Environmental Sciences, governing aqueous concentrations and University of Manchester, Manchester, location of arsenic release to pore water UK M13 9PL; ph. +44 161 275 3818; fax remain unresolved. This uncertainty is +44 161 306 9361; e-mail: partly attributed to a poor understanding of [email protected]); W Al groundwater flow paths altered by Lawati (School of Earth Atmospheric and extensive irrigation pumping in the Environmental Sciences, University of Ganges-Brahmaputra delta, where most Manchester, Manchester, UK M13 9PL; research has focused. Accordingly, we ph. +44 161 275 3818; fax +44 161 306 have established a field area on the 9361; e-mail: [email protected]); C J minimally disturbed Mekong delta of Ballentine (School of Earth Atmospheric Cambodia and conducted routine and Environmental Sciences, University of groundwater and surface water sampling in Manchester, Manchester, UK M13 9PL; order to constrain natural flow paths and ph. +44 161 275 3832; fax +44 161 306 arsenic distributions. 9361; e-mail: [email protected]); A Within our field area, water is cycled from Boyce (ICSF, SUERC, East Kilbride, UK, the Mekong River to inland wetlands and G75 0QF; ph. +44 1355 270143; fax +44 ponds, then through near-surface clays to 1355 229898; e-mail: the underlying sand aquifer and back to the [email protected]); C Bryant river. Dissolved chemical concentrations (NERC Radiocarbon Laboratory, East vary spatially and temporally and are Kilbride, UK, G75 0QF UK M13 9PL; ph. dominantly influenced by flow paths and +44 1355 260037; fax +44 1355 229829; sediment interactions. In particular, arsenic e-mail: [email protected]); J on floodplain sediments is released during Charnock (School of Earth Atmospheric the transition from aerobic to anaerobic and Environmental Sciences, University of conditions; while arsenic may be released Manchester, Manchester, UK M13 9PL; from aquifer sediments, arsenic gradients ph. +44 161 275 3814; fax +44 161 306 along flow paths indicate that the greatest 9361; e-mail: quantities of arsenic are liberated at the [email protected]); V near-surface. Owing to similarities in Coker (School of Earth Atmospheric and geologic deposition, aquifer source rock Environmental Sciences, University of and regional hydrologic gradients, our Manchester, Manchester, UK M13 9PL; results represent a model for understanding ph. +44 161 275 3803; fax +44 161 306 pre-disturbance conditions for other major 9361; e-mail: deltas in Asia. Furthermore, the [email protected]);D A
37 Cooke (University of Northumbria, ph. +44 161 275 3935; fax +44 161 306 Newcastle, UK; ph. +44 191 232 6002; fax 9361; e-mail: +44 191 227 3903; e-mail: [email protected]);B Van [email protected]); A G Gault Dongen (School of Earth Atmospheric and (Department of Earth Sciences, University Environmental Sciences, University of of Ottawa ,140 Louis Pasteur, Ottawa, ON, Manchester, Manchester, UK M13 9PL; K1N 6N5, Canada,; ph. + 613-562-5773 ; ph. +44 161 306 7460; fax +44 161 306 fax + 613-562-5192; e-mail: 9361; e-mail: [email protected]); M Hery (School of [email protected]); Earth Atmospheric and Environmental Key questions still to be comprehensively Sciences, University of Manchester, addressed regarding the origins of arsenic- Manchester, UK M13 9PL; ph. +44 161 bearing groundwaters in southern Asia 275 7155; fax + 44 161 306 9361; e-mail: include: (i) in a local context, where does [email protected]); M arsenic mobilization take place - does it Lawson (School of Earth Atmospheric and occur predominantly within the bulk of Environmental Sciences, University of such reducing aquifers or is mobilization Manchester, Manchester, UK M13 9PL; in narrow zones of high redox gradients ph. +44 161 275 3832; fax +44 161 306 more significant ?; (ii) when does arsenic 9361; e-mail: mobilization take place in relation to [email protected]. sedimentation history ?; (iii) why does uk); J R Lloyd (School of Earth mobilization occur ? , and in particular Atmospheric and Environmental Sciences, what is the role of various types of organic University of Manchester, Manchester, matter, including exogeneous organic UK M13 9PL; ph. +44 161 275 7155; fax matter, to controlling the rates of Fe(III) +44 161 306 9361; e-mail: and As(V) reduction considered by some [email protected]); P Lythgoe to be critical steps in transfer arsenic from (School of Earth Atmospheric and the sediment to the aqueous phase ? . the Environmental Sciences, University of timing of arsenic mobilization in relation Manchester, Manchester, UK M13 9PL; to sedimentation history; (ii) the location ph. +44 161 275 3834; fax +44 161 306 of arsenic mobilization with respect to the 9361; e-mail: distribution of saturated sediments and [email protected]); D redox zones ? (iii) the source of organic Mondal (School of Earth Atmospheric and matter (OM) utilized during the reduction Environmental Sciences, University of of Fe(III) and/or As(V) during these Manchester, Manchester, UK M13 9PL; processes; and (iv) the provenance of ph. +44 161 275 3818; fax +44 161 306 arsenic-bearing groundwaters. 9361; e-mail: [email protected] We summarise here organic, isotopic and c.uk); R Pancost (School of Chemistry, bio- geochemical evidence, obtained over University of Bristol, Bristol, UK BS8 the period 2002-2008 by the group at 1TS; ph. +44 117 9289178; fax +44 117 Manchester and our collaborators, that 9251295; e-mail: speaks to these issues. In particular, we [email protected]); H A L provide organic geochemical evidence for Rowland (eawag, Uberlandstraase 133, the widespread occurrence of natural Duebendorf, CH-8600, Switzerland; ph. petroleum in arsenic-bearing shallow +41 44 8235269; fax +41 44 8235028; e- groundwater systems in southern Asia, mail: [email protected]); D J Vaughan both in Ganges Delta and in the Mekong Dongen (School of Earth Atmospheric and Delta. The significance and implications of Environmental Sciences, University of this association ? and in particular whether Manchester, Manchester, UK M13 9PL; or not it is likely to be causal rather than a
38 function of the nature of the tectonic The iron oxides in the Red River sand and environments in which such aquifers are mud, as determined by Mössbauer found - are discussed. We further report spectroscopy, consist mainly of goethite stable isotope, organic geochemical and with subordinate amounts of hematite radiocarbon data that addresses the issue while less stable iron oxides like of the relative importance of labile surface ferrihydrite are absent. The goethite OM to accelerating arsenic mobilization present in the mud has a distorted and Lastly we present a discussion of the poorly crystalline structure. The reactivity relative importance of bulk aquifer and of the iron oxides, as determined by time narrow high redox gradient zones to dependant ascorbic acid leaching, shows overall observed groundwater arsenic for the sand a reactivity corresponding to budgets in these aquifers. goethite while the mud contains a pool of Fe(III) with a reactivity comparable to that of ferrihydrite. Reductive dissolution of Mobilization of Arsenic and Iron from iron oxides by ascorbic acid readily Red River Floodplain Sediments, releases both As(V) and As(III) from river Vietnam sand and mud and particularly from the mud the release of arsenic is high. [*D Postma*], F. Larsen (Department of Sediment incubations, unamended and Geochemistry, GEUS, Copenhagen, with added acetate, both release Fe and As. Denmark; e-mail: Again the release of arsenic is strongest [email protected]), Nguyen Thi from the mud, while the addition of acetate Minh Hue, Mai Thanh Duc, Pham Hung has no effect and the process is therefore Viet, (CETASD, Hanoi University of not carbon limited. The river mud Science, VNU), Pham Quy Nhan , (Hanoi apparently both contains reactive Fe-oxide, University of Mining and Geology), Søren high in As, as well as reactive organic Jessen, (Institute of Environment and carbon and can therefore be a powerful Resources, Technical University of source of arsenic when deposited on the Denmark), Christian Bender Koch, (LIFE, floodplain Copenhagen University) The aquifer sediments from the oxidized Sands and muds, transported by the Red and reduced zone also contain goethite and River, have been deposited on the hematite, but here relatively more hematite floodplain. In these sediments, aquifers is present. The oxidized sediment releases and aquitards developed which gradually Fe, but little As, by reductive dissolution became anoxic and released arsenic to the with ascorbic acid while almost nothing is groundwater. If this scenario is correct, released by HCl. For the reduced aquifer then we must expect to find differences in sediment the reversed pattern is observed. the chemical composition and the HCl readily releases Fe and As and mineralogy of river and aquifer sediments nothing more comes out with ascorbic as well as in their ability to release arsenic. acid. Apparently a Fe(II) phase like We have used a broad suite of methods to siderite is present in the reduced sediment investigate this matter, starting with which dissolves in HCl. The experiments mineralogy and traditional sequential did run for 3 days and during this time the extraction schemes, followed by time reduced aquifer sediment did not to release dependant extractions with ascorbic acid much As by reductive dissolution of iron and HCl at pH 3, the determination of the oxides. However sediment incubations that reactivity of the Fe(III) pool and finally did run for 45 days did release some As incubation of unamended and amended and Fe while the addition of acetate to the sediments. incubations did strongly stimulate As and
39 Fe release. These results indicate a hydraulic gradient and groundwater continued potential of the aquifer chemistry have been investigated in Pach sediments to release arsenic which is Gao Char Para village, 24 km northeast of limited by the reactivity of the sedimentary Dhaka since December 2006. Monitoring organic matter. wells were installed in the sandy, raised village and in adjacent agricultural fields covered with silty clay bordered by a small Groundwater As Gradients in a Shallow stream. Dissolved As concentrations Aquifer of Bangladesh: The Role of increase from less than <5 to 500 ug/L Local Adsorptive Equilibrium over the 300 m distance separating the village and the stream. There is a strong [* K A Radloff*] (Department of Earth redox gradient across this distance and Environmental Engineering, Columbia indicated by with low dissolved Fe and University, New York, NY 10027, USA; high SO4 in the village and high Fe and ph. +1-845-365-8793; email: low SO4 towards the stream, respectively. [email protected]); Y Zheng Solid phase P-extractable arsenic (Queens College, City University of New concentrations vary less than ten-fold over York, Flushing, NY 11367; the same distance, from 0.4 to ~ 4 mg/kg, [email protected]); M Stute without showing any systematic spatial (Barnard College, Columbia University, trend. Head measurements over the entire New York, NY 10027; area show that annually-averaged [email protected]); J Matter groundwater flow leads from the village (Lamont-Doherty Earth Observatory of towards the stream. However, the Columbia University, Palisades, NY hydraulic gradient reverses, and flows 10964; [email protected]); Z from the stream towards the village, Aziz (Lamont-Doherty Earth Observatory between the peak of the dry season and the of Columbia University, Palisades, NY onset of the monsoon. 10964; [email protected]); M M Rahman (Queens College, City University The large gradient in groundwater As that of New York, Flushing, NY 11367; is unaccompanied by a systematic gradient [email protected]); M R in P-extractable As in the sediment Huq (Department of Geology, University suggests that either the sediment plays a of Dhaka, Dhaka 1000, Bangladesh; minor role in regulating groundwater As [email protected]); T Chowdury through adsorptive equilibrium or that the (Department of Geology, University of sediment-groundwater partitioning Dhaka, Dhaka 1000, Bangladesh; coefficient (Kd) decreases along the flow [email protected]); K M path. New results from batch adsorption Ahmed (Department of Geology, and push-pull experiments show that the University of Dhaka, Dhaka 1000, later is the case. Batch experiments Banglades; [email protected]); A van indicate that the Kd declines from about 30 Geen (Lamont-Doherty Earth Observatory to 1 L/kg from the village towards the of Columbia University, Palisades, NY stream, a range that is broadly consistent 10964; [email protected]) with the range determined from the field data. Push-pull experiments conducted in The hydrological and geochemical factors the fields to simulate the intrusion of that regulate the partitioning of sediment groundwater indicate a rapid adsorption or and groundwater As in an incompletely desorption, depending on the direction of flushed aquifer system is the focus of this the perturbation, with some form of re- study. Using a three dimensional array of equilibration achieved within 2 days. The monitoring wells, temporal changes in observed decrease in Kd may be linked to
40 the increasing reducing state of the basin has severely been affected with the amorphous Fe coatings (from 0.5 to 0.9 elevated Arsenic (As) contamination Fe(II)/total Fe extractable by HCl) along caused by the naturally occurring regional the transect, the input of sulfate with hydro-chemical phenomena. This As is recharge within the village, or a supposed to get leached from the interface combination of both. of the saturated-unsaturated zone sediment These observations suggest that with the potential interaction of the natural groundwater As concentrations are leaching agent such as HCO3 which may determined by the “upstream” essentially be evolved under the microbial groundwater concentrations and the local degradation of the highly carbon contained adsorption partitioning (Kd) of the sediments. The rate at which such leaching sediment. Whereas this partitioning reaction can be occurred was attempted to regulation does not specify how As is figure out in this study. To estimate the initially mobilized, it provides a reaction rate Kr , brown clay samples framework for understanding how containing 28.4 µg/g As, extracted at the interaction with the sediment affects depth of 10 m from the targeted aquifer of groundwater As concentrations during the South-Western Bangladesh were transport in sedimentary aquifers. Our subjected to undergo closely controlled goal is to represent the likely evolution of monitored leaching test for the time period As in groundwater of the study area into of 7, 13, 23 and 29 days until the the future by combining these observations equilibrium conditions for the respective with a simple groundwater flow model. experimental run varying in mixing speed had been reached. Distilled water enriched with Na2CO3 (0.01M) was the leaching Leaching Kinetic Rate of Arsenic solution and the sediment-liquid ratio of Bearing Minerals in the Ganges Delta 1:10 was maintaining in a suspension by Basin Subsurface Sediments: An employing a mechanical mixer. Based on Estimation Approach the relationship between computed reaction rate and the linear form of the [*M T Rahman*] (Disaster Control mechanical mixer speed, a linear Research Centre, School of Civil regression equation (R2 = 0.94) was Engineering, Tohoku University, Aoba 6- obtained that could predict the field based 6-11-1110, Sendai 980-8579, Japan; ph.& reaction rate, Kr = 7.03 10-13 /sec when fax 81-022-795-7525; e-mail: field obtained infiltration velocity through [email protected]); A the clay, 5.34 10-5 cm/sec was used. Mano (Disaster Control Research Centre, Rainfall infiltration getting interacted with School of Civil Engineering, Tohoku the brown clay may also be assumed to do University, Aoba 6-6-11-1110, Sendai potential leaching in its course of transport 980-8579, Japan; ph.& fax 81-022-795- through the aquifer sediments. The 7525); K Udo (Disaster Control Research laboratory estimated Kr value is nearly Centre, School of Civil Engineering, consistent with that of the in-situ one 5.25 Tohoku University, Aoba 6-6-11-1110, 10-15 /sec which was again computed Sendai 980-8579, Japan; ph.& fax 81-022- based on the moles of minerals obtained 795-7525); Y Ishibashi (Department of from inverse mass-balance modeling, Civil and Environmental Engineering, contact reaction time taken from the C14 Tohoku Gakuin University, 1-13-1 Chuo, data, the BET measured specific surface Tagajo, Miyagi Pref. 985-8537, Japan) area, porosity, particle density and the abundances of the minerals estimated In the recent decades subsurface from XRD data. This findings might help groundwater aquifers in the Ganges delta to explain the time span that is required for
41 the accomplishment of the As desorption part, mountainous areas supply the from the source mineral essentially at the groundwater to the Tonle Sap River in all contaminated sediment which can further seasons, while in Mekong delta, be incorporated into the vertical As groundwater elevations raised higher than transport code for assessing the river water in Bassac and Mekong River in vulnerability of the successive aquifers. dry season and vice versa in rainy season. This study promotes the knowledge of groundwater recharge areas and the Regional Groundwater Model: condition of groundwater environment in Contribution to Numerical Modeling of the polluted region. Arsenic transport Arsenic Transport in Mekong Delta model under redox condition considering Aquifer, Cambodia biogeochemical processes will be conducted in next phase of our research. [*Ramsey May *] (Urban and Environmental Engineering Department, Faculty of Engineering, Kyushu Arsenic Remobilization from Paddy University, 744, Motooka, Nishi-ku, Soils During Monsoon Flooding in Fukuoka, 819-0395, Japan; hp: +81-90- Munshiganj/Bangladesh 6633-4394; e-mail: [email protected]); Kenji [*L C Roberts*] (Swiss Federal Institute Jinno (Urban and Environmental of Aquatic Science and Technology Engineering, Faculty of Engineering, (Eawag), CH-8600 Dübendorf; ph. +41- Kyushu University, 744, Motooka, Nishi- 44-8235418; fax +41-44-8235210; e-mail: ku, Fukuoka, 819-0395, Japan; ph and [email protected]); S J Hug (Swiss fax:+81-92-802-3429; email: Federal Institute of Aquatic Science and [email protected]); Atsushi Technology (Eawag), CH-8600 TSUTSUMI (SG Gijutsu Consultant Co., Dübendorf; ph. +41-44-8235454; fax +41- Ltd., 4-18-25, Kounonishi, Saga City, 44-8235210 e-mail: [email protected]); J Japan) Dittmar (Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, CHN, Arsenic contamination of the Mekong CH-8092 Zürich; ph. +41-44-6336064; fax delta located at the southern part of +41-44-6331118; e-mail: Cambodia is recently identified as a [email protected]); A Voegelin serious groundwater crisis. More than one (Institute of Biogeochemistry and million people are living under the threat Pollutant Dynamics, ETH Zurich, CHN, of arsenic polluted groundwater, which CH-8092 Zürich; ph. +41-44-6336147; fax ranges the arsenic concentration between +41-44-6331118; e-mail: 100-1000 ppb. A systematic numerical [email protected]); R study is inevitable to understand the flow Kretzschmar (Institute of Biogeochemistry and transport of arsenic in this region. In and Pollutant Dynamics, ETH Zurich, this study, we highlight the comprehensive CHN, CH-8092 Zürich; ph. +41-44- groundwater flow simulation in regional 6336033; fax +41-44-6331118; e-mail: scale. A two dimensional groundwater [email protected]); B flow model and a groundwater recharge Wehrli (Swiss Federal Institute of Aquatic model are coupled to simulate the Science and Technology (Eawag), CH- groundwater flow of the selected area of 6047 Kastanienbaum; ph. +41-41- 26,600 km2. The fluctuations of river 3492117; fax +41-41-3492168; e-mail: water elevations are coupled to the model [email protected]); O A Cirpka to make it more realistic. The result (Center for Applied Geoscience, demonstrates that; in the north-western University of Tübingen, D-72076
42 Tübingen; ph. +49-7071-2978928; fax Based on vertical As concentration +49-7071-5059; e-mail: olaf.cirpka@uni- gradients measured in topsoil porewater tuebingen.de); G. C. Saha (Department of and the accumulation of As in floodwater Civil Engineering, Dhaka University of over time, we estimate that between 55 Engineering and Technology, Gazipur- and 250 mg m-2 of As, corresponding to 1700, Bangladesh; e-mail: 14-63% of the As annually added via [email protected]); M A Ali irrigation, were mobilized into floodwater (Department of Civil Engineering, over the course of one monsoon season. Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh; ph. +8802-9665650-80 Ext. 7625; fax 880-2- Incomplete Arsenic-Removal by Iron- 9663695; e-mail: [email protected]); A Amended BioSand Filters in Kandal B M Badruzzaman (Department of Civil Province, Cambodia Engineering, Bangladesh University of Engineering and Technology, Dhaka-1000, [*M L Sampson*] (Resource Bangladesh; ph. +8802-9665650 Ext- Development International, Royal Brick 7569; fax 880-2-9663695; e-mail: Road, Kien Svay, Kandal Cambodia; ph. [email protected]) 855-23-399-577; fax 855-24-399-577; [email protected]); H. Chiew (Resource Bangladesh relies strongly on groundwater Development International, Royal Brick resources, often containing high Road, Kien Svay, Kandal Cambodia; ph. concentrations of arsenic (As), for the 855-23-399-577; fax 855-24-399-577; irrigation of dry season rice (boro). Since [email protected]); S. Huch accumulation of As in paddy soils may (Resource Development International, adversely affect rice yield and quality, Royal Brick Road, Kien Svay, Kandal understanding the processes determining Cambodia; [email protected]); S. retention and release of As from paddy Ken (Resource Development International, soils is crucial. Monsoon flooding strongly Royal Brick Road, Kien Svay, Kandal attenuates As accumulation in the topsoil Cambodia; [email protected]); B of rice fields, but the underlying C Bostick (Department of Earth Sciences, mechanisms and their relative quantitative Dartmouth College, Hanover, NH 03755, importance remain unclear. Here we United States; ph. 603-646-3624; fax 603- present data from paddy fields near 646-3922; e-mail: Sreenagar (Munshiganj, Bangladesh) [email protected]) which show that As was reductively mobilized and released into the overlying Naturally occurring arsenic in groundwater floodwater throughout the duration of in Cambodia is common in the Mekong monsoon flooding. As concentrations in delta region. There are two principal topsoil porewater increased over time, strategies in dealing with this ubiquitous reaching values of up to 1160 μg L-1 at 3- contamination, including the identification 7 cm depth after 16 weeks of flooding. The and utilization of nearby uncontaminated floodwater column was either vertically water sources, or water treatment that can well-mixed exhibiting As concentrations remove both pathogens and arsenic. Here, between 5 and 20 μg L-1 over a height of we examine the long-term efficacy of an 1-2.7 m, or characterized by distinct iron-oxide modified BioSand filter as a gradients of decreasing As concentrations household water treatment option to with increasing distance from the soil. On remove arsenic and microbial pathogens days of limited vertical mixing, As from groundwater. The performance of concentrations ranged between 40-120 μg modified BioSand filters filled with three L-1 in floodwater 2.5 cm above the soil. natural arsenic-bearing groundwater
43 sources from Kandal province of varying Department of Geology, Tribhuvan compositions and spiked with lab-cultured University, Nepal; ph. 977-01-5545869; e- E. Coli and MS2. These filters were used mail: [email protected]) consistently under controlled conditions that mimic regular use. The effectiveness This paper discusses the occurrence, of arsenic and pathogen removal was not distribution of arsenic contamination in constant over time and was highly relation to geological, hydrological and dependent on the influent composition. geochemical aspects of the Rautahat After an initial period of stabilization, each district. Arsenic was analyzed in surface filter was relatively ineffective in treating water, groundwater and river sediments. arsenic contaminated groundwater and Arsenic testing in water samples at field effluent arsenic concentrations were was done by field kit and digital arsenator. between 70 and 250 ug L-1 , higher than Some groundwater samples exceeded accepted drinking water standards. The Nepal interim value and incase of surface overall average arsenic removal stabilized water arsenic content is extremely low. at 40-70% respectively (depending on River sediments contain appreciably high water source), with the extent of arsenic amount of arsenic. In majority of wells removal was not related to the influent arsenic contamination is found little high arsenic concentration. The poor arsenic in pre monsoon period than in post removal was due to the combination of monsoon period. Mineralogical high influent P (> 0.5 mg L-1 ) and low Fe examination of sediment samples showed (< 5 mg L-1 ) concentrations. E. Coli was the absence of arsenic bearing sulphide removed under most conditions; however, minerals. The arsenic contaminated tube the efficacy of microbial pathogen removal wells are more concentration in fine was strongly impacted by changing grained aquifer and near to river bank. influent water to rainwater, a common Water There is no apparent relationship local practice during, and subsequent to, between fluctuation of groundwater level the monsoon. The coliphage MS2 was not and arsenic occurrences. The arsenic removed by filtration. These findings concentrations in the groundwater are suggest that such amended filters should characterized by low concentration of not be widely deployed in areas of sulphate and slightly positive correlation widespread arsenic contamination until with iron, which can give some support to improvements are made to address the iron reduction as the process of arsenic consistency and efficacy of treatment. In mobilization. The available litho logs addition, the filter poses some potential show that thick clay layer on the top, so health risk associated with the production the possibility of direct groundwater of elevated nitrate levels in the effluent contamination by use of pesticides, within the filter, possibly due to fertilizers etc. are also limited. nitrification and high levels of ammonia in the groundwater. Chemical Characteristics of Dissolved Humic Substances From Arsenic-Rich Sources, Seasonal Variation and Shallow Groundwater in Bangladesh Mobilization of Arsenic in Groundwater of Rautahat District, Central Nepal [*Bailey Simone *](Deparment of Civil and Environmental Engineering, [*R. Shrestha *] (Central Department of University of Colorado, Boulder, CO Geology, Tribhuvan University, Nepal; 80309; ph. 413-454-2939; fax 303-492- ph.977-01-4355556, e-mail: 6388; e-mail: [email protected]); [email protected]); R. Sah (Central Teresa Legg (Department of Ecology and
44 Evolutionary Biology, University of samples, which were modeled using Colorado, Boulder, CO 80309; ph. 303- parallel factor analysis (PARAFAC) and 492-4687; fax 303-492-6388; e-mail: compared to both terrestrial and microbial [email protected]): Diane McKnight end-members, indicate that they are (Department of Civil and Environmental predominantly of terrestrial origin with a Engineering, University of Colorado, substantial content of quinone-like Boulder, CO 80305; ph. 303-492-4687; moieties. Characterization by 13C-NMR fax 303-492-6388; e-mail: provides a further indication of the [email protected]); Diana aromaticity of these samples and their Nemergut (Department of Ecology and ability to form complexes with iron and act Evolutionary Biology, University of as electron shuttles. Colorado, Boulder, CO 80309; ph. 303- 735-1239; fax 303-492-6388); Yan Zheng (Queens College, City University of New An Ecological Approach to York, Flushing, NY 11367; ph 718-997- Understanding Arsenic in Nepal 3329; fax 718-997-3299; e-mail: [email protected]) [*Linda S.S. Smith*], Anjana Singh, and Suresh D. Shrestha The dissolved organic material present in *Director, Filters for Families, PO Box groundwater has been shown to play a 2427; Kathmandu, Nepal; Phone, 977-1- significant role in mobilizing arsenic 543170; email: [email protected] through several pathways in Bangladesh To better understand the ecological cycling aquifers and other regions with As-rich of arsenic in Nepal, this research analyzed sediments. Firstly, labile organic substrates arsenic concentrations from Himalayan may stimulate the growth of heterotrophic rocks, identified arsenic tolerant microbes bacteria, resulting in anoxic conditions, in groundwater and rivers, measured which drives the use of alternate electron arsenic uptake and bioaccumulation of acceptors beyond oxygen, such as nitrate arsenic in jungle and wetland plants, and and ferric iron present in oxides in monitored monthly arsenic variations in sediment. Another potentially important tubewells. pathway is the electron shuttling by dissolved humic substances where the Arsenic analyses from the Nepal quinone moieties in the humic substances Himalayas and Terai show that arsenic is are reduced by microbial processes. These ubiquitous throughout the mountains, reduced humic molecules transfer rivers, and springs. The highest electrons to ferric iron in iron oxides along concentrations are found near two mining the flow path. This redox cascade areas, the Central Mineral Belt located promotes the release of arsenic and from Baglung to Palung and in the far potentially other toxic metals. Although all eastern district of Illam. Soil and mineral humic substances studied have shown samples in these areas are over 4000 ppm some electron shuttling capability, there is arsenic. Analyses of 104 cropping samples a large variation among fulvic and humic reveal that arsenic concentrations vary acids of different origins. We have isolated from 2 ppm to 85 ppm in the Lesser preparative quantities of fulvic acid and Himalayan rock formations . The highest transphilic acid from two well depths at a values are found in a Carboniferous site in Bangladesh with high arsenic marine shale, the Benighat Formation. concentrations in the groundwater. At this Soil and core samples were collected from site fulvic acid accounted for about 50 % two districts in the southern part of Nepal, of the total dissolved organic material. The Nawalparasi and Rautahat districts, fluorescence characteristics of these sediments are clay, silt, and fine to coarse
45 sand. The arsenic concentrations did not low vegetation pits, arsenic values were exceed 48 ppm in soils or core sediments, lower in the top of the pit and increased the average arsenic concentrations are toward the bottom. about 8 ppm. Several rivers in the central and north-central sessions of Nepal were Microbial cultures from tubewell waters analyzed for arsenic. River arsenic and rivers in both districts show a strong concentrations from Upper Mustang to relationship between arsenic wells and Jhapa varied from 0 to 40 ppb. Hot springs arsenic tolerant microbes. Four microbial in the Annapurna region are 76 ppb and species colony growth continued to 1000 cool springs are 40 ppb. ppm (MIC). Microbial redox reactions may be the key to arsenic mobilization in Groundwater arsenic concentrations in Nepal. Nawalparasi District reveal high monthly arsenic variations, particularly in the high arsenic wells. Monthly and seasonal Arsenic in Drinking Water Results in arsenic values may exceed 100 to 400 ppb the Highest Known Toxic Substance in the tubewells in Nawalparasi in Disease Risks tubewells located near the Churia Hills and in the more clay and silt rich sediments. [*Allan H Smith*] (School of Public Aquifer heterogeneity is high, most likely Health, University of California, Berkeley, due to the original depositional CA 94720-7360; ph. 510-843-1736; e- environment of braided streams on alluvial mail: [email protected]); Ayse fans. High clay overbank deposits are Ercumen (School of Public Health, barriers to strong lateral connectivity. A University of California, Berkeley, CA well in the Toribara Jungle and one in 94720-7360; ph. 510-843-1736; e-mail: Madhav village, Rautahat both at 50 ft. [email protected]); depth, show that the wells act as isolated units in the dry season, but in the monsoon Arsenic in drinking water is now linked to water depths in the wells indicate the wells many different adverse human health (aquifer) are connected. effects. Attention is often focused on skin effects which are unimportant and rarely Indigenous plants and surrounding soils occur without prolonged exposure to water from the Toribari Jungle and Chandhi concentrations of arsenic above 200 ug/L. River Wetland in Rautahat district are The greatest initial mortality impact comes analyzed to determine whole plant arsenic from acute myocardial infarction, followed uptake. Soils surrounding the jungle by even larger numbers of deaths from plants ranged from 3.54 ppm to 8.02 ppm cancer, in particular lung and bladder and wetland sediments contained 10.37 cancer. Early life exposure to arsenic ppm. Plant arsenic concentrations range results in marked increases in mortality in from 0.0078 ppm to 50.62 ppm. Results young adults from cancers of the lung, show that all jungle plants uptake arsenic bladder and kidney, and also increased and four wetland plants are arsenic mortality from non-malignant disease of bioaccumulators. To determine if plant both the lung and kidney. Based on very uptake of soil arsenic altered soil arsenic clear data from Chile, exposure to water concentrations sixty soil pits were containing arsenic in the range of 500 and installed in the jungle and non-jungle 1000 ug/L for about 10-15 years will areas. In the jungle pits, arsenic eventually result in mortality of 5-10% of concentrations were higher in the organic the population. These risk estimates are upper layer and decreased at the 30 inch firmly based and supported by data from depth. The reverse was observed in the other countries, and are the highest
46 mortality risks ever reported for any concentrations exceeding WHO drinking environmental exposure. There is reason to water guideline of 10 μg/L. Arsenic (III) believe the dose-response could be linear was found to be a dominant species in all such that long term consumption of water groundwater samples, constituting mostly containing 50-100 ug/L of arsenic might at least 60% of the total arsenic, with its result in mortality on the order of 1 in 100 concentrations varying from ND μg/L (the people. Using surface water has been DS village) to 1,334 μg/L (the PT village). proposed as one option to prevent In addition, about 50%, 63%, 43% and exposure to arsenic-containing 100% of groundwater samples had higher groundwater and is under debate because concentrations of barium, manganese, lead of the risk of microbial contamination. In and selenium than WHO drinking water contrast to mortality from arsenic, guideline, respectively. Finally, it is mortality risk estimates for consumption of clearly found the linear relationship surface water involve a large number of between arsenic level in human hair and in highly speculative assumptions with no groundwater. firm data to support them. Persons consuming drinking water contaminated In Lao PDR, twenty one groundwater with arsenic should be urged to stop such samples were collected in Champasak (11 exposure, with careful use of treated samples) and Attapu (10 samples) surface water being one option. provinces for determination the concentrations of both arsenic and trace elements. Arsenic concentration ranged Contamination of Arsenic and Other from ND to 278 μg/L, with its average and Trace Elements in Groundwater: A median values of 36 and 8 μg/L, Case Study in Cambodia and Lao PDR respectively. About 48% of these samples exceeded 10 μg As/L set by WHO. [*Suthipong Sthiannopkao*] Arsenic (III) was clearly found as a (International Environmental Research dominant species in the Champasak Center, Gwangju Institute of Science and province. Concerning the trace elements, Technology, 261 Cheomdan-gwagiro, about 24% and 10% of groundwater Buk-gu, Gwangju 500-712, Republic of samples had higher concentrations of Korea; fax +82-970-3394; e-mail: manganese and barium, respectively, [email protected]); Kyoung-woong Kim exceeding the WHO drinking water (Department of Environmental Science guideline. Finally, 22% of hair samples and Engineering, Gwangju Institute of had the total arsenic at the concentrations Science and Technology, 261 Cheomdan- 1.00 μg/g indicating of toxicity. gwagiro, Buk-gu, Gwangju 500-712, Republic of Korea; e-mail: [email protected]) Environmental Tracer Applications in Floodplain Aquifers with Elevated In Cambodia, concentrations of arsenic Arsenic Concentrations and other trace elements in groundwater were examined at six villages (PT, POT, [*M Stute*] (Barnard College and CHL, TT, DS and PPK) in the Kandal Lamont-Doherty Earth Observatory, Province. Arsenic in the groundwater Palisades, NY 10964; ph 845 365 8704; ranged from not detectable (ND) (the DS fax 845 365 8155; e-mail: village) to 1,543 μg/L (the PT village) [email protected] with average and median concentrations of 408 and 333 μg/L, respectively. About An understanding of the groundwater flow 83% of these samples contained arsenic and transport regime, e.g. determination of
47 flowlines, recharge and discharge areas Migration of Sb and As released from and rates is required to (a) constrain Ichinokawa Sb mine (ore mineral:stibnite) sources and processes that contribute to As in Ehime, Japan in a river-sediment system mobilization, as well as to (b) evaluate the wasinvestigated. The system consists of sustainability of currently low [As] two rivers; one is IchinokawaRiver aquifers. Floodplain aquifers are flowing close to the Sb mine, which is characterized by low relief, very high incurrent into a largerriver, Kamo Riever. geological and geochemical heterogeneity, The increase of Sb and As concentrations and in some cases (e.g. in Bangladesh) by fromup to down stream in Ichinokawa heavy pumping and irrigation, which River were similarly observed, complicates the application of classical suggestingthat the sources of the two hydrogeological methods. Environmental elements into the river are similar tracers (e.g. 3H/3He, SF6, noble gases, withoutsignificant fractionation of the two 18O, 2H, 14C, 13C,) serving as dyes or elements from the mine area. After the radioactive clocks can fill this gap and confluence of the two rivers, the provide constraints on sources, fluxes, concentration of Sb decreasedto flowlines and can ultimately serve as downstream, the trend of which was calibration targets of groundwater flow identical to that of As. EXAFS analyses and transport models. Case studies and sequential extraction of the sediments conducted by several research groups showed that Asand Sb were present as the illustrate the strengths and weaknesses of species sorbed on Fe hydroxides in this approach. The effects of flooding, gas thesediments, suggesting that the decrease stripping, subsurface production, mixing, of the two elements from theriver water is and geochemical processes on the caused by the scavenging on Fe applicability of these tracers in hydroxides. All theresults showed that geologically young floodplain aquifers the! two elements behave similarly at least will be discussed. under oxiccondition. Similar studies on the comparison of Sb and As behaviorin river-sediment-groundwater system in Similarity of Behavior of Arsenic and Ganges Delta Plain is in progressin our Antimony in River-SedimentSystems laboratory.
[*Y Takahashi*] (Department of Earth and Planetary Systems Science,Hiroshima Hydrological and sedimentary controls University, Higashi-Hiroshima, Hiroshima leading to arsenic contamination of 739-8526, JAPAN; ph.+81-82-424-7460; groundwater in the Hanoi area, fax +81-82-424-0735; e-mail: Vietnam: The impact of iron-arsenic [email protected]);Y. ARAKI ratios, peat, river bank deposits, and (Department of Earth and Planetary excessive groundwater abstraction Systems Science, HiroshimaUniversity, Higashi-Hiroshima, Hiroshima 739, 2PHAM THI KIM TRANG, 1MICHAEL JAPAN; ph. +81-82-424-7460;fax +81-82- BERG,*, 1CAROLINE STENGEL, 424-0735; e-mail: m072169@hiroshima- 1JOHANNA BUSCHMANN, 2PHAM u.ac.jp); T ITAI(Department of Earth and HUNG VIET, 1WALTER GIGER, and Planetary Systems Science, Hiroshima 3DORIS STÜBEN University,Higashi-Hiroshima, Hiroshima 1Eawag, Ueberlandstrasse 133, 8600 739-8526, JAPAN; ph. +81-82-424-7469; Dübendorf, Switzerland fax+81-82-424-0735; e-mail: itai- 2CETASD, Hanoi University of Science, [email protected]) 334 Nguyen Trai, Hanoi, Vietnam
48 3IMG, University of Karlsruhe, Low groundwater arsenic levels (<10 Adenauerring 20, D-76131 Karlsruhe, µg/L) generally exhibit manganese Germany reducing conditions with manganese levels * Corresponding author: reaching up to 8.7 mg/L. Elevated arsenic [email protected] levels are caused by reductive dissolution of sediment-bound arsenic under iron- and Groundwater contamination by arsenic in sulphate reducing conditions. They the Red River Delta (Vietnam) poses a averaged 121 µg/L at the river bank and 60 serious health threat to millions of people µg/L in the peat area. The lower levels of consuming this water without treatment. In arsenic contamination in the peat area are the larger Hanoi area, elevated arsenic likely controlled by the high abundance of levels are present in both, the Holocene iron present in both, the aqueous and and Pleistocene aquifers. Family-based sediment phases. With median molar tubewells predominantly tap the Holocene Fe/As ratios of 350 in water and 8'700 in aquifer for daily water needs, while the the sediments of the peat area, it is likely public drinking water supply of Hanoi city that reduced iron forms new mineral extracts >600,000 m3 of groundwater per phases that resorb previously mobilized day from the Pleistocene aquifer. Detailed arsenic to the sediment. Despite similar groundwater and sediment investigation redox conditions, resorption of arsenic is were conducted in three villages located in much less significant at the river bank different settings, i.e., high arsenic at the (Fe/As(aq) = 68, (s) = 4'700), and hence, river bank, low arsenic at the river bank, arsenic levels can reach considerably and medium arsenic in an area of buried higher concentrations. peat and excessive groundwater abstraction. In-depth chemical analysis of Drawdown of Holocene water to the water from Holocene and Pleistocene Pleistocene aquifer caused by the pumping tubewells, surface water, sediment cores for the public drinking water supply of (>30 m), sites of nested wells, as well as Hanoi did not show an observable increase sequential leaching of sediment samples of arsenic during the 14 month study. were conducted. Seasonal fluctuations in However, DOC, ammonium, and iron are water chemistry were studied over a time leaching down from the Holocene aquifer, span of 14 months. thereby enhancing the reducing conditions in the Pleistocene. Seasonal fluctuations Sediment-bound arsenic (1.3–22 µg/g) is (11–66%) of redox sensitive species in 70 in a natural range of alluvial sediments, it m deep Pleistocene wells were concurrent correlates with iron (r2 >0.8), and its with water table fluctuations. This variation is largely related to grain size (or indicates shifted mixing ratios of deep surface area). Fractions of 23–84% (av. groundwater with iron-reduced 56%) arsenic were extracted with 1 M groundwater that is seeping down from the phosphate from all sediments, indicating Holocene aquifer. that arsenic can readily be mobilized at each of the three locations. Vertical migration of DOC-enriched groundwater The Impact of Groundwater Chemistry from the young clayey sediments to the on the Performance of the Kanchan aquifer at the river bank, or from the Arsenic Filter in Cambodia Holocene to the Pleistocene aquifer in the peat area, were found to promote iron- [*D Uy*] (Institute of Technology reducing conditions leading to arsenic Cambodia, Blvd. Pochentong, BP. 86- contamination in the aquifers. Phnom Penh, Cambodia, ph. +855-(0)-12- 213982; fax +855-(0)-23-880369; e-mail
49 [email protected]) ; TKK Ngai, T (5 kg of nails placed in the diffuser basin Mahin and M Adam (CAWST Bay 12, of an otherwise traditional biosand filter); 2916 Fifth Ave NE, Calgary, Alberta T2A pre-rusted nails configuration; submerged 6K4 Canada, e-mail [email protected]); S nails configuration; manual aeration Chea and S Mao (Ministry of Rural configuration and mechanical aeration Development, Cambodia); S Murcott configuration. (MIT) Phase 2 which is currently ongoing, The Kanchan Arsenic Filter (KAF) was consists of testing KAFs at 30 different developed by the Massachusetts Institute tubewells in Cambodia under varying of Technology (MIT) and a Nepali NGO, groundwater chemistry conditions. The Environment and Public Health results from the KAF testing and the Organization (ENPHO) based on extensive importance of each of the individual laboratory and field studies in rural groundwater chemistry parameters will be villages of Nepal with up to 10,000 discussed in detail during the conference households having received KAFs since presentation. Specific levels of these 2002 from ENPHO and other small non- parameters that are likely to impact profits, large agencies (UNICEF, UN- performance will be identified and Habitat) and the Nepali government. The discussed. These specific levels wills be KAF is currently being tested in Cambodia compared against levels of these to determine the applicability of this parameters generally found in groundwater technology for use in high-arsenic areas of in other high arsenic areas of Cambodia Cambodia. A total of 40 KAFs have been from other published studies. tested at 31 different tubewells in Cambodia as part of this evaluation. Key results to date have shown that Sustainability of Groundwater Pumping groundwater chemistry of the specific From Low-arsenic Aquifers in Southern tubewell that is being treated is the most Asia: Proposal for a Case-Study in important issue relative to predicting Vietnam South of Hanoi arsenic removal performance. This is consistent with the field of drinking water [*A van Geen*] (Lamont-Doherty Earth treatment in general, that the chemistry of Observatory of Columbia University, the source water is typically considered a Palisades, NY 10964, USA; ph. +1-845- very important parameter for achieving 365-8644; fax +1-845-365-8154; e- effective treatment. Some of the mail:[email protected]); T groundwater chemistry parameters that Eglinton (Woods Hole Oceanographic have been evaluated in Cambodia for their Institution; Woods Hole, MA 02543, USA; importance relative to impact on KAF e-mail: [email protected]); B Bostick treatment performance include: pH, total (Dartmouth College, Hanover NH 03755, hardness levels, phosphates, iron, raw USA; e-mail: [email protected]); B water arsenic levels, and total dissolved Weinman (Vanderbilt University, solids. Nashville, TN 37240; e-mail: The work in Cambodia consists of two [email protected]); P Oates phases. Phase 1 includes field research (Quantitative Environmental Analysis, carried out over a 30 week period during LLC, Montvale, NJ 07645, USA; e-mail: 2008. During Phase 1, a total of 10 KAFs [email protected]); K Radloff, Z. Aziz were installed in 5 different (Lamont-Doherty Earth Observatory of configurations, 2 filters for each Columbia University, Palisades, NY configuration. The configurations were: 10964, USA; e-mail: the original configuration applied in Nepal [email protected],
50 [email protected]); M Berg, R provide a basis for testing several working Kipfer (Eawag, Swiss Federal Institute of hypotheses. H1: Reductive dissolution of Aquatic Science and Technology, CH- Fe oxyhydroxides associated with the 8600 Duebendorf, Switzerland; e-mail: release of As to groundwater is driven [email protected], primarily by the microbial degradation of [email protected]); P H Viet, P T K POC deposited at the same time as the Trang (Research Centre for Environmental aquifer sands. H2: DOC advected by Technology and Sustainable Development, groundwater flow does not result in Hanoi University of Science, Vietnam significant reductive dissolution of Fe National University, Hanoi, Vietnam; e- oxyhydroxides and therefore does not mail: [email protected], [email protected]) trigger conversion of orange sands to grey or the release of As. H3: Mixing of high- Emphasis on the elevated level of arsenic sulfate (SO4) groundwater with high-As in groundwater tapped by millions of groundwater results in precipitation of As- shallow tubewells across southern Asia sulfides fueled by the oxidation of POC in over the past two decades tends to obscure the aquifer deposit. The proposed research that anoxic aquifers that are low in As are will also help to determine whether the As also widespread and often within reach of content of groundwater tapped by the drilling in the affected regions. There are municipal water supply of the city of two key issues for assessing the Hanoi, and similarly situated groundwater vulnerability of such low-As aquifers: (1) pumping stations throughout southern whether dissolved or particulate organic Asia, could be lowered at the source by carbon (DOC or POC) drives aquifers favoring entrainment of river water, towards microbial dissolution of Fe herewith reducing the need for treatment. oxyhydroxides and (2) to what extent adsorption and precipitation of As attenuate the impact of high-As Targeting Low-Arsenic Aquifers by groundwater drawn into low-As aquifers. Processing and Re-Distributing Field- The village of Van Phuc, 15 km south of Kit Data Hanoi, presents an opportunity to address both issues because large groundwater [*A van Geen*] (Lamont-Doherty Earth withdrawals by the city of Hanoi have Observatory of Columbia University, laterally drawn groundwater elevated in As Palisades, NY 10964, USA; ph. +1-845- from Holocene grey sands through orange 365-8644; fax +1-845-365-8154; e-mail: Pleistocene sands for several decades. [email protected]); J J Immel (e-mail: [email protected]); A In order to assess the vulnerability of the Gelman (e-mail: low-As aquifer in Van Phuc, we have [email protected]); S Ehrenberg proposed to apply an unprecedented (e-mail: [email protected]); M combination of analytical methods to the Trevisani (e-mail: transition from grey to orange sands: 14C- [email protected]); J Shen analysis of phospholipid fatty acids (e-mail: [email protected]); Y Zheng (PLFAs) constituting the membranes of ([email protected]); M Stute living cells, probing of the redox state and ([email protected]); K M bonding environment of As and Fe in Ahmed (Department of Geology, aquifer sands by X-ray absorption University of Dhaka, Dhaka 1000, spectroscopy, 3H-3He dating of Bangladesh; ph. +880-2-966-1920 Ext. groundwater, and optically-stimulated 7316; fax +880-2-861-5583; e-mail: luminescence (OSL) dating of quartz [email protected]) grains. The proposed measurements will
51 Close to 5 million tubewells distributed well as text messaging. The probability of across 45,000 villages of Bangladesh were success calculated by processing field-kit systematically tested for As with a field-kit data at the village level could also help between 2001 and 2004. The data have calculate the premium needed to sustain a been compiled by the government and money-back guarantee program that would used primarily to install ~800 ft deep wells reimburse households that installed a new in the subset of 7500 villages where >80% tubewell at the prescribed depth but failed of existing tubewells contain >50 ug/L As. to reach low-As groundwater. Systematic The data show that initial exposure of the processing and re-distribution of test data population in these particularly affected via mobile phones should be considered in villages averaged 250 ug/L As and neighboring countries that are affected by contrasts with an average exposure of <10 arsenic in groundwater. ug/L in the subset of 10,500 villages with <20% of existing tubewells containing >50 ug/L. Well-switching in response to field- Equilibrium and Kinetics of As kit testing and the installation of deep Sorption to Bangladesh Gray and wells has significantly reduced exposure Orange Sediments Determined by Batch throughout the country. Experiments
The available data, processed by [*Y. Zheng *] ( Queens College, City aggregating at the village level and taking University of New York, Flushing, NY into account depth information provided 11367 and Lamont-Doherty Earth by households, could be disseminated Observatory of Columbia University; ph much more widely to guide the large 718-997-3329; fax 718-997-3299; e-mail: number of households that continue to [email protected]); Kathleen A. install tubewells. The processed data are Radloff (Department of Earth and particularly valuable in the 27,000 villages Environmental Engineering, Columbia with 20-80% of tubewells, for 13,000 of University, New York, NY 10027, USA. which the depth of a transition to [email protected]); Alexander van groundwater that is systematically low in Geen (Lamont-Doherty Earth Observatory As can be estimated with a probability of of Columbia University, Palisades, NY success >0.8. The depth of these 10964, USA, transitions can vary widely between [email protected]) neighboring villages and should therefore not be averaged over large areas. Unlike the shallower grey Holocene Monitoring of 50 community wells aquifers of Bangladesh, deeper Pleistocene installed in Araihazar according to this aquifers typically consist of orange colored approach has shown that, by and large, sands and are low in groundwater As and these deeper aquifers have been easily mobilizable sediment As. It is not dependable sources low-As drinking water clear, however, to what extent this for up to 7 years. attractive source of drinking water is protected by adsorption should some Safe depth estimates may soon be used shallow groundwater elevated in As be more widely as the government is introduced by leakage. To address this expected to approve their dissemination by issue, batch experiments were conducted Grameenphone, the largest mobile phone by adding As(III) or As(V) to a mixture of service provider in Bangladesh with over sediment and groundwater in the field 20 million subscribers. Grameenphone will immediately upon sample collection in provide this service at a nominal cost Araihazar, Bangladesh. Care was taken to through a popular call-in health line as maintain anoxic conditions by conducting
52 experiments in a nitrogen filled glove box. Sorption equilibrium and kinetic results Four sediment samples were obtained at from batch experiments conducted using depths of 130, 150, 180 and 190 ft. The Bangladesh Pleistocene aquifer sediment first two intervals were gray fine sands and support the potential of using this aquifer the second two fine orange fine sands. The as a sustainable drinking water source. gray sediments were mixed with Iron Plaque on Rice Root Surface and groundwater pumped from 130 ft with 220 Arsenic Dynamics in Paddy Soils: ug/L As, whereas the orange sediments Microbial-Mediated Processes were mixed with groundwater pumped from 190 ft with < 2 ug/L As. [*Y-G Zhu*] (Institute of Urban Environment and Research Center for Eco- The kinetics experiments started with ~ environmental Sciences, Chinese 4000 ug/L As(III) in the solute in a Academy of Sciences, Beijing/Xiamen, mixture of ~ 50 g of wet sediment and 130 China. Email: [email protected]) mL of groundwater sealed in a serum bottle. For the gray sediment sample from Rice is the staple food for nearly half of 130 ft, the solute As concentration dropped the population globally, and arsenic (As) to ~ 2200 ug/L in 7 hrs and remained so to elevation in rice has recently been reported the end at 400 hrs. For the orange sediment to add cancer risks to populations in many sample from190 ft, the solute As regions (Zhu et al., 2008; Meharg et al., concentration dropped to ~ 2200 ug/L in 5 2009). Arsenic enters paddy soils from hrs and continued to decline exponentially anthropogenic (mining activities) and to reach a final concentration of 230 ug/L geogenic (As in groundwater used for at 400 hrs, i.e 95% of As(III) was adsorbed irrigation) sources. It is therefore an urgent in 16 days. Sorption of As(III) to both gray need to mitigate the accumulation of As in and orange sediment is fast, with half time rice grains, particularly in Southeast Asia. of hours. Rhizosphere processes, among many others are crucial in determining the The equilibrium experiments started with a mobility and bioavailability of As in soil- series of As(III) or As(V) concentration rice systems. Several studies have now ranging from 0 to 33,000 ug/L in a mixture pointed to the role of iron plaque on rice of ~ 7 g of wet sediment and ~ 10 mL of root surface in modulating the dynamics of groundwater also sealed in serum bottles As in soil-rice systems (Liu et al., 2004; for 6 days. For As(III) isotherms, all four Liu et al., 2006). It is well known that sediment samples follow Langmuir microbes are heavily involved in the sorption isotherms, but with distinctly oxidation and reduction of iron, but their different sorption capacities. The gray role in iron plaque formation/dissolution, sediment has a sorption capacity of 6-8 and thus As bioavailability is not clear. In mg/kg whereas the orange sediment has a the past five years or so, our group has sorption capacity of 35-40 mg/kg. For been investigating whether nitrate- As(V) isotherms, two sediment samples dependent iron oxidizing bacteria and iron from 130 ft and 190 ft used show nearly reducing bacteria are involved in As identical isotherms as for As(III). Whereas sequestration and release in paddy soils, this is not surprising for the sediment from and rhizosphere soils in particular. Since 130 ft because As(V) added to the nitrate might be involved in iron dynamics supernatant was found to be entirely in paddy soils (Chen, et al., 2008), we also reduced As(III), there was no evidence of examined the community structure of reduction of As(V) to As(III) in ammonia oxidizing microbes. Molecular experiment with sediment from 190 ft. tools, such as qRT-PCR were employed to study the microbial ecology. This review
53 aims to present a synthesis of the status of current knowledge, and discuss future needs in better understanding how microbes in paddy soils and rice rhizosphere are involved in determining As bioavailability, and possible ways of mitigating As accumulation in rice grains.
54