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Bangladesh Arsenic Case Study
Source: Ahmed (2002)
Persons(per unit)
Unit Cost($)
Option Cost per arsenicosis case avoided
Deep Tubewell $500 - 790 250 $2 - 3 $30 - 50
Dug Well $560 - 620 125 $4.5 - 5 $65 - 70
Pond Sand Filter $400 - 600 250 $2 - 4 $35 - 65
Rain Water $100 - 200 5 $20 - 40 $350 - 630
Household Treatment $5 - 50 5 $3 - 20 $55 - 330
Piped Supply $30,000 2000 $17 $280
Cost perPerson ($)
Cost comparison
Extent of Contamination and Health Effects
Predicted National Rates of Arsenicosis and Cancer
125,000 people ( 0.1%)
3,000 people/yr
1,860,000 people (1%)Arsenicosis
Skin Cancer
Internal Cancers
West Bengal Dataour model fit
Taiwan Dataour fit
Taiwan DataNRC model fit
150m Wells Remedy
690,000 people (0.57%)
37,000 people (0.04%)
800 people/yr
Present Conditions
The 150m well remedy:• Replaces 30% of the nations wells• That is 800,000 wells at a cost of $500/well• Total cost of $395,000,000 • $340 per reduction in arsenicosis prevalence
0 352515 30201050
2.5
1.5
0.5
3
2
1
Age of Well (years)
Groundwater Arsenic Concentrationvs. Age of Well
Each point represents an average of ~200 wells.Wells were sampled in 1997-1999.
Con
cent
ratio
n(ln
-ppb
)
Big Basic Questions:Why are dissolved arsenic levels so high?
• Where does it come from? -- Little solid phase arsenic• Why isn’t it flushed away? -- Flow + Little retardation
Why are arsenic concentrations so variable on small scales?
Important Questions for Decision Making:Will arsenic concentrations change? Can deep aquifers provide a long-term solution?
Key Scientific Questions:What is the solid state of arsenic?How do shifts in water chemistry affect arsenic mobility?
????
MIT/BUET Field Site
Padma River
Dhaleswari River
Field Site5 km
Biogeochemistry
CoreSurfaceClay
Sand
Clay
Sand
15 Piezometers0
20
40
60
80
100
120
140
160
Depth(m)
0 2 4 6 8 10
Solid phase Arsenicug/g or ppm
0 400 800
Dissolved As (ppb)
Arsenic Profile
Clay
0 200 400 600 800
Solid Fe(µmoles/g dry wt.)
Clay
Solid As0 20 40 60 80
0
20
40
60
80
100
120
140
160
(nmoles/g dry wt.)
Depth(m)
Mostly Fe II(Except for magnetite)
Carbonates, AVS, amorphous oxides
Weakly adsorbed Strongly adsorbed
Crystalline Fe oxides,amorphous Assulfides
Silicates, As2O3Crystalline Sulfides
pyrite
Arsenic Extraction Targets
0
0.01 0.1 1 10 100 1000
Phosphate SilicateArsenic
80
160
(µM)
Competing Anions
Depth(m)
1. quartz (SiO2) 2. Ca-phosphate3. rutile (TiO2) 4. REE-phosphate
SEM Bangladesh aquiferDepth: 91’Fraction: “non-magnetic heavy”
1
2
3
420 µm
0
20
40
60
80
100
120
140
160
180
-2 0 2 4 6 8log saturation index (SI)
Ca5(PO4)3OH (Hydroxyapatite)Fe3(PO4)2 (Vivianite)CaCO3 (Calcite)
FeCO3 (Siderite)
Dep
th (m
)
Dep
th (m
)
0
20
40
60
80
100
120
140
160
180
0.1 1 10 100 1000 10000
SO4
H2S
As
H2S detection limit
0.01 0.1 1 10 100
Solid phase Sulfur (umoles/g)
Total sulfurAVS
Dissolved Sulfur (uM) and As (nM)
Sulfur Chemistry
0 2 4 6 8 10
20
40
60
80
100
120
401
601
180
0 0.4. 0.8. 1.2. 1.6. 2
Methane
DOC
DIC
Dissolved Organic Carbon (DOC) (mM)
Inorganic (DIC) and Methane (mM)
Dissolved Carbon
Depth(m )
0
20
40
60
80
100
120
140
160
180
0 1 2 3 4 5 6 7 8
Depth(m)
0 0.5 1 1.5 2.52 3
Dissolved As ( µM)NH4
+ ( µM x 10 )
Arsenic, Ammonium and Calcium
Dissolved Ca (mM)
Comparison of MIT field site to BGS national data set
NH4 + ( M x 10) As ( M)2 4 61 3 5 70
210Calcium (mM )
As
NH4+
Ca
Munshiganj Calcium &Amm onium
BGS average Calcium
1.00 1.5 2.5(mM )
1 10 100Sulfate ( M)
Acid Volatile SulfideTotal Solid Sulfur ( mol/g)
AVS
Total solid phase S
0.1 1 10
BGS average SulfateMunshiganj Sulfate
2000 50 100 150 250( M)Dissolved ( M)
80 2 4 6
20
40
60
80
100
120
140
160
1000
Munshiganj Arsenic
Dissolved As
Solid phaseAs
7525 50Solid (nmol /g dry wt.)
Depth (m)
BGS average Arsenic
0.80 0.2 0.4 0.6 1.0( M)
Arsenic in Withdrawn Water after Injection of Low-Arsenic Groundwater Water
0 100 200 300 400
hours
0
50
100
150
200
250
300
ppb
Original Value = 700 ppb0 400 800
Dissolved As (ppb)
0
20
40
60
80
100
120
140
160
Depth(m)
0 400 800
Dissolved As (ppb)
0
20
40
60
80
100
120
140
160
Depth (m)
Injected Volume Removed
0
100
200
300
400
500
600
700
800
0 50 100 150 200 250 300 350 400 450
hours
ppb
Injectate: Nitrate Added to High-Arsenic Groundwater
Arsenic in Withdrawn Water after Injection of Nitrate
0
10
20
30
40
50
60
0 100 200 300 400 500
ppb
hours
Injectate: Molasses Added to Low-Arsenic Groundwater
Original Value = 120 ppb0 400 800
Dissolved As (ppb)
0
20
40
60
80
100
120
140
160
Depth (m)
Arsenic in Withdrawn Water after Injection of Molasses
InorganicCarbon
OrganicCarbon
30m19m3mMethanogenesis
CaCO3
(Atmospheric valuesover last 50 years)
60m
14C0/00
-1000
-500
0
500
1000
-30 -25 -20 -15 -10 -5 0-70
Methane
Surface Water Carbon
0700
40002000
Radiocarbon A
ge
Carbon Isotopes
• Inflow of young carbon
• Young carbon drives biochemistry
• Mixture of young and old carbon is not the result of pore water mixing, but mobilization of old organic carbon
13C0/00
Bangladesh Arsenic Case Study
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