Bangladesh Arsenic Case Study
Cost comparison
Option
Unit Cost
($)
Persons Cost per
(per unit) Person ($)
Cost per arsenicosis
case avoided
Deep Tubewell
$500 - 790
250
$2 - 3
$30 - 50
Household Treatment
$5 - 50
5
$3 - 20
$55 - 330
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
Piped Supply
$30,000
2000
$17
$280
Source: Ahmed (2002)
Extent of Contamination
and Health Effects
Predicted National Rates of Arsenicosis and Cancer
Present Conditions
150m Wells Remedy
Arsenicosis
West Bengal Data
our model fit
1,860,000 people (1%)
Skin Cancer
Taiwan Data
our fit
Internal Cancers
Taiwan Data
NRC model fit
125,000 people ( 0.1%)
3,000 people/yr
690,000 people (0.57%)
37,000 people (0.04%)
800 people/yr
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
Groundwater Arsenic Concentration
vs. Age of Well
Concentration (ln-ppb)
3
2.5
2
1.5
1
0.5
0
0
5
10
15
20
25
30
35
Age of Well (years)
Each point represents an average of ~200 wells.
Wells were sampled in 1997-1999.
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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
Dhaleswari River
5 km
Padma River
Field Site
Biogeochemistry
Arsenic Profile
Solid phase Arsenic
ug/g or ppm
Dissolved As (ppb)
Surface 0
Clay
Core
15 Piezometers
20
40
60
Depth
(m) 80
Sand
100
120
Clay
140
160
Sand
0
400
800
0
2
4
6
8
10
Solid As
0
0
(nmoles/g dry wt.)
20
60
40
Solid Fe
0
80
(µmoles/g dry wt.)
200 400 600 800
Clay
20
40
60
Depth
(m) 80
100
Arsenic Extraction Targets
Weakly adsorbed
Strongly adsorbed
Carbonates, AVS,
amorphous oxides
Crystalline Fe oxides,
amorphous As
sulfides
Silicates, As 2O3
Crystalline Sulfides
pyrite
120
Clay
140
160
Mostly Fe II
(Except for magnetite)
Competing Anions
0
Depth
(m)
80
Arsenic
Phosphate
Silicate
160
0.01
0.1
1
10
(µM)
100
1000
-2
log saturation index (SI)
0
2
4
6
8
0
SEM Bangladesh aquifer
20
Depth: 91’
Fraction: “non-magnetic heavy”
Depth (m)
40
60
3
80
100
120
140
160
180
2
Ca5(PO4)3OH
(Hydroxyapatite)
Fe3(PO4)2 (Vivianite)
CaCO3 (Calcite)
FeCO3 (Siderite)
1
4
20 µm
1. quartz (SiO2)
3. rutile (TiO2)
2. Ca-phosphate
4. REE-phosphate
Sulfur Chemistry
Dissolved Sulfur (uM) and As (nM)
0.1
1
10
100
1000
0
10000
0.01
Solid phase Sulfur
(umoles/g)
0.1
1
10
H2S
20
SO4
Depth (m)
40
As
60
80
100
120
H2S detection limit
140
Total sulfur
160
180
AVS
100
Dissolved Carbon
Dissolved Organic Carbon (DOC) (mM)
0
0.4
.
0.8
.
1.2
.
1.6
.
2
Methane
20
40
60
Depth
(m )
80
DIC
100
DOC
120
401
601
180
0
2
4
6
8
Inorganic (DIC) and Methane (mM)
10
Arsenic, Ammonium and Calcium
Dissolved As ( µM)
NH 4 + ( µM x 10 )
0
1
2
3
4
5
6
7
8
0
20
40
60
Depth
(m)
80
100
120
140
160
180
0
0.5
1
1.5
2
Dissolved Ca (mM)
2.5
3
Comparison of MIT field site to BGS national data set
Munshi gan j A rsen i c
0
D issolved ( M)
2
4
6
8
Munshi gan j Su lfate
B GS average A rsen i c
0
0.2
( M)
0.4 0.6
0.8
1
1.0
Sulfate ( M)
10
100
B GS average Su lfate
0
50
( M)
100 150 200 250
Munshi gan j C al ci um & B GS average C al ci um
A m m onium
(mM )
C alcium (mM )
0
1
2
AVS
20
NH
+
4
40
D issolved As
60
As
D epth
(m )
Ca
80
Solid phase
As
100
120
140
Total solid phase S
160
0
25
50
75
100
Solid (nmol /g dry wt.)
0.1
1
10
Total Solid Sulfur ( mol/g)
A cid Volatile Sulfide
0
1 2
3 4
5
6 7
N H4 + ( M x 10) A s ( M)
0
1.5
1.0
2.5
Arsenic in Withdrawn Water
after Injection of Low-Arsenic Groundwater Water
Dissolved As (ppb)
0
0
20
40
400
800
Original Value = 700 ppb
300
250
200
ppb
150
60
Depth
(m)
100
80
100
120
140
160
50
0
0
100
200
hours
300
400
Arsenic in Withdrawn Water after Injection of Nitrate
Dissolved As (ppb)
0
0
400
Injectate: Nitrate Added to
High-Arsenic Groundwater
800
800
20
700
40
600
60
Depth
(m)
Injected Volume Removed
500
ppb
80
400
300
100
200
120
100
140
0
0
160
50
100
150
200
250
hours
300
350
400
450
Arsenic in Withdrawn Water after Injection of Molasses
Injectate: Molasses Added to
Low-Arsenic Groundwater
Dissolved As (ppb)
0
0
400
800
Original Value = 120 ppb
60
20
Depth
(m)
40
50
60
40
80
ppb
30
100
20
120
10
140
0
0
100
200
300
160
hours
400
500
Carbon Isotopes
1000
• Inflow of young
carbon
Surface Water Carbon
(Atmospheric values
over last 50 years)
500
• Young carbon
drives biochemistry
Inorganic
Carbon
C0/00
0
Methanogenesis
Methane
3m
19m
0
700
30m
60m
2000
4000
Organic
Carbon
-500
CaCO3
-1000
-70
-30
-25 -20 -15 -10
13
C0/00
-5
0
Radiocarbon Age
14
• Mixture of young
and old carbon is
not the result of
pore water mixing,
but mobilization of
old organic carbon