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?

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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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