Transcript As in Bangladesh - Columbia University

Arsenic!
Martin Stute et al.
Barnard College &
Lamont-Doherty Earth Observatory
Columbia University, New York, NY
Outline
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[As] in drinking water – a global problem
Columbia Superfund program
[As] standards & health effects
As mobilization in Bangladesh
Mitigation options
[As] – a global problem
BGS and DPHE (2001)
http://www.bgs.ac.uk/arsenic/Bangladesh/
As drinking water standards
World Health Organization (WHO) guideline: 10 mg/L
US standard
10 mg/L
Bangladesh standard for drinking water:
50 mg/L
Range in Bangladesh:
<1 to over 1000 mg/L
Health effects of (chronic) As exposure
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Early studies in Taiwan, Argentina, and Chile
Cardiovascular disease
Skin lesions (few years of exposure)
Cancers of the skin, lung, liver, and bladder (several
decades of exposure)
• Children’s intellectual function
Cancer
Results indicated at least a doubling of lifetime mortality risk
from liver, bladder, and lung cancers (230 vs. 104 per
100,000 population) in Bangladesh owing to arsenic in
drinking water.
Chen & Ahsan, 2004
As and intellectual function in 10
year-old children
Wasserman et al., 2004, 2005
Arsenic in
Bangladesh
25 million people > 50µg/L
(Bangladesh standard)
51 million people > 10µg/L
(US/WHO standard)
BAMWSP (Bangladesh Arsenic
Mitigation and Water Supply Program)
http://www.bamwsp.org/
Why is there [As] in Bangladesh?
In Bangladesh:
As in groundwater
=> 1000 ug/L
As(III)
As in sediment
1-10 mg/kg
BGS and DPHE (2001)
Need:
• As in sediments (not
much)
• Organic matter
• Reducing conditions (no
oxygen)
Araihazar
One of 464 thanas
(counties) in
Bangladesh
Population: 300,000
Size: 170 km2
Population density:
1800 people/km2
Sources: C. Small, LDEO, Landsat 7 image from USGS EROS Data Center, Sioux Falls, SD, 1991 National Census.
High spatial variability
Arsenic in 5,966 wells
As - depth distribution in Araihazar
6000 wells
Van Geen et al., 2002
Wellnests
Wash boring well drilling method
Wellnests in Araihazar
E
A
C
B
G
H
F
Bangladesh
is a flat place
Dhaka
Zheng et al., 2004
Bangladesh is a flat place
Well As (ug/L)
WHO guideline
Bangladesh standard
Zheng et al., 2004
BGS/DPHE (2001)
…and complicated (heterogeneous)
Surface, last glacial maximum
Local, intermediate,
and regional flow systems
Ravenscroft et al., 2005
Groundwater ‘dating’ with 3H and 3He
1000
1000
Shillong
Yangoon
Allahabad
Dhaka
Groundw. 100
3H (TU)
100
Groundw.
10
1
1960
1970
1980
year
1990
2000
b
3He
T1/2 = 12.43y
10
1
1950
3H
3H/3He
age t:
12.43y  3 He 
t
ln1  3 
ln(2) 
H 
• 3H, 3H+3He as dye
Use of:
• 3H/3He as radioactive clock
One field site as example
Residence time
10’s of y
1000’s of y
Site A, Zheng et al., 2005
Groundwater 3H+3He & 3H in precipitation
Stute et al., 2007
3H/3He
ages and [As]
 Fairly uniform increase
of As concentrations with
3H/3He age
 Hydrology important
factor controlling
variability of As
concentrations
Stute et al., 2007
Two potential mechanisms:
1. As mobilization kinetics slow: groundwater
accumulates As at a ~uniform rate
2. As mobilization kinetics fast: dissolved As
equilibrates quickly with solid phase As,
shorter groundwater residence time
 higher degree of As removal
 Lower dissolved As concentration
Remediation options
Existing wells
Alternative sources
New wells
As removal Well switching
Safi filter @$18
3-kolshi filter @$5
Tube well sand filter
Maintenance
Monitoring
Bacterial growth
Spatial variability
Social resistance
Surface water
Shallow wells Deep wells Pond water Rain collection
Dug wells
$50 for 150 ft
Seasonality
Pathogens
Installation
Distribution
Pond sand filter
Rainwater harverster
50 families @$16 ea. 1 family @ $160/$40 ea.
Bacteria 1/100
Aquaculture
Boiling
Storage-seasonality
Back to surface waters?
< 5 years
infants
Kabir et al., 1999
Back to surface waters?
Filters?
20 L-bucket sand filter
Xiaoguang Meng – Stevens Tech.
As co-precipitation with ~ 20 mg/L Fe
Competition of phosphate and silicate
FeCl3 and NaClO addition
3” sand layer for filtration
648
raw water
As (m g/L)
600
filtrate
400
Initial cost $7/family
Reagents $4/year
329
247
220
205
188
200
11
11
17
15
18
15
0
34
Gravity flow 1.5 to 0.5 L/hour
Cleaning of sand twice a week
11
21
2
Initial Fe/As
112
32
As - depth distribution in Araihazar
6000 wells
Van Geen et al., 2002
Deep community wells
van Geen et al., Water Resources Research, 2003
van Geen et al., Bulletin World Health Organization, 2003
Community wells can fail
van Geen et al., J. Env. Sci. Health, in press.
van Geen et al., Water Resources Res., 2003
Aquifer Sustainability
Aquifer
shallow
deep
Residence time
10’s of years
1000’s of years
Recharge rate
>10 cm/year
0.5 cm/year
Personal
consumption
Irrigation
Supply
2 cm/year
(2640 persons/km2; 20L/person/day)
Demand
60 cm/year
=> Deep aquifer will likely sustain personal,
but not necessarily irrigation use
Irrigation increases
Irrigation technologies used in 1996
BGS, 2001
Some success!
Urinary creatinine-adjusted
arsenic (μg/g creatinine)
600.0
Baseline urinary
creatinine-adjusted As
500.0
Follow up urinary
creatinine-adjusted As
400.0
300.0
200.0
100.0
0.0
5
N
1579
6-38
1477
39-90
1413
91-177
178-864 Baseline well [As
1503
1590
Ahmed et al., Science, 2006
Scale of human tragedy
• West Bengal, India
-1 million people drink high arsenic groundwater.
-200,000 cases of skin-lesions as of 1996.
-62% of 20,000 sampled tube wells exceed 50 mg/L.
• Bangladesh:
-25/51 million people drink groundwater with arsenic.
above Bangladesh (50 mg/L) /WHO (10 mg/L) standard.
-21% of 18,000 people examined with skin lesions.
-35% of 22,000 sampled tube wells exceed 50 mg/L.
• Number of deaths of children under 5 has declined from 250/1000 live
births in 1974 to ~100/1000 in 1994 –cause of decline disputed.
Sources:
Das et al. (1996), Saha (1998), Dhar et al. (1997), Mandal et al. (1998), BGS/Mott McDonald (1999)
D. Chakraborti et al. (2000), Kabir et al. (1999).
Time-line for arsenic crisis
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Starting in 1960’s: Tube wells promoted by UNICEF to reduce infant
mortality from water-borne diseases.
Mid-1980’s: First cases of arsenicosis reported in West Bengal, India.
-1 million people drink high arsenic groundwater.
-200,000 cases of skin-lesions as of 1996.
-62% of 20,000 sampled tube wells exceed 50 ug/L.
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Early 1990’s: First cases of arsenicosis reported in Bangladesh.
Dhar et al. (1997): Survey of thousands of tube wells in Bangladesh by
Depankra Chakraborti’s group in Calcutta.
British Geological Survey/Mott MacDonald (1999): Landmark
compilation of existing and new data
-25/51 million people drink groundwater with arsenic.
above Bangladesh (50 mg/L) /WHO (10 mg/L) standard.
-21% of 18,000 people examined with skin lesions.
-35% of 22,000 sampled tube wells exceed 50 mg/L.
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June 2000: Launch of Columbia University Superfund/Basic Research
Program, following pilot studies since January 1999.
Conclusions
• As is a global health problem
• Hydrology is important factor controlling spatial
variability of dissolved As
– Control by reaction kinetics or flushing rate
• Deep wells seem to be the best intermediate
term solution, at least in Araihazar
• While deeper wells provide a source of low As
drinking water they might not be able to sustain
massive irrigation