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Arsenic!

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Removal of Arsenic by Bucket Filters, Araihazar, Bangladesh, January 2001. Fe/As. 4145.00 6.34 246.60 11.00 11.31 34.44 1000.00 56.00 75.00 4108.00 2.74 328.70 11.00 ... – PowerPoint PPT presentation

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Title: Arsenic!


1
Arsenic!
  • Martin Stute et al.
  • Barnard College
  • Lamont-Doherty Earth Observatory
  • Columbia University, New York, NY

2
Outline
  • As in drinking water a global problem
  • Columbia Superfund program
  • As standards health effects
  • As mobilization in Bangladesh
  • Mitigation options

3
As a global problem
BGS and DPHE (2001)
http//www.bgs.ac.uk/arsenic/Bangladesh/
4
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 lt1 to over 1000 mg/L
5
Health effects of (chronic) As exposure
  • 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)
  • Childrens intellectual function

6
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
7
As and intellectual function in 10 year-old
children
Wasserman et al., 2004, 2005
8
Arsenic in Bangladesh
25 million people gt 50µg/L (Bangladesh
standard) 51 million people gt 10µg/L (US/WHO
standard)
BAMWSP (Bangladesh Arsenic Mitigation and Water
Supply Program) http//www.bamwsp.org/
9
Why is there As in Bangladesh?
Need
In Bangladesh As in groundwater gt 1000 ug/L
As(III) As in sediment 1-10 mg/kg
  • As in sediments (not much)
  • Organic matter
  • Reducing conditions (no oxygen)

BGS and DPHE (2001)
10
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.
11
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12
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13
High spatial variability
Arsenic in 5,966 wells
14
As - depth distribution in Araihazar
6000 wells
Van Geen et al., 2002
15
Wellnests
16
Wash boring well drilling method
17
Wellnests in Araihazar
18
Bangladesh is a flat place
Dhaka
Zheng et al., 2004
19
Bangladesh is a flat place
Well As (ug/L)
WHO guideline Bangladesh standard
Zheng et al., 2004
BGS/DPHE (2001)
20
and complicated (heterogeneous)
Surface, last glacial maximum
Local, intermediate, and regional flow systems
Ravenscroft et al., 2005
21
Groundwater dating with 3H and 3He
b
  • 3H, 3H3He as dye
  • 3H/3He as radioactive clock

Use of
22
One field site as example
Residence time
10s of y
1000s of y
Site A, Zheng et al., 2005
23
Groundwater 3H3He 3H in precipitation
Stute et al., 2007
3H3Hetime2
24
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
Asage3
25
Two potential mechanisms
  • As mobilization kinetics slow groundwater
    accumulates As at a uniform rate
  • 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

26
Remediation options
Existing wells Alternative sources
New wells Surface water
As removal Well switching Shallow wells
Deep wells Pond water Rain collection
Safi filter _at_18 3-kolshi filter _at_5 Tube well
sand filter Maintenance Monitoring Bacterial
growth
Pond sand filter 50 families _at_16 ea. Bacteria
1/100 Aquaculture Boiling
Rainwater harverster 1 family _at_ 160/40
ea. Storage-seasonality
Dug wells Seasonality Pathogens
50 for 150 ft Installation Distribution
Spatial variability Social resistance
27
Back to surface waters?
lt 5 years
infants
Kabir et al., 1999
28
Back to surface waters?
29
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 Gravity
flow 1.5 to 0.5 L/hour Cleaning of sand twice a
week Initial cost 7/family Reagents 4/year
30
As - depth distribution in Araihazar
6000 wells
Van Geen et al., 2002
31
Deep community wells
van Geen et al., Water Resources Research,
2003 van Geen et al., Bulletin World Health
Organization, 2003
32
Community wells can fail
van Geen et al., J. Env. Sci. Health, in
press. van Geen et al., Water Resources Res., 2003
33
Aquifer Sustainability
Aquifer shallow deep
Residence time 10s of years 1000s of years
Recharge rate gt10 cm/year 0.5 cm/year
Supply Demand
Personal consumption 2 cm/year (2640 persons/km2 20L/person/day)
Irrigation 60 cm/year
  • gt Deep aquifer will likely sustain personal,
    but not necessarily irrigation use

34
Irrigation increases
Irrigation technologies used in 1996
BGS, 2001
35
Some success!
Urinary creatinine-adjusted arsenic (µg/g
creatinine)
Baseline well As
N
1579
1477
1413
1503
1590
36
Ahmed et al., Science, 2006
37
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).
38
Time-line for arsenic crisis
  • Starting in 1960s Tube wells promoted by UNICEF
    to reduce infant mortality from water-borne
    diseases.
  • Mid-1980s 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.
  • Early 1990s First cases of arsenicosis reported
    in Bangladesh.
  • Dhar et al. (1997) Survey of thousands of tube
    wells in Bangladesh by Depankra Chakrabortis
    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.
  • June 2000 Launch of Columbia University
    Superfund/Basic Research Program, following
    pilot studies since January 1999.

39
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
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