1. Martin Stute Barnard College & L-DEO
Arsenic in Bangladesh
Martin Stute
Barnard College & L-DEO

2. Outline As standards, health effects History of As issue in Bangladesh
Causes for As mobilization
Remediation options

3. BGS and DPHE (2001)

5. Drinking water standards for arsenic
World Health Organization (WHO) guideline: mg/L
Current US standard mg/L
> mg/L
Bangladesh standard for drinking water: mg/L
Range in Bangladesh: <1 to over 1000 mg/L

6. Health effects of (chronic) arsenic exposure
Previous 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

7. Time-line for arsenic crisis
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.
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.
June 2000: Launch of Columbia University Superfund/Basic Research Program, following pilot studies since January 1999.

8. Araihazar
Dhaka * *
Source: M. Steckler, LDEO, based on GTOPO30 digital elevation model (USGS EROS Data Center).

9. Araihazar
Bangladesh Arsenic
Mitigation and Water Supply Program
5 million wells so far?

10. Satellite image: Araihazar, one of 464 thanas in Bangladesh Population 300,000; 170 km2 (density 1800/km2)
Sources: C. Small, LDEO, Landsat 7 image from USGS EROS Data Center, Sioux Falls, SD, 1991 National Census.

13. Arsenic in 5,966 wells

14. As - depth distribution in Araihazar

15. Wellnests

16. Wellnests in AraihazarC E G F B H

17. Global positioning system

18. Site A

19. High resolution head measurements

20. Average high-resolution vertical hydraulic head gradients
Recharge rates:
from 4 to 60 cm/y
Large uncertainty
Averages over 1 year, 20 data points
Averages over 1 year, 20 data points

21. Conceptual model dry => wet season wet => dry season
BGS and DPHE, 2001

24. Frequency EM data
Penetration ~10m or so, very rough extimate
Z. Aziz

25. Recharge rate, As and local EM dataB F C G E
EM conductivity Color Scale (mS/m)
low high EM
coarse fine
sediments
high low
recharge rate
cm/y
Low high As

26. Stratigraphy, geophysical logs
Site F, Bangladesh

27. Environmental tracers, CH4

28. 3H/3He versus SF6 age 10 20 30 40
3H/3He age
SF6 age (y) A F G
1/1

29. Stable water isotopes d2H (‰) d18O (‰) 40 30 20 10 -10 -8 -6 -4 -2 2 4
-10 -8 -6 -4 -2 2 4 6
-10
MWL
slope 6
Precip Bangkok SW RF
Av precip
ML wells
C wells RW
Linear (RF)
-20
-30
-40
-50
d18O (‰)
-60

31. Site A 10’s of y 1000’s of y Residence time Site A, Zheng et al., 2005
peat
1000’s of y
Site A, Zheng et al., 2005

32. What’s needed for elevated As concentrations?
Iron oxyhydroxides with adsorbed As
Perhaps other phases?
reducing conditions (no O2, low ORP)
natural organic matter
peat?
anthropogenic organic matter?

33. There is plenty of As in sediments
Bangladesh
As in groundwater
=> 1000 ug/L
As(III)
As in sediment
1-10 mg/kg
BGS and DPHE (2001)

34. <= more reducing
more reducing=>

36. groundwater ‘dating’ with 3H and 3He1 10
100
1000
1950
1960
1970
1980
1990
2000
Shillong
Yangoon
Allahabad
Dhaka
D/v 2
=1y
=0.2y 3
H (TU)
year b
3H He
T1/2 = 12.43y
3H/3He age t:
3H, 3H+3He as dye
3H/3He as radioactive clock
Use of:

37. As and groundwater age

38. Existing wells Alternative sources
Remediation options
Existing wells Alternative sources
New wells Surface water
As removal Well switching Shallow wells Deep wells Pond water Rain collection
Safi
3-kolshi
Tube well sand filter
Maintenance
Monitoring
Bacterial growth
Spatial variability
Social resistance
Dug wells
Seasonality
Pathogens
$50 for 150 ft
Installation
Distribution
Pond sand filter
50 ea.
Bacteria 1/100
Aquaculture
Boiling
Rainwater harverster
1 $160/$40 ea.
Storage-seasonality

39. Xiaoguang Meng – Stevens Tech.
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

40. Existing wells Alternative sources
Remediation options
Existing wells Alternative sources
New wells Surface water
As removal Well switching Shallow wells Deep wells Pond water Rain collection
Safi
3-kolshi
Tube well sand filter
Maintenance
Monitoring
Bacterial growth
Spatial variability
Social resistance
Dug wells
Seasonality
Pathogens
$50 for 150 ft
Installation
Distribution
Pond sand filter
50 ea.
Bacteria 1/100
Aquaculture
Boiling
Rainwater harverster
1 $160/$40 ea.
Storage-seasonality

41. As - depth distribution in Araihazar

42. Domestic
use As As

43. Domestic
use As As

44. irrigation
Domestic
use As As

45. irrigation
Domestic
use As As

46. irrigation
Domestic
use As As As As

47. irrigation
Domestic
use As As As As As

48. In situ experiments Acetate & Br tracer pump packer packer
Aim C.6 Perform push/pull and forced gradient injection experiments using purposefully injected tracers including SF6 and Br-.
pump
packer
packer
Extraction Well
Injection Well
Sampling Well

49. Aquifer Sustainability
shallow
deep
Residence time
10’s of years
1000’s of years
Recharge rate
>>10 cm/year
0.5 cm/year
Supply
Demand
Personal consumption
1 cm/year
(2640 persons/km2; 10L/person/day)
Irrigation
60 cm/year
A personal water use of 10L/person/day for drinking and washing amounts to an approximate additional water table drop by about 2cm/year, while massive irrigation might lower the water table by up to 2m/year (BGS, 2001; Harvey et al., 2002). Groundwater residence times have been estimated for the top 100m as <100y, for m depth as ~3000y, and for formations >200m as 20,000y (Aggarwal et al., 2000), corresponding to recharge rates of <1 m/y, 3cm/y, and perhaps 1cm/y, respectively. These are very rough estimates and it is not clear, if these recharge artes are representative for today's recharge or might be affected by increased pumping. However, it appears likely the deeper aquifers will sustain personal water use, but might be stressed too much by an increase in irrigation with water from deep aquifers. In all cases, care must be taken when constructing new wells to avoid leakage along the well casings between aquifers.
One uncertainty concerns the extent to which the recharge rate could increase if the groundwater abstraction from deep aquifers were enhanced, and whether that recharge rate could sustain the demand of withdrawal. In the following we estimate this increased rate of withdrawal but note that potential increases for irrigation are not included. For a population density of Araihazar of ~ 2640 persons per km2 (van Geen et al., 2002) the withdrawal rate amounts to 9600 m3/ km2/yr or 1cm/yr of water, assuming a domestic water demand of 10L/person/day. This is of the same order of magnitude as the natural recharge rates estimated. If most of the personal water use would shift to the deeper aquifer it therefore appears that the deeper aquifer might be able to sustain these withdrawals in the near future, in particular in view of the likeliness of an increase recharge rate as a consequence of increased withdrawal. If, however, the withrawal rate of the deep aquifer would be dramatically increased, e.g. to values of 60cm/yr (versus 1cm/yr) reported for other regions affected by irrigation (Harvey et al., 2002; equivalent to an additional water table drop of 2m/yr) hydraulic gradients between shallow and deep aquifer might increase significantly and leakage rates would increase in proportion, which then would increase the potential of water with elevated [As] or [DOC] to reach the deeper aquifer. The latter would change the balance of the redox state in the deeper aquifer, which then potentially would release absorbed As as observed in incubation experiment (cite van Geen, in prep). We recommend that withrawal rates should be limited to values near the recharge rate in order to reduce the chance of exporting the As problem into the deeper aquifer until aquifer response to enhanced withdrawal is better understood.
=> Deep aquifer will likely sustain personal, but not necessarily irrigation use

50. van Geen et al., Water Resources Research, 2003
van Geen et al., Bulletin World Health Organization, 2003

51. Irrigation
Irrigation technologies used in 1996
BGS, 2001

52. Conclusions As concentrations are highly variable in Bangladesh
As is of natural, but we do not know yet if there are anthropogenic factors influencing the As distribution
Hydrology (groundwater age) is an important factor
Deeper wells appear a feasible remediation option, although we need to keep irrigation in check