groundwater arsenic occurrences in bangladesh and mitigation options kazi matin ahmed, phd...
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Groundwater Arsenic Occurrences inBangladesh and Mitigation Options
Kazi Matin Ahmed, PhDDepartment of Geology
University of DhakaDhaka, Bangladesh
kmahmed@du.ac.bd
Goldschmidt2015Prague, CZ, 16-21 August 2015
Groundwater as the Sources for Drinking & Irrigation Water
Map of Arsenic Occurrence1998-99 Survey1998-99 Survey 2002-03 Survey2002-03 Survey
Over 5 million wells tested!Most severely affected
areas are in the southern part of the deltaic plains
Some contamination in the north east, northwest is least contaminated
Hills in the southeast safe
Distribution is controlled by surface geology
Deeper wells are mostly safe
Geology and Arsenic Distribution
Basin Model
Conceptual Model of Arsenic Distribution in the Bengal Basin
I : Source Area
- Erosion and transportation dominant
- Detrital sulphides and/or oxides
- Oxidation & dissolution of sulphides
- Precipitation of ferric hydroxide
- Adsorption of As.
III : Distributary Channels & Swamps
- Sedimentation dominant, abundant detritus
- Locally brackish water
- Strongly reducing - dissolution of oxyhydroxides anddesorption of arsenic
- Diagenetic pyrite
- Fe & As to solution
IV : Estuarine / Marine Environment
- Saline water- Arsenic transferred to oceans
II : Braided & Meandering Channels
- Alternating deposition and resuspension.
Channels :oxidising - precipitation of hydroxides and adsorption of As.
Point barsreducing - dissolution of oxyhydroxides and desorption of arsenic
- Iron rich coatings- Separation of SO 4 from Fe and As.
Impact of Arsenic on Rural Water Supply
Source: WaterAid Bangladesh
Possible Impacts on Rice Production
0
2
4
6
8
10
0 10 20 30 40 50 60 70
Soil-As (mg/kg)
Rice
Gra
in Y
ield
(ton
s/he
ctar
e)
50% reduction
‘Parrot beak’
Duxbury et al
Number of People with Skin Lesions
• Surveys identified around 30,000 having arsenical skin lesions
• Overall prevalence is about 1 in 1000, however, local studies reported much higher numbers;
• Argoss et al - double mortality rate due to CVD for exposure in access 150 ppb; Wasserman et al reported reduced intellectual development of kids.
• Alan Smith predicts 1 in 100 dying of cancer at 50 ppb, and 1 in 10 at 500 ppb
10
READ-F MAGC/ALCANSono 45-25 Sidko
Arsenic Removal TechnologiesA –Household ARTs: Alcan, Nelima, Read F, Shawdesh, SonoB - Community ARTs: Sidko
Well Switching
Alternative Safe Water Options
Deep Tube Wells
(GOB, 2002)
Rural Piped Water Systems
(GOB, 2002)
Subsurface Arsenic Removal
Number of People Exposed to >50 ppb
GOB, 2002
GOB/UNICEF 2009 MICS
• The results of the Multiple Indicator Cluster Survey (MICS) in 2009 estimated that approximately 22 million people were exposed to arsenic concentrations above 50 μg/L, and approximately 36 million above 10 μg/L.
• The results of the Multiple Indicator Cluster Survey (MICS) in 2013 estimated that approximately 19.6 million people were exposed to arsenic concentrations above the Bangladesh Drinking Water Quality Standard of 50 μg/L
http://www.unicef.org/bangladesh/knowledgecentre_6868.htm
Arsenic in BRAC WASH Area
Source: Nepal C Dey, Fazlul Karim and Sifat-E-Rabbi, 2013. Use of tubewell water for different purposes at household level: safety practices in rural Bangladesh, in Achievements of BRAC Water, Sanitation and Hygiene Programme Towards Millennium Development Goals and Beyond, Research Monograph Series No. 60, p11-31, Research and Evaluation Division (RED), BRAC.
Large Number of Untested Wells
176/357 wells49% untested
50% of households(53/105) knowingly drinkfrom unsafe well
20
Possible Safe Water Options for Different Regions
Out of 19.0 million, 10.9 million people can be covered by Deep TW with No 6 or TARA hand pump
The rest 8.1 million people are to be covered by PSF, DW, AIRP etc
If well can be installed up to deep aquifer having gravel problem, nearly 5.7 million out of 8.1 million can be served with Tubewell
Concluding Remarks• Natural arsenic occurrence in the alluvial aquifer is and will remain Natural arsenic occurrence in the alluvial aquifer is and will remain
as a major challenge for water supply in Bangladesh ;as a major challenge for water supply in Bangladesh ;• A major public health concerns; thousands of patients with visible A major public health concerns; thousands of patients with visible
symptoms; likely impacts on food security; symptoms; likely impacts on food security; • A large number of mitigations options are available, DTW has been
the most effective one;• Still millions are exposed to arsenic above current BD limit (50 ppb),
number almost doubles if WHO provisional guide line value (10 ppb) is considered;
• Targeted efforts are necessary to provide safe water to all who are still drinking water having As above safe limits;
• Impacts of As on Irrigation and food security need special attention.
Thank you all!
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