Arsenic Contamination in Bangladesh: A look into how arsenic enters the groundwater

1
Arsenic Contamination
in Bangladesh A look
into how arsenic enters the groundwater

• Kate Butler
• Environmental Forensics
• April 27th, 2004

2
Introduction

• The groundwater contamination of arsenic in
  Bangladesh is considered one of the largest mass
  poisonings in the world. Since the 1970s, the
  people have been drinking and cooking with well
  water that exceeds the permissible arsenic limit.
  As of now, there is no determined source of the
  arsenic or method of contamination. This makes
  it difficult to resolve the problem. This
  presentation will highlight key factors in the
  arsenic case study as well as give a detailed
  discussion for possible mechanisms of the release
  of arsenic in groundwater.

3
What Is Arsenic?

• Natural and abundant element found in soil, air,
  and water
• Solubility
• Insoluble in water when in natural form
• Soluble in water when oxidized
• More toxic in this form
• Most likely to form compounds with oxygen,
  chlorine, sulfur, carbon, hydrogen, lead, gold,
  and iron
• 2 types
• Inorganic usually with oxygen, chlorine, or
  sulfur most toxic (ex. arsenite)
• Organic usually with carbon or hydrogen (ex.
  di-methyl arsonic acid)

Arsenite
Di-methyl arsonic acid
www.chemfinder.com
4

• Arsenic pollution is mainly the result of natural
  geological processes (ex. Natural mineral
  weathering)
• Most dangerous when orally consumed
• Harmful effects depend on arsenics chemical and
  physical form
• Known carcinogen
• Natural Concentrations
• Rock 1.5 2.0 mg/kg
• Contaminated Soil Up to 500 mg/kg
• Natural Water 1 2 mg/kg
• Safe Intake Rates for Humans
• Approximately 150 ug/kg/day for an average,
  healthy person
• Some sensitive people can see side effects at 20
  ug/kg/day
• Arsenic Intake Limits
• EPA has a Maximum Concentration Limit (MCL) of 20
  ug/L
• World Health Organization (WHO) has a limit of 10
  ug/L

Medical Information Group, Dhaka Medical
College www.angelfire.com/ak/medinet/intro.html
www.dchtrust.org/arsenic20pollution20in20grou
ndwater.htm
5
Bangladesh Background

• Deltaic country located northeast of India in the
  Bengal basin
• Major rivers deposit sediments into Bangladesh
• Ganges, Brahmaputra, Meghna, and Teesta
• Area of 148,393 km2
• Population of 120 million (20.1 urban, 79.9
  rural)
• 64 districts
• 97 of the population use tube-well water

www.dchtrust.org/arsenic20pollution20in20grou
ndwater.htm www.engr.uconn.edu/faisal/research/
ars_gis.html
6
History of Arsenic Contamination

• During the 1970s, tube-wells were dug all over
  the country
• A solution to contaminated surface water that was
  causing cholera and typhoid
• Tube-wells became the main source for
  drinking/cooking water
• Over 4 million wells were dug
• In 1992, the British Geological Survey (BGS)
  analyzed about 150 wells to test the purity of
  the water
• Did not test for arsenic
• In 1997, scientists from India re-tested the
  wells for arsenic and found the water to be
  contaminated
• The government had the safe wells painted green
  and the contaminated wells painted red until a
  solution was found
• Many wells, when retested years later, were found
  to be marked the wrong color
• Poor testing kits

Pearce, Fred. Poisoned Wells Is the British
Geological Survey Responsible for a massive
arsenic poisoning in Bangladesh?. The Boston
Globe. June 3rd, 2003. health.nzoom.com/health_
detail/0,2811,219603-399-403,00.html
www.ozgreen.org.au/WWD/arsenic_poisoning_in_bangla
desh.htm
7
Statistical Results of Arsenic Poisoning

• Districts tested for Contamination 64
• Districts with arsenic above 0.01 mg/L 54
• Districts with arsenic above 0.05 mg/L 47
• Districts surveyed for arsenicosis patients 32
• Districts found with patients 30
• Out of 210 villages
• 83.15 of hair samples were above toxicity limit
• 93.77 of nail samples were above toxicity limit
• Population at Risk 62
• Number of Known Patients 7,000
• Number of Tube-wells 4 million
• Number of Affected Tube-wells 1.12 million

www.nvo.com/ghosh_research/arseniccontaminationi
nthebengalbasin1/ www.engr.uconn.edu/faisal/res
earch/ars_gis2.html Basu, Gautam. Ground Water
Arsenic Contamination in Bangladesh. Jadavpur
University, April 2000, p. 8-10.
8
Medical Effects of Arsenic

• Arsenic poisoning is called arsenicosis
• Mode of testing people for arsenicosis
• Recent exposure urine
• Instant exposure blood
• Chronic exposure hair, nails, and skin (usually
  caused by water contamination)
• Illnesses resulting from arsenicosis
• Various cancers skin, lung, bladder, kidney,
  liver
• Heart attacks and strokes
• Melanosis spotting of the skin, blemishes, etc.
• Keratosis hardening of palms and soles, ulcers
• Hepatomegaly liver enlargement
• Splenomegaly spleen enlargement
• Ascitis abdominal fluid
• Death
• Social Problems
• Arsenicosis victims are rejected from society

Basu, Gautam C., et al. Groundwater Arsenic
Contamination in Bangladesh and West Bengal,
India. Environmental Health Perspectives. Vol.
108, May 2000. www.dchtrust.org/arsenic20pollut
ion20in20groundwater.htm
9
Arsenicosis Pictures
Severe keratosis www.siliconeer.com/past_issues/
2000/may2000.html
Squamous cell carcinoma aquaticpath.umd.edu/appl
iedtox/chowdhury-full.html
Hyperkeratosis aquaticpath.umd.edu/appliedtox/ch
owdhury-full.html
Skin cancer geoenv.hp.infoseek.co.jp/Presen/Intr
o/intro01-jprg.html
10
Source of Arsenic

• The source and method of arsenic entering the
  groundwater is a controversial issue and has yet
  to be determined
• Possible sources
• Naturally eroded from the Himalayas by the Ganges
  River over 20,000 years ago
• Sediments migrate from the 4 main rivers in
  Bangladesh
• Sediment deposition during the Quaternary Period,
  also known as the Younger Deltaic Deposition
  (25,000 to 80,000 years ago)
• Geological processes weathering, erosion,
  sedimentation
• Agriculture use, irrigation, and fertilizers

www.bangladesh.net/article_bangladesh/health/hlt
_05_arsenicosis_how_pollution_spreads.htm
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Oxidation of Arsenic Pyrites or Ferrous Hydroxides

• Arsenopyrite and ferrous hydroxide
• Arsenic rich
• Stable in a reducing environment (under the water
  table)
• Concentrated in organic deposits
• When oxidized, arsenic is released and adsorbed
  onto iron hydroxide
• Cause of Oxidation
• Lowering of the water table below the organic
  deposits
• Result of dry seasons, pumping of wells, and dams
  built in the 1970s
• Release of Poisonous Arsenic
• During recharge, the arsenic adsorbed onto iron
  hydroxide returns to the reduced environment
  under the water table
• The arsenic is released and reduced to a toxic
  form

Arsenopyrite
Iron Hydroxide
www.fabre-minerals.com/specimens/15-oliete-colle
ction-mineral-specimens.php www.geology.reab.net
/pictures/indx0010.htm Bridge, Thomas., et al.
Groundwater Arsenic Poisoning and a Solution to
the Arsenic Disaster in Bangladesh
www.eng-consult.com/arsenic/article/meerarticle5.h
tml
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Oxidation of Arsenic Pyrites or Ferrous Hydroxides

• Iron pyrite, FeS2
• Oxidation of Iron Pyrite
• Found in sediment layers
• Decomposes into oxides of iron, sulfuric acid and
  arsenic
• Arsenic is available, but in non-toxic form
• During recharge, sediments return to the reduced
  environment under the water table
• Non-toxic oxides of arsenic are reduced to toxic
  forms

2 FeS2 7 O2 2 H2O
2 Fe2 4 SO42- 4 H
4 Fe2 O2 4 H
4 Fe3 2 H2O
4 Fe3 12 H2O
4 Fe(OH)3 12 H
FeS2 14 Fe3 8 H2O
15 Fe2 2 SO42- 16 H
www.sos-arsenic.net/english/natural_origin/india
.html Bridge, Thomas, et al. The Increased
Drawn Down and Recharge in Groundwater Aquifers
and their Relationship to the Arsenic Problem in
Bangladesh
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Oxyhydroxide Reduction

• Reduction of arsenic in oxyhydroxides that have
  been present since the YDD
• Organic matter deposited in the sediments reduce
  the arsenic adsorbed on the oxyhydroxides and
  releases arsenic into the groundwater
• Dissolution occurs during recharge
• Caused by microbial oxidation of the organic
  matter as bacteria dissolves surrounding oxygen
• Arsenic is naturally transported and adsorbed
  onto fine-grained iron or manganese oxyhydroxides
• Highest arsenic concentrations are usually found
  in fine-grained sediments
• Aerobic bacteria activities
• Oxidizes arsenite to arsenate

Volcanic sediment covered in arsenic rich iron
oxyhydroxide
2 H3AsO3 O2
HAsO4- H2AsO4- 3 H
Iron oxyhydroxide rich streambeds
Bridge, Thomas., et al. Groundwater Arsenic
Poisoning and a Solution to the Arsenic Disaster
in Bangladesh www.eng-consult.com/arsenic/artic
le/meerarticle5.html chuma.cas.usf.edu/pichler/
images/Photo_Gallery/Feni_Images/31.html
www.nbmg.unr.edu/slides/eim/15.htm
14
Conclusion

• Further analyses are needed since neither method
  of arsenic release has proven to be correct
• Possible Solutions
• Restore the water by tearing down some dams and
  decreasing irrigation
• Dig deeper wells
• Research medical relief for those already
  affected
• An antioxidant, composed of vitamins and
  minerals, is in the making