Transcript Groundwater Arsenic Contamination in Bangladesh

Groundwater Arsenic
Contamination in Bangladesh
Nadiah Mohd Nordin
Erica Islas
Arsenic Contamination in
Bangladesh
 By the late 1980s surface water was the main source of
drinking water.
 Unfortunately, it was severely polluted
 So the government, UNICEF and a few other groups
decided that they should use groundwater as an
alternative.
 Ironically, the installations of tube wells triggered the
naturally occurring arsenic that already existed in the
earth to dissolve into the drinking water.
 The arsenic that was present in the water was colorless,
tasteless and odorless, therefore people did not realize
that their drinking water was contaminated by arsenic
until there was a widespread of people suffering from
various diseases, such as warts, skin lesions, and
cancers.
Causes of Arsenic Contamination in
Bangladesh
 Pyrite Oxidation Hypothesis
 Arsenic is assumed to be
present in certain sulphide
minerals (pyrites) that are
deposited within the aquifer
sediments. Due to the
lowering of water table below
deposits, arseno-pyrite
oxidized in the vadose zone
releases arsenic as arsenic
adsorbed on iron hydroxide.
During the subsequence
recharge period, iron
hydroxide releases arsenic
into groundwater. According to
this hypothesis, the origin of
arsenic rich groundwater is
man-made, which is a recent
phenomenon.
Continued...
 Oxy-hydroxide Reduction Hypothesis
Arsenic is assumed to be present in alluvial
sediments with high concentrations in sand grains
as a coating of iron hydroxide. The sediments were
deposited in valleys eroded in the delta when the
stream base level was lowered due to the drop in
sea level during the last glacial advance. The
organic matter deposited with the sediments
reduces the arsenic bearing iron hydroxide and
releases arsenic into groundwater. According to this
hypothesis, the origin of arsenic rich groundwater is
due to a natural process, and it seems that the
arsenic in groundwater has been present for
thousands of years without being flushed from the
delta.
Arsenic in Nature
 Rock contains 1.5-2.0 milligram of arsenic per kilogram. But, in
contaminated soil, concentration of arsenic may be up to 500 mg/kg.
 Arsenic content of natural water may be up to 1-2 g/L.
 Most fruits, vegetables, meats and fishes contain arsenic; but
arsenic levels in sea water and sea fishes are higher. Sea fish may
contain 5 mg of arsenic per kg weight.
 An intake of 150 microgram of arsenic per day should not cause any
harmful effect to human being, but very sensitive person often
becomes sick with as low as 20 microgram of arsenic a day
Chemistry of Arsenic
 H2AsO4- + 3H+ + 2eH3AsO3 + H2O
 In the environment, arsenic can occur in several
oxidation states (-3, 0, +3, +5)
 In natural waters, arsenic is mostly found in inorganic
form as oxyanions of trivalent arsenite [As(lll)] or
pentavalent arsenate [As(V)].
 As(lll) is more toxic (40-60 times) than As(V)
 As(lll) exists in most natural water as As(OH)3 (pKa =
9.2) and is more mobile than As(V) because it is less
strongly absorbed on most mineral surfaces than the
negatively charged As(V) oxyanions (H3AsO4; pKa =
2.22, 6.98, 11.53).
 However, it is widely believed that arsenate is the major
water-soluble species in groundwater because arsenite
is usually prevalent in anaerobic conditions.
What makes Arsenic Unique as a
Contaminant?
 Most toxic trace metals occur in solution as cations (e.g. Pb2+, Ni2+,
Cd2+) which become insoluble as the pH increases.
 However, arsenate, like most oxyanions, tend to become less strongly sorbed as
the pH increases.
 As a result, arsenic anions can persist in solution at relatively high concentrations
(tens of g l-1) even at near-neutral pH values.
 Arsenic is problematic in the environment due to its relative mobility
over a wide range of natural processes, such as:




Weathering reactions
Biological activity
Volcanic emissions
Range of anthropogenic activities
 Arsenic is also distinct by becoming relatively mobile under reduced
conditions. Its oxyanions can be found at concentrations in the mg l-1
range when all other oxyanion-forming elements are present in the
g l-1 range. Example:
 Selenium is mobile as selenate (SeO42-) oxyanion under oxidising conditions, but
immobilized under reducing conditions.
 Chromium behaves like other trace cations (i.e. is relatively immobile at nearneutral pH values) under reducing environments.
Arsenicosis: Toxic Effects of Arsenic
in Humans
 Arsenic is a poison and its lethal dose for human is 125
milligram.
 It is 4 times as poisonous as mercury.
 Toxicity depends on the amount of arsenic intake, which
is classified into acute, sub-acute and chronic toxicity
respectively. Drinking water contamination causes the
last variety of toxicity.
 Most of the ingested arsenic is excreted from the body
through urine, stool, skin, hair, nail and breath. In
excessive intake, some amount of arsenic is deposited in
tissues and inhibits cellular enzyme activities.
 Almost all organs are affected; but clinical symptoms
appear insidiously after 6 months to 2 years or more
depending upon the amount of arsenic intake.
Arsenic Toxicity in Different Organ
Systems
Organ System
Problems
Skin
Symmetric hyperkeratosis of palms and soles, melanosis or
depigmentation, bowen's disease, basal cell carcinoma and
squamous cell carcinoma.
Liver
Enlargement, Jaundice, cirrhosis, non-cirrhotic portal
hypertension
Nervous System
Peripheral neuropathy, hearing loss
Cardiovascular System Acrocyanosis and Raynaud's Phenomenon
Hemopoietic System
Megalobastosis
Respiratory System
Lung Cancer
Endocrine System
Diabetes mellitus and goiter
Effects on human health
 Cancer
 Melanosis
 Hyperkeratosis
Clinical Feature of Arsenicosis observed
in Bangladesh
PRE-CLINICAL
STAGE
No clinical
manifestation
INITIAL
STAGE
Melanosis,
keratosis,
conjunctivitis,
bronchitis,
gastroenteritis
SECOND
STAGE
Depigmentation
(leucomelanosis),
hyperkeratosis,
non-pitting edema
of legs, peripheral
nephropathy,
hepatopathy
LAST
STAGE
Nephropathy,
hepatopathy,
gangrene,
cancer of
skin, bladder
and lung
• In Bangladesh, majority of patients are in initial and second stages
Treatment for Arsenicosis
 Unfortunately there is no specific treatment for chronic arsenicosis.
Stopping further intake of arsenic contaminated water and drinking arsenicfree water improves the cases.
 A recent report of DCH (2000) states that chronic arsenicosis cannot be
cured, but the symptoms are reversible up to certain point if a patient
discontinues ingesting contaminated water.
 Chelation therapy helps relief of symptoms and improves clinical manifestations.
 D-penicillamine (250 mg 3-4 times a day for 3 months)
 Dimercapto succinic acid (10 mg/kg body weight daily for 7 days followed by 10 mg/kg
body weight thrice daily for 14 days)
 Dimercapto procane sulphonate (100 mg 3-4 times a day every alternate weeks up to 3
such courses).
 Vitamins:
 Vitamin A- 50,000 i.u. daily, Vitamin E- 200 mg daily and Vitamin C- 500 mg daily for
adults.
 Symptomatic treatments, viz. antihistamines, local ointments, etc.
 Nutritious diets.
 If a patient crosses this threshold, he/she still needs medical assistance to
save his/her life. For instance, amputation may save the life of a patient
suffering from gangrene. Palliative drugs may also be administered along
with micronutrient supplement.
In Bangladesh, following de-arsination
methods are used:
 Arsenic Removal Chemical Method
 Developed by the Department of Occupational and Environmental
Health of NIPSOM, which is based on the principle of iron coagulation
with a pre-oxidation step. Removal of arsenic by this method is almost
99%.
 Alum Method
 This cheap method allows 70% removal of arsenic. 300-500 grams of
alum wrapped in a clean cloth is sinked in a bucket full of arsenic
contaminated water for 12 hours. Upper 2/3rd of the water is separated
using decantation or two layered clean cloth. Lower third of water
contains arsenic and not suitable for drinking.
 Ferric oxide-manganese dioxide clay based filter columns
 This earthen column packed with the above substances is attached to
the tube well outlet. The method is claimed to remove significant
amount of arsenic at the water flow rate of 90-110 mL/minute and the
system can filter up to 5000 L of water before disposal.
Control Measures Taken by
Government of Bangladesh
 Short Term Programs
 Conduct survey to detect problem prone population group who is
drinking arsenic contaminated water.
 Detect arsenicoses patients
 Provide treatment to arsenicoses patients and ensure follow-ups.
 Create alternate source of drinking water in problem prone areas.
Distribute de-arsination filters and digging deep tube wells. Encourage
people use alum to de-arsinate contaminated water.
 Create laboratory facilities for quantitative analysis of arsenic and
determine its toxicity levels in humans.
 Conduct training courses for officers and staff in the health services.
 Conduct national survey to identify new problem prone areas.
 Conduct appropriate health education campaigns.
 Create outpatient services for detection and treatment of arsenicoses
patients throughout the country.
 Build communications programs with national and international
organizations for collaboration in the control measures.
Continued...
 Long Term Programs
 Find out causes of arsenic contamination of soil water, identify sources
and take control measures.
 Create a Surveillance Team starting from grass-root level up to the
central level to identify, treat, follow up and conduct water-testing
activities.
 Establish 10-bed arsenic hospitals in the affected districts with a view to
provide treatment to the complicated patients and also conduct
research.
 Launch a national training course for the health personnel and staff.
 Find out long term alternate source of safe drinking water.
 Launch effective water management scheme for encouraging people
ensure rational use of ground water.
 Include media people in the prevention of arsenic contamination
program.
 Develop necessary information, education and communication (IEC)
materials to enhance awareness of the people.