.
Arsenic is a semi metal with atomic no.
33
.
It is odourless and tasteless, and is
naturally occurring in rocks and soil.
.
Arsenic can be combined with other
elements to make chemicals that are
used to preserve wood or as insect
killers on cotton crops.
.
Organic arsenic which is mainly found
The arsenic that concerns scientists is inorganic
arsenic that pollutes the groundwater. Despite
its high toxicity, inorganic arsenic occurs
naturally on earth in small amounts.
Inorganic arsenic is a known and documented
carcinogen, leading to skin, lung, liver, bladder,
kidney, and prostate cancer.
Inorganic arsenic is one of the most toxic
The undesirable change in the
chemical,biological and physical quality of
water due to the presence of arsenic leading
to its degradation and detoriation and
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
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
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
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
H
2
AsO
4-+ 3H
++ 2e
-H
3AsO
3+ H
2O
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 (H
3AsO
4; pKa = 2.22, 6.98, 11.53).
However, it is widely believed that arsenate is the major
Most toxic trace metals occur in solution as cations (e.g. Pb
2+, Ni
2+,
Cd
2+) 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
-1range when all other oxyanion-forming elements are
present in the
g l
-1range. Example:
Selenium is mobile as selenate (SeO
42-) oxyanion under oxidising conditions, but
immobilized under reducing conditions.
Chromium behaves like other trace cations (i.e. is relatively immobile at
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
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
Cancer
Melanosis
PRE-CLINICAL STAGE INITIAL STAGE SECOND STAGE LAST STAGE No clinical manifestation Melanosis, keratosis, conjunctivitis, bronchitis, gastroenteritis Depigmentation (leucomelanosis), hyperkeratosis, non-pitting edema of legs, peripheral nephropathy, hepatopathy Nephropathy, hepatopathy, gangrene, cancer of skin, bladder and lung
•
A symptom is felt by the sufferer and described to the
doctors, such as pain or dizziness, while a sign is noticed
by other people too. Examples of signs include a rash,
pallor, or swelling.
If the arsenic has been ingested orally, the first signs and
symptoms of arsenic poisoning will appear within thirty
minutes, and may include some of the following:
drowsiness
•
headaches
•
confusion
•
terrible diarrhea
headaches
confusion
Please note that if the arsenic has been inhaled, or a less concentrated amount has been ingested, symptoms may take longer to emerge. As the arsenic poisoning develops, the patient may start suffering convulsions and their fingernail pigmentation may change (leukonychia).
The following signs and symptoms are associated in more severe cases of arsenic poisoning: metallic taste in the mouth
mouth produces excess saliva problems swallowing
blood in the urine cramping muscles loss of hair
stomach cramps convulsions
excessive sweating
breath smells like garlic vomiting
Unfortunately there is no specific treatment for chronic arsenicosis.
Stopping further intake of arsenic contaminated water and drinking arsenic-free 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
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
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
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
World Health Organization -
http://www.who.int/mediacentre/factsheets/fs
210/en/index.html
USGS -
http://www.usgs.gov/nawqa/trace/arsenic/
US EPA -
http://www.epa.gov/safewater/arsenic/index.h
tml
CDC -
http://www.cdc.gov/ncidod/dpd/healthywater/f
actsheets/pdf/arsenic.pdf
