| Properties :
Arsenic is a metalloid widely
distributed in the earth?s crust and present at
an average concentration of 2 mg/kg. It occurs
in trace quantities in all rock, soil, water and
air. Arsenic can exist in four valency states
: -3, 0, +3 and +5. Under reducing conditions,
arsenite (As(III)) is the dominant form; arsenate
(As(V)) is generally the stable form in oxygenated
environments. Elemental arsenic is not soluble
in water. Arsenic salts exhibit a wide range of
solubilities depending on pH and the ionic environment.
Sources and occurrence
of arsenic in the environment
:
Arsenic is present in more than 200 mineral species,
the most common of which is arsenopyrite.
It has been estimated that about one-third of
the atmospheric flux of arsenic is of natural
origin. Volcanic action is the most important
natural source of arsenic, followed by low-temperature
volatilization.
Inorganic arsenic of geological origin is found
in groundwater used as drinking-water in several
parts of the world, for example India and Bangladesh.
Organic arsenic compounds such as arsenobetaine,
arsenocholine, tetramethylarsonium salts, arsenosugars
and arsenic-containing lipids are mainly found
in marine organisms although some of these compounds
have also been found in terrestrial species.
Elemental arsenic is produced by reduction of
arsenic trioxide (As2O3)
with charcoal. As2O3 is
produced as a by-product of metal smelting operations.
It has been estimated that 70% of the world arsenic
production is used in timber treatment as copper
chrome arsenate (CCA), 22% in agricultural chemicals,
and the remainder in glass, pharmaceuticals and
non-ferrous alloys.
Mining, smelting of non-ferrous metals and burning
of fossil fuels are the major industrial processes
that contribute to anthropogenic arsenic contamination
of air, water and soil. Historically, use of arsenic-containing
pesticides has left large tracts of agricultural
land contaminated. The use of arsenic in the preservation
of timber has also led to contamination of the
environment.
Environmental levels and
human exposure :
Mean total arsenic concentrations in air from
remote and rural areas range from 0.02 to 4 ng/m3.
Mean total arsenic concentrations in urban areas
range from 3 to about 200 ng/m3; much
higher concentrations (> 1000 ng/m3)
have been measured in the vicinity of industrial
sources, although in some areas this is decreasing
because of pollution abatement measures. Concentrations
of arsenic in open ocean seawater are typically
1-2 mg/litre.
Arsenic is widely distributed in surface freshwaters,
and concentrations in rivers and lakes are generally
below 10 mg/litre,
although individual samples may range up to 5
mg/litre near anthropogenic sources. Arsenic levels
in groundwater average about 1-2 mg/litre
except in areas with volcanic rock and sulfide
mineral deposits where arsenic levels can range
up to 3 mg/litre. Mean sediment arsenic concentrations
range from 5 to 3000 mg/kg, with the higher levels
occurring in areas of contamination. Background
concentrations in soil range from 1 to 40 mg/kg,
with mean values often around 5 mg/kg. Naturally
elevated levels of arsenic in soils may be associated
with geological substrata such as sulfide ores.
Anthropogenically contaminated soils can have
concentrations of arsenic up to several grams
per 100 ml.
Effects on human health :
Soluble inorganic arsenic
is acutely toxic, and ingestion of large doses
leads to gastrointestinal symptoms, disturbances
of cardio-vascular and nervous system functions,
and eventually death. In survivors, bone marrow
depression, haemolysis, hepatomegaly, melanosis,
polyneuropathy and encephalopathy may be observed.
Long-term exposure to arsenic in drinking-water
is causally related to increased risks of cancer
in the skin, lungs, bladder and kidney, as well
as other skin changes such as hyperkeratosis and
pigmentation changes. These effects have been
demonstrated in many studies using different study
designs. Exposure-response relationships and high
risks have been observed for each of these end-points.
The effects have been most thoroughly studied
in Taiwan but there is considerable evidence from
studies on populations in other countries as well.
Increased risks of lung and baldder cancer and
of arsenic associated skin lesions have been reported
to be associated with ingestion of drinking-water
at concentration ?
50 mg
arsenic/litre.
Occupational exposure to arsenic, primarily by
inhalation, is causally associated with lung cancer.
Exposure-response relationships and high risks
have been observed. Increased risks have been
observed at cumulative exposure levels ?
75 mg
(mg/m3), year (e.g. 15 years of exposure
to a workroom air concentration of 50 mg/m3).
Tobacco smoking has been investigated in two of
the three main smelter cohorts and was not found
to be the cause of the increased lung cancer risk
attributed to arsenic; however, it was found to
be interactive with arsenic in increasing the
lung cancer risk.
Even with some negative findings, the overall
weight of evidence indicates that arsenic can
cause clastogenic damage in different cell types
with different end-points in exposed individuals
and in cancer patients. For point mutations, the
results are largely negative.
Chronic arsenic exposure in Taiwan has been shown
to cause blackfoot disease (BFD), a severe form
of peripheral vascular disease (PVD) which leads
to gangrenous changes. However, there is good
evidence from studies in several countries that
arsenic exposure causes other forms of PVD.
Conclusions on the causality of the relationship
between arsenic exposure and other health effects
are less clear-cut. The evidence is strongest
for hypertension and cardiovascular disease, suggestive
for diabetes and reproductive effects and weak
for cerebrovascular disease, long-term neurological
effects, and cancer at sites other than lung, bladder,
kidney and skin.
Global Scenario :
Occurrence of? Arsenic in
ground water has been reported from various parts
of United States? of? America, Alaska, Arizona,
California, Oregon, Nevada, Idaho and Washington
and some other? such areas.
In? the South East port of Hungary,? drinking
water wells were contamination with arsenic in
concentration high enough to pose long term health
hazard to about 4 lakh? persons.? Such contamination
is believed to be arising from leaching? of rocks
containing Arsenic by the percolating? water.
In Autofagasta, Chili, a? large number of? children
were affected from Arsenic contamination in ground
water in 1960 through leaching of arsenical wastes
from mining operations into spring water. Arsenic
contamination of streams and Wells has been reported
from OBUSI gold mine area of?Ghana. Arsenic has
been found to be accumulated in the soils of extensive
areas of Audean mountain. Argentina and Chili
found to be affected badly.
Calcinating furnances from a refinery in Taroku
village on?the?Island of?Kyushu in Japan sterted
liberating? Arsenite and Sulphaer Dioxide during
1920.? The environment was polluted? to such an
extent that there were sick people in every house.?
It was only in 1971 that the Toroku episode??
was known and in? 1973 steps were taken to stop
the furnances.? In north of? Chilli, Arsenic occurs
naturally.? In Taiwan Arsenic contamination of?
ground water was reported in 1967 and a large
number of people?suffered from Arsenical dermatosis.
From Trans_baikalie province? of Russia and also?
New Zealand, Arsenic contamination of ground water
has been reported. Arsenic pollution in ground
water is a problem in many countries of the?Globe.
The affected? Countries? required decades to?
ascertain the cause in some cases.
Occurrence in West Bengal :
Areas identified as Arsenic
Affected as on 31/03/2004
6148 Habitations & 18 Non-Municipal urban areas[NMOG] (in
76
Blocks of 8 Districts)
Population at risk 28 million
Arsenic Affected Blocks of West Bengal :
|
District : MALDAH |
|
Blocks |
| 1 |
Manikchak |
| 2 |
English Bazar |
| 3 |
Kaliachak-I |
| 4 |
Kaliachak-II |
| 5 |
Kaliachak-III |
| 6 |
Ratua-I |
| 7 |
Ratua-II |
| District : MURSHIDABAD |
| Blocks |
| 8 |
Beldanga-I |
| 9 |
Noada |
| 10 |
Hariharpara |
| 11 |
Domkal |
| 12 |
Berhiarpara |
| 13 |
Jalangi |
| 14 |
Murshidabad Jiaganj |
| 15 |
Raninagar-I |
| 16 |
Raninagar-II |
| 17 |
Bhagawangola-I |
| 18 |
Bhagawangola-I |
| 19 |
Farakka |
| 20 |
Suti-I |
| 21 |
Suti-II |
| 22 |
Raghunathganj-II |
| 23 |
Shamsherganj |
| 24 |
Lalgola |
| 25 |
Beldabga-II |
|
District : NADIA |
| Blocks
|
| 26 |
Santipur |
| 27 |
Chakadha |
| 28 |
Hanskhali |
| 29 |
Ranaghat-I |
| 30 |
Ranaghat-II |
| 31 |
Haringhata |
| 32 |
Kaliganj |
| 33 |
Krishnaganj |
| 34 |
Karimpur-I |
| 35 |
Karimpur-II |
| 36 |
Nakashipara |
| 37 |
Nabadwip |
| 38 |
Chapra |
| 39 |
Tehatta-I |
| 40 |
Tehatta-II |
| 41 |
Krishnanagar - I |
| 42 |
Krishnanagar - II |
|
 |
| District : NORTH 24-PARAGANAS |
| Blocks |
| 43 |
Habra-I |
| 44 |
Habra-II |
| 45 |
Barasar-I |
| 46 |
Barasat-II |
| 47 |
Amdanga |
| 48 |
Deganga |
| 49 |
Rajarhat |
| 50 |
Bagda |
| 51 |
Bongaon |
| 52 |
Gariahat |
| 53 |
Baduria |
| 54 |
Haroa |
| 55 |
Swarupnagar |
| 56 |
Hasnabad |
| 57 |
Sandeshkhali-II |
| 58 |
Basirhat-I |
| 59 |
Basirhat-II |
| 60 |
Barrackpur-I |
| 61 |
Barrackpur-II |
|
| District : SOUTH 24 PARGANAS |
| Blocks |
| 62 |
Baruipur |
| 63 |
Bhangar-I |
| 64 |
Bhangar-II |
| 65 |
Bishnupur-I |
| 66 |
Bishnupur-II |
| 67 |
Sonarpur |
| 68 |
Budge Budge-II |
| 69 |
Jaynagar-I |
| 70 |
Magrahat-II |
| District : BARDDHMAN |
| Blocks |
| 71 |
Purbasthali - I |
| 72 |
Purbasthali - II |
| District : HAORA |
| Blocks |
| 73 |
Uluberia-II |
| 74 |
Shyampur-II |
| District : HUGLI |
| Blocks |
| 75 |
Balagarh |
|
Sub-Surface Lithological Correlations :
| District North 24 Parganas |
District Malda |
Nadia & 24-Parganas |
 |
 |
 |
| District Bardhaman |
District South 24 Parganas |
District Nadia |
 |
 |
 |
| District Murshidbad |
District Hugli |
|
 |
 |
|
|
