Arsenic is known as 'Senko Bish' among the Bengali-speaking people. This is also used in the Bengali books of medical science.

The use of Arsenic as a deadly poison has been known since long long years back. After winning the war of Waterloo, the British force reportedly used Arsenic to kill French Emperor Napoleon Bonaparte who was in exile at St. Helena island. After his death on may 5, 1821, it was announced that Napoleon died in stomach cancer. But many people though that the Englishmen applied slow poisoning to kill Napoleon.

The British people denied the allegation. But after many years, the hair of the French Emperor, reserved at a, museum, was tested and it was proved that he was killed by poison and the name of poison is Arsenic. Arsenic was found in Napoleon's hair 13 times more than the normal level.

Arsenic is a crystal-shape metalloid element, which is brittle in nature and gray of tin white in color. Arsenic is a Group V element in the periodic chart with its atomic number is 33 and atomic weight 74.92.

Arsenic cannot be found in nature as a free element. It exhibits a broad range of chemical reactivity with an ability to form alloys with other elements and covalent bonds. Arsenic participates readily in oxidation-reduction– methylation- demethylation and acid base reactions.

Arsenic can not only create compounds with oxygen, chlorine, sulfur, carbon and hydrogen, but also with lead, mercury, gold and iron. It mainly remains as oxide, hydrate, sulfide, Arsenate and Arsenate. Gold, silver, copper, zinc, iron and other metals exist with Arsenic in these chemical comical compounds.

As many as 150 species of Arsenic bearing minerals exist in the earth. But only three of them are considered as Arsenic ore. Because, the amount of Arsenic id higher in these three compounds. Moreover, they are more available than other Arsenic compounds. These tree compounds are Reagan of Arsenic disulfide (As₂ S₂ ) orpiment or Arsenic disulfide (As₂S₃ ) and arsenopyrite or fetus Arsenic sulfide (Feasts). There are differences in the physical properties of these three types of Arsenic minerals. But a common feature of them is a garlic like odor. Arsenopyrite has been primarily identified as the main source of Arsenic pollution in the Groundwater of Bangladesh and West Bengal. When arsenopyrite oxidizes and mixes with water no smell is found in the water. Arsenic burns in air giving off an odor of garlic and dense white fumes of Arsenic trioxide.

Chemically Arsenic compounds are two types inorganic and organic Arsenic inorganic Arsenic are divided into two types-trivalent and pentavalent  Arsenic are more toxic than the organic ones. The trivalent Arsenic is 60 times more toxic than pentavalent Arsenic. Trivalent Arsenic compounds are known as Arsenic and the pen types of Arsenic acid. But in the groundwater Arsenic predominantly occurs in the tri and pentavalent form. These two were found in the groundwater of Bangladesh and West Bengal.

The name of some inorganic Arsenic compounds can be mentioned here- arsonous oxide or Arsenic trioxide (As₂ O₃) sodium arsenate (Na₃AsO₃) potassium arsenate (K₃AsO₃), copper arsenate (CuHAsO₃) , copper acetoarsenite, Arsenic acid (H₃AsO₄) sodium arsenate (Na₃AsO₄) potassium arsenate (K₃AsO₄). Arsenic disulfide or railcar, orpiment or Arsenic disulfide, arsenopyrite, arsine (AsH₃), Arsenic trioxide (Asl₂) etc. Organic Arsenic compounds include monomethyl Arsenic acid, diethyl Arsenic acid or acetylic acid, sodium caboodle, ataxia, sterol, sulpharsinamine etc.
 

Presence of Arsenic in Environment

Arsenic is a ubiquitous element being widely distributed in the earth. Nature itself is an adequate source of Arsenic. According to availability of natural elements in environment, the position of Arsenic is 20^th.

Arsenic is found in atmosphere, in the aquatic environment, in soils and sediments and in organisms. Different minerals of Arsenic are mixed with underground rock the Arsenic contents of the earth crust in 1.5 -2 mg/kg. However, Arsenic upto 550 mg can prevail in per kg polluted soil. Arsenic poison can spared in air from the industrial wastes. Generally, per liter natural water contains 1-2 microgram of Arsenic.

Trace quantity of Arsenic is also found in most of the fruits, vegetables, fish and meat. But high level of Arsenic exists in sea water. Food of marine origin are much richer in Arsenic than other foods. Arsenic unto 5 milligram can be found in per kilogram of sea fish. It means, human being are receiving some amount of Arsenic through air food. and drinks everyday. But the Arsenic doesn't cause damage of human bodies, as its extent is very minimum. The Arsenic its poisonous effect is low in comparison to inorganic Arsenic. Usually, a man can receive Arsenic upto 150 microgram for per kilogram weight of his or her body without any efface. But, sensitive individual may fall sick for only 20 microgram Arsenic.

There are a lot of Arsenic in earth's bio-mass. Arsenic also exists in lava of volcano. Geothermal system and uranium and gold mines are sources of the Arsenic. It occurs in the air in areas where coal is burnt, particularly near smelters and refineries.
 

Uses of Arsenic

Arsenic compounds are mainly used in agriculture, forestry and industrial processes. Arsenic tri-oxide is used in manufacturing of agricultural chemicals (pesticides), glass and glassware, industrial chemicals, copper and lead alloys and pharmaceuticals.

In agriculture, Arsenic compounds such as lead arsenate, copper aceto arsenite, sodium Arsenate, calcium Arsenate and organic Arsenic compounds are used as pesticides. Substantial amount of methyl Arsenic acid and diethyl Arsenic acid are used as selective herbicides.

Chromate copper arsenate, sodium Arsenate and zinc arsenate are used wood preservatives. Some phenyl Arsenic compounds such as arsenal acid are used as feed additives for poultry and swine.

Small amount of Arsenic compounds continue to be used as drugs in some countries. As medicine Arsenic is used since the fifth century BC when Hypocrites recommended the use of an Arsenic sulfide for the treatment of abscess. Arsenic preparation was used for the treatment of skin disorder, tuberculosis, leukemia, asthma, leprosy, syphilis, amoebic dysentery etc. Homeopaths are also using Arsenic as drug.

Besides Arsenic is used in the preparation at dyes, poisonous gas, transistor, as a component of semiconductor, as a preservative in tanning and in the industry of textile, paper etc.
 

Extensity of Arsenic Contamination

The Arsenic pollution problem took a severe shape in present world. The pollution has been spread more or less in every continent. It occurs as results of geological processes and different development activities- agriculture exploration of mineral resource and their processing -by human being. Arsenic pollution took place in different states of the world due to various reasons. The latest pollution was detected in Bangladesh and Indian state of west Bengal. Experts pointed out that there are some similar geological reasons behind the Arsenic contamination in these two regions.