Arsenic Affected Areas
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Arsenic pollution of ground water in West Bengal was first reported in the early eighties. The occurrence of arsenic is mainly due to two reasons: natural and anthropogenic. Arsenic is widely distributed in nature and principally occurs in the form of inorganic or organic compounds. Inorganic compounds consist of arsenite, the most toxic form and arsenate the less toxic form. The main ores of Arsenic are arsenopyrite, arpiment, realgar and arsenopalledenite. It is present in nature as iron arsenate, iron sulphate and in calcareous soil as calcareous arsenolite. In flood deposits, it is found as arsenite. The main anthropogenic sources are industrial waste, phosphate, fertilizers, coal, oil, cement, mine tailing, smelting, ore processing, metal extraction, metal purification, chemicals, glass, leather, textiles, alkali, petroleum refineries, acid mines, alloys, pigments, insecticides, herbicides and catalysts.
The problem of arsenic contamination in ground water from the vast tract of alluvial aquifers in Bengal, Bihar and UP is known to have affected a population of about 50 million in different districts of India and an equal number in Bangladesh. About 63 lakh people in West Bengal State live in the arsenic belt; 69 blocks are arsenic-affected, while two are affected by fluoride. Arsenic in ground water have been reported in a range (0.05-3.2) mg/l in shallow aquifers from 61 block in 8 districts of West Bengal namely Malda, Mushirbad, Nadia, North and South 24 Pargana, Bardhaman, Howrah, and Hugli.
In West Bengal, there is increasing concern of arsenic induced diseases due to exposure of high concentration of arsenic in the Natural Geochemical environment. In this area the source of arsenic is geogenic and associated with iron pyrites in arsenic rich layers occurring in the alluvium along the Ganga River. The availability of arsenic is possible due to excessive use of ground water irrigation (e.g. up to 80% of the annual replenishable recharge in north 24 Parganas for multiple cropping which causes dropping of water levels resulting exposure of the arsenic rich beds to air – oxidation of the pyrite and soubilisation of arsenic).
Arsenic concentration in ground water has been found to be in excess of permissible limit of 0.05 mg/l in a number of localized patches in Murshidabad and North 24- Pargana Districts in West Bengal. Population in the area is reported to be suffering from “Arsenic Dermatosis” by drinking arsenic rich ground water. In Ramnagar and Domkal blocks of Murshidabad district, Arsenic levels range form 0.06 mg/l to 1.90 mg/l, while in North 24-Parganas, it ranges from 0.66 to 0.9 mg/l.
Consumption of ground water with elevated arsenic levels (up to 3,700 mg/l in certain wells) over a prolonged period of time has resulted in serious health hazards, especially among the rural and semi-urban population in the region. Symptoms of arsenic toxicity are manifested as skin lesions, hyperkeratosis, melanosis, cancer in different organs and several other health disorders, which in some cases have proved to be lethal. Need of water for domestic as well as irrigation purposes had triggered rapid development of ground water resources in the region during the last two decades. Overdraft of ground water in an indiscriminate manner is one of the key factors responsible for the spreading of arsenic epidemic in this region. A large number of government organizations and NGO are working on this problem and to find a lasting solution.