ARSENIC AND FLUORIDE IN GROUNDWATER

Arsenic Contamination
Groundwater in a large part of the Bengal Basin contains high levels of arsenic. Large number of people of India and Bangladesh are compelled to drink water having arsenic concentration above the permissible limit.

At present, the primary source of drinking water in rural areas is the private domestic tube wells, which withdraws water from shallow aquifers (50 to 200 ft). Data from different sources indicate high arsenic content in water from such shallow aquifers in extensive areas in the delta. However, in many areas the deeper (> 500 ft) aquifers too show arsenic content above the permissible limit of 0.05 mg/litre according to the Indian standards.

Several countries in the world suffer from arsenic contamination of groundwater. The highest magnitude of this contamination is seen in Bangladesh and West Bengal. But in other parts of the world, e.g. Mongolia, Brazil, United States, Argentina, Ghana, Nepal, Pakistan etc are worst effected. In India, arsenic contamination is reported from Bihar, Uttar Pradesh, Madhya Pradesh, Tripura and Assam.

Arsenic Toxicity
Acute: severe abdominal pain, fever, cardiac arrhythmia.
Chronic: muscle weakness and pain, gross edema, Gastrointestinal disturbances, liver and kidney damage, swelling of peripheral nerves (neuritis), paralysis, liver injury, jaundice, peripheral vascular disease - blackfoot disease. Chronic drinking water exposure causes cancer (skin, lung and other organs).

Fluoride Contamination
Fluoride is another toxic material generally present in ground water. Prolonged drinking of water containing high fluoride may cause degeneration of bone and teeth. This is called fluorosis. About 300 people from the village of Nasipur (with a population of about 2000) in Birbhum, have been paralysed after drinking water contaminated with fluoride. According to media report, the local residents claim that the number is more than 1200. Investigations have proved that the fluoride content in Nasipur's water is 14 ppm, against the permissible limit of 1 to 1.5 ppm. There are other districts in West Bengal where fluoride is also found in groundwater.

Fluoride contamination in groundwater is not new in India. Fluoride above toxic limit is found in groundwater of many states like Jharkhand, Assam, Meghalaya, Madhya Pradesh, Orissa, Chhattishgarh, Tamil Nadu, and Andhra Pradesh. In West Bengal presence of fluoride in groundwater has been detected in the year 1998 by the State Water Investigation Directorate, West Bengal. It was found that in a single village of Birbhum district about 2000 people fell victim of the contamination.

Fluoride is readily incorporated into the crystalline structure of bone, and accumulates over time. The condition of fluoride poisoning is called skeletal fluorosis which increases risks of bone fracture. Skeletal fluorosis is a bone and joint condition associated with prolonged exposure to high concentrations of fluoride. Fluoride increases bone density and causes changes in the bone that lead to joint stiffness and pain.

Arsenic and fluoride contamination in groundwater are geogenic in nature. Detection of contamination through hydrogeological investigation is the only preventive measure.

WATER CRISIS IN PURULIA

WAter crisis in Purulia district is not new. Every year some parts of this district face severe water crisis during the summer. But whenever drought or similar situation arrives the development authorities oft for sinking tubewells in the affected area. But while sinking such tube wells attention should be given to the hydrogeological condition of the district. This district is mainly a granitic terrain consisting of crystalline basement rocks thinly covered with weathered mantle. There is a shallow fracture zone. This thin porous medium can not store sufficient quantity of groundwater. So most of the tube wells fail to yield water for a long time. It is always wise to opt for harnessing rainwater on the surface. Here is a high resolution hydrogeological map of Purulia.