Fluoride in groundwater scourge of the dry zone

Access to clean water is every one's right. Water paradoxically, is a life saver as well as a killer. Millions of people mostly in the developing world die due to water-borne diseases. Clean water is therefore one of the prime necessities of life and every citizen of this country must have access to this precious commodity. While very strong emphasis is placed on pollution and contamination (both industrial and biological) of water bodies, far less emphasis has been placed on the quality of water in different terrains due to the natural chemical composition. Nearly 70 percent of the Sri Lankan population still depends on dug wells, deep wells, reservoirs, rivers and such water bodies for their water requirements. By far the majority of this 70 percent is from middle and low income groups and their general health is bound to be influenced by the quality of the water they drink.

As an example, a 65 year old person from a village who drinks the water he obtains from his own well in the garden, would have had his health influenced either beneficially or detrimentally depending on the chemical and biological quality of the water in his well. The dry zone of Sri Lanka has some unique features as far as the groundwater is concerned. Maps prepared jointly by the Institute of Fundamental Studies and the Department of Geology, University of Peradeniya with valuable support from the National Water Supply and Drainage Board have shown that the water quality of the dry zone is markedly different from that of the wet zone. The dry zone water generally tends to be higher in dissolved solids and hardness in addition to some other chemical parameters. Fluoride is particularly unique in that the dry zone has generally markedly enriched fluoride in the groundwater.

Fluoride is considered as the most reactive electronegative element of all the halides such as chloride, bromide and iodide. In the natural environment fluoride occurs as the fluoride ion. Fluorine, the element of fluoride, associates with many mineral deposits containing fluoride-bearing minerals such as fluorite, apatite and mica. Weathering, dissolution and other pedogenic processes can release fluoride from the rocks and minerals into the groundwater. The longer a rock stays in contact with the groundwater, the greater the dissolution and entry of fluoride into the water. Many deep wells therefore contain rather high quantities of fluoride. Even though fluoride is considered as an essential element for human health, especially for the strengthening of tooth enamel, excessive doses can be harmful. Among dental health concerns, dental fluorosis is the most common sign of excessive intake of fluoride rich drinking water. At the same time, low fluoride levels in the human body can lead to dental caries (decaying teeth and cavity formation). Presence of fluoride in water does not impart any colour, odour or taste. Therefore it acts as an invisible poison such as arsenic in groundwater.................

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