Abstract
Fluoride ions in drinking water is well known for both beneficial and detrimental effects on health. Millions of inhabitants in the Dry Zone of Sri Lanka are vulnerable to fluorosis due to consumption of high fluoride groundwater. The objective of this study is to upgrade the spatial distribution map of groundwater fluoride levels in Sri Lanka. The map was prepared using nearly 14000 groundwater fluoride data that were collected from primary and secondary sources. The fluoride map of Sri Lanka indicates that the climate and hydrological conditions appear to play a major role in the geochemical distribution of fluoride in groundwater. In some cases, over 25 % of wells have more than 2 mg/L of fluoride, which is much higher than the recommended level for tropical countries. As shown in the map, even within the Dry Zone region, some low fluoride regions can be observed. This may probably be due to the effect of surface water, which contains fairly low levels of fluoride. In general, from among the chemical parameters in groundwater, fluoride stands out as an ion that appears to seriously affect the water quality of the Dry Zone. Doi: http://dx.doi.org/10.4038/jnsfsr.v40i4.5044 J.Natn.Sci.Foundation Sri Lanka 2012 40 (4):303-309
Highlights
The fluoride map of Sri Lanka indicates that the climate and hydrological conditions appear to play a major role in the geochemical distribution of fluoride in groundwater
The hydrogeochemical distribution of fluoride is of great importance in delineating areas where dental and skeletal fluorosis caused by excess fluoride are prevalent in Sri Lanka
An important feature to note is that the rocks and minerals in both the Wet and Dry Zones are similar and the fluoride variation is mainly a climatic feature and not a geological one, even though the fracture intensity of rocks may play a minor role
Summary
The fluoride map of Sri Lanka indicates that the climate and hydrological conditions appear to play a major role in the geochemical distribution of fluoride in groundwater. In hot tropical lands where people consume large quantities of water, higher fluoride levels in drinking water may result in excessive intake of fluoride leading to a health risk. Fluoride in drinking water has become a serious problem in the world as 200 million people, mostly from tropical countries, are vulnerable to dental and/or skeletal fluorosis. Many countries, such as China, India, Sri Lanka, Mexico, Argentina and many nations in Africa among others, have very high incidences of dental and in some cases skeletal fluorosis mainly caused by excessive fluoride in drinking water (Edmunds & Smedley, 2005; Dissanayake & Chandrajith, 2007). In Sri Lanka, the optimal level of fluoride in groundwater for caries protection should be 0.6−0.9 mg/L (Warnakulasuriya et al, 1992)
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