Abstract:
There has been increasing global attention focused on elevated levels of fluoride contents in water especially in developing countries. The latest estimates suggest that around 200 million people, from among 25 nations the world over, are under the dreadful fate of fluorosis. It is most prevalent in subtropical countries whereas India and China, the two most populous countries of the world, are the worst affected. Monaragala District; the study area in the Southeastern part of Sri Lanka, belongs to dry zone and was recorded as with a high number of patients with dental fluorosis recently. It was revealed from a questionnaire survey on a representive 370 families that 131 (35.4%) were affected from various stages of dental fluorosis especially from Wellawaya, Sewanagala, Buttala, Thanamalwila and Kataragama areas that are located in the South and Southwestern part of the Monaragala District. Males (58.2%) were susceptible for the fluorosis compare to Female (41.8%) population in the affected areas. Fluoride concentration levels of drinking water (with spring or other groundwater sources) in 11 Divisional Secretariat divisions (DS) of Monaragala District determined by the standard SPADNS method using a spectrophotometer shows that a farely large area of the Distict has low fluoride concentration in groundwater between 0.0 and 1.0 mg/L. Also, relatively high fluoride concentrations ranging between 0.61 and-2.82 mg/L are found in the water sources in South and Southwestern part of the district. From questionnaire survey and hydrogeochemical analyses it was revealed that the southern part of the Monaragala district has high groundwater fluoride and hence is more susceptible for dental fluorosis than the northern part. We conclude that rock-water interaction is the main process in which F-rich minerals are decomposed/dissociated from the source rock and F-is dissolved in the groundwater by dissolution. Source rocks could be identified as hornblende-biotite gneiss or nearby serpentinite rock. High concentration of Fin deeper aquifers compared to shallow aquifers could be due to high residence time of groundwater in the aquifer system, thereby having longer contact time for dissolution of F-bearing minerals. The influence of local lithology, aided by other factors like semi-arid climate of the region may be responsible for higher concentration of Fin the groundwater of the region.
