Re-examining the Spatial Distribution of Fluoride in Groundwater of Sri Lanka: A Field Study at Nochchiyagama, Anuradhapura

Fluoride is well known for both beneficial and detrimental effects on human health. Fluorideimproves the dental health by preventing cavities. However, excessive amounts of fluoridelead to the development of dental and skeletal fluorosis. There is a narrow range betweenfluoride intake which is advantageous and those which begin to be damaging. Dentalfluorosis caused by fluoride rich drinking water is a common health issue in the dry climatezone of Sri Lanka. The spatial distribution of fluoride in groundwater in Sri Lanka has beenextensively studied and several fluoride distribution maps have been published to date.However, careful analysis of these maps reveal that the fluoride distribution presented insome geographical regions does not agree with each other. This study focused on examiningthe fluoride distribution in Nochchiyagama, Anuradhapura to re-evaluate its fluoridedistribution. During the study, approximately 200 water samples were collected from dug andtube wells, water reservoirs and canals. Fluoride concentration of the samples was determinedby the fluoride selective electrode method. Other physico-chemical properties of water suchas pH, conductivity, hardness etc. were determined by internationally accepted standardmethods. The average fluoride concentration in Nochchiyagama was 1.1±0.8 mg/l (n=202) inthe range 0.29 to 5.52 mg/l; however, many of the published maps state the fluoridedistribution in the Nochchiyagamaarea as 0.5 to 1.0 mg/l. A careful examination of thefluoride data reveals two distinct fluoride distribution patterns. The geographical areabetween the Puttlam-Anuradhapura highway (A12) and the Wilpaththu National Parkgenerally has a higher fluoride content with an average 1.2±1.0 mg/l (n=103) in the range0.31 to 5.52 mg/l. The area between Puttlam-Anuradhapura highway (A12) andThabuththegama-Anuradhapura highway (A28) has an average fluoride concentration of0.9±0.5 mg/l (n=99) in the range 0.29 to 2.53 mg/l. The first geographical area had abouteight fluoride hot spots (<2.5 mg/l) while other region had only two. One of the most visiblehydrological differences in these two regions is that the first region solely depends onrainwater for water requirements while the other one has a complex network of irrigationalcanals distributing water from the Kala Oya irrigational scheme