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

Abstract

Fluoride is well known for both beneficial and detrimental effects on human health. Fluoride
improves the dental health by preventing cavities. However, excessive amounts of fluoride
lead to the development of dental and skeletal fluorosis. There is a narrow range between
fluoride intake which is advantageous and those which begin to be damaging. Dental
fluorosis caused by fluoride rich drinking water is a common health issue in the dry climate
zone of Sri Lanka. The spatial distribution of fluoride in groundwater in Sri Lanka has been
extensively studied and several fluoride distribution maps have been published to date.
However, careful analysis of these maps reveal that the fluoride distribution presented in
some geographical regions does not agree with each other. This study focused on examining
the fluoride distribution in Nochchiyagama, Anuradhapura to re-evaluate its fluoride
distribution. During the study, approximately 200 water samples were collected from dug and
tube wells, water reservoirs and canals. Fluoride concentration of the samples was determined
by the fluoride selective electrode method. Other physico-chemical properties of water such
as pH, conductivity, hardness etc. were determined by internationally accepted standard
methods. The average fluoride concentration in Nochchiyagama was 1.1±0.8 mg/l (n=202) in
the range 0.29 to 5.52 mg/l; however, many of the published maps state the fluoride
distribution in the Nochchiyagamaarea as 0.5 to 1.0 mg/l. A careful examination of the
fluoride data reveals two distinct fluoride distribution patterns. The geographical area
between the Puttlam-Anuradhapura highway (A12) and the Wilpaththu National Park
generally has a higher fluoride content with an average 1.2±1.0 mg/l (n=103) in the range
0.31 to 5.52 mg/l. The area between Puttlam-Anuradhapura highway (A12) and
Thabuththegama-Anuradhapura highway (A28) has an average fluoride concentration of
0.9±0.5 mg/l (n=99) in the range 0.29 to 2.53 mg/l. The first geographical area had about
eight fluoride hot spots (<2.5 mg/l) while other region had only two. One of the most visible
hydrological differences in these two regions is that the first region solely depends on
rainwater for water requirements while the other one has a complex network of irrigational
canals distributing water from the Kala Oya irrigational scheme.