DISTRIBUTION OF FLUORIDE IN TWO DRY ZONE AREAS IN SRI LANKA: IMPLICATIONS TO HUMAN HEALTH

Abstract

Groundwater is the major source of water in Sri Lanka, especially in the dry zone,where surface water resources are inadequate. The presence of excess fluoride in groundwater particularly in dry zone is a major contributor to the dental epidemiology in Sri Lanka. The ingestion of excess fluoride most commonly in drinking water can cause dental and skeletal fluorosis. Therefore, the estimation of present levels of fluoride in groundwater of Sri Lanka has become important. A survey on chemical quality of groundwater in Moneragala and Anuradhapura districts was carried out with special reference to the fluoride concentration.Altogether 36 water samples were collected from dug wells and tube wells in both districts and analyzed for different parameters such as fluoride, iron, manganese,magnesium, pH and TDS. The mean fluoride concentrations are 1.9 ppm and 2.6 ppm for Moneragala and Anuradhapura districts respectively and both are above the World Health Organization guideline value of 1.5 ppm for drinking water. The difference in fluoride levels in these two districts can be attributed to the dissimilarity in the underlying lithological units. In Anuradhapura district the concentrations of Fe, Mn and Mg remarkably vary as 1 3 - 5 5 ppb, 6 - 403 ppb and 7.2 - 141 ppm, respectively and similarly in Moneragala district they vary as 12 - 75ppb, 1 - 381 ppb and 5.9 - 105 ppm. This variation is due to the heterogeneity in rock types even within a few kilometers. The average measured concentrations of Mn and Mg in Anuradhapura are higher than those in Moneragala district. On the other hand, the average concentration of Fe in Anuradapura district is relatively lower than that from Moneragala district. The causes for these differences cannot be singled out at this stage due to the limited number of samples that were analyzed in this study. Therefore, it is important to investigate the interrelation between the chemical composition of groundwater and the local geological/geochemical conditions in all wells of the both districts.