Fluoride releasing kinetics in a weathered bearing biotite gneiss

In several regions of the dry zone of Sri Lanka, excessive quantities of fluoride (F-) in groundwater have affected the water quality significantly. Apart from the well-known prevalence of dental fluorosis, Chronic Kidney Disease of uncertain etiology (CKDu) is widespread in different pockets in the dry zone of Sri Lanka [1]. Fluoride is one of the substances suspected of being causative of CKDu in the area. Since the kidneys retain more F- than in any other soft tissue and excess F- exposure can cause kidney disease. Within the same zone, the prevalence of CKDu varies by geographic area in a ground water and spatial distribution of selected trace elements in groundwater. The optimum F- level in drinking water, according to WHO guidelines, is 1.5 (mg/L); however, due to the unfavorable climatic conditions that exist in tropical countries, people ingest more water than normal intake, resulting in a high F- intake. The source of F- is geogenic. It has been found that the F- content of basement rocks ranges from 9.5×10-5 to 1.44×10-3 kg/L in the region [3]. Farmers consume about 2-3 liters of water a day to quench their thirst, resulting in a daily F- intake of 3×10-3-1×10-2 kg/L [4].