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Fluoride (F¯) concentration over and above the permissible limits (1.5 mg/l) in drinking water leads to human health hazards, such as dental and skeletal fluorosis affecting millions of people in many parts of India. Preliminary investigations indicate that severe health disorders have been identified in parts of the Kachnarwa region, which is in the upper Panda river basin, Sonbhadra District, Uttar Pradesh, due to excess intake of fluoride through drinking water. The lithological units of the study area mainly consist of granite and gneissic complex rocks of the Chota-Nagpur Plateau. In order to understand the probable source of fluoride and its concentration, 17 groundwater samples mostly from granite and phyllite regions were collected for fluoride estimation during May 2006. The concentration of fluoride in the groundwater of the study area varies from 0.483 to 6.7 mg/l. Among the 17 samples analysed, 8 exceeded the maximum permissible limits of fluoride in the study area. The source of fluoride in the groundwater of the study area is mainly from geological occurrence (i.e. fluoridebearing minerals, viz. apatite and biotitic mica). Microscopic analysis of the rock samples showed 5-10% apatite and 20-25% biotite, but other fluoride-bearing minerals like fluorite and hornblende were characteristically absent. X-ray diffraction studies showed that apatite mineral peak profile of the rock samples corroborated with the fluorapatite of the standard set by the JCPDS. The worst fluoride-affected villages are Rohiniyadamar, Madhuri, Neruiyadamar, Gobardaha and Kunrwa. Most people in these villages suffer from dental and skeletal fluorosis such as mottling of teeth, deformation of ligaments, bending of spinal column and ageing problem. An urgent need is to educate the people on the causes of fluorosis, encouraging rainwater harvesting and providing fluoride-free drinking water in the study area. [ABSTRACT FROM AUTHOR]