Fluoride Contamination in Groundwater of Central Assam, India

Fluoride contamination of groundwater of the central region of the state of Assam, India, has been studied. The study area includes five districts, viz., Karbi Anglong, North Cachar Hills, Nagaon, Morigaon and Golaghat. A total of 388 groundwater samples have been analyzed for fluoride contamination and 25 of them have been analyzed for fluoride as well as other related parameters. High fluoride contamination has been observed in the groundwater of areas having ancient alluvial red soil and Precambrian metamorphic rock complex basement in the Kapili-Jamuna sub -basin, viz., the plains of Diphu and Hojai subdivisions of Karbi Anglong and Nagaon districts, respectively. Moderate fluoride has been found in groundwater of some places in Morigaon and Golaghat districts also. Besides fluoride, presence of high concentrations of SO42-, much above the guideline values, have also been recorded in some samples. The fluoride contents, as a whole, have poor positive correlation with Na+, K+, pH and depth of source, and poor negative correlation with Mg2+, Ca2+ and total hardness with cumulative data spread over entire area of study. The observed poor correlation has been attributed to the diversity of the study area. However, fluoride showed fairly good positive correlation with depth of sources when plotted separately for different localities.