Groundwater quality: focus on fluoride concentration in rural parts of Guntur district, Andhra Pradesh, India

Hydrogeological investigations have been carried out in rural parts of Guntur district, Andhra Pradesh, India where agriculture is the main occupation. Granite gneisses associated with schists and charnockites are the main lithological formations, which are overlain by black cotton soils. Groundwaters are alkaline, very hard and mostly brackish. Possible sources of fluoride (F-) are weathering and leaching of F--bearing minerals under the alkaline environment. A high rate of evapotranspiration, longer residence time of waters in the aquifer zone, intensive and long-term irrigation, and heavy use of fertilizers are the supplementary factors to further increase the F- content in the groundwaters. The investigated area has been classified into three types with reference to concentration of F- prescribed for drinking: low-F- (<0.60 mg l(-1)), moderate-F- (0.60-1.20 mg l(-1)) and high-F- (>1.20 mg I-1). Forty-five percent of the total groundwater samples belong to the high-F- category. Dental fluorosis is noticed in the region. A groundwater management programme is suggested.