Mobilization of F~- from rocks and soils in to the groundwater, Morel River basin, Rajasthan, IndiaMobilization of F~- from rocks and soils in to the groundwater, Morel River basin, Rajasthan, India

摘要

The drinking water of about 260 million people in 30 countries worldwide contains more than 1 ppm of F~-.In India alone, approximately 62 million people suffer from dental and skeletal fluorosis. We present here results of our investigation from the eastern part of Rajasthan, one of the three states in India that are highly endemic for F~-.Groundwater was sampled from 69 villages, covering approximately 2200 km~2 of the Morel River basin, and F~- concentrations of 0.1 to 13.8ppm were measured. In the absence of known anthropogenic activity, thick alluvial deposits and the underlying bedrock appear to be the main source of F~-in the water. Local units include F-rich rocks such as mica schist, granite gneiss and conglomerate that in most areas are overlain by 50-100m thick alluvial cover. Alluvium of the area is rich in micaceous minerals and produced the highest F concentrations in leaching experiments. Although the conglomerates have high F content, the amount of F~- leached from conglomerates was low (on the order of 0.75 ppm after 105 days of contact time). However, larger amounts of F~-(1.2-1.5 ppm) were leached from granite gneiss and mica schist over a similar amount of contact time. The present study indicates that prolonged water-rock and water-alluvium interaction due to deficient rainfall and lack of sufficient flushing of aquifers are factors causing poor water quality in the Morel basin.