ABSTRACT

The first reports on adverse effects of high-fluoride groundwater used as drinking water date back to the late 1930s. Since then, this has been recognized as a nationwide problem in India. The mechanisms of mobilization are largely known; the problem exists in 20 out of 35 Indian states and is most pronounced in the semi-arid parts of the country. There is a close correlation between the concentration of fluoride in groundwater and soil conditions, which is more pronounced in areas with alkaline-sodic soils. This means that high-fluoride groundwater is also closely related to irrigation practices. An urgent task at hand is to decrease the alkalinization and salinization of soils in a way that will also benefit agricultural production in terms of soil conditions and nutrient supply, notably trace element availability. Water harvesting and improving irrigation practices will help in lowering fluoride concentrations in groundwater. Even if such remedial actions are inadequate, they will at least lower the demands placed on ex situ treatment of water in terms of water filters, etc. The past four decades have largely revealed the mechanisms behind the mobilization which in turn has helped in the development and implementation of combined flow and reaction modeling. However, there is still a need to investigate which mechanism limits the concentration of fluoride. In this regard, it has been suggested that fluorite constitutes a secondary solid phase determining the higher concentrations. However, in many cases, the high-fluoride groundwater turns out to be undersaturated with respect to fluorite. Moreover, ion-exchange is a possible mechanism that could explain the commonly seen accumulation of fluoride in calcrete.