This review describes the occurrence, distribution and impacts of fluoride mobilization in groundwater. Although most groundwater has low concentrations of F, certain natural hydrogeological and geochemical conditions can render concentrations high and potentially detrimental to human health through long-term exposure via drinking water. The literature has documented these in at least 85 countries and on most continents. High-F groundwaters are especially prevalent in arid and semi-arid areas of the world.
Generation of high-F groundwater is a function of regional geology (interaction with F-rich host rocks such as felsic or alkaline igneous rocks or phosphorites) and water-rock interaction processes including:
- development of Na-HCO3 water;
- development of saline, low-Ca, groundwater or brine;
- development of extreme pH;
- changes in carbonate equilibria including precipitation of calcite; and,
- changes in temperature.
Fluoride has also been observed to derive from anthropogenic sources through activities such as combustion of F-bearing fossil fuels, brick manufacture and disposal of industrial and domestic wastewater. However, these are local occurrences and not widespread as are the high-F groundwaters of geogenic origin.
This review outlines the dominant controls on F mobilization in groundwater through several case studies from published works and describes approaches to F mitigation that have been tried or adopted. It also catalogues world occurrences in tabular form from the vast literature available on the topic.
Much knowledge has been acquired on the occurrences and causes of high-F groundwater. Rather more challenging is providing sustainable solutions to the problems in F-vulnerable aquifers, especially in parts of the world with already scarce groundwater resources and limited economic resources.