This IGRAC's special project resulted in refining of boundaries of regions which have been reported as having problems with high fluoride concentrations in groundwater. Additional regions were defined as potential sources of fluoride rich groundwater on the basis of a geological map of the world, distribution of climatic zones and geochemical knowledge.
The geological map used, distinguishes only four types of formations: sedimentary rocks, endogenous rocks (plutonic and metamorphic), extrusive volcanic rocks and Quaternary (unconsolidated) sediments and focuses rather on chronostratigraphy than on lithostratigraphy. The large scale of the map (1:25 000 000) allows only for a general insight in distribution of potential fluoride rich formations. More detailed lithological information is therefore needed, especially on the distribution of granitic rocks. As outlined in section 2.1, granites often consist of residual magma melts, and during the intrusion, contact metamorphism will enrich the host rock with fluorine by metasomatic processes.
The available geological map largely indicates only the rocks at the surface. A multilayered aquifer system may include rock formations which act as sources of fluoride at various depths. Cross sections of potential contaminated areas would increase the accuracy of the fluoride maps as well.
Depending on the flow direction of the groundwater, also aquifers neighboring fluorine-rich formation can be contaminated with fluoride. However, the groundwater flows were not taken into account during this study.
Input from regional experts will result in additional information and consequently more detailed specification of areas (aquifers, geological formations) contaminated with fluoride.