**7. Conclusion**

A high fluoride concentration has been reported in groundwater in tertiary volcanics, from Yemeni terrain. The major ion chemistry data from groundwater of this rock revealed that Na+ is the most predominant cationic constituent followed by Ca2+ and Mg2+, the HCO3 − and SO4− are found to be the most predominant anions followed by Cl<sup>−</sup> and NO3. High fluoride ion concentration in the Yemeni groundwater appears to be caused by high alkalinity due to HCO3 − ions. Na+ has a positive correlation with F− , whereas Ca2+ has a negative correlation, resulting in an equilibrium condition in groundwater. CaCO3 precipitation at high pH can increase fluoride ions in groundwater by removing Ca2+ from solution and allowing more fluorite to dissolve.

Dental fluorosis is the widely fluoride disease observed in the affected areas, whereas skeletal fluorosis is observed in some villages from Al-Dhalla region. The principal causes of fluorosis among the Yemeni population appear to be related to high fluoride concentration in drinking water and Khat chewing habits, which are cultivated in the volcanic soil and irrigated by the high fluoride concentration water.

Despite the high dental fluorosis prevalence in the affected areas, no restorative treatment is being carried out. Therefore, it is highly recommended to provide safe drinking water to fluoride-affected areas.

### **Acknowledgements**

I would like to thank the National Water Resources Authority (NWRA) Yemen and UNDP for funding this research. Also I would like to thank the publisher and anonymous reviewers for valuable suggestions and comments that have enhanced the chapter quality.

*Origin and Hydrogeochemistry of Fluoride in the Context of the Yemen Regime DOI: http://dx.doi.org/10.5772/intechopen.104255*
