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Water 2018, 10(12), 1799; https://doi.org/10.3390/w10121799

Geochemical Evolution of Fluoride and Implication for F Enrichment in Groundwater: Example from the Bilate River Basin of Southern Main Ethiopian Rift

1,2,3
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1,2,3
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1,2,4,* and 1,2,3
1
Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
2
Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China
3
University of Chinese Academy of Sciences, Beijing 100049, China
4
Academician Zhaiming Guo working station, Sanya University, Hainan 572000, China
*
Author to whom correspondence should be addressed.
Received: 1 November 2018 / Revised: 3 December 2018 / Accepted: 3 December 2018 / Published: 7 December 2018
(This article belongs to the Section Water Quality and Ecosystems)
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Abstract

Groundwater is the most important source of drinking water. Fluoride was found in high concentrations in the groundwater from deep wells of the water supply in the southern main Ethiopian rift. The high concentration of fluoride is dominantly geogenic rather than anthropogenic in origin, as the agricultural area was not found to be contaminated with NO3. Knowledge of fluoride enrichment will help to provide management plans for developing deep groundwater and minimizing the health risks of exposure to fluoride. The chemical processes of fluoride were investigated in the waters in the Bilate River basin using hydrochemical and isotopic tools. The F concentration ranged from 0.5 to 1.29 mg/L in water from shallow wells and from 0.48 to 5.61 mg/L in water from deep wells. Seventy percent of deep well samples had F > 1.5 mg/L higher than the World Health Organization potable guideline. The high fluoride concentration in the groundwater was mainly situated in the rift valley of the Bilate River basin, in contrast with low F groundwater in the highland. The concentration of fluoride was lowest in Ca-Mg-HCO3 type groundwater and highest in Na-HCO3 type groundwater. Moreover, F was positively correlated with HCO3, Na+, Na+/Ca2+ and pH in groundwater and Na+/Ca2+ ratios were increased along the flow path. Hydrogeological, hydrodynamic and hydrochemical conditions are responsible for fluoride accumulation in the deep aquifers. Strong dynamic flow in highland areas flush away weathered chemical components (e.g., F). Thus, surficial weathering is not a major controlling factor for high concentrations of Fluoride in deep groundwater but the combination of silicate hydrolysis and ion exchange mainly control fluoride enrichment in stagnant flow environments. View Full-Text
Keywords: fluoride; hydrochemical characteristics; water–rock interaction; geochemical modeling; bilate river basin; South Ethiopia fluoride; hydrochemical characteristics; water–rock interaction; geochemical modeling; bilate river basin; South Ethiopia
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Haji, M.; Wang, D.; Li, L.; Qin, D.; Guo, Y. Geochemical Evolution of Fluoride and Implication for F Enrichment in Groundwater: Example from the Bilate River Basin of Southern Main Ethiopian Rift. Water 2018, 10, 1799.

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