Geogenic fluoride enrichment in groundwater of a volcanic terrain: hydrogeochemical processes, exposure pathways, and human health risk assessment.

Abstract

Original abstract online at
https://link.springer.com/article/10.1007/s10653-026-03165-0

Elevated fluoride in groundwater is increasingly recognized as a major geogenic and public health concern in volcanic terrains. In the Taftan volcanic region of southeastern Iran, fluoride concentrations ranged from 0.04 to 1.77 mg/L, with 43% of samples exceeding the WHO drinking-water guideline value (1.5 mg/L) and approximately 57% exceeding the regionally optimal concentration of 0.68 mg/L. A total of 28 water samples collected from rivers, wells, springs, and qanats were analyzed for major ions, physicochemical parameters, stable isotopes (?¹?O and ?²H), and fluoride-related health risk indicators. Hydrochemical facies evolved from Ca–HCO₃ waters toward Ca–Cl–SO₄ and mixed types, reflecting progressive water–rock interaction and localized evaporative effects. Correlation analysis, ionic ratios, mineral saturation indices, and principal component analysis consistently indicate that fluoride mobilization is primarily controlled by silicate weathering processes, particularly the dissolution of fluoride-bearing aluminosilicate minerals such as biotite and muscovite, coupled with calcium removal through carbonate precipitation and ion exchange. Distinct relationships among Ca²⁺–F^–, HCO³–F^–, and SO₄²–F^– suggest combined contributions from fluorite equilibrium, surface desorption mechanisms, and minor sulfate-associated fluoride phases. The fluoride–pH relationship exhibits a characteristic U-shaped trend, with minimum concentrations near neutral pH and enhanced solubility under both acidic and alkaline conditions. Stable isotope signatures differentiate meteoric recharge-dominated groundwater from surface waters affected by evaporation, supporting the interpretation of contrasting hydrogeochemical evolution pathways. Health risk assessment reveals elevated non-carcinogenic risk for children in approximately 38% of the samples, emphasizing the vulnerability of younger populations to chronic fluoride exposure. These findings highlight the critical role of volcanic lithology in governing fluoride enrichment and underscore the need for targeted groundwater management and health risk mitigation strategies in arid and semi-arid volcanic regions.

This is a preview of subscription content:

Data availability

The datasets generated and analysed during the current study are not publicly available due to restrictions related to institutional policy and regional confidentiality of groundwater well information, but they are available from the corresponding author on reasonable request.

References

Aghapour, S., Bina, B., Tarrahi, M. J., Amiri, F., & Ebrahimi, A. (2018). Distribution and health risk assessment of natural fluoride of drinking groundwater resources of Isfahan, Iran, using GIS. Environmental Monitoring and Assessment, 190, Article 137. https://doi.org/10.1007/s10661-018-6505-1

Article Google Scholar
APHA. (2017). Standard Methods for the Examination of Water and Wastewater (23rd ed.). American Public Health Association.

Google Scholar
Askari Malekabad, F., Jahanshahi, R., & Bagheri, R. (2020). Characterization of the Bazman geothermal field, the southeast of Iran. Geopersia, 10(2), 405–418. https://doi.org/10.22059/geopersia.2019.277776.648

Article Google Scholar
Azhdarpoor, A., Radfard, M., Rahmatinia, M., Hashemi, H., Hashemzadeh, B., Nabavi, S., Akbari, H., Akbari, H., & Adibzadeh, A. (2018). Data on health risk assessment of fluoride in drinking water in the Khash city of Sistan and Baluchistan Province, Iran. Data in Brief, 21, 1508–1513. https://doi.org/10.1016/j.dib.2018.11.170

Article Google Scholar
Bahadori, D., Jahanshahi, R., Dehghani, V., & Mali, S. (2019). Variations of stable oxygen and hydrogen isotope ratios in the cold and thermal springs of the Bazman Volcanic Area (southeast Iran). Environmental Earth Sciences, 78, 663. https://doi.org/10.1007/s12665-019-8677-4

Article Google Scholar
Battaleb-Looie, S., Moore, F., Jacks, G., & Ketabdari, M. R. (2012). Geological sources of fluoride and acceptable intake of fluoride in an endemic fluorosis area, southern Iran. Environmental Geochemistry and Health, 34(5), 641–650. https://doi.org/10.1007/s10653-012-9459-y

Article CAS Google Scholar
Bennett, G., Van Reybrouck, J., Shemsanga, C., Kisaka, M., Tomašek, I., Fontijn, K., Kervyn, M., & Walraevens, K. (2021). Hydrochemical characterisation of high-fluoride groundwater and development of a conceptual groundwater flow model using a combined hydrogeological and hydrochemical approach on an active volcano: Mount Meru, Northern Tanzania. Water, 13(16), Article 2159. https://doi.org/10.3390/w13162159

Article CAS Google Scholar
Berberian, M., & King, G. (1981). Toward a plaeogeograpgy and tectonic. Canadian Journal of Earth Sciences, 18(2), 210–265.

Article Google Scholar
Biabangard, H., & Moradian, A. (2008). Geology and geochemical evaluation of Taftan Volcano, Sistan and Baluchestan Province, southeast of Iran. Chinese Journal of Geochemistry, 27, 356–369. https://doi.org/10.1007/s11631-008-0356-2

Article CAS Google Scholar
Bretzler, A., & Johnson, C. A. (2015). The geogenic contamination handbook: Addressing arsenic and fluoride in drinking water. Applied Geochemistry, 63, 642–646. https://doi.org/10.1016/j.apgeochem.2015.08.016

Article CAS Google Scholar
Buccianti, A., Grunsky, E. C., & Egozcue, J. J. (2020). Compositional data analysis in geochemistry: Are we sure to do it right? Geoscience Frontiers, 11(5), 1559–1575. https://doi.org/10.1016/j.gsf.2020.02.004

Article CAS Google Scholar
Clark, I. D., & Fritz, P. (1997). Environmental Isotopes in Hydrogeology. Lewis Publishers.

Google Scholar
Craig H, Gordon LI (1965) Deuterium and oxygen 18 variations in the ocean and the marine atmosphere. In: Proceedings of a Conference on Stable Isotopes in Oceanographic Studies and Paleotemperatures, Spoleto, Italy
Craig, H. (1961). Isotopic variations in meteoric waters. Science, 133, 1702–1703.

Article CAS Google Scholar
Currell, M., Cartwright, I., Raveggi, M., & Han, D. (2011). Controls on elevated fluoride and arsenic concentrations in groundwater from the Yuncheng Basin, China. Applied Geochemistry, 26(4), 540–552. https://doi.org/10.1016/j.apgeochem.2011.01.017

Article CAS Google Scholar
Dehbandi, R., Moore, F., & Keshavarzi, B. (2017). Provenance and geochemical behavior of fluorine in soils of an endemic fluorosis belt, central Iran. Journal of African Earth Sciences, 129, 56–71. https://doi.org/10.1016/j.jafrearsci.2017.01.010

Article CAS Google Scholar
Dehbandi, R., Moore, F., & Keshavarzi, B. (2018). Geochemical sources, hydrogeochemical behavior, and health risk assessment of fluoride in an endemic fluorosis area, central Iran. Chemosphere, 193, 763–776. https://doi.org/10.1016/j.chemosphere.2017.11.063

Article CAS Google Scholar
Edmunds, W. M., & Smedley, P. L. (2013). Fluoride in natural waters. In O. Selinus (Ed.), Essentials of Medical Geology (pp. 311–336). Springer.

Chapter Google Scholar
Enalou, H. B., Moore, F., Keshavarzi, B., & Zarei, M. (2018). Source apportionment and health risk assessment of fluoride in water resources, south of Fars province, Iran. Applied Geochemistry, 98, 197–205. https://doi.org/10.1016/j.apgeochem.2018.09.020

Article CAS Google Scholar
Esmaeili, S., Moghaddam, A. A., Barzegar, R., & Tziritis, E. (2018). Multivariate statistics and hydrogeochemical modeling for source identification of major elements and heavy metals in the groundwater of Qareh-Ziaeddin plain, NW Iran. Arabian Journal of Geosciences, 11, Article 5. https://doi.org/10.1007/s12517-017-3351-9

Article Google Scholar
Fekri, M., & Kasmaei, L. S. (2013). Fluoride pollution in soils and waters of Koohbanan region, southeastern Iran. Arabian Journal of Geosciences, 6, 157–161. https://doi.org/10.1007/s12517-011-0359-x

Article CAS Google Scholar
Gaillardet, J., Dupré, B., Louvat, P., & Allègre, C. J. (1999a). Global silicate weathering and CO? consumption rates deduced from the chemistry of large rivers. Chemical Geology, 159(1–4), 3–30. https://doi.org/10.1016/S0009-2541(99)00031-5

Article CAS Google Scholar
Gaillardet, J., Dupré, B., Louvat, P., & Allègre, C. J. (1999b). Global silicate weathering and CO₂ consumption rates deduced from the chemistry of large rivers. Chemical Geology, 159(1), 3–30. https://doi.org/10.1016/S0009-2541(99)00031-5

Article CAS Google Scholar
Gallagan, D. J., & Vermillion, J. R. (1957). Determining optimum fluoride concentrations. Public Health Reports, 72, 491–493.

Article Google Scholar
Gat, J. R. (1996). Oxygen and hydrogen isotopes in the hydrologic cycle. Annual Review of Earth and Planetary Sciences, 24, 225–262. https://doi.org/10.1146/annurev.earth.24.1.225

Article CAS Google Scholar
Ghiglieri, G., Pittalis, D., Cerri, G., & Oggiano, G. (2012). Hydrogeology and hydrogeochemistry of an alkaline volcanic area: The NE Mt. Meru slope (East African Rift-Northern Tanzania). Hydrology and Earth System Sciences, 16, 529–541. https://doi.org/10.5194/hess-16-529-2012

Article CAS Google Scholar
Gibbs, R. J. (1970). Mechanisms controlling world water chemistry. Science, 170(3962), 1088–1090. https://doi.org/10.1126/science.170.3962.1088

Article CAS Google Scholar
Gibson, J. J., Edwards, T. W. D., & Birks, S. J. (2005). Quantitative unifying approach for interpreting water isotope data in lakes. Journal of Paleolimnology, 34, 1–12. https://doi.org/10.1007/s10933-005-6346-8

Article Google Scholar
Graffelman, J., Pawlowsky-Glahn, V., Egozcue, J. J., & Buccianti, A. (2018). Exploration of geochemical data with compositional biplots. Journal of Geochemical Exploration, 194, 120–133. https://doi.org/10.1016/j.gexplo.2018.07.009

Article CAS Google Scholar
Hounslow AW (1995) Water Quality Data: Analysis and Interpretation. CRC Press.
Jahanshahi, R., Allahdadi, A., & Mali, S. (2025a). Hydrogeological and environmental assessment of groundwater quality under urban stress: A case study from Zahedan, Iran. Environmental Geochemistry and Health, 47, Article 341. https://doi.org/10.1007/s10653-025-02650-2

Article CAS Google Scholar
Jahanshahi, R., Mahmoodinejad, N., & Mali, S. (2025b). Hydrogeochemistry and groundwater origin in the Sarduiyeh area, Iran. Geopersia, 15(2), 297–314. https://doi.org/10.22059/geope.2025.390781.648810

Article Google Scholar
Jahanshahi R, Zare M (2017) Delineating the origin of groundwater in the Golgohar Mine area of Iran using stable isotopes of ²H and ¹?O and hydrochemistry. Mine Water and the Environment, 36(4): 550–563.
LaFayette, G. N., Knappett, P. S. K., Li, Y., Loza-Aguirre, I., & Polizzotto, M. L. (2020). Geogenic sources and chemical controls on fluoride release to groundwater in the Independence Basin, Mexico. Applied Geochemistry, 123, Article 104787. https://doi.org/10.1016/j.apgeochem.2020.104787

Article CAS Google Scholar
Li, P., Wu, J., Qian, H., Zhang, Y., Yang, N., Jing, L., & Yu, P. (2021). Human health risk assessment of fluoride in drinking water using Monte Carlo simulation: A case study in arid and semi-arid regions. Environmental Geochemistry and Health, 43, 193–207. https://doi.org/10.1007/s10653-020-00566-9

Article Google Scholar
Linhares, D., Gaspar, D., Bernardo, F., Beney, I., Garcia, P., & Rodrigues, A. (2025). Fluoride levels in water sources inside the crater of Furnas volcano: Potential health implications for local communities and tourists. Science of the Total Environment, 982, Article 179635. https://doi.org/10.1016/j.scitotenv.2023.179635

Article CAS Google Scholar
Mali, S., Jafari, H., Jahanshahi, R., & Bagheri, R. (2022). Groundwater source identification and invasion model of Dareh-Zar Copper Mine in central Iran by chemo-isotopic techniques. Mine Water and the Environment, 41, 921–937. https://doi.org/10.1007/s10230-022-00870-1

Article CAS Google Scholar
Meybeck, M. (1987). Global chemical weathering of surficial rocks estimated from river dissolved loads. American Journal of Science, 287(5), 401–428. https://doi.org/10.2475/ajs.287.5.401

Article CAS Google Scholar
Moghaddam, A. A., & Fijani, E. (2008). Distribution of fluoride in groundwater of Maku area, northwest Iran. Environmental Geology, 56(2), 281–287. https://doi.org/10.1007/s00254-007-1166-6

Article Google Scholar
Mokhtari Z, Ahmadi A (2010) Geochemistry of mineral and thermal springs of Taftan volcano, SE Iran. (In Persian). Conference: 28th Symposium on Geosciences, Geological Society of Iran.
Motalane, M. P., & Strydom, C. A. (2004). Potential groundwater contamination by fluoride from South African phosphogypsum. Water SA, 30(4), 465–468.

Article CAS Google Scholar
Naderi, M., Jahanshahi, R., & Dehbandi, R. (2020). Two distinct mechanisms of fluoride enrichment and associated health risk in springs’ water near an inactive volcano, southeast Iran. Ecotoxicology and Environmental Safety, 195, Article 110503. https://doi.org/10.1016/j.ecoenv.2020.110503

Article CAS Google Scholar
Onipe, T., Edokpayi, J. N., & Odiyo, J. O. (2020). A review on the potential sources and health implications of fluoride in groundwater of Sub-Saharan Africa. Journal of Environmental Science and Health. Part a, Environmental Science and Engineering, 55, 1078–1093. https://doi.org/10.1080/10934529.2020.1770516

Article CAS Google Scholar
Pazand, K., & Agavali, N. (2022). Hydrogeochemistry of fluoride-enriched groundwater in Khaled Abad basin, semi-arid region of Central Iran. Applied Water Science, 12, Article 64. https://doi.org/10.1007/s13201-021-01553-2

Article CAS Google Scholar
Poureslami, H. R., Khazaeli, P., & Noori, G. R. (2008). Fluoride in food and water in Koohbanan, Iran. Fluoride, 41, 216–219.

CAS Google Scholar
Putirka, K. D. (2008). Thermometers and barometers for volcanic systems. Reviews in Mineralogy and Geochemistry, 69, 61–120.

Article CAS Google Scholar
Radfard, M., Yunesian, M., Nabizadeh, R., Biglari, H., Nazmara, S., Hadi, M., Yousefi, N., Yousefi, M., Abbasnia, A., & Mahvi, A. H. (2019). Drinking water quality and arsenic health risk assessment in Sistan and Baluchestan, Southeastern Province, Iran. Human and Ecological Risk Assessment, 25(4), 949–965. https://doi.org/10.1080/10807039.2018.1458217

Article CAS Google Scholar
Rezaei, M., Nikbakht, M., & Shakeri, A. (2017). Geochemistry and sources of fluoride and nitrate contamination of groundwater in Lar area, south Iran. Environmental Science and Pollution Research, 24(18), 15471–15487. https://doi.org/10.1007/s11356-017-9155-6

Article CAS Google Scholar
Richards, J. P., Razavi, A. M., Spell, T. L., Locock, A., Sholeh, A., & Aghazadeh, M. (2018). Magmatic evolution and porphyry–epithermal mineralization in the Taftan volcanic complex, southeastern Iran. Ore Geology Reviews, 95, 258–279. https://doi.org/10.1016/j.oregeorev.2018.02.005

Article Google Scholar
Shojaei Baghini, S., Jahanshahi, R., Mali, S., & Nasiri, M. A. (2020). Destruction of groundwater quality and the risk of saltwater intrusion in the aquifers nearby Sirjan salt playa, Iran. International Journal of Environmental Analytical Chemistry, 100(6), 647–661. https://doi.org/10.1080/03067319.2019.1596971

Article CAS Google Scholar
U.S. Environmental Protection Agency (USEPA) (2011) Exposure factors handbook: 2011 edition (Final Report). EPA/600/R-09/052F. Washington, DC: U.S. EPA.
Winter JD (2010) Principles of Igneous and Metamorphic Petrology (2nd ed.). Pearson Education.
World Health Organization. (WHO) (2017). Guidelines for Drinking Water Quality (4th ed.). WHO Press.

Google Scholar
Young, S. M., Pitawala, A., & Ishiya, H. (2011). Factors controlling fluoride contents of groundwater in north-central and northwestern Sri Lanka. Environmental Earth Sciences, 63(6), 1333–1342. https://doi.org/10.1007/s12665-010-0793-3

Article CAS Google Scholar
Yousefi, M., Ghoochani, M., & Mahvi, A. H. (2018). Health risk assessment to fluoride in drinking water of rural residents living in the Poldasht city, Northwest of Iran. Ecotoxicology and Environmental Safety, 148, 426–430. https://doi.org/10.1016/j.ecoenv.2017.10.032

Article CAS Google Scholar
Yousefi, M., MoghaddamV, K. M., Nasab, S., Nabizadeh, R., Hadei, M., Zarei, A., Baghal Asghari, F., & Mohammadi, A. A. (2019). Northwest of Iran as an endemic area in terms of fluoride contamination: A case study on the correlation of fluoride concentration with physicochemical characteristics of groundwater sources in Showt. Desalination and Water Treatment, 155, 183–189. https://doi.org/10.5004/dwt.2019.23761

Article CAS Google Scholar

Download references

Acknowledgement

The authors would like to thank the Sistan and Baluchestan water and wastewater Co.

Funding

This work was supported by the Iran National Science Foundation (INSF) under Grant No. 4037853. No other funds, grants, or financial support were received for the preparation of this manuscript.

Author information

Authors and Affiliations

School of Geology, College of Science, University of Tehran, Tehran, Iran

Reza Jahanshahi
Department of Geology, University of Sistan and Baluchestan, Zahedan, Iran

Reza Jahanshahi & Hafizeh Rigi Karvandari
Faculty of Earth Sciences, Shahrood University of Technology, Shahrood, Iran

Sepideh Mali

Contributions

All authors contributed to the study conception and design. Material preparation, field sampling, laboratory analyses, data processing, hydrogeochemical modelling, and statistical computations were performed by **Reza Jahanshahi**, **Hafizeh Rigi Karvandari**, and **Sepideh Mali**. The first draft of the manuscript was written by **Reza Jahanshahi**, and all authors provided critical revisions and comments on previous versions of the manuscript. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Reza Jahanshahi.

Ethics declarations

Conflict of interest

The authors declare no conflict of interest.

Ethics approval

This study involved no human participants, animal subjects, or identifiable personal data. All groundwater sampling and field procedures complied with institutional and national guidelines. Ethics approval was not required, as the research was limited to environmental water sampling and chemical analysis.

Consent to participate

Not applicable. No human participants were involved in this study.

Consent for Publication

Not applicable. The manuscript does not contain data from any individual person, images of human subjects, or identifiable personal information.

Research Studies

Study Tracker

Geogenic fluoride enrichment in groundwater of a volcanic terrain: hydrogeochemical processes, exposure pathways, and human health risk assessment.

Abstract