Fluoride Action Network

Top 20 countries in population potentially affected by fluoride concentrations in groundwater greater than 1.5mg/L.

Source: Nature Communications | August 16th, 2022 | By Joel Podgorski & Michael Berg
Location: International

The following information comes from:

Podgorski, J., Berg, M. Global analysis and prediction of fluoride in groundwater. Nature Communications 13, 4232 (2022).

Read the full-text study at https://doi.org/10.1038/s41467-022-31940-x (also in pdf)


Table 1. Top 20 countries in population potentially affected by fluoride concentrations in groundwater greater than 1.5 mg/L.

Rank Country Population at risk (range) Rank Country Population at risk (range)
(million) (million)
1 India 49 (26–89) 11 Malawi 4.0 (3.5–4.8)
2 China 22 (1–50) 12 Zambia 3.4 (1.4–3.6)
3 Dem. Rep. Congo 15 (2–16) 13 Mozambique 2.6 (1.7–3.4)
4 Ethiopia 9.6 (4.0–13.8) 14 Angola 2.2 (0.7–2.4)
5 Pakistan 7.6 (2.3–14.5) 15 Afghanistan 1.7 (0.5–4.8)
6 Kenya 7.5 (4.2–8.3) 16 Cameroon 1.6 (0.3–2.5)
7 Nigeria 7.4 (1–17) 17 Madagascar 1.4 (0.7–2.3)
8 Tanzania 6.9 (3.7–7.9) 18 Chad 1.2 (0.1–2.2)
9 Uganda 4.8 (0.9–8) 19 Niger 1.2 (0.2–2.6)
10 Yemen 4.3 (2.6–4.4) 20 Myanmar 1.1 (0.07–3.3)

See Full size image

Fig. 1: Fluoride in groundwater.
figure 1

a Probability of naturally occurring fluoride in groundwater exceeding the WHO drinking water guideline of 1.5 mg/L. The map was developed by applying the final random forest model to the 12 most statistically important predictor variables. Panel b shows the fluoride data points (n = 402,452) used in analysis and modeling. Closer views of the global map are given for the western U.S. and Mexico (c), eastern South America (d), the southern half of Africa (e), and western South Asia (f). The data sources are listed in Supplementary Table 1 and a large-scale map of the fluoride points is shown in Supplementary Fig. 1 along with large-scale versions of the prediction map focused on each continent in Supplementary Figs. 38.

Two regions with large potentially affected populations for which only relatively few direct measurements of groundwater quality were available to constrain the model are China and Central Africa (Fig. 1b and Supplementary Fig. 1). The model also indicates a particularly elevated fluoride risk across much or most of Angola, Cameroon, Chad, Democratic Republic of the Congo (DRC), Ethiopia, Eritrea, Kenya, Madagascar, Malawi, Mozambique, Nigeria, Somalia, Tanzania, Zambia, and Zimbabwe as well as Yemen (Table 1). The at-risk population figures provide only a rough estimate of the actual number of people affected, which can only be verified by epidemiological studies on the ground. Nevertheless, Fig. 4 provides a meaningful broad-scale indication of where such investigations are most needed.

Open in a separate window

An external file that holds a picture, illustration, etc. Object name is 41467_2022_31940_Fig4_HTML.jpg

This study was funded by:

Federal Department of Foreign Affairs | Direktion für Entwicklung und Zusammenarbeit (Swiss Agency for Development and Cooperation)
and the Swiss National Science Foundation


1. Ayoob S, Gupta AK. Fluoride in drinking water: A review on the status and stress effects. Crit. Rev. Environ. Sci. Technol. 2006;36:433–487. doi: 10.1080/10643380600678112. [CrossRef] [Google Scholar]
2. Ali S, Thakur SK, Sarkar A, Shekhar S. Worldwide contamination of water by fluoride. Environ. Chem. Lett. 2016;14:291–315. doi: 10.1007/s10311-016-0563-5. [CrossRef] [Google Scholar]
3. Lacson, C. F. Z., Lu, M.-C. & Huang, Y.-H. Fluoride containing water: A global perspective and a pursuit to sustainable water defluoridation management-an overview. J. Cleaner Prod.280, 124236 (2020).
4. Handa B. Geochemistry and genesis of fluoride?containing ground waters in india. Groundwater. 1975;13:275–281. doi: 10.1111/j.1745-6584.1975.tb03086.x. [CrossRef] [Google Scholar]
5. Hudak PF. Fluoride levels in Texas groundwater. J. Environ. Sci. Health Part A. 1999;34:1659–1676. doi: 10.1080/10934529909376919. [CrossRef] [Google Scholar]
6. Brunt, R., Vasak, L. & Griffioen, J. Fluoride in Groundwater: Probability of occurrence of excessive concentration on global scale. unigrac.org (2004).
7. Jacks G, Bhattacharya P, Chaudhary V, Singh K. Controls on the genesis of some high-fluoride groundwaters in India. Appl. Geochem. 2005;20:221–228. doi: 10.1016/j.apgeochem.2004.07.002. [CrossRef] [Google Scholar]
8. Rao NS. High-fluoride groundwater. Environ. Monit. Assess. 2011;176:637–645. doi: 10.1007/s10661-010-1609-y. [Abstract] [CrossRef] [Google Scholar]
9. Edmunds, W. M. & Smedley, P. L. Essentials of Medical Geology 311–336 (Springer, 2013).
10. Alarcón-Herrera MT, et al. Co-occurrence of arsenic and fluoride in groundwater of semi-arid regions in Latin America: Genesis, mobility, and remediation. J. Hazard. Mater. 2013;262:960–969. doi: 10.1016/j.jhazmat.2012.08.005. [Abstract] [CrossRef] [Google Scholar]
11. Wen D, et al. Arsenic, fluoride and iodine in groundwater of China. J. Geochem. Exploration. 2013;135:1–21. doi: 10.1016/j.gexplo.2013.10.012. [CrossRef] [Google Scholar]
12. Malago J, Makoba E, Muzuka AN. Fluoride levels in surface and groundwater in Africa: A review. Am. J. Water Sci. Eng. 2017;3:1–17. doi: 10.11648/j.ajwse.20170301.11. [CrossRef] [Google Scholar]
13. Alarcón-Herrera MT, et al. Co-occurrence, possible origin, and health-risk assessment of arsenic and fluoride in drinking water sources in Mexico: Geographical data visualization. Sci. Total Environ. 2020;698:134168. doi: 10.1016/j.scitotenv.2019.134168. [Abstract] [CrossRef] [Google Scholar]
14. Islam, M. S. & Mostafa, M. Meta?analysis and risk assessment of fluoride contamination in groundwater. Water Environ. Res.93, 1194–1216 (2021). [Abstract]
15. Fawell, J., Bailey, K., Chilton, J., Dahi, E. & Magara, Y. Fluoride in Drinking-Water (IWA Publishing, 2006).
16. Maithani, P. et al. Anomalous fluoride in groundwater from western part of Sirohi district, Rajasthan and its crippling effects on human health. Curr. Sci.74, 773–777 (1998).
17. Xiong X, et al. Dose–effect relationship between drinking water fluoride levels and damage to liver and kidney functions in children. Environ. Res. 2007;103:112–116. doi: 10.1016/j.envres.2006.05.008. [Abstract] [CrossRef] [Google Scholar]
18. Barbier O, Arreola-Mendoza L, Del Razo LM. Molecular mechanisms of fluoride toxicity. Chem.-Biol. Interact. 2010;188:319–333. doi: 10.1016/j.cbi.2010.07.011. [Abstract] [CrossRef] [Google Scholar]
19. Jha S, et al. Fluoride in groundwater: Toxicological exposure and remedies. J. Toxicol. Environ. Health, Part B. 2013;16:52–66. doi: 10.1080/10937404.2013.769420. [Abstract] [CrossRef] [Google Scholar]
20. Yadav KK, et al. Fluoride contamination, health problems and remediation methods in Asian groundwater: A comprehensive review. Ecotoxicol. Environ. Saf. 2019;182:109362. doi: 10.1016/j.ecoenv.2019.06.045. [Abstract] [CrossRef] [Google Scholar]
21. Aravinthasamy P, et al. Fluoride contamination in groundwater of the Shanmuganadhi River basin (south India) and its association with other chemical constituents using geographical information system and multivariate statistics. Geochemistry. 2020;80:125555. doi: 10.1016/j.chemer.2019.125555. [CrossRef] [Google Scholar]
22. Schlesinger WH, Klein EM, Vengosh A. Global biogeochemical cycle of fluorine. Glob. Biogeochem. Cycles. 2020;34:e2020GB006722. doi: 10.1029/2020GB006722. [CrossRef] [Google Scholar]
23. WHO. Guidelines for drinking-water quality. WHO Chron. 2011;38:104–108. [Abstract] [Google Scholar]
24. WHO. Fluoride in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality, Geneva (2004).
25. Reddy, K. N. Revised guidelines of National Water Quality Sub-Mission (Government of India, Ministry of Drinking Water and Sanitation, 2017).
26. U.S. EPA. Six-Year Review 3—Health Effects Assessment for Existing Chemical and Radionuclide National Primary Drinking Water Regulations—Summary Report (U.S. Environmental Protection Agency, 2016).
27. Vithanage M, Bhattacharya P. Fluoride in the environment: Sources, distribution, and defluoridation. Environ. Chem. Lett. 2015;13:131–147. doi: 10.1007/s10311-015-0496-4. [CrossRef] [Google Scholar]
28. Wang, Y. et al. Genesis of geogenic contaminated groundwater: As, F and I. Crit. Rev. Environ. Sci. Technol.51, 1–39 (2020).
29. He, X. et al. Groundwater arsenic and fluoride and associated arsenicosis and fluorosis in China: Occurrence, distribution, and management. Exposure Health12, 1–14 (2020).
30. Guo Q, Wang Y, Ma T, Ma R. Geochemical processes controlling the elevated fluoride concentrations in groundwaters of the Taiyuan Basin, Northern China. J. Geochem. Exploration. 2007;93:1–12. doi: 10.1016/j.gexplo.2006.07.001. [CrossRef] [Google Scholar]
31. Saxena V, Ahmed S. Inferring the chemical parameters for the dissolution of fluoride in groundwater. Environ. Geol. 2003;43:731–736. doi: 10.1007/s00254-002-0672-2. [CrossRef] [Google Scholar]
32. Schafer D, et al. Model-based analysis of reactive transport processes governing fluoride and phosphate release and attenuation during managed aquifer recharge. Environ. Sci. Technol. 2020;54:2800–2811. doi: 10.1021/acs.est.9b06972. [Abstract] [CrossRef] [Google Scholar]
33. Johnston RB, Berg M, Johnson CA, Tilley E, Hering JG. Water and sanitation in developing countries: Geochemical aspects of quality and treatment. Elements. 2011;7:163–168. doi: 10.2113/gselements.7.3.163. [CrossRef] [Google Scholar]
34. Bretzler A, Johnson CA. The geogenic contamination handbook: Addressing arsenic and fluoride in drinking water. Appl. Geochem. 2015;63:642–646. doi: 10.1016/j.apgeochem.2015.08.016. [CrossRef] [Google Scholar]
35. Lombard MA, et al. Machine learning models of arsenic in private wells throughout the conterminous United States as a tool for exposure assessment in human health studies. Environ. Sci. Technol. 2021;55:5012–5023. doi: 10.1021/acs.est.0c05239. [Europe PMC free article] [Abstract] [CrossRef] [Google Scholar]
36. Mukherjee A, et al. Occurrence, predictors, and hazards of elevated groundwater arsenic across India through field observations and regional-scale AI-based modeling. Sci. Total Environ. 2021;759:143511. doi: 10.1016/j.scitotenv.2020.143511. [Abstract] [CrossRef] [Google Scholar]
37. Podgorski J, Berg M. Global threat of arsenic in groundwater. Science. 2020;368:845–850. doi: 10.1126/science.aba1510. [Abstract] [CrossRef] [Google Scholar]
38. Podgorski JE, Labhasetwar P, Saha D, Berg M. Prediction modeling and mapping of groundwater fluoride contamination throughout India. Environ. Sci. Technol. 2018;52:9889–9898. doi: 10.1021/acs.est.8b01679. [Abstract] [CrossRef] [Google Scholar]
39. Amini M, et al. Statistical modeling of global geogenic fluoride contamination in groundwaters. Environ. Sci. Technol. 2008;42:3662–3668. doi: 10.1021/es071958y. [Abstract] [CrossRef] [Google Scholar]
40. Rosecrans CZ, Belitz K, Ransom KM, Stackelberg PE, McMahon PB. Predicting regional fluoride concentrations at public and domestic supply depths in basin-fill aquifers of the western United States using a random forest model. Sci. Total Environ. 2022;806:150960. doi: 10.1016/j.scitotenv.2021.150960. [Abstract] [CrossRef] [Google Scholar]
41. Breiman L. Random forests. Mach. Learn. 2001;45:5–32. doi: 10.1023/A:1010933404324. [CrossRef] [Google Scholar]
42. Jia Y, et al. Distribution, formation and human-induced evolution of geogenic contaminated groundwater in China: A review. Sci. Total Environ. 2018;643:967–993. doi: 10.1016/j.scitotenv.2018.06.201. [Abstract] [CrossRef] [Google Scholar]
43. Podgorski, J. E. et al. Extensive arsenic contamination in high-pH unconfined aquifers in the Indus Valley. Sci. Adv.10.1126/sciadv.1700935 (2017). [Europe PMC free article] [Abstract]
44. Podgorski J, Wu R, Chakravorty B, Polya DA. Groundwater arsenic distribution in India by machine learning geospatial modeling. Int. J. Environ. Res. public health. 2020;17:7119. doi: 10.3390/ijerph17197119. [Europe PMC free article] [Abstract] [CrossRef] [Google Scholar]
45. Ayotte JD, Medalie L, Qi SL, Backer LC, Nolan BT. Estimating the high-arsenic domestic-well population in the conterminous United States. Environ. Sci. Technol. 2017;51:12443–12454. doi: 10.1021/acs.est.7b02881. [Europe PMC free article] [Abstract] [CrossRef] [Google Scholar]
46. Gizaw B. The origin of high bicarbonate and fluoride concentrations in waters of the Main Ethiopian Rift Valley, East African Rift system. J. Afr. Earth Sci. 1996;22:391–402. doi: 10.1016/0899-5362(96)00029-2. [CrossRef] [Google Scholar]
47. Borgnino L, et al. Mechanisms of fluoride release in sediments of Argentina’s central region. Sci. Total Environ. 2013;443:245–255. doi: 10.1016/j.scitotenv.2012.10.093. [Abstract] [CrossRef] [Google Scholar]
48. McMahon PB, Brown CJ, Johnson TD, Belitz K, Lindsey BD. Fluoride occurrence in United States groundwater. Sci. Total Environ. 2020;732:139217. doi: 10.1016/j.scitotenv.2020.139217. [Abstract] [CrossRef] [Google Scholar]
49. Alcaine AA, et al. Hydrogeochemical controls on the mobility of arsenic, fluoride and other geogenic co-contaminants in the shallow aquifers of northeastern La Pampa Province in Argentina. Sci. Total Environ. 2020;715:136671. doi: 10.1016/j.scitotenv.2020.136671. [Abstract] [CrossRef] [Google Scholar]
50. Hossain M, Patra PK. Hydrogeochemical characterisation and health hazards of fluoride enriched groundwater in diverse aquifer types. Environ. Pollut. 2020;258:113646. doi: 10.1016/j.envpol.2019.113646. [Abstract] [CrossRef] [Google Scholar]
51. JMP. Global data on Water Supply, Sanitation and Hygiene (WASH), https://washdata.org/data/household#!/ (2019).
52. Gao, J. (ed.) Global Population Projection Grids Based on Shared Socioeconomic Pathways (SSPs), Downscaled 1-km Grids, 2010-2100. NASA Socioeconomic Data and Applications Center (SEDAC) (2019).
53. Araya, D., Podgorski, J., Kumi, M., Mainoo, P. A. & Berg, M. Fluoride contamination of groundwater resources in Ghana: Country-wide hazard modeling and estimated population at risk. Water Res.212, 118083 (2022). [Abstract]
54. Cao H, Xie X, Wang Y, Liu H. Predicting geogenic groundwater fluoride contamination throughout China. J. Environ. Sci. 2022;115:140–148. doi: 10.1016/j.jes.2021.07.005. [Abstract] [CrossRef] [Google Scholar]
55. Bretzler A, et al. Groundwater arsenic contamination in Burkina Faso, West Africa: Predicting and verifying regions at risk. Sci. Total Environ. 2017;584:958–970. doi: 10.1016/j.scitotenv.2017.01.147. [Abstract] [CrossRef] [Google Scholar]
56. Wu, R., Podgorski, J., Berg, M. & Polya, D. A. Geostatistical model of the spatial distribution of arsenic in groundwaters in Gujarat State, India. Environ. Geochem. Health43, 2649–2664 (2020). [Europe PMC free article] [Abstract]
57. Craig L, Lutz A, Berry KA, Yang W. Recommendations for fluoride limits in drinking water based on estimated daily fluoride intake in the Upper East Region, Ghana. Sci. Total Environ. 2015;532:127–137. doi: 10.1016/j.scitotenv.2015.05.126. [Abstract] [CrossRef] [Google Scholar]
58. Ayoob S, Gupta A, Bhat VT. A conceptual overview on sustainable technologies for the defluoridation of drinking water. Crit. Rev. Environ. Sci. Technol. 2008;38:401–470. doi: 10.1080/10643380701413310. [CrossRef] [Google Scholar]
59. Scott DW. Sturges’ rule. Wiley Interdiscip. Rev.: Comput. Stat. 2009;1:303–306. doi: 10.1002/wics.35. [CrossRef] [Google Scholar]
60. R: A Language and Environment for Statistical Computing. Vienna: R Foundation for Statistical Computing (2014).
61. Wright, M. N. & Ziegler, A. ranger: A fast implementation of random forests for high dimensional data in C++ and R. Journal of Statistical Software 77:1-17, https://arxiv.org/abs/1508.04409 (2015).
62. Diaz-Uriarte, R. & de Andrés, S. A. Variable selection from random forests: Application to gene expression data. https://arxiv.org/abs/q-bio/0503025 (2005).
63. Kuhn M. Building predictive models in R using the caret package. J. Stat. Softw. 2008;28:1–26. doi: 10.18637/jss.v028.i05. [Abstract] [CrossRef] [Google Scholar]
64. Podgorski, J. & Berg, M. Podgorski_and_Berg_2022. ERIC/open10.25678/0006GQ (2022).